Utilization of the copper(II) complex with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol as an absorption spectroscopic probe for nucleic acids assay

Abstract Based on the binding interaction of nucleic acids and the copper(II) complex with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP), a new spectrophotometric assay for nucleic acids is described. At pH 5.7–7.5 the binding reaction is completed within 2 min at room temperature, and causes an absorbance decrease at the wavelength of maximum absorption of the complex, 553 nm. The calibration graphs for calf thymus DNA, fish sperm DNA, and yeast RNA are linear up to 14.5, 16.0 and 14.0 μg ml −1 , respectively, and their 3 σ detection limits are correspondingly 84, 94 and 99 ng ml −1 . Compared with some existing assays, the new method is sensitive, stable, simple, reproducible and relatively free from interference from co-existing species. The analytical results of synthetic samples are satisfactory, with relative standard deviations of five determinations of 0.52–1.94%. The association constant of calf thymus DNA with the complex is estimated by two graphical methods; every base pair of the nucleic acid can bind one molecule of Cu(II)–5-Br-PADAP complex with a 1 : 1 mole ratio of Cu(II) to 5-Br-PADAP.