Kimya Bölümü

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  • Öge
    A quantum mechanical approach to the mechanism of asymmetric synthesis of chiral amine by imine reductase from stackebrandtia nassauensis
    (Wiley, 2024) Kopar, Merve ; Senyurt Tuzun, Nurcan ; orcid.org/0000-0003-2100-3844 ; orcid.org/0000-0001-5225-3876 ; Kimya Bölümü
    The asymmetric synthesis of tetrahydroisoquinolines (THIQs) has gained importance in recent years due to their significant potential in drug development studies. In this study, the conversion of 1-methyl-3,4-dihydroisoquinoline substrate to a chiral amine, 1-methyl-1,2,3,4-tetrahydroisoquinoline, under the catalysis of the stereoselective imine reductase enzyme from Stackebrandtia nassauensis (SnIR) was investigated in detail to elucidate the mechanism and explain the experimental enantioselectivity. The results were found to be in agreement with the experimental data. To elucidate the reaction mechanism, quantum mechanical calculations were performed by considering a large cluster of the active site of the enzyme. In this regard, possible reaction pathways leading to both R- and S-products with the corresponding intermediates and the transition states for the hydride transfer from the cofactor to the substrate were considered by density functional theory (DFT) calculations, and the factors contributing to the observed stereoselectivity were sought. The calculations supported a stepwise mechanism rather than the concerted protonation and the hydride transfer steps. The stereoselectivity in the hydride transfer was found to be due not only to the stability of the enzyme-subtrate complex but also to the corresponding reaction barriers. The calculations were performed at the wB97XD/6-311+G(2df,2p)//B3LYP/6-31G(d,p) level of theory using the PCM approach.
  • Öge
    A thienothiophene and anthracene based functional hyperbranched polymer: synthesis, photophysical properties and photocatalytic studies
    (Royal Society of Chemistry, 2024) İşçi, Recep ; Bildirir, Hakan ; Gunturkun, Dilara ; Gomez-Mendoza, Miguel ; Liras, Marta ; O’Shea, Victor A. de la Peña ; Öztürk, Turan ; https://orcid.org/0000-0001-9909-4585 ; https://orcid.org/0000-0003-3777-5320 ; Kimya Bölümü
    Conjugated polymer photocatalysts have been receiving extensive attention in the field of photocatalytic hydrogen evolution, owing to their tunable molecular structures and electronic properties. Herein, we report a hyperbranched conjugated polymer, containing thienothiophene and anthracene units (TT-Ant), synthesized via Pd(0) catalyzed Suzuki coupling. Its structural, photophysical and electrochemical features were investigated by using UV-vis and fluorescence spectroscopy, cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS). Photocatalytic hydrogen evolution tests, combining the material with two different additives, resulted in high hydrogen production rates from water. A steady state production rate of around 286 μmol g−1 h−1 for its hybridization with TiO2 was recorded, which is more than 3 times that for pristine TiO2 under the same conditions. Moreover, the combination of the polymeric material with platinum (1% wt) resulted in a maximum rate value of 700 μmol g−1 h−1. The surface properties of the latter combination before and after the reaction were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which demonstrated successful Pt deposition on the surface of the polymer. This work may provide a new strategy to construct stable photocatalysts with thienothiophene and anthracene cores as active sites for efficient catalytic reactions in energy conversion applications.
