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  • Öge
    Development of supramolecular hydrogels with adjustable viscoelastic, mechanical and self-recovering properties
    (Lisansüstü Eğitim Enstitüsü, 2021) Su, Esra ; Okay, Oğuz ; 709854 ; Kimya
    Biological systems are living systems with unique features such as self-healing, reorganization, and being able to respond to external stimuli. The production of synthetic materials with similar properties by imitating biological systems will prevent the loss of both raw material and energy and will increase the quality of life. Thanks to the new generation hydrogels with these features, soft and smart materials, underwater adhesives, wound dressings, actuators, sensors and many more will be used in daily life to replace the living tissues. Today, many research groups continue their studies for the production of hydrogels with a double network structure, nanocomposite hydrogels, cryogels, tough and shrinkable gels, as well as cost-effective soft devices. Despite all these efforts, the design of autonomous self-healing soft materialswith a high mechanical strength is still a big problem. In the first part of the thesis, self-healing hybrid crosslinked poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS)-based hydrogels with a high mechanical strength were synthesized by solution polymerization of AMPS without using any initiator. Although PAMPS hydrogels have been in use for many years due to their large swelling capacities, they are brittle and exhibit no self-healing behavior limiting their applications. Recently, PAMPS hydrogels were prepared without an initiator by thermal polymerization. However, these hydrogels were easily soluble in water and their use was also limited due to their poor mechanical properties. To develop high mechanical strength in PAMPS hydrogels and hinder their water solubility, three strategies were applied in the first part of the thesis, namely, clay nanoparticles and a chemical crosslinker were included into the reaction system both separately and together to produce nanocomposite, chemically cross-linked, and hybrid cross-linked PAMPS hydrogels, respectively. Although both nanocomposites and chemically cross-linked hydrogels up to 2 mol% crosslinker content PAMPS hydrogels were weak and easily soluble in water, hybrid crosslinked ones formed using both clay nanoparticles and chemical crosslinkers were water insoluble, and exhibited good compressive mechanical properties with a Young's modulus of around 0.7 MPa together with a sel-healing ability. The hybrid strategy thus developed within the framework of the thesis is a novel and general approach for the production of nanocomposite ionic hydrogels with self-healing ability. The synthesis of water-stable PAMPS hydrogels formed by only H-bonding interactions has not reported before. This is due to the 100-fold weaker strength of H-bonds compared to the covalent bonds, leading to the dissociation of H-bonds between the PAMPS chains in water. However, cooperativity of H-bonds similar to those in double-stranded DNA would create H-bonded physical hydrogels of high mechanical strength. This was the idea behind the experiments conducted in the second part of the thesis. UV photopolymerization of AMPS in water was conducted in the presence of 2-hydroxy-4'-(2-hyroxyethoxy)-2-methylpropiophenone (Irgacure 2959) photoinitiator at a high AMPS concentration without using any chemical crosslinkers. As compared to the thermal polymerization at 80 °C leading to water soluble PAMPS hydrogels, UV polymerization at 23±2 °C produces water-insoluble hydrogels exhibiting an equilibrium swelling ratio of 1013±53, i.e., the mass of the hydrogel around 1013-fold increases upon swelling in an excess of water. Although the hydrogels are stable in water, they all could be dissolved in aqueous urea solutions due to the breaking of H-bonds. The network chains of PAMPS hydrogels formed by UV polymerization was found to have a much higher molecular weight as compared to those obtained by thermal polymerization. This reflects strengthening of H-bonds with increasing chain length due to the so-called proximity effect. Moreover, the addition of N,N-dimethylacrylamide (DMAA), a non-ionic monomer, to the UV polymerization system further improved both the mechanical properties and self-healing behavior of PAMPS hydrogels. The results could be explained with the hydrogen donor-acceptor relationship between DMAA-AMPS units. Because the hydrogels are physically