Spectrophotometric determination of nucleic acids using palladium(II) complex with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol Original Research Article

The use of palladium(II) complex with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) is proposed for the spectrophotometric quantification of nucleic acids. At pH 5.9–7.5 and in the presence of 0.6% p-octylpolyethyleneglycol phenylether, nucleic acids bind with the complex within 7 min at room temperature, resulting in a maximum decrease in absorbance of the complex at 582 nm. The calibration graphs for calf thymus DNA, fish sperm DNA, yeast RNA are linear up to 5.0, 6.0 and 3.5 μg ml−1, respectively, with corresponding detection limits of 44, 48 and 43 ng ml−1. The recoveries of nucleic acids from synthetic samples are 97.2–103.5%. DNA extracts from rice and human brain are analyzed with the calibration graph for calf thymus DNA, and the results are close to those by ethidium bromide fluorometric assay. Compared with existing colorimetic methods, the procedure is sensitive, selective, simple, reproducible and practical. The association constant of calf thymus DNA with the complex is estimated by Rosenthanl and Wolfe graphic methods, and every 4 molecules of Pd(II)–5-Br-PADAP complex (1:1 molar ratio of Pd(II) to 5-Br-PADAP) can bind a base pair of nucleic acids, perhaps in an intercalation way.