  • Öge
    Anionic starch-based hybrid cryogel-embedded ZnO nanoparticles: tuning the elasticity and pH-functionality of biocomposites with dicarboxylic acid units
    (Royal Society of Chemistry, 2024) Ciftbudak, Sena ; Orakdogen, Nermin ; https://orcid.org/0000-0001-7578-9649 ; Kimya Bölümü
    Weakly anionic semi-interpenetrating polymer network (semi-IPN) biocomposites based on starch (ST)-incorporated poly(acrylamide-co-itaconic acid)/ZnO (ST-PAI/ZnO) were synthesized by a simple one-pot method via free radical aqueous polymerization. Hybrid biocomposites exhibited lower equilibrium swelling compared with neat copolymer gel. For both hydrogels and cryogels, swelling followed a decreasing order as copolymer PAI > starch-free PAI/ZnO > ST-PAI/ZnO gels. With the addition of 9% ST and ZnO, the swelling ratio of gels decreased from 898 to 68.3, resulting in a significant increase in elastic modulus. Compared with a fixed amount of ST, biocomposite cryogels exhibited significantly higher modulus than hydrogels. With the addition of 9% ST, the elastic modulus of cryogels reached 22.2 kPa while it was 2.7 kPa for the hydrogels. An equation expressing the effective cross-linking density of semi-IPNs presented by a cubic polynomial as a function of starch was obtained. As pH increased with the presence of dicarboxylic acid units, a gradual increase in swelling occurred at two different pH values. A gradually reproducible swelling change of semi-IPNs was depicted with pH ranging from 2.1 to 11.2. Biocomposite cryogels showed rapid swelling in a buffer solution of pH 11.2 and rapid shrinking in pH 2.1. Salt-induced swelling testing showed that the ability to reduce the degree of swelling and solubility of starch was Br− > Cl− > NO3− > SO42− for anions consistent with the Hofmeister series. Adsorption efficiency for the removal of methyl violet (MV) dye was analyzed using Langmuir, Freundlich, Dubinin–Radushkevich and Temkin isotherm models. The results confirmed that the Langmuir isotherm and pseudo-second-order model are suitable for describing MV adsorption on semi-IPN biocomposites. The synthesized biocomposites with good swelling/deswelling kinetics in different pH-buffer solutions, high saline absorbency, desirable adsorption efficiency, and acceptable pH-dependent swelling reversibility can be considered as smart hybrid materials for the adsorption of the dye in water purification tasks.
  • Öge
    Biological properties of 4-trifluoromethylbenzyloxy-substituted cobalt phthalocyanine-gold nanoparticle conjugates
    (Wiley, 2024) Göller, İrem ; Yenilmez, H. Yasemin ; Farajzadeh Öztürk, Nazlı ; orcid.org/0009-0001-7264-2921 ; orcid.org/0000-0001-9009-5741 ; orcid.org/0000-0002-3857-5673 ; Kimya Bölümü
    In this article, peripheral and non-peripheral cobalt phthalocyanines (2 and 3) were synthesized and characterized by applying the spectroscopic methods (FT-IR, 1H NMR, 13C NMR, Maldi-Toff mass, and UV–vis). The synthesized compounds were used for the surficial modification of gold nanoparticles (AuNP). The novel conjugates (2-AuNP and 3-AuNP) were characterized using transmission electron microscopy. The antioxidant activities of bioagents (2, 3, 2-AuNP, 3-AuNP, and AuNP) were examined by performing three different methods, and the results were compared. When their antioxidant properties were examined, it was shown that the capacities of phthalocyanines were higher compared with the modified gold nanoparticles. In addition, antibacterial analysis of the compounds was carried out by applying two different methods. As a result of the analysis, it was determined that both cobalt phthalocyanines and nanoconjugates showed antibacterial activities against Escherichia coli. Phthalocyanine compounds showed lower IC50 results than phthalocyanine-modified gold nanoparticles, while unmodified gold nanoparticles showed no α-glucosidase inhibitory activity.
  • Öge
    Combination of polyethylenimine and vanillin-based benzoxazine as a straightforward self-healable system with excellent film-forming ability
    (American Chemical Society, 2024) Gülyüz, Sevinç ; Kışkan, Barış ; 0000-0002-3028-6455 ; 0000-0001-9476-2054 ; Kimya Bölümü
    This study introduces a straightforward and efficient route for synthesizing self-healable polybenzoxazine networks by utilizing dynamic imine bond exchanges under mild conditions. The process involves combining polyethylenimines with aldehyde-functional bisbenzoxazine, which was produced from vanillin, using a Sc(OTf)3 catalyst and subjecting them to moderate heating at 150 °C. Remarkably, the resulting polybenzoxazine films exhibit good self-healing capabilities at low temperatures and pressures, without requiring any additional additives to facilitate the healing process. The degree of recovery was assessed through tensile tests, while rheologic measurements were utilized to analyze stress relaxation and activation energy of dynamic bonding, providing insights into the self-healing process. Additionally, comprehensive spectral characterizations and investigations of thermal behaviors were conducted to gain a deeper understanding of the material’s properties and performance. Moreover, the polybenzoxazine networks demonstrated enhanced hydrolysis stability compared to conventional imine-based systems, benefiting from the specific Mannich linkages and inherent hydrophobic nature of polybenzoxazines.
