Cristina M. F. Barros

University of Aveiro, Aveiro, Aveiro, Portugal

Are you Cristina M. F. Barros?

Claim your profile

Publications (18)37.7 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Rapid Communications in Mass Spectrometry 10/2011; 25(20):3185-95. · 2.51 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Analytical and Bioanalytical Chemistry 11/2009; 396(2):887-97. · 3.66 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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 H(2)O. 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,alpha)A - 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.
    European Journal of Mass Spectrometry 02/2009; 15(5):605-16. · 1.26 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS) have been used to differentiate the 2- and 4-methylpyridyl isomers of free-base and metallated cationic beta-vinylpyridylporphyrins. The analysis by ESI-MS/MS of the deuterated analogs and semiempirical calculations of structural and electronic parameters were also undertaken. The two free-base isomers are easily differentiated by ESI-MS/MS but the presence of a metallic center renders differentiation of the metallated isomers less effective. The data acquired show that of all the studied compounds, the free-base 2-methylpyridyl isomer, which was operative in the in vitro photoinactivation of Herpes simples virus, has a different gas-phase behavior. Local distortion of the macrocycle due to the presence of the beta-vinylpyridyl substituent occurs for all the compounds, but a different electron density distribution can account for the observed gas-phase behavior of this potential virus photoinactivator.
    Journal of the American Society for Mass Spectrometry 03/2007; 18(2):218-25. · 3.59 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Liquid secondary ion and electrospray mass spectrometry were used to study the complexation in-source of 5,10,15-tris(pentafluorophenyl)corrole with several divalent transition-metal ions. The metallocorrole ions formed in-source were identified by comparing their product ion mass spectra with the spectra of the same ions formed from metallocorroles obtained from classical procedures. Positive metallocorrole ion formation is accompanied by oxidation of the metal centre. Mechanisms were proposed for the oxidation processes, and data from negative-ion spectra reinforced these mechanisms.
    Journal of Mass Spectrometry 03/2007; 42(2):225-32. · 3.21 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Electrospray ionisation mass spectrometry (ESI-MS), electrospray ionisation tandem mass spectrometry (ESI-MS/MS) and Ultraviolet-visible (UV-vis) spectroscopy were used to investigate the non-covalent interactions between small oligonucleotide duplexes with the GC motif and a group of cationic meso(N-methylpyridynium-4-yl)porphyrins (four free bases with one to four positive charges, and the zinc complex of the tetracationic free base). The results obtained point to outside binding of the porphyrins, with the binding strength increasing with the number of positive charges. Fragmentations involving losses from both chains were observed for the porphyrins with N-methylpyridinium-4-yl groups in opposite meso positions.
    Journal of Mass Spectrometry 12/2005; 40(11):1439-47. · 3.21 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The zinc complexes of diaryl bis(p-nitrophenyl)porphyrins and beta-(1,3-dinitroalkyl)tetraphenylporphyrins were studied by electrospray ionization (ESI) tandem mass spectrometry (MS/MS). All porphyrins showed the protonated molecule under ESI conditions. The protonated molecules were induced to fragment and the corresponding ESI tandem mass spectra were analysed. Porphyrins with two p-nitrophenyl groups showed, as expected, characteristic fragmentations including either loss of one nitro group, as the major fragment of the tandem mass spectra, and loss of both nitro groups. In contrast, MS/MS of the beta-(1,3-dinitroalkyl)porphyrins provided interesting and unexpected results such as the absence (or in insignificant abundance) of the ions formed by loss of one nitro group. However, these porphyrins show an abundant fragment due to combined loss of the two nitro groups. Also, the typical beta-cleavage of the alkyl chain is not observed per se, only when combined with loss of HNO2 or *NO2. Instead, alpha-cleavage, with loss of the beta-pyrrolic substituent, is the most favourable process.
    Journal of Mass Spectrometry 02/2005; 40(1):117-22. · 3.21 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A new series of ruthenium(II) complexes with the general formula [RuII([12]aneS4)(NN)]X2, where NN are bidentate diimines, [12]aneS4 is 1,4,7,10-tetrathiacyclododecane, and X is Cl− or PF6−, were studied by electrospray mass spectrometry (ESMS). Thiacrown fragmentation and intact diimine loss are the two major types of gas-phase reactions observed. The diimine losses occur mainly from the ion pairs formed by the inner sphere cations with halogen anions and are more significant for the complexes with flexible cross-bridged diimines. The fragmentations occur predominantly without changes in the oxidation state of the metal centre.
    International Journal of Mass Spectrometry - INT J MASS SPECTROM. 01/2005; 243(3):257-268.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Neutral and cationic pyrrolidine-fused chlorins and isobacteriochlorins derived from meso-tetrakis(pentafluorophenyl)porphyrin undergo cycloreversion reactions in the gas phase, either when desorbed from a liquid matrix by ion bombardment or when electrosprayed. Cycloreversion occurs through loss of either neutral or charged moieties, with and without hydrogen and methyl radical migration, and both as high- and low-energy collision processes. For the doubly charged isobacteriochlorin, one-electron reduction with methyl loss occurs under ion bombardment and electrospray, through hypervalent pyrrolidinium radical formation.
