LEE- Kimya-Yüksek Lisans

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http://hdl.handle.net/11527/19352

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Swelling dynamics and thermomechanical properties of multifunctional hybrid systems based on N-alkyl methacrylate esters

(Graduate School, 2021-12-16) Bozbay, Rabia ; Orakdöğen, Nermin ; 509191216 ; Chemistry

Increasing demand for functional polymers in applications based on smart materials has led to the need for modified synthetic tools and new ways to design advanced materials containing specific functional groups. Improved material design is possible using specific monomers with functional groups that remain proactive under polymerization conditions and can be selectively converted to other functional groups in subsequent steps. N-alkyl methacrylate-based monomers, which can be easily polymerized under mild conditions, are widely used in design of various precisely defined functional materials. Thanks to these extraordinary features of smart gels; hydrogels have many applications in processes ranging from industrial to biological. In particular, it have many uses in many areas from food industry, pharmaceutical applications, drug delivery systems, agriculture, contact lenses, sensors, tissue engineering, controlled drug release and water purification, etc. In the first part of this study, a synthesis group was designed for the preparation of n-alkyl methacrylate ester-based multifunctional hybrid systems. It was aimed to perform the synthesis of a series of n-alkyl-methacrylate estrer-based terpolymer hydrogels consisting 2-(dimethylamino)ethyl-methacrylate (DMAEMA), hydroxypropyl-methacrylate (HPMA), and glycidyl-methacrylate (GMA) using different monomer feed compositions at a fixed crosslinker ratio. The aim of the second part of this study was to successfully synthesize terpolymer cryogels using the monomers and crosslinkers in equal proportions to those synthesized in the first part and to investigate the effect of tertiary amine groups of DMAEMA and epoxy functional groups of GMA on the gel properties. In the third part of the study; the effect of the gel preparation temperature on the gel properties was investigated. For this purpose, the results obtained from the first and second part were interpreted and the terpolymer with 20 mol% HPMA, 70 mol% DMAEMA and 10 mol% GMA structure was selected, and In this part, the terpolymer gel prepared by free radical crosslinking in water at constant monomer and crosslinker concentrations was successfully synthesized by changing the polymerization temperature between -18 and 60 oC. The effect of the change in DMAEMA/GMA mol percent ratio from 80/0 to 0/80 in the terpolymer matrix on the gel properties was investigated and it was observed that the gel properties are controlled by the tertiary amino groups in the structure of DMAEMA as well as the GMA monomer. In order to evaluate the macroscopic properties of terpolymer gels, the specific structural properties of the groups in the terpolymer matrix and their physico-chemical properties that vary depending on the monomer feed composition and gel preparation temperature were investigated. In the first part of the experimental work, it is aimed to develop a new polycationic ternary gel system with different functional groups and to evaluate the scaling relationships between the network parameters and the elastic properties. Multifunctional ternary-gels based on 2-(dimethylamino)ethyl methacrylate (DMAEMA), hydroxypropyl methacrylate (HPMA) and glycidyl methacrylate (GMA) were prepared in a wide gel preparation concentration range. The resulting gels denoted as terpolymeric poly(hydroxypropyl methacrylate-co-glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate), PHDm/Gn-Hgs, were characterized by ATR-FTIR, and TGA measurements. The thermal stability of the terpolymer hydrogels was observed to be improved with the increase in GMA content. Swelling of ternary-gels in different solvents showed that cyclohexanol was a good solvent for the present terpolymer gel system. Swelling is controlled by DMAEMA portion of terpolymers and DMAEMA-rich gels tended to swell more than GMA-rich gels and increase in GMA content increased the polymer-solvent interaction parameter. It was determined that the addition of hydrophobic GMA to the terpolymer matrix led to a significant increase in the stiffness. The increase in elastic modulus as-prepared state is not monotonic and can be thoroughly controlled by adjusting DMAEMA/GMA ratio since tertiary amine groups triggers cascading epoxy ring-opening reaction. Dependence of swelling on the gel preparation concentration as a function of solvent quality was examined. A good solvent prediction indicated a crossover between entanglement-dominated case and strongly cross-linked case corresponding to low and moderate degrees of swelling. It has been observed that the reduced modulus decreased with increasing degree of swelling. The scaling relationship between the modulus and degree of swelling which indicates that ternary-hydrogels, limited to weak stretching regime, obey Gaussian statistics. In the second part of the experimental work, pH/thermo-responsive cationic terpolymer cryogels were successfully prepared by varying the feeding DMAEMA/GMA mol ratio. Terpolymer cryogels with different DMAEMA/GMA ratio have been extensively characterized with ATR-FTIR, X-ray diffraction analysis (XRD) and TGA measurements. The presence of GMA imparts hydrophobic character that reduces the swelling and provides additional crosslinks leading to a significant increase in the flexibility. Reducing the polymerization temperature below the freezing point of the solvent resulted in harder and non-brittle cryogels. With the increase in the amount of DMAEMA in the terpolymer matrix, the pH-dependent transition point was found to be 7.7. The water transport was strongly affected by incorporation of hydrophobic component GMA and protonation of amine functional groups. The swelling mechanism was shifted from anomalous to diffusion controlled with increasing GMA and overall swelling processes followed Schott second order dynamic equation. It was observed that lower equilibrium volume swelling at constant temperature was achieved by increasing GMA content of the terpolymers. In low temperature range, while DMAEMA-rich terpolymer gels were swollen, swelling decreased significantly when the gels were enriched in GMA. A significant difference was observed in salt-sensitive swelling in dilute salt solution, which is controlled by the amount of DMAEMA in terpolymer structure. This part of the work is important in that it provides new ideas for the design of (meth)acrylate ester-based cationic terpolymer cryogels and explains the relationship between the gel matrix and their specific swelling behavior. From the first and second part of the experimental study, the terpolymer PHDG structure containing 10% mol of GMA, 70% mol% of DMAEMA and 20 mol% of HPMA was selected and an attempt was made to establish a relationship between the the gel preparation temperature and the elasticity as well as pH/temperature sensitivity of n-alkyl methacrylate ester-based cationic gels. In the third part of the experimental study, the gel preparation temperature Tprep was changed and terpolymer gels were prepared at -18, 1, 5, 8, 24, and 60 oC. The structure and physical properties of ternary gels was fully characterized using TGA, ATR-FTIR and XRD. Tprep has been shown to be an effective independent variable to adjust both macroscopic and microscopic properties of ternary gels as desired. The dependence of the swelling and compressive elasticity on the gelation temperature was investigated and it was determined that terpolymer gels synthesized at 5 °C showed maximum swelling capacity. A significant change in the elastic modulus was observed as Tprep decreased from 60°C to -18°C. Terpolymer gels showed pH-sensitive swelling characteristic of cationic DMAEMA monomer and exhibited high swelling ratio in acidic solutions induced by the electrostatic repulsion between quaternary amine groups. It was observed that the swelling ratio decreased due to hydrophobic effect of the alkyls when environmental pH is higher than 7.7. Regardless of Tprep, the gels gradually contracted as the swelling temperature increased from 25°C to 75°C. The effectiveness of terpolymer gels to remove the anionic dye Methyl Orange from aqueous solution was tested and the results showed that the terpolymer gels prepared under low temperature conditions were promising for removing anionic dyes from wastewater. The adsorption was spontaneous and found to be a multistep process with the surface adsorption followed by the intraparticle diffusion. The results obtained will assist in the design of n-alkyl methacrylate ester-based ternary gels as an effective adsorbent for dye removal from wastewater and pharmaceutical preparations.
Demir(III) iyonuna hassas, tiyofen ile modifiye edilmiş rodamin tabanlı yeni tip sensörün sentezi, karakterizasyonu ve uygulamaları

(Lisansüstü Eğitim Enstitüsü, 2022-01-24) Arıbuğa, Hülya ; Yılmaz, İsmail ; 509181315 ; Kimya

