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ÖgeSynthesis and applications of supramolecules and macromolecules containing multiple triazole units(Graduate School, 2023-12-05)Triazole derivatives are cyclic structures with the closed formula of C2H3N3 consisting two different isomers namely, 1,2,3-triazole and 1,2,4-triazole. Their distinctive qualities including anti-microbial, anti-cancer, anti-epileptic, anti-inflammatory and anti-viral properties make them employable in drug designs and attrached the interest of scientists across the globe. As an indication of this interest, last year's Nobel Prize was awarded to Prof. Sharpless for his works on "Click Chemistry" focusing on triazoles, as an easy linker group for several applications. While there are numerous green methods to synthesize triazoles, being environmentally friendly itself, it can offer new horizons to organic chemists to develop novel approaches. Additionally, their long shelf life and highly efficient yet straightforward reaction conditions allow them to be synthesized in larger amounts and made them popular in several research areas. In this thesis, we aimed to synthesize novel supramolecules and macromolecules containing more than one triazole ring and to investigate the possible applications of the resulting structures. In the first chapter, the aim of the thesis, the scientific novelty and the topics of each chapter are briefly discussed. The second chapter focuses on the synthesis of dibenzoxanthene derivatives that possess triazole rings. Dibenzoxanthenes have extensive utility in the field of metal ion sensing applications. Fluorescent dibenzoxanthene derivatives exhibit significant guarantees as candidates for the detection of metal ions across different solvent systems. Nevertheless, the majority of research conducted thus far has mostly concentrated on the detection of metals in aqueous solutions, with a special focus on the identification of very hazardous metal ions, such as lead (II) (Pb2+) and mercury (II) (Hg2+). The present investigation involved the synthesis of a newly developed benzyl-functionalized dibenzoxanthene (BDBX) derivative and a novel fluorescent anthracene functionalized dibenzoxanthene (ADBX) derivative. These compounds were designed to detect metal ions in polar aprotic solvent systems. The detection process employed ultraviolet-visible (UV-Vis) spectroscopy and fluorescence spectroscopy techniques. The compound benzyl dibenzoxanthene exhibited sensitivity towards several metal ions, namely lead II (Pb2+), cobalt II (Co2+), and copper II (Cu2+). In contrast, the newly synthesized anthracenyl-dibenzoxanthene compound demonstrated sensitivity exclusively towards Cu2+ ions. Notably, each anthracenyl-dibenzoxanthene molecule exhibited a binding capacity for three Cu2+ ions, resulting in an enhanced sensitivity towards copper. The analysis of the affinity for binding between Cu2+ and dibenzoxanthene derivatives has been conducted using proton nuclear magnetic resonance (1H NMR) and high-resolution X-ray photoelectron spectroscopy (XPS). In the third chapter of the thesis, the synthesis of three novel molecular cages is described. These cages are based on a bis-structure derived from 8,16-methano-16H-dinaphtho[2,1-d: 1',2'-g].A compound known as [1,3]dioxocine (DNDO), consisting of interconnected triazole rings, has been reported in the scientific literature. The bis-DNDO structures are connected by linkers that possess both etheric structures and bis(1,2,3-triazole) moieties, which also serve as coordination ligands. The molecular cages' cavities undergo alterations dependent upon the position in space of the oxygen atoms within the dioxolane ring. In chapter four, triazole-containing flame retardants were synthesized. The utilization of contemporary chemical routes and the advancement of inventive material designs offer intelligent resolutions to the challenges experienced in the field of materials science, hence expanding opportunities for future academic studies. In the third study, we used two-click reactions to synthesize a reactive flame retardant that contains phosphorus (P) and nitrogen (N) atoms. The para-fluoro substituents of bis(pentafluorophenyl)phenyl phosphine oxide were subjected to azidation, followed by the subsequent interaction of the resulting product with propargyl acrylate by the use of a copper-catalyzed azide-alkyne cycloaddition reaction (CuAAC). The present study aimed to explore the effect of different concentrations (10%, 20%, and 30%) of a synthetic monomer on the mechanical, thermal, and flame retardancy properties of an aliphatic polyurethane acrylate. The utilization of the recently synthesized monomer resulted in a notable decrease in the conversion rates of double