  • Öge
    Comparison of dye adsorption of chitosan and polyethylenimine modified bentonite clays : optimization, isotherm, and kinetic studies
    (American Chemical Society, 2024) Kahya, Nilay ; Şen, Begüm ; Berber, Demet ; Öztekin, Nevin ; 0000-0002-7884-5113 ; 0000-0003-3676-5147 ; Kimya Mühendisliği
    The aim of this study was to compare the effect of modifying calcium bentonite (Bent-Ca) clay with two cationic polymers, chitosan (Chi) and polyethylenimine (PEI), on the removal of remazol black B (RB-B) dye from an aqueous solution. The samples were characterized by using scanning electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. The fractional factorial design of 2(6–1) was applied to investigate the effects of pH, temperature, amount of adsorbent, initial dye concentration, contact time, and shaking rate on the adsorption process. To further optimize RB-B removal from an aqueous solution, a Box–Behnken design with three factors and a response surface methodology was used. The optimum conditions were a pH of 3.77, a temperature of 40.45 °C, and an initial RB-B concentration of 77.27 mg L–1 for Bent-Ca-Chi, whereas for Bent-Ca-PEI, the optimum conditions were a pH of 5.53, a temperature of 41.06 °C, and an initial dye concentration of 238.89 mg L–1. To understand the adsorption behavior, the Langmuir and Freundlich isotherms were fitted to the experimental data. It was found that the Langmuir isotherm model matched well with the dye adsorption by Bent-Ca-Chi and Bent-Ca-PEI. The kinetics study was performed using three kinetic models: pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. Among these models, the RB-B dye kinetics were best represented by the pseudo-second-order model equation for the adsorbents.
  • Öge
    Drug encapsulation and release with a nonionic amphiphilic calix[4]pyrrole
    (Royal Society of Chemistry, 2024) Mirabolghasemi, Mana ; Bektaş, Necla ; Sancaklı, Buse ; Dağ, Aydın ; Aydoğan, Abdullah ; https://orcid.org/0000-0001-6377-5143 ; Kimya Bölümü
    A polyethylene glycol-tethered amphiphilic calix[4]pyrrole compound (C4P-PEG) was synthesized via an esterification reaction between the corresponding alcohol-functionalised calix[4]pyrrole and carboxylic acid ended polyethylene glycol. The structure of C4P-PEG was confirmed by means of NMR spectroscopy and high-resolution mass spectrometry. The complexation ability of the control compound octamethylcalix[4]pyrrole and C4P-PEG with chemotherapeutic cancer drug, doxorubicin-HCl, was shown with the aid of various NMR techniques in DMSO, containing 1.5% (wt) water. Nonionic amphiphilic calix[4]pyrrole compound C4P-PEG was then shown to produce stable micelles in water. The title compound was also used to encapsulate doxorubicin-HCl in aqueous medium and its concurrent drug release ability was illustrated under acidic and basic conditions. While the characterizations of drug-free and drug-loaded micelles were carried out with dynamic light scattering experiments and transmission electron microscopy, the drug loading capacity, encapsulation efficiency and in vitro drug release profiles were studied with the aid of UV-vis spectrophotometry.
