Binding modes of V(=O)meso-tetrakis(N-methylpyridinium-4-yl)porphyrin to various synthetic DNAs studied by polarized spectroscopy.
The interactions between water-soluble cationic oxovanadyl[meso-tetrakis(4-N-methylpyridiumyl)]porphyrin (VOTMPyP) and various synthetic polynucleotide including poly[d(A-T)2], poly[d(G-C)2], and poly[d(I-C)2] were studied using absorption, circular dichroism (CD), and linear dichroism (LD) spectroscopy. When VOTMPyP formed a complex with poly[d(A-T)2] and poly[d(I-C)2], a positive CD signal at low [VOTMPyP]/[DNA] ratios (R ratios) and strong excitonic CD signals at above R > or = 0.15 were induced. The appearance of the CD spectra of the VOTMPyP-poly[d(G-C)2] complex were very different: a small negative CD at low R ratios and very small excitonic CD at high R ratios were observed. Considering the facts that the minor grooves of the former two polynucleotides resemble and the major groove of poly[d(I-C)2] is similar with that of poly[d(G-C)2], it is conclusive that VOTMPyP binds to the minor groove of all DNA at lower R ratios while they stack at the outside of DNA at higher R ratios. The binding geometry of VOTMPyP to all polynucleotides studied by LD seemed to be homogenous, irrespective of the R ratio. It has been found that VOTMPyP can have five- and six-fluxional coordination states. Comparing the absorption spectra of VOTMPyP complexed with poly[d(A-T)2] and poly[d(G-C)2], the distinctive absorptions of the five- and six-coordinated species were observed at lower R ratios which centered at 420-430 nm and 442 nm, respectively. While the six-coordinated VOTMPyP favored the poly[d(A-T)2], the five-coordinated species favored the poly[d(G-C)2] at the low R ratios. As the stacked species increased with an increasing R ratio, the six-coordinated species became the major bound species. These observations lead us to conclude that the guanine base' amino group plays a crucial role not only in determining the binding mode of VOTMPyP but also in the conversion of the six-coordinated species to the five-coordinated species.
Park
Tae Gi
TG
Department of Chemistry, Yeungnam University, Dae-dong, Kyoungsan City, Kyoung-buk 712-749, Republic of Korea.
Ko
Jae Hong
JH
Ryoo
Ah Young
AY
Kim
Jong-Moon
JM
Cho
Dae Won
DW
Kim
Seog K
SK
D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry*; D008665:Metalloporphyrins / Q000737:chemistry*; D011067:Poly dA-dT / Q000737:chemistry; D011089:Polydeoxyribonucleotides / Q000737:chemistry*; D013053:Spectrophotometry; D013056:Spectrophotometry, Ultraviolet
D008665:Metalloporphyrins; D011089:Polydeoxyribonucleotides; C510094:oxovanadyl(meso-tetrakis(4-N-methylpyridiumyl))porphyrin; C031156:poly d(I-C); D011067:Poly dA-dT; C019530:poly(dC-dG); D004247:DNA