[Charge-transfer complexes of hematoporphyrin with pteridine derivatives].

Charge-transfer complexes of hematoporphyrin with pteridine derivatives (folic acid, folinic acid, methotrexate) were studied in solutions buffered at pH 7.5 - 9 -10. The association constants for folic acid are pH dependent; at pH 7.5 the constant is 1240 wheras at pH 10 it is only 65. The association constant for folinic acid was determined only at pH 7.5 and was found to be 55. The association constants of methotexate are approximately the same at different pH's.