  • Öge
    Elemental composition of household dusts extracted in simulated body fluids and their impact on culturable pathogenic bacteria responses
    (Springer, 2024) Baysal, Aslı ; Zora, Sevilay ; Saygın, Hasan ; 0000-0002-0178-7808 ; 0000-0002-6534-0538 ; 0000-0003-2479-7635 ; Kimya Bölümü
    In the last decade, a great deal of research has focused on the determination of potential toxic elements by total concentration and identification the microorganisms in dust. However, determining bio-relevant (e.g., inhalable) forms of elements instead of total contents in acids is necessary for human health. Moreover, examination of the behavior of microorganism under these bio-relevant conditions and revealing the interaction between elements and pathogens is vital and necessary for deeper understanding. However, previous studies have ignored these topics. Therefore, the present study aimed to (i) investigate elements in household dusts extracted in simulated lung fluids, (ii) examine the total concentration of culturable bacteria and their biochemical responses with exposure to bio-fractions of household dusts, and (iii) assess their relations and risks using the model approaches by inhalation. Here, settled dusts were collected in 25 houses, and extracted in four simulated body fluids to determine bio-fractions of elements. Moreover, total count of potentially pathogenic and heterotrophic bacteria, and four clinically important culturable pathogens were incubated in the presence of household-dusts extracted in simulated body fluids. The activity, biofilm, biochemical and oxidative responses of pathogens were measured following household-dust exposures. Afterward, the relationship between elements and pathogen responses were evaluated, and model and derived approaches were used for risk assessments of elements and pathogens. The higher daily intake of elements obtained in artificial lysosomal fluid fraction of household dust mimicking the inflammatory condition compared to other body fluids. Moreover, bacterial responses were mainly influenced from bio-fractions of household dusts and their elemental contents.
  • Öge
    Enhancement of the surface and mechanical properties of polyurethane coating through changing the additive ratio of silane
    (Wiley, 2024) Kant, İrem Elmas ; Tarkuç, Simge ; Köken, Nesrin ; Yeşilçubuk, Süleyman Alper ; Kızılcan, Nilgün ; orcid.org/0000-0002-6455-7479 ; orcid.org/0000-0002-9850-7517 ; orcid.org/0000-0001-8531-1577 ; orcid.org/0000-0002-0934-7882 ; orcid.org/0000-0003-2350-5098 ; Kimya Bölümü
    Continuous development in the formulation and processing techniques of polyurethane (PU) coatings improves an aesthetic appearance as well as protection against environmental factors. In this study, the formulation of PU coating with polyethylene glycol 600 (PEG600), isophorone diisocyanate (IPDI), and trimethoxysilylpropylcarbamoyloxyhexane (TMSCH) silane-based additive is optimized to obtain high scratch-resistant coating. An addition of 43.1 wt.% TMSCH in PU formulation resulted in a significant improvement in the scratch resistance and wettability properties compared with pure PU film. The homogenously prepared micron-thick coatings are characterized using scanning electron microscopy analysis and Fourier transform infrared spectroscopy. The results confirm the presence of silane additives in the PU coating matrix. The mechanical properties improved due to the increased crosslinking networks via the formation of urethane bonds by increasing the TMSCH in PU formulation. Prepared PU coating showed combined features of transparency, hydrophobicity, scratch resistance, and mechanical strength that make it a promising candidate for household appliances.
  • Öge
    Fluorescent poly(β-amino ester)s containing aza-BODIPYs as theranostic agents for bioimaging and photodynamic therapy
    (Royal Society of Chemistry, 2024) Sari, Seyma ; Ünver, Sena ; Avsar, Timucin ; Özçelik, Şennur ; Kilic, Turker ; Kahveci, Muhammet U. ; https://orcid.org/0000-0001-7287-6181 ; Kimya Bölümü
    Photodynamic therapy (PDT) as a promising approach in cancer treatment has garnered significant attention due to its minimal invasiveness and low toxicity, as well as its ability to avoid side effects and facilitate combination therapies. The photosensitizer (PS) is the key component of PDT and can be employed in the diagnosis or visualization of cells. Herein, a water-dispersible, biodegradable and fluorescent poly(β-amino ester) (PBAE) based PS was developed for efficient PDT and imaging. The PBAE was specifically designed and synthesized to incorporate fluorescent groups, such as aza-BODIPY, and water soluble poly(ethylene glycol) segments into the polymer backbone by aza-Michael addition-based poly-condensation polymerization. Subsequently, the amine-end functionalized PBAEs with different aza-BODIPY contents (3.6 and 7.2 mol%) were end-capped with folic acid to increase the cancer-cell-targeting potential of the polymers. The polymeric PSs were then tested on brain tumor (U87-MG), cervical tumor (HeLa) and healthy (HUVEC) cell lines for the dual modality of imaging and PDT. The polymeric PSs demonstrated significant anti-cancer potential as evaluated via reactive oxygen species generation, photocytotoxicity, colony formation and cell invasion assays.
