Confinement effects on the interactions of native DNA with Cu(II)-5-triethyl ammonium methyl salicylidene orto-phenylendiiminate in C12E4 liquid crystals

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.