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da Silva Borges L, Batista JHC, Bozzini L, Lourenço CD, Lopes NP, Clososki GC, Vessecchi R. Are benzoylium and nitrilium ions produced from substituted 2-arene-2-oxazolines during mass spectrometry? A study based on density functional theory calculations, quantum theory of atoms in molecules, and electrospray ionization tandem mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2023; 37:e9449. [PMID: 36459945 DOI: 10.1002/rcm.9449] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Revised: 11/25/2022] [Accepted: 11/27/2022] [Indexed: 06/17/2023]
Abstract
RATIONALE Oxazolines are important compounds for drug development, synthesis, and pharmaceutical applications. Interest in analyzing and developing methods to characterize reaction products from these small heterocyclics has led us to study the gas-phase reactivity and fragmentation of seven 2-arene-2-oxazolines compounds using computational chemistry combined with mass spectrometry. METHOD Protonation sites were investigated using computed proton affinity, gas-phase basicity, and some quantum chemistry descriptors of reactivity; the B3LYP/6-31+G(d,p) computational model was used. Fragmentation mechanisms were suggested by employing data from collision-induced dissociation (CID), energy-resolved plots from MS/MS spectra, multiple-stage experiments, and survival-yield method. RESULTS Protonation studies based on quantum theory of atoms in molecules (QTAIM) and computational thermochemistry were useful to describe the reactivity of the investigated 2-arene-2-oxazolines, which can be protonated at the nitrogen atom. Three major fragmentation pathways were identified for the protonated molecules: formation of (a) benzoylium or (b) nitrilium ions through elimination of 71 and 72 u from the protonated molecules, respectively, and (c) elimination of 54 u from [M+H]+ . These pathways were exploited by the density functional theory calculations combined with QTAIM studies. CONCLUSIONS Our results can help in identifying 2-arene-2-oxazoline derivatives using electrospray ionization tandem mass spectrometry (ESI-MS/MS), which can be applied for monitoring reactions through the identified diagnostic ions (product ions). Also, we can suggest that benzoylium and nitrilium ions emerge during fragmentation under CID conditions.
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Affiliation(s)
- Letícia da Silva Borges
- Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, Brasil
| | - João Henrique Carvalho Batista
- Núcleo de Pesquisa em Produtos Naturais e Sintéticos (NPPNS), Departamento Ciências Moleculares, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, Brasil
| | - Leandro Bozzini
- Núcleo de Pesquisa em Produtos Naturais e Sintéticos (NPPNS), Departamento Ciências Moleculares, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, Brasil
| | - Celso Donizete Lourenço
- Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, Brasil
| | - Norberto Peporine Lopes
- Núcleo de Pesquisa em Produtos Naturais e Sintéticos (NPPNS), Departamento Ciências Moleculares, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, Brasil
| | - Giuliano Cesar Clososki
- Núcleo de Pesquisa em Produtos Naturais e Sintéticos (NPPNS), Departamento Ciências Moleculares, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, Brasil
| | - Ricardo Vessecchi
- Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, Brasil
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Kaczorowska MA, Kaczmarek-Kędziera A, Ośmiałowski B. Tautomeric equilibrium, proton affinity and mass spectrometry fragmentation of flexible hydrogen-bonded precursors and rigid [Formula: see text] fluorescent dyes. Sci Rep 2021; 11:15995. [PMID: 34362952 PMCID: PMC8346630 DOI: 10.1038/s41598-021-94978-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Accepted: 07/12/2021] [Indexed: 11/09/2022] Open
Abstract
The stability of two groups of conformationally locked molecules, similar in topology, but differing only by the type of the bridge rigidifying their structure, is studied. The series of the less-rigid 2-phenacylheterocyclic compounds and their stiff difluoroboranyl derivatives are investigated for the determination of the effect of [Formula: see text]/S/O replacement in a five-membered heterocyclic ring and the presence of a strong electron-donating group on the tautomeric equilibrium, protonation affinity, and fragmentation pattern observed in the structural elucidation by means of mass spectrometry technique. The results of the [Formula: see text]B97X-D/6-311++G(d,p) calculations, the topological analysis of electron density as well as the experimental MS measurements show the importance of the number of heteroatoms, their properties, and location in the molecule for the rational design of the systems of desired stable tautomers or the favorable protonation sites. The obtained data allow for the understanding of the fundamentals of the novel highly fluorescent difluoroborates fragmentation behavior, vital for their structural elucidation with the application of high-resolution tandem mass spectrometry methods.
