O. Berkesi

University of Szeged, Algyő, Csongrád, Hungary

Are you O. Berkesi?

Claim your profile

Publications (62)153.31 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The conformational as well as the structure-forming properties of E-3-(x-pyridyl)propenoic acids (x = 2, 3 or 4) have been studied with a combination of computational and spectroscopic methods. IR spectroscopy revealed that in the solid state the zwitterionic species predominate, while NMR measurements showed that dimers, kept together by strong CO⋯HO hydrogen bonds, were formed in a dipolar aprotic solvent (DMSO). In concentrated solution, extended aggregation occurred through the cooperative effect of (aromatic) CH⋯N weak hydrogen bonds. Conformational search was performed at the HF/6-31G(d,p) level of theory. Comparison with experimental values as well as benchmarking calculations at several different levels of theory to probe the performance of the methods, B3LYP/6-31G++(d,p) method was found to be able to provide reasonable geometries as well as quantitative formation energies for the dimers and the tetramers, too.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Psoriasis is a T lymphocyte-mediated inflammatory disorder that affects the skin. A number of studies have demonstrated the occurrence of lipid alterations in psoriatic skin, resulting in a highly perturbed stratum corneum (SC). Relatively little attention has been paid to the protein conformation of the SC. In this study, the attenuated total reflection Fourier transform infrared (ATR-FTIR) spectrum of the untreated psoriatic patients' unharmed SC was obtained after tape stripping. We focused on the amide-I band components in order to establish whether there are any protein alterations in the intact areas of psoriatic skin. Fourier self-deconvolution (FSD) of the amide-I band was followed by curve-fitting to generate the underlying components. Integration of band areas provided an estimate of the secondary structure. The results indicated decreases in all amide-I band components, the peak at 1660 cm− 1 revealing the most dramatic change. This peak is characteristic of the turn structure in the protein chain. The decrease is marked in the case of the β-sheet structure at 1630 cm− 1 too. This ATR-FTIR imaging is a rapid and simple noninvasive method, promotes a better understanding of the disease, and would be helpful in following the treatment.
    Microchemical Journal 11/2014; 117:183–186. DOI:10.1016/j.microc.2014.07.003 · 3.58 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Two different preparation methods were developed to cover successfully multi-walled carbon nanotubes (MWCNT) with tin-dioxide (SnO2) nanoparticles using SnCl2x2H2O as precursor under different solvent conditions. The applied mass ratios of the components were 1:4, 1:8, 1:16, 1:32 and 1:64, respectively. As-prepared tin-dioxide coverages were characterized by TEM, SEM, SEM-EDX, Raman microscopy, BET and X-ray diffraction techniques. Photocatalytic efficiencies of selected composites were investigated in a self-made photoreactor, equipped with UV-A fluorescence lamps. Photocatalytic degradation of phenol solution was followed by using HPLC. Observations revealed that using hydrothermal method we can easily control the layer of SnO2 nanoparticles on the surface of MWCNTs. Using various solvents SnO2 nanoparticles with different morphologies formed. The nanocomposites have low photocatalytic efficiencies under conditions used generally (when λ>300 nm).
  • [Show abstract] [Hide abstract]
    ABSTRACT: The identity of the predominating tin(II)-hydroxide complex formed in hyper-alkaline aqueous solution (0.2  CNaOH  12 mol⋅dm-3) has been determined by potentiomet¬ric titrations, Raman, Mössbauer and XANES spectroscopy, supplemented by quantum chemical calculations. Thermodyna¬mic studies using a H2/Pt electrode up to free hydroxide concentrations of 1 mol⋅dm-3 showed the presence of a single monomeric complex with a tin(II):hydroxide ratio of 1:3. This observation together with Raman and Mössbauer spectroscopic measurements supplemented by quantum mechanical calculations proved that the predominating complex is [Sn(OH)3]–, and that the presence of the other possible complex, [SnO(OH)]–, could not be proven with neither experiments nor simulations. The structure of the trihydroxido-stannate(II) complex, [Sn(OH)3]-, was determined by EXAFS and was found to be independent of the applied hydroxide and tin(II) concentrations. The mean Sn-O bond distance is short, 2.078 Å, and in very good agreement with the only structure reported in the solid state. It is also shown that at pH values above 13 the speciation of the predominating trihydroxidostannate(II) complex is not affected by the presence of high concentrations of chloride ions.
