Browsing by Subject "Chemistry"

Now showing 1 - 20 of 43

Open Access
Angiogenic peptide nanofibers repair cardiac tissue defect after myocardial infarction
(Acta Materialia Inc, 2017) Rufaihah, A. J.; Yasa, I. C.; Ramanujam, V. S.; Arularasu, S. C.; Kofidis, T.; Güler, Mustafa O.; Tekinay, A. B.
Myocardial infarction remains one of the top leading causes of death in the world and the damage sustained in the heart eventually develops into heart failure. Limited conventional treatment options due to the inability of the myocardium to regenerate after injury and shortage of organ donors require the development of alternative therapies to repair the damaged myocardium. Current efforts in repairing damage after myocardial infarction concentrates on using biologically derived molecules such as growth factors or stem cells, which carry risks of serious side effects including the formation of teratomas. Here, we demonstrate that synthetic glycosaminoglycan (GAG) mimetic peptide nanofiber scaffolds induce neovascularization in cardiovascular tissue after myocardial infarction, without the addition of any biologically derived factors or stem cells. When the GAG mimetic nanofiber gels were injected in the infarct site of rodent myocardial infarct model, increased VEGF-A expression and recruitment of vascular cells was observed. This was accompanied with significant degree of neovascularization and better cardiac performance when compared to the control saline group. The results demonstrate the potential of future clinical applications of these bioactive peptide nanofibers as a promising strategy for cardiovascular repair. Statement of Significance We present a synthetic bioactive peptide nanofiber system can enhance cardiac function and enhance cardiovascular regeneration after myocardial infarction (MI) without the addition of growth factors, stem cells or other biologically derived molecules. Current state of the art in cardiac repair after MI utilize at least one of the above mentioned biologically derived molecules, thus our approach is ground-breaking for cardiovascular therapy after MI. In this work, we showed that synthetic glycosaminoglycan (GAG) mimetic peptide nanofiber scaffolds induce neovascularization and cardiomyocyte differentiation for the regeneration of cardiovascular tissue after myocardial infarction in a rat infarct model. When the peptide nanofiber gels were injected in infarct site at rodent myocardial infarct model, recruitment of vascular cells was observed, neovascularization was significantly induced and cardiac performance was improved. These results demonstrate the potential of future clinical applications of these bioactive peptide nanofibers as a promising strategy for cardiovascular repair.
Open Access
Antibacterial electrospun nanofibers from triclosan/cyclodextrin inclusion complexes
(Elsevier, 2014) Celebioglu A.; Umu, O. C. O.; Tekinay, T.; Uyar, Tamer
The electrospinning of nanofibers (NF) from cyclodextrin inclusion complexes (CD-IC) with an antibacterial agent (triclosan) was achieved without using any carrier polymeric matrix. Polymer-free triclosan/CD-IC NF were electrospun from highly concentrated (160% CD, w/w) aqueous triclosan/CD-IC suspension by using two types of chemically modified CD; hydroxypropyl-beta-cyclodextrin (HPβCD) and hydroxypropyl-gamma-cyclodextrin (HPγCD). The morphological characterization of the electrospun triclosan/CD-IC NF by SEM elucidated that the triclosan/HPβCD-IC NF and triclosan/HPγCD-IC NF were bead-free having average fiber diameter of 520±250nm and 1100±660nm, respectively. The presence of triclosan and the formation of triclosan/CD-IC within the fiber structure were confirmed by 1H-NMR, FTIR, XRD, DSC, and TGA studies. The initial 1:1molar ratio of the triclosan:CD was kept for triclosan/HPβCD-IC NF after the electrospinning and whereas 0.7:1molar ratio was observed for triclosan/HPγCD-IC NF and some uncomplexed triclosan was detected suggesting that the complexation efficiency of triclosan with HPγCD was lower than that of HPβCD. The antibacterial properties of triclosan/CD-IC NF were tested against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. It was observed that triclosan/HPβCD-IC NF and triclosan/HPγCD-IC NF showed better antibacterial activity against both bacteria compared to uncomplexed pure triclosan.
Open Access
BilKristal 4.0: A tool for crystal parameters extraction and defect quantification
(Elsevier, 2015) Okuyan, E.; Okuyan, C.
In this paper, we present a revised version of BilKristal 3.0 tool. Raycast screenshot functionality is added to provide improved visual analysis. We added atomic distance analysis functionality to assess crystalline defects. We improved visualization capabilities by adding high level cut function definitions. Discovered bugs are fixed and small performance optimizations are made. © 2015 Elsevier B.V. All rights reserved.