bonds, an enhancement in the tensile strength of the photocured samples, and a decrease in the values of elongation at break values. The observed trend shows an upward correlation between the quantity of the flame retardant monomer and both the glass transition temperatures (Tg) and the limiting oxygen index (LOI) values. A significant improvement of around 25% in the Limiting Oxygen Index (LOI) values was observed when the flame retardant percentage in the formulations approached 30%. In the fifth chapter, in contrast to the fourth, fire-resistant materials were developed using bio-based materials. The use of bio-based building blocks for the synthesis of polymers is increasing day by day. Among the bio-based building blocks, eugenol is a highly promising monomer for the preparation of thermoset materials. In the fourth study, we combined thiol-ene photopolymerization (TEP) and thermal azide-alkyne cycloaddition click reactions to prepare eugenol-based thermally stable, P-, N-, and silicon (Si)-containing networks. To this end, we synthesized a P-containing, eugenol-based monomer-bearing azide group and a siloxane compound containing an alkyne group. By mixing these monomers with multifunctional thiols and by utilizing a dual-curing strategy, we managed to obtain optically transparent and thermally stable coatings with excellent adhesion to glass substrates. The thermal stability, optical transmittance, pendulum hardness, solvent resistance, and adhesion performance of the coatings were evaluated. The gel contents of the thermoset materials were found to be over 95%. At 600oC, the char yields of the dual-cured coatings were found to be over 30%. Coatings were also found to be resistant to acidic and basic conditions as well as solvents. Within the scope of this thesis, several novel molecules containing multiple triazole rings have been synthesized and their possible applications have been investigated. The studies conducted in each section of the thesis have been published in well-respected international scientific journals.
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ÖgeDesign and synthesis of fluorescent molecules for the detection of biologically and environmentally important species(Graduate School, 2023-03-10)Chemosensors are widely used for the detection of biologically and environmentally important substances. Especially cyanide, hydrazine, hypochlorite and gold ions are very important due to their high toxicity and wide usage area in the industry and daily life. Ingestion of toxic cyanide by humans in a certain amount can cause nausea, vomiting, unconsciousness, shock and even death. Similarly, taking hydrazine can have toxic and severe health effects that can cause allergies, nausea, vertigo, temporary blindness, acute poisoning, burns by skin contact or inhalation, and even cancer. When hypochlorite is taken in high amounts, it causes various diseases such as cardiovascular diseases, acute lung injuries, neurodegenerative disorders, Alzheimer, Parkinson, and cancer. Although gold ions have positive effects on the body in low amounts, they can cause some health problems through interactions with proteins, DNA and biomolecules when taken in high levels. Conventional techniques such as electrochemical analysis, chromatography, capillary electrophoresis, potentiometry and ion chromatography, which are instrumental devices used to detect these substances, are time-consuming and require expensive devices and complex operations. On the other hand, fluorescent probes have attracted significant attention due to their excellent sensitivity and selectivity, fast response, inexpensive instrumentation, easy operation, real-time imaging, and possible detection with the naked eye. The triphenylamine, thienothiophene and barbituric acid-based probe TTB enables discriminative detection of cyanide, hydrazine, and hypochlorite in different emission wavelengths. Rhodamine and triphenylamine-based probe RH-TPA enables multi-channel (colourimetric, fluorometric and electrochemical) detection of gold ions and BODIPY, and malononitrile-based probe BOD-CN enables fast, selective and sensitive detection of hypochlorite ions. In this thesis, the preparation of specific probes for fluorescence detection of cyanide, hydrazine, hypochlorite and gold ions were carried out. At the same time, practical applications of the probe molecules have been performed in various water samples, fruit, vegetable and dairy products.
