Enhanced Molecular Diffusivity through Destructive Interference between Electrostatic and Osmotic Forces

Molecular charge asymmetrically distributed in a diffusing tagged particle causes a nonzero electrostatic force balanced by an opposing van der Waals (vdW) force. Fluctuations of electrostatic and vdW forces are highly correlated, and they destructively interfere in the force variance. This phenomenology is caused by the formation of a structurally frozen hydration layer for a particle diffusing in water and is responsible for a substantial speedup of translational diffusion compared to traditional theories of dielectric friction. Diffusion of proteins is insensitive to charge mutations, while smaller particles with asymmetric charge distribution can show a strong dependence of translational and rotational diffusion on molecular charge. Dielectric calculations of the electrostatic force require low values of similar or equal to 5 for the effective dielectric constant of interfacial water to be consistent with simulations.

Automated summary

Asymmetrically distributed molecular charge in diffusing tagged particles leads to a nonzero electrostatic force balanced by opposing van der Waals force, with correlated fluctuations that interfere destructively in force variance. This phenomenon, caused by the formation of a structurally frozen hydration layer, accelerates translational diffusion speed compared to traditional theories. The diffusion of proteins is insensitive to charge mutations, while smaller particles with asymmetric charge distribution show a strong dependence on translational and rotational diffusion based on molecular charge. Dielectric calculations suggest a low effective dielectric constant of interfacial water to be consistent with simulations.