Magnetic field affects enzymatic ATP synthesis

The rate of ATP synthesis by creatine kinase extracted from V. xanthia venom was shown to depend on the magnetic field. The yield of ATP produced by enzymes with 24Mg2+ and 26Mg2+ ions in catalytic sites increases by 7-8% at 55 mT and then decreases at 80 mT. For enzyme with 25Mg2+ ion in a catalytic site, the ATP yield increases by 50% and 70% in the fields 55 and 80 mT, respectively. In the Earth field the rate of ATP synthesis by enzyme, in which Mg2+ ion has magnetic nucleus 25Mg, is 2.5 times higher than that by enzymes, in which Mg2+ ion has nonmagnetic, spinless nuclei 24Mg or 26Mg. Both magnetic field effect and magnetic isotope effect demonstrate that the ATP synthesis is an ion-radical process, affected by Zeeman interaction and hyperfine coupling in the intermediate ion-radical pair.     

Decoupling approximations for quantum vibrational predissociation dynamics: The tests on the low-level golden rule approaches for some rare gas—Cl2, ICl complexes

Vibrational and rotational decoupling approximations are tested in three-dimensional Fermi Golden Rule calculations on energies, lifetimes, and product state distributions of the vibrationally predissociating atom—diatom van der Waals complexes. The validity of approximate separations of diatom vibration, decoupling of stretching and bending intermolecular motions, and rotational infinite order sudden approximation for product scattering is characterized by comparison with the results of accurate calculations on the Ne ··· Cl₂, Ne ··· ICl, and He ··· ICl systems. The most accurate approximate schemes are recommended. © 1996 by John Wiley & Sons, Inc.     

An Insight into the Helicase Functioning Through the Hydrogen Isotope Effects

The replacement of hydrogen atoms by deuterium in hydrogen bonds of base pairs AT and GC decreases the rate of unwinding DNA by more than 30% per each unzipped base pair. In active helicases this isotope effect refers to the ratio of the rate constants for unzipping closed base pairs in protiated and deuterated DNA. In passive helicases the effect is controlled by ratio of equilibrium constants for opening and closing base pairs in protiated and deuterated DNA. Hydrogen/deuterium isotope effects on the unwindening of double strand DNA seems to explain, at least partly, biological and pharmacological effects of heavy water on living organisms and may be used as a means to explore new facets of the helicase functioning.     

Chemical bond inside endohedral complexes H@C59B and H@C59P

The geometries, electronic structures, and spin densities on the atoms of paramagnetic heterofullerenes C₅₉X (X = B, P) and their endohedral derivatives H@C₅₉X were obtained from B3LYP/6-31G* density functional calculations. The encapsulated hydrogen atom can form a C-H bond inside the fullerene sphere. The energies of the C-H(endo) bonds are 40–50 kcal mol⁻¹ lower than those of the corresponding exo-bonds. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1239–1243, July, 2007.     

Long-range interaction and the dynamics of nonadiabatic transitions in collisions of the I2(E) molecule with inert gas atoms

A special form of perturbation theory based on intermolecular interaction was used to analyze the contributions to the interaction energy between a homonuclear diatomic molecule with dipole-coupled electronic states n and n′ and a neutral particle A. At large distances, the energy of the system in both states n and n′ is determined by the induction contribution similar to the induction interaction of particle A and a polar molecule. The presence of a constant electric moment of particle A gives an electrostatic contribution to the matrix element of the nonadiabatic coupling of the states n and n′. The equations obtained were specialized to describe the interaction of the iodine molecule excited to ion-pair states with an inert gas atom and used as corrections to the potential energy surfaces of this system constructed within the diatomics-in-molecule approximation. The dynamics of transitions between the ion-pair states of the I₂ molecule induced by collisions with the Ar and He atoms was calculated. The results demonstrate the importance of correctly including long-range interaction.     

Magnetic isotope effect

The electron spin selectivity of radical reactions is accompanied by nuclear spin selectivity, i.e., sorting of the isotopic nuclei relative to their magnetic moment. This property of spin-selective reactions produces separation of magnetic and nonmagnetic isotopes known as the magnetic isotope effect. The chemical physics of this phenomenon is examined along with the conditions and magnitude of its manifestation as well as the prospects for its use in theoretical and experimental chemistry.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 31, No. 3, pp. 144–152, May–June, 1995.