COMPLEXATION OF ETHIDIUM-BROMIDE WITH SINGLE-STRANDED SELF-NONCOMPLEMENTARY TETRADEOXYNUCLEOTIDE 5'-D(APAPGPC)

Complexation of ethidium bromide (3,8-diamino-6-phenyl-5-ethylphenanth ridine) dye with single-stranded self-noncomplementary tetradeoxynucle otide 5'-d(ApApGpC) in water-salt solution was studied by one-dimensio nal (500 MHz) and two-dimensional (600 MHz) H-1 NMR spectroscopy. Chem ical shift versus concentration experiments were performed at 298 degr ees K. Various scenarios of complexation were considered; the stabilit y constants for complexes as well as the limit chemical shifts of prot on resonances of complexed EthBr were determined. The fractions of com plexes were analyzed, and the dynamic equilibrium was described in rel ation to the dye/tetranucleotide concentration ratio. Sequence-specifi c binding of EthBr to the single-stranded nucleotide was inferred. The most probable configurations of 1:1 and 2:1 complexes of EthBr with t he tetradeoxynucleotide were proposed basing on the calculated values of induced H-1 chemical shifts of the dye and on 2D NOE data.