Hacettepe Üniversitesi Açık Erişim Sistemi (HÜAES)
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Poli(Epiklorohidrin-Ko-(Etilen Oksit)-Ko-(Allil Glisidil Eter)) (GECO)’nun Yapısal Parametrelerinin Epiklorohidrin Temelli Elastomerlerin Mekanik ve Dinamik-Mekanik Özelliklerine Etkisi
(Fen Bilimleri Enstitüsü, 2025) Yalaki, Yalçın; Polimer Bilimi ve Teknoloji
Elastomers containing epichlorohydrin (ECH) not only possess the dynamic properties of
natural rubber but also exhibit superior resistance to fuel, oil, and chemicals. These
elastomers have high heat resistance and low-temperature flexibility due to the
chloromethyl groups attached to oxygen-containing saturated main chains. In the polymer
industry, in addition to homopolymers of epichlorohydrin, co- and terpolymers formed
with ethylene oxide (EO) and allyl glycidyl ether (AGE) monomers are industrially
produced. Thanks to advancements in production methods, the industrial use of the ter-
polymer poly(epichlorohydrin-co-ethylene oxide-co-allyl glycidyl ether), abbreviated as
GECO, has been increasing. GECO elastomers can be prepared with different physical
properties, such as vibration damping and mechanical strength, depending on the
monomer ratios. In this thesis study, elastomer blends of GECO polymers with varying
ECH, EO and AGE monomer ratios were prepared according to specific formulations,
and the mechanical, thermo-mechanical, and damping properties of the obtained
elastomers were examined. The aim of the study was to investigate the effects of GECO’s
structural parameters on mechanical and thermo-mechanical properties. In the study,
different types of GECO polymers, containing varying ECH, EO and AGE monomer
ratios were used to prepare various elastomers with the curing agent 2,4,6-Trimer-capro-
s-triazine (Trithiocyanuric acid) (TMT) and silica (Coupsil 6109) and phenolic resin as
filler materials and other auxiliary chemicals. For this purpose commercially available
GECO polymers with varying monomer ratios produced by the Zeon Company under the
codes T3000LL, T3100, T3102, and T3108 were used. The curing properties of the
prepared formulations were examined using a moving die rheometer (MDR) at
temperatures of 170, 180, 190, and 200 °C. The MDR data obtained were used to
determine the optimal curing conditions for GECO mixtures and to analyze curing
kinetics. After determining the optimal curing conditions, the mechanical properties of
the GECO mixtures were examined using a universal testing machine. The influence of
the structural properties of GECO polymers on their mechanical properties was analyzed
by evaluating stress-strain curves. To investigate the dynamic-mechanical properties of
GECO elastomers, cyclic compression tests were performed on disk-shaped samples
cured under optimal conditions and changes in the energy damping, stress relaxation, and
permanent deformation characteristics were investigated. The temperature-scanning
stress relaxation (TSSR) behavior of GECO elastomers was analyzed in the temperature
range of 25-300 °C using a TSSR device. Through TSSR analyses, the effects of the
structural parameters of GECO polymers on their long-term mechanical performance
were determined. As a result of the evaluations, among the ECH, EO, and AGE
monomers, the EO monomer was found to have the most significant impact on physical
properties. The elastomer prepared with T3108, which had the highest EO content,
exhibited the highest energy damping capacity, whereas the elastomer prepared with
T3100, which had the lowest EO content, had the lowest energy damping capacity.
Besides the EO content, it was determined that poly dispersity index and long chain
branching were also important factors that influenced the mechanical properties of
elastomers. The results of this study contribute to the literature on the preparation of
GECO-based functional elastomers and on the determination of energy dissipation
properties that have not been previously presented in this field.
