Efficient electrospray ionization from polymer microchannels using integrated hydrophobic membranes

A simple process for realizing stable and reliable electrospray ionization (ESI) tips in polymer microfluidic systems is described. The process is based on the addition of a thin hydrophobic membrane at the microchannel exit to constrain lateral dispersion of the Taylor cone formed during ESI. Using this approach, ESI chips are shown to exhibit well-defined Taylor cones at flow rates as low as 80 nL min(-1) through optical imaging. Furthermore, stable electrospray current has been measured for flow rates as low as 10 nL min(-1) over several hours of continuous operation. Characterization of the electrospray process by optical and electrical monitoring of fabricated ESI chips is reported, together with mass spectrometry validation using myoglobin as a model protein. The novel process offers the potential for low-cost, direct interfacing of disposable polymer microfluidic separation platforms to mass spectrometry.     

Chromatographic analysis of hydrocarbons in marine sediments and seawater.

The low concentration of hydrocarbons anticipated in pollution baseline studies necessitates the development of analytical techniques sensitive at the sub-microgram per kilogram concentration level. The method of analysis developed in this laboratory involves dynamic headspace sampling for volatile hydrocarbon components of the sample, followed by coupled-column liquid chromatography for the non-volatile components. These techniques require minimal sample handling, reducing the risk of sample component loss and/or sample contamination. Volatile sample components are separated from the matrix in a closed system and concentrated on a TENAX-GC packed pre-column, free from large amounts of solvent and ready for GC/GC-MS analysis. Non-volatile compounds, such as the benzpyrenes, may be extracted from large volumes of water and concentrated on a Bondapak C18 packed pre-column for coupled-column liquid chromatographic separation and analysis. Results of the application of these techniques to the analysis of samples from sites of known low level hydrocarbon contamination are presented and discussed.     

Relaxation of the optical Kerr effect of anisotropic molecules in mixed liquids

The relaxation time of the Kerr effect of nitrobenzene and m-nitrotoluene in various mixtures with carbon tetrachloride and various alcohols was determined by measuring the kinetics of the Kerr effect using picosecond laser techniques. These measurements yield information on the rotational motion of molecules in liquids. The relaxation time data are interpreted in terms of an effective local viscosity effect, pair correlation, and coupling of rotational motion with shear modes.     

Synthesis, structure, and alpha-elimination chemistry of hafnocene triarylstannyl complexes

New hafnocene triarylstannyl complexes were prepared and were shown to undergo clean thermal decompositions via alpha-aryl-elimination to produce the corresponding stannylene and a hafnocene aryl complex. The rate of the decomposition is highly dependent on the nature of the ancillary ligand, with the stabilities of the CpCp*Hf(SnPh(3))X compounds following the order X = NMe(2) > Np (alpha-agostic) > OMe > Cl > Me. Mechanistic information suggests that alpha-aryl-elimination may be viewed as a concerted process involving nucleophilic attack of the migrating aryl group onto the electrophilic metal center.     

Mass spectrometric study to characterize thioisoindole derivatives of aminoglycoside antibiotics

Aminoglycoside antibiotics are widely used to treat serious Gram-negative and Gram-positive bacterial infections. The lack of a UV chromophore presents a problem in the analysis of aminoglycosides. Derivatization with 1,2-phthalic dicarboxaldehyde (OPA) in the presence of a thiol made it possible to introduce a UV chromophoric thioisoindole moiety. A qualitative mass spectrometry study was carried out to confirm the molecular identity of the products formed. The conditions described earlier to derivatize gentamicin and kanamycin yielded products in which all primary amino groups are fully derivatized. On the other hand, with tobramycin and amikacin, there was also formation of incompletely derivatized products that contained one thioisoindole group less than the fully derivatized product. This study has therefore brought an additional insight into the nature of the OPA-aminoglycoside derivatives studied.     

