SOLVENT EFFECT ON THE DISSOCIATION-CONSTANTS AND SORET BAND MAXIMA OFHEMATOPORPHYRIN DIACID

Dissociation constants (K-D) and solvatochromic shifts of the Soret ba nds of the dicationic form of hematoporphyrin dichloride measured agai nst the solvatochromic parameters of Taft, Dimroth, Gutmann and Swan. Taft's parameter beta representing solvent capacity of proton acceptan ce from the solutes was accepted as the best cybotactic parameter. Sor et bands of the spectrum undergo blue shifts upon changing nonpolar to polar solvents. The difference in hydrogen bond energy calculated bet ween the pyrrolic proton and Cl- in hexane and isopropanol is 2.8 kcal /mol.