  • Öge
    High-performance thienothiophene and single wall carbon nanotube-based supercapacitor as a free-standing and flexible hybrid energy storage material
    (American Chemical Society, 2024) İşçi, Recep ; Dönmez, Koray Bahadır ; Karatepe, Nilgün ; Öztürk, Turan ; 0000-0003-3086-4478 ; 0000-0001-5315-3148 ; 0000-0002-7392-4103 ; 0000-0003-3777-5320 ; Kimya Bölümü
    Long cycle life and high energy/power density are imperative for energy storage systems. Similarly, flexible and free-standing electrodes are important for supercapacitor applications. Herein, we report, for the first time, use of thienothiophene (TT) and a single-walled carbon nanotube (SWCNT)-based free-standing and flexible hybrid material (TT-TPA-SWCNT) as a high-performance supercapacitor. The synthesized TT derivative, TT-TPA, was directly attached to SWCNT through noncovalent interactions to obtain the TT-based SWCNT hybrid, TT-TPA-SWCNT, as a flexible film. The hybrid film was clarified by surface analysis methods of scanning electron microscopy and atomic force microscopy. TT-TPA-SWCNT was used as a flexible and free-standing electrode in a two-electrode system for supercapacitor and energy storage applications. It displayed a high energy storage capacity of 83.2 F g–1 at 5 mV s–1 scan rate, an excellent cyclic stability with 110% retention of its initial specific capacitance after 7000 cycles and a long power density ranged from 100 to 3000 W·kg–1, demonstrating that TT-TPA-SWCNT is a promising hybrid nanomaterial for high-performance energy storage applications.
  • Öge
    Highly sensitive OFET based room temperature operated gas sensors using a thieno[3,2-b]thiophene extended phthalocyanine semiconductor
    (Royal Society of Chemistry, 2024) İşçi, Recep ; Yavuz, Özgür ; Faraji, Sheida ; Gunturkun, Dilara ; Eroğlu, Mehmet ; Majewski, Leszek A. ; Yılmaz, İsmail ; Öztürk, Turan ; https://orcid.org/0000-0003-3086-4478 ; https://orcid.org/0000-0002-0660-7474 ; https://orcid.org/0000-0001-6544-1286 ; https://orcid.org/0000-0002-5046-7456 ; https://orcid.org/0000-0003-3777-5320 ; Kimya Bölümü
    Over the past decades, organic field-effect transistor (OFET) gas sensors have maintained a rapid development. However, the majority of OFET gas sensors show insufficient detection capability towards oxidizing and hazardous gases such as nitrogen dioxide (NO2) and sulfide dioxide (SO2). In this report, a sustainable approach toward the fabrication of OFET gas sensors, consisting of a thieno[3,2-b]thiophene (TT) and phthalocyanine (Pc) based electron rich structure (TT-Pc) for the detection of both nitrogen dioxide (NO2) and sulfide dioxide (SO2) is disclosed for the first time. Khaya gum (KG), a natural, biodegradable biopolymer is used as the gate dielectric in these OFET-based sensors. Thin film properties and surface morphology of TT-Pc were investigated by UV-Vis, SEM, AFM and contact angle measurements, which indicated a uniform and smooth film formation. The UV-Vis properties were supported by computational chemistry, performed using density functional theory (DFT) for optimizing geometry and absorption of TT-Pc models. Sensitive and selective responses of 90% and 60% were obtained from TT-Pc OFET-based sensors upon exposure to 20 ppm of NO2 and SO2, respectively, under ambient conditions. One of the lowest limits of detection of ∼165 ppb was achieved for both NO2 and SO2 using a solution-processed TT-Pc sensor with a natural, biodegradable dielectric biopolymer. The sensors showed excellent long-term environmental and operational stability with only a 7% reduction of the sensor's initial response (%) upon exposure to NO2 and SO2 over nine months of operation in air.
