  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.
