Twenty singly-charged dipeptide ions with N-terminal arginine were photodissociated using 157 nm light in both a linear ion-trap mass spectrometer and a MALDI-TOF-TOF mass spectrometer. Analogous to previous work on dipeptides containing C-terminal arginine, this set of samples enabled insights into the photofragmentation propensities associated with individual residues. In addition to familiar products such as a-, d-, and immonium ions, m2 and m2+13 ions were also observed. Certain side chains tended to cleave between their β and γ carbons without necessarily forming d- or w-type ions, and a few other ions were produced by the high-energy fragmentation of multiple bonds.
A recent statistical study (Savitski, M. M.; Falth, M.; Eva Fung, Y. M.; Adams, C. M.; Zubarev, R. A. J. Am. Soc. for Mass Spectrom. doi: 10.1016/j.jasms.2008.08.003) of a large spectral database indicated that the product ion spectra of doubly protonated
tryptic peptides fall into two distinct classes. The main factor distinguishing the two classes is the relative abundance
of the yN-2 fragment: for Class I spectra yN-2 is the most abundant y fragment while for Class II other y ions dominate the corresponding spectra. To explain the dominance of yN-2 for Class I spectra formation of a nontraditional b2 ion with a diketopiperazine (6-membered cyclic peptide) rather than an oxazolone structure was proposed. Here we present
evidence from tandem mass spectrometry, hydrogen/deuterium exchange, and density functional calculations that do not support
this proposal. Namely, that CID of doubly protonated YIGSR, YGGFLR, and YIYGSFK produce Class I product ion spectra, yet the
b2 fragment is shown to have the traditional oxazolone structure. 相似文献
In the preceding papers of this series, we reported the synthesis of liquid-crystalline polyurethanes containing mesomorphic moieties in the main chain and in side chains [1–4]. Liquid crystalline polymers with side groups containing the cholesterol moiety have also been studied [5, 6]. The main focus of attention has centered around the study of phase transitions of acrylic and methacrylic derivatives of cholesterol. This paper describes the synthesis of a new type of liquid-crystalline polyurethane containing the cholesterol moiety in side chains. 相似文献
Proteins containing dinuclear Cu (II), Zn (II) centers play paramount roles in biology1. As mimetic of metal-dependent esterase, dinuclear Cu (II) and Zn (II) complexes have received a great deal of attentions2~6. They are of interest in the field of biomimetic chemistry to provide an improved understanding of the function of the biological sites and as potential catalysts for substrate oxidations. Schiff base type polydentate ligands which contain centeral hydroxyl group have been wid… 相似文献
Using a large set of high mass accuracy and resolution ETD tandem mass spectra, we characterized ETD-induced neutral losses.
From these data we deduced the chemical formula for 20 of these losses. Many of them have been previously observed in electron-capture
dissociation (ECD) spectra, such as losses of the side chains of arginine, aspartic acid, glutamic acid, glutamine, asparagine,
leucine, histidine, and carbamidomethylated cysteine residues. With this information, we examined the diagnostic value of
these amino acid-specific losses. Among 1285 peptide–spectrum matches, 92.5% have agreement between neutral loss-derived peptide
amino acid composition and the peptide sequences. Moreover, we show that peptides can be uniquely identified by using only
the accurate precursor mass and amino acid composition based on neutral losses; the median number of sequence candidates from
an accurate mass query is reduced from 21 to 8 by adding side chain loss information. Besides increasing confidence in peptide
identification, our findings suggest the potential use of these diagnostic losses in ETD spectra to improve false discovery
rate estimation and to enhance the performance of scoring functions in database search algorithms. 相似文献
Accurate identification of fragments in tandem mass spectrometry experiments is aided by knowledge of relevant fragmentation mechanisms. Herein, novel radical addition reactions that direct unexpected side-chain dissociations at tryptophan and tyrosine residues are reported. Various mechanisms that can account for the observed dissociation channels are investigated by experiment and theory. The propensity for radical addition at a particular site is found to be primarily under kinetic control, which is largely dictated by molecular structure. In certain peptides, intramolecular radical addition reactions are favored, which leads to the observation of numerous unexpected fragments. In one pathway, radical addition leads to migration of an aromatic side chain to another residue. Alternatively, radical addition followed by hydrogen atom loss leads to cyclization of the peptide and increased observation of internal sequence fragments. Radical addition reactions should be considered when assigning fragmentation spectra obtained from activation of hydrogen deficient peptides.
A novel biphenyl side-chained diamine with alkyloxy spacer and alkyloxy tail,4'-butoxy-4-(3,5-diami-nobenzoyloxy)hexyloxybiphenyl(C6BBC4),was synthesized and characterized by FTIR and 1H NMR.A series o... 相似文献
High-accuracy MS/MS spectra of deprotonated ions of 390 dipeptides and 137 peptides with three to six residues are studied. Many amino acid residues undergo neutral losses from their side chains. The most abundant is the loss of acetaldehyde from threonine. The abundance of losses from the side chains of other amino acids is estimated relative to that of threonine. While some amino acids lose the whole side chain, others lose only part of it, and some exhibit two or more different losses. Side-chain neutral losses are less abundant in the spectra of protonated peptides, being significant mainly for methionine and arginine. In addition to the neutral losses, many amino acid residues in deprotonated peptides produce specific negative ions after peptide bond cleavage. An expanded list of fragment ions from protonated peptides is also presented and compared with those of deprotonated peptides. Fragment ions are mostly different for these two cases. These lists of fragments are used to annotate peptide mass spectral libraries and to aid in the confirmation of specific amino acids in peptides.
