Circular dichroism spectroscopic study of non-covalent interactions of poly-L-glutamic acid with a porphyrin derivative in aqueous solutions

Abstract

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.

Investigation of Guanosine‐Quartet Assemblies by Vibrational and Electronic Circular Dichroism Spectroscopy, a Novel Approach for Studying Supramolecular Entities

“…Thus, VCD give structural information on chiral molecules that is not easily obtainable by other nonchiroptical techniques. Some of us have been developing VCD not only to study noncovalent interactions of biologically interesting molecules, [38][39][40][41][42][43] but also to extend its applicability to the field of supramolecular chemistry. [44][45][46] Experimental Section Materials: Guanosine-5'-hydrazide (G-1) was synthesized and characterized as described previously.…”

Bioinspired interactions studied by vibrational circular dichroism

“…At a concentration about 10 times higher needed for VCD measurements, the addition of methanol or dioxan is necessary to prevent precipitation at acidic pH. It was shown 65 that in the ternary system consisting of poly(L-glutamic acid), TPPS, and TATP, the interaction prevents the precipitation of poly(L-glutamic acid) at acidic pH, and the VCD spectrum in the amide I region can be simulated by the mixture of a-helical and PPII structures of polypeptide part of complex (Fig. 14).…”

“…63,64 Interactions with the cationic porphyrins meso-tetrakis(1-methyl-4-pyridyl)porphin tetra-p-tosylate (TMPyP) and meso-tetrakis(a-trimethyl-ammonio-p-tolyl)porphine (TATP) was studied using poly(L-glutamic acid). 64,65 VCD can provide quite detailed information on the peptidic part of the complexes, while the porphyrin segment is more profitably observed using spectroscopies in the visible region. The interaction with porphyrins changed the spatial structure of matrices depending on the length of the polypeptide chain, as is evident from Figs.…”

Chiral memory and self-replication study of porphyrin and bilirubin aggregates formed on polypeptide matrices

“…The complex of polyglutamic acid and CuT4 has been well described [2,4,5,7] through the application of electronic circular dichroism (ECD) spectroscopy. At low pH, when the polyglutamic chain adopts an α-helical conformation, induced circular dichroism (ICD) in the form of a characteristic doublet in the Soret region is observed, indicating that CuT4 interacts with the polyglutamic matrix and creates a chiral architecture.…”