    Dalton Transactions 10/2014; DOI:10.1039/C4DT02706J · 4.10 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Effective bio-electrocatalysts require stable immobilization of sufficient amounts of the bioactive component. In this study, a novel and efficient method for specific binding of laccase enzyme onto magnetite nanoparticles (NPs) is presented. The interaction between the chemically modified magnetite NPs and the enzyme was evidenced by both infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). Subsequently, the enzyme-coated magnetite NPs were successfully incorporated into polypyrrole (PPy) matrix during galvanostatic electropolymerization. The encapsulation of laccase covered NPs was proved by EQCN, TEM, and FT-IR spectroscopy; whereas the electrochemical behaviour of the formed bionanocomposite was characterized by cyclic voltammetiy. In oxygen saturated solution a cathodic charge surplus was observed, related to the electrochemical reduction of oxygen. This surplus was two times higher in the case of the laccase containing layer compared to its only magnetite containing counterpart. Kinetic aspects of the oxygen reduction reaction (ORR) on the laccase containing films were investigated by hydrodynamic voltammetry, and the four-electron route was found to be exclusive, which is promising from the fuel cell perspective. Such synergistic combination of inorganic NPs and enzymes may open new avenues in the application of these bio-nanocomposite materials.
    Electrochimica Acta 03/2014; 122:282-288. DOI:10.1016/j.electacta.2013.08.175 · 4.09 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The plasmonic Ag-TiO2 (with 0.5 wt% Ag) photocatalyst was prepared on P25 TiO2 surface. The presence of AgNPs on the titania was indicated by the UV–vis spectrum, which showed a plasmonic absorbance band in the visible range (λ max = 455 nm). XPS measurements suggested that Ag was in metallic (Ag) and in oxide forms on TiO2. Ag-TiO2 photocatalyst and TiO2 were embedded in [poly(ethyl acrylate-co-methyl methacrylate; p(EA-co-MMA)] copolymer to attain mechanically stable, photocatalytically active nanocomposite films. The photooxidation of ethanol was slower on the photocatalyst/polymer nanocomposites, but it could be significantly improved by irradiating them with UV light. The photoaging was applied as a post-preparation treatment to improve the photocatalytic activity of the nanocomposite films. Changed surface morphology and the partial destruction of the polymer were supported by AFM and FTIR results. Contact angle measurements were used to determine the surface free energies of the prepared and the photoaged nanocomposite films.
    Colloid and Polymer Science 01/2014; 292(1). DOI:10.1007/s00396-013-3063-1 · 2.41 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have prepared multiwalled carbon nanotube (MWCNT)/In2O3 composites using a simple impregnation method. The precursor compound indium(III) chloride (InCl3) was used to cover the surface of MWCNTs and distilled water was used as solvent. The applied mass ratio was 4:1 (In2O3/MWCNT), and during the calcination process different temperatures (300, 350 and 400 °C) were investigated. The produced materials were characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, transmission and scanning electron microscopy, and a thermogravimetric analysis was executed also. The average thickness of the produced surface layer and the average sizes of the In2O3 particles were calculated with the Scherrer formula and the ImageJ-program. The results show that the heat treatment temperature affected the characteristic morphology and the crystal structure of the as-prepared composite. These multiwalled carbon nanotube-based composites are promising candidates as gas sensors and catalyst.
