Magnetic Biological Effect: Quantum Constraints

The spin-chemical mechanism of radical pairs is considered today as the most probable molecular mechanism explaining the observed biological effects of weak magnetic fields. The magnitude of these effects depends on the spin relaxation rate, but no explicit functional dependence has been proposed. In this paper, an analytical solution of the Liouville–Neumann equation for a system of two electrons and a nucleus is found, taking into account spin relaxation and chemical kinetics. A relationship is obtained that relates the magnitude of the magnetic effect to the rate of relaxation due to thermal disturbances. The effect obeys a general quantum constraint. At plausible relaxation rates, the calculated effects are small and cannot explain the observations. It can be concluded that today, despite the attractiveness of the radical pair mechanism and the increased theoretical understanding, the problem of magnetobiology still does not have a conceptual solution free from contradictions.