Theory of Solutions of Molecules Containing Widely Separated Charges with Special Application to Zwitterions

The electrical contribution to the chemical potential of an ion having an arbitrary charge distribution is calculated with the aid of the Debye-Hückel theory. The calculation is based upon a general solution in polar coordinates of the approximate Debye-Hückel equation, Δψ—κ2ψ=0. In addition, the Born relation between the free energy of solvation of a spherical ion and the dielectric constant of the solvent, is generalized to include ions of arbitrary charge distribution. Application of the theory to a study of the influence of simple electrolytes, and of the dielectric constant of the solvent on the solubilities of the aliphatic amino-acids in alcohol water mixtures, is discussed.