Extensions of thermochemical, analytical and mechanistic studies by mass spectroscopy

Jeffrey Scott Patrick, Purdue University

Abstract

In the biomimetic surfaces studies nucleotides, DNA and dithiophosphate oligonucleotides are adsorbed to a metal surface through chemistry familiar from self-assembled monolayers (SAM). The adsorbed constituents can be covalently or non-covalently modified and the surface can be interrogated by static secondary ion mass spectrometry to provide ions characteristic of the immobilized nucleotide or oligonucleotide. The development of affinity membrane introduction mass spectrometry (MIMS) is described. A microporous cellulose membrane is chemically derivatized to incorporate an amino group and this amino group is then used to trap benzaldehydes displace them by acidification detect the analytes using a benchtop ion trap mass spectrometer. The detection of glycerol by glow discharge MIMS with the addition of xenon as a reagent gas additive. Other polar compounds detected by MIMS include 5-hydroxymethylfurfuradehyde, epichlorohydrin and dialkyldithiocarbamates. Finally, MIMS, in combination with positive and negative chemical ionization and the various forms of tandem mass spectrometry, is utilized to provide support for the identification of halogenated 4-methoxybenzaldehydes (anisaldehydes) in broths of the fungus Bjerkandera adusta. The gas-phase basicity (GB) of the zwitterion betaine and related compounds using the kinetic method. These experiments show the GB of betaine to be $232.9\pm0.8$ kcal/mol, while that of its transmethylation isomer, N,N-dimethylglycine methyl ester was found to be $220.2\pm0.9$ kcal/mol and the conjugate base of N,N-dimethylglycine was found to be $337.1\pm0.5$ kcal/mol. The presence of the quaternary ammonium group on betaine induces a shift of approximately 105 kcal/mol. The kinetic method is also used to investigate the effect of stereoisomerism on the rates of dissociation of proton-bound dimers of amino acids. Comparisons are made for collisions of a variety of cationic projectiles, including those containing Si, P, Br, I and W, with a fluorinated self-assembled monolayer surface and collisions of the same projectiles with analogous target gases such as perfluorohexane, difluoroethane and tetrafluoromethane. The results show parallels between the reactions observed in the surface and gas-phase systems including multiple fluorine atom abstractions.

Degree

Ph.D.

Advisors

Cooks, Purdue University.

Subject Area

Analytical chemistry|Biochemistry|Chemistry

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