Rodamin bileşiği, ilk olarak 1905 yılında m-aminofenol ve ftalik anhidritin Lewis asidi varlığında gerçekleşen reaksiyonu sonucunda sentezlenmiş ve o günden beri pek çok alanda kullanılmıştır. Ksanten grubunun bir üyesi olan rodamin moleküllerinin ksanten gruplarında ve ksantene bağlı benzenin üzerinde bulunan sübstitüsyonlara göre farklı türevleri bulunmaktadır. Kompleksleşme reaksiyonları benzene bağlı fonksiyonel gruplardaki heteroatomlar üzerinden gerçekleşmektedir. Rodamin bileşiklerinin fotofiziksel ve fotokimyasal açıdan avantajlı özelliklere sahip olması, son yıllarda yapılan araştırmalara konu olmalarında önemli bir faktördür. Bu özelliklere yüksek floresan kuantum verimi, yüksek absorpsiyon katsayısı, uzun uyarma ve emisyon dalga boyları ve büyük sönümleme katsayısı örnek olarak verilebilir. Molekül üzerindeki spirolaktam halkası, ortamın pH değerine bağlı olarak ya da analit ilavesi ile açılarak, görünür bölgede şiddetli bir ışıma yapmasına neden olmaktadır. Ayrıca spirolaktam halkasının kolayca açılıp kapanabilmesi, tekrar kullanılabilirlik özelliğine sahip olduklarını göstermektedir. İnsan vücudunda en bol bulunan geçiş metali olan demir, enzimatik reaksiyonlar, DNA ve RNA sentezleri, kas kasılması, vücut ısısının düzenlenmesi, kanda oksijenin taşınması, kalp, böbrek, pankreas gibi organların işlevlerinin düzenlenmesi gibi hayati metabolik işlemlerde yer alır. Ayrıca dünya üzerinde doğrudan veya dolaylı yollarla demir ve türevleri ile çevrilmiş durumdayız ve bu türevler ekosistemdeki yaşamın uygun şekilde sürdürülmesinde büyük etkiye sahiptir. Demir; su yoluyla, gıdalardan veya çevresel kaynaklardan vücuda alınabilir ve vücuttaki miktarının fazla ya da eksik olması durumunda Alzheimer, Parkinson, kansızlık ve organların işlevlerinin bozulması gibi hayati hastalıklara neden olmaktadır. Bu nedenle endüstriyel, çevresel ve biyolojik numunelerde demir iyonlarının ölçümü için hem hassas ve seçici hem de hızlı tepki süresine sahip bir sensör tasarlamak önem arz etmektedir. Günümüze dek, AAS ve ICP-MS gibi analitik yöntemler Fe3+ tayini için kullanılmıştır, fakat bu yöntemler pahalı ekipman ve karmaşık numune hazırlama aşamaları gerektirdiğinden bu yöntemler yerine hem kolorimetrik hem de florometrik ölçüm sağlayabilen, kullanımı kolay ve gerçek zamanlı analiz gerçekleştiren kemosensörler son yıllarda büyük ilgi görmektedir. Buna bağlı olarak, bu tez çalışması kapsamında hem UV-Gör hem floresan yöntemiyle Fe3+ analizi yapabilen, tiyofen ile modifiye edilmiş, rodamin B tabanlı yeni bir sensör başarıyla sentezlenmiştir. Sentezlenen sensör bileşiğinin karakterizasyonu NMR, IR, MALDI-TOF ve X-Işını Kristallografisi gibi yöntemlerle gerçekleştirilerek yapısı aydınlatıldıktan sonra pH 7 tamponlu etanol/su çözücü ortamında Fe3+ analizi yapılmıştır. Spirolaktam halkasının kapalı formunda floresan aktif olmayan ve renksiz bir çözeltiye sahip olan sensör bileşiğinin Fe3+ iyonu varlığında 580 nm'de şiddetli bir floresan emisyonu ve UV-Gör spektrumunda 559 nm'de yeni bir band oluşumu görülmesinin yanında çözeltinin rengi de pembemsi kırmızıya dönmüştür. Fe3+ iyonuna karşı seçici olduğu görüldükten sonra sensöre ppm mertebesinde Fe3+ ilaveleri yapılarak titrasyon çalışması yapılmış ve hassasiyeti incelenmiştir. Bu çalışmalar sonucunda UV-Gör yöntemi için tespit limiti 5,99×10-8 M ve çalışma aralıkları 33,3-55,0 µM olarak belirlenmiştir. Florometrik yöntem sonucunda ise tespit limiti 4,85×10-9 M ve çalışma aralığı 25,3-50,7 µM olarak belirlenmiştir. Bağlanma sabiti (Ka) değeri ise UV-Gör titrasyon verilerinden hesaplanarak 1,89×104 M-1 olarak bulunmuştur. Sensör bileşiğinin Fe3+'ü tayin etme süresi ise florometrik olarak incelenmiş olup 4 dakika gibi kısa bir süre olduğu belirlenmiştir. Daha sonra sensör ile Fe3+ analizi yapılmasının diğer metal iyonları tarafından girişime uğrayıp uğramadığı incelenmiş ve çinko hariç hiçbir metalin belirgin bir girişim göstermediği görülmüştür. Ayrıca, Fe3+ varlığında alınan spektral tepkinin Na2EDTA ilavesiyle tersine çevrilebildiği ve Fe3+ ilavesi ile tekrar tepki alınabildiği görülmüş olup sensörün tersinir bir şekilde tayin sağlayabildiği belirlenmiştir. Buna ek olarak, içme suyu örneklerinde Fe3+ tespiti için yüksek geri kazanım oranına sahip bir sensör olduğu UV-Gör ve florometrik çalışmalar ile gösterilmiştir. Son olarak sensörün bir diğer pratik uygulaması olarak kâğıt testi çalışmaları yapılmış ve böylece sensör çözeltisine bağlı kalmadan sensörle yüklenmiş kâğıt şeritleri ile gerçek zamanlı Fe3+ analizi yapılabileceği görülmüştür. Böylece rodamin B tabanlı, UV-Gör ve floresan olmak üzere çift kanallı analiz gerçekleştiren seçici ve hassas bir Fe3+ sensörü literatüre kazandırılmıştır.
Shape-memory semicrystalline interconnected IPNs based on various commercial rubbers

(Graduate School, 2022-02-02) Zengin Akça, Özge ; Okay, Oğuz ; 509191215 ; Chemistry

Rubber is a long-lasting polymer that can be generated naturally from the milky sap of the Hevea brasiliensis tree or synthesized from petroleum and alcohol. Rubber whose application in daily life increased with Charles Goodyear's discovery of the vulcanization process; nowadays, it is widely utilized in industrial products, particularly in the automotive industry, agriculture, health care, and a variety of other fields, from raw materials to finished products. With the growing industrialization, the consumption rate of rubber increases, as does the rate of waste rubber. Their large-scale usage has a negative impact on the environment, and their chemical bonds, which have been vulcanized, significantly extend their self-destruct time. Rubber with self-healing and shape memory properties has gained popularity in recent years to prevent it from becoming waste after use. Self-healing materials can heal and recover their original properties after being damaged by thermal, mechanical, physical, or other methods. On the other hand, shape memory is the ability to be programmed into a temporary shape and afterward return to a permanent shape when external stimuli such as temperature are applied. There should be at least two different cross-links in the polymer matrix for the shape-memory ability to appear. Self-healing and shape-memory polymers are appealing materials for a wide range of applications, including implants, actuators, sensors, superconducting devices, smart medical devices, and flexible electronics, because of their unique properties. Moreover, in recent years, developing similar smart features in commercially accessible and frequently used rubbers has received a lot of attention. Within the scope of this thesis, a series of IPNs have been obtained by UV polymerization of n-octadecyl acrylate (C18A) monomer using Irgacure 2959 UV initiator in the presence of varying proportions of styrene-butadiene rubber (SBR), cis-butadiene rubber (CBR), and two different types of natural rubbers (NR), together with butyl rubber (IIR) as a reference. The aim of this thesis is to understand how the degree of unsaturation of commercial rubber affects the thermal and mechanical properties and intelligent functions of IPNs. After examining the properties of IPNs prepared using IIR rubber, natural rubber, cis-polybutadiene, and styrene-butadiene rubbers were used in the IPN preparation. As a result of the mechanical and thermal measurements of the obtained IPNs, it has been observed that they all have high mechanical strength and exhibit shape memory properties. Increasing the degree of unsaturation of the rubber increased the chemical crosslink density of the generated IPNs and significantly improved their mechanical properties. The melting temperatures Tm, which can be modified depending on the amount and kind of rubbers used, range from 45 to 50 oC, while the crystallization temperatures Tcry range from 35 to 40 oC. All IPNs exhibit significant temperature sensitivity in their viscoelastic and mechanical properties when the temperature is varied above and below Tm and Tcry. The shape memory feature is facilitated by the existence of a crystalline area in the structure. The IPN material presented here can be programmed into a temporary shape with an increase in temperature above Tm followed by a decrease in temperature below Tm to fix the temporary shape, while it can simply return to the permanent shape by increasing the temperature again. In this thesis, although the self-healing ability of IPNs is disappeared by replacing IIR with other rubbers due to the increased number of chemical crosslinks, they all exhibit a strong shape memory function, as demonstrated for use as a thermo-responsive soft robotic gripper.
Calix[4]pyrrole based supramolecular polymers via orthogonal interactions

(Graduate School, 2022-02-07) Budak, Ayşegül ; Aydoğan, Abdullah ; 509191205 ; Chemistry

Supramolecular polymers are based on reversible intermolecular interactions. Rather than linking the monomers in the desired arrangement via a covalent of polymerization reaction, the monomers are designed in such a way that they self-assemble autonomously into the desired structure. The type and strength of non-covalent interactions varies, ranging from very weak Van der Waals interactions, π-π stacking, hydrogen bonding, solvophobic interactions to dipole-dipole interactions and very strong metal-ligand or ion-ion interactions. A well-known natural supramolecular system is DNA, whose unique architecture results from cooperative non-covalent interactions, such as multiple hydrogen bonds and hydrophobic interactions. By exploiting the reversibility of the interactions, materials with fascinating properties such as self-healing, shape memory and responsive behaviour can be produced. These materials have been prepared by using cationic guests and the host molecules that can interact with these guests and found various applications in energy, regenerative medicine, nanotechnology, environment and synthetic chemistry. Calix[4]pyrroles are non-conjugated tetrapyrrolic macrocycles capable of binding anions and neutral substrates in organic media via hydrogen bonding. Moreover, upon anion binding, they change their conformation from 1,3-alternate to cone conformation to facilitate the hydrogen bonding. Apart from that, cation-π interaction between appropriate cations and π-electron cloud of cone-shaped calix[4]pyrroles are also well known. Non-covalent and reversible supramolecular interactions provide functional materials within one polymer system. These specific interactions can be designated independently and simultaneously giving orthogonal self-assembly. The aim of this thesis is to synthesize and characterize supramolecular polymers based on anion recognition chemistry of calix[4]pyrroles via orthogonal self-assembly. In this thesis pyrimidinone functionalized calix[4]pyrrole derivative (UPyCP2) and a bis-carboxylate (TBAS) salt were used as host and guest molecules, respectively. Another supramolecular polymeric system was also prepared by host-guest, cation-π and van der Walls interactions that has been built from a bis-calix[4]pyrrole (BisCP) and bis-carboxylate (CTAS) as host and guest moieties, respectively. These supramolecular polymers prepared in an organic solvent and were found tho have thermo-, chemical-responsive behaviour. The above systems have been analyzed by NMR, viscosity measurements and scanninng electron microscopy.
Simetrik olmayan oksotitanyum ftalosiyaninlerin sentezi, karakterizasyonu ve fotovoltaik uygulamaları

(Lisansüstü Eğitim Enstitüsü, 2022-06-09) Arslan, Nuray ; Sevim, Altuğ Mert ; 509201220 ; Kimya

