Search

Methylation is an essential metabolic process in the biological systems, and it is significant for several biological reactions in living organisms. Methylated compounds are known to be involved in most of the bodily functions, and some of them serve as biomarkers. Theoretically, all α-amino acids can be methylated, and it is possible to encounter them in most animal/plant samples. But the analytical data, especially the mass spectral data, are available only for a few of the methylated amino acids. Thus, it is essential to generate mass spectral data and to develop mass spectrometry methods for the identification of all possible methylated amino acids for future metabolomic studies. In this study, all N-methyl and N,N-dimethyl amino acids were synthesized by the methylation of α-amino acids and characterized by a GC-MS method. The methylated amino acids were derivatized with ethyl chloroformate and analyzed by GC-MS under EI and methane/CI conditions. The EI mass spectra of ethyl chloroformate derivatives of N-methyl (1-18) and N,N-dimethyl amino acids (19-35) showed abundant [M-COOC 2 H 5 ] + ions. The fragment ions due to loss of C 2 H 4 , CO 2 , (CO 2  + C 2 H 4 ) from [M-COOC 2 H 5 ] + were of structure indicative for 1-18. The EI spectra of 19-35 showed less number of fragment ions when compared with those of 1-18. The side chain group (R) caused specific fragment ions characteristic to its structure. The methane/CI spectra of the studied compounds showed [M + H] + ions to substantiate their molecular weights. The detected EI fragment ions were characteristic of the structure that made easy identification of the studied compounds, including isomeric/isobaric compounds. Fragmentation patterns of the studied compounds (1-35) were confirmed by high-resolution mass spectra data and further substantiated by the data obtained from 13 C 2 -labeled glycines and N-ethoxycarbonyl methoxy esters. The method was applied to human plasma samples for the identification of amino acids and methylated amino acids. Copyright © 2016 John Wiley & Sons, Ltd., (Copyright © 2016 John Wiley & Sons, Ltd.)

The cation binding strength of calix[4]pyrroles in the gas phase has been evaluated by computational studies and further substantiated by ESI mass spectrometry experiments. The DFT optimized geometries of [CP + X](+) complexes are found to be stable in a 1,3-alternate conformation through cation-π interactions and interestingly CPs are found to be better cation receptor than calix[4]arenes. The binding energy values of [CP + X](+) complexes computed at B2PLYP/TZVP//M05-2X/TZVP follows the binding order, Li(+) > Na(+) > K(+) > Rb(+) > Cs(+). The diameter of Li(+) matches very well with the cavity size of CP and thus is optimally disposed to interact simultaneously with all four pyrrole rings through multiple cation-π interactions. However, other cations, due to the increase in their size, drift away from the cavity center towards the rim of the cavity exhibiting weak cation-π interactions. Energy decomposition analysis (EDA) reveals that the electrostatic and polarization effects act as the major driving force in these interactions. The important outcome of the current study is that the stability of precursor and product ions is found to be crucial in the experimental evaluation of binding affinity of Li(+) and Na(+) complexes of CP. The ESI-MS/MS experiments on the cation complexes of different substituted CPs revealed that the binding strength of CPs towards cations is also dependant on the substituents at the meso-position.

A series of isomeric 2-aryl-6,6-dimethyltetrahydro-5-quinolinones (set I) and 2-aryl-7,7-dimethyltetrahydro-5-quinolinones (set II) were studied under positive ion electron ionization (EI) and electrospray ionization (ESI) techniques. Under EI conditions, the molecular ions were found to be less stable in set I isomers, and they resulted in abundant fragment ions, i.e., [M-CH(3)](+), [M-CO](+.), [M-HCO](+), [M-(CH(3),CO)](+), and [M-(CH(3),CH(2)O)](+), when compared with set II isomers. In addition, the set I isomers showed specific fragment ions corresponding to [M-OH](+) and [M-OCH(3)](+). The retro-Diels-Alder (RDA) product ion was always higher in set II isomers. The ESI mass spectra produced [M + H](+) ions, and their decomposition showed favorable loss of CH(3) radical, CH(4) and C(2)H(6) molecules in set I isomers. The set II isomers, however, showed predominant RDA product ions, and specific loss of H(2)O. The selectivity in EI and ESI was attributed to the instability of set I isomers by the presence of a gem-dimethyl group at the α-position, and it was supported by the data from model compounds without a gem-dimethyl group. Density functional theory (DFT) calculations successfully corroborated the fragmentation pathways for diagnostic ions. This study revealed the effect of a gem-dimethyl group located at the α-position to the carbonyl having aromatic/unsaturated carbon on the other side of the carbonyl group., (Copyright © 2011 John Wiley & Sons, Ltd.)

Anaesthesia was given from a Boyle's apparatus to 100 patients, using compressed air as the carrier gas.