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Affiliation(s)
- Małgorzata A. Kaczorowska
- Faculty of Chemical Technology and Engineering, UTP University of Science and Technology, Seminaryjna 3, 85-326 Bydgoszcz, Poland
| | - Anna Kaczmarek-Kędziera
- Faculty of Chemistry, Nicolaus Copernicus University in Torun, Gagarina 7, 87–100 Toruń, Poland
| | - Borys Ośmiałowski
- Faculty of Chemistry, Nicolaus Copernicus University in Torun, Gagarina 7, 87–100 Toruń, Poland
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Dias HJ, Bento MVB, da Silva ÉH, Saturnino-Júnior A, de Oliveira MF, Vessecchi R, Parreira RLT, Crotti AEM. Gas-phase fragmentation reactions of protonated cocaine: New details to an old story. JOURNAL OF MASS SPECTROMETRY : JMS 2018; 53:203-213. [PMID: 29247586 DOI: 10.1002/jms.4053] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2017] [Revised: 11/22/2017] [Accepted: 12/05/2017] [Indexed: 06/07/2023]
Affiliation(s)
- Herbert J Dias
- Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil
- Núcleo de Pesquisas em Ciências Exatas e Tecnológicas, Universidade de Franca, Franca, SP, Brazil
| | - Mariana V B Bento
- Núcleo de Pesquisas em Ciências Exatas e Tecnológicas, Universidade de Franca, Franca, SP, Brazil
| | | | - Andrade Saturnino-Júnior
- Núcleo de Pesquisas em Ciências Exatas e Tecnológicas, Universidade de Franca, Franca, SP, Brazil
| | - Marcelo F de Oliveira
- Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil
| | - Ricardo Vessecchi
- Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil
| | - Renato L T Parreira
- Núcleo de Pesquisas em Ciências Exatas e Tecnológicas, Universidade de Franca, Franca, SP, Brazil
| | - Antônio E M Crotti
- Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil
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Cabral LIL, Brás EM, Henriques MSC, Marques C, Frija LMT, Barreira L, Paixão JA, Fausto R, Cristiano MLS. Synthesis, Structure, and Cytotoxicity of a New Sulphanyl-Bridged Thiadiazolyl-Saccharinate Conjugate: The Relevance of S⋅⋅⋅N Interaction. Chemistry 2018; 24:3251-3262. [PMID: 29283203 DOI: 10.1002/chem.201705319] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2017] [Indexed: 01/08/2023]
Abstract
Reports showing that the copper concentration is considerably higher in neoplasms than in normal tissues prompted the need to develop selective copper chelators. We disclosed recently that some N-linked tetrazole-saccharinates bind selectively to copper, forming complexes that are highly cytotoxic towards cancer cells. Because tetrazole-saccharinates are photolabile, due to the photoreactivity of tetrazoles, we proposed thiadiazolyl-saccharinates as an alternative. Herein we describe the synthesis, structure, and monomeric photochemistry of a sulphanyl-bridged thiadiazolyl-saccharinate, 3-[(5-methyl-1,3,4-thiadiazol-2-yl)sulphanyl]-1,2-benzothiazole 1,1-dioxide (MTSB). The monomeric structure, charge density analysis, and characteristic infrared spectrum of MTSB were investigated theoretically, using quantum chemical calculations, and also experimentally, using matrix-isolation infrared spectroscopy. The crystal structure was investigated by combining X-ray crystallography with infrared and Raman spectroscopies. Results show that the structure of isolated MTSB is similar to that found in the crystal, with an S⋅⋅⋅N interaction clearly contributing to the structure of the molecule and of the crystal. Matrix irradiation revealed a high photostability of MTSB, compared to parent tetrazole-saccharinates and to the 5-methyl-1,3,4-thiadiazole building block, emphasizing the photostabilizing effect of the saccharyl system. Finally, in vitro toxicity assays of MTSB showed a copper concentration-dependent toxicity against cancer cells, without affecting normal cells. In particular, MTSB was most effective towards the hepatic (HepG2), neuroblastoma (SH-SY5), and lymphoma cell lines (U937). Thus, MTSB represents a promising lead for cancer chemotherapy based on chelating agents.