Ftalosiyaninler, doğada bulunabilen porfirinlerin tamamen sentetik analoglarıdır. 18 π-elektron sistemi bulunduran düzlemsel ve aromatik makroheterohalkalı yapılardır. İlk olarak 1907 yılında tesadüfen keşfedilmişlerdir. Metalli ve metalsiz olarak iki kategoride incelenebilirler. Ftalosiyaninlerin 70'ten fazla metal ile kompleks yapabildikleri bilinmektedir. Halka oyuklarında bulundurdukları bu metal atomlarına bağlı olarak ayrıca periferal ve non-periferal konumlara takılan sübstitüentlerin yapısına bağlı olarak ftalosiyaninlerin fiziksel ve kimyasal özellikleri değişkenlik göstermektedir. Kimyasal ve termal olarak oldukça kararlıdırlar. Bu durum ftalosiyaninlerin çok çeşitli ve özgün özellikler göstermelerini ve kimyasal sensör, non-lineer optik, fotodinamik terapi, boya ve pigment, katalizör ve sıvı kristal gibi birçok farklı alanda uygulama imkanı bulmalarını sağlamıştır. Ftalosiyaninlerin ftalonitril, ftalik asit, ftalik anhidrit ve ftalimid gibi çeşitli başlangıç bileşiklerinden yola çıkarak sentezlenmesi mümkündür. Sodyum, lityum gibi halka oyuğundan kolay ayrılabilen metaller içeren metalli ftalosiyaninlerden merkez metallerin çıkarılması ile metalsiz ftalosiyanin elde edilebildiği gibi, metalsiz ftalosiyaninlerin metal tuzları ile kaynatılmasıyla metalli ftalosiyanin elde edilmesi de mümkündür. Uç grupları aynı olan ftalosiyaninler simetrik ftalosiyaninler olarak adlandırılırlar. Farklı uç gruplar bulunduran ftalosiyaninler ise asimetrik ftalosiyaninlerdir. Asimetrik ftalosiyaninler istatiksel kondenzasyon, polimer destekli sentez yöntemi ve subftalosiyaninlerin halka büyümesi yöntemi olmak üzere üç yolla sentezlenebilirler. Son yıllarda fosil yakıtların azalması ve çevreye verdiği zararların yarattığı endişe ile temiz ve yenilenebilir enerjiye olan ihtiyaç artmıştır. Bu doğrultuda sınırsız bir temiz enerji kaynağı olan güneş ve bu enerjiyi elektriğe dönüştürebilen güneş pilleri üzerine olan çalışmalar hız kazanmıştır. Ftalosiyaninlerin bir başka uygulama alanı ise duyarlaştırıcı boya olarak boya duyarlı güneş pillerinde kullanımıdır. Bir güneş pili çeşidi olan boya duyarlı güneş pillerinde ftalosiyaninler yakın kızılötesi bölgede absorpsiyon yapabilmeleri ve yüksek molar absorpsiyon katsayıları sebebiyle organik boya duyarlaştırıcılar sınıfı içinde ilgi çeken malzemeler olmuşlardır. Bu çalışmada, başlangıç bileşikleri olarak 4-(ferrosenilfeniloksi) ftalonitril, 4-(4-karboksifeniletinil)ftalonitril, 4-(karboksi etinil) ftalonitril ve 4-(tert-butil) sülfanil ftalonitril bileşiklerinin sentezi gerçekleştirilmiştir. Ardından [2(3),9(10),16(17)-tris(ferrosenilfeniloksi)-23-(4-karboksifenilasetilenil) ftalosiyaninato] oksotitanyum (IV),[2(3),9(10),16(17)-tris(ferrosenilfeniloksi)-23-(4-karboksiasetilenil) ftalosiyaninato] oksotitanyum(IV), [2(3),9(10),16(17)-tris(4-ter-butilsülfanil)-23-(4-karboksifenilasetilenil)ftalosiyaninato] oksotitanyum(IV), [2(3),9(10),16(17)-tris(4-ter-butilsülfanil)-23-(karboksiasetilenil)ftalosiyaninato] oksotitanyum(IV) asimetrik ftalosiyaninlerinin sentezi gerçekleştirilmiştir. Sentezi gerçekleştirilen ftalosiyaninler kolon kromatografisi ve preparatif TLC yöntemleriyle saflaştırılmıştır. Sentezi gerçekleştirilen bileşiklerin yapısı UV-Vis, FT-IR, 1H NMR, 13C NMR ve kütle spektroskopisi teknikleri kullanılarak aydınlatılmıştır. Sentezlenen oksotitanyum ftalosiyaninlerin boya duyarlı güneş pillerinde duyarlaştırıcı olarak kullanılarak çalışmanın uygulamaları yapılmıştır. Agregasyonu önleyici hacimli gruplar ve boya duyarlı güneş hücrelerinde kullanılan TiO2 katmanına tutunmayı sağlayıcı çapa grubu olarak karboksilik asit fonksiyonel grubu içeren asimetrik oksotitanyum ftalosiyaninlerin uygulamaları için ticari olarak elde edilen YD2 isimli porfirin ile farklı oranda karışımları hazırlanmıştır. Bu karışımları hazırlayarak elektromanyetik spektrumun daha geniş bir alanında hem yakın kızılötesi bölgede hem görünür bölgede absorpsiyon yapabilmeleri ve bu sayede güneş ışığından daha fazla yararlanarak güneş pilinin verimini arttırmak amaçlanmıştır.
Charged functionalized semi-ipn nanocomposite materials with enhanced physico-chemical properties

(Graduate School, 2022-06-15) Ersoy Kara, Kübra ; Orakdöğen, Nermin ; 509201213 ; Chemistry

In this thesis, fibrous nano clay embedded and anionically-modified semi-interpenetrating (semi-IPN) gels were designed as new promising materials. The study mainly focuses on the investigation of the effect of a fibrous nanofiller-type clay sepiolite (SEP), anionic comonomer sodium acrylate (NaA), and linear polymer polyethylene glycol-2000 (PEG) on the final properties of semi-IPN poly(acrylamide-co-sodium acrylate)/PEG-SEP nanocomposite gels.
To elucidate the interaction mechanism of CNS selective carbamate-type cholinesterase (CHE) inhibitor rivastigmine with dsDNA by multi-spectroscopic, electrochemical, and viscosimetric methods

(Graduate School, 2022-06-22) Alizadeh, Neda ; Gölcü, Ayşegül ; 509181319 ; Chemistry

Alzheimer's disease (AD) is one of the major causes of death, affecting the elderly most and a type of dementia. Cell death in the brain caused by neurodegenerative disorders is suggested as the leading cause of AD. Over time, it impairs the patient's cognitive function, learning capacity, and ability to remember new information, leading to speech impairment and death. Inadequate symptomatic therapies may intensify these challenges, and without Alzheimer's therapy, the number of people dying from dementia over the age of 75 roughly doubles every 20 years. Although there is no treatment for Alzheimer's disease, acetylcholinesterase inhibitors like Rivastigmine tartrate, Galantamine, and Donepezil can help lessen the effects of cholinesterases and temporarily relieve symptoms. In recent years, scientists have been working to develop and advance potential treatments and clinical trials for Alzheimer's disease. Rivastigmine tartrate (RT) is a carbamate derivative and a cholinesterase inhibitor with a chemical formula of C18H28N2O8. It is used for the treatment of mild to moderate Alzheimer's disease (AD) and Parkinson's disease dementia (PDD). As a cholinesterase inhibitor, RT inhibits both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) enzymes, increasing the reversible inhibition of acetylcholine breakdown by cholinesterase and so raising the amount of ACh in the brain and promoting cholinergic function. Leading to this mechanism of action, RT in both oral and transdermal path forms is used to relieve the symptoms of Alzheimer's patients. Characterizing and interpreting the processes, binding modalities to DNA or RNA, and potential toxicity locations of these medicines are thought to be important subjects for pharmaceutical and biochemical studies. In the literature research, we have done, no interaction mechanism between RT and double-stranded deoxyribonucleic acid (dsDNA) has been encountered so far. For this reason, the interaction mechanism between RT and dsDNA has been examined using different analytical techniques, considering the possibility that it may contribute to the healthier and higher life quality of users, with the thought that possible side effects can be evaluated. This study used a variety of analytical and multi-spectroscopic methods under physiological conditions to investigate the mechanism of interaction between RT and dsDNA, including UV, fluorescence, thermal denaturation, electrochemical, and viscosity measurements. Based on all described techniques, the results showed that RT binds to dsDNA via the minor groove binding mode.
Yakın kızılötesi bölgede Ag+, Cu2+ ve Hg2+ iyonlarının maskeleme ajanları ile ayrımsal ve hassas tespiti için ftalosiyanin tabanlı kimyasal sensörün geliştirilmesi

(Lisansüstü Eğitim Enstitüsü, 2022-06-22) Çetin, Dila ; Yılmaz, İsmail ; 509201206 ; Kimya

