Quantum chemical study of molecular ion complexes with hydrogen bonds (Review)

Institute of Bioorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 6, pp. 157–183, November–December, 1992.     

Charge transfer in DNA: hole charge is confined to a single base pair due to solvation effects

We include solvation effects in tight-binding Hamiltonians for hole states in DNA. The corresponding linear-response parameters are derived from accurate estimates of solvation energy calculated for several hole charge distributions in DNA stacks. Two models are considered: (A) the correction to a diagonal Hamiltonian matrix element depends only on the charge localized on the corresponding site and (B) in addition to this term, the reaction field due to adjacent base pairs is accounted for. We show that both schemes give very similar results. The effects of the polar medium on the hole distribution in DNA are studied. We conclude that the effects of polar surroundings essentially suppress charge delocalization in DNA, and hole states in (GC)(n) sequences are localized on individual guanines.     

Extension of MNDO to d orbitals: Parameters and results for the halogens

A recently proposed extension of the MNDO formalism to d orbitals has been parameterized for the halogens CI, Br, and I. Extensive test calculations indicate slight consistent improvements for normalvalent molecules and dramatic improvements for hypervalent molecules, in comparison with established MNDO -type methods without d orbitals. The mean absolute errors in calculated heats of formation are 3.9 kcal/mol for 155 normalvalent compounds and 2.8 kcal/mol for 23 hypervalent compounds. The predicted structures of the hypervalent molecules are qualitatively correct, with a mean absolute error of 2° in 19 bond angles.     

Use of AM1 and PM3 methods for the investigation of energies and structures of compounds O=PXYZ,S=PXYZ

Novosibirsk Institute for Bioorganic Chemistry, Academy of Sciences of the USSR, Military Section 61469. Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 4, pp. 171–173, July–August, 1990.     

Application of the MNDO method to investigation of properties and reactivity of molecules

Novosibirsk Institute of Bioorganic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 29, No. 1, pp. 138–162, January–February, 1988.     

Quantum-chemical investigation of the mechanism of nucleophilic addition in the HCNO molecule

Calculations by the MNDO, AM1, and MNDO/M methods were undertaken for the reaction of HCNO and CH₃OH. It was shown that the MNDO and AM1 methods overestimate the activation energy of the reaction involving proton transfer, and this leads to an incorrect conclusion about the mechanism of the process. It was concluded that the reaction of the HCNO molecule with nucleophiles takes place in a single stage by a concerted asynchronous mechanism. The product in the Z configuration is formed as a result of the stereospecific reaction.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 6, pp. 719–722, November–December, 1989.     

MNDO calculations of systems with hydrogen bonds S-H

The MNDO method has been modified for the calculation of the properties of complexes with hydrogen bonds S-H-X, X = N, O, F, S. The results obtained are in good agreement with the experimental data.