Determination of nucleic acids by a resonance light-scattering technique with alpha, beta, gamma, delta-tetrakis[4-(trimethylammoniumyl)phenyl]porphine.

The resonance light-scattering technique, using a spectrofluorometer, was first developed as a sensitive instrumental analysis method. At pH 7.48 and ionic strength 0.004, the extent of light-scattering of alpha, beta, gamma, delta-tetrakis[4-(trimethylammoniumyl)phenyl]porphine (TAPP) is enhanced by nucleic acids near 432 nm. There are linear relationships between the enhanced extents of light-scattering and the concentrations of nucleic acids in the range of 1.8 x 10(-7)-10.8 x 10(-7) M for calf thymus and fish sperm DNA and in the range of 1.8 x 10(-7)-1.8 x 10(-6) M for yeast RNA. The limit of determination (3 sigma) is 4.1 x 10(-8) M for calf thymus DNA, 4.6 x 10(-8) M for fish sperm DNA, and 6.7 x 10(-8) M for yeast RNA. Mechanism study indicates that nucleic acids react with the title porphyrin in two modes, depending on the concentrations of nucleic acids. When the molar ratio of nucleic acids to TAPP is smaller than 4:1, the hypochromicity and fluorescence quenching of TAPP by nucleic acids appear, and the enhancement of resonance light-scattering can be observed. When the molar ratio of nucleic acids to TAPP is larger than 4:1, a new fluorescent complex is formed.