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The binding of gold nanoparticles capped with N-(2-mercaptopropionyl)glycine (Au@tiopronin) with double-stranded DNA has been investigated and quantified in terms of free energies by using two different approaches. The first approach follows the DNA conformational changes induced by gold nanoparticles using the CD technique. The second methodology consists in the use of pyrene-1-carboxaldehyde as a fluorescent probe. This second procedure implies the determination of the "true" free energy of binding of the probe with DNA, after corrections through solubility measurements. Working at different salt concentrations, the nonelectrostatic and electrostatic components of the binding free energy have been separated.The results obtained revealed that the binding is of nonelectrostatic character, fundamentally.The procedure used in this work could be extended to quantify the binding affinity of other AuNPs/DNA systems. [ABSTRACT FROM AUTHOR]

ABSTRACT The electron transfer reaction between [Ru(NH3)5pz]2+ and [Co(C2O4)3]3− was studied in the presence of monomers and aggregates of bile salts (sodium deoxycholate, sodium taurodeoxycholate, and sodium glycocholate) at 298.2 ± 0.1 K. The results show a decreasing rate constant with the successive addition of bile salts. To rationalize the trends of the reaction rate on the [bile salts], two models were used. One of them takes into account the aggregation feature by considering a stepwise self-association between monomers, whereas the other assumes the formation of a critical micellar concentration. Binding constants between [Ru(NH3)5pz]2+ species and deoxycholate or taurodeoxycholate aggregates were higher than that for glycocholate aggregates. These results are consistent with the way in which the monomers are added to form the bile anion aggregates. [ABSTRACT FROM AUTHOR]

The kinetics of electron transfer reactions between [Fe(CN)6]4- and [Co(NH3)5pz]3+ and between [Ru(NH3)5pz]2+ and [Co(C2O4)3]3- was studied in concentrated salt solutions (Na2SO4, LiNO3, and Ca(NO3)2). An analysis of the experimental kinetic data, kobs, permits us to obtain the true (unimolecular) electron transfer rate constants corresponding to the true electron transfer process (precursor complex → successor complex), ket. The variations of both, kobs and ket, with salt concentrations are opposite for these reactions. These opposite tendencies can be rationalized by using the Marcus–Hush treatment for electron transfer reactions. The conclusion is that the negative salt effect found for the first reaction ([Fe(CN)6]4- + [Co(NH3)5pz]3+) is due to the increase of the reaction and reorganization free energies when the concentration of salt increases. In the case of the second reaction ([Ru(NH3)5pz]2+ + [Co(C2O4)3]3-), the positive salt effect observed is caused by the fact that the driving force becomes more favorable when the concentration of salt increases. Thus, it is shown that for anion/cation electron transfer reactions the kinetic salt effect depends on the charge sign of the oxidant (and the reductant). © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 81–89, 2005 [ABSTRACT FROM AUTHOR]