Nucleic Acid Base Pair and Mispair Interactions with Metal IonsA Thermodynamic Aspect

Abstract

Potentiometric equilibrium measurements were made for some metal ions (M(II) = Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Ca(II), Sr(II), and Ba(II)) with guanine (A) in a 1:1 (M(II):A) ratio and with cytosine, cytidine, 5-bromocytosine, 5-azacytosine, and 5-fluorocytosine as primary ligands (L) and guanine as secondary ligand in a 1:1:1 (M(II):L:A) ratio at (25.0, 35.0, and 45.0) °C and I = 0.1 mol·dm-3 NaNO3 in aqueous solution. The experimental pH-titration data were analyzed by using a BEST computer program in order to evaluate the formation constants of various intermediate species and their relative distribution. The experimental conditions were selected in such a way that the self-association of the nucleobases and their complexes due to stacking interaction was negligibly small, so that only the neutral monomeric and hydroxo ternary complexes were studied. The enthalpy (Δf H°) and entropy (Δf S°) changes for the formation of binary and ternary complexes were calculated from temperature coefficient data. The δΔf S° values are positive for all the metal ligand systems. The negative δΔf H° values indicate the extra stabilization of most of the ternary complexes by the exothermic enthalpy change (δΔf S° = ΔT S° − ΔB S° and δΔf H° = ΔT H° − ΔB S° where ΔT S°, ΔT H° and ΔB S°, ΔB H° are the entropy and enthalpy values associated with the ternary and binary complexes, respectively). On the basis of IR data for metal complexes with the 5FC−G mispair, it has been proposed that the guanine is bonded to metal ions through N1/C6O and N7, whereas cytosine and its derivatives are bonded through N3 atoms in ternary complexes.

Solution Equilibria of Ternary Systems Involving Transition Metal Ions, Hydroxamic Acids, and Bioligands

“…However, an inverse behavior was observed in case of the Cu(II)−Sham (Table ) binary system compared to its corresponding ternary ones (Table ). This may be due to the fact that some more water molecules may still be attached to the metal ion in 1:1 binary systems and, when a 1:1:1 complex is formed, more energy is needed in the bond breaking process . The values of Δ S o substantiate the suggestion that the different binary and ternary complexes are formed due to coordination of the ligand anion to the metal cation.…”

“…This may be due to the fact that some more water molecules may still be attached to the metal ion in 1:1 binary systems and, when a 1:1:1 complex is formed, more energy is needed in the bond breaking process. 48 The values of ∆S o substantiate the suggestion that the different binary and ternary complexes are formed due to coordination of the ligand anion to the metal cation. Furthermore, the positive values of ∆S o suggest also a desolvation of the ligands, resulting in weak solvent-ligand interactions, to the advantage of the metal ion-ligand interaction.…”

Theoretical investigation on DNA/RNA base pairs mediated by copper, silver, and gold cations

“…43 In addition, Ag + gives rise to ternary complexes with nucleotides, and other ligands. 44 Silver complexes are used in the construction of DNA-based electronic devices. 45 Besides, it seems that Ag + has a tendency for binding to endocyclic ring nitrogen atoms of the heterocyclic bases of DNA.…”

Structure and bonding of Ag(I)–DNA base complexes and Ag(I)–adenine–cytosine mispairs: An ab Initio study

“…21 Ag forms ternary complexes with nucleobases, nucleosides, nucleotides, and other ligands. 22 Silver complexes are employed in the construction of DNA-based electronic devices. 23 Some Ag(I)-containing DNA complexes exhibit antibacterial activity, 24 but the binding mode of Ag(I) in the Ag-polynucleotides are unclear.…”