Chemical Engineering / Kimya Mühendisliği
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Article Citation - WoS: 6Citation - Scopus: 6Effect of Ammonia on Cobalt Fischer-Tropsch Synthesis Catalysts: a Surface Science Approach(Royal Society of Chemistry, 2019) Kızılkaya, Ali Can; Niemantsverdriet, J. W.; Weststrate, C. J.Ammonia adsorption and decomposition on defect-rich hcp-Co(0001) surfaces were investigated under ultra-high vacuum conditions in order to provide a fundamental explanation for industrially observed ammonia poisoning of cobalt based Fischer-Tropsch synthesis (FTS) catalysts. Temperature-programmed desorption, infrared spectroscopy and work function measurements indicate that undercoordinated sites bind ammonia stronger than sites on flat Co(0001), and they also induce its dehydrogenation. Density functional theory calculations were employed to explore the reactivity of defective Co surfaces using the fcc-Co(211) as a model. The results indicate that the decomposition products (NH x ) adsorb strongly on or around the step site on fcc-Co(211). We find that NH (+2H ad ), adsorbed in the threefold site on the upper terrace, is equally stable as NH 2 (+H ad ), adsorbed in the bridge position at the step edge, both being significantly more stable than the equivalent species adsorbed on the flat Co(0001). The calculated activation barriers for NH 3,ad dehydrogenation steps are in reasonable agreement with the barriers obtained by fitting experimental data. Based on these fundamental insights, poisoning of cobalt nanoparticles during FTS by NH 3 contaminants can be linked mainly to the blocking of undercoordinated sites by strongly adsorbed NH 2 species.Article Citation - WoS: 17Citation - Scopus: 22Responsive pentablock copolymers for siRNA delivery(Royal Society of Chemistry, 2015) Uz, Metin; Mallapragada, Surya K.; Alsoy Altınkaya, SacideIn this study, temperature and pH responsive cationic and amphiphilic pentablock copolymers, which consist of the temperature responsive triblock Pluronic F127 sandwiched between pH responsive PDEAEM (poly(2-diethylaminoethyl methacrylate)) end blocks, were used for the first time in the development of polyplex and gold nanoparticle (AuNP) based multicomponent siRNA delivery systems (MCSs). Copolymers in both systems protected siRNA from external effects, provided cell entry and endosomal escape. The thermoreversible micellization of the hydrophobic PPO block facilitated the cellular entry while the PDEAEM blocks enhanced the endosomal escape through protonated tertiary amine groups by pH buffering. The synergistic advantages of the different blocks showed an enhanced effect in the MCSs due to attachment and surface configuration reasons. The siRNA transfection efficiency of MCSs against luciferase expressing SKOV3 cells was 15% higher than both the polyplexes alone and the commercial siRNA transfection agent Lipofectamine RNAiMax at the same applied dose, without any toxicity. The results indicated that the multicomponent systems based on the responsive cationic pentablock copolymers and gold nanoparticles have promising potential as an efficient siRNA delivery vector for future applications.Article Citation - WoS: 11Citation - Scopus: 12Calf Thymus Dna Characterization and Its Adsorption on Different Silica Surfaces(Royal Society of Chemistry, 2015) Yetgin, Senem; Balköse, DevrimDNA adsorption is the initial stage of gene therapy for drug delivery systems and solid phase extraction methods of DNA purification. High pore volume and high adsorption capacity are simple requirements not only for producing 'smart' drug delivery systems but also the development of purification kits. Silica is the most used material for this purpose. The present study aimed at elucidating the calf thymus DNA biosorption process by the characterization of calf thymus DNA and silica to increase the efficiency of the currently used silica material. Mesoporous silica has long been used for