Limits of the quantum cognition hypothesis: 31P singlet order lifetimes of pyrophosphate from experiment and simulation

Abstract

A proposal of quantum cognition advances the hypothesis that quantum entanglement between 31P nuclei could serve as a means of information storage in the brain. Testing this hypothesis requires an understanding of how long-lived these quantum effects may be. We used NMR spectroscopy and molecular dynamics simulations to study the mechanisms that limit these quantum processes in 18O-enriched molecules of pyrophosphate, the simplest biomolecule that can sustain quantum-entangled 31P nuclear spin singlet states. We confirmed that chemical shift anisotropy limits the singlet magnetization order lifetimes in high magnetic fields, and we discovered that rapid rotation of the phosphate groups limits the lifetime in low magnetic fields. These findings represent an important starting point in studying whether quantum cognition can be a true biological phenomenon.

The Biological Qubit: Calcium Phosphate Dimers, Not Trimers

“…Additionally, the latter study suggests that singlet lifetimes may be reduced further in a more realistic biological environment, and identifies spin-rotation relaxation as the dominant relaxation pathway. 21 While our model neglects spin-rotation relaxation (due to the larger size of the Posner molecule), it will be interesting to see how our results differ after its inclusion. The singlet lifetimes reported in the above studies are of the same order as that of the Posner molecule in the current study and suggest that, without conclusive evidence of the presence of isolated Posner molecules in vivo, the longevity of the singlet state reported in this study is comparable to that found in other phosphorus compounds in vitro.…”

“…Any dipolar coupling with the solvent is expected to average out to zero in the presence of rapid, independent tumbling motion of the molecule. Finally, spin-rotation relaxation, which is thought to be the dominant relaxation mechanism for pyrophosphates, , is neglected here under the assumption that the standard deviation in the angular velocity is expected to be much smaller for the larger Posner molecule. Of all these pathways then, the intermolecular contribution is clearly negligible at reasonable concentrations, and the dominant relaxation is induced by the 15 pairwise intramolecular dipolar nuclear spin couplings, the detailed form of which can be found in the SI.…”

“…It may be possible that coherence is transferred from one pair of 31 P nuclei to the other, but as shown in earlier studies and, to a greater extent, in our SI, this does not increase the singlet probability yield over time in any way. Moreover, recent findings on 31 P– 31 P singlet lifetimes in common organic phosphorus compounds of interest (e.g., adenosine diphosphate, nicotinamide adenine dinucleotide, tetrabenzyle pyrophosphate, pyrophosphate) show that the singlet lifetime ranges from less than half a second in large diphosphates and pyrophosphates to a few tens of seconds in small, highly symmetric pyrophosphates. Additionally, the latter study suggests that singlet lifetimes may be reduced further in a more realistic biological environment, and identifies spin-rotation relaxation as the dominant relaxation pathway .…”

“…Moreover, recent findings on 31 P– 31 P singlet lifetimes in common organic phosphorus compounds of interest (e.g., adenosine diphosphate, nicotinamide adenine dinucleotide, tetrabenzyle pyrophosphate, pyrophosphate) show that the singlet lifetime ranges from less than half a second in large diphosphates and pyrophosphates to a few tens of seconds in small, highly symmetric pyrophosphates. Additionally, the latter study suggests that singlet lifetimes may be reduced further in a more realistic biological environment, and identifies spin-rotation relaxation as the dominant relaxation pathway . While our model neglects spin-rotation relaxation (due to the larger size of the Posner molecule), it will be interesting to see how our results differ after its inclusion.…”