Pirol halkasında iki imino hidrojen atomu ve dört diiminoizoindol birimi tarafından oluşturulan, simetrik ve merkezindeki boşlukta birçok metal iyonunu barındırabilen makro yapılı ftalosiyanine ismi ilk olarak Profesör Reginald P. Linstead tarafından, 1933 yılında verilmiştir. 1935 yılında büyük miktarda üretilmelerinin ardından her geçen gün kullanımları artan ftalosiyanin ve türevleri; indirgeme prosesleri, katalitik oksidasyon reaksiyonları, kanser tedavisinde fotodinamik terapi ajanı, fotobaşlatıcı, lineer olmayan optik materyaller ve kimyasal sensörler gibi pek çok alanda kullanılmaktadır. Uzun ömürlü olmasının yanında fotokimyasal ve fotofiziksel olarak kararlı olan ftalosiyaninler, 18-π elektronik sistemine sahip olması sebebiyle görünür bölgede şiddetli absorpsiyon ve emisyona sahiptir. Belirli özelliklere sahip farklı ligantlar ile ftalosiyaninler, periferal ve periferal olmayan konumlarından çeşitlendirilebilir. Benzer bir yaklaşım, merkezindeki metale müdahale ile oksidasyon/indirgeme potansiyeli ve akım değerleri değiştirilerek de gerçekleştirilebilir. Çevre ve insan sağlığına zararları nedeniyle ağır geçiş metallerinin tayini çok önemlidir. Bu metaller arasında; gümüş (I) (Ag+), bakır (II) (Cu2+) ve cıva (II) (Hg2+), böbrek, karaciğer, sinir sistemi vb. üzerindeki yıkıcı etkileri nedeniyle hassas tespit için en dikkat edilmesi gerekenlerdir. Tüm geçiş metalleri arasında en yüksek termal ve elektriksel iletkenliğe sahip olan gümüş, insan vücuduna mukoza zarları, gastrointestinal sistem, cilt lezyonları ve akciğerler yoluyla giriş yapabilir ve bu durum argyria olarak bilinmektedir. Alkali pillerde, mücevheratlarda, aynalarda ve elektrikli aletlerde birçok kullanımı olan gümüşe uzun süre maruziyet sonucu anemi, kalp sorunları ve enzimatik sorunlar gerçekleşmektedir. Bakır metali; borular, vanalar ve bağlantı parçalarının kaplanabilmesinde, alaşımlarda ve yüzeydeki alglerin kontrolü gibi birçok alanda yararlı işlev göstermesinin yanında, hipoglisemi, mide hastalıkları gibi insan sağlığına ve kirletici olarak çevreye ciddi derecede zararları bulunan bir ağır geçiş metalidir. Havada, toprakta ve suda bulunabilen cıva, toksisitesi nedeniyle çevre ve insan sağlığı için büyük bir tehlikedir. Klor/kostik, elektronik cihaz ve aletlerin kimyasal üretiminde kullanılması gibi avantajlarından ziyade bağışıklık sistemi, nöro sistem endokrin sistemi üzerindeki dikkat çekici toksisitesi nedeniyle cıvanın tüm ağır geçiş metalleri arasında en tehlikelisi olduğuna inanılmaktadır. Cıva vücuda girdiğinde beyinde, sinir sisteminde ve böbreklerde birçok soruna neden olabilir. Her cıva türünün farklı toksisitesi vardır, ancak nihayetinde tüm formları çevre ve insan sağlığı için sorundur. Cıva, insan vücudunun karaciğer, beyin, doku veya kemik gibi kısımlarında birikebilir. Ve bu birikim böbrek yetmezliğine, sinir sistemi sorunlarına ve hatta ölüme neden olabilir. Yukarıda belirtilen nedenlerle; bu ağır metalleri ayrımsal olarak saptamak elzemdir. Bilim insanları için uzun yıllardır Ag+, Cu2+ ve Hg2+'nın tespiti zorlu olmuştur. Atomik absorpsiyon/emisyon spektroskopisi, indüktif eşleşmiş plazma kütle spektroskopisi, elektrokimyasal yöntemler, kromatografi ve iyon seçici elektrotlar bu ağır geçiş metallerini saptamak için kullanılan birçok yöntem arasında sayılabilir. Ne yazık ki, bu geleneksel yöntemler Ag+, Cu2+ ve Hg2+'yı düşük hassasiyet ve seçicilikle tespit edebilme gibi dezavantajlarının yanında, yüksek maliyetli olması, numune hazırlama ve uygulama için zaman alması ve deneyimli bir profesyonele ihtiyaç duyması nedenleriyle oldukça zahmetlidirler. Bu nedenlerden ötürü, ağır metal tayini için hızlı ve ekonomik, algı hassasiyeti yüksek, kullanımı kolay, daha az sinyal-gürültü oranı gibi özelliklere sahip UV-Gör ve floresan gibi metotlara yüksek bir talep olduğu fark edilmiştir. Buna bağlı olarak, bu tez çalışması kapsamında UV-Gör ve floresan yöntemiyle Ag+, Cu2+ ve Hg2+ iyonlarının ayrımsal olarak analizini yapabilen, merkaptokinolin modifiyeli ftalosiyanin tabanlı yeni bir kimyasal sensör (SQZnPc) başarıyla sentezlenmiştir. Sentezlenen sensör bileşiğinin karakterizasyonu NMR, IR, MALDI-TOF gibi yöntemlerle gerçekleştirilerek yapısı aydınlatıldıktan sonra DMF çözücü ortamında Ag+, Cu2+ ve Hg2+ iyonlarının ayrımsal analizi maskeleme yöntemi kullanılarak gerçekleştirilmiştir. Ag+, Cu2+ ve Hg2+ iyonlarının her birinin ayrı ayrı ilavesi sonucu, UV-Gör spektrumunda, ftalosiyanin ünitesine ait Q bandının (710 nm) belirgin bir şekilde azaldığı ve kaymaya uğradığı gözlemlenmiştir. Metal katyonlarını (Ag+, Cu2+, Hg2+) ayrı ayrı tespit edebilmek için literatürde EDTA, KI ve NaCl gibi maskeleme ajanları kullanılmıştır. Örneğin, Lou ve arkadaşları gibi biz de bu çalışmada EDTA kullanarak Cu2+ ve Hg2+ iyonlarını maskelemiş ve Ag+ iyonları spesifik olarak tayin etmiş bulunmaktayız. Ek olarak, Cu2+'nin seçici ve hassas tayini için KI tuzu kullanılarak Ag+ ve Hg2+ iyonları maskelenmiş ve spesifik Cu2+ tayini gerçekleştirilebilmiştir. Son olarak Hg2+'nın seçici ve hassas tayini için NaCl kullanılmış ve Ag+ ve Cu2+ iyonları maskelenebilmiştir. Böylece, UV-Gör ve floresan olmak üzere çift kanallı analiz gerçekleştiren, üç metali iyonunu (Ag+, Cu2+, Hg2+) ayrı ayrı ve hassas olarak tespit edebilen SQZnPc sensörü literatüre kazandırılmıştır.
Piren modifiyeli rodamin-siyanin platformuna sahip, yeni sensör bileşiğinin sentezi, karakterizasyonu ve sensör çalışmaları

(Lisansüstü Eğitim Enstitüsü, 2022-06-22) Ertuğral, Utku ; Yılmaz, İsmail ; 509191260 ; Kimya

1905 yılında sentezlendiğinden bu zamana rodamin bileşiği, ksanten grupları üzerinden ve benzene bağlı fonksiyonel gruplar üzerinden birçok farklı türevleri elde edilebildiğinden ve bu türevlerin her biri farklı özelliklere sahip olduğundan, floresan kemosensör, biyo-işaretleyici ve benzeri pek çok alanda ilgi görmüştür. Rodamin türevleri genel olarak yüksek kuantum verimi, yüksek absorpsiyon katsayısı, uzun uyarma ve emisyon dalga boyları ve büyük sönümleme katsayısına sahiptir. Dolayısıyla, son yıllardaki araştırmalarda rodamin moleküllerinin fotofiziksel ve fotokimyasal avantajlarının üzerine durulmakta, bu avantajları gerçek örnekler üzerinde uygulama girişimlerine dönüştürülmektedir. Rodaminlerin genel sensör mekanizması, spirolaktam halkası üzerinden çalışmaktadır. Spirolaktam halkası, sensörün hassas olduğu analit konsantrasyonunun artmasıyla birlikte açık konuma gelir bu değişim sonucu molekülde konjugasyon daha geniş bir alana yayılır ve sonuç olarak görünür bölgede güçlü bir absorpsiyon ve emisyon şiddeti oluşur. Ek olarak rodaminlerdeki bu spirolaktam halkasının açık-kapalı konum arasında geçiş yapabilme kapasitesi sayesinde, rodamin bileşikleri tekrar kullanılabilirlik açısından birçok kemosensöre göre daha avantajlıdır. Rodaminler, siyanin gibi başka moleküllerle modifiye edilerek yakın kızılötesi bölgede çalışabilen kemosensörler haline getirilebilirler. Bu bölgede çalışan bir sensör geliştirebilmek iki açıdan çok önemlidir. Birincisi bu bölgede çalışma yaparken hücreiçi analizlerde hücreye verilen zarar en aza indirilir. İkincisi ise bu bölgede otofloresan şiddeti veya cihaz gürültüsü gibi istenmeyen şiddetler daha az olduğundan çok daha hassas ölçümler yapılabilmektedir. Cıva, çok düşük miktarlarda bile hayati risklere sebep olabilen, doğada var olan zehirli bir ağır metaldir. Canlılarda merkezi sinir sistemi başta olmak üzere birçok organda ciddi sorunlara yol açabilmektedir. Çok az miktarlarda bile cıvaya maruz kalan bir insan kısa zamanda merkezi sinir sistemi hastalıkları ve salgı bozuklukları gibi semptomlar göstermeye başlar. Bunlara ek olarak kardiyak aritmiler ve böbrek hastalıkları da cıva zehirlenmesinin bir başka belirtisi olabilmektedir. Cıvanın vücutta parçalanmaması ve vücuttan uzaklaştırılmaması onu daha da tehlikeli bir metal yapmaktadır. Temizlenemediği için bir birikim sürecine girer ve bu biyobirikim sonucunda cıvanın merkezi sinir sisteminin üzerindeki etkileri artarak nörotoksik sonuçlar doğurur. Cıvanın tehlikeleri bütün dünya tarafından kabul edilmiştir ve ABD Çevre Koruma Ajansı'na göre (EPA), vücut ağırlığından yola çıkılarak, günlük olarak maruz kalınan cıva miktarı kilogram başına 0,1 µg miktarını aşılması durumunda, vücutta biriken cıva artık ölümcül sonuçlara yol açabilmektedir. Tüm bu nedenlerle cıva miktarının doğru ve hızlı bir şekilde tayin edilmesi çok önemlidir. Günümüzde bilinen yöntemler arasında cıva tayini için AAS ve ICP-MS gibi analitik yöntemler kullanılmaktadır. Ancak bu yöntemler pahalı cihaz ve ekipman gerektirmesi, karmaşık hazırlık süreci gerektirmesi, kalifiye-uzman eleman gerektirmesi bakımından dezavantajlıdır. Bu yöntemlere alternatif olarak florometrik ölçüm sağlayabilen kemosensörler, hem kullanım kolaylığı hem gerçek zamanlı analiz yapabilme yetenekleri başta olmak üzere, hassas, seçici, pahalı ekipman gerektirmeme, basit ve kolay hazırlık aşamalarına sahip olma gibi avantajlarından dolayı son zamanlarda daha çok ilgi görmektedirler. Bu bağlamda, bu tez çalışmasında hem UV-Gör hem de floresan teknikleriyle Hg 2+ analizi gerçekleştirebilen, piren ile modifiye edilmiş, kromenilyum-siyanin tabanlı bir yakın kızıl ötesi bölgede ölçüm yapabilme özelliğine sahip sensör platformu (CS2P) sentezlenmiştir. Sentezlenen bu sensör bileşiğin karakterizasyonu X-Işını Kristallografisi, NMR, IR ve MALDI-TOF gibi yöntemlerle yapılarak, sensörün yapısı net bir biçimde aydınlatılmıştır. Çalışma koşullarında sensör DMF çözücüsü ile çözülerek çalışılmıştır. Normalde uçuk sarı renge sahip olan bu sensör çözeltisi Hg 2+ iyonu varlığında koyu yeşile dönerek hem kolorimetrik hem de bu dönüşüm sonucunda 750 nm'de şiddetli bir floresan emisyonu ve UV-Gör spektrumunda 723 nm'de yeni bir bant oluşumu görülmektedir. Hg 2+ iyonuna seçici ve hassas olan sensörün titrasyon çalışmaları yapılmıştır ve bu veriler ışığında tespit limiti UV-Gör ve floresan titrasyon ölçümleri için sırasıyla 2,09 × 10 -8 M ve 1,27 × 10 -8 M olarak bulunmuştur. Bağlanma sabiti (K a ) değeri, UV-Gör titrasyon verileri üzerinden hesaplanmış ve 1,39 × 10 4 M -1 olarak tespit edilmiştir. Tasarlanan CS2P kemosensörünün, Hg 2+ iyonunu tayin etme süresi ise florometrik olarak incelenmiş olup 10 saniye gibi çok kısa bir sürede analite yanıt verebildiği belirlenmiştir. Daha sonra sensör ile Hg 2+ analizi yapılmasının diğer metal iyonları tarafından girişime uğrayıp uğramadığı incelenmiş ve çinko ve demir(II) katyonları hariç hiçbir metalin belirgin bir girişim göstermediği görülmüştür. Buna ek olarak, içme suyu örneklerinde Hg 2+ tespit potansiyeline sahip bir sensör olduğu UV-Gör ve florometrik çalışmaları ile ortaya konulmuştur. Böylelikle, piren modifiyeli rodamin- siyanin tabanlı, UV-Gör ve floresan olmak üzere çift kanallı analiz yapabilen, Hg 2+ iyonuna seçici ve hassas bir kemosensör literatüre kazandırılmıştır.
Visible light induced conventional step-growth and chain-growth condensation polymerizations by electrophilic aromatic substitution

