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Two methods have been used to measure the chlorine leaving group kinetic isotope effect for the [S.sub.N]2 reduction of benzyl chloride to toluene by sodium borohydride in DMSO at 30.000 [degrees] C. The reaction was monitored by titrating the unreacted borohydride ion. One method involved determining the chlorine isotope effect using the classical IRMS method, which requires the conversion of the chloride ions into gaseous methyl chloride that is analyzed in an isotope ratio mass spectrometric analyses (Hill, J. W.; Fry, A. J. Am. Chem. Soc. 1962, 84, 2763. Taylor, J. W.; Grimsrud, E. P. Anal. Chem. 1969, 41, 805.). Two different measurements using this method yielded isotope effects of [k.sup.35]/[k.sup.37] = 1.007 19 [+ or -] 0.000 19 and 1.007 64 [+ or -] 0.000 19. The second method was a new technique where the ratio of the chlorine isotopes was obtained by fast atom bombardment mass spectrometry on the silver chloride recovered from the reaction, i.e., from the first step in the classical procedure. Therefore, the new method is much simpler and avoids the time-consuming preparation, purification, and recovery of the gaseous methyl chloride. Although the experimental error is larger ([k.sup.35]/[k.sup.37] = 1.008 03 [+ or -] 0.00 10 and 1.008 02 [+ or -] 0.000 65) when the new technique is used to analyze the silver chloride samples from the same set of experiments that were used to measure the isotope effect by the classical method, the chlorine isotope effect found by the two methods is identical within experimental error. This large chlorine kinetic isotope effect indicates there is considerable [C.sub.[Alpha]]-Cl bond rupture in the [S.sub.N]2 transition state.

In this study a nano-electrospray emitter is constructed by precisely positioning entrapped octadecylsilane (ODS) particles within a photoinitiated polymer at the exit aperture of a capillary. Following poly-merization, the microsphere/polymer hybrid material is able to withstand pressures greater than 4000 psi for 1 cm length of material. Smaller microspheres (3 microm) patterned at the exit aperture of a capillary generated the most sensitive/stable electrospray from 100 to 1000 nL/min and moderately stable signal under 100 nL/min. Constant infusion of a standard PPG solution from a batch of eleven emitters resulted in a relatively small variance in total ion current (TIC) counts (8%). The entrapped microsphere emitter design yields an emitter that minimizes clogging and eliminates dead volume between the chromatographic bed and the electrospray emitter. The entrapped ODS microspheres can also be used for sample preparation prior to mass spectrometry (MS) analysis. We show the solid-phase extraction and preconcentration of 20-700 fmol of a peptide (leucine enkephalin) prior to MS analysis on an emitter with 1 cm of entrapped microspheres.

Coupling low-flow analytical separation instrumentation such as capillary electrophoresis, capillary electrochromatography, nano-HPLC, and microfluidic-based devices with electrospray ionization mass spectrometry has yielded powerful analytical tools. However, conventional coupling methodologies such as nanospray suffer from limitations including poor conductive coating robustness, constant clogging, complicated fabrication processes, and incompatibility with large flow rate regimes. This study demonstrates that robust nanospray emitters can be fabricated through the formation and utilization of a porous polymer monolith (PPM) at the end of a fused-silica capillary. Stable electrosprays can be produced from capillaries (75-100-microm i.d.) at a variety of flow rates (50-1000 nL/min) without the need to taper the capillaries by etching or pulling. The PPM is photopatterned to be present only near the capillary exit aperture using conditions that generate pore sizes similar to those seen with nanospray tips. The porous nature of the PPM aids in developing a stable electrospray generating a single clearly visible Taylor cone at relatively high flow rates while at low flow rates (<100 nL/min) a mist, presumably from multiple small Taylor cones, develops. The hydrophobic nature of the PPM should limit problems with band broadening associated with droplet spreading at the capillary exit, while the multiple flow paths inherent in the PPM minimize clogging problems associated with conventional nanospray emitters. Total ion current traces for a constant infusion of standard PPG and cytochrome c solutions are very stable with deviations ranging from only 3 to 8%. The PPM-assisted electrospray produces mass spectra with excellent signal-to-noise ratios from only a few femtomoles of material.

The secondary deuterium kinetic isotope effect (DKIE) for the epoxidation of ethylene and d(4)-ethylene by m-chloroperoxybenzoic acid (MCPBA) is determined to be 0.83, or 0.95/alpha-H. The second-order rate constants for MCPBA and MCPBA-O-D epoxidation of a variety of alkenes that differ in the steric access to the double bond (anti-sesquinorbornene (2), tetramethylethylene (3), adamantylideneadamantane (4), 7-norbornylidene-7'-norbornane (5), bis(bicyclo[3.3.1.]non-9-ylidene) (6), bis(homoadamantane) (7), cyclohexene (8), 1-octene (9), trans-5-decene (10) and 2-methyl-1-pentene (11)) have been determined in dichloroethane at 25 degrees C using UV kinetics, and the primary DKIE, k(OH)/k(OD), is 1.05 +/- 0.05 in all cases. By comparison of the rates of epoxidation of sterically encumbered alkenes, it is suggested that the spiro epoxidation transition state is favored over a planar one. The products of the epoxidation of anti-sesquinorbornene are determined to be the epoxide and a cis-hydroxy ester, the latter most probably being formed by acid-catalyzed ring opening of the epoxide by in situ-produced m-chlorobenzoic acid produced in situ to form a beta-hydroxy carbocation and carboxylate ion pair that collapses to product.

Homonuclear two-dimensional proton nuclear Overhauser effect (2-D-NOE) spectra have been obtained for asialo-GM2 (4) and gangliosides GM2 (8) and GM1 (9) at 500 MHz and 40 degrees C in Me2SO-d6-D2O (98:2 v/v). The anomeric protons of each oligosaccharide residue of 4, 8, and 9 are observed to NOE couple via intraresidue 1,3- and 1,5-diaxial interactions and interresidue interactions across the glycosidic linkages. The former couplings are used to confirm the H-3 and H-5 assignments for each residue. From the latter couplings the sequence and glycosidic linkage sites of all oligosaccharide residues, except the sialic acid residues, are revealed. Sialic acid attachment sites are determined for the monosialogangliosides (6-9) through consideration of sialylation-induced glycosidation shifts. Combination of the above sequence and linkage-site data with the monosaccharide composition, anomeric configurations, and characterization of the aglycon (information obtained via two-dimensional spin-echo J-correlated spectroscopy or 2-D-SECSY) allows complete assignment of monosialoganglioside primary structure, independent of other methods of structural analysis. Compared to conventional chemical and enzymatic methods, high-resolution two-dimensional proton nuclear magnetic resonance spectroscopy has the advantages of speed, sensitivity, and sample preservation.