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ABSTRACT: A method using headspace solid-phase microextraction (HS-SPME) followed by gas chromatography/mass spectrometry (GC/MS) analysis has been developed to gain insight into the degradation of the chemical warfare agent sulfur mustard in solution. Specifically, the described approach simplifies the sample preparation for GC/MS analysis to provide a rapid determination of changes in sulfur mustard abundance. These results were found to be consistent with those obtained using liquid-liquid extraction (LLE) GC/MS. The utility of the described approach was further demonstrated by the investigation of the degradation process in a complex matrix with surfactant added to assist solvation of sulfur mustard. A more rapid reduction in sulfur mustard abundance was observed using the HS-SPME approach with surfactant present and was similar to results from LLE experiments. Significantly, this study demonstrates that HS-SPME can simplify the sample preparation for GC/MS analysis to monitor changes in sulfur mustard abundance in solution more rapidly, and with less solvent and reagent usage than LLE.
Rapid Communications in Mass Spectrometry 12/2010; 24(23):3419-24. · 2.79 Impact Factor
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ABSTRACT: The alkaline perhydrolysis of the nerve agent O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (VX) was investigated by studying the ion-molecule reactions of HOO(-) with O,S-dimethyl methylphosphonothioate in a modified linear ion-trap mass spectrometer. In addition to simple proton transfer, two other abundant product ions are observed at m/z 125 and 109 corresponding to the S-methyl methylphosphonothioate and methyl methylphosphonate anions, respectively. The structure of these product ions is demonstrated by a combination of collision-induced dissociation and isotope-labeling experiments that also provide evidence for their formation by nucleophilic reaction pathways, namely, (i) S(N)2 at carbon to yield the S-methyl methylphosphonothioate anion and (ii) nucleophilic addition at phosphorus affording a reactive pentavalent intermediate that readily undergoes internal sulfur oxidation and concomitant elimination of CH(3)SOH to yield the methyl methylphosphonate anion. Consistent with previous solution phase observations of VX perhydrolysis, the toxic P-O cleavage product is not observed in this VX model system and theoretical calculations identify P-O cleavage to be energetically uncompetitive. Conversely, intramolecular sulfur oxidation is calculated to be extremely exothermic and kinetically accessible explaining its competitiveness with the facile gas phase proton transfer process. Elimination of a sulfur moiety deactivates the nerve agent VX and thus the intramolecular sulfur oxidation process reported here is also able to explain the selective perhydrolysis of the nerve agent to relatively nontoxic products.
The Journal of Organic Chemistry 11/2009; 74(24):9319-27. · 4.45 Impact Factor
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ABSTRACT: The hypothiocyanate anion (OSCN)(-) is reported to be a major product of the lactoperoxidase/H(2)O(2)/(SCN)(-) system, and this anion is proposed to have significant antimicrobial properties. The collision induced (CID) negative ion mass spectrum of "(OSCN)(-)" has been reported: there is a pronounced parent anion at m/z 74, together with fragment anions at m/z 58 (SCN)(-) and 26 (CN)(-). These fragment anions are consistent with structure (OSCN)(-). However there is also a lesser peak at m/z 42 (OCN(-) or CNO(-)) in this spectrum which is either formed by rearrangement of (OSCN)(-) or from an isomer of this anion. The current theoretical investigation of (OSCN)(-) and related isomers, together with the study of possible rearrangements of these anions, indicates that ground-state singlet (OSCN)(-) is a stable species and that isomerization is unlikely. The three anions (OSCN)(-), (SCNO)(-), and (SNCO)(-) have been synthesized (in the ion source of a mass spectrometer) by unequivocal routes, and their structures have been confirmed by a consideration of their collision induced (negative ion) and charge reversal (positive ion) mass spectra. The CID mass spectrum of (SCNO)(-) shows formation of m/z 42 (CNO(-)), but the corresponding spectra of (OSCN)(-) or (SNCO)(-) lack peaks at m/z 42. Combined theoretical and experimental data support earlier evidence that the hypothiocyanite anion is a major oxidation product of the H(2)O(2)/(SCN)(-) system. However, the formation of m/z 42 in the reported CID spectrum of "(OSCN)(-)" does not originate from (OSCN)(-) but from another isomer, possibly (SCNO)(-).
