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Highly accurate electron affinities and ionization potentials of chemical systems were described by means of the procedure called GHV-EOM (Valdemoro et al, in Int J Quantum Chem 112:2965, 2012), which combines the G-particle-hole hypervirial (GHV) equation method (Alcoba et al, in Int J Quantum Chem 109:3178, 2009) and that of the equations-of-motion (EOM), by Simons and Smith (Simons and Smith, in J Chem Phys 58:4899, 1973). The present work improves that hybrid method by introducing the point group symmetry within its framework, providing a higher computational efficiency. We report results which show the achievements attained by using the symmetry-adapted methodology. The new formulation turns out to be particularly suitable for characterizing solid models, as cyclic one-dimensional chains. [ABSTRACT FROM AUTHOR]

Herein the performance of a modification within the hybrid algorithm implemented in the AUTOMATON program is introduced and evaluated. For the creation of the initial population, AUTOMATON combines a probabilistic automata procedure with a genetic algorithm used to evolve this population. The proposed modification is addressed to efficiently identify the minimum energy structures of systems composed of more than one type of atom and with a low computational cost. The effectiveness of this approach is evaluated in the determination of the minimum energy structures of Be6B11−. The modification, aimed to explore the potential energy surface, consisted of filling the cells first with Be atoms in the process of creating the initial population. This order obeys the structural pattern established in the Be–B clusters reported to date. The results show that this variation not only identifies a more significant number of viable isomers but also to find a better putative global minimum than those previously reported in the literature. Therefore, it is recommended to be used as a complement to the standard searching process. [ABSTRACT FROM AUTHOR]

The nature of the chemical bonds in the EC3+, EC4+, EC5+, and EC6+ species (E = Sc, Y and La) has been examined in depth using a combination of different theoretical strategies. Firstly, exhaustive explorations of the relevant potential energy surfaces using a combination of stochastic and gradient-based search procedures provide us with fan-like structures in singlet and triplet spin states as the most energetically stable configurations. Secondly, the chemical bonding analysis, using natural bond orbital theory, energy decomposition analysis, quantum theory of atoms in molecules, and the adaptive natural density partitioning analysis, indicate that metal–carbon interaction in these species is best described as an intermediate point between ionic and covalent. [ABSTRACT FROM AUTHOR]

A series of small planar boron clusters has extensively been studied in the past using different theoretical approximations, and their chemical bonding has been rationalized in terms of aromaticity, antiaromaticity and conflicting aromaticity. Here, we study these systems by means of our recently proposed orbital localization procedure based on the partitioning of the space according to the electron localization function (ELF) topology. The results are compared with those obtained from the adaptive natural density partitioning (AdNDP) method, which is a most extensively tested orbital localization procedure. Minor discrepancies have been found, especially in large clusters. In those cases, an alternative set of localized AdNDP orbitals recovered the representation obtained by ELF localization procedure. These results support the need for multicenter bonding incorporation into the localization models for rationalizing chemical bonding in atomic clusters. Additionally, the aromatic character of the clusters, when it is present, is adequately supported by the more classical treatment based on the ELF topological analysis. [ABSTRACT FROM AUTHOR]

The stronger antioxidant capacity of the flavonoid quercetin (Q) compared with taxifolin (dihydroquercetin, T) has been the subject of previous experimental and theoretical studies. Theoretical work has focused on the analysis of hydrogen bond dissociation energies (BDE) of the OH phenolic groups, but consider mechanisms that only involve the transfer of one hydrogen atom. In the present work we consider other mechanisms involving a second hydrogen transfer in reactions with free radicals. The relative stability of the radicals formed after the first hydrogen transfer reaction is considered in discussing the antioxidant activity of Q and T. In terms of global and local theoretical reactivity descriptors, we propose that the radical arising from Q should be more persistent in the environment and with the capability to react with a second radical by hydrogen transfer, proton transfer and electron transfer mechanisms. These mechanisms could be responsible of the stronger antioxidant capacity of Q. [ABSTRACT FROM AUTHOR]

Quantum chemical calculations were used to analyze the chemical bonding and the reactivity of phosphorus oxides (PO (n = 0-4)). The chemical bonding was studied using topological analysis such as atoms in molecules (AIM), electron localization function (ELF), and the reactivity using the Fukui function. A classification of the P-O bonds formed in all structures was done according to the coordination number in each P and O atoms. It was found that there are five P-O bond types and these are distributed among the five phosphorus oxides structures. Results showed that there is good agreement among the evaluated properties (length, bond order, density at the critical point, and disynaptic population) and each P-O bond type. It was found that regardless of the structure in which a P-O bond type is present the topological and geometric properties do not have a significant variation. The topological parameters electron density and Laplacian of electron density show excellent linear correlation with the average length of P-O bond in each bond type for each structure. From the Fukui function analysis it was possible to predict that from PO until PO the most reactive regions are basins over the P. [ABSTRACT FROM AUTHOR]

We have performed docking of imidazo[1,2-a]pyrazines complexed with checkpoint kinase1 (Chk1) to better understand the structural requirements and preferred conformations of these inhibitors. The study was performed on a selected set of 33 compounds with variation in structure and activity. In addition, the predicted inhibitor concentrations (IC) of the imidazo[1,2-a]pyrazines as Chk1 inhibitors were obtained by comparative molecular similarity analysis (CoMSIA). The best CoMSIA model included electrostatic and hydrophobic fields, had a good Q value of 0.589, and adequately predicted the compounds contained in the test set. Furthermore, plots of the CoMSIA fields allowed conclusions to be drawn for the selection of suitable inhibitors. [ABSTRACT FROM AUTHOR]