Ana M. Cardoso

Identification of vertebrate type steroid hormones in the shrimp Penaeus japonicus by tandem mass spectrometry and sequential product ion scanning

The identification of testosterone, pregnelonone, and 17α-hydroxyprogesterone by tandem mass spectrometry and of progesterone by sequential product ion scanning in the shrimp gonads of Penaeus japonicus is described. The identification of these substances in biological samples is usually done by gas chromatography-mass spectrometry and involves several liquid chromotographic purification steps followed by derivatization. The utilization of tandem mass spectrometry in this analysis has simplified considerably the sample pretreatment and provided a very simple method of screening these substances in complex mixtures.

PROTON AFFINITIES OF PHENYLALKYLAMINES BY THE KINETIC METHOD

Abstract The kinetic method was used to determine the proton affinities of phenylalkylamines of general formula R1R2C6H3CHR3(CH2)nNR4R5 where R1 = H or OH; R2 = H, F, NO2, OH or OCH3; R3 = H or OH; R4 and R5 = H and/or CH3; n = 1−3. Amines were used as reference bases and the proton affinities of the phenylalkylamines were bracketed by a pair of reference bases that give rise, in the MIKE spectra of the heterodimer, to more or less intense signals than the compound under study. The influence of the aliphatic chain length and of the substituents on the aromatic ring, on the proton affinities of the phenylalkylamines is presented and discussed. The formation of an hydrogen bond between the amino group and the aromatic ring is proposed to explain the results obtained.

Fragmentation reactions of molecular ions and dications of indoleamines

The combination of techniques such as two-dimensional mass spectrometry and mass analysed ion kinetic energy spectrometry (with and without collision gas) in the study of gas-phase ion chemistry of indole, gramine, tryptamine and serotonine enabled us to establish the fragmentation pathways of their singly- and doubly-charged molecular ions generated by electron impact. The measurement of the kinetic energy released in the charge separation reactions of the molecular dications produced information on the intercharge distance on the transition state for the fragmentation, assuming that it arises entirely from the coulombic energy released. For the singly-charged molecular ions of indoleamines, loss of the neutral molecule CH2=NR (R = H or CH3), by hydrogen transfer from the amino (or methyl) group to the indole nucleus, is the only fragmentation occurring in the third field-free region of the mass spectrometer. Upon collision of the molecular ion with He gas, a competing process of bond cleavage by loss of the radical •CH2NH2 (or •N(CH3)2 for gramine) is observed for tryptamine and serotonine. The doubly-charged ions dissociate by elimination of neutral molecules or radicals to generate doubly-charged fragment ions or by charge separation reactions. The intercharge distance, calculated from the kinetic energy released in the fragmentation, was, whenever possible, correlated with charge location in the ion.

dimethyl ether chemical ionization of arylalkylamines.

The gas-phase reactions of dimethyl ether (DME) ions with a number of biologically active arylalkylamines of the general formula R(1)R(2)C(6)H(3)CHR(3)(CH(2))(n)NR(4)R(5), where R(1) = H or OH, R(2) = H, F, NO(2), OH or OCH(3), R(3) = H or OH, R(4) and R(5) = H or CH(3), have been studied by means of chemical ionization mass spectrometry. Under the experimental conditions used, the most abundant DME ion is the methoxymethyl cation (CH(3)OCH(2)(+), m/z 45). The unimolecular metastable decompositions of the [M + 45](+), [M + 13](+) and [M + 15](+) adducts formed have been interpreted in terms of the initial site of reaction with the amines and the presence of different functional groups in the molecule. This has permitted establishment of general fragmentation patterns for the adducts, and their correlation with structural features of the molecules. The main site of reaction of the ion CH(3)OCH(2)(+) with the amines seems to be the amino group, particularly if the amine is primary, although a competition with attack on the aromatic ring and especially on the benzylic hydroxy group is observed. In a few cases the reaction mechanisms have been elucidated through the use of deuterated amines obtained by H/D exchange with D(2)O.

Gas‐phase deprotonation of arylalkylamines. A collision‐induced dissociation study

The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd.

The role of distonic ions in the formation of CH3NH3+ and (CH3)2NH2+ from the molecular ions of octopamine and synephrine

It is shown by mass-analyzed ion kinetic energy spectrometry that the metastably decomposing molecular ions of octopamine (p-HOC6H4CH(OH)CH2NH2) and synephrine (p-HOC6H4CH(OH)CH2NHCH3) yield only protonated methylamine and dimethylamine, respectively, as product ions. From deuterium labeling and variation of the internal energy of the molecular ions, experimental support has been obtained that these product ions are generated via the occurrence of a distonic ion-neutral complex. In the case of octopamine, this complex would consist of a nitrogen-protonated aminomethyl radical and p-hydroxylbenzaldehyde in which the former species abstracts the aldehydic or phenolic hydrogen atom from the latter to give protonated dimethylamine.

Behaviour of arylalkylamines toward trimethyl borate as a gas-phase reagent.

Abstract Gas-phase reactions of a number of arylalkylamines of general structure R 1 R 2 C 6 H 3 CHR 3 (CH 2 ) n NR 4 R 5 , where R 1 = H, F, NO 2 , OH or OCH 3 , R 2 = H or OH, R 3 = H or OH, R 4 and R 5 = H or CH 3 with the dimethoxyborinium ion, (CH 3 O) 2 B + , m/z 73, obtained by electron ionization of trimethyl borate have been studied. Mass-analysed ion kinetic energy (MIKE) spectra of the [M + 73] + adducts, generated in a chemical ionisation source, together with MIKE spectra of some of their decomposition products, have been taken and interpreted. The interpretation is discussed in terms of structural features present in the neutral molecules, such as aliphatic chain length, methyl substitution at the amino group, presence of electron-donating or electron-withdrawing substituents in the aromatic ring and, finally, presence of a benzylic hydroxy group. The analysis of the results shows that the fragmentations of the adduct ions [M + 73] + are much more structurally sensitive than those for the [M + 45] + adducts previously observed with dimethyl ether, with the loss of methanol generating the most abundant ion only for three of the amines studied. The amino group is an important, but not always the dominant site of initial reaction, the exceptions being: (1) the aromatic ring, if substituted by activating substituents, and (2) a benzylic hydroxy group, if present in the structure. The 2-(4-nitrophenyl)-ethylamine constitutes the only exception to the general behaviour just described, because in that case the site of reaction of the electrophilic dimethoxyborinium ion is the oxygen atom of the nitro group.

Gas-phase reactions of the oxygen radical anion with arylalkylamines

Abstract The gas-phase reactions of the oxygen radical anion O ·− with a number of biologically active arylalkylamines of general formula R 1 C 6 H 4 CHR 2 (CH 2 ) n NHR 3 , where R 1 =H, F, NO 2 , OH, or OCH 3 , R 2 =H or OH, and R 3 =H or CH 3 , have been studied by means of chemical ionization mass spectrometry, using a mixture of N 2 O and N 2 (1:9) to generate the O ·− reagent ions. The collision-induced dissociation spectra of the [M−H+O] − adduct ions formed in the ion source of the mass spectrometer have been interpreted in terms of the aliphatic chain length and the presence of different functional groups in the molecule. The analysis of data indicates that the preferred site of oxygen radical anion attachment is the benzylic carbon atom, except for the amines with a benzylic hydroxy group (octopamine and synephrine), where a competition between the aromatic ring and the benzylic carbon atom, becomes evident. The fragmentation pathways observed for octopamine and synephrine are unique as compared with all the other amines, in which the chain length also exerts an important influence on the observed decompositions.