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The ability of substituted boranes, X nBH3− n, to form stable complexes with the hydrogen molecule is analyzed by making use of computational chemistry and local reactivity parameters. In these complexes, the hydrogen molecule acts as a Lewis base while the borane moiety is the Lewis acid. Electronegative groups (X = CF3, F, OH) are selected to increase the acidity of the borane and it is found that the energetic stability of the complexes is only increased for the trifluoromethyl-substituted Lewis acids, at the MP2/6-311++g(3df, 3pd) level. It is also found that the BLYP density functional underestimates the adduct stability of these species. On the other hand, fluoroboranes and hydroxyboranes do not form donor-acceptor adducts with the hydrogen molecule; instead, we find weakly bounded van der Waals complexes. Additional features on the intrinsic reactivity of boranes are analyzed with the molecular electrostatic potential and the acceptor Fukui function. The nature of the interaction among the boranes and the hydrogen molecule is explored by using the topological analysis of the electron density through the Bader's Atoms-in-Molecules theory. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Molecular recognition between peptide blockers and ionic channels is a complex process that involves many effects. To determine if the short-range charge transfer effects play a significant role in this interaction, a chemical reactivity analysis of charybdotoxin (ChTX) and six of its mutants was carried out using global and local reactivity indices. The results show that global softness correlates with the affinity of ChTX, and its mutants to the channel indicating that soft-soft interactions play a role in the recognition process between ChTX and a potassium channel. The analysis of the local reactivity indicates that the toxin as a whole can be seen as a complex polydentate ligand with several places to coordinate with the external vestibule of the pore of the potassium channels. The successful treatment of point mutations supports the idea of using this tool in the study of chemical reactivity in proteins, in a similar way as substituent effects in organic chemistry. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

A Koopmans-like approximation is introduced in the spin-polarized version of the Kohn-Sham (KS) density functional theory to obtain a relation between KS orbital energies and vertical ionization potential and electron affinity. Expressions for reactivity indexes (like electronegativity, hardness, electrophilicity, and excitation energies) include KS frontier orbital energies and additional contributions associated with the self-interaction correction. Those reactivity parameters were computed with different exchange-correlation functionals to test the approach for a set of small molecules. The results show that the present approximation provides a better way to estimate hardness, electronegativity, and electrophilicity than just the use of frontier orbital energy values. However KS HOMO and LUMO energy gap gives a better agreement with excitation energies.