Raman spectroscopic studies on interactions of water soluble cationic oxovanadyl (IV) meso-tetrakis(1-methylpyridium-4-y1) porphyrin with nucleic acids

Raman spectroscopic studies on interactions of water soluble cationic oxovanadyl (IV) meso-tetrakis(1-methylpyridium-4-y1) porphyrin with nucleic acids

  Interactions of water soluble cationic oxovanadyl (IV) meso-tetrakis(1-methylpyridium-4-yl)porphyrin (OV<SUP>IV</SUP>(TMPyP)⁴？) with double stranded poly[d(A-T)₂], poly[d(G-C)₂] nucleotides and calf thymus DNA were studied by the Raman spectroscopic techniques as well as the polarization spectroscopic measurements. The ground state Raman bands of OV<SUP>IV</SUP>(TMPyP)⁴？ observed in the presence of poly[d(A-T)₂] were almost the same as those observed in a pure water solution except the slightly up-shifted Raman band (963㎝？¹) which is ascribed to the V-O stretching mode of six-coordinated complex, OV<SUP>IV</SUP>(H₂O)(TMPyP)⁴？. On the other hand, in the presence of poly[d(G-C)₂], a markedly up-shifted Raman band was observed at 992㎝？¹, indicating that OV<SUP>IV</SUP>(TMPyP)⁴？ interacts with poly[d(G-C)₂] by losing the sixth axial ligand. In the presence of calf thymus DNA, the V-O stretching band was observed to be resulted by combination of those observed in poly[d(A-T)₂] and poly[d(G-C)₂]. The polarization spectroscopic studies with these results imply that OV<SUP>IV</SUP>(TMPyP)⁴？ interacts with DNA in different groove binding patterns originated from the formation of five-coordinated adducts in the G-C pair-rich regions and six-coordinated adducts in the A-T pair-rich regions. The down-shifts of core-size sensitive transient Raman bands (v₂ and v₄ modes) in the presence of nucleic acids illustrate an increase of the core-size of porphyrin macrocycle in the excited triplet state. The transient Raman bands related to pyridine group were observed, and they are interpreted to be due to the excited-state charge transfer from porphyrin ring to peripheral substituents.   ？ 2005 Elsevier B. V. All rights reserved.