Materials Science and Engineering / Malzeme Bilimi ve Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4719
Browse
10 results
Search Results
Article Citation - WoS: 7Citation - Scopus: 7Increasing Spontaneous Wet Adhesion of Dopa With Gelation Characterized by Epr Spectroscopy(Elsevier Ltd., 2019) Göksel, Yaman; Akdoğan, YaşarThe presence of water molecules around both adhesive materials and surface results in the hydration barriers that weaken adhesion. In nature, mussels attach to various types of surfaces by using 3,4-dihydroxyphenylalanine (DOPA) containing mussel foot proteins. DOPA shows wet adhesive properties before and after contribution in the hydrogel formation. Here, the wet adhesive properties of DOPA modified four armed poly (ethylene glycol) polymer (PEG-(DOPA)(4)) and its hydrogels induced by (IO4)(-) or (Cr2O7)(2-) ions are compared by using electron paramagnetic resonance (EPR) spectroscopy in terms of their surface coverages. In water, spin labeled hydrophobic polystyrene (SL-PS) and hydrophilic silica (SL-SiO2) nanoparticles are prepared, and the percentages of their covered surface values are obtained. Without applying force, the adhesion to SL-PS increases in the order of PEG-(DOPA)(4) < PEG-(DOPA)(4) + (IO4)(-) hydrogel < PEG-(DOPA)(4) + (Cr2O7)(2-) hydrogel with the percentages of surface coverages 65%, 76% and 93%, respectively. Although, neither of PEG-(DOPA)(4) polymer and (IO4)(-) induced PEG-(DOPA)(4) hydrogel adhere to SL-SiO2 nanoparticle spontaneously, (Cr2O7)(2-) induced PEG-(DOPA)(4) hydrogel adhere to SL-SiO2 with a 59% of surface coverage. These results show that gelation mechanisms of DOPA have effect on the spontaneous adhesion of DOPA to the wet surfaces even for the hydrophilic silica surface.Article Citation - WoS: 33Citation - Scopus: 40Preparation of Albumin Nanoparticles in Water-In Liquid Microemulsions(Elsevier Ltd., 2019) Demirkurt, Begüm; Çakan Akdoğan, Gülçin; Akdoğan, YaşarIonic liquids (Its) with a variety of properties have been considered a unique class of solvents. Using ILs in microemulsions as oil substitutes provides environmentally benign media for various applications including nanoparticle synthesis. Here, bovine serum albumin nanoparticles (BSA NPs) widely used in drug delivery studies were prepared in nano-sized water droplets of water-in-IL (W/IL) microemulsion systems. A hydrophobic IL of 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)) was used as oil component in place of oils (castor oil, olive oil, etc.) and/or conventional organic solvents (cyclohexane, dichloromethane, etc.) in an emulsification method. In order to obtain spherical BSA NPs, high speed homogenizer treatment was applied followed by glutaraldehyde addition. Effects of glutaraldehyde, speed of homogenizer, type of surfactants and compositional fractions of the microemulsion components on the formation of water droplets and/or preparation of BSA NPs were studied using FTIR, EPR, DLS, and SEM techniques. Optimization of these preparation parameters showed that 3 wt% of BSA in a water/Tween 20/BmimPF(6) microemulsion with 20:50:30 wt% yielded similar to 100 nm average sized BSA NPs based on the SEM analysis. Although, water droplet size strongly depends on the water content, BSA nanoparticle size did not show a significant dependency on the water content. On the other hand, surfactant/IL weight ratio is more crucial for obtaining more uniformly size distributed albumin nanoparticles. A significant cellular uptake of BSA NPs prepared in IL based microemulsions with high cell viability showed the potential of this technique in preparation of albumin nanoparticles that can be used also in drug delivery studies. (C) 2019 Elsevier B.V. All rights reserved.Article Citation - WoS: 17Citation - Scopus: 18Development of an Ionic Liquid Based Method for the Preparation of Albumin Nanoparticles(John Wiley and Sons Inc., 2018) Demirkurt, Begüm; Akdoğan, YaşarAlbumin based nanocarriers have been widely used in drug delivery studies. Here, we developed a water-in-ionic liquid (IL) emulsion-like method to prepare bovine serum albumin (BSA) nanoparticles as alternative to the traditional organic solvents containing techniques. Conformational changes of albumin induced by the imidazolium based ILs at the water-IL interface triggers the BSA nanoparticle formation. The albumin nanoparticle formation are dependent on the experimental parameters and the hydophobicity of the IL. At pH 9.0, using 1.3%wt of BSA in water/1-butyl-3-methyl imidazolium tetrafluoroborate (BmimBF4) (50/50 mol%) and TX-100/butanol surfactant mixture yields uniformly distributed 200 nm average sized BSA nanoparticles. Different than BmimBF4, using a more hydrophilic IL, EmimBF4 yielded albumin aggregates. Instead, using a more hydrophobic IL, HmimBF4 produced albumin nanoparticles but a non-uniform size distribution was obtained. These results indicate that the ionic liquids