Consecutive loss of two benzyl radicals from the [M + Na](+) adduct ions of pyrogallol tribenzyl ether and its derivatives

Kuck D, Heitkamp S, Letzel M, Ahmed I, Krohn K. Consecutive loss of two benzyl radicals from the [M + Na](+) adduct ions of pyrogallol tribenzyl ether and its derivatives. EUROPEAN JOURNAL OF MASS SPECTROMETRY. 2018;24(1):23-32.The electrospray ionization-collision-induced dissociation mass spectra of nine pyrogallol tribenzyl ethers, 2-10, and a catechol dibenzyl ether, 11, that bear various functional groups or larger structural extensions have been studied with respect to the occurrence of a highly characteristic consecutive loss of two benzyl radicals from the sodiated molecular ions, [M + Na](+). It is shown that this specific fragmentation reaction strongly dominates other fragmentation routes, such as loss of carbon monoxide, formaldehyde and water. In addition, elimination of benzaldehyde occurs as a minor fragmentation channel in most cases. In contrast to these aryl-benzyl ethers, the consecutive two-fold loss of C7H7 center dot is suppressed in the [M + Na](+) ions of dibenzyl ethers derived from multiply benzylated gallocatechin and catechin, where the elimination of benzyl alcohol prevails the primary fragmentation almost completely. The secondary fragmentation of the [M + Na](+) ions, which also comprises the two-fold loss of C7H7 center dot, as well as a remarkable primary fragmentation of a flavene-based congener leading to particularly stable sodium-free chromylium product ions is also presented

The Role of Ion/Neutral Complexes in the Fragmentation of N-Benzyl-(alkylpyridinium) Ions

Kuck D, Grützmacher H-F, Barth D, Heitkamp S, Letzel MC. The Role of Ion/Neutral Complexes in the Fragmentation of N-Benzyl-(alkylpyridinium) Ions. International Journal of Mass Spectrometry. 2011;306(2-3):159-166

Consecutive losses of two benzyl radicals from the [M + Na](+) adduct ions of di- and tri(benzyloxy)benzenes under ESI/CID conditions

Kuck D, Heitkamp S, Sproß J, et al. Consecutive losses of two benzyl radicals from the [M + Na](+) adduct ions of di- and tri(benzyloxy)benzenes under ESI/CID conditions. International Journal of Mass Spectrometry. 2015;377:23-38.The successive loss of two benzyl radicals from the [M +Na](+) ions of the isomeric dihydroxybenzene dibenzyl ethers (2-4) and of the isomeric trihydroxybenzene tribenzyl ethers (5-7) under ESI/CID conditions has been studied by deuterium labelling, MS experiments and DFT calculations. The fragmentation of the [M + Na](+) ions of 2 and 4 consists exclusively of the consecutive losses of two C7H7* (benzyl) radicals. This process is largely suppressed in the corresponding [M + Na](+) ions of the meta isomer 3 and also in those of the 1,3,5-analog, phloroglucinol tribenzyl ether (6), suggesting the facile formation of sodiated ortho- and para-quinone ions, [C6H4O2 + Na](+), in the cases of 2 and 4, respectively. This finding is corroborated by a detailed investigation of the sodiated tribenzyl ethers of pyrogallol, [5 + Na](+), and 1,2,4-trihydroxybenzene, [7 + Na](+), and their isotopologs bearing differently labelled benzyl residues. Again, the successive loss of two C7H7* radicals is the only fragmentation channel for ions [7 + Na](+) and strongly predominates for ions [5 + Na](+), with the primary and secondary losses being highly regiospecific: ions [5 + Na](+) lose the first benzyl residue almost exclusively from the central position (0-2) and only then a lateral C7H7* radical (from 0-1 or 0-3). Surprisingly, the very minor primary loss of a lateral benzyl group is followed by that of the other lateral one, suggesting a two-step isomerization process initiated by a 1,4-H* shift. Ions [7 + Na](+) lose the first benzyl radical almost exclusively from 0-1, in very minor amounts from 0-2 but not at all from 0-4. The secondary loss of C7H7* subsequent to the major primary loss occurs from both 0-2 and 0-4 in similar amounts, reflecting the relative stabilities of the sodiated benzyloxy-substituted ortho- and para-benzoquinones. This and several other details of the energy profiles associated with the twofold benzyl loss from ions [5 + Na](+) and [7 + Na](+) were calculated by use of the DFT methodology and were found to agree very well with the regioselectivities observed. Finally, the pyrogallol-based ions [5 + Na](+) were found to eliminate benzaldehyde in minor but significant relative amounts, which takes place with high regioselectivity from 0-1 or 0-3. (C) 2014 Elsevier B.V. All rights reserved

Microbial functional changes mark irreversible course of Tibetan grassland degradation

The Tibetan Plateau’s Kobresia pastures store 2.5% of the world’s soil organic carbon (SOC). Climate change and overgrazing render their topsoils vulnerable to degradation, with SOC stocks declining by 42% and nitrogen (N) by 33% at severely degraded sites. We resolved these losses into erosion accounting for two-thirds, and decreased carbon (C) input and increased SOC mineralization accounting for the other third, and confirmed these results by comparison with a meta-analysis of 594 observations. The microbial community responded to the degradation through altered taxonomic composition and enzymatic activities. Hydrolytic enzyme activities were reduced, while degradation of the remaining recalcitrant soil organic matter by oxidative enzymes was accelerated, demonstrating a severe shift in microbial functioning. This may irreversibly alter the world´s largest alpine pastoral ecosystem by diminishing its C sink function and nutrient cycling dynamics, negatively impacting local food security, regional water quality and climate