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ÖgeSelülozik atıklardan hareketle iletken kompozit eldesi karakterizasyonu ve bazı uygulamaları(Lisansüstü Eğitim Enstitüsü, 2023-03-07)Bilim ve teknolojinin hızlı bir şekilde ilerlemesi ve sürekli artan çeşitli tüketim ihtiyaçlarını karşılamak amacıyla son yıllarda yeni ve pratik pek çok ürünün geliştirilmesini sağlamıştır. İletken polimer endüstrisinin tekstil bilimi ile iş birliğine girmesi ile savunma, sağlık, iletişim, otomasyon amacıyla kullanılabilecek tekstil ürünleri, endüstri, askeri, uzay, tıp gibi birçok alanda rol almaya başlamıştır. İletken polimerlerin kullanım alanları, elektrolüminesans, mikroelektronikler, tekstil, yarı iletken çipler, entegre devreler, piller, sensörler, antistatik kaplamalar ve ambalajlar olarak sıralanabilir. Bunlara ek olarak, transistörler, televizyon ekranları ve güneş panelleri, ısı jeneratörleri ve elektromanyetik kalkanlama, elektroaktiviteyi kullanan elektriksel indikatörler, LED, biosensör tipi materyallerin yapılarında iletken polimerler kullanılmaktadır. Günümüzde, kullanılan iletken polimerleri PPy, PCz, PANI, PTh olarak sıralayabiliriz. Tüm bunların yanısıra iletken polimerlerin düşük mekanik özellikleri, çözünemez olmaları kullanım amaçlarını kısıtlamaktadır. İletken tekstil, iletken polimerlerin kaplanması ile elektriği iletme özelliğine sahip bir kumaş anlamına gelmektedir. Bu, tekstilin yapısal ve mekanik özelliklerinin ve iletken polimerlerin elektriksel özelliklerin kombinasyonunu sağlar. İletken filmin inceliği, polimerin sentezlenme süresi ve oksidant konsatntrasyonuna bağlı olarak değişir ve mikron ile ifade edilir. Elde edilen (tekstil/iletken polimer) kompoziti birçok kullanım alanı sunmaktadır. Tekstilin mekanik ve elastik özellikleri, elektriksel özelliğin avantajları ve biyouyumluluk özellikleri birleştirildiğinde bu kompozitler elektromanyetik kalkanlama, geniş bant dalga absorpsiyonu, statik yük dağıtma, biyomedikal ve doku mühendisliğinde kullanılabilmektedir. Doğal lifler ve iletken polimerlerden doğal lif/iletken polimer kompozit eldesine dair öncülük edebilecek detaylı çalışma olmaması tezin çıkış amacı olmuştur. Doğal liflerin kimyasal yöntemle çözeltide oluşturulan iletken polimerlerle kaplanması ile elde edilecek kompozitlere, doğal lifler ile esneklik, iletken polimerler ile de iletkenlik özelliği kazandırılması kurgulanmıştır. Ekonomik, esnek, hafif, aşındırıcı olmayan ve iletken özellikte olması amaçlanan iletken/doğal kompozitlerin literatüre kazandırılması hedeflenmiştir. Kapasitörler, basit bir anlatımla elektronların kutuplaşarak elektriksel yükü bir elektrik alan içerisinde depolayabilme özelliklerinden faydalanılarak, bir yalıtkan malzemenin iki metal tabaka arasına yerleştirilmesiyle oluşturulan pasif bir elektronik devre elemanıdır. Elektrokimyasal kapasitörler veya başka bir deyişle süperkapasitörler, temelde kapasitör gibi davranan ancak yüksek enerji ve güç yoğunluğu bakımından kapasitörlerden ayrılan enerji depolama sistemleridir. Elektrokimyasal kapasitör ya da süperkapasitör olarak bilinen bu yeni tip enerji depolama sistemleri birçok araştırmaya konu olmuştur. Süperkapasitöreler, pil ve kapasitörlerin kullanılamadığı yüksek enerji ve güç yoğunluğu gerektiren uygulamalar için bir alternatif olarak önem kazanmakta ve yük tutma kabiliyetlerini arttırmak için birçok araştırma yapılmaktadır. Bu araştırmalar da özellikle elektrot malzemesi üzerine yoğunlaşmaktadır. Pillere oranla enerjiyi daha hızlı bir şekilde alıp dağıtabilmektedir. Ancak süperkapasitörlerin enerji depolama kapasitesi pillere oranla çok düşüktür. Şarj edilip boşaltılma döngüsünü sonsuz sayıda gerçekleştirebilir. Fakat piller şarj edilebilme özelliklerini belirli döngü sayısına ulaştıktan sonra kaybetmektedirler. Ek olarak süper kapasitörlerin giyilebilir şarj depolama devreleri için en ideal adaylar olduğu düşünülmekte ve bu yönde çalışmalar yapılmaktadır. Tez kapsamında Türkiye'de yetiştirilen ürünlerden elde edilen doğal lifler (pamuk, luffa, enginar, muz) ve teknoloji alanında ilerleme gösteren iletken polimer teknolojisinden faydalanarak doğal lif/doğal lif esaslı yüzey-iletken polimer kompoziti elde edilecektir. Tezde kullanılacak doğal lifler (enginar, pamuk, muz ve luffa), yerli tarımsal gövde atıklarından elde edilmiştir. Kullanılan doğal liflerin tamamı, çevreye dost, düşük yoğunluklu, aşındırıcı olmayan ve ekonomik açıdan kolay elde edilebilir liflerdir. Tez kapsamında kullanılacak iletken polimerlerden PCz literatürde iyi kapasitif özelliği ile, PPy iletkenliği, kimyasal stabilitesi ve kolay sentezlenebilirliği ile, PANI suda çözünebilmesi ve iletken tekstillerde en çok tercih edilen polimer olması ile, PEDOT iyi iletkenlik özelliklerine sahip olması ile raporlanmıştır. Enginar, pamuk, muz ve luffa bitki atıklarının PCz, PANI, PPy, PEDOT iletken polimerleri ile kimyasal polimerizasyon yöntemi ile doğal lif/iletken kompozitleri elde edilmiş ve elde edilen kompozitlerin kritik olan elektriksel iletkenlik, kapasitif, mekanik, termal ve fiziksel özellikleri, FTIR, TGA, 4-nokta iletkenlik, SEM, çekme-kopma analizleri ile karakterize edilmiştir. Optimum koşulları sağlayan doğal lif ve iletken polimer çifti kompoziti EL/PEDOT iletken polimeri ile elde edilmiştir. 