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SynopsisA computer program, based upon the method of Trautman, has been developed to calculate density-gradient proportionality constants, /3O, as a function of density for any salt for which density and activity coefficient data are available. Results are given for twenty 1: 1 electrolytes at 25°C. These salts are the chlorides, bromides, iodides, and nitrates of the five alkali cations. The program is available for use for any other salt and for a variety of temperatures if the necessary data can be found or measured. Between six and eleven centrifuge runs at different densities were performed for each of seven of these salts experimentally to determine Po. In general, the experimental and theoretical values agree within 3% except a t the extremes of density. This demonstrates the validity of the computer program and is the first extensive demonstration that the thermodynamic calculation of density gradients is correct. Five new quadratic relationships between refractive index and density are given.

synopsisThe buoyant density and potentiometric titrations of six ionizable homopolypeptides in concentrated CsCl solutions have been studied. These six homopolypeptides were chosen as models of the behavior of ionizable residues in proteins. Their buoyant and potentiometric results will be of value in interpreting the buoyant and potentiometric results observed for proteins.The buoyant densities for all six homopolypeptides were found to increase sigmoidally as the pH is increased. These density changes are interpreted in terms of changes in the hydrations and ion binding which are associated with the titration of the residues. Preferential hydrations for the homopolypeptides are calculated. The buoyant density titrations are combined with the potentiometric titrations to determine the relationship between the buoyant density and the degree of ionization.The slope of p ( p ) has been computed for CsCl using least-squares curve fitting and this is used in calculating the isoconcentration position. This method has been found to be more accurate than calculating the isoconcentration position from the normalized isoconcentration ratio, which is known only under limited conditions.A better method of computing buoyant densities of proteins is described.