The interactions of three different porphyrins, without axial ligands - 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin-Cu(II) tetrachloride (Cu(II)TMPyP), with axial ligands - 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin-Fe(III) pentachloride (Fe(III)TMPyP), and with bulky meso substituents - 5,10,15,20-tetrakis(N,N,N-trimethylanilinium-4-yl)-porphyrin tetrachloride (TMAP), with calf thymus DNA were studied by combination of vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectroscopy, and by IR and UV-VIS absorption spectroscopy. It has been shown that Cu(II)TMPyP prefers the intercalative binding mode with DNA in the GC-rich regions and the intercalative sites are saturated at the c(DNA)/c(Cu(II)TMPyP) ratio ~3:1, where c(DNA) and c(Cu(II)TMPyP) are total molar concentrations of nucleic acid in base pairs and porphyrin, respectively. Fe(III)TMPyP does not intercalate between the GC base pairs but binds to DNA in the minor groove. At higher c(DNA)/c(TMAP) ratios, TMAP interacts with DNA in the minor groove, but at lower ratios in the major groove and by the external binding mode accompanied by self-stacking of porphyrins along the phosphate backbone. VCD spectroscopy reliably discriminates the binding modes and specifies the conformational changes of the DNA matrices. It has been also shown that VCD spectroscopy is an effective tool for the conformational studies of DNA-porphyrin complexes. New spectroscopic "markers" in VCD spectra have been found for the specific DNA-porphyrin interactions.
QM/MM study of the binding of H2 to MoCu CO dehydrogenase: development and applications of improved H2 van der Waals parameters
