Theoretical Approaches for Understanding the Interplay Between Stress and Chemical Reactivity.

The use of mechanical stresses to induce chemical reactions has attracted significant interest in recent years. Computational modeling can play a significant role in developing a comprehensive understanding of the interplay between stresses and chemical reactivity. In this review, we discuss techniques for simulating chemical reactions occurring under mechanochemical conditions.

Dramatic substituent effects on the mechanisms of nucleophilic attack on Se-S bridges.

The reactions of XSeSX, XSeSY, and YSeSX (X, Y = CH3, NH2, OH, F) with F(-) and CN(-) nucleophiles have been investigated by means of B3PW91/6-311+G(2df,p) and G4 calculations. In systems where the two substituents are not identical (XSeSY), the more stable of the two possible isomers corresponds to those in which the most electronegative substituent is attached to Se. Nucleophilic attack takes place at Se, independent of the nature of the nucleophile, with the only exception being XSeSF (X = CH3 , NH2 , OH), in which case the attack occurs at S.

Revealing unexpected mechanisms for nucleophilic attack on S-S and Se-Se bridges.

The reactivity of disulfide and diselenide derivatives towards F(-) and CN(-) nucleophiles has been investigated by means of B3PW91/6-311+G(2df,p) calculations. This theoretical survey shows that these processes, in contrast with the generally accepted view of disulfide and diselenide linkages, do not always lead to SS or SeSe bond cleavage. In fact, SS or SeSe bond fission is the most favorable process only when the substituents attached to the S or the Se atoms are not very electronegative.

Mechanism of the Reduction of an Oxidized Glutathione Peroxidase Mimic with Thiols.

N,N-dimethylbenzylamine-2-selenol is a well-known, efficient glutathione peroxidase mimic. This compound reduces peroxides through a three-step catalytic mechanism, of which the first step has been well-characterized computationally. The mechanism for the reaction of N,N-dimethylbenzylamine-2-selenenic acid with a thiol, the second step in the catalytic cycle, is studied using reliable electronic structure techniques.

Substituent-controlled reactivity in the Nazarov cyclisation of allenyl vinyl ketones.

Alkyl substitution α to the ketone of an allenyl vinyl ketone enhances Nazarov reactivity by inhibiting alternative pathways involving the allene moiety and through electron donation and/or steric hindrance. This substitution pattern also accelerates Nazarov cyclisation by increasing the population of the reactive conformer and by stabilising the oxyallyl cation intermediate. Furthermore, α substitution by an alkyl group does not alter the regioselectivity of interrupted Nazarov reactions when the oxyallyl cation intermediate is intercepted by addition of an oxygen nucleophile, or by [4+3] cyclisation with acyclic dienes.

Systematic study of the performance of density functional theory methods for prediction of energies and geometries of organoselenium compounds.

A variety of density functional theory (DFT) methods are paired with Pople basis sets of varying sizes and evaluated for use with organoselenium compounds. The ability of each method to predict reliable geometries and energies is determined through comparison with quadratic configuration interaction with single and double excitations (QCISD) results. The recommended procedure for accurate prediction of energies and geometries is to use the B3PW91 functional with the 6-311G(2df,p) basis set.

Theoretical investigations on the reaction of monosubstituted tertiary-benzylamine selenols with hydrogen peroxide.

The effects of introducing electron-donating (NH(2), OCH(3), CH(3)) and electron-withdrawing (NO(2), CF(3), CN, F) groups to N,N-dimethylbenzylamine-2-selenol are studied to determine the effect of the selenium electron density on the efficiency of the reduction of hydrogen peroxide. Introducing substituents in the meta and para positions decreases or increases the energy barrier of the reaction in the expected way, due to changes in the electronic environment of the reacting selenium center. Ortho substituents are found to have a greater effect on the electronic environment of the selenium center, which is mitigated by changing the steric environment.

Reduction of hydrogen peroxide by glutathione peroxidase mimics: reaction mechanism and energetics.

The reaction mechanism for the reduction of hydrogen peroxide by N,N-dimethylbenzylamine diselenide, its selenol analogue, and the charged analogues of the diselenide and selenol are elucidated using reliable electronic structure techniques. It is found that the reaction using the diselenide has a large Gibbs energy barrier of 173.5 kJ/mol.