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The kinetics of the electron transfer reactions between pentaammine(pyrazine)ruthenium(ii), [Ru(NH₃)₅pz]2+ and tris(oxalate)cobalt(iii), [Co(C₂O₄)₃]3− and pentaammine(pyridine)ruthenium(ii), [Ru(NH₃)₅py]2+ and tetraammine(pyrazinecarboxylate)cobalt(iii), [Co(NH₃)₄pzCO₂]2+ have been studied in aqueous solutions of DNA over the concentration ranges 0 to 2.46 × 10−3 mol dm−3 and 1.23 × 10−4 to 1.00 × 10−3 mol dm−3, respectively. The results are interpreted on the basis of a modified pseudophase model which takes into account the anticooperative character of the binding of the cationic reactants to DNA.

The kinetics of proton transfer between poly(A—AH) (partially protonated double-stranded polyadenylic acid) and CPR (chlorophenol red), and between poly(C—H—C) (partially protonated double-stranded polycytidylic acid) and the indicators CPR, BCP (bromocresol purple), and BCG (bromocresol green) have been investigated at 25°C and ionic strength 0.1 M (NaClO4) by the temperature-jump method. The acidic proton of poly(C—H—C) is engaged in a hydrogen bond (N3H⁺––––N3) which is believed to contribute to stabilizing the double-strand conformation, whereas the acidic proton of poly(A—A—H) does not form hydrogen bonds. The analysis of the dependence of the relaxation times on the concentrations of the reactants has enabled the evaluation of the rate constants for the direct proton transfer and for the protolysis paths. The rate constants for proton recombination with the deprotonated forms of the polynucleotides and the indicators are of the order of magnitude expected for diffusion controlled processes involving oppositely charged ions (k2=(0.2−1.6)×1010 M⁻¹s⁻¹). The direct proton transfer from poly(C—H—C) to BCG is thermodynamically disfavored and its rate constant, k1, is lower than k2 by about three orders of magnitude. The (thermodynamically favored) proton transfers from poly(A—A—H) to CPR and from poly(C—H—C) to CPR and BCP are characterized by similar values of k1. This result indicates that the hydrogen bonds in poly(C—H—C) are very weak and suggests that the stabilization of the double-stranded conformation of this polynucleotide could be ascribed to the large number of hydrogen bonds rather than to their specific strength. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 161–169, 1998.

The kinetics of the reaction between Ni2+and pyrophosphate have been investigated over a wider range of conditions than previously. At 25°, a variation of the ionic strength between 0.02 and 0.20 M (achieved by adding potassium nitrate at appropriate concentrations) showed that the salt effect, though acting on the formation constant of an ion pair rather than on the rate constant of the rate‐determining step, is essentially “classical”. By varying the pH between 4.5 and 7.0, at least two parallel reaction paths were observed, involving Ni2+and the ions HP2O3−7and H2P2O2−7. The latter path has a rate constant that is ∼28 times smaller than that of the former and makes an appreciable contribution to the observed rate only at the two lowest pH values. Possible reasons for this difference in reactivity are discussed. The rate constant for the path involving HP2O3−7was 1.61 × 106M−1s−1at 25°, I = 0.1 M. The activation parameters for this path are ΔH≠= 18.8 Kcal mole−1and ΔS≠= 33 e.u. All kinetic experiments were carried out by the T‐jump method. The equilibrium constants necessary for the evaluation of the results were determined by potentiometric titration.