    physica status solidi (b) 12/2013; 60:266–272. DOI:10.1016/j.carbon.2013.04.035 · 1.61 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have prepared multiwalled carbon nanotube (MWCNT)/In2O3 composites using a simple impregnation method. The precursor compound indium(III) chloride (InCl3) was used to cover the surface of MWCNTs and distilled water was used as solvent. The applied mass ratio was 4:1 (In2O3/MWCNT), and during the calcination process different temperatures (300, 350 and 400 �C) were investigated. The produced materials were characterized by Xray diffraction, energy-dispersive X-ray spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, transmission and scanning electron microscopy, and a thermogravimetric analysis was executed also. The average thickness of the produced surface layer and the average sizes of the In2O3 particles were calculated with the Scherrer formula and the ImageJ-program. The results show that the heat treatment temperature affected the characteristic morphology and the crystal structure of the as-prepared composite. These multiwalled carbon nanotube-based composites are promising candidates as gas sensors and catalyst.
    Carbon 12/2013; 60(12):266-272. DOI:10.1002/pssb.201300077 · 6.16 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: One of the aims of our long-term research is the identification of metal ion-ligand coordination sites in bioinspired metal ion-C- or N-protected amino acid (histidine, tyrosine, cysteine or cystine) complexes immobilised on the surface of chloropropylated silica gel or Merrifield resin. In an attempt to reach this goal, structurally related, but much simpler complexes have been prepared and their metal ion-ligand vibrations were determined from their low-frequency IR spectra. The central ions were Mn(II), Co(II), Ni(II) or Cu(II) and the ligands (imidazole, isopropylamine, monosodium malonate) were chosen to possess only one-type of potential donor group. The low-frequency IR spectra were taken of the complexes for each ion-ligand combination and the typical metal ion-functional group vibration bands were selected and identified. The usefulness of the obtained assignments is demonstrated on exemplary immobilised metal ion-protected amino acid complexes.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 11/2013; 122C:257-259. DOI:10.1016/j.saa.2013.11.082 · 2.13 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Cinnamic acid derivatives are important actors in the metabolism of plants, in the shikimic acid pathway [1]. They are capable of hydrogen bonding as any carboxylic acid, however; in the solid state they, and especially their heteroatom-containing derivatives, form extended quasi two-dimensional aggregates kept together by hydrogen bonds of various strengths [2]. These molecular networks may be turned three-dimensional if they are allowed to self-assemble over polycrystalline noble metal (Au, Pt, Ag) surfaces [3, 4]. In most cases acid dimers are the fundamental units and they are kept together by weaker but very significant CH...O (N, S) hydrogen bonding interactions. The structural features of the dimers as well as the hydrogen bonded aggregates can be explored by various experimental methods like IR, Raman and NMR spectroscopies, microscopic techniques (AFM, SEM) as well as computational methods at different theoretical levels. In this contribution results of such calculations are shown both for the oxygen-, sulfur- and the nitrogen-containing acids both for the dimers and the more extended aggregates, too. The dimers of the furyl-, thienyl- and pyridyl-substituted acrylic acids, having the heteroaryl groups and the heteroatoms in varying positions, were constructed and their conformational space was studied by semiempirical as well as ab initio calculations through applying various basis sets. The results of the computational and the experimental work were also correlated. It has been found the even though the dimers had numerous conformers, they are not of planar stucture. It was possible to build extended hydrogen-bonded two-dimensional networks of various kinds, to identify the hydrogen bonding acceptor and donor sites and to give good estimates for the hydrogen bond lengths and angles. It was found that by increasing the size of the hydrogen-bonded network, the overall geometry got closer to being planar, i.e., the