Amin ve Fenollerin Tespiti ve Farklandırılmasını Sağlayan Kemosensörlerin Geliştirilmesi
(Fen Bilimleri Enstitüsü, 2025) Çalış, Emine; Kimya
BODIPY compounds stand out among fluorophores used in fluorescent sensor design due to their high fluorescence quantum yields, photostability, narrow emission bands, and chemically functionalizable structures. The BODIPY core enables the development of effective sensor systems for critical areas such as environmental and food safety through selective interactions with specific analytes via appropriately attached functional groups. The detection of amine and phenol compounds is of great importance in terms of environmental
sustainability and public health. Identifying organic contamination in wastewater and microbial spoilage in food products relies on the accurate and reliable detection of such compounds. Therefore, chemosensor systems developed for the determination of amines and phenolic compounds have gained significance. Within the scope of this thesis, a new fluorescence-based chemosensor was designed for the detection of amine and phenol compounds by utilizing the superior properties of BODIPY. For this targeted system, a new fluorophore structure was obtained by bromination at the α- and β-positions of meso-trimethoxyphenyl BODIPY to be used in sensor studies. With this structure, in line with the aim of the study, observable photophysical changes (turn-on type response) were achieved upon chemical reactions with the target analytes, amines and phenols. The developed system reacts directly with amines, whereas it reacts with phenols in the presence of K₂CO₃. In both cases, the fluorescence intensity increases, enabling the system to distinguish between amines and phenols depending on the medium used. The
system showed systematic fluorescence changes in response to increasing amine concentrations, allowing quantification of amines with low detection limits (LOD). This study demonstrates that BODIPY derivatives can serve as effective and innovative tools in the design of sensors aimed at monitoring significant environmental and foodderived contaminants.
Sarcotragus Foetidus Süngerinin Sert ve Yumuşak Doku Mühendisliği Uygulamaları İçin Fabrikasyonu ve İn Vitro Karakterizasyonu
(Fen Bilimleri Enstitüsü, 2025) Çakır, Demet; Kimya Mühendisliği
In this doctoral study, multifunctional systems were developed using natural spongin structures derived from the marine sponge Sarcotragus foetidus, a member of the class Demospongiae, for potential biomedical applications in both tissue engineering and glioblastoma multiforme (GBM) therapy.
In the first part of the study, it was hypothesized that scaffolds derived from Sarcotragus foetidus, due to their spongin content, would support osteogenic differentiation, and that this effect would be further enhanced by boron-doped hydroxyapatite (B-HAp) coating through the stimulation of additional differentiation pathways. Within this hypothesis, three-dimensional (3D) spongin-based scaffolds were initially isolated from the marine sponge Sarcotragus foetidus. The scaffolds were then coated with hydroxyapatite and boron-doped hydroxyapatite to improve their osteoinductive properties. In vitro studies using MC3T3-E1 preosteoblast cells demonstrated that the scaffolds maintained cell viability and promoted osteogenic differentiation. Particularly in the B-HAp coatedgroup, expression levels of Col1a1 and Ocn genes increased approximately 2.5-fold.
Histological examinations confirmed enhanced mineralization, while antibacterial tests showed that especially B-HAp coated scaffolds exhibited pronounced bacteriostatic activity against both Gram-positive and Gram-negative bacteria. In the second part of the study, collagen was successfully isolated from Sarcotragus foetidus with high yield and purity. The isolated collagen showed a protein yield of approximately 12%, a total protein content of ~350 mg/g dry weight, and a hydroxyproline content of ~9%. Structural and chemical characterization, conducted through various analytical methods, revealed that the collagen retained its triple helical structure and showed high similarity to Type I collagen, indicating a high-quality material. This collagen was crosslinked via EDC/NHS to form a hydrogel and provided a biocompatible matrix suitable for soft tissue engineering applications.
In the final part of the study, PBAT (poly(butylene adipate-co-terephthalate))
nanoparticles loaded with gallic acid (GA) were developed for GBM therapy and coated with Opuntia ficus indica mucilage (ONM) to enable controlled drug release. The optimized formulations yielded nanoparticles with an average size of 190 ± 69 nm and approximately 87% encapsulation efficiency. These nanoparticles were successfully integrated into Sarcotragus foetidus sponge-based scaffolds. In vitro analyses using T98G glioblastoma cells revealed that GA-loaded and ONM-coated nanoparticles exhibited significant cytotoxic and apoptotic effects, increasing caspase-3 gene expression while
significantly suppressing tumor-associated genes c-Myc and β-catenin.