cross-linked by H-bonds, they heal completely within minutes without any external stimuli. In addition to self-healing, the combination of supramolecular crosslinks also imparted shape-memory properties to the PAMPS hydrogels. Cryogelation is a simple and environmentally friendly technique for the production of macro-porous hydrogels, called cryogels, which exhibit extraordinary properties such as a large porosity, full squeezability, high toughness, and super-fast responsiveness. Cryogelation reactions are usually conducted at 10 to 20 °C below the freezing temperature of the reaction solution and hence, the reactions proceed in the unfrozen domains of the apparently frozen reaction system. Because of the cryoconcentration, the concentrations of the reactants in the unfrozen domains significantly deviate from those in the initial reaction system. Therefore, the cryogel studies reported so far are incomplete as they consider the initial conditions instead of the real conditions of the cryogelation system. Within the scope of the third part of the thesis, the relationship between the real conditions of the cryogelation, that is, the conditions in the unfrozen domains, and the cryogel properties were investigated. For this purpose, cryogelation of AMPS in the presence of N,N'-methylene(bis)acrylamide (BAAm) as a crosslinker was conducted in aqueous solutions at 18 °C. Two series of experiments were carried out to highlight the effects of the chemical crosslinker BAAm, and the initial monomer concentration C0 on the cryogel properties. In the first series, the amount of BAAm was changed in the range of 1.2-9.1 mol% while the monomer concentration, C0 was fixed at 10%. It was found that the swelling capacity of the cryogels decreases with the increasing amount of the crosslinker while, their mechanical strength increases. This improvement was reflected in a 7-fold increase in Young's modulus and 4-fold increase in the fracture stress of the cryogels. In the second series, the initial monomer concentration C0 was changed between 10 and 25 wt% at a crosslinker content of 1.2 mol%. The mechanical properties of the cryogels remained almost unchanged by varying C0 while their swelling capacity decreased as C0 is increased. It was also observed that the cryogels formed at 10 and 15 wt% monomer concentration were transparent when swollen in water, while those formed at 20 and 25 wt% were opaque indicating the onset of a phase separation during reactions. As mentioned above, the main aim of this last section was to determine the actual reaction condition under which cryogelation took place and to examine its reflection on the final cryogel properties. For this purpose, the real monomer concentration (Ctrue) in the unfrozen domains, and the volume of ice Vice acting as a template for the pores were determined by DSC measurements conducted on apparently frozen reaction solutions. Although the real monomer concentration Ctrue was independent on the actual concentration Co, both the ice volume Vice and the ratio Ctrue/Co decreased with increasing Co. These changes determined both the morphology and mechanical properties of PAMPS cryogels. In short, the experiments carried out in this section have shown that it is possible to control the structure of the final cryogels by controlling the real synthesis conditions during cryogelation.
  • Öge
    Rational design of hydro- and organo-cryogels
    (Lisansüstü Eğitim Enstitüsü, 2021) Yetişkin, Berkant ; Okay, Oğuz ; 709838 ; Kimya
    Over billions of years of evolution, nature has selected soft materials, i.e. cells and tissues, as vital components for living beings. For instance, articular cartilage tissue in Homo Sapiens covers the bone ends and joints and it provides the actualization of basic movements such as bending of the arms and legs. This tissue can endure almost 1 million cycles per year, and it can be compressed up to a stress of 10 MPa without fraction. In addition, it possesses direction-dependent mechanical properties, i.e. anisotropy. However, these extraordinary mechanical properties of the tissues providing continuity in the lifespan of a living being can not be easily observed in man-made soft materials, i.e. hydrogels. In another word, hydrogels prepared by traditional methods are very brittle materials and some of them can not be endured to even one cycle, and break at Pa- or kPa-order stress values. Besides, their mechanical properties are not direction-dependent and they have isotropic mechanical properties. After