(Graduate School, 2022-06-29) Gençosman, Emirhan ; Yağcı, Yusuf ; 509201210 ; Chemistry

The importance of photochemical processes has been on the rise over the last two decades, this being both due to their numerous self-evident advantages over conventional processes, and the ever growing need for making existing processes more environmentally friendly, which is among the superior aspects of photochemical processes in contrast to conventional ones. Some of the most prominent features of photochemical processes are: spatial and temporal control, cost-effectiveness, the ability to work at low temperatures, and as formerly mentioned, being eco-friendly. Photochemical processes, particularly photoinduced polymerizations, have various applications, including dental fillings, 3D printing, inks, adhesives, coatings, and photoresists. The implementation of photomediation into step growth polymerization, which is widely used and is of the two general modes of polymerization, has thus far received less investigation and development compared to its alternative. PPM, also known as "polybenzyl", is one of the earliest compounds synthesized belonging to the class of poly(phenylene alkylene). Its usual methods of synthesis involve the use of strong Lewis or Bronsted acids in order to induce the step growth condensation polymerization of either benzyl halides or benzyl alcohol. PPM polymers are known to have a very interesting property, that is photoluminescence activity in the absence of conventional mechanisms that may cause a compound to fluoresce, such as pi conjugation along the polymer chain or excimer formation as seen in compounds like anthracene and pyrene. In this thesis, a PPM derivative has been synthesized by the visible light induced step-growth cationic polymerization of the monomers dihalomethane and dimethoxybenzene in the presence of Mn2(CO)10 and an onium salt. The pathway that was chosen for this polymerization reaction was expected to lead to a situation where growing chains would have higher reactivities than monomers, leading to polymerization kinetics that would differ from being purely step growth. Such polymerization reactions, called chain condensation polymerizations (CCP), in which the reactivities of dimers, trimers and so on towards monomers, are higher than the reactivities of the monomers towards themselves, have been established by others in the literature, and are known to respond positively to deviations from the 1:1 stoichiometric ratio, contradictive to the trends seen in step growth polymerizations. Polymerizations using different monomer to monomer ratios were carried out and the polymer molecular weights were indeed found to increase with larger stoichiometric imbalances rather than decline, confirming that the polymerization follows a CCP mechanism at imbalanced monomer ratios. Moreover, the telechelic nature of the polymer was evaluated with a grafting reaction that was carried out using the same cationic photoinitiating system and PPM was successfully grafted onto a poly(MMA-co-GMA) prepolymer as confirmed by GPC and 1H-NMR measurements, confirming the presence of bromine terminating ends on the polymer.
Synthesis, properties and device applications of thienothiophene containing polymers with different functional groups

(Graduate School, 2022-06-30) Güntürkün, Dilara ; Öztürk, Turan ; 509201207 ; Chemistry

Conjugated polymers have received increasing attention for use in various optical and electronic applications, such as organic light emitting diodes (OLEDs), organic solar cells, luminescent sensors, electrochromic devices, capacitors, organic field effect transistors (OFETs), and biological imagery. Many π-conjugated aromatic units, such as benzene, thiophene, pyridine, fluorene and carbazole, have been introduced in the conjugated polymer backbone. Amongst them, thiophene exhibits outstanding properties, due to its high π-electron density, band gap tunability, more reactivity and stability. Extension of the π system increases the conjugated length of the molecule, leading to a decreased band gap and often increased charge carrier mobility. Thienothiophenes (TTs) are the simplest fused and π-extended structures of the thiophene family. Especially, thieno[3,2-b]thiophene, is the most stable and highly conjugated isomer of TTs. Due to their electron rich, flat, rigid, and good electron delocalized skeleton, thienothiophene (TT) is one of the most impressive organic cores, and has gained significant attention in the organic polymeric materials in recent years. In this thesis, possessing cyano (CN), carboxylic acid (COOH) and dimethylamine (N(CH3)2) substituted thieno[3,4-b]thiophene (TT), π-extended conjugated three novel polymers (P1-P3) with 3- hexylthiophene were successfully synthesized by Suzuki coupling. All the polymers were found to be well soluble owing to the side chains. Effects of the functional groups (CN, COOH and N(CH3)2) on the polymers were compared and examined by optical, electronic, thermal, sensor study and memory applications as well as time-dependent DFT calculations for both monomers and dimers. Moreover, the photophysical characterization of the novel polymers demonstrated a significant mega Stokes shift, reaching 138 nm with a bathochromic shift, and a changing electronic band gap between 1.91 and 2.33 eV as well as good thermal stability of degradation temperature around 320 oC. Also, their F− anion-recognition abilities have been investigated with selectivity of different fluoride concentration for UV and emission titration spectra. Memristive switching properties were examined by using synthesized polymers as an active layer in memory devices. The highest ON/OFF ratio of the memory devices were recorded to be 106 with good stability, which makes them suitable for electronic applications.
Efficient post-polymerization modification of pendant aldehyde functional polymer via reductive etherification reaction

(Graduate School, 2022-10-14) Akar, Emre ; Durmaz, Hakan ; 509201209 ; Chemistry

Providing novel synthesis methods for functional polymers designed for specific applications is crucial in polymer chemistry research. While the most straightforward method for preparing functional polymers is the polymerization of specifically designed functional monomers, post-polymerization modification (PPM) of polymers is also an essential tool to obtain desired polymers. PPM is particularly useful when direct polymerization of functional monomers is not suitable due to the possibility of side reactions in the polymerization conditions that can lead to the loss of desired functionality. A good PPM technique should fulfill some requirements such as quantitative yields, easy to conduct under mild conditions, and easy to purify. The reactions classified under the term "click" chemistry are commonly used for the PPM of polymers. Aldehydes have always been a privilege in polymer science since the aldehyde carbonyl readily undergoes several reactions efficiently under mild conditions, ranging from non-aldol reactions to multicomponent reactions, mostly without any additive. Aldehyde-functional polymers can be synthesized via polymerization of monomers with aldehyde functionality. Polymers with pendant aldehyde groups are known as good platforms for PPM given the reactivity of the aldehyde group. Reductive etherification reaction (RER) is a method to synthesize ethers from ketone or aldehyde groups in the presence of an organosilane reductant, generally along with a Lewis or Bronsted-Lowry acid catalyst. Both symmetrical and unsymmetrical ethers can be obtained via the RER. While self-reduction of carbonyl compounds yields to symmetrical ethers, alcohols are used as nucleophiles to prepare unsymmetrical ethers. The RER is known to have high efficiency and good functional group tolerance under optimum conditions. It was shown that chlorodimethylsilane (CDMS)-mediated RER is a robust method for both synthesis and PPM of polymers. In the current study, the versatility of the aldehyde group has been exploited using the RER. For this purpose, a polymer platform containing pendant aldehyde units was synthesized via free radical polymerization (FRP) and modified with a variety of alcohols using CDMS as the reducing agent. The resulting polymers were characterized by using 1H NMR, 13C NMR, GPC, and FT-IR.
Design of biopolymer-based advanced functional materials

(Graduate School, 2022-12-16) Çiftbudak, Sena ; Orakdöğen, Nermin ; 509201251 ; Chemistry

