Small but Statistically Reliable Magnetic Field Effect Observed in the Recombination of a Non-Correlated Pair of Biologically Relevant Radicals Nitric Oxide and Superoxide Anion

Abstract

Magnetic and spin effects, well studied in photo- and radiation-generated chemical systems involving spin-correlated radical pairs, are often called upon as possible mechanisms underlying magnetic effects (MFE) in highly complex biological systems. Although several biologically relevant systems do exist for which this had been indeed verified, often the radical pair mechanism is invoked solely based on the presence of radicals, such as nitric oxide, in the system. This logic has three serious problems: the complexity of the real biological systems, the lack of correlation in thus reacting radicals, and their difference from “normal” partners of the spin-correlated pairs. To address all these issues we created a model chemical system of nitric oxide and superoxide radical recombining to produce peroxynitrite, and studied MFE in it.The radicals were produced as a pair via decomposition of 3-morpholinosydnonimine (SIN-1) in aqueous phosphate buffer. MFE was monitored by comparing the efficiency of peroxynitrite production in exposed and otherwise identical control samples with additional temperature controls. We used static magnets with induction 0.5T and 4.7T. No statistically significant effects were found in the field 0.5T and in temperature controls. In magnetic field 4.7T magnetic field effect of (1.8±0.5)% was obtained.The effect is small, as expected for a non-correlated pair, but statistically reliable. It is apparently limited by extremely fast relaxation of nitric oxide in liquid due to unquenched orbital momentum in the diatomic molecule with electronically degenerate ground state, and develops in f-pairs via the Δg mechanism. Any MFE due to radical pair involving nitric oxide in biological system would probably require either rather strong magnetic field in the Tesla range, or some internal enhancer of magnetic field.