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Affiliation(s)
- Lília I L Cabral
- Department of Chemistry and Pharmacy, F.C.T., University of Algarve, 8005-039, Faro, Portugal.,Center of Marine Sciences, CCMar, University of Algarve, 8005-039, Faro, Portugal
| | - Elisa M Brás
- CQC, Department of Chemistry, University of Coimbra, 3004-535, Coimbra, Portugal
| | - Marta S C Henriques
- CFisUC, Department of Physics, University of Coimbra, 3004-516, Coimbra, Portugal
| | - Catia Marques
- Center of Marine Sciences, CCMar, University of Algarve, 8005-039, Faro, Portugal
| | - Luís M T Frija
- CQE, Centro de Química Estrutural, IST, University of Lisbon, Av. Rovisco Pais, 1049-001, Lisbon, Portugal
| | - Luísa Barreira
- Department of Chemistry and Pharmacy, F.C.T., University of Algarve, 8005-039, Faro, Portugal.,Center of Marine Sciences, CCMar, University of Algarve, 8005-039, Faro, Portugal
| | - José António Paixão
- CFisUC, Department of Physics, University of Coimbra, 3004-516, Coimbra, Portugal
| | - Rui Fausto
- CQC, Department of Chemistry, University of Coimbra, 3004-535, Coimbra, Portugal
| | - Maria Lurdes S Cristiano
- Department of Chemistry and Pharmacy, F.C.T., University of Algarve, 8005-039, Faro, Portugal.,Center of Marine Sciences, CCMar, University of Algarve, 8005-039, Faro, Portugal
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Martínez-Cifuentes M, Clavijo-Allancan G, Zuñiga-Hormazabal P, Aranda B, Barriga A, Weiss-López B, Araya-Maturana R. Protonation Sites, Tandem Mass Spectrometry and Computational Calculations of o-Carbonyl Carbazolequinone Derivatives. Int J Mol Sci 2016; 17:ijms17071071. [PMID: 27399676 PMCID: PMC4964447 DOI: 10.3390/ijms17071071] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2016] [Revised: 06/10/2016] [Accepted: 06/28/2016] [Indexed: 11/16/2022] Open
Abstract
A series of a new type of tetracyclic carbazolequinones incorporating a carbonyl group at the ortho position relative to the quinone moiety was synthesized and analyzed by tandem electrospray ionization mass spectrometry (ESI/MS-MS), using Collision-Induced Dissociation (CID) to dissociate the protonated species. Theoretical parameters such as molecular electrostatic potential (MEP), local Fukui functions and local Parr function for electrophilic attack as well as proton affinity (PA) and gas phase basicity (GB), were used to explain the preferred protonation sites. Transition states of some main fragmentation routes were obtained and the energies calculated at density functional theory (DFT) B3LYP level were compared with the obtained by ab initio quadratic configuration interaction with single and double excitation (QCISD). The results are in accordance with the observed distribution of ions. The nature of the substituents in the aromatic ring has a notable impact on the fragmentation routes of the molecules.
