Magnetic Field Effect on the Oxidation of Unsaturated Compounds by Molecular Oxygen

A quantum-chemical analysis of the effect of a constant magnetic field on radical formation in the processes of chain oxidation of organic compounds by molecular oxygen is presented. The calculation of the total electronic energies and thermodynamic functions of the compounds involved in the reactions was performed by the density functional method with the hybrid exchange-correlation functional of Becke, Lee, Yang and Parr DFT B3LYP/6-311G** using the NWChem software package. The effect of the magnetic field on the individual stages of chain oxidation is associated with the evolution of radical pairs. It is assumed that the dipole–dipole interaction in a radical pair is not averaged by the diffusion of radicals and should be taken into account. To a large extent, the magnetic field effect (MFE) value is influenced by the ratio between the relaxation time of the oscillatory-excited state in the radical pair (tvib) and the relaxation time of the inter-combination transitions (tst). Although the developed technique refers to liquid-phase reactions, it can be used to study the MFE for oxidation of biologically significant compounds in multiphase systems, such as micelles, liposomes and membranes.

Dynamics of polystyrene probed by muon spin spectroscopy

Muon spin spectroscopic measurements were made on atactic low-molecular-weight (LMW) (1.3 kg mol^-1) and high-molecular-weight (HMW) (202 kg mol^-1) polystyrene. Muoniated cyclohexadienyl radicals, which are formed by muonium addition to the phenyl side groups, are used as local probes of bulk dynamics. Muon spin relaxation is caused by the secondary γ-relaxation process, which involves motion of the phenyl rings, and is sensitive to the glass transition. The activation energy of the γ-relaxation process in the rubbery state is 0.60(2) eV in the HMW sample and 0.37(3) eV in the LMW sample.