Nuclear spin alignment of sodium ions via electric field gradients in phospholipid membranes

Abstract

The electric field gradient (EFG) has the potential to control both the direction and energy levels of nuclear spins greater than 1/2, a phenomenon known as nuclear electric resonance. Sodium ions on phospholipid membranes, having a nuclear spin of 3/2, can be influenced by surrounding EFGs. Driven by the complex behavior of anisotropic rotation and diffusion of phospholipid molecules, we conducted theoretical investigations and molecular dynamics simulations to study the characteristics of the EFG in this unique environment. Our results demonstrate a tendency for the principal axis of the maximum component of the effective EFG to align orthogonally to the membrane at the position of sodium ions coordinated with phospholipids. This alignment provides a unified precession axis for the nuclear spins of sodium ions, which potentially leads to a consistent definition of quantum information across the membrane. The values of the effective EFG's maximum component suggest energy level gaps of the nuclear spins in the range of tens of kHz, frequencies that have been identified in nerve electromagnetic waves. Consequently, such coherent directionality and energy levels may influence nearby proton and phosphorus nuclear spins, opening the possibility of constructing biological quantum computing systems based on membrane-associated spin interactions and evolutions.