experi-mental fact that cinnamic acids have layered structures were mirrored by the calculations as well. By computing the geometric parameters of the dimers and comparing them to the experimentally determined thickness of the three-dimensional acid layer over the polycrystalline noble metal surfaces, it was possible to estimate the length of oligomer grown in a fashion nearly perpendicular to the metal surface. Acknowledgement: This research was funded by the TÁMOP-4.2.2.A-11/1/KONV-2012-0047 and TÁMOP-4.2.2/C grants from by the European Union and co-financed by the European Regional Fund. All these financial supports are highly appreciated. References: [1] J. Mann, in Secondary Metabolism, Clarendon Press, Oxford, 1987, Ch. 4, p. 173. [2] I. Pálinkó, Trends in Organic Chemistry, 13 (2009) 1734. [3] K. Csankó, M. Darányi, G. Kozma, Á. Kukovecz, Z. Kónya, P. Sipos, I. Pálinkó, J. Mol. Struct. 993 (2011) 6772. [4] K. Csankó, G. Kozma, L. Valkai, Á. Kukovecz, Z. Kónya, P. Sipos, I. Pálinkó, J. Mol. Struct. (in press
    European conference on Computational Chemistry, Sopron, Hungary; 09/2013
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The investigation of free films is an essential part of the preformulation studies, because it is necessary to know, weather the given formulation is suitable to coat the corpus or not. As preformulation, the relationships between surface properties, and the structure of ethylcellulose free films containing different amount of plasticizer were studied. The structure analysis, and the incorporation of the plasticizer was performed with the use of FT-IR analysis. The results showed that the films are suitable to produce diffusion coatings.
    Microchemical Journal 09/2013; 110:36-39. DOI:10.1016/j.microc.2013.02.005 · 3.58 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The intercalation of biosurfactants (lysolecithin and lecithin) in layered clay mineral supports was investigated to assess the suitability of the resulting nanohybrid materials as flavor and fragrance delivery system. The protonated biosurfactant molecules (pH = 2.3) were intercalated into the Na-montmorillonite, whereas the deprotonated biosurfactants (pH ~ 12) were intercalated into Mg–Al layered double hydroxides. The amount of lysolecithin and lecithin bound to the layered adsorbents was estimated by measuring adsorption isotherms. The basal spacing obtained from X-ray diffraction measurements suggested that the molecules are arranged in parallel with the layers of montmorillonite, whereas in the case of layered double hydroxides, the adsorbed molecules are in a vertical position between the layers. The interaction of layered adsorbents and biosurfactants was further evidenced by infrared spectroscopy. The intercalated montmorillonite and LDH particles were then probed for their ability to intercalate limonene molecules. Only the lysolecithins modified samples adsorbed limonene. The theoretical sizes of molecules and their possible arrangement between the layers were modeled by HyperChem 7.0 molecular calculations to correlate the ability to bind the lecithins in the confined space of the layered materials.
    Applied Clay Science 02/2013; 72:155–162. DOI:10.1016/j.clay.2012.11.008 · 2.70 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The preparation and application of heterogeneous chiral catalysts are described. Heterogeneous Pd, Ir and Ru catalysts were tested in the enantioselective hydrogenations of N-heterocyclic compounds, namely 6,7-dimethoxy-3,4-dihydroisoquinoline and 1-methylene-2-ethoxycarbonyl-6,7-dimetoxy-3,4-dihydroisoquinoline in the presence of optically pure cinchonidine, (S,S)- and (R,R)-Ts-DPEN ligands. Cinchonidine-modified metal catalysts exhibited low ee, whereas catalysts stabilized by triphenylphosphane and modified by (S,S)-Ts-DPEN afforded promising ee values (70–80 %). Immobilized Ru(II)-aminophosphane complexes were found to be active in these hydrogenations producing the corresponding tetrahydroisoquinoline derivatives in high optical purities (up to 97 %). The latter catalysts were characterized by infrared spectroscopy, solid-state MAS NMR spectroscopy and elemental analysis. Recycling of these catalysts showed constant or increasing activities in racemic hydrogenation, whereas the presence of the chiral ligands led to leaching of the active species in the liquid phase.