The Journal of Physical Chemistry A 05/2006; 110(14):4930-6. · 2.95 Impact Factor
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ABSTRACT: Calculations at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G* level of theory indicate that doublet [CCCCO]-* is a stable species which should undergo collision-induced Franck-Condon vertical oxidation under neutralisation-reionisation conditions (-NR+) to produce both triplet CCCCO (ground state) and singlet CCCCO. Some of the neutral CCCCO species formed (particularly the triplet) should be stable for the microsecond duration of the NR experiment, whereas others will be energised (particularly the singlet) and should decompose to C3 and CO. The [CCCCO]-* radical anion has been formed in the ion source of the mass spectrometer by the reaction CH3OCH2C[triple bond]C-CO-CH(CH3)2 + O-* --> [CCCCO]-* + CH3O* + H2O + (CH3)2CH*. The -NR+ spectrum of [CCCCO]-* shows a recovery signal at m/z 64 corresponding to ionised CCCCO, together with a pronounced peak at m/z 36 (CCC+*) produced by ionisation of CCC (formed by the reaction CCCCO --> CCC + CO). The experimental observations are in agreement with the predictions of the theoretical study.
Organic & Biomolecular Chemistry 04/2005; 3(5):901-10. · 3.70 Impact Factor
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ABSTRACT: The stability and reactivity of the neutral species CNCCO generated by one electron oxidation of the anion [CNCCO](-) have been investigated by a combination of theoretical calculations (carried out at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory) and tandem mass spectrometric experiments. Some of the neutrals formed in this way are stable for the microsecond duration of the experiment, but others are energised. The neutrals which are energised may either (i) dissociate [CNCCO --> CNC + CO (+92 kJ mol(-1))], and/or (ii), undergo the isonitrile to nitrile rearrangement to yield NCCCO energised neutrals (barrier 133 kJ mol(-1), reaction exothermic by 105 kJ mol(-1)). Some of these rearranged neutrals NCCCO have excess energies as high as 238 kJ mol(-1) and will dissociate [NCCCO --> NCC + CO (+203 kJ mol(-1))].
Organic & Biomolecular Chemistry 06/2004; 2(12):1742-7. · 3.70 Impact Factor
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ABSTRACT: It has been reported that irradiation of cyanoacetylene and ozone on a water ice surface at 255 nm yields both hydrogen peroxide and cyanoacetylene (NCCHCO), and it has been proposed that this overall process may involve a crucial step where NCCCHO rearranges to NCCHCO.The isomers NCCHCO and NCCCHO have been prepared in this study by one-electron vertical oxidation of [NCCHCO]-• and [NCCCHO]-• in collision cells of a VG ZAB 2HF mass spectrometer. -NR+ experiments indicate that singlet NCCHCO is stable for the microsecond duration of the experiment. In contrast, calculations at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory indicate that singlet NCCCHO does not occupy a minimum on the singlet neutral potential surface, but rearranges to singlet NCCHCO. Some of the singlet NCCHCO neutrals formed in this way are stable, whereas others have sufficient excess energy to effect decomposition to give NCCH and CO. Triplet NCCCHO is stable but, when energized, may (i) rearrange over a barrier of 49.0 kcal mol-1 to give triplet NCCHCO, which is energized and decomposes to NCCH and CO, and/or (ii) undergo intersystem crossing to yield singlet NCCHCO. It is concluded that, in principle, the rearrangement NCCCHO to NCCHCO could occur in regions of interstellar ice.
04/2004;
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ABSTRACT: Neutrals CCCO, CC(13)CO, CCCS and CC(13)CS have been prepared by one-electron vertical (Franck-Condon) oxidation of the precursor anion radicals (CCCO)(-*), (CC(13)CO)(-*), (CCCS)(-*) and (CC(13)CS)(-*)respectively in collision cells of a reverse sector mass spectrometer. Ionisation of the neutrals to decomposing cations shows the neutrals to be stable for the microsecond duration of the neutralisation-ionisation ((-)NR(+)) experiment. No rearrangement of the label in energised CC(13)CO or CC(13)CS occurs during these experiments. In contrast, minor rearrangement of (CC(13)CO)(+*) is observed [(CC(13)CO)(+*)-->(OCC(13)C)(+*), while significant rearrangement occurs for (CC(13)CS)(+*) [(CC(13)CS)(+*)-->(SCC(13)C)(+*)]. Theoretical calculations at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory show that the cationic rearrangements occur by stepwise processes via key rhombic structures. Overall, the degenerate processes result in O and S migration from C-3 to C-1. The cations (CCCO)(+*) and (CCCS)(+*) require excess energies of > or = 516 and > or = 226 kJ mol(-1) respectively to effect rearrangement.