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Affiliation(s)
- Maximiliano Martínez-Cifuentes
- Programa Institucional de Fomento a la Investigación, Desarrollo e Innovación, Universidad Tecnológica Metropolitana, Las Palmeras 3360, Casilla 9845, Santiago 7800003, Chile.
| | - Graciela Clavijo-Allancan
- Departamento de Química, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Casilla 653, Santiago 7800003, Chile.
| | - Pamela Zuñiga-Hormazabal
- Departamento de Química, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Casilla 653, Santiago 7800003, Chile.
| | - Braulio Aranda
- Departamento de Química, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Casilla 653, Santiago 7800003, Chile.
| | - Andrés Barriga
- Unidad de Espectrometría de Masas, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Santos Dumont 964, Casilla 233, Santiago 8380494, Chile.
| | - Boris Weiss-López
- Departamento de Química, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Casilla 653, Santiago 7800003, Chile.
| | - Ramiro Araya-Maturana
- Instituto de Química de Recursos Naturales, Universidad de Talca, Av. Lircay s/n, Casilla 747, Talca 3460000, Chile.
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Demarque DP, Crotti AEM, Vessecchi R, Lopes JLC, Lopes NP. Fragmentation reactions using electrospray ionization mass spectrometry: an important tool for the structural elucidation and characterization of synthetic and natural products. Nat Prod Rep 2015; 33:432-55. [PMID: 26673733 DOI: 10.1039/c5np00073d] [Citation(s) in RCA: 276] [Impact Index Per Article: 30.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Over the last decade, the number of studies reporting the use of electrospray ionization mass spectrometry (ESI-MS) in combination with collision cells (or other activation methods) to promote fragmentation of synthetic and natural products for structural elucidation purposes has considerably increased. However, the lack of a systematic compilation of the gas-phase fragmentation reactions subjected to ESI-MS/MS conditions still represents a challenge and has led to many misunderstood results in the literature. This review article exploits the most common fragmentation reactions for ions generated by ESI in positive and negative modes using collision cells in an effort to stimulate the use of this technique by non-specialists, undergraduate students and researchers in related areas.
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Affiliation(s)
- Daniel P Demarque
- Departamento de Física e Quimica, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Av. Café, s/n, Ribeirão Preto, SP, Brazil.
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Asfandiarov NL, Pshenichnyuk SA, Vorob'ev AS, Nafikova EP, Elkin YN, Pelageev DN, Koltsova EA, Modelli A. Electron attachment to some naphthoquinone derivatives: long-lived molecular anion formation. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2014; 28:1580-1590. [PMID: 24895255 DOI: 10.1002/rcm.6934] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2014] [Revised: 04/23/2014] [Accepted: 04/27/2014] [Indexed: 06/03/2023]
Abstract
RATIONALE Electron Affinity (EA) is one of the fundamental properties of a molecule. EA values can be measured with various experimental methods, although their availability is still relatively limited. We make an attempt to use Dissociative Electron Attachment Spectroscopy (DEAS) data for evaluation of the EAs of twelve naphthoquinone (NQ) derivatives. METHODS Naphthoquinone (NQ) and eleven of its hydroxyl derivatives were investigated by means of DEAS. A combined investigation of NQ and juglone by means of the Electron Transmission Spectroscopy (ETS) and DEAS techniques, with the support of density functional theory (DFT) calculations, allowed us to elucidate the empty-level structures of NQ and its hydroxyl derivatives. RESULTS All molecules under investigation form extremely long-lived molecular anions associated with three resonant states (except for NQ, where only two long-lived resonances were observed). The hydroxyl substituents of NQ cause an increase in EA and number of internal degrees of freedom (N), and, as a result, an increase in the mean electron autodetachment lifetimes of the molecular negative ions (NIs). Evaluation of the EAs from the measured lifetimes of the molecular NIs through a simple Arrhenius approximation gives results in reasonable agreement with those obtained with DFT calculations. CONCLUSIONS NI lifetime measurements by means of a modified DEAS instrumentation can provide quantitative data of EA. A simple Arrhenius approximation seems to be adequate to describe the process of electron detachment from molecular anions.