  • Öge
    Imide-yne click polymerization: a new and versatile tool for the toolbox of X-yne click polymerization
    (Royal Society of Chemistry, 2024) Aslanturk, Oguzhan ; Sagdic, Gokhan ; Cakmakci, Emrah ; Durmaz, Hakan ; Gunay, Ufuk Saim ; https://orcid.org/0009-0002-4431-9841 ; https://orcid.org/0000-0003-4710-2496 ; https://orcid.org/0000-0002-3085-3763 ; Kimya Bölümü
    The Michael reaction, a cornerstone in organic chemistry, continues to revolutionize the field with its unparalleled versatility in forming carbon–carbon, carbon–oxygen, carbon–nitrogen, and carbon–sulfur bonds, paving the way for groundbreaking advancements in complex molecule and macromolecule construction. In this study, imide-yne reaction was employed at the macromolecular level for the first time to prepare linear poly(imide ester)s. A wide range of bisimides and dipropiolates were reacted through imide-yne click polymerization in the presence of 1,4-diazabicyclo[2.2.2] octane (DABCO) at room temperature. The polymerizations proceed in an anti-Markovnikov fashion, yielding the E-isomer as the major product. Polymers were obtained in high yields and their molecular weights were found to be in the range of 5.64–12.67 kDa. The remaining unreacted double bonds in the linear polymers were found to undergo further functionalization with thiols using a strong organocatalyst 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), which was also supported by a model study. Post-polymerization modification study prompted us to prepare imide-yne monomers that can react with dithiols to synthesize poly(imide thioether)s through nucleophilic thiol–ene click reaction using TBD as the catalyst. The obtained polymers displayed a wide range of glass transition temperatures and thermal stability. Thus, it can be said that the proposed method enables the synthesis of new polyimide-based structures with tailorable thermal properties. It is believed that the proposed strategy will make a significant contribution to expanding the versatility of active alkyne chemistry at the macromolecular level.
  • Öge
    Indium-based quantum dots trapped in solid-state matrices: a one-pot synthesis, thermoresponsive properties, and enhanced micropollutant removal
    (Royal Society of Chemistry, 2024) Ük, Nida ; Aykut, Sümeyye ; Jahangiri, Hadi ; Nar, Ilgın ; Ünlü, Caner ; https://orcid.org/0000-0001-6626-8665 ; https://orcid.org/0000-0001-7544-5360 ; https://orcid.org/0000-0003-2300-3071 ; https://orcid.org/0000-0002-0612-3111 ; Kimya Bölümü
    Indium-based quantum dots (QDs), such as copper indium disulfide and zinc copper indium sulfide, have been the center of research for decades due to their low toxicity and unique photophysical properties. In contrast, versatile indium-based materials like In2S3 and ZnIn2S4 have been rarely studied in their QD form because of the challenges in their synthesis and used in solid-state material based applications because of their colloidal nature. In this study, a one-pot single-step method to synthesize In2S3, ZnIn2S4, and Cu-doped ZnIn2S4 QDs trapped in insoluble solid-state oleic acid matrices was developed. The QDs in solid-state matrices exhibited bright orange colored fluorescence with controllable emission properties achieved by altering the chemical composition. Among these QDs, the ZnIn2S4 QDs displayed thermo-responsive properties. As the temperature increased, the fluorescence intensity of ZnIn2S4 QDs decreased. In addition, all QDs demonstrated high removal efficiency for micropollutants in the aqueous medium, especially against cationic organic dyes. This study represents one of the first attempts at the direct development of QDs trapped in insoluble solid-state matrices. The QDs in solid-state matrices hold promise for applications in thermal sensors and studies related to the micropollutant removal.
  • Öge
    Investigation of advanced biological properties of carbon, carbon-boron quantum dots, and copper (II) phthalocyanine nanoconjugates
    (Wiley, 2024) Özçeşmeci, Mukaddes ; Gümrükçü, Selin ; Ünlü, Caner ; Coşkun, İbrahim Yağız ; Özdemir, Sadin ; Yalçın, M. Serkan ; Tollu, Gülşah ; Özçeşmeci, İbrahim ; orcid.org/0000-0002-6723-6902 ; orcid.org/0000-0002-3135-6590 ; orcid.org/0000-0002-0612-3111 ; orcid.org/0000-0002-8723-383X ; Kimya Bölümü
    Non-peripherally, glycerol terminal groups substituted copper (II) phthalocyanine were non-covalently (electrostatic and/or π–π interaction) attached to carbon (CQD) and carbon-boron quantum dots (CBQD) to form QDs-Pc nanoconjugate systems. Synthesized novel phthalocyanine compounds and QDs-Pc conjugate systems were characterized using different spectroscopic techniques. Various biological assessments were applied to newly synthesized compounds. Conjugates 4 and 5 had a maximal free radical scavenging activity of 71.3% and 68.1% at a 100 mg/L concentration. Compounds exhibited high antidiabetic activities at 200 mg/L. Also, compounds showed significant DNA nuclease activity at all tested concentrations. The most efficient MIC value was obtained as 4 mg/L against Enterococcus hirae and Enterococcus feacalis. This MIC value was further decreased after photodynamic therapy, and it was observed that the antimicrobial effects of the compounds increased. Inhibition of microbial cell viability was obtained as 100% for all compounds. In addition, compounds exerted perfect biofilm inhibitory effects.
