Self-organization of water in lithium/nitrobenzene system.

The effect of lithium ion on the ordering of water in water-saturated nitrobenzene has been probed by 2H NMR, diffusion ordered spectroscopy and neutron scattering. It was shown that increased water concentration in LiClO4/wet nitrobenzene results in the formation of a metastable solvatomer with mixed water and nitrobenzene character, Li+(W/NB). This species is shown to decay over hours to two solvatomers, one dominated by nitrobenzene Li+(NB) and the other dominated by water Li+(W). To confirm the assignment of these solvation states, diffusion ordered deuterium NMR spectroscopy has been used to elucidate the hydrodynamic radii of these solvatomers. Neutron scattering yields vibrational spectroscopy information that shows how addition of lithium to the nitrobenzene/water system results in relatively slow self-organization of the water environment (hours).

1H NMR investigation of thermally triggered insulin release from poly(N-isopropylacrylamide) microgels.

We describe investigations of insulin release from thermoresponsive microgels using variable temperature (1)H NMR. Microgel particles composed of poly(N-isopropylacrylamide) were loaded with the peptide via a swelling technique, and this method was compared to simple equilibrium partitioning. Variable temperature (1)H NMR studies suggest that the swelling loading method results in enhanced entrapment of the peptide versus equilibrium partitioning. A centrifugation-loading assay supports this finding. Pseudo-temperature jump (1)H NMR measurements suggest that the insulin release rate is partially decoupled from microgel collapse. These types of direct release investigations could prove to be useful methods in the future design of controlled macromolecule drug delivery devices.

Iso-coenzyme A.

Iso-coenzyme A is an isomer of coenzyme A in which the monophosphate is attached to the 2'-carbon of the ribose ring. Although iso-CoA was first reported in 1959 (Moffatt, J. G., and Khorana, H. G. (1959) J. Am. Chem. Soc. 81, 1265-1265) to be a by-product of the chemical synthesis of CoA, relatively little attention has been focused on iso-CoA or on acyl-iso-CoA compounds in the literature. We now report structural characterizations of iso-CoA, acetyl-iso-CoA, acetoacetyl-iso-CoA, and beta-hydroxybutyryl-iso-CoA using mass spectrometry (MS), tandem MS, and homonuclear and heteronuclear NMR analyses. Although the 2'-phosphate isomer of malonyl-CoA was recently identified in commercial samples, previous characterizations of iso-CoA itself have been based on chromatographic analyses, which ultimately rest on comparisons with the degradation products of CoA and NADPH or have been based on assumptions regarding enzyme specificity. We describe a high performance liquid chromatography methodology for separating the isomers of several CoA-containing compounds. We also report here the first examples of iso-CoA-containing compounds acting as substrates in enzymatic acyl transfer reactions. Finally, we describe a simple synthesis of iso-CoA from CoA, which utilizes beta-cyclodextrin to produce iso-CoA with high regioselectivity, and we demonstrate a plausible mechanism that accounts for the existence of iso-CoA isomers in commercial preparations of CoA-containing compounds. We anticipate that these results will provide methodology and impetus for investigating iso-CoA compounds as potential pseudo-substrates or inhibitors of the >350 known CoA-utilizing enzymes.

NMR study of lithium ion in nitrobenzene/water system.

The goal of this project has been to elucidate the solvation states and kinetics involved in the transfer of Li ions between nitrobenzene and water. A large interface area has been realized by confining one phase in polymer beads and suspending them in the other phase. A 2D 7Li-NMR spectroscopic result of such a system obtained on a 400 MHz instrument has shown that the rate of the Li ion transfer exchange between nitrobenzene and water is too fast to resolve individual solvatomers. A pair of well-resolved 7Li-NMR peaks corresponding to different solvation environments of Li+ in "wet" nitrobenzene has been observed. The most surprising result is that the ratio of those two peaks and their separation changes over a period of days, but it can be reversibly changed by mechanical disturbance, such as ultrasonication. This effect is reproducible and suggests spontaneous but slow formation of metastable solvatomers of Li+. Another surprising observation has been slow and irreversible incorporation of lithium ion from wet nitrobenzene into the walls of the silica-containing vessels.