Open Access
Boradiazaindacene (Bodipy)-based building blocks for the construction of energy transfer cassettes
(Elsevier, 2009-04-15) Barin, G.; Yilmaz, M. D.; Akkaya, E. U.
Energy transfer cassettes composed entirely of boradiazaindacene (Bodipy) units were designed and synthesized to capture photonic energy and convert it to longer wavelength fluorescence emission. The new energy transfer systems obtained by simple condensation reactions are capable of elaborating efficient energy transfer from donor Bodipy units to the distyryl-Bodipy acceptor.
Open Access
Cyclodextrin-functionalized mesostructured silica nanoparticles for removal of polycyclic aromatic hydrocarbons
(Academic Press Inc., 2017) Topuz, F.; Uyar, T.
Polycyclic aromatic hydrocarbons (PAHs) are the byproducts of the incomplete combustion of carbon-based fuels, and have high affinity towards DNA strands, ultimately exerting their carcinogenic effects. They are ubiquitous environmental contaminants, and can accumulate on tissues due to their lipophilic nature. In this article, we describe a novel concept for PAH removal from aqueous solutions using cyclodextrin-functionalized mesostructured silica nanoparticles (CDMSNs) and pristine mesostructured silica nanoparticles (MSNs). The adsorption applications of MSNs are greatly restricted due to the absence of surface functional groups on such particles. In this regard, cyclodextrins can serve as ideal functional molecules with their toroidal, cone-type structure, capable of inclusion-complex formation with many hydrophobic molecules, including genotoxic PAHs. The CDMSNs were synthesized by the surfactant-templated, NaOH-catalyzed condensation reactions of tetraethyl orthosilicate (TEOS) in the presence of two different types of cyclodextrin (i.e. hydroxypropyl-β-cyclodextrin (HP-β-CD) and native β-cyclodextrin (β-CD)). The physical incorporation of CD moieties was supported by XPS, FT-IR, NMR, TGA and solid-state 13C NMR. The CDMSNs were treated with aqueous solutions of five different PAHs (e.g. pyrene, anthracene, phenanthrene, fluorene and fluoranthene). The functionalization of MSNs with cyclodextrin moieties significantly boosted the sorption capacity (q) of the MSNs up to ∼2-fold, and the q ranged between 0.3 and 1.65 mg per gram CDMSNs, of which the performance was comparable to that of the activated carbon.
Open Access
Drug delivery system based on cyclodextrin-naproxen inclusion complex incorporated in electrospun polycaprolactone nanofibers
(Elsevier, 2014) Canbolat, M. F.; Celebioglu A.; Uyar, Tamer
In this study, we select naproxen (NAP) as a reference drug and electrospun poly (e-caprolactone) (PCL) nanofibers as a fibrous matrix for our drug-delivery system. NAP was complexed with beta-cyclodextrin (βCD) to form inclusion complex (NAP-βCD-IC) and then NAP-βCD-IC was incorporated into PCL nanofibers via electrospinning. The incorporation of NAP without CD-IC into electrospun PCL was also carried out for a comparative study. Our aim is to analyze the release profiles of NAP from PCL/NAP and PCL/NAP-βCD-IC nanofibers and we investigate the effect of CD-IC on the release behavior of NAP from the nanofibrous PCL matrix. The characterization of NAP-βCD-IC and the presence of CD-IC in PCL/NAP-βCD-IC nanofibers were studied by FTIR, XRD, TGA, NMR and SEM. The SEM imaging of the electrospun PCL/NAP and PCL/NAP-βCD-IC nanofibers reveal that the average fiber diameter of these nanofibers is around 300. nm, in addition, the aggregates of CD-IC in PCL/NAP-βCD-IC nanofibers is observed. The release study of NAP in buffer solution elucidate that the PCL/NAP-βCD-IC nanofibers have higher release amount of NAP than the PCL/NAP nanofibers due to the solubility enhancement of NAP by CD-IC.
Open Access
Dynamic tuning of plasmon resonance in the visible using graphene
(The Optical Society, 2016) Balci, S.; Balci, O.; Kakenov, N.; Atar, F. B.; Kocabas, C.
