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

Abstract

The present work is dedicated to the study of the interactions of CdCl(2) 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 CdCl(2), whereas in solution immediate and large effects were observed also at room temperature. The lack of effects of CdCl(2) 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 CdCl(2) dissociation that is not complete even in water. In fact, several of the numerous effects of CdCl(2) observed on the conformational stability of polyGC in aqueous solutions have also been ascribed to the limited dissociation of the cadmium salt.

Interaction of Cd(ii) and Ni(ii) terpyridine complexes with model polynucleotides: a multidisciplinary approach

“…2a), and, most interestingly, ICD signals appeared at l > 300 nm increasing with R. At variance, titration of 1 with polyGC ( Fig. 2b) only gave rise to CD spectra reminiscent of those of C-DNA or unwound B-DNA, 15,[39][40][41] but with no sign of ICD. For comparison, complex 1 was also titrated with calf thymus DNA (ct-DNA) in 1 mM Tris-2 mM NaCl.…”

“…[8][9][10][11][12] Among the many known metal complexes of terpyridine, we got particularly interested in those of Cd(II) and Ni(II), and in their interaction with model DNAs, as an extension of our studies on the poly(dA-dT)$poly(dA-dT) (briey polyAT) and poly(dG-dC)$poly(dG-dC) (briey polyGC) interactions with the Cd 2+ and Ni 2+ cations. [13][14][15] The synthesis of a Cd(II)-terpyridine complex was rst reported by Morgan and Burstall, 16 who proposed for the complex the formula [CdCl(terpy)]Cl, with the suggestion that its constitution would probably be more complicated than indicated by such formula. A distorted trigonal bipyramidal geometry has been proposed for Cd(terpy) Cl 2 , 17,18 though an X-ray study 19 reports a square pyramidal arrangement for the complex.…”

Natural or synthetic nucleic acids encapsulated in a closed cavity of amphiphiles

“…Such scarce effects were ascribed to the peculiar characteristics of the micellar core, in particular the low dielectric constant, that reduce almost to nothing the ionic dissociation of CdCl 2 , that is only partial even in water. 243 The results above reported underline, if necessary, once more the significance of microemulsion vs. solution studies of polynucleotides.…”

“…233,234 The cationic quaternary w/o microemulsion CTAB/hexane/ pentan-1-ol/water was employed in a series of studies on synthetic DNAs, namely high molecular weight poly(dA-dT)?poly(dA-dT) and poly(dG-dC)?poly(dG-dC) (polyAT and polyGC, respectively, in the following). [235][236][237][238][239][240][241][242][243] The aim of these investigations was to detect if and how the constraints imposed by the microemulsive medium (constricted volume, curvature and charge of the micellar wall, and reduced water activity and dielectric constant) could modify the chemical reactivity and conformational or thermal stability of the polynucleotides relative to aqueous solutions. It is, for instance, well known that solvent characteristics, in particular dielectric constant, are key factors in determining the conformational behaviour of nucleic acids in solution 10,11,244 and thus polymorphs of DNAs that are unusual in aqueous solutions could easily be observable in the water pool of microemulsions (Fig.…”

“…the molar ratio of metal to DNA-phosphate), NaCl concentration and temperature, many different conformations of the model DNAs, that are not observed in solution under comparable mild experimental conditions, but only at very high salt concentrations, or in alcohol rich aqueous solutions or at temperatures near 273 K. A similar study in microemulsion has been reported on the interactions of CdCl 2 with polyAT and polyGC. 243 Cadmium is a genotoxic metal and a diffuse occupational and environmental pollutant and its interactions with nucleic acids are the object of a very active research. [254][255][256][257][258] In contrast with the large and different effects observed in solution, depending on the ionic strength and metal-to-polynucleotide phosphate molar ratio, conformational and thermal stability of both polyAT and polyGC are hardly affected by CdCl 2 in the CTAB/hexane/pentan-1-ol/water microemulsions with matched composition of the aqueous compartment.…”