ESI-MS spectra

Effect of dimer formation on deactivation. Another possible mode of deactivation is formation of inactive Co dimers or oligomers. To test for these species, we examined the ESI-mass spectram of fresh and deactivated Co-salen catalysts in dichloromethane solvent (22). The major peak in the mass spectram occurred at m/z of 603.5 for both Jacobsen s Co(II) and Co(III)-OAc salen catalysts, whereas much smaller peaks were observed in the m/z range of 1207 to 1251. The major feature at 603.5 corresponds to the parent peak of Jacobsen s Co(II) salen catalyst (formula weight = 603.76) and the minor peaks (1207 to 1251) are attributed to dimers in the solution or formed in the ESI-MS. The ESI-MS spectrum of the deactivated Co-salen catalyst, which was recovered after 12 h HKR reaction with epichlorohydrin, was similar to that of Co(II) and Co(III)-OAc salen. Evidently, only a small amount of dimer species was formed during the HKR reaction. However, the mass spectram of a fresh Co(III)-OAc salen catalyst diluted in dichloromethane for 24 h showed substantial formation of dimer. The activity and selectivity of HKR of epichlorohydrin with the dimerized catalyst recovered after 24 h exposure to dichloromethane were similar to those observed with a fresh Co-OAc salen catalyst. Therefore, we concluded that catalyst dimerization cannot account for the observed deactivation. 

Flow injection analysis (FIA) ESI-MS and APCI-MS spectra for an EO/PO polyether modified silicone surfactant (PEMS) used as a personal care product have been obtained in positive and negative ionisation modes with the positive ionisation mode yielding the best results [41]. The spectra obtained in both modes were highly complicated, and thus no assignment was given. Significant differences in the ionisation results were obtained from the two interfaces, with those ions observed in the ESI-MS spectrum appearing in the lower... 

Fig. 2.10.7. (- )-LC-ESI-MS spectrum of C7-SPC. The position of the phenyl ring in the ions m/z 285 and 225 is arbitrarily chosen (Reprinted with permission from [17]. Copyright SETAC, Pensacola, Florida, USA.).

Fig. 5.4 Monitoring of the enzymatic reaction and cathepsin B inhibition by ESI-MS. MS instrument Shimadzu LCMS-2010 single-stage quadrupole mass spectrometer, (a) The ESI-MS spectrum obtained after analysis of the enzyme reaction, containing the cleavage products AMC (m/z 175.9) and Z-FR (m/z 456.1) m/z 244.9 and m/z 329.9 belong to...

FIGURE 8.2 ESI-MS spectrum of ubiquitin, showing the multiple-charged ions. 

FIGURE 8.4 ESI-MS spectrum in FIA of metamidophos, showing adduct ions with Na and... 

Yessotoxin and its analogues are disulfonated polyether toxins reported from shellfish from different countries, but a new derivative lacking a 1-sulfated substituent, 1-desulfoyessotoxin (YTX with R =H), has been isolated from mussels from Norway <1998MI235>. Its ESI-MS spectrum showed that this compound is 102 Da smaller than YTX 17, implying that one of the sulfate esters in YTX was desulfonated. The NMR data of 1-desulfoyessotoxin are similar to that of YTX 17 except for the 1-methylenic protons where desulfonation occurred they are shifted to upheld by 0.49ppm and their chemical shifts (3.72 and 3.78ppm) are typical of hydroxymethyl protons. 

Fig. 5. ESI-MS spectrum for the reaction mixture of 2,6dimethoxybenzoic acid as the substrate and acetonitrile as the reactant/solvent with using Pd(02CCF3)2 Reprinted with permission from [48). Copyright 2010 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim.

An alternative model for ESI was developed by the group of Siu [24-25]. They correlated the ion envelope of a protein with the predicted distribution of charge states of the protein in solution. The latter depends on pH and pK values of the acidic and basic amino acids in the protein. From the good correlation obtained, they conclude that the ion envelope nicely reflects the abundances of the preformed ions of the protein in solution. Based on further experiments, they postulate that the droplet evaporation is not that important and that the ESI-MS spectrum results from ions directly emitted from the Taylor cone [25-26]. 

To achieve structural and semi-quantitative information on the anthocyanins ESI-MS/MS direct-injection analysis of extract can be performed. An example of an ESI-MS spectrum is reported in Figure 3.16. 

Schematic representation of the ESI-MS spectrum of compounds present in a copper(II) ion and 1,2-ethanediamine (1 2) mixture in water. Peaks are defined in terms of m/z (mass/charge ratio).

Fig. 29. LC/ESI-MS analysis of the oxidation of a short double-stranded oligonucleotide by Mn-TMPyP/KHSOs. ODN I stands for the self complementary oligonucleotide 5 -CAGCTG. The oxidation was carried out in 50 mM Tris/HCl buffer pH = 7, NaCl 100 mM with the following concentrations of reactants duplex ODN I, Mn-TMPyP, KHSO5, 200 pM, 200 pM, 2mM, respectively. The reaction lasted 5 min at 0°C. A HPLC trace B in-line ESI-MS spectrum of ODN I (retention time, 44.5 min).

Figure 13.21 LC-MS analysis of protein peptide fragments, (a) Trypsin digestion of protein to yield peptide fragments, (b) LC-MS-TIC chromatograms of pepsin digest of a protein molecule, and (c) ESI-MS spectrum of the molecular ion of separated peptide fragment. (Adapted with permission from Applied Biosystems/MDS Sciex.)...

The ESI-MS spectrum of neurotensin, a peptide consisting of 13 amino acids with a molecular weight of 1,672 Da is shown in Fig. 4.16. Due to the soft ionisation, no fragments are observed. As mentioned earlier, ESI promotes the formation of multiply charged ions. Peptides and proteins, thus, give a series of signals with [M -b H]+, [M + 2H]2+, [M + 3H]2+ to [M -b nH]"+. 

Fig. 4.17. ESI-MS spectrum of lactose permease showing differently ions carrying 20 to more than 50 positive charges (redrawn with permission from J.P. Whitelegge et al. PNAS, 1999, 96 10695-10698, copyright 1999, National Academy of Sciences, U.S.A.).

Figure 5.16 Electrospray ionization-mass spectrometry (ESI-MS) spectrum of apomyoglobin.

Take 10 mg of the product powder, dissolve in 2 mL ultra-pure water and analyze directly. Figure 4.18 is the ESI-MS spectrum of the product. 

Fig. 4.18. ESI-MS spectrum of the product. Ionization mode ESI spray voltage 3.7 KV ion source temperature I20°C desolvation temperature 300°C ion energy 1.0 v [35].

Figure I. The ESI-MS spectrum (positive ion-mode) and sequential fragmentation spectrum (MS ) of a-PHB telechelic obtained in the polymerization of (R,S) P-butyrolactone initiated by l8-Crown-6 complex of 4-hydroxybutanoic acid sodium salt and terminated with bromoethanol.

It has been recently demonstrated that the equimolar reaction of (R,S) P-butyrolactone with o,L-lactic acid, conducted in bulk at the temperature of 70"C, leads to the copolymer containing hydroxyl and carboxylic end groups. The negative-ion ESI-MS spectrum of the copolymer obtained consisted with clusters of anions separated due to their different degree of oligomerization (from dimer up to 14-mer) and composition (Fig 3a). 

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