    Rapid Communications in Mass Spectrometry 02/2004; 18(22):2601-11. · 2.51 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Rapid Communications in Mass Spectrometry 11/1999; 13(19):1885-1888. · 2.51 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R1C6H4CHR2CH2NR32 (where R1 = H, OH, F or NO2; R2 = H or OH; R3 = H or CH3) generated by negative chemical ionization with H2O and D2O 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.
    Rapid Communications in Mass Spectrometry 10/1999; 13(19). · 2.51 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Introduction Dimethyl ether, when used in chemical ionization mass spectrometry, produces the CH 3 OCH 2 + cation, m/z 45, which behaves like an ambident electrophile 1 . The reactions of various types of compounds with DME have been studied 1,2 and reviewed 3 by several authors. A number of arylalkylamines structurally related to the important group of the biogenic amines has been the subject of recent work and their proton afinitties have been determined 4,5 . The present work extends the study of these amines, of general molecular formula R 1 R 2 C 6 H 3 CHR 3 (CH 2 ) n NR 4 R 5 , to their reactions with DME. Amine n R 1 R 2 R 3 R 4 R 5<F12
    08/1999;
  • Canadian Journal of Chemistry-revue Canadienne De Chimie - CAN J CHEM. 01/1999; 77(3):401-408.
  • [Show abstract] [Hide abstract]
    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.
    International Journal of Mass Spectrometry and Ion Processes 01/1998; 172(1):123-127.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The unimolecular metastable decompositions of protonated arylalkylamines 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; and n=1–3, generated by chemical ionization with water and ammonia as ionizing reagents, have been examined via the analysis of the mass-analysed ion kinetic energy spectra of the protonated molecules. The mechanisms proposed have been probed by chemical ionization of the deuterated analogues of the amines with D2O and ND3. The results show that protonation occurs preferentially on the amino group leading to abundant ions due to ammonia (or amine) loss, although ions resulting from transfer of the proton from the amino group to the aromatic ring, to the hydroxy group para to the aliphatic chain and to the benzylic OH, are also observed. Experimental evidence for H/D exchange between the deuteronated amino group and the aromatic ring is presented, and discussed in terms of the internal energy content of the deuterated ions and structural features of the amines, such as aliphatic chain length and the presence of a second hydroxy group on the aromatic ring. © 1998 John Wiley & Sons, Ltd.
    Rapid Communications in Mass Spectrometry 01/1998; 12(13):825-832. · 2.51 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The synthesis and mass spectra of three 3-aroyl-5-hydroxyflavones are reported. The interpretation of the mechanistic pathways for the fragmentation of the metastable molecular ions of these compounds was achieved through the analysis of their mass-analysed ion kinetic energy (MIKE) spectra and of the B2/E spectra of a few fragment ions. Labelling of the hydroxyl proton with deuterium and the analysis of the MIKE spectra of a model compound with chlorine atoms in the 2′,6′- and 2″,6″-positions led to a mechanism for the losses of OH• and HCO• which involves hydrogen migration from the 2″- or 6″-position to the 4-carbonyl oxygen atom. A mechanism for the loss of a neutral molecule of anisole from the molecular ion of the 3-aroyl-5-hydroxyflavone with a methoxyl group in the 4′- and 4″-positions is also suggested. For the flavones with hydrogen or chlorine substituents at these positions, loss of a phenyl (or chlorophenyl) radical occurs instead. © 1997 John Wiley & Sons, Ltd.
    Biological Mass Spectrometry 01/1997; 32(9):930-939. · 3.41 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: ß-Substitued-meso-tetraphenylporphyrins with 5,10-dioxobenzo[g]- or 5,6-dioxobenzo[h]chromene, pyrano[3,2-c]coumarin and benzopyran moieties and the corresponding Zn(II), Cu(II) and Ni(II) complexes were studied by electrospray mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). These heterocyclic moieties have well established pharmacological activities and as such the introduction of these motifs into the ß-pyrrolic position of the porphyrin macrocycle can alter the properties of the macrocycle and can produce new molecules with dual functions. The free base and Zn(II) complexes showed, in the ESI-MS spectra, the [M+H]+ ions while the Cu(II) and Ni(II) complexes showed the M+• ions. The [M+H]+ and M+• ions were induced to fragment and the corresponding ESI tandem mass spectra (MS/MS) were analyzed. The main fragmentation mechanism occurs in general via the retro hetero-Diels–Alder pathway while unexpected fragmentations or rearrangements were observed principally with the Zn(II) complexes. The analysis of the fragmentation pattern of all complexes indicates that the presence or absence of the carbonyl function in the ß-substituent led to the formation of secondary fragments. The differentiation of the isomers 2a and 2b was only possible by comparison of their MS/MS spectra.
    International Journal of Mass Spectrometry. s 343–344:1–8.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Journal of the American Society for Mass Spectrometry 8(4):365-370. · 3.59 Impact Factor