called green and designer solvents can be also used to synthesize albumin nanoparticles.Conference Object Citation - Scopus: 1Spontaneous Adhesion of Dopa and Tryptophan Functionalized Peg To Polystyrene Nanobeads: an Epr Study(Trans Tech Publications, 2018) Göksel, Yaman; Kırpat, İklima; Akdoğan, YaşarWet adhesion is achieved by mussels so naturally. Their adhesion mechanism has inspired scientists to obtain wet adhesives for a long time. The amino acid 3,4-dihydroxyphenylalanine (DOPA) produced by mussels adheres to different types of surfaces and also contributes to cohesive interactions. Here, we showed the spontaneous adhesion of DOPA functionalized four armed poly(ethylene glycol) (PEG) polymer to spin labeled polystyrene (SL-PS) nanosurfaces by electron paramagnetic resonance (EPR) spectroscopy. In addition to DOPA, adhesion property of another amino acid of tryptophan (Trp) was studied. Trp attached four armed PEG polymers did not adhere to the surface of SL-PS in the force free condition. However, two armed DOPA and two armed Trp functionalized PEG adhere to the PS.Article Citation - WoS: 5Citation - Scopus: 6Determination of Force-Free Wet Adhesion of Mussel-Inspired Polymers To Spin Labeled Surface(Elsevier, 2017) Kırpat, İklima; Göksel, Yaman; Karakuş, Erman; Emrullahoğlu, Mustafa; Akdoğan, YaşarHydration repulsive forces oppose the adhesive interactions, especially in the force-free conditions. Here, we studied spontaneous wet adhesion of 3,4-dihydroxyphenylalanine (DOPA) functionalized poly(ethylene glycol) (PEG) polymers inspired by marine mussels. Using electron paramagnetic resonance (EPR) spectroscopy, we can monitor spontaneous adhesion of DOPA containing polymer to suspended spin labeled hydrophobic polystyrene nanobeads at molecular level. The surface coverage up to 82% is obtained from EPR measurements. However, in the force-free condition, EPR measurements do not show any detectable DOPA based adhesion to hydrophilic silica nanobead.Article Citation - WoS: 13Citation - Scopus: 16Experimental Modeling of Silicate-Based Geothermal Deposits(Elsevier Ltd., 2017) Çelik, Aslı; Topçu, Gökhan; Baba, Alper; Akdoğan, Yaşar; Şentürk, Ufuk; Demir, Mustafa MuammerScaling by metal silicates represents a major obstacle for geothermal systems. A composition that enables the fabrication of artificial deposits is necessary for the rapid testing of potential inhibitors. In this work, artificial deposits were synthesized by employing experimental conditions similar to those in the Tuzla Geothermal Field in Turkey. Although refluxing enabled the formation of a precipitate that was similar to naturally formed deposits in color and texture, their elemental composition and morphology showed a mismatch. An autoclave enabled the production of a precipitate that more closely resembled naturally formed deposits in color, texture, elemental composition, and structure.Article Citation - WoS: 66Citation - Scopus: 71Signature of an Aggregation-Prone Conformation of Tau(Nature Publishing Group, 2017) Eschmann, Neil A.; Georgieva, Elka R.; Ganguly, Pritam; Borbat, Peter P.; Rappaport, Maxime D.; Akdoğan, Yaşar; Freed, Jack H.; Shea, Joan-Emma; Han, SongiThe self-assembly of the microtubule associated tau protein into fibrillar cell inclusions is linked to a number of devastating neurodegenerative disorders collectively known as tauopathies. The mechanism by which tau self-assembles into pathological entities is a matter of much debate, largely due to the lack of direct experimental insights into the earliest stages of aggregation. We present pulsed double electron-electron resonance measurements of two key fibril-forming regions of tau, PHF6 and PHF6∗, in transient as aggregation happens. By monitoring the end-to-end distance distribution of these segments as a function of aggregation time, we show that the PHF6 (∗) regions dramatically extend to distances commensurate with extended β-strand structures within the earliest stages of aggregation, well before fibril formation. Combined with simulations, our experiments show that the extended β-strand conformational state of PHF6 (∗) is readily populated under aggregating conditions, constituting a defining signature of aggregation-prone tau, and as such, a possible target for therapeutic interventions.Article Citation - WoS: 33Citation - Scopus: 36Epr Studies of Intermolecular Interactions and Competitive Binding of Drugs in a Drug-Bsa Binding Model(Royal Society of Chemistry, 2016) Akdoğan, Yaşar; Emrullahoğlu, Mustafa; Tatlıdil, Diğdem; Üçüncü, Muhammed; Çakan Akdoğan, GülçinUnderstanding intermolecular interactions between drugs and proteins is very important in drug delivery studies. Here, we studied different binding interactions between salicylic acid and bovine serum albumin (BSA) using electron paramagnetic resonance (EPR) spectroscopy. Salicylic acid was labeled with a stable radical (spin label) in order to monitor its