Protein solubility and the lyotropic series of ions

The surface tension of eight 1 m salt solutions with and without the addition of glycine and of valine have been measured and compared with solubilities of these amino acids. The interfacial tensions between decane and twelve 1 m salt soutions with and without the addition of egg albumin have been determined. A strong correlation exists between the interfacial tension of egg albumin adsorbed on decane and the salt solutions and the salting-out constants of acetyl tetraglycine ethyl ester as measured by D.R. Robinson and W.P. Jencks (1965, J. Amer. Chem. Soc. 87, 2470–2479) It is postulated that the lyotropic series of ions arises because of the effect of the ions on the interfacial tension between water and protein. A method is suggested for the estimation of the interfacial tension existing between protein molecules and water. The work of adhesion between a hydrated protein molecule of molecular weight 40,000 and undissolved hydrated protein is about 0.09 erg/cm 2. The work of adhesion for hemoglobin molecules dissociating into dimers is about 3.1 ergs/cm 2 in the T-state and about 2.4 ergs/cm 2 in the R-state. The meaning of the term hydrophobicity is considered and it is pointed out that it is a misnomer; there exist significant attractive forces between water and hydrocarbon.