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Affiliation(s)
- N L Asfandiarov
- Institute of Molecule and Crystal Physics, Ufa Research Centre, Russian Academy of Sciences, Prospect Oktyabrya 151, 450075, Ufa, Russia; Bashkir State Pedagogical University, Oktyabrskoy Revolutsii st. 3a, 450000, Ufa, Russia
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Ernst M, Silva DB, Silva RR, Vêncio RZN, Lopes NP. Mass spectrometry in plant metabolomics strategies: from analytical platforms to data acquisition and processing. Nat Prod Rep 2014; 31:784-806. [DOI: 10.1039/c3np70086k] [Citation(s) in RCA: 129] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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Vessecchi R, Emery FS, Lopes NP, Galembeck SE. Electronic structure and gas-phase chemistry of protonated α- and β-quinonoid compounds: a mass spectrometry and computational study. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2013; 27:816-824. [PMID: 23495028 DOI: 10.1002/rcm.6519] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2012] [Revised: 01/18/2013] [Accepted: 01/18/2013] [Indexed: 06/01/2023]
Abstract
RATIONALE The use of quinonoid compounds against tropical diseases and as antitumor agents has prompted the search for new naturally occurring and synthetic derivatives. Among these quinonoid compounds, lapachol and its isomers (α- and β-lapachone) serve as models for the synthesis of new compounds with biological activity, and the use of electrospray ionization tandem mass spectrometry (ESI-MS/MS) analysis as a tool to elucidate and characterize these products has furnished important information about these compounds. METHODS ESI-MS/MS analysis under collision-induced dissociation conditions was used to describe the fragmentation mechanisms for protonated 1,4-naphthoquinone, 1,2-naphthoquinone, α-lapachone, and β-lapachone. The B3LYP/6-31+G(d,p) model was used to obtain proton affinities, gas-phase basicities, and molecular electrostatic potential maps, thus indicating the probable protonation sites. Fragmentation pathways were suggested on the basis of the relative enthalpies of the product ions. RESULTS The ESI-MS signals of the cationized molecules of ortho quinonoid compounds were more intense than those of the protonated molecule. Formation of the major product ions with m/z 187 from protonated α- and β-lapachone has been attributed to a retro-Diels-Alder (RDA) reaction. CONCLUSIONS MS/MS studies on lapachol isomers (α- and β-lapachone) will facilitate the interpretation of the liquid chromatography (LC)-MS/MS analysis of new metabolites. MS/MS data on the 1,4-naphthoquinone, 1,2-naphthoquinone, α-lapachone and β-lapachone core will help characterize new derivatives from in vitro/in vivo metabolism studies in complex matrices. The product ions revealed the major fragmentation mechanisms and these ions will serve as diagnostic ions to identify each studied compound.
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Affiliation(s)
- Ricardo Vessecchi
- Núcleo de Pesquisa em Produtos Naturais e Sintéticos, Departamento de Física e Química, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Brasil.
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Vessecchi R, Emery FS, Galembeck SE, Lopes NP. Gas-phase reactivity of 2-hydroxy-1,4-naphthoquinones: a computational and mass spectrometry study of lapachol congeners. JOURNAL OF MASS SPECTROMETRY : JMS 2012; 47:1648-1659. [PMID: 23280754 DOI: 10.1002/jms.3101] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2012] [Revised: 09/03/2012] [Accepted: 09/04/2012] [Indexed: 06/01/2023]
Abstract
In order to understand the influence of alkyl side chains on the gas-phase reactivity of 1,4-naphthoquinone derivatives, some 2-hydroxy-1,4-naphthoquinone derivatives have been prepared and studied by electrospray ionization tandem mass spectrometry in combination with computational quantum chemistry calculations. Protonation and deprotonation sites were suggested on the basis of gas-phase basicity, proton affinity, gas-phase acidity (ΔG(acid) ), atomic charges and frontier orbital analyses. The nature of the intramolecular interaction as well as of the hydrogen bond in the systems was investigated by the atoms-in-molecules theory and the natural bond orbital analysis. The results were compared with data published for lapachol (2-hydroxy-3-(3-methyl-2-butenyl)-1,4-naphthoquinone). For the protonated molecules, water elimination was verified to occur at lower proportion when compared with side chain elimination, as evidenced in earlier studies on lapachol. The side chain at position C(3) was found to play important roles in the fragmentation mechanisms of these compounds.
