Interaction between meso-tetrakis(N-methylpyridinyl)porphyrin (TMPyP) and single strand DNA homopolymers, (dA)40, (dT)40, (dG)40 and (dC)40, has been investigated using absorption, fluorescence and circular dichroism (CD) measurements. Fluorescence intensity of TMPyP is quenched in the presence of (dG)40 due to photo-induced electron transfer from dG to the excited TMPyP dye. Changes in the CD spectra of the polynucleotides in the presence of TMPyP are found to be quite different and depend on the nature of the nucleotide bases, whether purine or pyrimidine. Excitonic induced CD spectra is observed for TMPyP in the presence of pyrimidine homopolymers while negative induced CD is observed in the presence of purine homopolymers. Based on photophysical studies and CD spectra, we propose multiple binding modes of TMPyP with polynucleotides. TMPyP can bind to oligonucleotides both in monomer form as well as in the form of short stretches of stacked aggregates along the oligonucleotide backbone.
Volume 135, 2023
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