Gas-liquid chromatography and mass spectrometry of deuterium-containing amino acids as their trimethylsilyl derivatives

Quantification of corticosteroids in human plasma by liquid chromatography-thermospray mass spectrometry using stable isotope dilution

Liquid chromatography-thermospray mass spectrometry (LC-TSP-MS) using isotope dilution was investigated for quantitative analysis of cortisol, cortisone, prednisolone and prednisone in human plasma. Complete separation attained by a LiChroCART Supersupher reversed-phase column and elution with 0.05 M ammonium formate-tetrahydrofuran-methanol (180:53:17, v/v/v) resulted in a significantly large isotope effect of the deuterium-labeled analogs on the HPLC behavior and caused difficulty in quantification. Reduction of the isotope effect on the retention times using 0.05 M ammonium formate-acetonitrile (65:35, v/v) permitted accurate quantification of cortisol and cortisone by the isotope dilution LC-TSP-MS, although separation between cortisol and prednisone was incomplete.

OH radical-induced products of tyrosine peptides

Reactions of radiation-generated OH radicals with tyrosine and its homopeptides, i.e. L-Tyr-L-Tyr and L-Tyr-L-Tyr-L-Tyr, in N2O saturated solutions were shown to give crosslinks between the peptide chains with high yields. High-performance liquid chromatography, capillary gas chromatography and mass spectrometry were used for isolation and identification of the monomeric and dimeric products. Evidence is presented for the crosslinking to occur through C-C and C-O-C bonds. To the best of our knowledge, the formation of the ether type of crosslink is demonstrated for the first time. Mechanisms of product formation are also discussed, which involve radicals that were described in previous pulse radiolysis studies.

The use of capillary gas chromatography-mass spectrometry for identification of radiation-induced DNA base damage and DNA base-amino acid cross-links

Application of capillary gas chromatography-mass spectrometry (GC-MS) to isolation and identification of radiation-induced DNA base damage including DNA base-amino acid crosslinks is reported. gamma-Irradiated samples of thymine (thy), thymidine (dT), thymidine-5'-monophosphate (pdT), cytosine(cyt),2'-deoxycytidine (dC), 2'-deoxycytidine-5'-monophosphate (pdC), and mixtures of thy, dT and pdT with tyrosine were used as model systems. Trimethylsilylation was used as the derivatization method. Samples containing nucleosides and nucleotides were first subjected to hydrolysis with formic acid or hydrochloric acid to remove sugar or sugar-phosphate moieties, then trimethylsilylated and analyzed by GC-MS. Trimethylsilyl derivatives of radiation-induced monomeric and dimeric products of the model systems mentioned above were shown to have excellent GC properties and easily interpretable mass spectra. The presence of the molecular ion (M+.) and a characteristic (M-CH3)+ ion in the mass spectra facilitated structural elucidation. The complementary use of tert.-butyldimethylsilyl derivatives was also demonstrated. These derivatives provided an intense characteristic (M-57)+ ion in their mass spectra, which may be used to corroborate the molecular weight and to monitor the corresponding compounds in a complex mixture by means of selected-ion monitoring. All gas chromatograms and mass spectra obtained are discussed in detail.

OH radical-induced crosslinks of methionine peptides

Reactions of radiation-generated OH radicals with methionine (Met) and its homopeptides, L-Met-L-Met and tri-L-Met, were investigated through reaction products. Samples of irradiated Met and HCl-hydrolysates of its irradiated homopeptides were trimethylsilylated and analysed by capillary gas chromatography-mass spectrometry. Mass spectra taken revealed the formation of three products, 2-amino-4-(methyldithio)butanoic acid, 4,4'-thiobis(2-aminobutanoic acid) and homocystine. G values of these products were determined to be 0.10, 0.16 and 0.30, respectively.

Isolation and characterization of radiation-induced aliphatic peptide dimers

alpha-Peptide radicals of L-Ala-L-Ala and tetra-L-Ala, formed from reaction with OH radicals, generated in H2O by ionizing radiation, were shown to give peptide dimers. These peptide dimers were separated and isolated by HPLC. On acid hydrolysis, all of the studied peptide dimers yielded alanine and 1,2-diamino-1,2-dimethyl succinic acid, which was characterized by gas chromatography-mass spectrometry as its TMS derivative. The described procedure is also suggested as a suitable method for isolation and characterization of amino acid dimers.

Gas chromatography of amino acids

This review summarizes all papers that have appeared on the gas chromatography of amino acids (including the iodoamino acids) and their enantiomers in the period 1956-mid-1974. It has been found that the methods used for analysis of amino acids can be divided into three classes: (1) degradative procedures and techniques for converting the amino acid into another chemical compound; (2) procedures based on esterification of the carboxyl group and derivatization of the a-amino and other reactive groups in at least two steps; and (3) procedures based on a simultaneous derivatization of the carboxyl and a-amino groups in one reaction medium. For the treatment of the amino acid or its alkyl ester, three approaches can be distinguished for the two latter cases, i.e., acylation, alkylation (including silylation) and condensation. Of the procedures used for the resolution of optical antipodes, two methods are discussed, namely analysis of diastereoisomers on optically inactive stationary phases and separation of enantiomers on optically active stationary phases.