We report active electrical tuning of plasmon resonance of silver nanoprisms (Ag NPs) in the visible spectrum. Ag NPs are placed in close proximity to graphene which leads to additional tunable loss for the plasmon resonance. The ionic gating of graphene modifies its Fermi level from 0.2 to 1 eV, which then affects the absorption of graphene due to Pauli blocking. Plasmon resonance frequency and linewidth of Ag NPs can be reversibly shifted by 20 and 35 meV, respectively. The coupled graphene-Ag NPs system can be classically described by a damped harmonic oscillator model. Atomic layer deposition allows for controlling the graphene-Ag NP separation with atomic-level precision to optimize coupling between them.
Open Access
The effects of achromatic and chromatic color schemes on participants' task performance in and appraisals of an office environment
(Wiley Periodicals, 2012-10) Öztürk, E.; Yilmazer, S.; Ural, S. E.
This study explores the effects of chroma on participants' performance and environmental appraisal of an office. The research was conducted in a full-scale experimental room designed as a private office where achromatic and chromatic color schemes with coequal values were applied. Sixty participants were assigned tasks and given a questionnaire to appraise the spatial color schemes. The findings show that chroma significantly affects performance and space appraisal. In terms of accuracy and time spent performance scores measured significantly better in the room with the chromatic scheme than those in the room with the achromatic scheme. The office with the chromatic scheme was found to be more pleasant, attractive, satisfying and dynamic than the one with the achromatic scheme, whereas the achromatic scheme was thought to be more formal and harmonious. Categorization of pleasantness, harmony, dynamism and spaciousness by factor analysis also showed differences between the achromatic and chromatic schemes.
Open Access
Effects of perfluorination on thiophene and pyrrole oligomers
(2010) Salzner, U.
The effect of perfluorination on thiophene and pyrrole oligomers in neutral, cationic, and anionic states was investigated with density functional theory at the (TD)B3P86-30%/6-31G* level. For the title compounds fluorination leads to planarization. For pyrroles a band gap reduction of 0.58 eV results, as unsubstituted pyrroles are nonplanar and disordered in the solid state. For thiophene the band gap is slightly increased as long thiophene oligomers are almost planar. Ionization energies and electron affinities increase upon fluorination by 0.65 and 0.60 eV for polythiophene and by 0.45 and 0.90 eV for polypyrrole. Conduction band widths increase by 0.5 for polythiophene and by 0.7 eV for polypyrrole. Spectra of charged (doped) forms are almost identical to those of the parent systems. Like parent systems, fluorinated oligomers with chain lengths of more than six rings develop a third UV absorption that increases in strength and decreases in energy upon chain length increase.
Open Access
Electrostatics of Polymer Translocation Events in Electrolyte Solutions
(American Institute of Physics Inc., 2016) Buyukdagli, S.; Ala-Nissila, T.
We develop an analytical theory that accounts for the image and surface charge interactions between a charged dielectric membrane and a DNA molecule translocating through the membrane. Translocation events through neutral carbon-based membranes are driven by a competition between the repulsive DNA-image-charge interactions and the attractive coupling between the DNA segments on the trans and the cis sides of the membrane. The latter effect is induced by the reduction of the coupling by the dielectric membrane. In strong salt solutions where the repulsive image-charge effects dominate the attractive trans-cis coupling, the DNA molecule encounters a translocation barrier of ∼10 kBT. In dilute electrolytes, the trans-cis coupling takes over image-charge forces and the membrane becomes a metastable attraction point that can trap translocating polymers over long time intervals. This mechanism can be used in translocation experiments in order to control DNA motion by tuning the salt concentration of the solution.
Open Access
Encapsulation of gallic acid/cyclodextrin inclusion complex in electrospun polylactic acid nanofibers: release behavior and antioxidant activity of gallic acid
(Elsevier, 2016-06) Aytac Z.; Kusku S. I.; Durgun, Engin; Uyar, Tamer
Cyclodextrin-inclusion complexes (CD-ICs) possess great prominence in food and pharmaceutical industries due to their enhanced ability for stabilization of active compounds during processing, storage and usage. Here, CD-IC of gallic acid (GA) with hydroxypropyl-beta-cyclodextrin (GA/HPβCD-IC) was prepared and then incorporated into polylactic acid (PLA) nanofibers (PLA/GA/HPβCD-IC-NF) using electrospinning technique to observe the effect of CD-ICs in the release behavior of GA into three different mediums (water, 10% ethanol and 95% ethanol). The GA incorporated PLA nanofibers (PLA/GA-NFs) were served as control. Phase solubility studies showed an enhanced solubility of GA with increasing amount of HPβCD. The detailed characterization techniques (XRD, TGA and 1H-NMR) confirmed the formation of inclusion complex between GA and HPβCD. Computational modeling studies indicated that the GA made an efficient complex with HPβCD at 1:1 either in vacuum or aqueous system. SEM images revealed the bead-free and uniform morphology of PLA/GA/HPβCD-IC-NF. The release studies of GA from PLA/GA/HPβCD-IC-NF and PLA/GA-NF were carried out in water, 10% ethanol and 95% ethanol, and the findings revealed that PLA/GA/HPβCD-IC-NF has released much more amount of GA in water and 10% ethanol system when compared to PLA/GA-NF. In addition, GA was released slowly from PLA/GA/HPβCD-IC-NF into 95% ethanol when compared to PLA/GA-NF. It was also observed that electrospinning process had no negative effect on the antioxidant activity of GA when GA was incorporated in PLA nanofibers.