12.8 S/cm ile en yüksek iletkenlik oksidan olarak FeCl3 kullanılarak EL/PEDOT(K) kompoziti ile elde edilmiştir. Devam eden çalışmalarda EL/PEDOT(K) elektrot olarak kullanılmış ve EDOT ile elektrokimyasal polimerizasyon gerçekleştirilmiştir. Elde edilen elektroktif EL/PEDOT(K)/PEDOT(E) kompozitinin elektrokimyasal karakterizasyonu CV ve EIS yöntemleri ile analiz edilmiştir. Detaylı karakterizasyon, bu kompozitin kapasitör olarak kullanılması için kimyasal polimerizasyonda 0,03 M EDOT ve 0,9 M FeCl3 kullanılması gerektiğini ve ardından 0,03 M EDOT'ta 10 döngü uygulanarak elektropolimerizasyona devam edilmesi gerektiğini göstermiştir. Tüm sonuçlar, EL atığının, şarj depolama, biyosensör, elektronik cihazlar gibi çeşitli elektronik uygulamalar için potansiyel olarak uygun malzeme olan sürdürülebilir EL/PEDOT(K)/PEDOT(E) iletken kompozitlere dönüştürülebileceğini göstermiştir. Aynı zamanda elde edilen sürdürülebilir doğal lif/iletken polimer kompozitlerinin esnek ve iletken yapıları dolayısıyla giyilebilir şarj depolama devreleri açısından değerlendirilmek üzere kapasitif özellikleri incelenmiştir. Bu doğrultuda bu çalışmada kullanılan EL ve muz liflerinden ML elde edilen esnek ve iletken kompozitleri kapasitör uygulamasında kullanılmış ve sonuçlar karşılaştırılmıştır. EL ve ML üzerine EDOT'in polimerizasyonu ile elde edilmiş EL/PEDOT ve ML/PEDOT kompozitlerinin süperkapasitör davranışı incelenmiştir. Karakterizasyonlar CV, GCD ve EIS yöntemleri ile ölçülmüştür. EL/PEDOT ile elde edilen sonuçlar raporlanmıştır. EL/PEDOT 5 mV s-1'de 369 mF cm-2 olarak ölçülen yüksek kapasitans özelliği göstermiştir. Buna ek olarak iki EL/PEDOT iletken kompoziti anot ve katot olarak kullanılmış ve jel elektrolitle bir süperkapasitör elde edilmiştir. Cihazın kapasitif özelliği 50 µA'de 43 mF cm-2, enerji yoğunluğu 60 mWh m-2 ve 736 mW m-2, güç yoğunluğu hesaplanmıştır. Bu sonuçlar, enginar atığından elde edilen, çok çeşitli fiber şekilli enerji depolama cihazlarına, ideal bir çevre dostu alternatif elektrot sunmaktadır.
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ÖgeNovel biopolymer applications as adsorbent, drug encapsulation and controlled drug release agents(Graduate School, 2023-10-05)Biopolymers are polymers derived from biological sources. Biopolymers can be subdivided into plant-derived polysaccharides and animal-derived proteins. Firstly, cellulose and then chitin as a polysaccharide are among the most well-known biopolymers thanks to their high abundance, wide distribution on earth and low production costs. The group of proteins mainly includes silk, gelatin, collagen and albumin. Similarly, chitin derivative chitosan, alginate (Alg), gum (gum), carboxymethyl cellulose (CMC) and starch are also included in the category of polysaccharides, and these biopolymers have found numerous applications by using them in various forms. The fact that biopolymers are non-toxic, biodegradable and create composite materials with different additives easily increases their applicability. Considering their sustainability, biocompatibility and mostly hydrophilic properties, biopolymers generally have high advantages over synthetic polymers. Due to their unique properties such as their renewable resources, abundance, biodegradability and ease of functionalization, biopolymers are being investigated for both academic and industrial applications. Water treatment with biopolymers and biopolymer composites is one of the most sought-after research topics today. Reducing the resulting pollutants from wastewater is of vital importance for living organisms. Biopolymer-based adsorbents have the potential to replace traditional adsorbents such as silica, alumina, and activated carbon. They can compete with other adsorbents in terms of adsorption capacity, cost-effectiveness, and biocompatibility. In the first and second steps in this thesis, adsorption studies were carried out to remove harmful substances from the aqueous environment by means of biopolymer-based adsorbents. Different biopolymer-containing materials prepared as adsorbent materials in the physical form of films and beads were used in the removal studies from aqueous media. Biopolymers also have potential applications in the pharmaceutical industry for the development of controlled drug release systems. Biopolymers, with their abundance and natural content, are of great interest as carriers that will realize controlled drug release with the compatibility they will show in the stages of degradation in biological systems. In the ongoing third and fourth steps of this thesis study, drug encapsulation into new