    Topics in Catalysis 08/2012; 55(11-13). DOI:10.1007/s11244-012-9854-7 · 2.22 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: An exact wavelength separation of the spectrum cannot be accomplished when utilizing common ultraviolet (UV) light sources, so the dependence of photodegradation on wavelength cannot be done directly. The photodegradation of wood resulted in by laser irradiation on various wavelengths can be studied by comparing the changes in the DRIFT spectra of various wood materials. The analysis of the difference spectrum is a widely used method to investigate the changes in the infrared spectrum. As this procedure cannot be used to compare the changes quantitatively, a new indicator was introduced, termed Band Damage Index (BDI). The BDI and the results obtained by its analysis are going to be discussed.
    Journal of photochemistry and photobiology. B, Biology 04/2012; 112:43-7. DOI:10.1016/j.jphotobiol.2012.04.006 · 2.80 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The ionic motion in connection with the redox transformation of poly(3,4-ethylenedioxythiophene) (PEDOT) conjugated polymer have been studied by both experimental-electrochemical (electrochemical quartz crystal nanobalance, EQCN) and spectroscopic (infrared spectroscopy, IR-ATR)-and theoretical methods. The observations have been completed by direct, semiquantitative analytical data, provided by energy dispersive X-ray (EDX) microanalysis. The EQCN results suggested an anomalous behavior, since only cationic movements have been observed for films deposited from chloride solutions. Chloride ions were proved to be immobile also when bulky tetrabutylammonium (Bu(4)N(+)) cations were substituted with even larger (hexadecyltrimethylammonium) cations. Since PEDOT films synthesized in the presence of other spherical, not too large anions-such as perchlorate and tetrafluoroborate-endowed mixed ion exchange behavior together with the Bu(4)N(+) cation, the possibility of a special interaction between chloride and the polymeric chain has been assumed. Semiempirical and DFT calculations indicated that chloride ions interact with the α carbon atoms of the thiophene rings of the oxidized EDOT oligomers, creating sp(3) type perturbations in the polymer chain. FTIR-ATR spectra evidenced the appearance of C-Cl bonds. Elementary analysis, performed by EDX spectroscopy with eight polymer samples at different doping levels clearly showed the permanent presence of constant amount of chlorine, independently of the oxidation state of the PEDOT layer. Finally, the presented observations call attention to the fact that unique dopant-polymer interactions during the electrochemical polymerization are of prime importance, being able to rule over conventions for the charge compensation of conjugated polymers, often solely based on steric parameters.
    The Journal of Physical Chemistry B 04/2012; 116(18):5491-500. DOI:10.1021/jp2107268 · 3.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The steps of formation of an inclusion complex produced by the co-grinding of gemfibrozil and dimethyl-β-cyclodextrin were investigated by differential scanning calorimetry (DSC), X-ray powder diffractometry (XRPD) and Fourier transform infrared (FTIR) spectroscopy with curve-fitting analysis. The endothermic peak at 59.25°C reflecting the melting of gemfibrozil progressively disappeared from the DSC curves of the products on increase of the duration of co-grinding. The crystallinity of the samples too gradually decreased, and after 35min of co-grinding the product was totally amorphous. Up to this co-grinding time, XRPD and FTIR investigations indicated a linear correlation between the cyclodextrin complexation and the co-grinding time. After co-grinding for 30min, the ratio of complex formation did not increase. These studies demonstrated that co-grinding is a suitable method for the complexation of gemfibrozil with dimethyl-β-cyclodextrin. XRPD analysis revealed the amorphous state of the gemfibrozil-dimethyl-β-cyclodextrin product. FTIR spectroscopy with curve-fitting analysis may be useful as a semiquantitative analytical method for discriminating the molecular and amorphous states of gemfibrozil.