DNA adsorption and silica aerogel is the new adsorbent investigated in the present study. When DNA solution was freeze dried on a silica wafer, self-assembled super helices formed as shown by atomic microscopy (AFM). Thus DNA existed not as single molecules but as large sized agglomerates in water. Thus it could be adsorbed in the macropores and on the external surface of adsorbents. Adsorption of calf thymus DNA to a silica aerogel, a mesoporous silica gel and a silica wafer was investigated in the present study. Silica aerogel was synthesized from TEOS by a supercritical ethanol drying process. The DNA adsorption capacity of the silica aerogel was nearly two times that of the mesoporous silica gel due to its macroporous structure and its higher silanol content. Silica aerogel was found to be a very promising material for DNA adsorption. Therefore silica aerogel can be considered as a good candidate for the delivery of DNA.Article Citation - WoS: 31Citation - Scopus: 32Synthesis, Self-Assembly and Stimuli Responsive Properties of Cholesterol Conjugated Polymers(Royal Society of Chemistry, 2012) Sevimli, Sema; Sagnella, Sharon; Kavallaris, Maria; Bulmuş, Volga; Davis, Thomas P.Reversible addition-fragmentation chain transfer (RAFT) polymerization was used to generate well-defined pH-responsive biofunctional polymers as potential 'smart' gene delivery systems. A series of five poly(dimethylamino ethyl methacrylate-co-cholesteryl methacrylate) P(DMAEMA-co-CMA) statistical copolymers, with similar molecular weights and varying cholesterol content, were prepared. The syntheses, compositions and molecular weight distributions for P(DMAEMA-co-CMA) were monitored by nuclear magnetic resonance (NMR), solid-state NMR and gel permeation chromatography (GPC) evidencing well-defined polymeric structures with narrow polydispersities. Aqueous solution properties of the copolymers were investigated using turbidimetry and light scattering to determine hydrodynamic diameters and zeta potentials associated with the phase transition behaviour of P(DMAEMA-co-CMA) copolymers. UV-Visible spectroscopy was used to investigate the pH-responsive behaviour of copolymers. Hydrodynamic radii were measured in the range 10-30 nm (pH, temperature dependent) by dynamic light scattering (DLS). Charge studies indicated that P(DMAEMA-co-CMA) polymers have an overall cationic charge, mediated by pH. Potentiometric studies revealed that the buffering capacity and pK a values of polymers were dependent on cholesterol content as well as on cationic charge. The buffering capacity increased with increasing charge ratio, overall demonstrating transitions in the pH endosomal region for all five copolymeric structures. Cell viability assay showed that the copolymers displayed increasing cytotoxicity with decreasing number of cholesterol moieties. These preliminary results show the potential of these well-defined P(DMAEMA-co-CMA) polymers as in vitro siRNA delivery agents.Article Citation - WoS: 22Citation - Scopus: 25The Endocytic Pathway and Therapeutic Efficiency of Doxorubicin Conjugated Cholesterol-Derived Polymers(Royal Society of Chemistry, 2015) Sevimli, Sema; Sagnella, Sharon; Macmillan, Alexander; Whan, Renee; Kavallaris, Maria; Bulmuş, Volga; Davis, Thomas P.Previously synthesized poly(methacrylic acid-co-cholesteryl methacrylate) P(MAA-co-CMA) copolymers were examined as potential drug delivery vehicles. P(MAA-co-CMA) copolymers were fluorescently labelled and imaged in SHEP and HepG2 cells. To understand their cell internalization pathway endocytic inhibition studies were conducted. It was concluded that P(MAA-co-CMA) are taken up by the cells via clathrin-independent endocytosis (CIE) (both caveolae mediated and cholesterol dependent endocytosis) mechanisms. The formation and characterization of P(MAA-co-CMA)-doxorubicin (DOX) nanocomplexes was investigated by fluorescence lifetime imaging microscopy (FLIM), UV-Visible spectroscopy (UV-Vis) and