biopolymer materials and controlled release of drugs into the desired environment were investigated. In the first stage of the thesis, an anionic surfactant sodium dodecyl benzene sulfonate (SDBS) was chosen as the harmful substance to remove from the aqueous medium. The uncontrolled mixing of surfactants into the environment is an important problem today. Cross-linked chitosan biopolymer films were utilized to the removal of SDBS from the aqueous solution. Sodium sulfate was chosen as the cross-linker. Batch adsorption studies show that the positively charged chitosan has an interaction with the negatively charged surfactant SDBS. In experimental studies, adsorption parameters such as contact time, pH, cross-linker concentration and adsorbent dose were investigated. The maximum amount of adsorbed SDBS was reached at pH 2 and 180 minutes. Experimental data was modeled using kinetic and adsorption isotherm models and it was found that the adsorption system followed pseudo-second-order kinetics and the Langmuir adsorption isotherm model. The adsorption capacity of the films for SDBS adsorption was calculated as 714 mg/g. This study proposes a potential use of cross-linked chitosan films for the removal of anionic surfactants from the aqueous medium. The results of the study have been published in an SCI journal (Journal of Polymers and the Environment, 2018, 26, 2166-2172). In the second stage of the thesis, it was aimed to demonstrate the use of the novel composite material prepared by adding CeO2 nanoparticles to carboxymethyl cellulose (CMC) beads cross-linked with Ce3+ ions as being an efficient adsorbent in fluoride ions removal from water. The characterization of the beads was carried out by swelling experiments, scanning electron microscopy and Fourier transform infrared spectroscopy. The adsorption of fluoride ions from aqueous solutions was carried out with both cerium ions cross-linked CMC beads (CMC-Ce) and CeO2-nanoparticle loaded CMC-Ce beads (CeO2-CMC-Ce) in a batch system. Optimized adsorption conditions were obtained under experimental conditions where parameters such as pH, contact time, adsorbent dose and agitation speed were investigated and a constant temperature value was 25 °C. Experimental data on adsorption showed good agreement with the Langmuir isotherm and pseudo-second-order kinetics. The maximum adsorption capacity of the adsorbents was obtained as 105 and 312 mg F-/g adsorbent for CMC-Ce and CeO2-CMC-Ce beads, respectively. Reusability studies have shown that adsorbent beads exhibit excellent sustainable properties up to 9 cycles. This study revealed that the CeO2 nanoparticle doped CMC-Ce composite is a very effective adsorbent in removing fluoride from water. The results of the study have been published in a SCI journal (International Journal of Biological Macromolecules, 2023, 242(1), 124595). In the third phase of the thesis, it was aimed to reduce the drug release in the acidic stomach environment and to transport the drug to the colon environment with the highest possible encapsulation amount. Protein-type drugs are disrupted at extremely acidic stomach pH. If such drugs reach the intestine without being degraded in the stomach environment, they can be absorbed by the intestinal mucosa. Therefore, research focuses on new approaches for colon-targeted delivery systems. The pH-sensitive properties of some polysaccharides make them colon-targeting agents. One of them is the biopolymer alginate. Alginate (Alg) shrinks in the stomach environment and mostly retains the drug encapsulated in the gel. In the thesis study, the biopolymer alginate was modified with sodium dodecyl sulfate (SDS), an agent whose interaction with protein is known. Bovine serum albumin (BSA) protein selected as the model drug was loaded onto SDS-modified calcium alginate beads (SDS/Ca-Alg). The encapsulation efficiency of BSA in SDS/Ca-Alg beads was found to be 96.3% with a high yield, which can be called complete confinement. The second remarkable result from the experimental studies is that the protein release from the SDS-modified calcium alginate beads into the artificial gastric fluid medium is significantly reduced compared to the protein release from the calcium alginate beads. At the same time, the release time of the entire drug from the SDS/Ca-Alg beads into the artificial intestinal medium was significantly prolonged compared to the Ca-Alg beads. SDS-modified alginate beads are recommended as suitable carriers for the passage of oral protein-type drugs into the colonic environment by preventing their degradation in acidic gastric fluid. The results of the study have been published in an SCI journal (Carbohydrate Polymers, 2019, 224, 115165). In the fourth phase of the thesis, barium