Browsing by Author "Mutlu, Ferhat"

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1926-1997 yılları arasında Türk Hava Kurumu ve kurban derisi tartışması
(Bilkent University, 2018) Anıl, Arca; Özbek, Elif Nur; Kibar, Emin; Mutlu, Ferhat; Erim, Öykü Tüzün
Türk Hava Kurumu’nun kuruluş amacı Türkiye’de havacılığı geliştirmektir. En önemli hedefler uçak üretebilmek ve pilot yetiştirmek olarak belirlenmiş. Gelir kaynağı olarak halkın yardımlarından ve devletin desteğinden faydalanılmıştır. Bu kurumun en önemli kaynağı kurban derilerinden gelen kardır. Deriler 1926 senesinden bu yana Kurban Bayramında THK’nın kurduğu deri toplama merkezleri yardımıyla halktan kamyonetlerle toplanmıştır. Ancak, derilerin toplanma süreci dini sebepler ve diğer kuruluşların artması sonucunda sıkıntılar ortaya çıkmıştır. Ayrıca, derileri kendi amaçları için kullanmak isteyen kişiler de derileri THK’ye vermek istememiştir. Bunların sonucunda THK bazı amaçlarından feragat etmek zorunda kalmış ve bazı dönemlerde çalışanlara bütçe sıkıntısı nedeniyle maaşlarını ödeyemediği zor zamanlar geçirmiştir. Derilerin nereye verileceği özellikle 1970 senesinden sonra ülke içinde tartışmalara sebep olmuş ve bu durum 2013 senesinde çıkarılan kanunla son bulmuştur.
Open Access
Elucidation of the denaturation mechanism of urea on macromolecules in aqueous medium
(2022-09) Mutlu, Ferhat
The urea molecule is a well-known denaturant for a wide range of macromolecules. To date, there is no unified molecular-level explanation for urea-induced denaturation of all macromolecules. As a result, considerable effort has been directed toward this subject in recent years, because osmolyte protein interactions are of central interest and have implications ranging from polymer physics to cell biology. Detailed urea denaturation mechanisms, focusing on the entropically driven formation of urea clouds, urea induced cross-linking mechanism, and osmolyte clouding around macromolecules, have been proposed in the literature. However, no agreement has been reached on the molecular machinery of urea denaturation. In this thesis, the urea-induced solubility changes of macromolecules in aqueous solutions were investigated by utilizing the lower critical solution temperature (LCST) of poly (N - isopropylacrylamide) (PNIPAM) and poly (N,N-diethylacrylamide) (PDEA) as a function of urea concentration up to 6.0 M. Due to the lack of suitable probing methods for the collapsed state of interested macromolecules, a temperature-controlled ATR – FTIR spectroscopy based method was developed to explore the interaction between urea and the collapsed state of macromolecule. LCST measurements revealed that the solubility of PDEA increases with increasing urea concentrations, whereas PNIPAM salts-out from the solution monotonically, despite the fact that both polymers have similar molecular structures. Temperature gradient ATR-FTIR measurements were carried out to further investigate this discrepancy. First, no favourable urea accumulation towards the collapsed form of macromolecules was observed up to 6.0 M urea, which puts doubt on the urea clouding mechanism. Moreover, at elevated (> 3.0 M) urea concentrations, the collapsed form of the PNIPAM and PDEA accumulated towards the cooler parts of temperature gradient in solution, indicating the preferred form of the macromolecule is the soluble (uncollapsed) form. These surprising results indicate that both PNIPAM and PDEA prefers the soluble form at elevated urea concentrations above the LCST. As a molecular mechanism, the urea molecules act as a "glue" between the amide groups of PNIPAM, bringing intra- and inter-molecular parts of the macromolecule into close proximity, and act as a collapsed form of macromolecules. Apparently, such a mechanism is not valid for the PDEA. Our findings shed new light not only on aqueous phase phenomena, but also on the aggregated (collapsed) phase of macromolecules in aqueous medium.
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Oil-in-water emulsions probed using fluorescence multivariate-curve-resolution spectroscopy
(American Chemical Society, 2024-06-11) Gündoğdu, Gülsüm; Topuzlu, Ezgi Yılmaz; Mutlu, Ferhat; Ertekin, Umay Eren; Okur, Halil İbrahim
Hydrophobic surfaces in contact with aqueous media are omnipresent in nature. A plethora of key biological and physiological processes occur at the interface of immiscible fluids. Besides its fundamental importance, probing such interfaces is rather challenging, especially when one medium is bathed in the other. Herein, we demonstrate a fluorescence-based method that probes the oil–water interface and interfacial processes through surface dielectric perturbations. The fluorescence response of Nile Red is measured in hexadecane in water nanoemulsions. Three major spectral components appear: two from the bulk liquid media (hexadecane and water) and a distinct band at around 640 nm due to the interfacial component. Such spectra are deconvoluted using the multivariate-curve-resolution algorithm, and interface-correlated fluorescence spectra are attained. The influence of anionic sodium dodecylbenzenesulfonate (SDBS) and cationic cetyltrimethylammonium bromide (CTAB) surfactants on the oil–water interface is elucidated with concentration-dependent measurements. A charge-dependent spectral shift is observed. The interface correlated band at 641 nm for bare hexadecane nanoemulsions red shifts in the presence of anionic surfactants, indicating an apparent dielectric increase. In contrast, the same band gradually blue shifts with increasing cationic surfactant concentration, indicating an apparent interface dielectric decrease. Such a method can be utilized to probe alterations at interfaces beyond the oil/water interface.