화학공학소재연구정보센터
Journal of Physical Chemistry B, Vol.108, No.44, 17106-17111, 2004
Stacking of meso-tetrakis(3-N-methylpyridiniumyl)porphyrin on poly[d(A-T)(2)]: Importance of the distance between Porphyrin's positive charges
The meso-tetrakis(3-N-tnethylpyridiniumyl)porphyrin (m-TMPyP)-poly[d(A-T)(2)] complex at a [porphyrin]/ [DNA base] ratio of 0.05 was investigated by polarized spectroscopy, including circular and linear dichroism (CD and LD). The spectroscopic properties of the complex depend on the NaCl concentration and time, and can be classified into three types. At a NaCl concentration below 10 mM, a strong bisignate CD spectrum and negative LD spectrum in the Soret band were apparent immediately after mixing. As time lapsed, the spectral properties changed and the complex exhibited a small bisignate CD spectrum and a strong negative LD spectrum. On the other hand, at a NaCl concentration above 10 mM, the bisignate feature of the CD spectrum in the porphyrin absorption region exhibited little change. The LD signal in the DNA absorption region collapsed at this condition, while the CD signal was retained, indicating that DNA remained in the B-form but was compactly aggregated. Surprisingly, a strong positive band in the Soret region was apparent, and its magnitude increased with time. The observed spectral properties for the m-TMPyP-poly [d(A-T)2] complex are in contrast with those of the meso-tetrakis(4-N-methylpyridiniumyl)porphyrin-poly[d(A-T)(2)] complex, which binds at the groove of a polynucleotide at a low NaCl concentration and stacks at a high NaCl concentration. The difference in the binding mode may be attributed to the difference in distance between negatively charged phosphate groups: this distance is variable in the m-TMPyP molecule.