revealing nature's design principles in cells and tissues, i.e. when understand their chemical compositions and physical organizations, material scientists started to fabricate mechanically durable materials via mimicking nature. For instance, the mechanical stability of the articular cartilage arises from the extracellular matrix (ECM), which is composed of a structural protein called collagen creating a strong framework, and proteoglycans such as hyaluronan acting as energy dissipative fragments within ECM. Therefore, techniques developed for the preparation of high strength and toughness hydrogels have been mainly based on creating an efficient energy dissipation mechanism within the gel network. Cryogels, i.e. cryogenically synthesized macroporous polymer gel matrices, exhibit this energy dissipation mechanism via poroelasticity effect, due to their interconnected micron-sized pores. Moreover, cryogels possess extraordinary compressive strength up to MPa order as their gel walls originate from unfrozen liquid fractions where the concentrations of the reactants are much higher than that of their initial state. Another advantage of the cryogels is their convenience to orienting the pores as desired to create anisotropy. Within the scope of this thesis, novel hydro- and organo-cryogels were prepared from aqueous and organic reaction solutions of specific polymers, respectively. Therefore, the thesis can be divided into two main parts associated with hydro- and organo-cryogels. The first part, i.e. hydro-cryogel part, is based on two publications, in which anisotropic silk fibroin (SF) cryogels possessing aligned pore morphologies were fabricated by using two different pathways. SF is a natural biopolymer derived from some spiders and silkworms. Due to its extraordinary properties such as biocompatibility, biodegradability and excellent mechanical toughness, it has become a very demanded biopolymer for biological applications. Therefore, SF was used in this thesis in order to fabricate hydro-cryogels. On the other hand, organic solutions of butyl rubber, i.e. synthetic isoprene-isobutylene rubber, were used to synthesize organo-cryogels as macroporous passive sampler sorbents. In the first publication, anisotropic SF cryogels were obtained after directly immersing the reactors containing aqueous SF reaction solutions into liquid nitrogen at various immersion rates. The cryogel scaffolds exhibited a Young's modulus in the range of MPa and sustained up to 20 MPa compressive stresses. In addition to high mechanical strength, they also exhibited anisotropic microstructure and hence anisotropic mechanical properties, e.g., the Young's modulus (E) is 3.4 ± 0.5 MPa and 0.8 ± 0.3 MPa when measured along with the directions parallel and vertical to the freezing direction, respectively. In the second publication, we presented a different experimental set-up consisting of a copper bottom plate and a cylindrical polytetrafluoroethylene (PTFE) mold in order to fabricate anisotropic SF cryogels. The copper bottom plate was immersed in a cold bath at -30 or -196 °C, whereas the cylindrical PTFE mold locating outside of the cold bath was filled with aqueous solutions of SF of various concentrations. Unidirectionally frozen SF solutions were then subjected to cryogelation at -18 °C. Finally, we obtained mechanically strong SF scaffolds exhibiting microstructural, swelling and mechanical anisotropies. The scaffolds exhibited the highest modulus anisotropy of 21 ± 5 so far reported to our knowledge, i.e., Young's moduli E = 2.3 ± 0.5 and 0.11 ± 0.03 MPa measured along parallel and perpendicular to the freezing direction, respectively. We also demonstrated that, independent on the fibroin concentration or direction of the measurements, 60% of the mechanical energy given to the cryogels are dissipated due to the friction between the fibroin pore walls, which is responsible for their squeezability and self-recoverability. In the organo-cryogel part, butyl rubber (IIR) based organo-cryogels as a macroporous passive sampler were fabricated. After obtaining a primer IIR cryogel, i.e. single network (SN) cryogel, double (DN) and triple network (TN) cryogels were also prepared via successive cryogelations that were conducted within the pores of the previous cryogel. These multiple network based-cryogelation technique provided fabrication of IIR cryogels with tunable mechanical properties and pore distributions. For instance, they can be stretched up to 400%, and compressed at