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

Based on the binding interaction of nucleic acids and the copper(II) comple x with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP), a new sp ectrophotometric assay for nucleic acids is described. At pH 5.7-7.5 the bi nding 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 y east RNA are linear up to 14.5, 16.0 and 14.0 mu g ml(-1), respectively, an d their 3 sigma 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 cc-existin g species. The analytical results of synthetic samples are satisfactory, wi th relative standard deviations of five determinations of 0.52-1.94%. The a ssociation constant of calf thymus DNA with the complex is estimated by two graphical methods; every base pair of the nucleic acid can bind one molecu le of Cu(II)-5-Br-PADAP complex with a 1 : 1 mole ratio of Cu(II) to 5-Br-P ADAP. (C)1999 Elsevier Science B.V. All rights reserved.