Plasma desorption mass spectra

Figure 5-3. Plasma desorption mass spectra of anthocyanidins extracted from A. chrysanthemum, B. begonia, C. carnation, and D. phlox. The data in this figure was published in the article Plasma desorption mass spectrometry of anthocyanidins , Rap. Comm. Mass Spectrom. 7 400-403, by Wood, K. V., Bonham, C. C., Ng, J., Hipskind, J. and Nicholson, R. L. 1993. Copyright John Wiley and Sons. Reproduced with permission.

Ladder Sequencing. Because plasma desorption mass spectra commonly reveal only molecular ions, it has become common to obtain amino acid sequences using carboxy or amino-peptidases to generate a mixture of truncated peptides whose mass differences correspond to the amino acid residues. One example of this is shown in Figure 4.15, in which bradykinin has been digested directly on the nitrocellulose foil with carboxypeptidase... 

FIGURE 4.14 Plasma desorption mass spectra of the HPLC fractions containing peptide (a)aT6 and (b) an aT6 variant. (Reprinted with permission from reference 31). 

An intense peak at m/e = 689, eonsistent with [Co(15b-H)2 ], was observed in the positive ion plasma desorption mass spectrum. 

Figure 4. Partial Californium-252 time-of-flight plasma desorption mass spectrum of Hez-PBAN.

Figure 2 Plasma desorption mass spectrum of glucuronic acid conjugates of propranolol glucuronldes. The spectrum is provided by Dr. Robert Cotter.

FIGURE 4. Plasma desorption mass spectrum of the isolated PSl-E polypeptide. The peaks at 3605.8 and 5412.4 correspond to the triple and double charged molecular ions. Correcting for the protons, an average molecular mass of 10,819 5 Da is calculated. Analysis of a different preparation of the isolated PSI-E polypeptide yielded a mass of 10,820 5 Da (not shown). 

FIGURE 4,13 Positive ion plasma desorption mass spectrum of the tryptic digest of recombinant human growth hormone after washing with deionized water. (Reprinted with permission from reference 30). 

FIGURE 4.16 Plasma desorption mass spectrum of papain, (a) structure and identity of sequence fragments, (b) mass spectrum showing the multiply charged molecular ions, and (c) expansion of the spectrum in the range m/z 1000-2520. (Reprinted with permission from reference 34). 

FIGURE 7.8 Comparison of the (a) FAB, (b) plasma desorption, (c) liquid SIMS, and (d) IRLD mass spectra of the phospholipids extracted from E coli. The mass spectra in (c) and (d) were obtained by delayed extraction after 20 and 50 (is, respectively.The molecular ions are MH in the FAB (a) and liquid SIMS spectra (c), M-H+2Na in the plasma desorption mass spectrum, (b) and MK in the IRLD mass spectrum (d). (Reprinted with permission from reference 20). 

FIGURE 11.1 Negative ion plasma desorption mass spectrum of the fully protected synthetic hexamer CAACCA. MTr = monomethox-ytrityl, = benzoylcytidine, and R = TBDMS. (Reprinted v ith permission from reference 2). 

It is thus very likely that this substituent is already present in chlorophyll -RCl in vivo and is responsible for the red-shifted absorption It should be noted, however, that chloride ions are present in the photosynthetic membrane Oxidation at C-I32 is principally possible too, but unlikely with the precautions taken by us The 52cf plasma desorption mass spectrum of chlorophyll -RCl (2) has a molecular ion indicative of one additional oxygen being present together with one chlorine atom already in the original pigment, too ... 

Because C-terminal amides have often been reported in insect neuropeptides (8), a 33 residue C-terminal amide consistent with the sequence data was synthesized by solid-phase methods. The peptide was purified by HPLC and its structure confirmed by automated Edman degradation. Californium-252 time-of-flight plasma desorption mass spectrometry provided additional evidence for the structure via a very broad peak for the singly-charged molecular ion at m/z 3902-3906. Because the calculated MW of Hez-PBAN (3899.6, based on the most abundant ion in the isotope cluster) was seen to differ from that observed in the mass spectrum of the isolated native peptide by ca. 32, it was presumed that the native peptide had undergone oxidation of both its methionines to their respective sulfoxides during the course of its isolation and purification. 

Very low basicity and nucleophilicity made the trifluoromethanesulfonate anion (TfO ) the counterion of choice for labile cationic species as in dication salts 53 and 54, which were characterized by FD, FAB and 252Cf-Plasma Desorption mass spectrometry40. In the FD mass spectrum of 53, the noteworthy presence of the dication itself ([D]2 + ) was found, giving the base peak, accompanied by a cation triflate cluster [D OTf]+ and fragment ions, involving cleavage at the ether bond. 

Plasma desorption mass spectrometry has been employed in only a few laboratories for peptide identification. Nevertheless, the techniques can yield useful structural information [see ref. (1), p. 1209]. For example, in the positive Cf spectrum of the 31-residue peptide P-endorphin, an [M -h Na] ion at m/z 3487 was readily identifiable. In a more recent... 

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