Mechanisms of Oxidation-Reduction Reactions Can Be Predicted by the Magnetic Isotope Effect

Vladimir N Epov

doi:10.1155/2011/450325

Abstract

Magnetic isotope effect can cause mass-independent isotope fractionation, which can be used to predict the mechanisms of chemical reactions. In this critical paper, the isotope fractionation caused by magnetic isotope effect is used to understand detailed mechanisms of oxidation-reduction reactions for some previously published experimental data. Due to the rule that reactions are allowed for certain electron spin state, and forbidden for others, magnetic isotopes show chemical anomalies during these reactions due to the hyperfine interaction of the nuclear spin with the electron spin. It is demonstrated that compound or complex in paramagnetic (triplet) state accepts electrons during the reactions of electron transfer. Also, ligand field strength is responsible for the magnitude and the sign of the mass-independent fractionation. From another side, magnetic isotope effect can be used to predict the ligand strength. According to the proposed mechanism, the following parameters are important for the sign and magnitude of mass-independent isotope fractionation caused by magnetic isotope effect (due to predominant either singlet-triplet or triplet-singlet evolution): (i) the arrangement of the ligands around the metal ion; (ii) the nature (strength) of the ligands surrounding the metal ion; (iii) presence/absence of light. The suggested approach is applied to understand Hg reduction by dissolved organic carbon or by Sn(II).

Highlights

Natural variations in the stable isotope composition of elements have been used by scientists to study different environmental, chemical, and biological processes
According to the nuclear-mass isotope effect, the isotope enrichment factor is proportional to the mass difference of the isotopes leading to Mass-dependent isotope fractionation (MDF), which is directly related to the difference in the nuclear mass among the isotopes of an element
(2) Nuclear magnetic isotope effect (MIE) [11, 12] takes place when nuclear spins and magnetic moments are responsible for isotope separation

Summary

Introduction

Natural variations in the stable isotope composition of elements have been used by scientists to study different environmental, chemical, and biological processes. (2) Nuclear magnetic isotope effect (MIE) [11, 12] takes place when nuclear spins and magnetic moments are responsible for isotope separation This effect is based on the fundamental physical chemistry principle: “chemical reactions are spin selective; they are allowed for those spin states of reagents whose total electron spin is identical to that of products; the reactions are forbidden if they require a change of spin” [13]. In this paper the author proposes the mechanisms of some oxidation-reduction reactions, for which high magnitude of MIF was experimentally detected These mechanisms for few reactions are described below in detail based on MIE electron transfer and type of ligands. This is the second paper describing reaction mechanisms using MIE, as the first one described ligand exchange (or complexation) reactions [14]

Discussions

C O oddHg evenHg Hg

Findings

Conclusions