  In this article, I summarize my theoretical developments in the statistical
field theory of salt solutions of zwitterionic and multipolar molecules. Based
on the Hubbard-Stratonovich integral transformation, I represent configuration
integrals of dilute salt solutions of zwitterionic and multipolar molecules in
the form of functional integrals over the space-dependent fluctuating
electrostatic potential. In the mean-field approximation, for both cases, I
derive integro-differential self-consistent field equations for the
electrostatic potential, generated by the external charges in solutions media,
which generalize the classical Poisson-Boltzmann equation. I derive for the
both cases a general expression for the electrostatic potential of a point-like
test ion, expressed through certain screening functions. I derive an analytical
expression for the electrostatic potential of the point-like test ion in a salt
zwitterionic solution, generalizing the well known Debye-Hueckel potential. In
the salt-free solution case, I obtain analytical expressions for the local
dielectric permittivity around the point-like test ion and its effective
solvation radius. For the case of salt solutions of multipolar molecules, I
find a new oscillating behavior of the electrostatic field potential of the
point-like test ion at long distances. I obtain a general expression for the
average quadrupolar length of a multipolar solute. Using the random phase
approximation (RPA), I derive general expressions for the excess free energy of
bulk salt solutions of zwitterionic and multipolar molecules and analyze the
limiting regimes resulting from them. I generalize the salt zwitterionic
solution theory for the case when several kinds of zwitterions are dissolved in
the solution. In this case, within the RPA, I obtain a general expression for
the solvation energy of the test zwitterion.