least 10-times without any significant mechanical deficiency as compared to the initial state. It was also shown that these IIR-based organo-cryogels can be used as an efficient passive sampler for polycyclic aromatic hydrocarbons (PAHs), whose sampling abilities mainly depend on their pore size distribution. For instance, SN rubber sorbent absorbed most rapidly PAHs which is attributed to its largest porosity and pore volume. On the other hand, TN sorbent had the highest sorption capacity because of its smaller pores and low porosity, preventing the escape of PAHs from the sorbent to the solution phase at longer time scales. SF-based hydro-cryogels and IIR-based organo-cryogels fabricated within the scope of the thesis are both novel macroporous materials with extraordinary properties. Due to tissue-like MPa-order mechanical properties and anisotropic architecture, SF cryogels are suitable for several biological applications, especially for tissue engineering. On the other hand, fatigue-resistant and stretchable IIR-based organo-cryogels with adjustable pore morphology can be used as a passive sampler sorbent for organic pollutants in environmental applications.
  • Öge
    Naftokinon tabanlı iyon sensörlerin geliştirilmesi
    (Lisansüstü Eğitim Enstitüsü, 2021) Mermer, Zeliha ; Yılmaz, İsmail ; 709867 ; Kimya
    Cıva (Hg) uçuculuğunun yüksek olması ve sinir sistemine olan etkileri nedeniyle ağır metaller arasından en çok bilinen toksik analittir. Bu yüzden cıvanın oldukça seçici ve hassas tayini için basit ve ileri teknikler geliştirilmesi hem insan sağlığı hem de çevre için bir hayli önem kazanmıştır. Geleneksel metotlar cıva tayini için; atomik absorpsiyon spektroskopisi (AAS), İndüktif olarak eşleştirilmiş plazma kütle spektroskopisi (ICP-MS) ve elektrokimyasal metotları içerir. Bu metotlar oldukça seçici ve hassas olmalarına karşın pahalı ve fazla miktarda numune gerekmektedir. Bu amaç için hazırlanan kimyasal sensörler ucuz, güvenilir ve basit yollarla elde edilebilir olması yönünden birincil önem kazanmaktadır. Bu tez kapsamında öncelikle kolay sentezlenebilen naftokinon tabanlı yeni ve çok kanallı kemosensörler sentezlenmiştir. Kemosensör kullanılarak seçici olarak eser miktarda Hg2+ iyonunun tespit edilmesinde kolorimetrik, florometrik ve voltametrik yöntemler kullanılmıştır. Geliştirilmiş yeni sensörlerin analitik özellikleri detaylı olarak incelenmiştir. Literatürde cıva veya diğer ağır metallere karşı seçici birçok ligant sentezlenmiş ve hassasiyeti UV-Gör ve floresans yöntemleri ile çalışılmıştır. Tez çalışması iki aşamadan oluşmaktadır. Birinci aşamada; 1,4-naftokinon ve anilin bileşiğinin metanol içerisinde substitüsyon reaksiyonu sonucunda hedeflenen Nq-An sensörü literarüre göre elde edilmiştir ve saflaştırılmıştır. FT-IR spektrumunda ve DMSO'da alınan 1H-NMR 13C-NMR spektrumlarında beklenen pikler görülmüştür. MALDI/TOF kütle spektrumu sonucu; bulunan kütle (m/z): 250,259 [M++ H] yapı ile uyum içerisindedir. MeOH içindeki Nq-An çözeltisine Hg(NO3)2.H2O ilave edilerek geri soğutucu altında 1 gece karıştırılıp çözücüsünün buharlaştırılması ve kalan katı ürünün saflaştırılması sonucunda [Hg—(Nq—An)2] cıva kompleksi elde edilmiştir. Kompleksleşme sonucunda FT-IR spektrumunda Nq-An'ye ait piklerin dışında kompleksleşmeye ait 598 (Hg-N), 567 (Hg-C) de beklenen pikler gözlenmiştir. DMSO' da alınan 1H-NMR spektrumu ve DMSO'da alınan 13C-NMR spektrumunda beklenen pikler gözlenmiştir. Civa kompleksinin 13C-NMR spektrumunda, Nq-An'nin C6 atomuna karşılık gelen 102,42 ppm'de gözlenen pik kompleksleşme sonucunda düşük alana kaymıştır. MALDI/TOF kütle spektrumu sonucu; bulunan 699,631 [M++3H] olmuştur. Elementel Analiz sonucunda: yapı ile uyumlu olduğu görülmüştür. 1,4 Naftokinon bileşiğinin piren amin ile olan metanol içerisindeki substitüsyon reaksiyonu sonucunda yeni Nq-Pyr sensörü elde edilmiştir. FT-IR spektrumunda. DMSO' da alınan 1H NMR ve 13C-NMR spektrumu sonucunda beklenen pikler gözlenmiştir. MALDI/TOF kütle spektrumu sonucu; bulunan kütle (m/z), 375,033 [M+] yapı ile uyum içerisindedir. pH 8'de 20 mL DMF/H2O (5:1 v/v) içindeki bir Nq-Pyr' ye Hg(NO3)2.H2O ilave edilerek, oda sıcaklığında 1 gece karıştırılmış ve nihai kalıntı yıkanarak istenilen [Hg— (Nq—Pyr)2] cıva kompleksi elde edilmiştir. Kompleksleşme sonucunda FT-IR spektrumunda beklenen pikler gözlenmiştir. Elementel Analiz sonucu yapı ile uyum içerisindedir. MALDI/TOF Kütle spektrumu sonucu bulunan kütle (m/z), 943,352 [M+] yapıyı doğrulamıştır. Tez çalışmasının ikinci aşamasında naftokinon