H-Gly-OH

H-Gly-OH

Why Are B ions stable species in peptide spectra?[Pubmed:24214067]

J Am Soc Mass Spectrom. 1995 Dec;6(12):1165-74.

Protonated amino acids and derivatives RCH(NH2)C(+O)X . H(+) (X = OH, NH2, OCH3) do not form stable acylium ions on loss of HX, but rather the acylium ion eliminates CO to form the immonium ion RCH = NH 2 (+) . By contrast, protonated dipeptide derivatives H2NCH(R)C(+O)NHCH(R')C(+O)X . H(+) [X = OH, OCH3, NH2, NHCH(R'')COOH] form stable B2 ions by elimination of HX. These B2 ions fragment on the metastable ion time scale by elimination of CO with substantial kinetic energy release (T 1/2 = 0.3-0.5 eV). Similarly, protonated N-acetyl amino acid derivatives CH3C(+O)NHCH(R')C(+O)X . H(+) [X = OH, OCH3, NH2, NHCH(R'')COOH] form stable B ions by loss of HX. These B ions also fragment unimolecularly by loss of CO with T 1/2 values of approximately 0.5 eV. These large kinetic energy releases indicate that a stable configuration of the B ions fragments by way of activation to a reacting configuration that is higher in energy than the products, and some of the fragmentation exothermicity of the final step is partitioned into kinetic energy of the separating fragments. We conclude that the stable configuration is a protonated oxazolone, which is formed by interaction of the developing charge (as HX is lost) with the N-terminus carbonyl group and that the reacting configuration is the acyclic acylium ion. This conclusion is supported by the similar fragmentation behavior of protonated 2-phenyl-5-oxazolone and the B ion derived by loss of H-Gly-OH from protonated C6H5C(+O)-Gly-Gly-OH. In addition, ab initio calculations on the simplest B ion, nominally HC(+O)NHCH2CO(+), show that the lowest energy structure is the protonated oxazolone. The acyclic acylium isomer is 1.49 eV higher in energy than the protonated oxazolone and 0.88 eV higher in energy than the fragmentation products, HC(+O)N(+)H = CH2 + CO, which is consistent with the kinetic energy releases measured.

Fragmentation reactions of protonated peptides containing glutamine or glutamic acid.[Pubmed:12577284]

J Mass Spectrom. 2003 Feb;38(2):174-87.

A variety of protonated dipeptides and tripeptides containing glutamic acid or glutamine were prepared by electrospray ionization or by fast atom bombardment ionization and their fragmentation pathways elucidated using metastable ion studies, energy-resolved mass spectrometry and triple-stage mass spectrometry (MS(3)) experiments. Additional mechanistic information was obtained by exchanging the labile hydrogens for deuterium. Protonated H-Gln-Gly-OH fragments by loss of NH(3) and loss of H(2)O in metastable ion fragmentation; under collision-induced dissociation (CID) conditions loss of H-Gly-OH + CO from the [MH - NH(3)](+) ion forms the base peak C(4)H(6)NO(+) (m/z 84). Protonated dipeptides with an alpha-linkage, H-Glu-Xxx-OH, are characterized by elimination of H(2)O and by elimination of H-Xxx-OH plus CO to form the glutamic acid immonium ion of m/z 102. By contrast, protonated dipeptides with a gamma-linkage, H-Glu(Xxx-OH)-OH, do not show elimination of H(2)O or formation of m/z 102 but rather show elimination of NH(3), particularly in metastable ion fragmentation, and elimination of H-Xxx-OH to form m/z 130. Both the alpha- and gamma-dipeptides show formation of [H-Xxx-OH]H(+), with this reaction channel increasing in importance as the proton affinity (PA) of H-Xxx-OH increases. The characteristic loss of H(2)O and formation of m/z 102 are observed for the protonated alpha-tripeptide H-Glu-Gly-Phe-OH whereas the protonated gamma-tripeptide H-Glu(Gly-Gly-OH)-OH shows loss of NH(3) and formation of m/z 130 as observed for dipeptides with the gamma-linkage. Both tripeptides show abundant formation of the y(2)'' ion under CID conditions, presumably because a stable anhydride neutral structure can be formed. Under metastable ion conditions protonated dipeptides of structure H-Xxx-Glu-OH show abundant elimination of H(2)O whereas those of structure H-Xxx-Gln-OH show abundant elimination of NH(3). The importance of these reaction channels is much reduced under CID conditions, the major fragmentation mode being cleavage of the amide bond to form either the a(1) ion or the y(1)'' ion. Particularly when Xxx = Gly, under CID conditions the initial loss of NH(3) from the glutamine containing dipeptide is followed by elimination of a second NH(3) while the initial loss of H(2)O from the glutamic acid dipeptide is followed by elimination of NH(3). Isotopic labelling shows that predominantly labile hydrogens are lost in both steps. Although both [H-Gly-Glu-Gly-OH]H(+) and [H-Gly-Gln-Gly-OH]H(+) fragment mainly to form b(2) and a(2) ions, the latter also shows elimination of NH(3) plus a glycine residue and formation of protonated glycinamide. Isotopic labelling shows extensive mixing of labile and carbon-bonded hydrogens in the formation of protonated glycinamide.

