title: Binding of meso-tetrakis(N-methylpyridinium-4-yl)porphyrin to AT oligomers: effect of chain length and the location of the porphyrin stacking.
abstract: Circular dichroism (CD) spectra of meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) that are associated with various duplex and triplex AT oligomers were investigated in this study. A strong positive CD was apparent for both the TMPyP complexed with duplex d[(A-T)(12)](2), d(A)(12).d(T)(12) and triplex d(A)(12).d[(T)(12)](2) at a low mixing ratio. As the mixing ratio increased, bisignate excitonic CD was produced for TMPyP complexed with duplexes, whereas the positive CD signal remained the same for the TMPyP-d(A)(12).d[(T)(12)](2) complex. This difference in the CD spectrum in the presence of duplex and triplex oligomers indicates that the moderate stacking of TMPyP occurs at the major groove of the duplex and the monomeric binding occurs in (or near) the minor groove. When TMPyP forms a complex with duplex d[(A-T)(6)](2) only excitonic CD was observed, even at a very low mixing ratio. Therefore, at least seven or more basepairs are required for TMPyP to exhibit a monomeric CD spectrum. After close analysis of the CD spectrum, the TMPyP-poly[d(A-T)(2)] complex could be explained by a combination of the CD spectrum of the monomeric, moderately stacked, and extensively stacked TMPyP.
authors.affiliation: Department of Chemistry, Yeungnam University, 214-1 Dae-dong, Kyoungsan City, Kyoung-buk 712-749, Republic of Korea.
authors.forename: Jin-Ok
authors.initials: JO
authors.lastname: Kim
authors.forename: Young-Ae
authors.initials: YA
authors.lastname: Lee
authors.forename: Byeong Hwa
authors.initials: BH
authors.lastname: Yun
authors.forename: Sung Wook
authors.initials: SW
authors.lastname: Han
authors.forename: Sam Tag
authors.initials: ST
authors.lastname: Kwag
authors.forename: Seog K
authors.initials: SK
authors.lastname: Kim
mesh_terms: D020856:AT Rich Sequence; D001483:Base Sequence; D001665:Binding Sites; D002942:Circular Dichroism; D004268:DNA-Binding Proteins / Q000737:chemistry*; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009841:Oligonucleotides / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry*; D011485:Protein Binding; D012996:Solutions; D013329:Structure-Activity Relationship; D014867:Water / Q000737:chemistry*
chemical_list: D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; D009841:Oligonucleotides; D011166:Porphyrins; D012996:Solutions; D014867:Water; C021096:tetra(4-N-methylpyridyl)porphine