moleküllerine dayalı eser miktarda Hg2+ iyonunun tayini üç kanallı (UV-Gör, florometrik ve voltametrik) olarak gerçekleştirilmiştir. Bu kapsamda çözücü etkisi, seçicilik, müdahale etme ve pH parametreleri incelenerek Hg2+ nin seçici ve hassas tayini için gerekli optimum koşullar belirlenmiştir. Nq—An ve Nq—Pyr sensörlerinin Hg2+ iyonuna karşı olan tepkisine pH etkisini araştırmak için, çeşitli asitlerin ve tuzlarının 1 ila 10 arasında değişen pH değerlerine sahip bir dizi tampon çözeltileri hazırlanmıştır. Nq—An ve Nq—Pyr'nin çözeltilerinin UV–Gör spektrumları, istenen pH' da (1-10) kaydedilmiştir. Bu reseptörlerin 7-8 pH aralığında Hg2+ katyonunu etkin bir şekilde algıladığı gösterilmiştir. Kolorimetrik olarak yapılan seçicilik çalışmasında problar, ortam sıcaklığında Hg2+ katyonu için turuncu'dan pembe'ye önemli bir renk geçişi gösterirken, rekabetçi katyonların varlığında renkleri değişmemiştir. Nq—An/Nq—Pyr ve bunların Hg2+ komplekslerinin [Hg—(Nq—An)2]/[Hg—(Nq—Pyr)2] elektronik spektrumları sırasıyla DMSO: H2O (1:1 v/v) ve DMF:H2O (5:1 v/v) pH 8' de kaydedilmiştir. Nq-An ve Nq-Pyr' nin Hg2+ ile bağlanma özelliklerini araştırmak için UV-Gör titrasyon çalışmaları da yapılmıştır. Nq—An ve Nq—Pyr tampon çözeltisine artan miktarlarda Hg2+ eklendiğinde, absorbansı 521 ve 506 nm' de izosbestik noktalarla birlikte 475 nm ve 473 nm' deki pikler düzenli olarak azalış, ancak 576 nm ve 571 nm'deki pikler ise artış göstermiştir. İzosbestik noktaların ortaya çıkması, komplekslerin oluşumunu doğrulamıştır. Jobs' un sürekli varyasyon yöntemiyle grafikteki eğrinin çizimi sonucunda 2:1 [Nq—An:Hg2+] oluşumu desteklenmiştir. Ayrıca, 1H-NMR titrasyonunda değişen miktarlarda cıva iyonun ilavesi sonucu 0,5 eşdeğerde beklenen piklerin kaybolması Nq-An'nin Hg2+ katyonu ile 2:1 bağlanmasını göstermiştir. Oransal UV-Gör titrasyon tekniğine dayalı olarak Nq—An ve Nq—Pyr sensörlerinin algılama limitleri, Hg2+ tayini için sırasıyla 1,6×10-6 ve 5,9×10-7 M olarak belirlenmiştir, bu da orta düzeyde Hg2+ algılama hassasiyetine işaret etmiştir. Diğer iyonların beş eşdeğerde bulunduğu Hg2+ varlığında rekabetçi çalışmalar uygulanmıştır. Hg2+, ortamdaki diğer metal iyonlarından etkilenmeyen Nq—An ve Nq—Pyr tarafından başarıyla tanınmış ve Nq—An ve Nq—Pyr sulu çözeltide Hg2+ katyonuna karşı yüksek seçicilik sergilemiştir. Ayrıca sensörlerin tepki süreleri de sırasıyla 10 ve 20 saniye olarak belirlenmiştir ve bu sonuç literatür değerlerine göre oldukça iyidir. Algılama işleminin tersinir olup olmadığını kontrol etmek için, Hg2+ ile inkübe edilen Nq—An ve Nq—Pyr çözeltisi Na2S ile muamele edilmiş ve UV-Gör spektral değişiklikleri kaydedilmiştir. Sonuç olarak her iki reseptörde ortamdan cıvanın uzaklaştırılması sonucu işlemin tersinir olduğu gösterilmiştir. Sensörün florometrik özelliğini ortaya koymak için Hg2+ ve Nq—Pyr etkileşimi floresans spektroskopik analiziyle incelenmiştir. Hg2+ katyonu varlığında, prob 432 nm' de belirgin bir floresans bandı sergilemiş, ancak diğer metal iyonları için herhangi bir özel değişiklik olmamıştır. Hg2+ iyonunun sensörle Hg-C ve Hg-N bağlanması sonucu Metal Şelat Oluşumuna Dayanan Artmış Floresans (MCHEF) mekanizması ortaya koyulmuştur. Florometrik tekniğe dayalı Nq—Pyr sensörünün tayin limiti, Hg2+ iyonu için 7,4×10-8 M olarak belirlenmiştir. Ek bir deney olarak floresans sensörün tepki süresi 75 saniye olarak belirlenmiştir. Kontamine musluk suyunda Hg2+'yi belirlemek için sensörlerin uygulanabilirliği gösterilmiştir. Ayrıca UV-Gör ve floresans için tüm sonuçlar iyi bilinen ICP-MS ve AAS yöntemleriyle karşılaştırılmıştır. Sensörlerimiz LOD açısından ortalama değerlere sahip olmasına rağmen, çok hızlı tepki sürelerinin yanı sıra yüksek doğruluk, kesinlik ve tekrarlanabilirliğe sahiptirler. Her iki sensörün de çok kanallı olması sensörlerin avantajını da arttırmıştır. Voltametrik kısımda ilk olarak Nq—An' nin elektrokimyası, CV ve DPV teknikleri kullanılarak DMSO' daki redoks davranışı ile aydınlatılmıştır. Nq—An' nin elektrokimyasal davranışı, 1,4-naftokinonun(Nq) kine benzerdir ancak, Nq—An ' nin indirgeme potansiyeli, katodik bölgeye kaymıştır. [Hg(Nq-An)2] kompleksinin redoks davranışı incelenmiş ve aynı deney koşullarında Nq—An' nin redoks davranışı ile kıyaslanmıştır. Beklenildiği gibi, [Hg—(Nq—An)2]'nin monoanyon ve dianyonuna karşılık gelen indirgeme potansiyelleri pozitif potansiyel değerlerine kaymıştır. Nq—An ile karşılaştırıldığında [Hg—(Nq—An)2]' nin indirgenme prosesinde akım kaybı gözlemlenmiştir. Kompleksin mono ve dianyon ürünlerine karşılık