In conclusion, this study demonstrated that the biological structures derived from Sarcotragus foetidus can be effectively utilized in multifunctional biomedical applications. These natural materials were successfully transformed into both scaffold systems supporting tissue regeneration and efficient carriers providing controlled drug release.
Zaman Serisi Yöntemleri ile Deprem Verilerinin Analizi
(Fen Bilimleri Enstitüsü, 2025) Gökmenoğlu, Kübra Simay; İstatistik
Turkey is situated on numerous active fault lines due to its unique geographical location, and as a result, it frequently experiences earthquakes of varying magnitudes. These earthquakes have profound and often irreversible effects on human life, both economically and psychologically.
To analyze the earthquake data, the study initially employed classical regression models, followed by the application of more advanced techniques such as quantile regression and the machine learning-based XGBoost regression model. From a statistical standpoint, the LSTM method was determined to be the most suitable among the methods applied. The modeling process considered earthquake magnitude (Mw), depth, and epicenter coordinates (latitude and longitude) as key variables.
In the application phase of the study, analyses were particularly focused on the Marmara Region and the province of Istanbul. For Istanbul's 39 districts, earthquake magnitude predictions were generated at varying depth levels (10 and 30 km). The resulting predictions were visualized using both line graphs and heat maps, enabling a comparative assessment of regional risk
distributions.
Furthermore, the impact of depth on earthquake magnitude was examined statistically through linear regression analysis. The results indicated a statistically significant relationship between depth and Mw, concluding that an increase in depth tends to lead to higher predicted Mw values.
Overall, the findings suggest that earthquakes exhibit certain statistical structures and spatial patterns. The developed models provide scientifically reliable forecasts for potential future earthquakes. This thesis demonstrates that it is possible to construct appropriate models for predicting earthquake magnitudes and that these models can yield robust and credible scientific
estimations.
Kaktüs Meyvesinden (Opuntia ficus-indica L.) Betalainlerin Yeni Yöntemlerle Ekstraksiyonu, Niyozomal Enkapsülasyonu ve Gıda Uygulaması
(Fen Bilimleri Enstitüsü, 2025) Akdeniz Oktay, Büşra; Gıda Mühendisliği
Prickly pear (Opuntia ficus-indica L.) is a fruit commonly cultivated in arid and semi-arid regions and is noteworthy rich in betalain pigments and various phenolic compounds. In recent years, betalains have grown in interest due to their visual and functional properties. Particularly, betalains are accepted as a natural alternative with rising consumer sensitivity to the synthetic colorants. However, the limited stability of these naturally derived compounds against environmental factors such as light, temperature, and pH could restrict their applicability. Therefore, the utilization of betalain-rich sources like cactus fruit and strategies to enhance the stability of these compounds in food systems has gained significance.In traditional extraction of natural pigments like betalains, the extended processing times, high solvent usage, and low extraction yield, are major limitations. Accordingly, there has been increasing interest in green extraction technologies, microwave and ultrasound-assisted methods, providing environmentally friendly, rapid, and high-yield alternatives. Furthermore, various encapsulation techniques have developed to enhance the stability of the extracted functional color pigments and other bioactives. For this purpose, niosomal encapsulation, a technology utilized for a long time in the pharmaceutical and