The CdCl2 effects on synthetic DNAs encaged in the nanodomains of a cationic water-in-oil microemulsion

The present work is dedicated to the study of the interactions of CdCl2 with the synthetic polynucleotides polyAT and polyGC confined in the nanoscopic aqueous compartment of the water-in-oil microemulsion CTAB/pentanol/hexane/water, with the goal to mimic in vitro the situation met by the nucleic acids in vivo. In biological structures, in fact, very long strings of nucleic acids are segregated into very small compartments having a radius exceedingly smaller than the length of the encapsulated macromolecule. For comparison, the behaviour of polyGC was also studied in aqueous solutions of matched composition. The conformational and thermal stabilities of both polynucleotides enclosed in the inner compartment of the microemulsion are scarcely affected by the presence of CdCl2, whereas in solution immediate and large effects were observed also at room temperature. The lack of effects of CdCl2 on the properties of the biopolymers entrapped in the aqueous core of the microemulsion has been attributed to the peculiar characteristics of the medium (low dielectric constant, in particular) which cause a total repression of the CdCl2 dissociation that is not complete even in water. In fact, several of the numerous effects of CdCl2 observed on the conformational stability of polyGC in aqueous solutions have also been ascribed to the limited dissociation of the cadmium salt.