gelen yarı dalga redoks potansiyeli, sırasıyla hesaplanmıştır. DPV ölçümü, kompleksteki naftokinon çekirdeğine karşılık gelen katodik pik potansiyellerinin iki pike yarıldığını, ve bu da kompleksteki iki naftokinon ünitesinin iki basamak halinde iki elektron indirgeme prosesi ile indirgendiğini göstermiştir. Nq—An reseptörünün tamponlu ortamındaki CV'si de gösterilmiştir. Bu sonuç tamponlu sulu ortamda kinonların genel elektrokimyasal davranışı ile tutarlıdır. Tampon çözeltisindeki Nq-An reseptörüne cıva tuzu eklenerek oluşturulan [Hg—(Nq—An)2] kompleksinin CV' leri gösterilmiştir. Nq-An sensörüne Hg2+ iyonunun eklenmesiyle, nihai voltommogram [Hg—(Nq—An)2] kompleksininkiyle aynıdır. Ayrıca sensörün 0–1x10-5 M konsantrasyonundaki Li+, Na+, K+,Cs+, Be2+, Ca2+, Mg2+, Ba2+, Zn2+, Cu2+, Hg2+, Co2+, Fe2+, Fe3+, Mn2+, Pb2+, Ni2+ iyonları ile kompleks oluşturup oluşturmadığı test edilmiştir. Diğer katyonların varlığında Nq-An'nin sulu çözeltideki voltametrik davranışında bir değişiklik gözlenmemiştir. Hg0/Hg2+ redoks çiftinden kaynaklanan anodik akımın Hg2+ iyon miktarına bağlı olarak 3,5-20,5 ppm konsantrasyonları arasında doğrusal olarak arttığı gözlenmiştir.
  • Öge
    İlaç taşıyıcı sistemlerde kullanılmak üzere kansere hedeflendirilmiş poli(2-etil-2-oksazolin) temelli nanopartiküllerin sentezleri ve karakterizasyonları
    (Lisansüstü Eğitim Enstitüsü, 2021) Gülyüz, Sevgi ; Yılmaz, Özgür ; Alptürk, Onur, ; 709862 ; Kimya
    Polimerik nanopartiküller, uzun dolaşım süreleri ve terapötik ajanların taşınmasına olanak sunmaları sayesinde, son zamanlarda özellikle kontrollü ilaç salım sistemleri ve gen taşıma alanlarında büyük ilgi görmektedir. Taşıyıcı sistemler için yapılan araştırmalarda özellikle kanser dokularına hedeflenme yaklaşımı ile akıllı ve nanoboyutlu taşıyıcıların geliştirilmesine odaklanılmıştır. Polimerik nanopartiküllerin özel olarak tasarımı, çoğunlukla istenen uyarıcıya yanıt veren yapıların polimerlere dahil edilmesiyle olur. Bununla birlikte, polimerlerin iyi tanımlanmış ve yeniden üretilebilir bir şekilde sentezlenmesi polimerik nanopartiküllerin tasarımı için önemlidir. Son yıllarda, polimerik salım sistemleri arasında, Poli(2-oksazolin)'ler (genellikle PAOx, POZ, POx veya POXA olarak kısaltılır), benzersiz yapısal özelliklerinden dolayı büyük ilgi görmüştür. Poli (2-oksazolin)'ler, çok yönlü ayarlanabilir özelliklere ve mükemmel biyouyumluluğa sahip olağanüstü polimer platformunlarını temsil eder ve bu da onları çok çeşitli uygulamalarda kullanılabilir hale getirir. Nanopartiküller, genellikle lipozom, misel, polimerzom, nanojel ve polimer-ilaç konjugatlarını temsil eder. Poli(2-oksazolin) (POx) esaslı polimerik terapötiklerin geliştirilmesi, yeni nesil polimerik nanopartikül platformların hazırlanmasına olanak sağlamıştır. Bu tez, ilaç/gen kapsülleme ve salım sistemleri için üç farklı yeni PEtOx esaslı, kansere hedefenebilir polimerik nanopartiküllerin tasarımını, sentezini, karakterizasyonunu ve optimizasyonunu sunmaktadır. Farklı yapıda polimerik nanopartiküllerin sentezi için üç farklı sentetik strateji geliştirilmiştir. İlk çalışmada, DOPE lipid yapısına PEtOx polimeri entegre edilerek kanser hücrelerine özgül olarak hedeflenebilen peptit 18 ve peptit 563 ile modifiye edilen lipopolimerlerin hazırlanabilirliği ve böylece gen transferi için potansiyel kansere hedeflenebilir taşıyıcı sistemin geliştirilebildiği gösterildi. İkinci diğer çalışmada, misel formülasyonları için P(EtOx-ko-EI)-b-PCL blok kopolimerler hazırlandı. Bu çalışmada hidrofilik blok olarak P(EtOx-ko-EI) ve hidrofobik yapı için PCL bloğu içeren yeni bir amfifilik ve katyonik özellikte blok kopolimeri tasarlandı ve klik reaksiyonları kullanılarak peptitlerle konjuge edildi ve sonra polimerik miseller hazırlandı. Üçüncü ve son çalışmada ise çok işlevli hale getirmeye yatkın PEtOx tabanlı nanojellerin tasarımı ve sentezi yapıldı. PEtOx üç kollu başlatıcı kullanılarak yaşayan katyonik halka açma polimerizasyonu ile yıldız şeklinde hazırlandı. Daha sonra azid-alkin konjugasyonu ile alkin içeren flüoresan etiket (BODIPY) yıldız PEtOx polimere konjuge edildi. Nanojelleri sentezlemek için ditiol bazlı bir çapraz bağlayıcı kullanıldı. Jelleşme sonrası azid fonksiyon grupları içeren nanojel hedefleme ajanı peptit 563 ile konjuge edildi. İlaç salımı elde etmek için nanojeller, kemoterapötik ilaç adayı SGK 636 ile yüklendi ve ilaç yükleme kapasitesi incelendi.PEtOx polimerler kolay bir şekilde hazırlanarak ve etkili konjugasyon kimyası kullanılarak çok işlevli hale getirilebilir ve terapötik ajanlar olarak yapılandırılabilir. Sonuç olarak, PEtOx'lara dayanan iyi tanımlanmış polimerik taşıyıcı sistemler, kanser tedavisi uygulamaları için umut verici adaylar olarak hizmet edebilir.
