Analysis and improvement of rate constant determination of reactions involving charged reactants.
Kinetics of tris(2,2'-bipyridine)ruthenium(ii), Ru(bpy)(3)(2+), luminescence quenching by copper(ii) (in the form of chloride, nitrate, sulfate and perchlorate salt) was studied using pulse laser photolysis technique. The pseudo-first order rate constant versus quencher concentration plots obtained were found to be nonlinear, bending upward. The ionic strength effect contribution was evaluated by applying the Debye-Hückel extended law and was found to be as important as other effects such as cation-counter anion complex and ion-pairing complex formation which were all found to be dependent on the counter anion. It is shown that the slope of the tangent line to the pseudo-first order curve at zero quencher concentration is equal to the quenching rate constants at zero ionic strength. Also, this value corresponds to quenching solely by Cu(2+) and is free from contributions from other species that are present at higher concentrations. This method produced a value, (1.6 +/- 0.2) x 10(7) M(-1) s(-1), (lower than previously published ones) which is in agreement with the quenching rate constant measurement analysis presented. Comparison between Stern-Volmer plots obtained using steady-state fluorimetry data and laser photolysis data showed that in 50 mM CuCl(2) and CuSO(4) aqueous solutions about 5% of Ru(bpy)(3)(2+) is in the form of ion-pairing complexes. Our method was also applied to quenching by another divalent cation, methyl viologen, where it was found that charge transfer complexation effect contribution was about 50% of that of ionic strength effect, while ion-pairing complexation was not significant in the concentration range used. The quenching rate constant at zero ionic strength was found to be (2.3 +/- 0.2) x 10(8) M(-1) s(-1). The method proposed is also applicable to pulse radiolysis and stopped flow measurements.
The effects of microviscosity, bound water and protein mobility on the radiolysis and sonolysis of hen egg white
There is a great deal of work on proteins in aqueous solutions aimed at understanding their radiological and ultrasonic damage and the associated biochemical impacts. However, how these data are used and interpreted when proteins (and other biomacromolecules) are organized in three-dimensional structures (as in real biological systems) has been explored to a much lesser extent even though in such structural arrangements important and unique physicochemical effects exist. In this Dissertation, the effects of such physicochemical properties, including microviscosity, bound water, and protein mobility, on the radiolytic and sonolytic denaturation of hen egg white were studied. To improve our understanding of the molecular level effects of radiation and ultrasound on protein biomacromolecular gels (as a step towards complex biological systems), the thick fraction of egg white is used as a convenient and economical model system for the luminal mammalian mucous membrane as both are hydrogels (~90% water) that contain highly glycosylated, cysteine-rich and hydrated proteins. In this Dissertation, measurement of rate constants for diffusion-controlled reactions were used to investigate the microlevel rheological properties of macromolecular aqueous solutions and protein gels; however, the kinetics of reactions with highly charged reactants were found to be complicated by ionic effects. We developed a method to give a second-order rate constant where these ionic effects were not operative (Krise et al. 2010. Phys. Chem. Chem. Phys. 12: 7695). As a precursor to studies in biological macromolecular aqueous gels (hen egg white thick fraction), we assessed the macroand microscale rheological properties of a simple polymeric model
Effect of micellar phase on the state and dynamics of some excited state charge transfer complexes. [Pyrene--N,N-dimethylaniline]
The effect of micellar phase of kinetic processes of electron transfer reactions of exciplexes formed by pyrene (P) and N,N-dimethylaniline (DMA) has been studied. Transitory species are produced by a 10-ns pulse of 347.1-nm light from a Q-switched ruby laser and detected by rapid spectrophotometric or conduction techniques. Singlet excited pyrene (P*) readily accepts an electron from DMA to form an ion pair (P/sup -/ and DMA/sup +/), and the fate of the ion pairs depends critically on the micellar environment. In the case of cationic micelles, DMA/sup +/ is quickly expelled from the micellar surface while P/sup -/ is retained, leading to a long anion lifetime (approximately 500 ..mu..s). On the other hand, an anionic micellar surface traps DMA/sup +/ ions and enhances the geminate ion recombination process with P/sup -/. Several pyrene derivatives such as pyrenebutyric acid, pyrenesulfonic acid, pyrenetetrasulfonic acid, pyrenedodecanoic acid, and pyrenecarboxalydehyde which are solubilized at different sites in micelles are also selected as e/sup -/ acceptors to investigate the effect of separation between P* and DMA on the forward and back e/sup -/ transfer processes. Similar studies were carried out with the molecule P-(CH/sub 2/)/sub 3/-DMA which forms intramolecular exciplexes. Here neither ion canmore » escape from the exciplex owing to the restraint of the propyl chain. The physical and chemical properties of excited states of this molecule-miscellar system are dramatically different from those of intermolecular complexes. Micellar systems suggest the constituent ions of exciplexes. This has implications for conversion of light energy into ionic fragments which can be subsequently utilized.« less