Binding Mode of Cationic Porphyrin with CT-DNA: Importanceof the Location and the Number of Positively Charged of PeripheryCationic Ions of Porphyrin

摘要

The binding modes of o-, m-, and p-trans-BMPyP with DNA were studied using their spectroscopic properties. Also, the binding modes were compared based on the location and number of periphery cationic methylpyridine ions of the cationic porphyrins. The optical absorption spectra of the o-, m-, and p-trans-BMPyP when bound to DNA presented red shifts and hypochromicity compared to the optical absorption spectrum of DNA-free cationic porphyrins. m-trans-BMPyP–DNA presented the largest red shifts and hypochromicity. The results of the circular dichroism spectral analysis indicated positive and negative bisignate absorption bands in the Soret band of the porphyrins in the case of all concentration ratios of o- and p-trans-BMPyP–DNA, and two negative absorption bands were observed in m-trans-BMPyP–DNA. Compared to the size of the absorption band of the DNA optical absorption spectrum, the results of the reduced linear (LD^r) spectral analysis indicated mainly small sizes of Soret absorption bands (the absorption spectrum of porphyrins) and positive LD^r values for o- and p-trans-BMPyP–DNA.In consideration of several of such spectroscopic properties, thebinding of o- and p-trans-BMPyP with DNA can be said to be distant to insertion modes. Althoughthe case of m-trans-BMPyP to DNAis an insertion mode, the m-trans-BMPyP molecular surface presented much tilt within the intercalationpocket. The results of comparing the binding modes of TMPyP havingfour periphery cationic methylpyridine ions of cationic porphyrinindicated that regardless of the number of periphery cationic methylpyridineions of cationic porphyrin, in the case of the ortho-position, nonplanaritydue to steric hindrance of the periphery cationic methylpyridine ionspresented outside or groove-binding modes indicative of interactionwith DNA phosphates. Unlike the ortho-position, the para-positionpresented different binding modes based on the number of peripherycationic methylpyridine ions. Only cationic porphyrins having fourperiphery cationic methylpyridine ions were inserted into the DNA.Lastly, regardless of the number of periphery cationic methylpyridineions, all meta-positions were inserted into the DNA. This indicatedthat at the least the location and the number of periphery cationicmethylpyridine ions of the porphyrins used in this experiment wereimportant elements that determine insertion into DNA base pairs.