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Affiliation(s)
- Ricardo Vessecchi
- Núcleo de Pesquisa em Produtos Naturais e Sintéticos, Departamento de Física e Química, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Brasil
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Vessecchi R, Tomaz JC, dos Santos GP, de Oliveira ARM, Lopes NP, Clososki GC. Gas-phase reactivity of protonated 2-oxazoline derivatives: mass spectrometry and computational studies. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2012; 26:1061-1069. [PMID: 22467456 DOI: 10.1002/rcm.6182] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
RATIONALE Oxazolines have attracted the attention of researchers worldwide due to their versatility as carboxylic acid protecting groups, chiral auxiliaries, and ligands for asymmetric catalysis. Electrospray ionization tandem mass spectrometric (ESI-MS/MS) analysis of five 2-oxazoline derivatives has been conducted, in order to understand the influence of the side chain on the gas-phase dissociation of these protonated compounds under collision-induced dissociation (CID) conditions. METHODS Mass spectrometric analyses were conducted in a quadrupole time-of-flight (Q-TOF) spectrometer fitted with electrospray ionization source. Protonation sites have been proposed on the basis of the gas-phase basicity, proton affinity, atomic charges, and a molecular electrostatic potential map obtained on the basis of the quantum chemistry calculations at the B3LYP/6-31 + G(d,p) and G2(MP2) levels. RESULTS Analysis of the atomic charges, gas-phase basicity and proton affinities values indicates that the nitrogen atom is a possible proton acceptor site. On the basis of these results, two main fragmentation processes have been suggested: one taking place via neutral elimination of the oxazoline moiety (99 u) and another occurring by sequential elimination of neutral fragments with 72 u and 27 u. These processes should lead to formation of R(+). CONCLUSIONS The ESI-MS/MS experiments have shown that the side chain could affect the dissociation mechanism of protonated 2-oxazoline derivatives. For the compound that exhibits a hydroxyl at the lateral chain, water loss has been suggested to happen through an E2-type elimination, in an exothermic step.
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Affiliation(s)
- Ricardo Vessecchi
- Núcleo de Pesquisa em Produtos Naturais e Sintéticos, Departamento de Física e Química, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brasil.
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Suni NM, Aalto H, Kauppila TJ, Kotiaho T, Kostiainen R. Analysis of lipids with desorption atmospheric pressure photoionization-mass spectrometry (DAPPI-MS) and desorption electrospray ionization-mass spectrometry (DESI-MS). JOURNAL OF MASS SPECTROMETRY : JMS 2012; 47:611-619. [PMID: 22576874 DOI: 10.1002/jms.2992] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
In this article, the effect of spray solvent on the analysis of selected lipids including fatty acids, fat-soluble vitamins, triacylglycerols, steroids, phospholipids, and sphingolipids has been studied by two different ambient mass spectrometry (MS) methods, desorption electrospray ionization-MS (DESI-MS) and desorption atmospheric pressure photoionization-MS (DAPPI-MS). The ionization of the lipids with DESI and DAPPI was strongly dependent on the spray solvent. In most cases, the lipids were detected as protonated or deprotonated molecules; however, other ions were also formed, such as adduct ions (in DESI), [M-H](+) ions (in DESI and DAPPI), radical ions (in DAPPI), and abundant oxidation products (in DESI and DAPPI). DAPPI provided efficient desorption and ionization for neutral and less polar as well as for ionic lipids but caused extensive fragmentation for larger and more labile compounds because of a thermal desorption process. DESI was more suitable for the analysis of the large and labile lipids, but the ionization efficiency for less polar lipids was poor. Both methods were successfully applied to the direct analysis of lipids from pharmaceutical and food products. Although DESI and DAPPI provide efficient analysis of lipids, the multiple and largely unpredictable ionization reactions may set challenges for routine lipid analysis with these methods.
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Affiliation(s)
- Niina M Suni
- Division of Pharmaceutical Chemistry, University of Helsinki, P.O. Box 56, Helsinki FI-00014, Finland.
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