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

The use of palladium(II) complex with 2-(5-bromo-2-pyridylazo)-5-diethylami nophenol (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-octylpolyeth yleneglycol phenylether, nucleic acids bind with the complex within 7 min a t room temperature, resulting in a maximum decrease in absorbance of the co mplex 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 mu g ml(-1), respectively, wi th corresponding detection limits of 44, 48 and 43 ng ml(-1). The recoverie s of nucleic acids from synthetic samples are 97.2-103.5%. DNA extracts fro m rice and human brain are analyzed with the calibration graph for calf thy mus DNA, and the results are close to those by ethidium bromide fluorometri c assay. Compared with existing colorimetic methods, the procedure is sensi tive, selective, simple, reproducible and practical. The association consta nt 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 m olar ratio of Pd(II) to 5-Br-PADAP) can bind a base pair of nucleic acids, perhaps in an intercalation way. (C) 2000 Elsevier Science B.V. All rights reserved.