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

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.