  • Öge
    Mechanically robust shape-memory organohydrogels based on silk fibroin with organogel microinclusions of various sizes
    (Wiley, 2023) Bas, Yahya ; Okay, Oguz ; orcid.org/0000-0003-2717-4150 ; Kimya Bölümü
    Organohydrogels (OHGs) are soft materials with antagonistic hydrophilic and hydrophobic domains that have great interest for many different applications. This study presents the preparation of mechanically strong OHGs with shape-memory function by incorporating semicrystalline organo-microgels within the pores of silk fibroin (SF) scaffolds. In the first step, SF cryogels with various pore diameters between 26 ± 8 and 17 ± 4 µm are synthesized by cryogelation of aqueous SF solutions at concentrations between 5 and 20 w/v%. In the second step, the pores of SF scaffolds are filled with an organogel precursor solution containing n-octadecyl acrylate (C18A), acrylic acid, N,N'-methylene(bis)acrylamide, and an initiator. Once the free-radical polymerization took place inside the pores, OHGs containing organo-microgels of various sizes are obtained. The incorporation of the organogel component in the cryogels generates crystalline areas due to the side-by-side packed C18 side chains. OHGs' melting temperature and crystallinity level can be varied from 42 to 54 °C and from 2 to 16%, respectively. The stiffness of OHGs increases from 5.9 ± 0.5 to 18 ± 1 MPa with increasing SF concentration from 5 to 20 w/v%, which is attributed to the decreasing pore size of the cryogels and increasing thickness of the pore walls.
  • Öge
    Melt-processable and electrospinnable shape-memory hydrogels
    (Wiley, 2024) Abdullah, Turdimuhammad ; Altınkök, Çağatay ; Okay, Oğuz ; orcid.org/0000-0003-2717-4150 ; Kimya Bölümü
    Due to their ability to adapt to subtle changes in response to various external and internal stimuli, smart hydrogels have become increasingly popular in research and industry. However, many currently available hydrogels suffer from poor processability and inferior mechanical properties. For example, the preparation of a hydrogel network that can be subjected to melt processing and electrospinning is challenging. Herein, a series of mechanically strong, shape-memory hydrogels based on polyacrylic acid (PAAc) chains containing 20–50 mol% of crystallizable n-octadecylacrylate (C18A) segments are prepared by an organosolv method followed by in situ physical cross-linking via hydrophobic interactions. The hydrogels exhibit a reversible strong to weak gel transition at 50–60 °C and can be melt-processed at 60–100 °C, depending on the molar fraction of C18A. Additionally, the hydrogels can be dissolved in chloroform/ethanol mixture to form a viscous solution, which can then be used to produce a nanofibrous network by electrospinning. Effects of polymer concentration, volume ratio of solvents, and mole fraction of C18A on electrospinning are investigated to produce smooth, uniform nanofibers with small fiber diameter. The produced nanofibers, while maintaining their chemical structure, show significantly improved water adsorption capacity, enhanced mechanical properties, and fast shape-memory performance.
