Confinement effects on the interaction of native DNA with Cu(ii)–5-(triethylammoniummethyl)salicylidene ortho-phenylendiiminate in C12E4 liquid crystals

Abstract

Confinement effects of native calf thymus DNA interacting with the complex Cu(II)–5-(triethylammoniummethyl)salicylidene ortho-phenylendiiminate (CuL²⁺) perchlorate in tetraethylene glycol monododecyl ether (C₁₂E₄) liquid crystals have been investigated by UV absorption spectrophotometry, circular dichroism (CD) and small angle X-ray scattering (SAXS). The results indicate the occurrence of dramatic structural changes of both the DNA and the CuL²⁺–DNA system, when going from aqueous solution to C₁₂E₄ liquid crystals, due to confinement constrains imposed by the closed structure of C₁₂E₄ reverse micelles. Further marked departures from the behaviour observed in aqueous solution have been emphasized by registering the spectral response of DNA and CuL²⁺–DNA confined in C₁₂E₄ reverse micelles after thermal treatment. It has been also ascertained that the confinement causes the formation of a more compact and thermoresistant DNA structure accompanied by a transition from the right- to left-handed form while a tight CuL²⁺–DNA binding has been revealed by the appearance of a broad induced CD band in the range 350–450 nm. From a biological point of view, these findings stress the need to account for confinement effects and the peculiarity of drug–DNA interactions occurring within the intra-cellular environment.