dynamic light scattering (DLS) studies. The toxicity screening between P(MAA-co-CMA)-DOX nanocomplexes (at varying w/w ratios) and free DOX, revealed nanocomplexes to exhibit higher cytotoxicity towards cancer cells in comparison to normal cells. FLIM and confocal microscopy were employed for investigating the time-dependent release of DOX in SHEP cells and the cellular uptake profile of P(MAA-co-CMA)-DOX nanocomplexes in cancer and normal cell lines, respectively. The endocytic pathway of P(MAA-co-CMA)-DOX nanocomplexes were examined in SHEP and HepG2 cells via flow cytometry revealing the complexes to be internalized through both clathrin-dependent (CDE) and CIE mechanisms. The drug delivery profile, reported herein, illuminates the specific endocytic route and therapeutic efficiency of P(MAA-co-CMA)-DOX nanocomplexes strongly suggesting these particles to be promising candidates for in vivo applications.Article Citation - WoS: 20Citation - Scopus: 22A New Proton Sponge Polymer Synthesized by Raft Polymerization for Intracellular Delivery of Biotherapeutics(Royal Society of Chemistry, 2014) Kurtuluş, Işıl; Yılmaz, Gökhan; Üçüncü, Muhammed; Emrullahoğlu, Mustafa; Becer, C. Remzi; Bulmuş, VolgaA spermine-like polymer was synthesized via reversible addition- fragmentation chain transfer polymerization as a potential endosomal escaping agent. A new methacrylate monomer, 2-((tert-butoxycarbonyl)(2-((tert- butoxycarbonyl)amino)ethyl)amino)ethylmethacrylate (BocAEAEMA), was prepared and then polymerized via RAFT polymerization at constant monomer or initiator concentration at varying [M]/[R]/[I] ratios. In all polymerizations, ln[M] 0/[M] increased linearly with time. The linear increase in M n with monomer conversion was also observed. P(BocAEAEMA)s with controlled molecular weights and narrow molecular weight distributions were obtained. The in vitro cytotoxicity and proton sponge capacity of deprotected polymers P(AEAEMA) were investigated in comparison with a widely used endosomal-disruptive polymer, PEI. P(AEAEMA)s were found to possess proton sponge capacity comparable with PEI. More importantly, P(AEAEMA)s were not toxic on NIH 3T3 cells at concentrations where PEI (25 kDa) was highly toxic (0.4 μM and above). P(AEAEMA) was able to fully condense a DNA fragment at nitrogen/phosphate (N/P) ratios of 10 and above, as evidenced by gel electrophoresis. P(BocAEAEMA) was then chain-extended with a model sugar monomer, mannose-acrylate (ManAc), to yield P(AEAEMA)-b-P(ManAc) block copolymers, to potentially provide cell-recognition ability to the polyplex particles. Although the presence of the P(ManAc) block partially inhibited the interaction of P(AEAEMA) with DNA, P(AEAEMA)13-b-P(ManAc)7 was able to form polyplexes with DNA at N/P ratios ranging between 20/1 and 2/1. Dynamic light scattering measurements showed that while P(AEAEMA) (M n = 5.5 kDa) and DNA formed polyplex particles having a hydrodynamic diameter (Dh) of 125 ± 51 nm, P(AEAEMA)13-b- P(ManAc)7 and DNA formed particles with a smaller Dh of 38 ± 10 nm.Article Citation - WoS: 21Citation - Scopus: 23Monetite Promoting Effect of Nacl on Brushite Cement Setting Kinetics(Royal Society of Chemistry, 2013) Şahin, Erdem; Çiftçioglu, MuhsinBrushite forming calcium phosphate cements (CPCs) have received growing interest for scaffold applications due to their high surface area and high bioresorbability. The dehydrated form of brushite, monetite, has a finer microstructure with higher surface area, higher strength and bioresorbability comparable to brushite, making it a viable alternative phase in CPCs. The increase in monetite content of the β-tricalcium phosphate (β-TCP)-monocalcium phosphate monohydrate (MCPM) cement system due to the reduction in its supersaturation upon addition of NaCl to excess setting liquid was investigated kinetically. The relaxation period was monitored by pH-stat titration of the cement solution by 0.1 M NaOH. Monetite growth was achieved