Bioengineering Research and Development Center

Kragujevac, Serbia

Bioengineering Research and Development Center

Kragujevac, Serbia
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Markovic Z.,State University of Novi Pazar | Milenkovic D.,Bioengineering Research and Development Center | Orovic J.,Bioengineering Research and Development Center | Dimitric Markovic J.M.,University of Belgrade | And 3 more authors.
Food Chemistry | Year: 2012

Due to intramolecular H-atom transfer, deprotonation of the most acidic 3-OH group of morin yields 2′-O- phenoxide anion. The reaction enthalpies related to mechanisms of free radical scavenging activity of this dominant species at a physiological pH of 7.4 were calculated by PM6 and DFT methods in gas-phase, water, benzene and DMSO. Results indicate the 4′-OH group of 2′-O- phenoxide anion is the active site for radical inactivation. The thermodynamically favoured mechanism depends on the polarity of the reaction media: in polar solvents (water and DMSO), the sequential proton loss electron transfer (SPLET) mechanism is preferred while in non-polar benzene (and in gas-phase), the hydrogen atom transfer (HAT) mechanism is responsible for the free radical scavenging activity of the morin phenoxide anion. Results show that the fast, semiempirical PM6 method fairly mimics more accurate, though time-consuming DFT methodologies. © 2012 Elsevier Ltd. All rights reserved.


Markovic Z.S.,State University of Novi Pazar | Dimitric Markovic J.M.,University of Belgrade | Milenkovic D.,Bioengineering Research and Development Center | Filipovic N.,Bioengineering Research and Development Center | Filipovic N.,Boston University
Journal of Molecular Modeling | Year: 2011

Density functional theory calculations were performed to evaluate the antioxidant activity of baicalein. The conformational behaviors of both the isolated and the aqueous-solvated species (simulated with the conductor-like polarizable continuum solvation model) were analyzed at the M052X/6-311+ G(d,p) level. The most stable tautomers of various forms of baicalein displayed three IHBs between O4 and OH5, O5 and OH6, and O6 and OH7. The most stable tautomer of the baicalein radical was obtained by dehydrogenating the hydroxyl at C6, while the most stable anion tautomer was obtained by deprotonating the C7 hydroxyl in gaseous and aqueous phases. The expected antioxidant activity of baicalein was explained by its ionization potentials (IPs) and homolytic O-H bond dissociation enthalpies (BDEs), which were obtained via the UM052X optimization level of the corresponding radical species. Heterolytic O-H bond cleavages (proton dissociation enthalpies, PDEs) were also computed. The calculated IP, BDE, and PDE values suggested that one-step H-atom transfer, rather than sequential proton loss-electron transfer or electron transfer-proton transfer, would be the most favorable mechanism for explaining the antioxidant activity of baicalein in the gas phase and in nonpolar solvents. In aqueous solution, the SPLET mechanism was more important. [Figure not available: see fulltext.] © 2011 Springer-Verlag.


Markovic Z.,State University of Novi Pazar | Milenkovic D.,Bioengineering Research and Development Center | Dorovic J.,Bioengineering Research and Development Center | Dimitric Markovic J.M.,University of Belgrade | And 3 more authors.
Food Chemistry | Year: 2012

Flavonoids have long been recognised for their general health-promoting properties, of which their antioxidant activity may play an important role. In this work, we have studied the properties of flavonoid morin using semiempirical and density functional theory (DFT) methods in order to validate the application of the recently developed parametric method 6 (PM6). Reaction enthalpies related to mechanisms of free radical scavenging by flavonoid morin were calculated by DFT and PM6 methods in gas-phase, water, DMSO and benzene. It has been shown that fast semiempirical PM6 method can mimic results obtained by means of more accurate time consuming DFT calculations. Thermodynamically favoured mechanism depends on reaction medium: SPLET (sequential proton loss electron transfer) is preferred in water and DMSO, and HAT (hydrogen atom transfer) is predominant in gas-phase. In benzene these two mechanisms are competitive. © 2012 Elsevier Ltd. All rights reserved.


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.


Markovic Z.,State University of Novi Pazar | Milenkovic D.,Bioengineering Research and Development Center | Crossed D Signorovic J.,Bioengineering Research and Development Center | Dimitric Markovic J.M.,University of Belgrade | And 2 more authors.
Monatshefte fur Chemie | Year: 2013

Reaction enthalpies related to mechanisms of free radical scavenging activity of ellagic acid and its phenoxide anions were calculated by density functional theory and the semiempirical PM6 method. In addition to the gas phase, calculations are performed for water and benzene as the solvents, which may represent biological liquids and the membrane lipids, i.e., a natural environment for antiradical action. The thermodynamically favored mechanism depends on the polarity of reaction media, deprotonation degree of ellagic acid as well as the properties of scavenging radicals. The most acidic 3-OH group of ellagic acid is the active site for radical inactivation. The ellagate monoanions and dianions possess progressively better scavenging potency than unionized ellagic acid. The sequential proton loss electron transfer mechanism is the preferred reaction pathway for the ellagate monoanion and dianion in water. In benzene, ellagic acid inactivates free radicals by the hydrogen atom transfer mechanism. In the gas phase the latter mechanism is favored for all ellagic acid species. © 2013 Springer-Verlag Wien.


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.


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.


PubMed | Bioengineering Research and Development Center, Josip Juraj Strossmayer University of Osijek, Serbian Institute of General and Physical Chemistry, Serbian Institute for Multidisciplinary Research and 2 more.
Type: | Journal: Food chemistry | Year: 2016

Naturally occurring flavonoids, delphinidin, pelargonidin and malvin, were investigated experimentally and theoretically for their ability to scavenge hydroxyl and nitric oxide radicals. Electron spin resonance (ESR) spectroscopy was used to determine antiradical activity of the selected compounds and M05-2X/6-311+G(d,p) level of theory for the calculation of reaction enthalpies related to three possible mechanisms of free radical scavenging activity, namely HAT, SET-PT and SPLET. The results obtained show that the molecules investigated reacted with hydroxyl radical via both HAT and SPLET in the solvents investigated. These results point to HAT as implausible for the reaction with nitric oxide radical in all the solvents investigated. SET-PT also proved to be thermodynamically unfavourable for all three molecules in the solvents considered.


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.


Markovic Z.,State University of Novi Pazar | Milenkovic D.,Bioengineering Research and Development Center | Dorovic J.,Bioengineering Research and Development Center | Jeremic S.,State University of Novi Pazar
Journal of the Serbian Society for Computational Mechanics | Year: 2013

The importance of the proton and electron transfer processes in solution is well-known. Nonetheless, there is still no systematic theoretical study on the proton and electron solvation enthalpies. We investigated the solvation enthalpies of the proton and electron in different solvents of various polarities (water, DMSO, acetonitrile, methanol, ethanol, acetone, aniline, benzene, and penthylethanoate) using the SMD solvation model. All calculations were performed at the B3LYP-D2 and M052-X levels of theory with 6-311++G(d,p) basis set. On the basis of our calculations, it was found that the B3LYP-D2 and M05-2X functionals provide similar solvation enthalpies for the proton. Also, the results obtained for the proton solvation enthalpies are in good agreement with the published results. On the other hand, the electron solvation enthalpies calculated by means of B3LYP-D2, and especially using M05-2X, are significantly different from the reported results.

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