  The potential role of spin in biological systems is a primary topic in
quantum biology. However, much of this research focuses on electron spin. A
recent hypothesis suggests that nuclear spin may be better suited to biological
processes, being less sensitive to decoherence. The hypothesis details how
phosphorus nuclei might be prepared in a spin-entangled state, how this
entanglement is protected by assembly into calcium phosphate (Posner)
molecules, and how this entanglement might modulate calcium ion production and
concomitant neural activation. In this paper, we investigate the robustness of
quantum effects such as coherence and entanglement in Posner molecules. We
investigate how these effects are directly dependent on specific parameters
such as spin-spin coupling strengths and Posner molecule symmetry. We also
investigate how lithium isotope-doped Posner molecules differentially modulate
quantum resources such as coherence and entanglement and whether this is a
viable explanation for lithium's mechanism of action in bipolar disease.
Finally, we illustrate how entanglement might possibly be preserved through the
exploitation of the biological environment.