cosmetic industries but relatively novel in food applications, has drawn attention as a promising carrier system for the delivery and controlled release of natural bioactives. Bioactive compounds such as betalains and phenolics not only have functional properties but also exhibit antimicrobial activity against certain pathogenic microorganisms. In addition, the application of these niosomal encapsulated bioactives to food systems contributes to both value-added product development and enhancement of bioaccessibility during digestion. Consequently, it is crucial to perform in-vitro digestion studies on extracts, niosomal capsules containing bioactive compounds, and niosome incorporated food matrices. To the best of our knowledge, there has been no investigation in the literature consisting of the extraction of betalains and phenolics from prickly pear using both ultrasound-assisted and vacuum microwave-assisted extraction methods in comparison with conventional method, also optimizing extraction conditions. Similarly, niosomal encapsulation of extracts, the optimization of encapsulation parameters, characterization of the niosomes, and application in a food matrix have not been previously reported. In this study, firstly extracts were prepared using conventional, ultrasound assisted, and vacuum microwave assisted extraction techniques, the extraction parameters were optimized, and extraction methods were compared. Since the promising results were obtained in vacuum microwave assisted extraction, the extract obtained in optimal extraction conditions was used in niosomal encapsulation process. During encapsulation, process parameters were optimized, the resulting niosomal formulation was characterized, and incorporated into a yogurt product. Finally, the effects of both the extract and the extract-loaded niosomes on the yogurt samples were analyzed, and in-vitro digestion studies were performed to evaluate the bioaccessibility of the bioactive compounds.In the beginning of the thesis, conventional extraction (CE), ultrasound assisted extraction (UAE), and vacuum microwave assisted extraction (VMAE) methods were used to extract betalains and phenolic compounds from prickly pear. Extraction conditions were optimized using a Box–Behnken design with 29 runs and four independent variables at three levels. For CE and UAE, variables were determined as extraction time (X₁) 1–3 hours and 30–90 min, extraction temperature (X₂) 30–50 °C, ethanol concentration in solvent (X₃) 40–80%, and sample-to-solvent ratio (X₄) 1:10–1:30 (g/mL). For VMDE, variables were vacuum pressure (X₁) 100–400 mmHg, extraction time (X₂) 2–8 min, ethanol concentration in solvent (X₃) 20–60%, and sample-to-solvent ratio (X₄) 1:10–1:30 g/mL. Total phenolic content (TPC), total antioxidant capacity (DPPH and CUPRAC methods), and total betalain content (TBC) were the responses. Second-order polynomial equations and variance analysis were obtained for each response using Response Surface Methodology. The optimization of extraction parameters was carried out for each extraction method. For CE, the optimum extraction conditions were an extraction time of 2.05 h, extraction temperature of 50 °C, 80% ethanol, sample-to-solvent ratio of 1:22.6 g/mL. For UDE the optimum extraction conditions were an extraction time of 30 min, extraction temperature of 50 °C, 40% ethanol, sample-to-solvent ratio of 1:30 g/mL. For VMDE the optimum extraction conditions were the vacuum value of 108.82 mmHg, extraction time of 2.47 min, 20% ethanol, sample-to-solvent ratio of 1:29.42 g/mL. Under optimal conditions, TPC values were 6.13, 6.38, and 7.79 mg GAE/g DW; TACDPPH were 13.96, 13.53, and 13.74 mmol TE/kg DW; TACCUPRAC were 34.87, 49.38, and 47.06 mmol TE/kg DW; and TBC values were 418.83, 471.82, and 715.50 mg betalain/kg DW for CE, UAE, and VMDE respectively.
