Nitroaniline diamine.poly(dA-dT) complexes: 1H and 19F NMR parameters for full intercalation of aromatic rings into...

High-resolution proton, fluorine, and phosphorus NMR studies have been undertaken on complexes of methyl- and trifluoromethyl-substituted nitroaniline diamines with the synthetic DNA poly(dA-dT) in 10 mM buffer solution. We demonstrate full intercalation of the nitroaniline group of these reporter molecules between base pairs, based on large upfield proton shifts (1.3-1.7 ppm) at all four aromatic proton markers on complex formation. The temperature and pH dependences of the thymidine H-3 Watson-Crick proton chemical shift and line width require the formation of intact and stable base pairs in this intercalative complex in solution. The 19F chemical shift of the trifluoromethyl-labeled nitroaniline diamine shifts downfield by approximately 2 ppm on formation of the synthetic DNA complex and most likely reflects the nonpolar environment of the aromatic ring when sandwiched between base pairs. A sequence specificity in the binding of the nitroaniline dication to poly(dA-dT) is implied by the observation of two partially resolved 31P resonances with the phosphodiester at the intercalation site shifting downfield by approximately 0.4 ppm on complex formation.