Zwitterions Layer at but Do Not Screen Electrified Interfaces

TL;DR

This study investigates how zwitterions, exemplified by glycine, layer at charged interfaces without screening or altering electrostatic forces, revealing their role in osmotic regulation without affecting surface potentials.

Contribution

It provides experimental evidence that zwitterions do not influence electrostatic surface forces or potentials, highlighting their unique role in osmotic balance without screening effects.

Findings

Zwitterions layer at interfaces but do not alter surface potentials.

Electrostatic forces remain unaffected by zwitterions across studied concentrations.

Zwitterions help extremophiles manage osmotic stress without disrupting electrostatic interactions.

Abstract

The role of ionic electrostatics in colloidal processes is well-understood in natural and applied contexts; however, the electrostatic contribution of zwitterions, known to be present in copious amounts in extremophiles, has not been extensively explored. In response, we studied the effects of glycine as a surrogate zwitterion, ion, and osmolyte on the electrostatic forces between negatively charged mica-mica and silica-silica interfaces. Our results reveal that while zwitterions layer at electrified interfaces and contribute to solutions' osmolality, they do not affect at all the surface potentials, the electrostatic surface forces (magnitude and range), and solutions' conductivity across 0.3-30 mM glycine concentration. We infer that the zwitterionic structure imposes an inseparability among the positive and negative charges and that this inseparability prevents the buildup of a counter charge at interfaces. These elemental experimental results pinpoint how zwitterions enable extremophiles to cope with the osmotic stress without affecting finely tuned electrostatic force balance.