Electrostatic repulsion, averaged charge

Average configuration-dependent physical properties are evaluated for tri- tetra-, and hexafunctional polyethylene stars perturbed by electrostatic repulsion of charges placed at the free chain ends. Configuration-dependent properties evaluated are the probability for a trarts placement, expansion of , the mean-square radius of gyration, asymmetry of the distribution of the chain atoms, and asymmetry of the distribution described by the atoms considered to bear the charges. 

The slope and intercept from plots of pH versus log(a/l-a) were made from the modified Henderson-Hasselbalch equation . The n value, which is the slope of the line, is a measure of the average electrostatic repulsion between charges on the chain. 

Recently Tanford and his collaborators have made use of the electrostatic term w to analyze the titration curves of a number of proteins. By combining graphical methods and trial-and-error selection they obtained values of p(Kint) and w from experimental titration curves. In each case the value for the apparent average net charge was corrected for the binding of anions and cations as determined by independent experimental methods. Differences between their experimental values of w and those calculated from theory were interpreted by these workers in terms of alterations in molecular parameters or structure. For example, observed values which were low, especially when they became low only at pH s far removed from neutrality, were attributed to alteration in the size or shape of the molecule brought about by electrostatic repulsion. Thus, with human serum albumin Tanford (1950) found that although the basic branch of the titration curve could be computed from theory, the acid branch was much too steep... 

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