Ni2+ ion effect on conformational equilibrium of polynucleotides: polyA·polyU, polyA and polyU under conditions close to physiological ones

Interaction of Zn(2+) ions with single-stranded polyU and polyC in neutral solutions

Effect of Zn(2+) ions on the conformation of single-stranded polynucleotides polyU and polyC in a wide temperature range at pH 7 was studied by differential UV spectroscopy and by thermal denaturation. The atoms coordinating Zn(2+) ions were determined (O4 and N3 in polyU and N3 in polyC). A three-dimensional phase diagram and its two-dimensional components were constructed for a polyC-Zn(2+) system. The phase diagram revealed a region in which ordered single-stranded structures, stabilized by Zn(2+)-mediated cross-links involving N3 atom of cytosine, are formed. The phase diagram also demonstrated that the behavior of the polyC-Zn(2+) system is similar to the effect of retrograde condensation observed in some binary solutions of simple liquids. A dependence of Zn(2+)-polyC binding constant on the metal ion concentration was obtained. The reason why zinc-induced transition of the sequences with adenine-uracil (AU) base pairs from A-form geometry to a metallized m-form requires higher pH compared to the sequences comprised of guanine-cytosine (GC) base pairs is explained. This information can be useful for the development of possible technological applications based on m-DNA.

Metallization of single-stranded polyI by Zn(2+) ions in neutral solutions

Metallization of single-stranded polyinosinic acid (polyI) by Zn(2+) ions at pH 7.0 was studied by differential UV spectroscopy at different temperatures. It was found that polyI is metallized at N7 and N1 atoms of hypoxanthine. The concentration dependence of the degree of binding of Zn(2+) ions to both N7 and N1 sites was obtained, and the corresponding binding constants were determined. Metallization of N1 occurs due to Zn(2+) substituting the imino protons and is effective not only at alkaline but also at neutral pH. This makes multistranded polyI-based systems more promising candidates for use in nanoelectronics than natural DNA sequences, metallization of which can be achieved only at alkaline pH.

Effect of Zn2+ and temperature on the conformational equilibrium of single-stranded polyA in neutral solutions

Effect of Zn(2+) ions on the conformation of polyA in cacodilic buffer at pH 7 was investigated by differential UV spectroscopy (DUV) and by thermal denaturation. The shapes of the DUV spectra and melting curves suggest a transition of polyA into a more ordered "metallized", possibly double-helical conformation at Zn(2+) concentrations above 3×10(-5) M. A phase diagram of polyA complexes with Zn(2+) was constructed for the temperature range from 20 °C to 95 °C and Zn(2+) concentrations between 10(-5) M and 5×10(-4) M. It was found that the transition of a single strand into the "metallized" form is possible only if the length of the disordered single-stranded region becomes larger than a certain critical value, ranging between 98% and 78% as the metal concentration increases from 3×10(-5) to 5×10(-4) M.