Rebecca M. O'Malley

Vasodilating procyanidins derived from grape seeds.

Abstract: We have shown in previous work that extracts of grape seeds (GSE) and skins, grape juice, and many red wines exhibit endothelium‐dependent relaxing (EDR) activity in vitro. This EDR activity involves endothelial nitric oxide (NO) release and subsequent increase in cyclic GMP levels in the vascular smooth muscle cells. The NO/cyclic GMP pathway is known to be involved in many cardiovascular‐protective roles. The current study focuses on the isolation and identification of EDR‐active compounds (procyanidins) from GSE. Crushed Concord grape seeds were extracted with methanol and the extract was separated into seven fractions (A‐G) on a Toyopearl TSK‐HW‐40 column. EDR‐active fractions (D‐G) were further separated into 25 individual compound peaks by HPLC, 16 of which were EDR active (threshold for relaxation ranged between less than 0.5 μg/mL and greater than 4 μg/mL). Procyanidin identification was accomplished by electrospray‐ion trap mass spectrometry (ES‐ITMS), MS/MS, and by tannase treatment and acid thiolysis, followed by HPLC and ES‐ITMS of the products. Activity of isolated procyanidins tended to increase with degree of polymerization, epicatechin content, and with galloylation. These EDR‐active compounds (many of which also possess antioxidant activity), individually or in the form of wines, juices, or nutritional supplements, may be useful in preventing or treating cardiovascular diseases.

Multiphoton ionization of aniline, aniline-15N and aniline-2,3,4,5,6-d5: ionization and fragmentation mechanisms

Abstract We report the resonant and non-resonant multiphoton ionization (MPI) spectra of aniline, aniline- 15 N and aniline-2,3,4,5,6- d 5 obtained at wavelengths of 266,355 and 532 nm. Consideration of plots of fragment ion currents vs. laser pulse energy and analysis of the contributions from deuterated ions to total fragment ion intensities (obtained using aniline-2,3,4,5,6- d 5 ) have allowed characterization of the mechanisms involved in the overall ionization/fragmentation process at the three wavelengths. The resonant MPI at 266 nm is found to take place via initial molecular ion formation, followed by photofragmentation of this ion. In both the non-resonant cases the first step appears to be a rapid dissociation of the neutral molecule into smaller neutral entities. These are subsequently ionized, and photofragmentation of the ions produced then takes place. At 355 nm a minor contribution to the ionization/dissociation mechanism appears to involve molecular ion formation followed by photofragmentation.

The involvement of ring hydrogen atoms in the reaction C6H5NH2+. → C5H6+. + HNC

Abstract We report electron impact and 266 nm MPI data obtained using an aniline/aniline-2,3,4,5,6-d5 mixture which indicate that both the rapid and the metastable decomposition reactions C6H5NH2+. → C5H6+. + HNC in the aniline system have two components. The major component involves the loss of a hydrogen atom originally attached to the nitrogen atom in the aniline molecule whereas the minor component involves the loss of a hydrogen atom originally attached to the ring. The relative rate constants for the two metastable decomposition reactions in aniline-2, 3,4,5,6-d5 have been measured.

The non-resonant multiphoton ionization and fragmentation of benzene, phenylacetylene and benzonitrile

Abstract The non-resonant multiphoton ionization fragmentation patterns of benzene, phenylacetylene and benzonitrile have been obtained at laser wavelengths of 532 and 355 nm. Observed ion fragmentation patterns are quite different from those obtained by electron impact, but show some similarities among themselves and with previously reported multiphoton ionization spectra of other aromatic molecules. The energy dependencies of the non-resonant ionic fragmentation patterns for all three systems show different behaviors in the low and high energy ranges studied. A mechanism for the fragment ion formation process which is consistent with the observed experimental data is proposed and discussed.

Non-resonant multiphoton ionization and fragmentation patterns of selected low-mass hydrocarbons: acetylene, ethylene, ethane, propylene, propane, isobutylene and cis-2-butene

Abstract We report the investigation of the non-resonant multiphoton ionization (MPI) fragmentation patterns of acetylene, ethylene, ethane, propylene, propane, isobutylene and cis-2-butene at 532 and 355 nm over a range of laser pulse energies. The results for acetylene at both wavelengths show that MPI of this neutral species may be important in the consideration of possible precursors of the ions C+ , CH+, C+ 2, C2H+ and C2H+ 2 commonly observed in MPI spectra of larger systems. Near-constant dependences of ionic fragmentation ratios on laser pulse energy for these systems approach the class C behavior defined previously.

The importance of the time-lag parameter in a laser/time-of-flight mass spectrometer

Abstract The time-lag delay has been shown to be an important experimental parameter in the measurement of fragmentation patterns in multiphoton ionization spectra obtained using a time-of-flight mass spectrometer. Experimental data indicate that ions formed by multiphoton ionization acquire greater translational energies and are lost more rapidly from the ionization region than those formed by electron-impact ionization. Time-lag focussing does produce improved resolution in multiphoton ionization, but it is only effective for those ions which have not moved out of the draw-out volume. Utilization of a low-level electron beam trap has been found to be ineffective in retarding ion loss in multiphoton ionization experiments.

Direct measurement of the rate constant for the reaction C6H5NH2+· → C5H6+· + CNH on the microsecond time scale

Abstract We report a new direct method by which the rate constant for the metastable decomposition reaction C 6 H 5 NH 2 +· → C 5 H 6 +· + CNH in the aniline system has been measured. Ionization was achieved by multiphoton absorption at 266 nm and the reaction time was varied by altering the time delay between the laser light crossing the source and the initiation of the draw-out pulse in a laser/time-of-flight apparatus. The C 5 H 6 +· product ion intensity was recorded directly as a function of time and the rate constant for the reaction was calculated from a simple kinetic plot. The obtained value for the rate constant, k = (1.7 ± 0.4) × 10 6 s −1 is in good agreement with previously reported experimental and theoretical values.