Mechanisms of Hypomagnetic Field Biological Effects: Quantum Rotator Versus Radical Pair.

The radical pair mechanism (RPM) struggles to explain the biological effects of weak magnetic fields due to rapid spin decoherence. To address this, we propose a mechanism based on the quantum dynamics of a sub-nanometric (<0.5 nm) molecular rotator modeling an amino acid residue within a biosynthesizing enzyme. Using the Liouville-von Neumann equation with chemical kinetics and phenomenological decoherence, we show that MF effects arise from modulation of the rotator's quantum interference pattern rather than from spin prohibition. Our results demonstrate that effects reaching several tens of percent occur in very weak magnetic fields (below 50 μT), are relatively robust to decoherence, and that while temperature promotes decoherence, it also enables the formation of a magnetic field-sensitive interference pattern. Under realistic parameters, the angular distribution of the rotator's probability density rotates by several degrees in the geomagnetic field. The rotator mechanism implies that evolution has adapted organisms to use the geomagnetic field for nearly error-free biosynthesis; under hypomagnetic fields, biosynthetic errors increase. Unlike the RPM, this mechanism achieves high sensitivity by operating via magnetic field-induced phase changes rather than magnetic moment energy, thereby circumventing the standard quantum limit. Although tentative and lacking direct experimental evidence, the quantum rotator mechanism provides a biophysically transparent interpretation of hypomagnetic field effects, magnetic storms, and animal magnetic navigation, opening new avenues for research and various applications.