  • Öge
    Syntheses, characterizations, and device fabrications of organic molecules for energy storage devices
    (Lisansüstü Eğitim Enstitüsü, 2022) Topal, Sebahat ; Öztürk, Turan ; 723442 ; Kimya
    In recent years, renewable energy systems have become an important research topic due to climate change and the depletion of fossil fuels. Supercapacitors and batteries are highly effective systems for storing energy electrochemically. The main difference between these systems is that the batteries have high energy densities and low power densities, whereas supercapacitors have high power densities and low energy densities. In the case of batteries, the charge is stored in the entire active material and through redox reactions. On the other hand, the supercapacitors work with the electrochemical double layer (EDLC) mechanism in which ions are stored on the electrode surface, and thus rapid charge-discharge can be achieved. The contributions of pseudocapacitive materials having redox reactions can be used in supercapacitors structure thus enhancing the energy density in supercapacitors. Today, lithium batteries are used in various electronic devices (cars, mobile phone, computers, medical devices etc.) due to their high capacities. Besides the literature suggests sodium-ion batteries as commercialization potential and can be used as alternatives since lithium sources are limited in nature. Additionally, there are different examples using aluminum, potassium, magnesium etc to find alternative resources. Many electrode materials used in battery design are prepared with inorganic compounds (minerals, metal, metal oxides, etc.). However, the effect of increasing production with the developing technology has accelerated the consumption of mineral resources on earth. This situation encouraged people to look for new alternatives. As a result, the use of organic molecules and conductive polymers have been found affective in the design of unlimited electrodes and they also have great advantages in recycling. Although the use of organic chemistry in energy storage systems has been limited to scientific studies, it is predicted that they will be used as active electrodes in commercialized batteries in the future because of highly consumption of mineral resources and the necessity of renewable systems. Organic molecules can undergo different types of redox reactions thanks to different functional groups in their structures. N-type organic materials give reactions between neutral (N) and negatively charged state (N-), while the p-type materials work between neutral (N) and positively charged state (P+). In this way, it is possible to design all organic batteries which consist of organic anode and organic cathode. In all organic battery systems, reduction of N and oxidation of P take place during charging. Meanwhile, cations and anions move from the electrolyte to the electrodes to neutralize negatively charged N- and positively charged P+, respectively. During the discharge process, cations and anions will migrate from the electrode back to the electrolyte. In addition, the flexibility of organic materials can eliminate the constraints on the electrolyte selection used in energy storage devices. While battery systems prepared in inorganic structure offer selectivity only for one ion which is the one used as the main electrode component. The organic electrodes can be used in many ions owing to their flexible structure. For example, LiCoO2 which is a common cathode electrode in Li-ion battery can only work for lithium-ion batteries because its rigid structure does not allow to be used it in different systems. However, organic PEDOT polymer was used in many energy storage (battery and supercapacitor) studies with lithium, sodium, aluminum, magnesium or organic electrolyte etc. In recent years, the goal of energy storage researches is to obtain devices with both high energy and high-power densities, which are called new generation energy storage devices. In this type studies, there are two suggested methods; (i) the combination of electrode systems where one works with the EDLC mechanism and the other works with the battery/pseudo-capacitive mechanism in the device (ii) the preparation of new hybrid electrode combining EDLC and battery type materials. There are many examples in