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Hydrogen–deuterium exchange reactions of 16 small rigid anions were examined using D 2 O, CH 3 OD, CH 3 CO 2 D, and (CF 3 ) 2 C(CH 3 )OD. Bimolecular rate constants and extensive computations are reported. These deuterated reagents were used because D 2 O and CH 3 OD are weak acids that cannot react via sequential deuteron/proton transfers (i.e., the conventional H/D exchange mechanism of DePuy et al.) with the selected anions, and they provide a means to probe alternative pathways. The relative acidity of CH 3 CO 2 D and (CF 3 ) 2 C(CH 3 )OD was measured (ΔΔ H acid ° = 1.1 ± 0.8 kcal mol −1 ) and their thermodynamic similarity but structural differences (i.e., the presence of a C O in the carboxylic acid but not the alcohol) were exploited to systematically investigate flip-flop and relay mechanisms. This has led to a number of generalizations relating to the occurrence of these pathways. [ABSTRACT FROM AUTHOR]

Abstract: The reactions of CH3 +, CH2Cl+ and CHCl2 + with standard reference bases were examined in a dual cell Fourier transform mass spectrometer. Deprotonation of methyl cation occurs rapidly via a spin forbidden process to afford triplet methylene even when the reaction is nearly thermoneutral. Bracketing results enable us to assign PA(CHCl)=209.7±2.2kcalmol−1 and PA(CCl2)=205.2±1.9kcalmol−1, the latter value of which is considerably larger than previous determinations. The resulting heats of formation, however, are in good accord with other measurements and lead to recommended values of (CHCl)=74.6±2.4kcalmol−1 and (CCl2)=53.0±2.6kcalmol−1. These values correspond to a 2–3kcalmol−1 lowering of these quantities and are within 1–2kcalmol−1 of high level G3 and W1 predictions based upon the atomization energies and a series of four isodesmic reactions. [Copyright &y& Elsevier]

N-glycosylation is a common post-translational modification (PTM) in plants that possesses important biological functions including protein folding, protein quality control, protein stability and protein-protein interactions. Nowadays, the interest in analysis of glycoproteins using mass spectrometry is increasing because of advances in instrumentation and automatic data analysis tools. Here, we describe the progresses in mass spectrometry-based N-glycomics and N-glycoproteomics in plants. We also provide a comprehensive summary of N-glycan structures in plants according to the biosynthetic rules and up-to-date reports, which serves as a theoretical database for all N-glycan-related search engines. [Display omitted] • Methods and application progresses in mass spectrometry-based N-glycomics was comprehensively reviewed. • Methods and application progresses in mass spectrometry-based N-glycoproteomics was comprehensively reviewed. • Structural characteristics and core structures of plant N-glycans were summarized as a theoretical reference database. [ABSTRACT FROM AUTHOR]