mobilized (free) or immobilized (bound to BSA) states. In addition to spin labeled salicylic acid (SL-salicylic acid), its derivatives including SL-benzoic acid, SL-phenol, SL-benzene, SL-cyclohexane and SL-hexane were synthesized to reveal the effects of various drug binding interactions. EPR results of these SL-molecules showed that hydrophobic interaction is the main driving force. Whereas each of the two functional groups (-COOH and -OH) on the benzene ring has a minute but detectable effect on the drug-protein complex formation. In order to investigate the effect of electrostatic interaction on drug binding, cationic BSA (cBSA) was synthesized, altering the negative net charge of BSA to positive. The salicylic acid loading capacity of cBSA is significantly higher compared to that of BSA, indicating the importance of electrostatic interaction in drug binding. Moreover, the competitive binding properties of salicylic acid, ibuprofen and aspirin to BSA were studied. The combined EPR results of SL-salicylic acid/ibuprofen and SL-ibuprofen/salicylic acid showed that ibuprofen is able to replace up to ∼83% of bound SL-salicylic acid, and salicylic acid can replace only ∼14% of the bound SL-ibuprofen. This indicates that ∼97% of all salicylic acid and ibuprofen binding sites are shared. On the other hand, aspirin replaces only ∼23% of bound SL-salicylic acid, and salicylic acid replaces ∼50% of bound SL-aspirin, indicating that ∼73% of all salicylic acid and aspirin binding sites are shared. These results show that EPR spectroscopy in combination with the spin labeling technique is a very powerful method to investigate drug binding dynamics in detail.Article Citation - WoS: 24Citation - Scopus: 27Physiological Concentrations of Albumin Favor Drug Binding(Royal Society of Chemistry, 2015) Tatlıdil, Diğdem; Üçüncü, Muhammed; Akdoğan, YaşarThe ability to track drug binding and release makes electron paramagnetic resonance (EPR) spectroscopy well suited for drug delivery studies. Using the continuous wave (cw) EPR technique to extract information about the dynamics of the spin labeled drugs we can simultaneously determine the bound and unbound drugs. Here, spin labeled salicylic acid (SLSA) binding to and release from bovine serum albumin (BSA) is investigated, as a model for drug-transport protein interaction. We studied SLSA-BSA binding in a wide concentration range and found that the stoichiometry of the drug-protein increases significantly when the physiological range of BSA concentration is reached. Our EPR results explicitly reveal that up to ∼7 SLSA can bind to one albumin at the physiological concentration, whereas at lower BSA concentrations (<0.125 mM) the SLSA-BSA stoichiometry is maximum 2. Moreover, we studied drug release and showed that the ratio of bound to unbound SLSA concentrations remains relatively stable during dialysis. This indicates that the binding equilibrium of SLSA is not altered through the process of dialysis. This study demonstrates that cw EPR spectroscopy in combination with spin labeled drugs is an effective technique for binding and release studies and stoichiometric analysis of drug-protein interactions.Article Citation - WoS: 58Citation - Scopus: 86Intrinsic Surface-Drying Properties of Bioadhesive Proteins(John Wiley and Sons Inc., 2014) Akdoğan, Yaşar; Wei, Wei; Huang, Kuo-Ying; Kageyama, Yoshiyuki; Danner, Eric W.; Miller, Dusty R.; Martinez Rodriguez, Nadine R.; Waite, J. Herbert; Han, SongiSessile marine mussels must "dry" underwater surfaces before adhering to them. Synthetic adhesives have yet to overcome this fundamental challenge. Previous studies of bioinspired adhesion have largely been performed under applied compressive forces, but such studies are poor predictors of the ability of an adhesive to spontaneously penetrate surface hydration layers. In a force-free approach to measuring molecular-level interaction through surface-water diffusivity, different mussel foot proteins were found to have different abilities to evict hydration layers from surfaces - a necessary step for adsorption and adhesion. It was anticipated that DOPA would mediate dehydration owing to its efficacy in bioinspired wet adhesion. Instead, hydrophobic side chains were found to be a critical component for protein-surface intimacy. This direct measurement of interfacial water dynamics during force-free adsorptive interactions at solid surfaces offers guidance for the engineering of wet adhesives and coatings. Home and dry underwater: Repulsive hydration forces hinder wet adhesion in the absence of applied external forces. The direct measurement of hydration-water dynamics by NMR relaxometry at 10 GHz revealed that the most hydrophobic mussel adhesive protein, and not the most enriched with 3,4-dihydroxyphenylalanine, effectively dries the surface and overcomes repulsive hydration forces to adsorb spontaneously to surfaces in preparation for adhesion.