Spectrophotometric Studies on the Proton Transfer from the Protonated DNA to 5,10,15,20-Tetrakis[4-(trimethyammonio)-phenyl]porphine

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Abstract
The interaction of nucleic acids with 5, 10, 15, 20-tetrakis[4-trimethy-ammonio)phenyl]porpine (TAPP) were investigated on the basis of a mechanistic discussion, and a spectrophotometric method for DNAs was accordingly proposed in the present paper. Depending on the acidity of the solution, TAPP can interact with nucleic acids, producing different absorption features. When the pH of the solution is higher than 6.39, TAPP can interact with both DNAs and RNA, giving a new absorption band at 420.3 nm. If the pH is lower than 6.39, however, the interactions with DNAs (but not RNA) can give an absorption band centered at 436.3 nm. It was found that the absorption band at 436.3 nm originates from the proton transfer from the protonated double-stranded structure of DNA to TAPP. At optimal conditions, the absorbance at 436.3 nm is in proportion to the concentration of the DNAs. Calibration curves were linear in the range of 0±3.0 μg.ml−1 for calf thymus and 0±3.2 μg.ml−1 for fish sperm DNA. No interference of 4-fold of RNA was found for the determination of DNAs. The limits of determination (3[sgrave]) were 34.6 ng.ml−1 for calf thymus DNA and 33.2 ng.ml−1 for fish sperm DNA, respectively. Four synthetic samples were determined with satisfaction.