Laurence Angel | Texas A&M University - Commerce (original) (raw)
Papers by Laurence Angel
Journal of Physical Chemistry A, 2008
Energy-resolved competitive collision-induced dissociation is used to investigate the proton-boun... more Energy-resolved competitive collision-induced dissociation is used to investigate the proton-bound heterodimer anions of a series of carboxylic acids (formic, acetic, and benzoic acid) and nitrous acid with their conjugate bases. The dissociation reactions of the complexes [CH 3 COO‚H‚OOCH] -, [CH 3 COO‚H‚ONO] -, [HCOO‚H‚ ONO] -, [C 6 H 5 COO‚H‚OOCH] -, and [C 6 H 5 COO‚H‚ONO]are investigated using a guided ion beam tandem mass spectrometer. Cross sections of the two dissociation channels are measured as a function of the collision energy between the complex ions and xenon target gas. Apparent relative gas-phase acidities are found by modeling the cross sections near the dissociation thresholds using statistical rate theory. Internal inconsistencies are found in the resulting relative acidities. These deviations apparently result from the formation of higherenergy conformers of the acids within the complex ions induced by double hydrogen bonding, which impedes the kinetics of dissociation to ground-state product acid conformations.
Journal of The American Society for Mass Spectrometry, 2011
Ion mobility-mass spectrometry is used to study the new conformers of bovine ubiquitin (Ub) and t... more Ion mobility-mass spectrometry is used to study the new conformers of bovine ubiquitin (Ub) and the palladium(II) binding sites after the incubation with cis-[Pd(en)(H2O)2]2+ where en = ethylenediamine. Palladium(II) complexes are potentially useful proteomic reagents because they selectively bind to the side groups of methionine and histidine and hydrolytically cleave the peptide bond. Incubating 1.0 mM solution of Ub with 10.0 molar excess of cis-[Pd(en)(H2O)2]2+ results with one to four Pd2+ or Pd(en)2+ being attached to intact Ub and two conformer families at each of the 4+ to 11+ charge states. The 4+ and 5+ species exhibit a compact form, which is also observed in untreated Ub, and a new highly folded conformer. The 6+ to 10+ exhibit an elongated form, also observed in Ub, and a new partially folded conformer. The new conformers are shown to be more stable if they contain at least one Pd2+, rather than all Pd(en)2+. IM-MS/MS of [UbPd2en+5H]9+ shows that both the partially folded and elongated conformers first lose the en ligand, followed by dissociating into product ions that indicate that Met1, Glu51/Asp52, His68, and Glu16 are binding sites for Pd2+. These results suggest that Pd2+ is simultaneously binding to multiple side groups across different regions of Ub. This type of sequestering of Pd2+ probably reduces the efficiency of Pd2+ ions to selectively cleave Ub because it prevents Pd2+ anchoring to only Met or His and to an adjacent backbone amide nitrogen and forming the “activated complex” necessary for specific peptide bond cleavage.
ABSTRACT Reaction cross sections, product axial velocity distributions, and potential energy surf... more ABSTRACT Reaction cross sections, product axial velocity distributions, and potential energy surfaces are presented for the hydrogen atom abstraction reactions S-+RH-->R+HS- (R=H, CH3, C2H5) as a function of collision energy. The observed threshold energy, E0, for S-+H2-->H+HS- agrees with the reaction endothermicity, DeltarH0. At low collision energies, the H+HS- products exhibit symmetric, low-recoil-velocity scattering, consistent with statistical reaction behavior. The S-+CH4-->CH3+HS- and S-+C2H6-->C2H5+HS reactions, in contrast, show large excess threshold energies when compared to DeltarH0. The excess energies are partly explained by a potential energy barrier separating products from reactants. However, additional dynamical constraints must account for more than half of the excess threshold energy. The observed behavior seems to be general for collisional activation of anion-molecule reactions that proceed through a tight, late transition state. For RH=CH4 and C2H6, the HS- velocity distributions show anisotropic backward scattering at low collision energies indicating small impact parameters and a direct rebound reaction mechanism. At higher collision energies, there is a transition to HS- forward scattering and high velocities consistent with grazing collisions and a stripping mechanism.