in shorter periods at higher NaCl concentrations where the supersaturation gap between brushite and monetite is thought to be narrowed due to high ionic strength in accord with Pitzer's ion interaction model. The brushite/monetite ratio decreased consistently with increasing NaCl concentration in the 3-6 M range.Article Citation - WoS: 24Citation - Scopus: 24Synthesis of Heterotelechelic Polymers With Affinity To Glutathione-S and Biotin-Tagged Proteins by Raft Polymerization and Thiol-Ene Reactions(Royal Society of Chemistry, 2011) Huang, Xin; Boyer, Cyrille; Davis, Thomas P.; Bulmuş, Volgaα-Glutathione (GSH), ω-biotin functionalized poly(N-isopropylacrylamide) (PNIPAAm) was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization using a new R-group allyl functionalized trithiocarbonate chain transfer agent (CTA) and thiol-ene reactions. GPC and 1H NMR results indicated that the allyl group had no adverse effect on the RAFT-controlled polymerization of NIPAAm and PEG-A, and the new CTA could efficiently control the polymerizations. Employing radical thiol-ene and Michael addition reactions, heterotelechelic α-allyl, ω-carboxylic acid-PNIPAAm was first aminolyzed in the presence of maleimide-modified biotin and subsequently reacted with GSH via radical thiol-ene addition to yield α-GSH, ω-biotin functionalized PNIPAAm. Glutathione S-transferase (GST) and streptavidin (SAv) were coupled in solution with heterofunctional PNIPAAm via bioaffinity interactions. Separately, α-GSH, ω-biotin functionalized PNIPAAm was further shown to bind GST-tagged Rac1, a potential cancer marker, and biotin-tagged bovine serum albumin (BSA).Article Citation - WoS: 52Citation - Scopus: 53Raft Polymerization Mediated Bioconjugation Strategies(Royal Society of Chemistry, 2011) Bulmuş, VolgaThis review aims to highlight the use of RAFT polymerization in the synthesis of polymer bioconjugates. It covers two main bioconjugation strategies using the RAFT process: (i) post-polymerization bioconjugations using pre-synthesized reactive polymers, and (ii) bioconjugations via in situ polymerization using biomolecule-modified monomers or chain transfer agents. © 2011 The Royal Society of Chemistry.Article Citation - WoS: 12Citation - Scopus: 12Controlling Assembly of Helical Polypeptides Via Pegylation Strategies(Royal Society of Chemistry, 2011) Top, Ayben; Zhong, Sheng; Yan, Congqi; Roberts, Christopher J.; Pochan, Darrin J.; Kiick, Kristi L.Recent studies in our laboratories have demonstrated that a helical polypeptide (17H6), equipped with a histidine tag and a helical alanine-rich, glutamic-acid-containing domain, exhibits pH-responsive assembly behavior useful in the production of polymorphological nanostructures. In this study, the histidine tag in these polypeptides was replaced by polyethylene glycol (PEG) with different molecular masses (5 kDa, or 10 kDa), and the self-association behavior of 17H6 and the PEGylated conjugates was characterized via dynamic light scattering (DLS), small angle neutron scattering (SANS), and cryogenic transmission electron microscopy (cryo-TEM). DLS experiments illustrated that the polypeptide and its PEG-conjugates undergo reversible assembly under acidic conditions, suggesting that the aggregation state of the polypeptide and the conjugates is controlled by the charged state of the glutamic acid residues. Nanoscale aggregates were detected at polypeptide/conjugate concentrations as low as 20 μM (∼0.3-0.5 mg ml -1) at physiological and ambient temperatures. Scattering and microscopy results showed that the size, the aggregation number, and the morphology of the aggregates can be tuned by the size and the nature of the hydrophilic tag. This tunable nature of the morphology of the aggregates, along with their low critical aggregation concentration, suggests that PEG-alanine-rich polypeptide conjugates may be useful as drug delivery vehicles in which the alanine-rich block serves as a drug attachment domain.