SPECTROPHOTOMETRY OF NUCLEIC-ACIDS BY THEIR EFFECT ON THE COMPLEX OF COBALT(II) WITH 4-[(5-CHLORO-2-PYRIDYL)AZO]-1,3-DIAMINOBENZENE

A new ternary ate-dye complex reaction involving nucleic acids has bee n studied to provide a sensitive spectrophotometric method for nucleic acids. In alkaline conditions, single-stranded nucleic acids react wi th the complex of Co(II) with 4-[(5-chloro-2-pyridyl)azo]-1,3-diaminob enzene (5-Cl-PADAB), resulting in purple ternary compounds with maximu m absorbance at 545.0 nm against the binary complex blank. The mole ra tio of Co(II) to 5-Cl-PADAB in the ternary compounds is 1:2, and each nucleotide residue can bind two binary complex molecules. There are Li near relationships between the absorbance and the concentrations of th e tested nucleic acids, such as calf thymus DNA, fish sperm DNA and ye ast RNA in the range 0-4.0 mu g ml(-1). The 3 sigma limit of detection for calf thymus DNA is 40 ng ml(-1), the relative standard deviation at 3.0 mu g ml(-1) is 0.79% (n = 10) and the Sandell's sensitivity is 5.3 ng cm(-2). The same parameters for fish sperm DNA are 41 ng ml(-1) 0.84% and 5.4 ng cm(-2), and for yeast RNA are 49 ng ml(-1), 0.58% an d 6.2 ng cm(-2). Synthetic samples were analyzed satisfactorily.