Journal of Physical Chemistry A, 2001
Journal of The Chemical Society, Faraday Transactions, 1997
Journal of Physical Chemistry A, 1999
Journal of Physical Chemistry A, 2008
Energy-resolved competitive collision-induced dissociation is used to investigate the proton-boun... more Energy-resolved competitive collision-induced dissociation is used to investigate the proton-bound heterodimer anions of a series of carboxylic acids (formic, acetic, and benzoic acid) and nitrous acid with their conjugate bases. The dissociation reactions of the complexes [CH 3 COO‚H‚OOCH] -, [CH 3 COO‚H‚ONO] -, [HCOO‚H‚ ONO] -, [C 6 H 5 COO‚H‚OOCH] -, and [C 6 H 5 COO‚H‚ONO]are investigated using a guided ion beam tandem mass spectrometer. Cross sections of the two dissociation channels are measured as a function of the collision energy between the complex ions and xenon target gas. Apparent relative gas-phase acidities are found by modeling the cross sections near the dissociation thresholds using statistical rate theory. Internal inconsistencies are found in the resulting relative acidities. These deviations apparently result from the formation of higherenergy conformers of the acids within the complex ions induced by double hydrogen bonding, which impedes the kinetics of dissociation to ground-state product acid conformations.
Journal of The American Society for Mass Spectrometry, 2011
Ion mobility-mass spectrometry is used to study the new conformers of bovine ubiquitin (Ub) and t... more Ion mobility-mass spectrometry is used to study the new conformers of bovine ubiquitin (Ub) and the palladium(II) binding sites after the incubation with cis-[Pd(en)(H2O)2]2+ where en = ethylenediamine. Palladium(II) complexes are potentially useful proteomic reagents because they selectively bind to the side groups of methionine and histidine and hydrolytically cleave the peptide bond. Incubating 1.0 mM solution of Ub with 10.0 molar excess of cis-[Pd(en)(H2O)2]2+ results with one to four Pd2+ or Pd(en)2+ being attached to intact Ub and two conformer families at each of the 4+ to 11+ charge states. The 4+ and 5+ species exhibit a compact form, which is also observed in untreated Ub, and a new highly folded conformer. The 6+ to 10+ exhibit an elongated form, also observed in Ub, and a new partially folded conformer. The new conformers are shown to be more stable if they contain at least one Pd2+, rather than all Pd(en)2+. IM-MS/MS of [UbPd2en+5H]9+ shows that both the partially folded and elongated conformers first lose the en ligand, followed by dissociating into product ions that indicate that Met1, Glu51/Asp52, His68, and Glu16 are binding sites for Pd2+. These results suggest that Pd2+ is simultaneously binding to multiple side groups across different regions of Ub. This type of sequestering of Pd2+ probably reduces the efficiency of Pd2+ ions to selectively cleave Ub because it prevents Pd2+ anchoring to only Met or His and to an adjacent backbone amide nitrogen and forming the “activated complex” necessary for specific peptide bond cleavage.
ABSTRACT Reaction cross sections, product axial velocity distributions, and potential energy surf... more ABSTRACT Reaction cross sections, product axial velocity distributions, and potential energy surfaces are presented for the hydrogen atom abstraction reactions S-+RH-->R+HS- (R=H, CH3, C2H5) as a function of collision energy. The observed threshold energy, E0, for S-+H2-->H+HS- agrees with the reaction endothermicity, DeltarH0. At low collision energies, the H+HS- products exhibit symmetric, low-recoil-velocity scattering, consistent with statistical reaction behavior. The S-+CH4-->CH3+HS- and S-+C2H6-->C2H5+HS reactions, in contrast, show large excess threshold energies when compared to DeltarH0. The excess energies are partly explained by a potential energy barrier separating products from reactants. However, additional dynamical constraints must account for more than half of the excess threshold energy. The observed behavior seems to be general for collisional activation of anion-molecule reactions that proceed through a tight, late transition state. For RH=CH4 and C2H6, the HS- velocity distributions show anisotropic backward scattering at low collision energies indicating small impact parameters and a direct rebound reaction mechanism. At higher collision energies, there is a transition to HS- forward scattering and high velocities consistent with grazing collisions and a stripping mechanism.
Journal of Physical Chemistry A, 2001
Journal of The Chemical Society, Faraday Transactions, 1997
Journal of Physical Chemistry A, 1999