Vibrational and electronic circular dichroism and absorption spectral study of the DNA–5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin interaction

Abstract

Vibrational circular dichroism (VCD), electronic circular dichroism (ECD) and IR and UV–Vis absorption spectra were measured for complexes of DNA with 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP) at the [DNA]/[TMPyP] ratios 2/1–10/1. The nitrogen base and phosphate spectral regions in IR and the Soret band and DNA regions were studied in UV–Vis. The VCD spectra indicate the priority of intercalation to external minor groove binding and the saturation of the intercalating sites for the [DNA]/[TMPyP]=4/1–5/1. The combination of spectroscopic results proved that all three binding modes, intercalation, minor groove binding and external binding to the phosphate backbone, take place for the ratio 3/1. It was shown that the melting point of the DNA–TMPyP complex is increased compared to pure DNA. The relative temperature stability of minor groove binding is smaller than of intercalation. The AT base-pair hydrogen bonds were disrupted at low pH for DNA–TMPyP complex contrary to pure DNA. Combination of VCD and ECD spectroscopy proved to be effective tool of the conformational study of the DNA–TMPyP complexes and its variations caused by different physico-chemical conditions in solution.