Open Access
Enhanced immunostimulatory activity of cyclic dinucleotides on mouse cells when complexed with a cell-penetrating peptide or combined with CpG
(Wiley - V C H Verlag GmbH & Co. KGaA, 2015) Yildiz, S.; Alpdundar, E.; Gungor, B.; Kahraman, T.; Bayyurt, B.; Gursel, I.; Gursel, M.
Recognition of pathogen-derived nucleic acids by immune cells is critical for the activation of protective innate immune responses. Bacterial cyclic dinucleotides (CDNs) are small nucleic acids that are directly recognized by the cytosolic DNA sensor STING (stimulator of IFN genes), initiating a response characterized by proinflammatory cytokine and type I IFN production. Strategies to improve the immune stimulatory activities of CDNs can further their potential for clinical development. Here, we demonstrate that a simple complex of cylic-di-GMP with a cell-penetrating peptide enhances both cellular delivery and biological activity of the cyclic-di-GMP in murine splenocytes. Furthermore, our findings establish that activation of the TLR-dependent and TLR-independent DNA recognition pathways through combined use of CpG oligonucleotide (ODN) and CDN results in synergistic activity, augmenting cytokine production (IFN-α/β, IL-6, TNF-α, IP-10), costimulatory molecule upregulation (MHC class II, CD86), and antigen-specific humoral and cellular immunity. Results presented herein indicate that 3′3′-cGAMP, a recently identified bacterial CDN, is a superior stimulator of IFN genes ligand than cyclic-di-GMP in human PBMCs. Collectively, these findings suggest that the immune-stimulatory properties of CDNs can be augmented through peptide complexation or synergistic use with CpG oligonucleotide and may be of interest for the development of CDN-based immunotherapeutic agents.
Open Access
Fast-dissolving, prolonged release, and antibacterial cyclodextrin/limonene-inclusion complex nanofibrous webs via polymer-free electrospinning
(American Chemical Society, 2016) Aytac Z.; Yildiz, Z. I.; Kayaci-Senirmak, F.; S. Keskin, N. O.; Kusku, S. I.; Durgun, Engin; Tekinay, T.; Uyar, Tamer
We have proposed a new strategy for preparing free-standing nanofibrous webs from an inclusion complex (IC) of a well-known flavor/fragrance compound (limonene) with three modified cyclodextrins (HPβCD, MβCD, and HPγCD) via electrospinning (CD/limonene-IC-NFs) without using a polymeric matrix. The experimental and computational modeling studies proved that the stoichiometry of the complexes was 1:1 for CD/limonene systems. MβCD/limonene-IC-NF released much more limonene at 37, 50, and 75 °C than HPβCD/limonene-IC-NF and HPγCD/limonene-IC-NF because of the greater amount of preserved limonene. Moreover, MβCD/limonene-IC-NF has released only 25% (w/w) of its limonene, whereas HPβCD/limonene-IC-NF and HPγCD/limonene-IC-NF released 51 and 88% (w/w) of their limonene in 100 days, respectively. CD/limonene-IC-NFs exhibited high antibacterial activity against E. coli and S. aureus. The water solubility of limonene increased significantly and CD/limonene-IC-NFs were dissolved in water in a few seconds. In brief, CD/limonene-IC-NFs with fast-dissolving character enhanced the thermal stability and prolonged the shelf life along with antibacterial properties could be quite applicable in food and oral care applications.
