Sol-gel yöntemiyle hazırlanmış silika matrislerde dna enkapsulasyonu.

Sol-gel processing routes for encapsulation of double stranded DNA in solid porous silica hosts have been established. The encapsulation was carried out in two steps: hydrolysis of a silica-forming alkoxide-based sol was followed by condensation/gelation to a solid form upon addition of a buffer solution containing DNA molecules. The effects of gelation chemistry and DNA amount on chemical and microstructural properties of resultant silica matrices and on DNA encapsulation efficiency were investigated. The analytical characterization was performed by UV-vis spectroscopy, 29Si nuclear magnetic resonance spectroscopy and by nitrogen adsorption studies. It was demonstrated that DNA incorporation had a pH-dependent catalytic effect on gelation kinetics and promoted silica network completion. In addition, the scale of porosity and the average pore size of the resultant silica increased with gelation pH and also with DNA-buffer solution in the starting sol-gel formulation. The chemistry-derived pore size variation controls the DNA encapsulation efficiency in the silica matrices and the DNA holding capacity strongly depends on the scale of the porosity attained. The selective adsorption of ethidium bromide- a DNA-intercalative reagent molecule- on DNA-silica gels confirmed that the DNA molecules remained entrapped within the silica host in their native state without any deterioration. Besides pure silica, amine-functionalized hybrid silica hosts were also formed by sol-gel. The hybrid gels were found not to be suitable for DNA encapsulation, as these matrices dissolve in aqueous environment due to incomplete silica network formation. The DNA-doped silica hosts may provide promising matrices for development of biosensors, bioreactors and bioassay platforms.M.S. - Master of Scienc

Potasyum titanat nanoyapı katkılı reçine kompozitlerin geliştirilmesi ve fotokatalitik özellikleri.

Structural and functional properties of potassium titanate (PT; K2O.nTiO2, n=2, 4) nanostructures synthesized by sol-gel and hydrothermal methods were investigated with respect to titanium/potassium (Ti/K) ratio and their nanogrowth mechanisms were elucidated. Produced powders were characterized by XRD, electron microscopy (SEM, TEM) and gas adsorption (BET) techniques for phase, morphology and surface analyses, respectively. PT nanostructures were mixed with three UDMA-TEGDMA (UT) resin monomer mixtures in the order of increasing TEGDMA molar ratio of UT-2 (30%), UT-1 (50%), UT-3 (70%). Polymerization of the composites was accomplished by halogen light curing. Tensile, hardness, wear, water sorption/solubility and bioactivity tests were performed to determine the performance of the composites. The energy band gap (Eg) of PT powders, the photocatalytic activity of PT powders and PTUT composites were measured by UV-Vis Spectroscopy equipped with diffuse reflectance (DR) module. Methylene Blue (MB) dye degradation tests were performed to evaluate photocatalytic performance. It was demonstrated that both sol-gel and hydrothermal growth of PTs originate from an amorphous-like network. Potassium hexa-titanate (PHT, n=6) nanowires could be obtained by calcination of sol-gel derived amorphous network at temperatures as low as 600 °C. As the calcination temperature increased to 800 °C, potassium tetra-titanate (PTT, n=4) formation became significant. In addition, the size and aspect ratio of PTs increased as the calcination temperature and time increased (1-3 h). In sol-gel process, potassium hollandite (PH, KTi8O16) was an intermediate phase upon PHT crystallization. However, PHT and PTT nanowires grew directly from the hydrothermal solution under autogeneous pressure. Analysis indicated that amorphous network combined into sheets, crystallized into PTs and then split due to increased strain. The highest average size of sol-gel derived PT whiskers depending on Ti/K ratio were measured as 214 ± 113 nm in diameter and 4.9 ± 2.5 µm in length. The size of split PT nanowires were measured as 39 ± 14 nm in diameter and 1.14 ± 0.4 µm in length, after 24 h of hydrothermal treatment at 180 °C. The size of the nanostructures decreased as the hydrothermal duration increased to 48 h due to further splitting. Hydrothermal treatment provided PTs having Eg lower than widely used commercial TiO2 (P25, Degussa®) powder. Analysis of PT-UT composites revealed that mechanical and functional performances of the composites were mainly related to the PT embedment amount and dispersion efficiency. The lowest specific wear rate was achieved for the composite containing 5 wt % hydrothermally synthesized PT embedded UT-1 (50% UDMA – 50% TEGDMA, molar) mixture as 6.5 ± 0.6 *10-6 mm3/Nm by 5 wt % hydrothermally produced PT embedded UT-1 (50% U-50% T, molar) mixture. Similarly, tensile strength and elastic modulus of UT-1 mixture increased from 40.4 ± 1.7 MPa to 42.5 ± 0.2 MPa, and from 0.7 ± 0.04 GPa to 0.9 ± 0.1 GPa, respectively by embedding 5 wt % hydrothermally synthesized PT. The water sorption and solubility values were higher than 40 µg/mm3. The MB degradation test and analyses after simulated body fluid immersion showed that PTs preserved their photocatalytic performance and bioactivity in the composite form. MB degradation of composites in 24 h increased with increased PT embedment in the composite.Ph.D. - Doctoral Progra

