The interactions of poly-L-glutamic acid and a cationic porphyrin derivative in aqueous solutions were studied by the combination of vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectroscopies. It was found that non-covalent interactions between both agents influence the structure of the polymeric matrix and the guest porphyrins and vice versa, but the physico-chemical properties of the solutions, especially the pH and the relative permittivity of the solvent, play a key role in the structure of the polypeptide part of the formed complexes. It was shown that the interaction with porphyrins prevents the precipitation of poly-L-glutamic acid in aqueous solution at acidic pH. In special conditions, the porphyrins attached to the polypeptide probably possess face-to-face interaction as demonstrated by the enhancement of the characteristic ECD signal and the appearance of sidebands on its short and long wavelength sides.

Department of Analytical Chemistry Institute of Chemical Technology Technická 5 166 28 Praha 6 Czech Republic

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Three Conformations of Polyglutamic Acid Monitored by Vibrational Optical Activity