Synthesis, X-ray diffraction analysis and NMR studies of (Z)-2-methyl-3-triphenylstannyl-3-pentene-2-ol

The synthesis of (Z)-2-methyl-3-triphenylstannyl-3-pentene-2-ol and its characterization by an X-ray diffraction study and multinuclear NMR are reported. The tin atom exhibits a distorted tetrahedral SnC₄ geometry with the four Sn---C bond distances experimentally equivalent. The slight distortion from the ideal tetrahedral geometry is because of the presence of a weak intramolecular HO → Sn interaction of 3.012(3) Å which produces a loose four-membered ring. The title compound was characterized in solution by ¹H, ¹³C and ¹¹⁹Sn NMR, and the persistence of the weak intramolecular HO → Sn coordination in solution was revealed by ¹³C and ¹¹⁹Sn secondary isotope multiplet of partially labelled entities (SIMPLE-NMR) experiments.     

The ionic product of water in concentrated tetramethylammonium chloride solutions

The ionic product of water, pK(w) = - log[H(+)][OH(-)] has been determined in aqueous solutions of tetramethylammonium chloride over the concentration range of 0.1-5.5 M at 25 degrees C using high-precision glass electrode potentiometric titrations. pK(w) data relating to aqueous potassium and sodium chlorides at ionic strengths up to 5 M are markedly lower than the tetramethylammonium chloride results. These differences are almost certainly due to weak associations between potassium and (especially) sodium and hydroxide ions.     

Covalent Schiff base catalysis and turnover by a DNAzyme: a M2+ -independent AP-endonuclease mimic

A DNAzyme, synthetically modified with both primary amines and imidazoles, is found to act as a M2+ -independent AP lyase-endonuclease. In the course of the cleavage reaction, this DNAzyme forms a covalent Schiff base intermediate with an abasic site on a complementary oligodeoxyribonucleotide. This intermediate, which is inferred from NaCNBH3 trapping as well as cyanide inhibition, does not evidently accumulate because the second step, dehydrophosphorylative elimination, is fast compared to Schiff base formation. The 5'-product that remains linked to the catalyst hydrolyzes slowly to regenerate free catalyst. The use of duly modified DNAzymes to perform Schiff base catalysis demonstrates the value of modified nucleotides for enhancing the catalytic repertoire of nucleic acids. This work suggests that DNAzymes will be capable of catalyzing aldol condensation reactions.     

Synthesis and characterization of scandium silyl complexes of the type Cp*2ScSiHRR'. sigma-Bond metathesis reactions and catalytic dehydrogenative silation of hydrocarbons

The scandium dihydrosilyl complexes Cp*(2)ScSiH(2)R (R = Mes (4), Trip (5), SiPh(3) (6), Si(SiMe(3))(3) (7); Mes = 2,4,6-Me(3)C(6)H(2), Trip = 2,4,6-(i)()Pr(3)C(6)H(2)) and Cp*(2)ScSiH(SiMe(3))(2) (8) were synthesized by addition of the appropriate hydrosilane to Cp*(2)ScMe (1). Studies of these complexes in the context of hydrocarbon activation led to discovery of catalytic processes for the dehydrogenative silation of hydrocarbons (including methane, isobutene and cyclopropane) with Ph(2)SiH(2) via sigma-bond metathesis.     

A simple convenient synthesis of trans-1,2,3,4,4a,5,6,10b-octahydrophenanthridines

trans-1,2,3,4,4a,5,6,10b-Octahydrophenanthridine, the 9-methoxy analog, and 5-methyl derivatives ( 6a,6b ) of each have been synthesized from trans-phenylcyclohexylamines ( 2a,2b ) and ethyl chloroformate followed by cyclization and reduction or by cyclization, N-methylation and reduction. The oximes ( la,1b ) of 2-phenylcyclohexanone and the m-methoxy relative, a mixture of the syn and anti isomers, were reduced to 2a and 2b with sodium and ethanol. Hydrogenation (platinum oxide-acetic acid) of 1a gave in addition to 2a , a small yield of 2-cyclohexylcyclohexyl-amine. Similar hydrogenation of 1b gave only this fully reduced compound.