alginate-carboxymethyl cellulose composite hydrogel beads were prepared as a controlled release agent that retards the release of the cancer drug methotrexate (MTX) into a phosphate-buffered saline (PBS) medium with a pH value of 7.4. The biggest advantage of alginate as a drug carrier in oral drug applications is its low level of swelling in the acidic gastric fluid environment. Thus, the drug entrapped in the alginate gel and taken orally is largely transported to the intestinal environment. However, in the basic pH environment, uncontrolled and rapid release of the drug is observed with sudden swelling and disintegration of the alginate gel. Recent innovative studies have focused on slowing the swelling rate of alginate in basic medium with suitable additives or forming composites of alginate and other polysaccharides. According to the literature review, this is the first study on MTX release from an alginate-carboxymethyl cellulose matrix into a PBS medium. Ba-Alg/CMC beads to be used in drug release experiments were prepared by adding the solution, which is a mixture of sodium alginate (NaAlg)/sodium carboxymethyl cellulose (NaCMC) biopolymers, into barium chloride solution. As a method in the preparation of the beads, dropping the polymer solution with a syringe into the solution containing barium ions was applied. Since MTX has low water solubility, the drug was first dissolved in DMSO and added to the polymer solution. The amount of DMSO added to the beads to dissolve the drug in the biopolymer solution (10% v/v) positively affected the morphology, swelling and release profiles of the beads. Scanning electron microscopy (SEM) and Fourier-transformed infrared (FTIR) spectroscopy analysis were used to characterize Ba-Alg/CMC composites. The results showed that the release of almost all the amount of MTX loaded on the beads was completed in 5 hours in PBS (pH 7.4 and 37 oC) with a release percentage of 98.1±2.64%. In addition, the synthesized Cu(II) (MXT-Cu) and Zn(II) (MXT-Zn) metal complexes of the drug were also loaded onto Ba-Alg/CMC beads and subjected to drug release studies. The entrapment efficiency of metal complexes of MTX in Ba-Alg-CMC and their release behaviour into PBS were compared with MTX. The data of the controlled release experiments was process to the first-order, Higuchi and Hixson-Crowell kinetic models, which are the most widely used drug release kinetic models. The results of the study have been published in an SCI journal (Journal of Drug Delivery Science and Technology, 2019, 54, 101324). The successive steps of this thesis study were completed in four stages on the applicability of new biopolymer-based materials for adsorption and controlled drug release. The results obtained from the experiments at each stage were presented to the literature as four original research articles published in journals within the scope of SCI in the Q1 (3) and Q2 (1) category. The fact that the materials containing biopolymer, which are successful adsorbent and controlled drug release agents, prepared in line with the outputs of the thesis study, will be beneficial to humanity in the coming years will be a complete indicator of the realization of the purpose. It is foreseen that the thesis will contribute to scientific knowledge through the articles published as a result of the research carried out within the scope of the thesis.
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ÖgeSynthesis of new mesogens and investigation of their liquid crystalline properties(Graduate School, 2022-12-02)Liquid crystals have been a subject of curiosity since the day they were discovered, and as time passed and their use developed, they gained an indispensable place in the rapidly expanding technology of the modern world. As a result of Friedrich Reinitzer's inability to explain this strange phenomenon, which he realized at the end of his work with turnips and which initially suggested that he could not purify cholesteryl benzoate, he sent Otto Lehnman samples. Otto Lehnman, who was the first person to try to define the Liquid Crystal Phase phenomenon as we define it today, who was a very competent name in the field of crystallography, attempted this definition with the expression "Fluid Crystals" in his time. Although he faced serious opposition because he introduced this definition in his period, the reality of this notion is obvious as it is brought by studies and modern science. Today, these intermediate phases, which are exhibited by liquid crystalline substances, are called mesophase, while chemical molecules displaying this feature are called mesogenes. Thanks to the studies on them, more than one mesophase of Liquid Crystals has been defined today. More than one mesophase, nematic, smectic, columnar, cholesteric (chiral nematic) and lyotropic, enables different usage areas and new materials are being developed in this context day by day. In this context, the main focus of this thesis has been to design, synthesize, characterize and examine the usage areas of different types of new mesogens, ranging from high molecular weight to low molecular weight or covalent to non-covalent bonded structures. For this reason, the studies in this thesis have been revealed in the form of presenting different articles under five main headings. In the first two studies, different complexes of known liquid crystal mesogens with different polymer chains, which are designed to carry hydrogen bond acceptor side-substituted groups, were prepared to form hydrogen bonds, and the change in their mesomorphic properties was investigated. They touch on a very important point, as the use of high molecular weight liquid crystal materials can spread to areas as wide as the usage areas of the polymers for which they are designed. In the third study, an original material from the chalcone compound class, which has very important biological and optical properties, was prepared in order to form a hydrogen bonded liquid crystal complex material and its properties were investigated. The focus of the fourth study was the establishment of a hydrogen bond between a new carbamate molecule, which has both hydrogen bond donor and acceptor properties, and LC11, a mesogen with previously studied boundaries. After investigations on that, drastic changes in the mesomorphic properties of the LC11 mesogen were observed. These changes were studied computationally and experimentally then the reasons for the change which were experimentally observed, were explained by computational methods. In the fifth study, two new mesogens were designed, synthesized and characterized. These new cholesterol-based materials are completely covalently bonded structures and do not require any intermolecular bonds to display mesomorphic properties. The dielectric properties of these materials, which have both biological and optical properties, have also been studied. In first study, a new polystyrene-based side chain liquid crystalline polymer (EP-PS-LC11)) has been prepared from polystyrene having ethylpiperazine moiety as a hydrogen bond acceptor polymer and 11-(4-cyanobiphenyl-4(-oxy) undekan-1-ol (LC11) as a bond donor bymolecular self-assembly processes via hydrogen-bond formation between nitrogen of ethylpiperazine on polymer chain and hydroxyl group of the LC11. The formation of hydrogen bond has been confirmed by using FTIR spectroscopy. The liquid crystalline behavior of the EP-PS-LC11 has been investigated by a differential scanning calorimeter (DSC) and polarized opticalmicroscopy. The thermal behaviors of the H-bonded liquid crystalline polymer have been investigated by DSC measurements. The dielectric properties and ac conductivity mechanism of EP-PS-LC11 have also been investigated by impedance spectroscopy within the frequency interval of 5 Hz–15 MHz. The dielectric relaxation type of EP-PS-LC11 has been analyzed by fitting dispersion curves of ε′-ω. The system obeys nearly Debye and non-Debye type relaxations for the low and high frequency regions. In addition, it has been revealed that since the dielectric strength decreases by increasing frequency, the LC compositemolecules can align more easily at high frequency. Moreover, the variation of imaginary component of dielectric constant with frequency shows two relaxation peaks. While the low frequency relaxation peak corresponds to molecular vibration, the high frequency relaxation peak is attributed to molecular orientation. The frequency dependence of ac conductivity has also been analyzed by means of frequency exponent, s. Depending on the frequency deal with, the system exhibit nearly dc, correlated barrier hopping (CBH) and super linear power law (SLPL) behaviors. In the second paper, a new PEG-containing liquid crystalline side chain block copolymer HBC-PEG550 was prepared from poly (ethylene glycol)-b-poly(2-(diethylamino) ethyl methacrylate copolymer (BC-PEG550) and 8-(4-cyanobiphenyl-4′-oxy) octan-1-ol (LC8) by molecular self-assembly processes via hydrogen bond formation between amine group of HBC-PEG550 and hydroxyl group of the LC8. The formation of H bond was confirmed by using FTIR spectroscopy. The liquid crystalline behavior of the HBC-PEG550 was investigated by differential scanning calorimeter (DSC) and polarized optical microscopy. Dielectric properties of BC-PEG550 and HBC-PEG550 has been studied by impedance spectroscopy. Real and imaginary parts of complex dielectric constant, impedance, and energy loss tangent factor for BC-PEG550 and HBC-PEG550 have been characterized in the frequency range