Owing to the growing environmental interest, the use of renewable vinyl compounds, multifunctional organic acids and natural raw materials has led to the development of different methods in innovative material design. Plant extracts and biopolymers have the potential to develop advanced functional materials providing an adequate balance between mechanical strength, adequate swelling ability and biodegradability. In particular, the improvements in environmental performance can be exploited with sustainable polymers, biomass from plants and biopolymers derived from renewable raw materials such as vegetable oils, starch, gelatin, cellulose or chitin. In new methodologies developed for agrochemical applications to improve ecosystem quality, the structures containing the anionic monomer itaconic acid (ITA) have found use in the removal of physical, chemical and biological pesticides. From collagen-derived natural polymers, gelatin (GLN) is an important hydrocolloidal polypeptide for biomedical applications because it has a number of attractive advantages such as renewable character, low cost, excellent biocompatibility/biodegradability, cell adhesive structure and various functional groups for labeling and/or targeting groups and chemical modifications. The research carried out in this thesis is centered around the design of advanced functional materials based on biopolymer and carbohydrate-derived aliphatic dicarboxylic acid. Two synthesis groups were designed for the preparation of anionically modified gelatin containing Semi-IPN hybrid materials. In the first part of the experimental study, the aim was to conduct the preparation of a series of anionic copolymer hydrogels consisting non-ionic mononmer acrylamide (AAm), and anionic comomer itaconic acid (ITA) ranged between 0 and 14 mol% in the feed at a fixed crosslinker ratio. The second goal of the study was to design semi-IPN hybrid hydrogels by selecting the most appropriate anionic copolymer structure from the first synthesis group and convert it into a semi-IPN structure using various amount of Gelatin (GLN). Semi-IPN gels based on poly(acrylamide-co-itaconic acid) and a natural polymer GLN were prepared through one-step in-situ simultaneous crosslinking copolymerization. The effects of the GLN content, the incorporation of carboxyl groups of anionic comonomer ITA and amine/carboxyl functional groups of GLN on the semi-IPN hydrogel properties were investigated by varying the AAm/ITA mol ratio. The effects of changes in various physical conditions such as pH, time, GLN content and salt solutions on the physicochemical properties of gelatin-containing semi-IPNs were investigated. The solvent effect on the swelling behavior and the extent of interactions between the solvent and network chains was evaluated. The first part of the experimental work covered the synthesis of anionic copolymer poly(acrylamide/itaconic acid) (PAAm/ITAx) hydrogels containing varying amounts of the anionic comonomer ITA, ranging from 0 to 14 mol% using redox initiator pair, ammonium persulphate (APS)/N,N,N,N-tetramethylethylenediamine (TEMED) and N,N'-methylenebisacrylamide (BAAm) as a crosslinking agent. It was mainly aimed to establish a relationship between microstructure and effective charge density of anionic PAAm/ITAx hydrogels. The effective charge density turned out to be the dominant factor determining the extent of swelling. The swelling behavior of these hydrogels in water, solutions with different pH values, anionic and cationic surfactants were investigated according to the varying ITA content. A systematic discussion has been made for the variation of pH-sensitive swelling with ITA content to modulate the on-off swelling properties according to the degree of protonation/depronation of the carboxyl moieties. The mechanical properties of anionic copolymer hydrogels, both after synthesis and after swelling, were investigated with Rubber elasticity theory. Considering the equilibrium swelling theory as a simple and reliable tool for calculating the structural network parameters, this methodology has been applied for anionic PAAm/ITA hydrogels. Cationic dye removing capacities of the prepared hydrogels were determined for adsorption of Methylene blue (MB) and Methyl violet (MV) selected as model dyes. The effect of ITA content in the anionic comonomer PAAm/ITAx structure on the adsorption capacity was studied and the adsorption data were tested using the four kinetics models. Kinetic study showed that the adsorption of cationic dyes on anionic PAAm/ITA follows a gradual process with intra-particle diffusion. Besides the application of the prepared hydrogels, the objective of this work was to determine the fraction of ITA used during the synthesis, which is actively involved in the swelling process, by combining the swelling and elasticity results. Depending on the amount of anionic comonomer ITA, the change of crosslink density and effective charge density was determined. The effective charge density turned out to be the dominant factor determining the extent of swelling. In the second part of the thesis, anionically modified gelatin-based multi-responsive semi-IPN hybrid gels were prepared by free radical copolymerization of AAm and ITA in varying amounts of GLN. In order to evaluate the effect of the composition on the physicochemical and mechanical properties, the semi-IPN hybrid hydrogels in this section were designed in two different ways. While weak anionic semi-IPN hybrid hydrogels were prepared by setting AAm/ITA molar ratio as 98/2 in the copolymer network, strong anionic semi-IPN hybrid hydrogels with AAm/ITA molar ratio of 95/5 were prepared to understand the extent of interaction between ITA and GLN parts. In order to observe the GLN effect in both structures, the GLN concentration was changed between 0% and 0.750% (w/v). Semi-IPN hybrid hydrogels were prepared in-situ by first copolymerizing and crosslinking AAm and ITA in the presence of various amounts of GLN using redox initiator pair, APS/TEMED, and BAAm as a crosslinking agent. The effects of changing the GLN content, thus changing the amine/carboxyl functional groups of GLN and incorporating the carboxyl groups of the anionic comonomer ITA into the semi-IPN structure on the swelling behavior, elasticity and physical properties of poly(acrylamide-co-itaconic acid)/gelatin (PAAm/ITA-GLN) hydrogels were investigated. To investigate the effect of gelatin content on the swelling and thermal behavior, gelatin-free anionic copolymeric hydrogels were also prepared as in the first part of the experimental study. Blank copolymer PAAm/ITA hydrogel and its hybrid with GLN were characterized using Fourier transform infrared spectroscopy, X-ray diffractometry, and thermogravimetric analysis. The morphologies of the anionic gel networks were characterized using Scanning electron microscope. The uniaxial compression tests were performed after preparation of hydrogels and after their equilibrium swelling in water. Comparable differences in the swelling properties and elasticity were observed as a result of variation in GLN concentration in the semi-IPN hybrid structure. The composition effect results from the interactions between the functional groups in semi-IPN hybrid network; −CONH2 of AAm, –COOH of ITA, -OH and −NH2 of GLN. The thermal gravimetric analysis (TGA) revealed that the semi-IPN hybrid hydrogels have a higher thermal stability than the conventional copolymer PAAm/ITA hydrogel. Maximum degradation temperatures of semi-IPN hybrid hyfrogels increased with addition of GLN to PAAm/ITA network, and thermal stability was increased with high GLN content compared to other compositions. The uniaxial compression testing indicated that there is a close relationship between the GLN content and the resulting elastic properties as well as the swelling of hybrid gels. Addition of GLN to the semi-IPN hybrid structure in desired ITA content significantly affected the swelling degree and elasticity depending on the extent of interaction between the carboxyl groups of anionic comonomer ITA, hydroxyl groups and the primary amino groups of GLN. The equilibrium swelling of semi-IPN hybrid gels was studied in deionized water as a function of the GLN content. For strongly anionic semi-IPN hybrid hydrogels with AAm/ITA content 95/5, the maximum equilibrium swelling was obtained at 0.225% (w/v) of GLN. The swelling first increased rapidly with increasing GLN concentration, but then a rapid decrease in the swelling of the hybrid gels was observed. For weakly anionic semi-IPN hybrid hydrogels with AAm/ITA content 98/2, the equilibrium swelling increased sharply with an increase in the content of GLN until 0.600% (w/v), then the swelling ratio slightly decreases with further increase in GLN. A highly hydrophilic and pH-responsive system was obtained by adding 5% mol of anionic comonomer ITA to the semi-IPN hybrid hydrogels. The pH sensitivity of the designed semi-IPN hybrid structure is due to both the carboxyl group COOH and NH2 amino groups in the side chain of GLN, as well as the dicarboxylic acid-containing ITA units that show two dissociation stages. While semi-IPN PAAm/ITA-GLN hydrogels did not swell much up to pH 4.87, their pH-sensitive swelling showed a double-step increase with the S-shaped curve around pH 4.7 and 8.0 with progressive ionization of carboxylic groups. All semi-IPN hybrid hydrogels displayed temperature-sensitive swelling behavior as well as the amount of GLN added to the hybrid structure significantly affected the swelling ratio. The swelling kinetics in NaNO3 solutions proceeds by Fickian diffusion and Schott's pseudo-second order model can be effectively used to evaluate swelling kinetics. Swelling tendency in various solvents; n-pentane, n-hexane, THF, acetonitrile, chloroform, acetone, ethylacetate, dimethyl formamide, methanol, cyclohexanol, 1,4-dioxane, DMSO, ethanol, 2-propanol, and toluene showed that semi-IPN hybrid hydrogels have the highest swelling in n-hexane and the lowest in cyclohexanol. Salt-sensitive swelling in Hofmeister salts revealed that semi-IPNs tended to swell more in NaAc solution, whereas they tended to swell less in NaNO3 and NaSCN solutions. The ability of semi-IPN hybrid hydrogels to adsorb cationic dyes MB and MG from aqueous solutions was investigated as a function of GLN content and it was found that GLN-based semi-IPN hybrid gels could be a good adsorbent for the removal of cationic dyes from the contaminated waters. With the method used in this thesis, a simple and effective approach to the design of chemically cross-linked protein-based semi-IPN hybrid hydrogels for dye removal from wastewater was presented, and thermodynamically network parameters were calculated. Keywords: Gelatin, itaconic acid, acrylamide, elasticity, swelling
Synthesis of ZnCdSSe, CdSSeTe quaternary and ZnCdSSeTe quinary alloy quantum dots via two phase synthesis method

(Graduate School, 2023-06-12) Erkan, Merve ; Ünlü, Caner ; 509201216 ; Chemistry

Altering the materials' size and reforming them in nano scale provide important scientific enhancements which facilitates invention and development of purpose-oriented technologies. Decreasing the size of the materials to nano scale leads them to gain beneficial and different chemical and physical properties compared to their original form, therefore nanotechnology term became important to improve revolutionary next generation technologies in accordance with human needs. With the knowledge of the importance of nanotechnology, one of the new nano sized materials called quantum dots becomes popular. Combining generally II-VI and III-V groups of elements found in periodic table while decreasing the size of the compound to 2 -15 nm forms quantum dots [1-3], which have unique optical properties and have great potential to provide important advances in solar cells (Nozik et al., 2010), biosensors (Hakimian et al., 2018), biomedical imagining systems (Mansur et al., 2018), photodetectors (Li et al., 2020), high efficiency LEDs (Pidluzhna et al., 2019), and drug delivery systems. (Ruzycka-Ayoush et al., 2021) [4-9]. Quantum dots are semiconductors, considered as zero-dimensional material and they obey the quantum confinement effect, which is the main reason why quantum dots have great potential to be used in such a wide range of application area. Their zero-dimensional form and having smaller size than their Bohr radius affect their energy bands, found in their conduction and valance band, make them to gain discreet form and this provides several advantages over their original bulk form whose energy band are in continuous form. Discrete form of the energy bands and quantum confinement effect enable quantum dots' optical properties become tunable by changing their size and composition, which leads a change in their band gaps. To understand the effect of the size on optical properties, Brus equation should be considered. (Brus, 1984) [10]. It describes that when size of the quantum dots decreases, their Bohr radius becomes smaller, which is the length of an exciton and exciton can be described as when a photon came, an electron passes through the conduction band, and it is considered that a hole is remained behind in the valance band. This electron and hole pair are called exciton and decreasing the size of the quantum dots causes a decrease in the distance between electron and hole pair while increasing the band gap, which provides the generation of small length of exciton. [1] Smaller length of an exciton requires more energy to separate its electron from its hole by a photon in order that the electron passes to the conduction band. As a result, recombination of electron and hole causes higher energy photon emission compared to the bigger size quantum dots. This is the main reason that decreasing the size of the quantum dots provides blue shift while increasing the size causes red shift in the absorption and the emission of the spectra. The tunability of the band gap by changing size and compositions provides diversity in optical properties of the quantum dots and this explains their importance to the improvements of the next generation display technologies. In addition, they are known as possessing high quantum yield, it provides signal brightness and helps them to eliminate other signal interferences for the display technology and their high surface to volume ratio makes them also attractive to be able to load more active ingredients for the future applications of the drug delivery systems. [11,12] The goal of making quantum dots feasible and suitable for the industry and improve their optical properties to expand their application area, synthesis methods are considered as one of the most important parameters, which have direct effect on size and generated quantum dots' type. Over the years, discovered synthesis methods enable to form not only core type quantum dots, which contain one component in their structure but also to form core -shell model and alloyed systems quantum dots, in which there is possibility to have more than one anion and cation in the structure [13,14]. This leads a great enlargement of the research area of the quantum dots and broaden the possibility of taking advantages on different composition features by affecting directly photophysical properties of the quantum dots. Hot injection method for synthesizing quantum dot is one of the most popular synthesis methods. However, it requires high temperatures and high boiling point solvents and dangerous chemicals. Moreover, fast injection is important as temperature to control the monodispersity, shape and size of the obtained quantum dots [15,16]. To enhance the similar defects of the other synthesis methods resembles to the defects of hot injection methods, two phase synthesis methods is discovered [18]. It allows to obtain quantum dots at low temperature 100 0C, which prevents usage of high boiling point solvents and lower the amount of dangerous chemicals. In addition, it provides slow growth, which enables full control over the shape, size and monodispersity of the obtained quantum dots in a more environmentally friendly medium. To obtain high luminescent quantum dots, cadmium precursors are widely used, and cadmium-based quantum dots are seen to be great candidate for display technology. However, although its high luminescent properties, cadmium toxicity limits the cadmium-based quantum dots usage in biomedical imagining systems and biological technologies. Free cadmium ions cause several damages such as kidney and liver failure while causing cell death on humans and animals, and considered as environmental pollutant [19,20]. In near future, it is expected that Global Environmental Regulations will strictly limit Cadmium usage in next generation display technologies. Therefore, scientists are investigating prevention of releasing cadmium ions from quantum dots structures by applying passivation methods on the surface of the quantum dots and they are trying to reduce the amount of cadmium in the structure. In this study, with the advantages of two-phase synthesis method and alloyed systems, quaternary alloyed CdSSeTe, ZnCdSSe and quinary alloyed ZnCdSSeTe quantum dots were synthesized to expand and ensure Cadmium-based quantum dots usage in next generation display technologies by decreasing the Cadmium amount in the structure while preserving and improving its current beneficial optical properties. Two strategies were followed to wider the application area of the cadmium-based quantum dots. First one was adding zinc to CdSSe ternary alloyed quantum dots in order to obtain ZnCdSSe, which enabled to lower the cadmium amount in the structure and second strategy was to add tellurium to CdSSe ternary alloyed quantum dots to broad absorption and controllable emission wavelength range. It is also planned to obtain ZnCdSSeTe quinary alloyed quantum dots to achieve the goal of lowering cadmium amount in the structure and broaden the controllable wavelength of the quantum dots at the same time. Syntheses were conducted at 100 0C. Toluene used as non-polar phase and distilled water used as polar phase. At the interface between the toluene contained cations and distilled water contained anions, growth of the quantum dots occurred within 3 hours and 24 hours. Zinc stereate (as Zinc precursor) and Cadmium Myristate (as Cadmium precursor) mixed with oleic acid, which was used as surfactant, in toluene phase. Selenium and Tellurium were reduced with sodium borohydride in distilled water to form NaHSe and NaHTe under nitrogen gas to prevent oxidation and added to the polar, distilled water phase. In every determined time frames, adequate amount of the quantum dots, which were passed from the interface to the toluene phase, were taken and their colored emissions, which gives information about the quantum dots' size, controlled by using UV lamp. To enlighten the composition effect and size on optical properties of the quantum dots, Fluorescence spectrometer and UV-Visible spectrometer were used. Absorption and the emission spectra of the synthesized quantum dots within the time interval 1 hour, 3 hours and 24 hours were obtained. It ensured the slow growth of the quantum dots, which was the main features of the two-phase synthesis method. For the samples collected at 1 hour and 3 hours, the peaks are wide and became sharper for the 24 hours samples. It showed the growth of the quantum dots became stable and 24 hours reaction time reduced the dispersity of the size of the formed quantum dots. For the structural characterization XRD was used and precipitated quantum dots after 24 hours reaction time was measured. The result showed that Zinc and Tellurium could be added to the ternary alloyed CdSSe structure to form ZnCdSSe and CdSSeTe. However, adding Zinc to the quaternary alloyed quantum dot ZnCdSSeTe could not be achieved, it was found that crystal structure was distorted while forming quinary alloyed quantum dots. Different amount of Cadmium contained ZnCdSSe quaternary alloyed quantum dots synthesized, and it enabled to understand the importance of the cadmium presence in the structure, and it allowed us to lower the amount of cadmium half of its amount found in CdSSe ternary alloyed quantum dots. In addition, CdSSeTe quaternary alloyed quantum dots synthesized with different ratio of Tellurium resulted to enlarge the absorption and controllable emission wavelength range and with the same amount of the cadmium found in CdSSe ternary alloyed quantum dots, which has blue color could be shift to the yellow with a great shift observed in the spectra.
Yeni tip Aza-BODIPY bileşiğinin sentezi ve karakterizasyonu