  • Öge
    Modulating spectral response of raw photosynthetic pigments via ternary cadmium chalcogenide quantum dots : simultaneous enhancement at green spectrum and inhibition at UV region
    (Springer, 2024) Aykut, Sümeyye ; Ük, Nida ; Coşkun, İbrahim Yağız ; Şahin Keskin, Sultan ; Nar, Ilgın ; Trabzon, Levent ; Ünlü, Caner ; 0000-0001-7544-5360 ; 0000-0001-6626-8665 ; 0000-0002-1666-7438 ; 0000-0001-6606-5622 ; 0000-0003-2300-3071 ; 0000-0002-7323-3943 ; 0000-0002-0612-3111 ; Kimya Bölümü
    Photosynthesis relies on the absorption of sunlight by photosynthetic pigments (PPs) such as chlorophylls and carotenoids. While these pigments are outstanding at harvesting light, their natural structure restricts their ability to harvest light at specific wavelengths. In this study, Oleic acid-capped CdSeS and CdTeS ternary quantum dots (QDs) were synthesized using a novel two-phase synthesis method. Then, these QDs were used to interact with raw PPs, a mixture of chlorophylls and carotenoids isolated from spinach. Our findings revealed the following: (1) Interacting QDs with raw PPs effectively inhibited the chlorophyll fluorescence of the pigments upon excitation in UV light region (250–400 nm) without causing any damage to their structure. (2) By forming an interaction with QDs, the chlorophyll fluorescence of raw PPs could be induced through excitation with green-light spectrum. (3) The composition of the QDs played a fundamental role in their interaction with PPs. Our study demonstrated that the photophysical properties of isolated PPs could be modified by using cadmium-based QDs by preserving the structure of the pigments themselves.
  • Öge
    Nature-Inspired Depolymerization of Soda Lignin: Light-Induced Free Radical Promoted Cleavage of β-O-4 Bonds
    (Wiley, 2024) Kaya, Kerem ; Atsay, Armağan ; Gündüz, Hande ; Slabon, Adam ; Yağcı, Yusuf ; orcid.org/0000-0002-5736-488X ; orcid.org/0000-0002-2070-5433 ; orcid.org/0000-0002-4452-1831 ; Kimya Bölümü
    The development of sustainable valorization methods for lignin is a challenging task because the vast majority of the reported studies involve either harsh conditions or expensive transition metal catalysts. Inspired by the sunlight degradation of lignin compounds, known as lignin yellowing, the use of a commercially available cheap organic photoinitiator, namely, phenacyl bromide (PAB) is reported here, for the efficient cleavage of lignin model compound 2-phenoxyacetophenone (2-PAP) and for the depolymerization of soda pulped lignin (SL) under UV-A irradiation and ambient conditions. Real-time NMR investigations of the photoreaction between 2-PAP and PAB shed light on the possible reaction mechanisms involving different radical species, HBr, and molecular oxygen. Interestingly, combined spectral, chromatographic, powder X-ray diffraction, and thermal studies of the photoreaction between PAB and SL indicate the formation of guaiacyl alcohol as the main product. The unprecedented performance of PAB is attributed to the excess generation of phenacyl radicals, the generation of photolabile brominated species, and HBr playing key roles in the cleavage of β-O-4 linkages. This work represents a new edge for sustainable lignin valorization under mild reaction conditions and offers the opportunity for large-scale production of valuable aromatics using technical lignins as feedstock.
  • Öge
    Polyether synthesis through reductive etherification reaction strategy
    (Wiley, 2023) Luleburgaz, Serter ; Tunca, Ümit ; Durmaz, Hakan ; orcid.org/0000-0002-3126-598X ; orcid.org/0000-0001-8767-6166 ; orcid.org/0000-0003-4710-2496 ; Kimya Bölümü
    The reductive etherification reaction (RER) of carbonyl groups (aldehydes or ketones) through silane as a reducing agent together with Bronsted or Lewis acid affords the synthesis of symmetrical and unsymmetrical ethers. This strategy is applied at the macromolecular level for the first time in 1993, and isophthalaldehyde is self-polymerized in the presence of triethylsilane (Et3SiH)/ tritylperchlorate (TrClO4) to yield polyethers with low to moderate molecular weights. Next, the polyethers with alternating structures are achieved by reacting isophthalaldehyde with bis(trimethylsilyl) ethers or diols as comonomers using reducing agent silane and Lewis acid. Moreover, in recent years, it is shown that polyether synthesis and post-polymerization modification (PPM) of polymers proceeds smoothly and effectively with the RER strategy in the presence of chlorodimethylsilane (CDMS), which acts as both a reducing agent and a Lewis acid.