Calcium Phosphate Mineralization on Calcium Carbonate Particle Incorporated Silk-Fibroin Composites

In this study, three anhydrous forms of calcium carbonate, namely vaterite, aragonite and calcite, with distinct morphologies were incorporated inside silk-fibroin to fabricate composite scaffolds for tissue engineering applications. To assess calcium phosphate mineralization, composite scaffolds were treated with simulated body fluid up to one month. It was observed that composite scaffolds having different calcium carbonate polymorphs expressed different mineralization. Incorporating 25 wt. % of vaterite polymorph, which was the least stable form of calcium carbonate under aqueous conditions, induced the highest calcium phosphate mineralization in silk-fibroin while calcium carbonate-free silk-fibroin scaffolds expressed no calcium phosphate deposition. Results highlighted the importance of calcium carbonate particles in enhancing the bioactivity of silk-fibroin based composite scaffold

Synthesis of DNA-encapsulated silica elaborated by sol-gel routes

The highly specific functions of DNA can be used for designing novel functional materials. However, aqueous solubility and biochemical instability of DNA impede its direct utilization as a functional component. Herein, preparation of a hybrid material encapsulating the DNA molecules (double-stranded salmon sperm, 50-5000 base pairs) in robust host-sol-gel-derived silica-has been described. The encapsulation was carried out in two steps: hydrolysis of an acidic tetraethylorthosilicate [Si(OC2H5)(4)] sol and was followed by condensation near physiological pH upon addition of alkaline DNA-containing solutions. The gelation behavior and structural properties of the DNA-silica hybrids were investigated by Si-29 nuclear magnetic resonance and by nitrogen adsorption. The selective adsorption of a DNA-interactive reagent molecule (ethidium bromide) in their diluted aqueous solutions on DNA-silica hybrids confirmed that the DNA molecules remained entrapped within the silica host without any deterioration. A DNA encapsulation mechanism correlating the silica microstructure and DNA holding efficiency has been proposed

Exploring encapsulation mechanism of DNA and mononucleotides in sol-gel derived silica

The encapsulation mechanism of DNA in sol-gel derived silica has been explored in order to elucidate the effect of DNA conformation on encapsulation and to identify the nature of chemical/physical interaction of DNA with silica during and after sol-gel transition. In this respect, double stranded DNA and dAMP (2-deoxyadenosine 5-monophosphate) were encapsulated in silica using an alkoxide-based sol-gel route. Biomolecule-encapsulating gels have been characterized using UV-Vis, Si-29 NMR, FTIR spectroscopy and gas adsorption (BET) to investigate chemical interactions of biomolecules with the porous silica network and to examine the extent of sol-gel reactions upon encapsulation. Ethidium bromide intercalation and leach out tests showed that helix conformation of DNA was preserved after encapsulation. For both biomolecules, high water-to-alkoxide ratio promoted water-producing condensation and prevented alcoholic denaturation. NMR and FTIR analyses confirmed high hydraulic reactivity (water adsorption) for more silanol groups-containing DNA and dAMP encapsulated gels than plain silica gel. No chemical binding/interaction occurred between biomolecules and silica network. DNA and dAMP encapsulated silica gelled faster than plain silica due to basic nature of DNA or dAMP containing buffer solutions. DNA was not released from silica gels to aqueous environment up to 9 days. The chemical association between DNA/dAMP and silica host was through phosphate groups and molecular water attached to silanols, acting as a barrier around biomolecules. The helix morphology was found not to be essential for such interaction. BET analyses showed that interconnected, inkbottle-shaped mesoporous silica network was condensed around DNA and dAMP molecules

Calcium Phosphate Mineralization on Calcium Carbonate Particle Incorporated Silk-Fibroin Composites

In this study, three anhydrous forms of calcium carbonate, namely vaterite, aragonite and calcite, with distinct morphologies were incorporated inside silk-fibroin to fabricate composite scaffolds for tissue engineering applications. To assess calcium phosphate mineralization, composite scaffolds were treated with simulated body fluid up to one month. It was observed that composite scaffolds having different calcium carbonate polymorphs expressed different mineralization. Incorporating 25 wt. % of vaterite polymorph, which was the least stable form of calcium carbonate under aqueous conditions, induced the highest calcium phosphate mineralization in silk-fibroin while calcium carbonate-free silk-fibroin scaffolds expressed no calcium phosphate deposition. Results highlighted the importance of calcium carbonate particles in enhancing the bioactivity of silk-fibroin based composite scaffold

Do the strategic innovative organizations reduce social loafing behaviors?

This research aims to determine the effects of strategic innovation on employees’ social loafing behaviors. This mentioned relationship has been analyzed with 138 out of 170 employees working at the same hotel chosen by the convenience sampling method from Antalya/Turkey. The results showed that there is a statistically significant and negative relationship between social loafing and strategic innovativeness. Furthermore, strategic innovativeness is a descriptor of social loafing behaviors. Satisfactory results were obtained as predicted before and some suggestions for the managers and future researchers were given. The topic has a unique value in relevant literature in terms of combining both management and marketing areas