Physico-chemical Approach to Biopharmaceutical Phenomena. III. Hydrophobic Bonding in the Adsorption of Tryptophan by Carbon Black from Aqueous Solution

The results obtained as follows were satisfactory enough to demonstrate the hydrophobic bonding mechanism of the adsorption of tryptophan by carbon black from aqueous solution and also the causative role of the hydrophobic moiety of molecule. Calculating the thermodynamic functions of the adsorption by carbon black from aqueous urea solution, the absoulte values of both free energy change and entropy change decreased, as was considered to be originated from the change of property of tryptophan in solution with the addition of urea. That is, the iceberg enclosing the tryptophan molecule in solution was broken down with the addition of urea. Glycine and leucine were negligibly little adsorbed by carbon black from aqueous solution. Phenylalanine was less adsorbed than tryptophan. These results followed the order of hydrophobicity of molecule. The temperature dependence of the adsorption of phenylalanine was usual one, that is, an energy-predominant adsorption took place contrary to the case of tryptophan, while leucylglycylphenylalanine gave the same type of temperature dependence as tryptophan. This means the entropy change of adsorption of phenylalanine was too small to overcome the enthalpy effect.