After optimization of the extraction methods, Q-TOF LC/MS analysis was performed to analyze betalain composition in extracts obtained in optimum conditions. The amounts of different types of betalains were calculated in terms of betanin standard equivalents. Antimicrobial activities of the extracts were investigated against Salmonella enteritidis subsp. enterica serovar Enteritidis (ATCC 13076), Escherichia coli O157:H7 (ATCC 25922), and Listeria monocytogenes via well diffusion and broth macrodilution methods. Extract obtained via VMDE exhibited activity against E. coli O157:H7 (ATCC 25922), while all extracts showed antimicrobial activity against Salmonella enteritidis subsp. enterica serovar Enteritidis (ATCC 13076). No inhibitory effect was detected against Listeria monocytogenes among extraction methods in well diffusion method. In brothmacrodilution method, the minimum inhibitory concentration (MIC) of extracts obtained in optimum extraction conditions was found only for Salmonella enteridis subsp. enterica serovar Enteritidis (ATCC 13076) in undiluted tubes. Since VMAE was founded as the best extraction method among other methods, niosomal encapsulation was performed using the extract obtained in optimum conditions of VMAE. Encapsulation conditions were optimized by response surface methodology with four independent variables at three levels: molar ratio of Span 60:Tween 80 molar (X₁) 1:1-3:1), the amount of the extract (X₂) 5–15 mg/100 mgsurfactant, the amount of the cholesterol (X₃) 0.1–0.3 mg/100 mg surfactant, and sonication time (X₄) 0–90 s. Responses were chosen as encapsulation efficiency (%), total phenolic content (TPC), total antioxidant capacity (TAC), b* value in color analysis, and total betalain content (TBC). Optimum encapsulation conditions were determined as molar ratio of Span 60:Tween 80 1.161, 14.44 mg extract/100 mg surfactant, 0.1 mg cholesterol/100 mg surfactant, and 89.99 s of sonication. In optimum conditions, the encapsulation efficiency, 96.06%; TPC, 3.06 mg GAE/g DW; TAC, 24.41 mmol TE/kg DW; b*, 2.81 and TBM, 687.30 mg betalain/kg DW. In niosomal capsule obtained in optimum encapsulation conditions, the betalain degradation kinetics over 30 days, evaluation of thermal stability, FT-IR, TEM, zeta potential, and particle size analyses were performed. In CE, UAE, and VMDE the thermal stability values of 55.5%, 60.8%, and 66.8% respectively increased to 92.91% after niosomal encapsulation. In the next stage of the thesis, for food application, yogurt was produced and optimal VMDE extract and optimum niosomal capsules were supplemented to yogurt at different concentrations (2-6%). Yogurts were stored at 4°C for 14 days, and the changes in physicochemical (pH, water holding capacity, dry matter, color, water activity), textural, rheological, microbiological (lactic acid bacteria count), and functional parameters (TPC, TAC and TBC) were analyzed, and results were compared with plain yogurt sample without any additives. Results indicated that bioactive properties were increased compared to plain yogurt leading to the development of a product with functional properties. Up to 4% concentration, yogurt quality maintained considerably in terms of physicochemical, textural and rheological characteristics. Niosome-added samples demonstrated better stability of bioactive compounds and betalains compared to extract-added samples during storage.In the final stage of the study, the simulation of in-vitro digestion was performed to evaluate the bioaccessibility of betalains and phenolic compounds in extract, extract loaded niosomes, and yogurt samples. After in-vitro digestion stages, TPC, TAC, and TBC were measured and compared with the results before digestion. Results showed that betalains and phenolic compounds declined in the gastric phase followed by an increase in the intestinal phase. In conclusion, in this study the potential of betalains and bioactive compounds extracted from prickly pear was investigated in terms of usage of natural food colorants and functional additives. Among the novel extraction technologies, vacuum microwave-assisted extraction (VMAE) was found to be the most efficient and environmentally friendly alternative compared to other extraction methods. Furthermore, it was determined that niosomal encapsulation is an effective technique for stabilization of betalains and sensitive bioactive compounds extracted via VMAE. The direct and encapsulated application of natural colorant components into plain yogurt yielded promising results in the development of an innovative product with functional properties.
Finally, the bioavailability of the extract obtained under VMDE optimal conditions, extract-loaded niosomal vesicles, and functional yogurt samples were evaluated by in- vitro digestion experiments. The behavior of bioactive compounds and betalains during digestion processes was analyzed in detail. These findings demonstrated the applicability of betalains in the food industry and contributed to the food integration of innovative technologies.
Accordingly, in further studies, the applicability of niosomal encapsulation
of betalains and bioactive compounds extracted via VMAE to various food could be tested, thereby increasing the diversity of functional products.