A sterically conservative, neutralizing mutation (glutamic acid to glutamine) in either of two different positions (15 or 48) of the soluble core tryptic fragment of cytochrome b5 results in two proteins with vastly different adsorption propenies. The kinetics of adsorption were measured under well-defined hydrodynamic conditions on a variety of different surfaces, of controlled electrostatic potential. prepared by modifying planar optical waveguides. Repeated measurement of the guided mode spectrum in the presence of protein solution allowed the temporal evolution of the number of adsorbed molecules to be determined. A highly positively charged surface acted as a perfect sink. Le.. adsorption was only limited by transport, adsorption to a highly negatively charged surface was fully reversible, and adsorption to a neuual phospholipid bilayer was very slow and practically irreversible. The macroscopic adsorption behavior can in large part be interpreted in terms of molecular-scale interactions between the protein and the adsorbent surface.

Oxygen-17 enriched methanol CD

Measurements by the nuclear magnetic resonance technique of the hydrogen exchange kinetics in methanol and ethanol are reported. The exchange reaction is both acid and base catalyzed. The observed kinetics can be interpreted as a simple proton transfer between a neutral alcohol molecule and an alcoxonium, or alcoxyde ion, respectively. In methanol a third mechanism, not involving ions, was also observed. In ethanol this reaction is presumably too slow for detection by the NMR technique. The hydrogen exchange was also studied in alcohol-water mixtures. Possible exchange mechanisms are discussed and values for their respective rate constants are given.

No abstract

The solvation of copper(i) in mixed solvent systems containing acetonitrile or benzonitrile and the co-solvents propionitrile, butyronitrile, valeronitrile, as well as trimethyl-, triethyl-and tributyl-phosphite has been examined by 63Cu NMR and also, in the case of the phosphites, by ''P NMR. The concentration dependence and the variation of the chemical shift of the silver-109 signal with solvent composition have been studied in solutions of si h e r trifluoroacetate (AgO,CCF,).