EFFECT OF IONIC-STRENGTH ON THE PROTONATION OF VARIOUS AMINO-ACIDS ANALYZED BY THE MEAN SPHERICAL APPROXIMATION

The dependence of the ionic strength of stoichiometric protonation con stants, obtained potentiometrically, of several amino acids has been a nalysed by the mean spherical approximation (MSA), a mathematically si mple statistical mechanical treatment based on integral equations. Unl ike the Debye-Huckel equation, which overestimates the effects of ion- ion interactions as the sizes of all ions are neglected, the MSA repre sents the electrolytes as a mixture of hard spheres immersed in a diel ectric continuum which represents the solvent. This approach fits expe rimental data using concentration, electrical charge and diameter conc epts and is an alternative to semiempirical models based on different ionic strengths with coefficients that defy theoretical interpretation . Analysis of data using both semiempirical models and a quasi-lattice model, not containing Debye-Huckel terms, is also included.