Characterization of synthetic N‐acetylcysteine conjugates by positive‐ and negative‐ion ²⁵²Cf plasma desorption mass spectrometry

Abstract

Dedicated to Professor Dr G. SpiteUer on the occasion of his 60th birthday N-Acetylcysteine and nine N-acetylcysteine conjugates of synthetic origin were characterized by positive-and negative-ion plasma desorption mass spectrometry. For sample preparation the electrospray technique and the nitrocellulose spin deposition technique were applied. The fkagmentation of these compounds, which are best seen as S-substituted desaminoglycylcysteiae dipeptides, shows a similar behaviour to that of linear peptides. In the positive-ion mass spectra intense protonated molecular ion peaks are observed. In addition, several sequence specific fragment ions (A+, B+, IY + 2H]+, Z'), immonium ions (I+) and a diagnostic fragment ion for mercap turic acids %+) are detected. The negative-ion mass spectra exhibit deprotonated molecular ions and in contrast only one fragment ion corresponding to sidechain specific cleavage ([ R,S] -) representing the xenobiotic moiety.In the case of a low alkali metal concentration on the target, cluster molecular ions of the [nM + HI+ or InM -H]ion type (n = 1-3) are observed. The analysis of an equimolar mixture of eight N-acetylcysteine conjugates shows diaerent quasi-molecular ion yields for the positiveand negative-ion spectra.

Characterization of Mercapturic Acids by Three Different Mass Spectrometric Methods

“…All the mercapturic acids investigated, analysed by PD-MS, exhibit abundant [M + H] + ions. Alkali metal adducts often appear in the positive-ion mode, as Pittenauer et al 15 showed for N-acetyl-L-cysteine and its nine conjugates. In this work, two new compounds, DIOL and EMA, were analysed.…”

“…The results obtained for MMA, BMA and PMA correspond to results already published. 15 Table 1) for mercapturic acids, which are typically observed for dipeptides, 23 are exhibited and presented in Table 2.…”

“…9 Assessment of exposure to toxic substances requires the specific and accurate detection of mercapturates at low concentrations in complex biological matrices. Therefore, a variety of ionization techniques have been used in the mass spectrometric determination of mercapturic acids, including electron ionization (EI), 10 positive and negative chemical ionization (CI), 11 field desorption (FD), 12 fast-atom bombardment (FAB), 13 thermospray, 13 electrospray ionization (ESI) 14 and plasma desorption 15 techniques. In general, FD and FAB have been the most successful in providing molecular ion information.…”

Characterization of braun’s lipoprotein and determination of its attachment sites to peptidoglycan by 252Cf-PD and MALDI time-of-flight mass spectrometry

“…Mo lecu lar wei ght dete rm ina tion of th e pe p tide fragm e nts ge nera te d b y cleavage of the free for m of th e ou ter m em b ran e 7-ku lip oprotein w ith cy anogen b romid e as w ell as the by-p rod ucts (e.g.. for myla tion, hydrolysis of the C-te rm in al h orn oser irie lac ton e) kn own to be p re sent in suc h d igests; the fragme n ts w ere sep ara ted by reverse ph ase HPLC " A n ast eri sk I") i n d ica tes po ss ib le pea k ove r la p pi n g of f ragm e nt io ns of sim ilar mass va lue d ue to i n s u ff ici e n t m ass reso l ut io n of this t i me -of -fl ig ht ins t r u m e nt 6b). The fragment ion s include d both peptide backbone as well as peptide side chain fragment ions classified according to the modifi ed Roepstorff-Fohlman nomenclature [46,47] as earlie r described by several groups for po sitive-ion PD TO F/ MS [48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63] (Tables 4 and 5).…”