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The electrode potential of cyanidin was determined both by experimental (cyclic voltammetry) and theoretical methods, at HF/6-311G(d) level of theory. An isodesmic reaction scheme, involving 1,2-benzoquinone as reference molecules, has been proposed for the computation of electrode potential of cyanidin. The results of the ab initio computations are in reasonable agreement with available experimental measurements; the differences between experiment and theory are within the range of 0.02-0.05V. Geometric parameters of the six more stable conformers of cyanidin are computed, as well as properties like atomic charges and contribution to the HOMO (Highest Occupied Molecular Orbital) energies of each hydroxyl group of the cyanidin.

Corrosion inhibitory effect of myricetin in alcoholic solutions has been studied by potentiodynamic polarization. Inhibitory efficiencies of 70%, 61%, 69% and 79% have been obtained for stainless steel, carbon steel, aluminum alloy, and aluminum, respectively. Adsorption Gibbs free energy, determined using Langmuir adsorption isotherms, has revealed that interactions between metal atoms and myricetin adsorbed molecules have chemical character. Moreover, quantum chemistry calculations have shown that myricetin, due to its molecular structure (O heteroatoms with lone pair electrons and π electrons from aromatic rings) has the ability to form an adsorption layer on the metal surface that inhibits the diffusion of molecules and ions participating in the global corrosion process. [ABSTRACT FROM AUTHOR]

Photodynamic therapy represents an alternative and/or adjuvant method for the treatment of superficial tumors; this way, there is an increased interest regarding the design of new photosensitizers with improved properties. The aim of the paper is to study the interactions among five substituted porphyrins and some rhombellanes (seven cube-rhombellane homeomorphs, C-rbl, with amide structures). The aforementioned porphyrins have been characterized and have been docked to the surface of the rhombellanes; comparisons with the results obtained for fullerene C60 have been performed. The best binding affinities have been obtained for the fluoro-substituted porphyrin docked on the larger rhombellane structures. The results outline that the hydrophobicity of the ligands plays an important role and represents a good indicator of searching for porphyrins with hydrophobic character for future investigations. [ABSTRACT FROM AUTHOR]

The influence of aza-substitution on sumanene and C52 fullerene was investigated. Various substitution patterns, derived for the structures of pyrrole, indolizine and pyridine have been proposed and aromaticity indices like HOMA, NICS, delocalization indices PDI and FLU were considered, at B3LYP/6-311+G(d) level of theory. The results outlined an enhanced aromatic character for the sumanene derivatives where similar aza-substitution patterns as encountered in pyrrole and indolizine have been considered. [ABSTRACT FROM AUTHOR]

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The aromatic character of three non-planar circulenes has been investigated at B3LYP/6-311+G(d,p) level of theory. Global aromaticity descriptors like HOMO-LUMO gap, enthalpy of formation and exaltation of magnetic susceptibility outline a possible aromatic character only for circulenes [4:64] and [7:67]. The viability of isodesmic reaction schemes -for evaluation of the enthalpies of formation- has been discussed. Local aromaticity descriptors like HOMA (Harmonic Oscillator Model of Aromaticity), NICS (Nucleus Independent Chemical Shift) and electronic delocalization indices have been calculated for each outer ring of circulenes. [ABSTRACT FROM AUTHOR]

ABSTRACT The stability and aromaticity of 36 heterobenzenes containing group 15 elements were evaluated at the B3LYP/6-311+G(d,p) level of theory. Stability evaluation was performed based on the enthalpies of formation calculated from imaginary reactions and on the absolute hardness reactivity descriptor. The aromaticity was investigated by means of geometric (Bird, Harmonic Oscillator Model of Aromaticity (HOMA) indices), energetic (aromatic stabilization energy), and magnetic criteria (nucleus-independent chemical shifts [NICS] index). Also, within the conceptual density functional theory (DFT) theory, reactivity-based descriptors (highest occupied molecular orbital and lowest unoccupied molecular orbital [HOMO-LUMO] energy gap, absolute hardness, electrophilicity) were computed. The results led to the conclusion that all heterobenzenes exhibit aromatic character, which generally decreases from N to As containing compounds and from one to six substituted CH groups. [ABSTRACT FROM AUTHOR]

