Peptides deprotonated

It is not an exaggeration to say that electrospray has introduced a new era, not only for the analytical mass spectroscopist, but also for the more physically oriented researcher interested in physical measurements involving the above ions, which are of such great importance in condensed-phase ion chemistry. In particular, gas-phase ions produced by electrospray allow, for the first time, thermochemical measurements involving ions of biochemical significance such as protonated peptides, deprotonated nucleotides, and metal ion complexes with peptides and proteins. It is to be expected that such data will be of importance in the development of theoretical modeling of the state of these systems in the condensed phase.34,35... 

Stability constants for Cu11 complexation of Gly—X and X—Gly dipeptides show that even relatively small alkyl side chains can influence coordination. 3 At low pH, for example, the bidentate chelates N(amino),0(peptide) of L-Leu-Gly and L-Ile-Gly are the thermodynamically less stable, presumably due to steric hindrance from the branched side chains. Similar coordination by Gly—X is virtually independent of the nature of X. This latter result is not unexpected since only the Gly moiety is coordinating. However, on raising the solution pH (> 4) the peptide deprotonation that occurs to give tridentate N(amino),N(peptide),0(carboxyl) chelation is slightly inhibited by the Leu and lie residues (by 0.7-0.8 log units). 

Table 10 Ionization Constants of Some Coordinated Glycine Peptides, Showing Metal-ion-promoted Peptide Deprotonations ...

Fast-atom bombardment (FAB) is an ionization technique that produces a protonated or deprotonated molecular ion, hence a molecular mass for the sample. It can be used for analysis of peptides up to m/z about 5000. 

Laser-desorption mass spectrometry (LDMS) or matrix-assisted laser desorption ionization (MALDI) coupled to a time-of-flight analyzer produces protonated or deprotonated molecular ion clusters for peptides and proteins up to masses of several thousand. 

To summarize, we have systematically tested all possible three- and two-layer ONIOM combinations of high-level QM (HQ=B3LYP/6-31G ), low-level QM (LQ=AM1), and MM (Amber) for the deprotonation energy and structure of a test molecule, an ionic form of a peptide. We find the errors introduced in the ONIOM approximation, in comparison with the target HQ (or HQ HQ HQ) calculation, generally increases in the order ... 

The crystal structure of chloro-pentamethylcyclopentadienyl-S-leucyl-S-leucyl methyl ester-iridium(III), (86), indicates that the Ir—N(NH2-linkage) is longer (2.129 A) than that to the deprotonated peptide N atom (2.090 A).131... 

Zinc complexes of peptides with N-terminal cysteine are monomeric of the form ZnL2 where the peptide is an anion with the SH deprotonated. Tetrahedral N2S2 coordination is observed with the chelating peptides and Zn(Cys-Gly-NH2)2 was structurally characterized.857... 

Tandem mass spectrometry has become an important tool for determining the sequence of amino acids in protonated peptides98 and the sequence of bases in deprotonated nucleic acids such as DNA.99 Despite the importance and widespread use of CID-MS to sequence peptides and nucleic acids, the mechanistic details of the dissociation processes are poorly understood. A better understanding of the... 

Ni2 + bound to deprotonated peptide nitrogens in tri- and tetrapeptides can be oxidized to Ni3+ [331-333]. The presence of Ni3+ has been reported in bacterial hydrogenases and dehydrogenases [334, 335], which suggests a biological role for the Ni3 + /Ni2+ redox couple. 

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