of 100 Hz–15 MHz. To investigate a low molecular weigth system, a new chalcone based nematic schlieren texture liquid crystalline material was prepared from 3-(4-(dimethylamino) phenyl)-1-(4-hydroxyphenyl) prop-2-en-1-one (DMAC) and 8-(4-cyanobiphenyl-4′-oxy) octan-1-ol (LC8) by molecular self-assembly processes via hydrogen bond formation between tertiary amine group of DMAC and hydroxyl group of the LC8. Hydrogen bond formation was observed by FTIR spectroscopy. Dielectric properties of DMAC has been studied by impedance spectroscopy. The Cole-Cole analysiswas used to determine the Resistance-Capacitance (RC) components equivalent circuit situation of doped LC8 on theDMAC. Dependent angular frequency variation of dielectric parameters and ac conductivity properties are non-Debye type relaxation mechanism of interfacial dopant in the liquid crystal molecular structure of the reorientation polarization effects. To understand the effect of hydrogen bond, it is presented a combined experimental and theoretical study on the novel hydrogen-bonded liquid crystalline complex (UR-LC11) exhibiting both nematic and smectic phases upon cooling. The complex was prepared by mixing 2-(2-methoxyethoxy) ethylbutyl carbamate (UR) as H-bond acceptor with calamitic mesogen 4′-((11- hydroxyundecyl) oxy)-[1,1′-biphenyl]-4‑carbonitrile (LC11) as H-bond donor. The complex was characterized by FTIR technique and its liquid crystalline properties were studied by differential scanning calorimetry (DSC) and polarized optical microscope (POM). The experimental IR spectra were compared with theoretically obtained IR spectra by Density Functional Theory (DFT) to suggest the structure of hydrogen-bonded liquid crystal (LC). The molecular dynamics (MD) simulationswere performed to understand the impact of hydrogen bonding on the mesomorphic behaviour of the complex and the temperature dependency of the transitions between the mesophases. We determined that UR-LC11 is a stable H-bond acceptor/donor type complex and a single H-bond forms between the carbonyl oxygen atom of the amide moiety of UR and the hydrogen atom of the terminal hydroxyl group of the LC11. Although LC11 is present only in nematic liquid crystalline form, the new complex displayed both nematic and smectic phases during cooling. The reason for the two distinctive LC phases was explained by the presence of hydrogen bond interactions, which provides structural flexibility. Besides, H-bond maintains uniaxial rod shape of the molecule to promote self-assembly behaviour and induces positional ordering in the smectic phase. The enhancement in the self-assembly of the H-bonded chains in the complex is reflected in the increased ΔHfusion values. Due to the intermolecular π-π interactions of the phenyl rings and the formation of strong dipoles on the backbone, especially at the cyanobiphenyl end of the chains, the longrange directional order of the dipoles along their long axes are preserved at elevated temperatures and nematic to isotropic phase transition is observed at around 370 K both experimentally and theoretically. After working on hydrogen-bonded complexes, for the purpose of investigating newly designed biologically effective and chiral mesogens two materials prepared. Cholesteryl chloroformate which is known liquid crystal material was modified to give the new molecules a long-lasting LC phases with the stability of the carbamate and aromatic functions. Two new mesogens cholesteryl 1H-imidazole-1-carboxylate (Cho-Imi) and Cholesteryl (4-((E)-phenyldiazenyl) phenyl) carbamate (Cho-Diazo) were synthesized starting from Cholesteryl chloroformate and (E)-4-(phenyldiazenyl) aniline in the presence of triethylamine (TEA) as an acid scavenger at room temperature. Structural characterization of the obtained LC compounds was performed by FTIR and H-NMR. These new compounds, which show more than one LC phase different from the LC phases of the starting material, showed that they are promising as a result of the analyses. The mesomorphic properties were examined by polarized optical microscope (POM) and thermal properties of theLCcompounds were determined by DSC and TGA. The dielectric properties of synthesized liquid crystal samples were investigated using dielectric spectroscopy technique. It was seen that both new syntheses mesogen cholesteryl carbamates-based liquid crystal samples exhibit non-Debye type relaxation properties. The cole–cole analysis by dielectric spectroscopy was used to determine the equivalent devices of this new Cholesteryl carbamate-based mesogens. The samples have different dielectric properties in different frequency regions will provide significant flexibility as a working frequency region in engineering, biological and genetic application areas.