Entity

Time filter

Source Type


Markovic Z.,State University of Novi Pazar | Tosovic J.,University of Kragujevac | Milenkovic D.,Bioengineering Research and Development Center | Markovic S.,University of Kragujevac
Computational and Theoretical Chemistry | Year: 2016

In scientific literature there are only several values for solvation enthalpies and free energies of the proton and electron, the quantities from which the enthalpies and free energies of the solvated proton and electron can be issued. The latter quantities are of significance in thermodynamic modeling of antioxidative properties in the media where the reactions really occur. This work fills this gap in scientific literature. Namely, a systematic investigation of the solvation enthalpies and free energies of the proton and electron in twenty commonly used solvents of different polarities was performed. For this purpose eleven ab initio and DFT methods were used in combination with the 6-311++G(d,p) basis set and SMD solvation model. Due to very good overall performance, B3LYP was selected for further computations with larger basis sets. The thermodynamic values obtained at the B3LYP/Aug-cc-pVTZ level of theory are in very good agreement with the existing several values for solvation enthalpies of the proton and electron, and they are recommended for application in the examinations of antioxidative activity in different solvents. © 2015 Elsevier B.V. Source


Markovic Z.,State University of Novi Pazar | Amic D.,Josip Juraj Strossmayer University of Osijek | Milenkovic D.,Bioengineering Research and Development Center | Dimitric-Markovic J.M.,University of Belgrade | Markovic S.,University of Kragujevac
Physical Chemistry Chemical Physics | Year: 2013

It has been generally accepted that, due to high ionization potential values, single electron transfer followed by proton transfer (SET-PT) is not a plausible mechanism of antioxidant action in flavonoids. In this paper the SET-PT mechanism of quercetin (Q) was examined by revealing possible reaction paths of the once formed quercetin radical cation (Q+•) at the M0-52X/6311+G(d,p) level of theory. The deprotonation of Q+• was simulated by examining its chemical behavior in the presence of three bases: methylamine (representative of neutral bases), the MeS anion (CH 3S-) and the hydroxide anion (representative of anionic bases). It was found that Q+• will spontaneously be transformed into Q in the presence of bases whose HOMO energies are higher than the SOMO energy of Q+• in a given medium, implying that Q cannot undergo the SET-PT mechanism in such an environment. In the reaction with the MeS anion in both gaseous and aqueous phases and the hydroxide anion in the gaseous phase Q+• accepts an electron from the base, and so-formed Q undergoes the hydrogen atom transfer mechanism. On the other hand, SET-PT is a plausible mechanism of Q in the presence of bases whose HOMO energies are lower than the SOMO energy of Q+• in a given medium. In such cases Q +• spontaneously donates a proton to the base, with energetic stabilization of the system. Our investigation showed that Q conforms to the SET-PT mechanism in the presence of methylamine, in both gaseous and aqueous phases, and in the presence of the hydroxide anion, in the aqueous solution. © 2013 the Owner Societies. Source


Markovic Z.S.,State University of Novi Pazar | Markovic S.,University of Kragujevac | Dimitric Markovic J.M.,University of Belgrade | Milenkovic D.,Bioengineering Research and Development Center
International Journal of Quantum Chemistry | Year: 2012

Neutral baicalein, corresponding radical cation, and three possible radicals obtained by proton removal from the radical cation were investigated using density functional theory. The structure and UV spectrum of baicalein were very well reproduced by the B3LYP/6-311+G(2df,p) level of theory. The results showed that the loss of an electron from baicalein molecule induced the transfer of H4 to O5. The reasons for this rearrangement were pointed out. It was found that delocalization of spin density is most pronounced in the thermodynamically most stable C6-OH radical. It was supposed that this radical plays a significant role in the antioxidant activity of baicalein within the single-electron transfer-proton transfer mechanism. © 2011 Wiley Periodicals, Inc. Source


Dimitric Markovic J.M.,University of Belgrade | Markovic Z.S.,State University of Novi Pazar | Krstic J.B.,Serbian Institute of Chemistry | Milenkovic D.,Bioengineering Research and Development Center | And 2 more authors.
Vibrational Spectroscopy | Year: 2013

Density functional theory calculations, with M05-2X functional and 6-311++G(d,p) basis set implemented in the Gaussian 09 package, are performed with the aim to support molecular structure and spectroscopic characteristics of morin, a bioflavonoid molecule known for its antiproliferative, antitumor, and antiinflammatory effects. Detailed vibrational spectral analysis and the assignments of the bands, done on the best-fit basis comparison of the experimentally obtained and theoretically calculated IR and Raman spectra, match quite well indicating DFT calculations as very accurate source of normal mode assignments. The assignment of the most prominent normal modes of morin is qualitatively verified through comparative spectral analysis with quercetin, a structurally isomeric molecule of morin which differs only by the substitution pattern of the B ring. Performed comparative analysis reflects quite accurately all the structural differences between the investigated molecules additionally proving the applied theoretical method. © 2012 Elsevier B.V. All rights reserved. Source


Dimitric Markovic J.M.,University of Belgrade | Markovic Z.S.,State University of Novi Pazar | Milenkovic D.,Bioengineering Research and Development Center | Jeremic S.,State University of Novi Pazar
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2011

This paper addresses experimental and theoretical research in fisetin (2-(3,4-dihydroxyphenyl)-3,7-dihydroxychromen-4-one) structure by means of experimental IR and Raman spectroscopies and mechanistic calculations. Density Functional Theory calculations, with M05-2X functional and the 6-311+G (2df, p) basis set implemented in the Gaussian 09 package, are performed with the aim to support molecular structure, vibrational bands' positions and their intensities. Potential energy distribution (PED) values and the description of the largest vibrational contributions to the normal modes are calculated. The most intense bands appear in the 1650-1500 cm -1 wavenumber region. This region involves a combination of the CO, C2C3 and C-C stretching vibrational modes. Most of the bands in the 1500-1000 cm -1 range involve C-C stretching, O-C stretching and in-plane C-C-H, C-O-H, C-C-O and C-C-C bending vibrations of the rings. The region below 1000 cm -1 is characteristic to the combination of in plane C-C-C-H, H-C-C-H, C-C-C-C, C-C-O-C and out of plane O-C-C-C, C-C-O-C, C-C-C-C torsional modes. The Raman spectra of baicalein and quercetin were used for qualitative comparison with fisetin spectrum and verification of band assignments. The applied detailed vibrational spectral analysis and the assignments of the bands, proposed on the basis of fundamentals, reproduced the experimental results with high degree of accuracy. © 2011 Elsevier B.V. Source

Discover hidden collaborations