A quantum protective mechanism in photosynthesis

TL;DR

This paper proposes a quantum-based protective mechanism in photosynthesis where a high-spin iron in photosystem II reduces triplet states via an effective magnetic field, safeguarding organisms from reactive oxygen species.

Contribution

It introduces a novel quantum mechanism involving high-spin iron acting as an effective magnetic field to protect photosynthetic systems from damage.

Findings

The model explains how the iron's spin reduces triplet yield.

The protective effect is robust across realistic parameters.

The mechanism links quantum effects to biological protection.

Abstract

Since the emergence of oxygenic photosynthesis, living systems have developed protective mechanisms against reactive oxygen species. During charge separation in photosynthetic reaction centres, triplet states can react with molecular oxygen generating destructive singlet oxygen. The triplet product yield in bacteria is observed to be reduced by weak magnetic fields. Reaction centres from plants' photosystem II share many features with bacterial reaction centres, including a high-spin iron whose function has remained obscure. To explain observations that the magnetic field effect is reduced by the iron, we propose that its fast-relaxing spin plays a protective role in photosynthesis by generating an effective magnetic field. We consider a simple model of the system, derive an analytical expression for the effective magnetic field and analyse the resulting triplet yield reduction. The protective mechanism is robust for realistic parameter ranges, constituting a clear example of a quantum effect playing a macroscopic role vital for life.