The fluorescent probe, 2-hydroxynaphthalene(dodecylo)-6-sulfonamide (NSDA) bound selectively to shear plane of various electrostatic charges was synthesized and its photophysical properties have been investigated by means of steady state fluorescence and nanosecond time-resolved spectroscopy. Our experimental data allowed us to determine the excited state proton transfer (ESPT) rate and equilibrium constants of NSDA bound to micelles and to estimate the electric potential value (Ψ) at the particle surface. The spatial dependence of proton movement velocity through electric double layer (EDL) of micelles has been thoroughly analyzed. In this article, a new approach of estimating the values of the micelle potential (Ψ(R)) from the excited state proton transfer rate constant of the fluorescent probe bound at a certain distance (R) to a micellar surface has been proposed. The Ψ(R) values, obtained in this way, are compared with electrophoretic values of the particle potential (ζ). Our results on electrophoretic potentials and the reaction course of the ESPT in colloidal environment may contribute to a deeper understanding of micellar interactions and behavior of the living cells in contact with various diluted substances such as pharmacological drugs, hormones, proteins, and other colloidal particles.
[Show abstract][Hide abstract] ABSTRACT: 1Sulphonic acids and carboxylic acids which do not react with thionyl chloride under normal conditions give the corresponding acid chlorides with this reagent in excellent yields when dimethylformamide is present as a catalyst.2The reaction of thionylchloride with dimethylformamide yields the corresponding amide chloride which has not been isolated before in pure state. This amide chloride reacts with acids under formation of acid chlorides. The mechanism of these reactions is discussed.
[Show abstract][Hide abstract] ABSTRACT: An understanding of local surface pH and binding of peptides to membranes is of interest for a number of biological processes. Ionic dispersion forces that give rise to Hofmeister effects have not previously been taken into account by theories. It is demonstrated that pH-changes near surfaces (e.g. membrane and mica) and binding of peptides to membranes depend on the specific ionic species. Near mica surfaces, the effect can be especially large: some anions, for example, Br-, experience large attractive dispersion forces that can give rise to strong co-ion adsorption and enhanced pH-gradients. The concentration of hydronium ions at a model membrane surface is obtained from a modified nonlinear Poisson−Boltzmann equation that includes ionic dispersion potentials consistently. The fraction of ionizable surface groups is treated as a self-consistent functional of the electrostatic potential. We finally demonstrate that good agreement between theoretical and experimental binding energies of peptides to membranes requires ionic dispersion potentials that are consistent with our previous estimates based on surface tension of salt solutions.
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