Surrey simulations suggest lithium-6 and lithium-7 steer a flavin reaction differently through nuclear spin

An atomic nucleus with spin behaves like a tiny magnet. It can act on nearby electrons strongly enough to change how a chemical reaction turns out ^[3]. Lithium-6 and lithium-7 are chemically almost identical, but their nuclei have different spins ^[4]. In the Surrey simulations, that spin difference was enough for the two isotopes to affect the modelled reaction differently ^[8]. The paper's title names the system: flavin-ascorbyl radical pairs ^[13].

The choice of partner molecules is the part of the design I like best. Flavin is derived from vitamin B2 and helps proteins transfer electrons ^[6]. Vitamin C is abundant in neurons, where it helps protect against oxidative stress, and its radical holds its spin state for relatively long periods ^[7]. A radical that keeps its spin longer gives a weak nuclear magnet more time to influence the reaction ^[7]. The authors picked a molecule neurons hold in quantity, with the property most favourable to a spin effect ^[7].

The model's check against reality was the size of the effect. Its predicted gap between the isotopes was similar to the one derived from earlier animal studies comparing their behavioural effects ^[9]. The release does not give that figure, or explain how a difference in rat behaviour was converted into a quantity comparable with a reaction outcome.

That comparison could have failed. A predicted effect far too small to matter would have ended the idea. Clearing it shows the idea survives on size; it does not show that the animals' behaviour ran through this reaction.

Marco Sacchi, an associate professor of physical and computational chemistry and co-director of the Quantum Biology Centre ^[14], stated the limit plainly. "Our results do not show that quantum spin effects are responsible for lithium's therapeutic action. What they do show is that such a mechanism is physically plausible in a biologically relevant molecular system and can generate an isotope effect of the right order of magnitude," Sacchi said ^[11]. Amina Mouhamed, the University of Surrey PhD researcher who is the paper's first author ^[13], said of the proposed link from nuclei to behaviour: "That possibility remains to be tested experimentally." ^[10]

In my view the study deserves attention because its prediction can be checked in chemistry alone, before any question about patients comes up ^[12]. Mouhamed described the payoff if it holds. "Confirming such a link could open a new avenue for treatment design: fine-tuning how a medicine works by changing its isotopic composition," Mouhamed said ^[15].