  Charge regulation is an important aspect of electrostatics in biological and
colloidal systems, where the charges are generally not fixed, but depend on the
environmental variables. Here, we analyze the charge regulation mechanism in
patchy, inhomogeneously charged spherical particles, such as globular proteins,
colloids, or viruses. Together with the multipole expansion of inhomogeneously
charged spherical surfaces, the charge regulation mechanism on the level of
linear approximation is shown to lead to a mixing between different multipole
moments depending on their capacitance -- the response function of the charge
distribution with respect to the electrostatic potential. This presents an
additional anomalous feature of molecular electrostatics in the presence of
ionic screening. We demonstrate the influence of charge regulation on several
examples of inhomogeneously charged spherical particles, showing that it leads
to significant changes in their multipole moments.
