AFM-correlated CSM-coupled Raman and fluorescence properties of water-soluble oxo-titanium (IV) porphyrin bound with DNA

Abstract

The Raman and fluorescence spectroscopic properties of water-soluble oxo-titanium (IV) meso-tetrakis (1-methyl pyridium-4-yl) porphyrin (O=Ti(TMPyP)(4+)) bound with calf thymus DNA and artificial DNAs such as double stranded poly[d(A-T)(2)] and poly[d(G-C)(2)] have been investigated on the single DNA molecule basis by atomic force microscopy (AFM)-correlated confocal scanning microscope (CSM)-coupled Raman and fluorescence spectroscopic techniques as well as the ensemble-averaged spectroscopy. The ensemble-averaged spectroscopic studies imply that the porphyrin interacts with DNA in different groove binding patterns depending on the base pairs. AFM-images of the different DNAs bound with O=Ti(TMPyP)(4+) were measured, and their morphologies are found to depend on kind of base pairs interacting with O=Ti(TMPyP)(4+). Being correlated with the AFM images, the CSM-coupled Raman and fluorescence spectral properties of the three different single O=Ti(TMPyP)(4+)-DNA complexes were observed to be highly resolved and sensitive to base pair-dependent axial ligation of Ti-O bond as compared to the corresponding ensemble-averaged spectral properties, which affect the groove binding and its strength of the O=Ti(TMPyP)(4+) with DNA. The axial ligation was found to be accompanied by vibration structural change of the porphyrin ring. leading to keep the shape of double stranded poly[d(A-T)(2)] rigid while poly[d(G-C)(2)] and calf thymus DNA flexible after binding with the oxo-titanyl porphyrin. The base pair dependence of the fluorescence decay times of the DNA-bound porphyrins was also observed, implying that an excited-state charge transfer takes place in the G-C rich major groove in calf thymus DNA. These results suggest that binding of O=Ti(TMPyP)(4+) is more preferential with the G-C rich major groove than with the A-T rich minor groove in calf thymus DNA so that the morphology of DNA is changed. (C) 2009 Elsevier B.V. All rights reserved.