Cristina M. F. Barros

Phenolic characterization of Northeast Portuguese propolis: usual and unusual compounds.

In this study, an ethanolic extract from Portuguese propolis was prepared, fractionated by high-performance liquid chromatography, and the identification of the phenolic compounds was done by electrospray mass spectrometry in the negative mode. This technical approach allowed the identification of 37 phenolic compounds, which included not only the typical phenolic acids and flavonoids found in propolis from temperate zones but also several compounds in which its occurrence have never been referred to in the literature. Four of the novel phenolic compounds were methylated and/or esterified or hydroxylated derivatives of common poplar flavonoids, although six peculiar derivatives of pinocembrin/pinobanksin, containing a phenylpropanoic acid derivative moiety in their structure, were also identified. Furthermore, the Portuguese propolis sample was shown to contain a p-coumaric ester derivative dimer.

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.

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.

Tandem mass spectrometry based investigation of cinnamylideneacetophenone derivatives: valuable tool for the differentiation of positional isomers

Cinnamylideneacetophenones have been extensively used as versatile starting materials in numerous different transformations. The structural characterization of this type of compounds is, therefore, of crucial importance since it can give information on the chemistry, reactivity and also the potential biological activity of this type of compounds. Thus, 24 derivatives were systematically studied by tandem mass spectrometry (MS(2)) with electrospray ionization (ESI), in positive ion mode. The protonated molecules, [M + H](+), formed under ESI conditions were induced to dissociate and the fragmentation patterns were studied. The information collected provided important structural information on the type of substituents present and constitute an important database concerning this family of compounds. Overall, it was found that the substitution pattern of the cinnamylideneacetophenone derivatives changes the ESI-MS(2) fragmentation considerably. These results indicate that ESI-MS(2) is a useful technique for distinguishing positional isomers of these cinnamylideneacetophenone derivatives.

Structural characterization of nitrated 2′-hydroxychalcones by electrospray ionization tandem mass spectrometry

Isomeric 2′-hydroxychalcones bearing nitro and methoxy groups in different positions of their skeleton were analyzed by tandem mass spectrometry (MS/MS) with electrospray ionization (ESI), in positive mode. Collision-induced dissociation of the protonated molecules, [M + H]+, formed under electrospray conditions were studied and it was found that the product ion spectra of these chalcones presented different fragmentation patterns depending on the position of the substituents on the molecule. The product ion spectra (ESI-MS/MS) of the B ring ortho-nitro substituted 2′-hydroxychalcone and of the 4′-methoxychalcones showed loss of OH•, 2OH• and combined losses of OH• and H2O. These fragment ions were absent in the spectra of the respective meta- and para isomers. The observed differences in the product ion spectra of these nitrochalcones allowed identification of the o-nitro derivatives. Distinction between the meta- and para-derivatives was not achieved. Chalcones bearing 6′-methoxy substituents showed distinct fragmentation from the one observed for their isomers, 4′-methoxychalcones, since they present only one fragment ion, a typical (0,αA – H)+ and, therefore, do not allow detailed structural information to be obtained, nor to differentiate between the o-, m- or p-nitro isomers. Overall, it was found that small changes in the substitution pattern of chalcones change their fragmentation considerably in the ESI-MS/MS, and that these features permit the differentiation of specific isomers of these 2′-hydroxynitrochalcones.

Gas-phase structural characterization of neuropeptides Y Y1 receptor antagonists using mass spectrometry: Orbitrap vs triple quadrupole

Graphical abstract Figure. No caption available. HighlightsStructural assignment of accurately measured ions of NPY Y1 receptor antagonists.Similar qualitative structural information for CID‐QqQ and HCD Orbitrap instruments.Report of quantifying ions and characteristic ‘signature’ fragments.Limit of quantification by QqQ instrument is suitable for biological applications. ABSTRACT Collision induced dissociation of triple quadrupole mass spectrometer (CID‐QqQ) and high‐energy collision dissociation (HCD) of Orbitrap were compared for four neuropeptides Y Y1 (NPY Y1) receptor antagonists and showed similar qualitative fragmentation and structural information. Orbitrap high resolution and high mass accuracy HCD fragmentation spectra allowed unambiguous identification of product ions in the range 0.04–4.25 ppm. Orbitrap mass spectrometry showed abundant analyte‐specific product ions also observed on CID‐QqQ. These results show the suitability of these product ions for use in quantitative analysis by MRM mode. In addition, it was found that all compounds could be determined at levels >1 &mgr;g L−1 using the QqQ instrument and that the detection limits for this analyzer ranged from 0.02 to 0.6 &mgr;g L−1. Overall, the results obtained from experiments acquired in QqQ show a good agreement with those acquired from the Orbitrap instrument allowing the use of this relatively inexpensive technique (QqQ) for accurate quantification of these compounds in clinical and academic applications.