Glycine buffered synthesis of layered iron(II)-iron(III) hydroxides (green rusts).[Pubmed:27894515]

J Colloid Interface Sci. 2017 Jul 1;497:429-438.

Layered Fe(II)-Fe(III) hydroxides (green rusts, GRs) are efficient reducing agents against oxidizing contaminants such as chromate, nitrate, selenite, and nitroaromatic compounds and chlorinated solvents. In this study, we adopted a buffered precipitation approach where glycine (GLY) was used in the synthesis of sulfate-interlayered GR (GRSO4) by aerial oxidation of Fe(II) or co-precipitation by adding Fe(III) salt to an aqueous solution of Fe(II) at constant pH. In both the oxidation and the co-precipitation methods pure crystalline GRSO4 was precipitated in the presence of 70mM GLY (pH 8.0), whereas in the absence of GLY, synthesis failed under similar conditions. Gycine functions as both a pH buffer and a ligand; Fe(II)-GLY complexes serve as a source of base (Fe(II)-GLY+H2O-->Fe(II)+H-GLY+OH(-)) during GR formation, supplying about 45% of the total base required for the synthesis. The GLY buffer decreases pH fluctuations during base addition and hence allows for fast GRSO4 precipitation, minimizing byproduct formation. The use of other pH buffers [4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid and 2-amino-2-(hydroxymethyl)-1,3-propanediol] was also tested but failed. Mossbauer spectroscopy, X-ray diffraction, Fourier transform infrared, transmission electron microscopy, and Fe(II) measurements confirmed the purity, stoichiometry, and pyroaurite-type structure of the obtained GRSO4. The formula of GRSO4 was found to be Fe(II)4.08Fe(III)1.98(OH)11.6(SO4)1.00, and the tabular GR crystals had a lateral size of 100-500nm and a thickness of about 40nm. Upscaling of the synthesis by either 25 times in volume or 20 times in Fe(II) concentration resulted in pure GRSO4 products. Compared with the conventional unbuffered GRSO4 synthesis method, the present method can provide pure products with a controllable, fast, and low-cost process.

Glycine receptors: heterogeneous and widespread in the mammalian brain.[Pubmed:1722365]

Trends Neurosci. 1991 Oct;14(10):458-61.

The amino acid glycine is an established inhibitory neurotransmitter in the spinal cord and brain stem. Its postsynaptic receptor has been purified, and cDNAs of the receptor subunits have been cloned and sequenced. Recent molecular studies indicate considerable diversity of the inhibitory glycine receptor (GlyR); this diversity stems from both the existence of several alpha-subunit genes encoding isoforms of distinct pharmacology, and alternative splicing of their primary transcripts. In situ hybridization studies reveal a widespread expression of GlyRs throughout the mammalian CNS, suggesting that glycinergic neurotransmission may be implicated in many higher brain functions.

Glycine is an inhibitory neurotransmitter in the CNS and also acts as a co-agonist along with glutamate, facilitating an excitatory potential at the glutaminergic N-methyl-D-aspartic acid (NMDA) receptors.

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