(Lisansüstü Eğitim Enstitüsü, 2023-06-15) Bayrak, Esra ; Kahveci, Muhammet Übeydullah ; Özçelik, Şennur ; 509201211 ; Kimya

Yakın kızılötesi bölgesinde (NIR) absorpsiyon ve emisyon yapabilen boyalar sensörler, lazerler, fotovoltaik hücreler ve optoelektronik dahil olmak üzere geniş uygulama yelpazesi nedeniyle uzun yıllardır önemli bir rol oynamaktadır. NIR bölgesinde absoriyon ve emisyon yapan bu boyalar, biyogörüntüleme, boron nötron yakalama terapisi ve fotodinamik terapi dahil olmak üzere biyouygulamada da kullanım bulabilmektedir. Bu boyalar, ışığı absorbe edebilmekte ve daha yüksek bir enerji seviyesine uyarabilmekte ve daha sonra ışık emisyonu ile temel duruma dönerek floresans meydana getirmekte ve böylece biyouygulama için önemli bir araç haline gelmişlerdir. NIR ışığı daha uzun dalga boylarına kayarak, azaltılmış saçılma ve azaltılmış foto hasar ve derin doku penetrasyonu avantajı sağlar. Porfirin ve porfirazin bileşikleri, NIR bölgesinde absorpsiyon ve emisyon yapabilen organik boyalardır. Porfirin ve porfirazinler, fotofiziksel ve fotoelektrokimyasal özelliklerinden dolayı birçok alanda geniş uygulamalara sahiptir. Ne yazık ki zahmetli sentez yöntemleri, saflaştırma adımlarındaki zorluklar ve verimlerinin düşük olması gibi kullanımlarını sınırlayan bazı nedenler vardır. Bu zorluklar, dipirometenler ve aza-dipirometenler boyaları olarak adlandırılan yapısal analoglarının keşfi ile çözülmüştür. Bu dipirometen ve aza-dipirometen bileşiklerinin fotofiziksel özellikleri, BF2+ ve d blok geçiş metali bileşiklerinin şelatları ile ayarlanabilir. Ayrıca bu dipirrometen ve aza-dipirometen boyaları ucuz başlangıç malzemelerinden hazırlanabilir ve basit ve zahmetsiz sentetik yöntemlerle hazırlanabilir. Bu bileşikler düşük konjugasyona sahip olmalarına rağmen, yoğun floresans, yüksek elektron afinitesi ve yüksek molar absorpsiyon katsayısı değerleriyle görünür ve yakın kızılötesi bölgede absorpsiyon ve emisyon özellikleri gibi göze çarpan fotofiziksel özelliklere sahiptirler. Aza-BODIPY adı verilen organoboron NIR boyaları, aza-dipirometenlerin bor kompleksleri olmakla birlikte BODIPY çekirdeğinin mezo konumunda karbon yerine bir nitrojen atomu bulunan BODIPY boyalarının yapısal analoglarıdır. BF2 şelatlanması, aza-dipirometen bileşiklerine kıyasla Aza-BODIPY bileşiklerine daha rijit bir yapı sağlar. BODIPY ve Aza-BODIPY boyaları, güneş pilleri, biyogörüntüleme, lazerler ve fotodinamik terapi gibi çok çeşitli uygulamalarda kullanımları dikkate alındığında karakteristik özellikleri nedeniyle büyük ilgi görmüştür. BODIPY ve Aza-BODIPY boyaları olarak adlandırılan d blok geçiş metali şelatları ile dipirometen ve aza-dipirometen bileşiklerinin temel farkı biyolojik uygulamalarda çok önemi bulunan floresans emisyonunun olmamasıdır. Aza-BODIPY bileşikleri iki farklı yöntemle sentezlenebilir. İlk yöntem, 2,4-diaril pirolden başlayan sentezi içerir. Diğer yöntem, uygulanabilirliğe daha uygun olan O-Shea yöntemi denir. Nispeten daha az sentetik yöntem içermektedir ve bu yöntemler xx kullanılarak reaksiyonlarda yüksek verimle BODIPY ve Aza-BODIPY bileşikleri hazırlanmaktadır. Aza-BODIPY bileşiğinin hazırlanmasına yönelik bu 4 adımlı O-Shea sentetik yöntemi, kalkon bileşik sentezi ile başlar. Birinci adımda, aldol kondenzasyon reaksiyonu ile kalkon türevi bileşik sentezi gerçekleştirilir. Bu O-Shea yönteminin ikinci adımı, Michael ilavesiyle kalkon türevinin nitrasyonunu içerir. Aza-dipirometen türevi üçüncü adımda dimerizasyon yoluyla elde edilir. O-Shea yönteminin son adımında oda sıcaklığında BF3.OEt2 kullanılarak BF2 şelatanmasıyla ile Aza-BODIPY bileşiği elde edilir. Aza-BODIPY boyaları terapötik pencerede güçlü absorpsiyon ve emisyon bantlarına sahip olduğundan, bu bileşikler Fotodinamik Terapi (PDT) için ideal bir ışığa fotouyarıcılardır. Fotodinamik Tedavinin (PDT) işlevsel olabilmesi için doku penetrasyonunun sağlanması ve bunun için NIR bölgesinde (özellikle NIR-II bölgesinde) penetrasyon derinliği için güçlü absorpsiyonun sağlanması gerekir. Aza-BODIPY bileşikleri, BODIPY boyalarınınkine kıyasla nispeten yüksek singlet oksijen kuantum verimlerine sahiptir, çünkü BODIPY'lerin Fotodinamik Terapide (PDT) bir fotouyarıcı olarak uygulamalarını sınırlayan şiddetli floresansları vardır. Aza-BODIPY boyalarının maksimum absorpsiyon ve emisyon dalga boyları, BODIPY bileşiklerine kıyasla belirgin şekilde daha yüksek dalga boylarında görülmektedir. BODIPY bileşikleri genellikle 550 ila 600 nm civarında absorpsiyon piklerine sahipken, Aza-BODIPY bileşiklerinin absorpsiyon pikleri, yüksek penetrasyon sağlayan biyolojik uygulamalar için uygun olan 650 nm'nin ötesinde bulunabilir. Aza-BODIPY boyalarının absorpsiyon pikleri, 1300 nm'ye kadar batokromik olarak kaydırılabilir. Bu batokromik kayma, HOMO-LUMO enerji aralığındaki azalma ile açıklanabilir. Bu modifikasyon, elektron veren grubun 3,5-fenillerin para konumuna veya elektron çeken grubun 1,7-fenillerin para konumuna sokulmasıyla uygulanabilir. İki ana modifikasyon yöntemi uygulanabilir: Distal ve proksimal fenil gruplarına elektron alıcı ve donörü fonksiyonel grupların eklenmesi. Ayrıca Aza-BODIPY emisyonları, BODIPY türevlerine kıyasla yaklaşık 80 nm daha fazla batokromik kaydırılabilir. Aza-BODIPY bileşikleri ile ilgili çalışmalar son yıllarda dikkat çekici fotofiziksel ve fotokimyasal özelliklerinden dolayı önemli ölçüde artmıştır. Ayrıca, güçlü ve keskin absorpsiyon ve emisyon özellikleri, distal ve proksimal fenil gruplarına elektron alıcı ve donör fonksiyonel grupların eklenmesi veya π konjugasyonunun arttırılması ile ayarlanabilir. Bu modifikasyonlar fotostabiliteye, yüksek floresans kuantum verimine, yüksek singlet oksijen kuantum verimlerine, yüksek moleküler absorpsiyon katsayılarına, görünür aralıkta ve NIR bölgesinde güçlü absorpsiyon ve emisyon dalga boylarına neden olur. Günümüzde PDT gibi biyouygulamalarda kullanılabilecek en umut verici organik bileşiklerden biri, yukarıda belirtilen karakteristik özellikleri nedeniyle Aza-BODIPY boyalarıdır. Bununla birlikte, Aza-BODIPY'nin biyomedikal uygulamalarda kullanımını sınırlayan ana dezavantajı, aromatik halkaların varlığı ve Aza-BODIPY çekirdeğinin oldukça düzlemsel yapısı nedeniyle agregasyondan kaynaklanan suda zayıf çözünürlükleridir. Bu tez kapsamında, etkinlik alanını genişletmek ve farklı uygulamalara kapı açmak amacıyla suda çözünür polimerlerin sentezinde kullanılabilecek Aza-BODIPY türevi içeren monomer bileşiğinin sentezi ve karakterizasyonu hedeflenmiştir. Bu amaçla, öncelikle distal fenil gruplarının para pozisyonlarında hidroksil grupları taşıyan bir Aza-BODIPY türevi sentezlenmiş ve akabinde bu hidroksil gruplarını içeren Aza-BODIPY, polimerleşebilen bir metakrilat sübstitüe Aza-BODIPY monomerine dönüştürülmüştür. Elde edilen monomer bileşiği, FT-IR, UV-Vis ve 1H-NMR spektroskopik yöntemleri ile karakterize edilmiştir. Elde edilen Aza-BODIPY yapılı monomer bileşiğinin, UV-Vis absorbansında Aza-BODIPY bileşiğine göre 6 nm hipsokromik kayma yaptığı gözlemlenmiştir.
White led induced degradation of polyacrylates as a green alternative for polymer recycling