Open Access
Fluorescent chemosensors: The past, present and future
(Royal Society of Chemistry, 2017) Wu, D.; Sedgwick, A. C.; Gunnlaugsson, T.; Akkaya, E. U.; Yoon, J.; James, T. D.
Fluorescent chemosensors for ions and neutral analytes have been widely applied in many diverse fields such as biology, physiology, pharmacology, and environmental sciences. The field of fluorescent chemosensors has been in existence for about 150 years. In this time, a large range of fluorescent chemosensors have been established for the detection of biologically and/or environmentally important species. Despite the progress made in this field, several problems and challenges still exist. This tutorial review introduces the history and provides a general overview of the development in the research of fluorescent sensors, often referred to as chemosensors. This will be achieved by highlighting some pioneering and representative works from about 40 groups in the world that have made substantial contributions to this field. The basic principles involved in the design of chemosensors for specific analytes, problems and challenges in the field as well as possible future research directions are covered. The application of chemosensors in various established and emerging biotechnologies, is very bright.
Open Access
Gemcitabine integrated nano-prodrug carrier system
(American Chemical Society, 2017) Hamsici, S.; Ekiz, M. S.; Ciftci, G. C.; Tekinay, A. B.; Güler, Mustafa O.
Peptide nanomaterials have received a great deal of interest in drug-delivery applications due to their biodegradability, biocompatibility, suitability for large-scale synthesis, high drug-loading capacities, targeting ability, and ordered structural organization. The covalent conjugation of drugs to peptide backbones results in prolonged circulation time and improved stability of drugs. Therapeutic efficacy of gemcitabine, which is used for breast cancer treatment, is severely compromised due to its rapid plasma degradation. Its hydrophilic nature poses a challenge for both its efficient encapsulation into nanocarrier systems and its sustained release property. Here, we designed a new peptide prodrug molecule for the anticancer drug gemcitabine, which was covalently conjugated to the C-terminal of 9-fluorenylmethoxy carbonyl (Fmoc)-protected glycine. The prodrug was further integrated into peptide nanocarrier system through noncovalent interactions. A pair of oppositely charged amyloid-inspired peptides (Fmoc-AIPs) were exploited as components of the drug-carrier system and self-assembled into one-dimensional nanofibers at physiological conditions. The gemcitabine integrated nanoprodrug carrier system exhibited slow release and reduced the cellular viability of 4T1 breast cancer cell line in a time- and concentration-dependent manner.
Open Access
Glycosaminoglycan-Mimetic Signals Direct the Osteo/Chondrogenic Differentiation of Mesenchymal Stem Cells in a Three-Dimensional Peptide Nanofiber Extracellular Matrix Mimetic Environment
(American Chemical Society, 2016-02) Arslan, E.; Güler, Mustafa O.; Tekinay, A. B.
Recent efforts in bioactive scaffold development focus strongly on the elucidation of complex cellular responses through the use of synthetic systems. Designing synthetic extracellular matrix (ECM) materials must be based on understanding of cellular behaviors upon interaction with natural and artificial scaffolds. Hence, due to their ability to mimic both the biochemical and mechanical properties of the native tissue environment, supramolecular assemblies of bioactive peptide nanostructures are especially promising for development of bioactive ECM-mimetic scaffolds. In this study, we used glycosaminoglycan (GAG) mimetic peptide nanofiber gel as a three-dimensional (3D) platform to investigate how cell lineage commitment is altered by external factors. We observed that amount of fetal bovine serum (FBS) presented in the cell media had synergistic effects on the ability of GAG-mimetic nanofiber gel to mediate the differentiation of mesenchymal stem cells into osteogenic and chondrogenic lineages. In particular, lower FBS concentration in the culture medium was observed to enhance osteogenic differentiation while higher amount FBS promotes chondrogenic differentiation in tandem with the effects of the GAG-mimetic 3D peptide nanofiber network, even in the absence of externally administered growth factors. We therefore demonstrate that mesenchymal stem cell differentiation can be specifically controlled by the combined influence of growth medium components and a 3D peptide nanofiber environment.
Open Access
Heparin mimetic peptide nanofiber gel promotes regeneration of full thickness burn injury
(Elsevier Ltd, 2017) Yergoz, F.; Hastar, N.; Cimenci, C. E.; Ozkan, A. D.; Güler, Mustafa O.; Tekinay, A. B.; Tekinay, T.; Güler, Mustafa O.