the literature where 2D compounds (graphene, graphene oxide, germanene, borophene and stannene, transition metal oxides, transition metal carbides/nitrides (MXenes)) are combined with polymer and porous carbons to form hybrid electrodes. Polymers proposed as pseudocapacitive materials have also contributed to the EDLC mechanism since the syntheses of porous polymers. In the literature, many materials such as covalent organic framework (COF), covalent microporous polymer (CMP) have been developed and used as active electrode in energy storage devices targeting both high power density and high energy density. With the technological developments, it is seen that the multifunctional devices have great attention. It is known that some special conductive polymers change their color during oxidation/reduction process due to changing their structure and occur polaron/bipolaron form. This process is very similar to the process during charging and discharging and electrochromic energy storage systems have been created. The integration of electrochromic, color-changing materials under different potentials, into energy storage systems, is one of the best examples of this. It is very difficult to determine the remaining energy level in the batteries. However, this integration allows monitoring the level of the energy by color change. Within the scope of the thesis, which is thought to make important contributions to the literature, thienothiophene and dithienothiophene skeletons are functionalized with triphenylamine (TPA) and EDOT groups. Six organic monomers (TTpTPA, DTTpTPA, TTpEDOT, DTTpEDOT, EDOT3TT and EDOT4DTT) were synthesized and characterized by 1H NMR, 13C NMR, Mass spectroscopy, FTIR, UV-vis and electrochemical methods. Optimization and polymerization mechanisms of the designed monomers were performed by computational chemistry, DFT method and experimental data were supported with the results. Electropolymerization of monomers was carried out by cyclic voltammetry method on ITO and graphene sheet (GS) as the working electrode. In addition, electrochemical copolymer films were prepared by using different monomer ratios of TTpTPA and DTTpTPA monomers with EDOT. Surface characterizations, electrochromic, and energy storage properties of all electropolymers were investigated. The active mass of electropolymer films were found by three different methods to obtain the exact gravimetric capacity. These are (i)Faraday Law, (ii) Lambert Beer Law (using thickness, absorptions and density of electropolymers) and (iii) electrochemical quartz crystal microbalance (EQCM) (monitoring the frequency changing during the electropolymerization). In the next stage of the study, energy storage devices were made using the prepared electropolymer films (on ITO or GS). In these device structures, gel electrolytes were prepared and combined with separators. As an alternative for the commercially purchased polypropylene separator, polyacrylonitrile (PAN) nanofiber separators were prepared by electrospinning method and used in the studies. To conclude the study, the chemical polymers (CP), CPTTpTPA, CPTTpEDOT, and CP(T1-1E) were prepared with the oxidative chemical polymerization method using FeCl3 for using as active material in the cathode electrode. In addition, PAQS, which is used as an anode electrode in the literature, was synthesized within study of this thesis. The insoluble polymers were characterized by FTIR, TGA and electrochemical methods. For the fabrication of electrodes, slurries were prepared by mixing the obtained polymers with conductive carbon and binders in different ratios and then coated on Al foils using the Doctor Blade method. The new cathode electrodes, designed within the thesis, were combined with lithium foil anode electrode as a half-cell namely, CPTTpTPA//Li, CPTTpEDOT//Li, CP(T1-1E)//Li. For the all organic battery the new chemical polymers (CP) were used as cathode and combined with PAQS as a anode electrode (CPTTpTPA//PAQS, CPTTpEDOT//PAQS ve CP(T1-1E)//PAQS). All coincell form batteries were investigated by EIS, CV and GCD measurements. As a result, the energy storage properties of polymers containing TT and DTT skeletons synthesized within the scope of this thesis were investigated. In the literature, organic electrode materials, which are desired to be developed in the last period, have been provided with original alternatives. It is believed that this thesis will be an important resource for researchers working on next-generation energy storage devices.