Studies on the physical state of water in living cells and model systems. X. The dependence of the equilibrium distribution coefficient of a solute in polarized water on the molecular weights of the solute: experimental confirmation of the "size rule" in model studies.

The equilibrium distribution of 14 sugars, sugar alcohols, and other nonelectrolytes in solutions of polyethylene oxide (PEO) and of native and alkali-denatured bovine hemoglobin were studied over wide concentration ranges. The results show that the equilibrium concentrations of all the solutes studies are rectilinearly related to their external concentrations. This straight-line relationship demonstrates the existence of these solutes entirely or almost entirely in the aqueous phase of these systems. Therefore the slope of each of these straight lines equals the equilibrium distribution coefficient or q-value of the solute involved. In general, the q-values decrease with increasing molecule weights (M.W.) of the solutes in 15% solutions of PEO, 20% solutions of alkali-denatured hemoglobin (and in 18% gelatin) but not in 39% solution of native hemoglobin. In solutions of PEO, of alkali-denatured hemoglobin studied (and of gelatin) a fraction of the water (20% to 30%) appears to have solvency similar to that of normal liquid water. The experimental findings of M.W.-dependent solute exclusion were discussed in the light of four alternative theories that have been offered to explain this type of phenomena. Among these four theories only the polarized multilayer theory agrees with most, if not all the facts known.