Burn injuries are one of the most common types of trauma worldwide, and their unique physiology requires the development of specialized therapeutic materials for their treatment. Here, we report the use of synthetic, functional and biodegradable peptide nanofiber gels for the improved healing of burn wounds to alleviate the progressive loss of tissue function at the post-burn wound site. These bioactive nanofiber gels form scaffolds that recapitulate the structure and function of the native extracellular matrix through signaling peptide epitopes, which can trigger angiogenesis through their affinity to basic growth factors. In this study, the angiogenesis-promoting properties of the bioactive scaffolds were utilized for the treatment of a thermal burn model. Following the excision of necrotic tissue, bioactive gels and control solutions were applied topically onto the wound area. The wound healing process was evaluated at 7, 14 and 21 days following injury through histological observations, immunostaining and marker RNA/protein analysis. Bioactive peptide nanofiber-treated burn wounds formed well-organized and collagen-rich granulation tissue layers, produced a greater density of newly formed blood vessels, and exhibited increased re-epithelialization and skin appendage development with minimal crust formation, while non-bioactive peptide nanofibers and the commercial wound dressing 3M™ Tegaderm™ did not exhibit significant efficiency over sucrose controls. Overall, the heparin-mimetic peptide nanofiber gels increased the rate of repair of burn injuries and can be used as an effective means of facilitating wound healing.
Open Access
Increased quantum efficiency and reduced red-shift in polymer nanoparticle luminophors
(IEEE, 2008-11) Huyal, İlkem Özge; Özel, Tuncay; Tuncel, Dönüş; Demir, Hilmi Volkan
In this paper, using a polyfluorene derivative, increased fluorescence quantum efficiency and reduced red-shift in the film form of polymer nanoparticle luminophors is achieved, when compared to directly spin coated polymer thin films.
Open Access
Inhibition of VEGF mediated corneal neovascularization by anti-angiogenic peptide nanofibers
(Elsevier, 2016-11) Senturk, B.; Cubuk, M. O.; Ozmen, M. C.; Aydin B.; Güler, Mustafa O.; Tekinay, A. B.
Atypical angiogenesis is one of the major symptoms of severe eye diseases, including corneal neovascularization, and the complex nature of abnormal vascularization requires targeted methods with high biocompatibility. The targeting of VEGF is the most common approach for preventing angiogenesis, and the LPPR peptide sequence is known to strongly inhibit VEGF activity by binding to the VEGF receptor neuropilin-1. Here, the LPPR epitope is presented on a peptide amphiphile nanofiber system to benefit from multivalency and increase the anti-angiogenic function of the epitope. Peptide amphiphile nanofibers are especially useful for ocular delivery applications due to their ability to remain on the site of interest for extended periods of time, facilitating the long-term presentation of bioactive sequences. Consequently, the LPPR sequence was integrated into a self-assembled peptide amphiphile network to increase its efficiency in the prevention of neovascularization. Anti-angiogenic effects of the peptide nanofibers were investigated by using both in vitro and in vivo models. LPPR-PA nanofibers inhibited endothelial cell proliferation, tube formation, and migration to a greater extent than the soluble LPPR peptide in vitro. In addition, the LPPR-PA nanofiber system led to the prevention of vascular maturation and the regression of angiogenesis in a suture-induced corneal angiogenesis model. These results show that the anti-angiogenic activity exhibited by LPPR peptide nanofibers may be utilized as a promising approach for the treatment of corneal angiogenesis.
Open Access
Investigation of binding properties of dicationic styrylimidazo[1,2-a]pyridinium dyes to human serum albumin by spectroscopic techniques
(John Wiley and Sons Ltd, 2017) Özdemir, A.; Gökoğlu, E.; Yılmaz, Esra; Yalçın, E.; Gökoğlu, E.; Seferoğlu, Z.; Tekinay, T.
The binding interaction between two dicationic styrylimidazo[1,2-a]pyridinium dyes and human serum albumin (HSA) was investigated at physiological conditions using fluorescence, UV–vis absorption, and circular dichroism (CD) spectroscopies. Analysis of the fluorescence titration data at different temperatures suggested that the fluorescence quenching mechanism of HSA by these dyes was static. The calculated thermodynamic parameters (ΔG°, ΔH° and ΔS°) indicated that hydrogen bonding and van der Waals forces played a major role in the formation of the dye–HSA complex. Binding distances (r) between dyes and HSA were calculated according to Förster's non-radiative energy transfer theory. Studies of conformational changes of HSA using CD measurements indicate that the α-helical content of the protein decreased upon binding of the dyes.