Three aza-phospha-compounds, derivatives of coronenes with N and P atoms in ortho, meta and para positions, were proposed. Their possible aromatic character was evaluated by means of local and global aromaticity indices like HOMA, NICS, PDI and HOMO-LUMO gap. The influence of the heteroatom has been discussed, all the results being compared to the ones obtained for coronene. Graphical representations of the Laplacian of electron density outline the influence of the heteroatoms on the aromaticity of the investigated compounds. [ABSTRACT FROM AUTHOR]

The aromatic character of three different flowers of general formula [ n:( p, p)], namely [8:(5,7)], [8:(6,6)] and [8:(5,6)], has been evaluated by means of geometric (HOMA index), energetic (heats of formation) and magnetic criteria (NICS index, exaltation of magnetic susceptibility). Also, the reactivity descriptors within the DFT approach -absolute hardness, electrophilicity, Fukui functions - have been computed. All the different methods used for estimating the aromaticity led to a unitary conclusion. Two fullerene structures, patched by the most stable 8-Sumanene flower, have been designed and evaluated by means of ab initio computations [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Stability measures, such as the total energy and the HOMO-LUMO gap, calculated at the Hartree-Fock and DFT levels of theory, and the aromatic character of five circulenes/flowers with a hexagonal core and petals consisting of 5-, 6- and 7-membered rings are investigated. Geometric (HOMA) and magnetic (NICS) criteria are used to estimate the local aromatic character of every ring of the investigated circulenes. The local aromaticity of the coronene and sumanene patches in two tetrahedrally spanned fullerenes were calculated and compared with the HOMA and NICS values of the corresponding isolated circulenes. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The paper presents the application of Laplacian matrix and its modifications in the characterization of the chemical graphs associated to chemical structures. The eigenvalues of these matrices and some derived topological descriptors were computed. The alkane series C3 to C9 was used as the benchmark set in the ordering/discriminating analysis as well as in the QSPR with the normal boiling points. [ABSTRACT FROM AUTHOR]

A theoretical study regarding the evaluation of the antioxidant character of three of the most wide-spread anthocyanidins (cyanidin, delphinidin and malvidin) was carried out at ab initio level. Different parameters (bond dissociation enthalpy, ionization potential, proton affinity, and electron transfer enthalpy) were computed for each OH group of the compounds in order to predict their antioxidant capacity. Several molecular descriptors based on frontier molecular orbital theory (hardness, electrophilicity, frontier charge density) were also calculated, as well as the atomic charges corresponding to the O atoms of the hydroxyl groups. [ABSTRACT FROM AUTHOR]

Hydrolysis reaction of 2‐dichloromethylbenzimidazole with aqueous diethylamine was studied both experimentally and theoretically. The behavior of two other aromatic dihalides (dibromomethylbenzene and 2‐fluoro‐dichloromethylbenzene) was also theoretically studied, starting from already known experimental results. The theoretical calculations of local DFT‐based descriptors (i.e., Fukui function, electrophilicity index) successfully account for the different reactivity of the three aromatic dihalides in the same hydrolysis reaction. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

The aromaticity of the heterobenzenes containing 15-group elements, namely the six-membered homocycles (λ³-X)6 (X = CH, N, P, As) and the six-membered alternant heterocycles (λ³-X- λ³-Y)3 (X, Y = CH, N, P, As) is investigated using magnetic and geometric criteria at B3LYP/6-31G (d,p) level. The NMR isotropic shielding values of a molecule of H2 placed at a distance of 2.5Å above the center of the heterobenzenes were computed using the GIAO method at 6-31G(d,p) level. The results are compared with the negative values of the absolute magnetic shielding, computed at the center of ring (NICS index), at B3LYP/6-31G (d,p) level. An angle-based index is used as geometric criterion for the evaluation of the aromatic character. [ABSTRACT FROM AUTHOR]