(Graduate School, 2023-06-19) Çakır, Yüsra Bahar ; Kışkan, Barış ; 509211277 ; Chemistry

In today's world, plastic materials are used almost every day due to their advantageous properties. However, widespread use of plastics has resulted in serious environmental issues, such as the buildup of plastic waste and its damaging effects on ecosystems. Efforts are underway to find effective recycling methods for widely used polymers as part of the journey towards a greener and more sustainable world, aiming to reduce this dependence. The topic of enhancing the sustainability of polymers is at the forefront of the discipline of polymer science and engineering, and it includes a variety of strategies, from mechanical recycling to degradation and chemical recycling. Poly(methyl methacrylate) (PMMA) is a polymer that holds great significance within the realm of materials due to its remarkable combination of high-impact strength, optical clarity, and lightweight characteristics. Various applications of PMMA have resulted in considerable consumption and generation of noticeable amounts of waste. By 2027, it is projected that the consumption of polymers will reach a level of 4 million tons per year and as the years pass, it could further increase. Since PMMA does not have a hydrolysable main chain, depolymerization or degradation requires advanced recycling methods. These methods involve some requirements that are both economically and environmentally harmful, such as high temperatures and heavy toxic metal catalysts. Despite the challenging conditions, the research conducted contributes to polymer recycling. However, replacing these requirements with some green alternatives is highly appealing. Photochemical reactions, with advantages such as being environmentally friendly and low energy consumption, have gained attention both in industry and academia. The idea of adapting light-induced reactions to this field and using a catalyst other than metal-based catalysts, which are another environmental pollutant factor, shed light on this study. In this study, we take advantage of the efficient properties of light in the field of degradation. We present a novel approach utilizing a white LED light source and a metal-free method for the degradation of PMMA derivatives that contain halogen in the main chain. A copolymerization incorporated PMMA derivatives containing light-triggerable halogen atoms into the main chain. The Reversible Addition-Fragmentation Chain Transfer (RAFT) controlled polymerization technique was employed for the synthesis of methyl methacrylate-methyl α-chloroacrylate and methyl methacrylate-ethyl cis-3 bromoacrylate copolymers. In the presence of organodyes (metal-free catalysts) the synthesized copolymers undergo efficient degradation into low molecular weight oligomers when irradiated with visible light. This study serves as a realistic approach to polymer recycling and leading to the development of more sustainable recycling methods for polymers.
The interaction of CD-based chalcogenide quantum dots with raw photosynthetic pigments

(Graduate School, 2023-08-28) Aykut, Sümeyye ; Ünlü, Caner ; 509211271 ; Chemistry

The detrimental effects of global warming caused by usage of fossil fuels and toxic gas emission to the atmosphere could be dramatically decreased by environmental sustainability and renewable energy resources. Moreover, coal, oil and gas classified as fossil fuels which almost the whole energy of the world derived from is going to respectively be over in 107, 35 and 37 years. That is why alternative renewable energy sources are quite important according to scientists. It is possible to utilise renewable energy resources in almost all areas where fossil fuels have a usage. Renewable energy is able to be used in the production of electricity, in transportation and logistics as a fuel, in buildings and industrial processes as a heat release after conversion. Wind, flowing water, sunlight, the internal heat of the earth and biomass are natural resources of renewable energy. Biomass is a significant renewable energy source because of its economic potential, easiness in production and functional usage in many areas. Biomass is defined as organic materials in total produced by a living organism like plants and animals in a stated time and place in the world. Biomass could be manufactured by almost all organic materials we know such as seed waste, wood, wastewater, paper waste, straw and manure. These days, better half of biomass production is produced by products of agriculture which are known as energy crops. That makes photosynthesis that underlies formation of food and fibre along with biomass-based biofuels quite an important process. Photosynthesis and the energy conversion required for the production of biomass are utterly related to each other. In this thesis, quantum dots having three various structures were interacted with photosynthetic pigments which are responsible for light harvesting to increase and simplify biomes production by enhancing the efficacy of photosynthesis. In addition, photosynthetic pigments were extracted by spinach leaves that are easily provided and they are kept intact during the interactions. The compositions of quantum dots' structures were designated in accordance with the absorption wavelengths of photosynthetic pigments. The quantum dots interacted were oleic acid-capped CdSSe QDs, CdSTe QDs with the Te-riched core and CdSTe QDs with the outer S-enriched region. Also, all quantum dots were synthesis two-phase synthesis method which is one of the bottom-up approaches. The CdSSe QDs were synthesised as they have an emission in the same UV range in electromagnetic spectrum that photosynthetic pigments absorb light. The CdSTe QDs with the Te-riched core have a stated composition owing to the same reason and emission spectrum in the near IR region that pigments have also absorption. The CdSTe QDs with the outer S-enriched region have no emission of light in any common region with photosynthetic pigments that absorb radiation. Those quantum dots are synthesised to examine the quantum dot-photosynthetic pigment interaction when there is no possibility of energy transfer. The results of the interactions were analysed by UV-Visible Spectrophotometer and Fluorescence Spectroscopy and experimental data was exhibited in the section of Results & Discussion in detail. As a result of all experiments, the absorption intensity of the photosynthetic pigments interacted with the Te-enriched CdSTe QDs was increased by 50% at the excitation wavelength of 410 nm. Additionally, the light harvesting capacity of photosynthetic pigments was enhanced at 500-575 nm in the green-light range of spectrum in the presence of the CdSTe QDs with the Te-riched core.
Alev geciktirici 9,10-dihidro-9-oksa-10-fosfafenantren 10-oksit (DOPO) ile fonksiyonelleştirilmiş epoksi reçine sisteminin geliştirilmesi ve karakterizasyonu

(Lisansüstü Eğitim Enstitüsü, 2023-09-15) Arslan, Fatma Zeynep ; Sevim, Altuğ Mert ; 509181313 ; Kimya

Epoksi reçineler, mekanik özellikleri, boyutsal kararlılığı, uygun kimyasal ve termal direnci sayesinde kaplamalar, kompozit malzemeler, yapıştırıcılar ve enjeksiyonlu kalıplama malzemelerinde kullanılmaktadır. Ancak epoksi malzemeler iyi özeliklerinin yanında kolay alevlenebilir oluşundan dolayı havacılık, otomotiv ve yapı sektöründe bazı standartlarla belirlenmiş kısıtlamalara tabidir. Mukavemet gibi özelliklerine zarar vermeden alev direncinin geliştirilmesi gerekir, bu doğrultuda istenen alev direnci özelliklerinin sağlanması için epoksiye katkılama ajanlarının optimum oranlarda eklenmesi gerekmektedir. Toksik özellikleri değerlendirilerek, çevre dostu ürünlerle alev direncinin sağlanması üzerine son yıllarda çalışmalar artmıştır. Alev direnci sağlanırken mekanik özelliklerin korunmasına yönelik yapılan bu çalışmada ilk olarak amonyumpolifosfat (APP) ile epoksilerde alev direnci geliştirilmeye çalışılmıştır. APP'nin epoksi reçine sisteminde alev direnci sağlayabilmesi için % 30' un üzerinde katkılama yapılır. Mukavemet değerlerinin yüksek katkılama oranlarında korunamaması, çalışmanın yakın konsantrasyonlarda yüksek verim sağlayan 9,10-Dihidro-9-Oksa-10-Fosfafenraten 10-Oksit (DOPO) ve türevleri ile sürdürülmesini gerekli kılmıştır. Hazırlanan deney prosedüründe öncelikli olarak mevcut epoksi reçine sisteminde DOPO' nun katkılanabileceği optimum miktar belirlenmiş, UL 94 dikey yanma testine göre %30 katkılama ile V1 seviyesinde yanma direnci elde edilebildiği görülmüştür. Azot (N) yapısı içeren amin ve aldehitlerle ligand sentezleri yapılarak organik yapıya dahil edilmiş, DOPO türevi bileşenlerin(6-(((4-hidroksifenil)amino (piridin-4-ilmetil)dibenzo)okza fosfin 6 oksit), 6-(((4-hidroksifenil)amino (piridin-2-ilmetil)dibenzo)okza fosfin 6 oksit), 6-((4-dimetilamino)fenil(4-hidroksifenil)amino)metil dibenzo okza fosfin 6 oksit) reaksiyonda hem alev geciktirici hem katalizör etkisi göstermesi beklenmiştir. Molekülün epoksi yapısına doğrudan dahil edilmesiyle yanma direnci sağlanırken, mukavemet değerlerinin korunması da hedeflenmiştir. Sentez sonucunda elde edilen en iyi numune ile metal komplekslerinin sinerjist etkisi sağlanmak üzere bakır, çinko ve kobalt ile reaksiyon gerçekleştirilmiştir. Çalışma kapsamında sentezlenen DOPO türevi bileşenin epoksi içerisindeki yanma direnci ve mukavemet değerleri modifiye edilmemiş epoksi reçine sistemiyle kıyaslanmıştır.

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