    Journal of pharmaceutical and biomedical analysis 08/2011; 57:62-7. DOI:10.1016/j.jpba.2011.08.034 · 2.83 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The compatibility of aceclofenac with various tableting excipients was investigated by means of differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR). The excipients applied in the direct pressing retard tablets were Carbopol 940, hydroxypropyl-methyl-cellulose, microcrystalline cellulose, Aerosil 200 and magnesium stearate. The ingredients alone and their 1:1 (w/w) binary mixtures were investigated before and after accelerated storage. An interaction was observed only between aceclofenac and magnesium stearate. The DSC and FT-IR examinations indicated formation of the magnesium salt of aceclofenac. For the other mixtures, there was no incompatibility between the components. KeywordsCompatibility–Aceclofenac–Magnesium stearate–DSC–FT-IR
    Journal of Thermal Analysis and Calorimetry 04/2011; 104(1):265-271. DOI:10.1007/s10973-010-1105-1 · 2.21 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Conducting polymers are getting more and more interest as both supporting matrixes and electrocatalysts in the oxygen reduction reaction (ORR). A polypyrrole-magnetite nanocomposite layer has been synthesized by using potassium tetraoxalate as the conducting electrolyte. FT-IR measurements proved that chemical modification of the iron oxide by a reaction between the nanoparticles and the salt-leading to an iron oxalate layer on their surface-endows a negative charge to the particles, which leads to their penetration into the polymeric film as a part of the charge compensation. The new hybrid material showed significant photoelectrocatalytic behavior in the ORR. The ratio observed between the stabilized stationary currents under and without illumination is 2.0 for this hybrid. Separate studies on the electrochemical decomposition of H2O2 also indicated an enhanced catalytic activity of the polypyrrole/magnetite hybrid compared with the neat polymer. The results may open new opportunities in the next generation of solar fuel cell applications.
    The Journal of Physical Chemistry C 11/2010; 114:19338-19344. DOI:10.1021/jp105338f · 4.84 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Potential metal-organic-framework precursors, Zn(4)O complexes with various alicyclic or aromatic carboxylate ligands, were prepared, in many cases quantitatively, from ZnO and the relevant carboxylic acids in the presence of trace amounts of water. The complexes obtained were characterized with various classical (titration) and instrumental (IR and NMR spectroscopies) methods and molecular modeling (PM3 and PM6 semiempirical quantum chemical methods and HF/6-31G** ab initio calculations). Structural peculiarities reflected in the success or failure in the synthesis could be rationalized with the combination of IR and NMR spectroscopies and molecular modeling.
    Inorganic Chemistry 05/2010; 49(10):4620-5. DOI:10.1021/ic100205n · 4.79 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The aim of this work was to investigate the skin penetration enhancer effect of a sucrose ester (SE) in an Ibuprofen (IBU) containing hydrogel and to examine its influence on the special lipid bilayer of the stratum corneum (SC). ATR-FTIR spectroscopic measurements were performed combined with tape stripping method on hairless mice in vivo. A SE containing gel was compared to another gel without SE. It was found that the preparations caused only minimal modifications in the lipid and the protein structure, promoting the skin hydration and therefore also the penetration of IBU. Although the degree of moisturization and penetration were more intense in the case of the SE containing gel treatment, it did not cause greater alterations in the SC structure than the gel without SE. It has been proven that SE acts as an effective and non-irritating hydration and penetration enhancer for IBU through skin.
    Pharmaceutical Development and Technology 01/2010; 17(1):125-8. DOI:10.3109/10837450.2010.508076 · 1.34 Impact Factor

Publication Stats

779 Citations
153.31 Total Impact Points

Institutions

  • 1995–2014
    • University of Szeged
      • • Department of Physical Chemistry and Materials Science
      • • Institute of Chemistry
      • • Department of Pharmaceutical Technology
      • • Department of Optics and Quantum Electronics
      • • Department of Experimental Physics
      Algyő, Csongrád, Hungary
  • 1997
    • University of Pannonia, Veszprém
      • Department of Analytical Chemistry
      Veszprém, Veszprem megye, Hungary
  • 1992
    • University of East Anglia
      Norwich, England, United Kingdom
  • 1991–1992
    • Hungarian Academy of Sciences
      • Department of Structural Chemistry
      Budapeŝto, Budapest, Hungary