In this work, three compounds having the same organic moiety (N-methyl-5-azahelicenium salts) but different counterions (I-, NO3- and COOCF3-) have been investigated in buffered aqueous solutions and in the presence of DNA to give information on the counterion effects on the binding. In particular, the absorption spectra, fluorescence quantum yields and fluorescence lifetimes in aqueous solution for free organic molecules have been determined by steady-state and time-resolved spectrofluorimetric measurements. The obtained values are compared with those of the chromophores in the presence of increasing concentrations of DNA. The results allow determination of the association constants (K(a)) and the number of base couples per chromophore molecule (n) by means of the McGhee Von Hippel model. The binding parameters are strongly affected by the nature of counterions since the highest K(a) value was determined for the compound having COOCF3-; on the other hand the NO3- derivative is able to interact with the highest number of binding sites. The morphology and structural properties of the DNA-chromophore complexes were investigated by circular dichroism (CD) and atomic force microscopy (AFM). The data revealed that I- and COOCF3- derivatives preferentially form intercalation complexes, while the NO3- salt is able to form intercalation and grove binding complexes at the same time.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.