Nebojša Begović

Influence of different free radicals on scavenging potency of gallic acid.

AbstractThe M05-2X/6-311++G(d,p) and B3LYP-D2/6-311++G(d,p) models are used to evaluate scavenging potency of gallic acid. The hydrogen atom transfer (HAT), sequential proton loss electron transfer (SPLET), and single electron transfer followed by proton transfer (SET-PT) mechanisms of gallic acid with some radicals (•OO−, •OH, and CH3OO•) were investigated using the corresponding thermodynamic quantities: bond dissociation enthalpy (BDE), ionization potential (IP), and proton affinity (PA). Namely, the ΔHBDE, ΔHIP, and ΔHPA values of the corresponding reactions in some solvents (water, DMSO, pentylethanoate, and benzene) are investigated using an implicit solvation model (SMD). An approach based on the reactions enthalpies related to the examined mechanisms is applied. This approach shows that a thermodynamically favored mechanism depends on the polarity of reaction media and properties of free radical reactive species. The most acidic 4-OH group of gallic acid is the active site for radical inactivation. The results of this investigation indicate that the SPLET mechanism can be a favored reaction pathway for all three radicals in all solvents, except for •OH in the aqueous solution. In water, gallic acid can inactivate •OH by the HAT mechanism. FigureInfluence of different solvents on antioxidative mechanisms of gallic acid

Ni(II) complex with bishydrazone ligand: synthesis, characterization, DNA binding studies and pro-apoptotic and pro-differentiation induction in human cancerous cell lines

A new Ni(II) complex, [Ni(L)(H2O)] (1), with diethyl 3,3′-(2,2′-(1,1′-(pyridine-2,6-diyl)bis(ethan-1-yl-1-ylidene))bis(hydrazin-1-yl-2-ylidene))bis(3-oxopropanoate) ligand (H2L) was synthesized as a potential chemotherapeutic agent. Polidentate ligand was coordinated to Ni(II) NNN-tridentately, in dianionic form, while monodentate water coordination completed square-planar geometry around metal. Structure in the solution was determined by NMR spectroscopy and the same coordination mode was observed in the solid state using IR spectroscopy and further verified by DFT calculations and electrochemical studies. Thermal stability of 1 was determined in both air and nitrogen atmosphere. Anticancer activity of 1 was investigated on acute monocytic leukemia (THP-1) and pancreatic adenocarcinoma (AsPC-1) cell lines. On THP-1 cells 1 induced powerful apoptotic response (ED50 = 10 ± 3 μM), which was revealed to be only partially caspase-dependent, with activation of caspase-8 as the dominant course. This suggested that experimentally validated covalent binding of 1 to DNA is not the only mechanism responsible for programmed cell death. This was supported with experiments on AsPC-1 cells. Although treatment of those cells with 1 resulted in poor apoptotic response, cell cycle changes showed concentration-dependent shifts indicating a dual mechanism of activity. This study also reviews the results of preliminary biological screening, which demonstrates that 1 displays a unique pattern of anticancer activity with at least two mechanisms involved.

Antiradical activity of delphinidin, pelargonidin and malvin towards hydroxyl and nitric oxide radicals: The energy requirements calculations as a prediction of the possible antiradical mechanisms

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.

Thermal stability and degradation of binuclear hexaaqua-bis(ethylenediamine)-( μ 2 -pyromellitato)dinickel(II) tetrahydrate

Thermal degradation of ternary transition metal complex containing tetraanion of pyromellitic acid, pyr, and ethylenediamine, en, [Ni2(en)2(H2O)6(pyr)]·4H2O, 1, was investigated under non-isothermal conditions. The mechanism of thermal degradation, which occurs in three steps, was clarified by TG/DSC measurements in conjunction with FT-IR spectroscopy and XRPD analysis. The complexity of all degradation steps has been revealed using isoconversional methods. Dehydration comprises the loss of ten water molecules in a relatively narrow temperature interval, resulting in a very complicated reaction mechanism. In addition, density functional theory calculations have been applied for better understanding of dehydration. The second degradation step, related to loss of en, was separated into two single-step processes with Fraser–Suzuki function. The obtained individual steps were described by Johnson–Mehl–Avrami A2 model and Šesták–Berggren model, respectively. Validation of the proposed kinetic triplets for individual steps was performed using master plot and Pérez-Maqueda criteria. The third degradation step is related to the fragmentation of pyr ion most likely followed with the release of a number of gaseous products.

Synthesis and thermal stability of cis -dichloro[ (E) -ethyl-2-(2-((8-hydroxyquinolin-2-il)methylene)hidrazinyl)acetate-κ 2 N ]-palladium(II) complex

The structure of new cis-dichloro[(E)-ethyl-2-(2-((8-hydroxyquinolin-2-il)methylene)hidrazinyl)acetate-κ2N]-palladium(II) complex was determined using a combination of XRD and IR measurements and DFT calculations. Inherent flexibility of its structure is evident from the complexity of its IR spectrum, which could only be theoretically reproduced as a combination of several closely related structures, involving rotation around C–O bond and changes in hydrogen interactions of its –OH group. Its thermal stability and decomposition were studied non-isothermally, and the thermal decomposition mechanism was proposed using correlation with DFT calculations at the molecular level. It was determined that the initial degradation step consists of the release of Cl free radical, which then reacts with both the initial compound and the degradation products. Besides the endothermic steps, there are exothermic ones, contributing to the complex shape of the DSC curve, consisted of overlapping endothermic and exothermic peaks. Deconvolution of DTG curve allowed identification of primary fragments of the initial degradation process and, in conjunction with DFT calculations, construction of the most likely reaction mechanism.