Organic & Biomolecular Chemistry 04/2004; 2(7):999-1006. · 3.70 Impact Factor
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ABSTRACT: One-electron vertical Franck−Condon oxidation of [CCCCBO]- (using O2 as collision gas in the dual collision cell region of an HF-ZAB/AMD 604 four-sector mass spectrometer) forms doublet neutrals C4BO in the first stage of a neutralization−reionization (-NR+) experiment. Reionization of these neutrals to decomposing positive ions shows that the majority of neutrals (formed in the first collision cell) correspond to CCCCBO which are stable for the microsecond duration of the NR experiment. However, a minor fraction of neutrals CCCCBO is energized and rearranges to form an isomer which decomposes by loss of CO. A theoretical study of this system at the MP4SDTQ/aug-cc-pVDZ//MP2(full)/6-31G(d) level of theory suggests that the rearranged species corresponds to OCCCCB. The rearrangement occurs by six-center cyclization of CCCCBO, involving O−C(1) bond formation followed by B−O bond cleavage to form OCCCCB. The reaction is endothermic by only 4.5 kcal mol-1 but requires an excess energy of ≥ 53.5 kcal mol-1 in order for the system to surmount the first transition state. This energy requirement is 45.5 kcal mol-1 more than the Franck−Condon excess energy of 8 kcal mol-1 of CCCCBO produced by the vertical oxidation process. The additional energy may be provided by keV collisions of CCCCBO with the collision gas O2 following Franck−Condon-controlled neutralization of [CCCCBO]-.
03/2004;
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ABSTRACT: Stable (CC13CHO)- may be formed in the chemical ionisation ion source of a VG ZAB 2HF mass spectrometer by the SN2(Si) reaction between Me3SiC[triple bond]C13CHO and F-. Vertical (Franck-Condon) one-electron oxidation of (CC13CHO)- in the first of the tandem collision cells of a VG ZAB 2HF mass spectrometer gives CC13CHO. Some of these neutrals have sufficient excess energy to effect rearrangement to HCC13CO, some of which are energised and to decompose to HCC. and 13CO. Thus the neutral rearrangement exclusively involves H migration: no products from O migration are detected. The corresponding two-electron oxidation of (CC13CHO)- gives mainly unrearranged (CC13CHO)+. A minority of these cations are energised and rearrange by H and O migration to yield (HCC13CHO)+ and (OCC13CHO)+ respectively. All experimental observations are backed up by molecular modelling at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory.
European Journal of Mass Spectrometry 02/2004; 10(4):441-8. · 1.21 Impact Factor
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ABSTRACT: Neutrals MeCCCO, CCC(O)Me, PhCCCO and CCC(O)Ph have been made by neutralisation of [MeCCCO](+), [CCC(O)Me](-), [PhCCCO](+) and [CC(CO)Ph](-). Neutrals MeCCCO, CCC(O)Me and PhCCCO are stable for the microsecond duration of the neutralisation experiment. A joint experimental and theoretical study (energies calculated at the B3LYP/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory) suggests that the neutral radical CCC(O)Ph rearranges via a four-centred ipso radical cyclisation/ring opening to form the isomer PhCCCO in an exothermic reaction. (13)C labelling confirms that the rearrangement does not involve O migration. Some of the PhCCCO radicals formed in this reaction are sufficiently energised to effect decomposition to give PhCC and CO.
Rapid Communications in Mass Spectrometry 02/2004; 18(10):1008-16. · 2.79 Impact Factor
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ABSTRACT: Theory suggests that CCBCC (1) will rearrange to planar cyclo-C4B (19) if the excess energy of 1 is ≥16.1 kcal mol-1 [calculations at the CCSD(T)/aug-cc-pVTZ//B3LYP/6-31G(d) level of theory]. Cyclo-C4B lies only 1.1 kcal mol-1 above CCBCC. The planar nature of symmetrical cyclo-C4B is attributed to multicentered bonding involving boron. If cyclo-C4B (19) has an excess energy of ≥24.4 kcal mol-1, it may ring open to form CCCCB (3).
11/2003;
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ABSTRACT: Theoretical studies at the CCSD(T)/aug-cc-pVDZ//B3LYP/aug-cc-pVDZ level of theory indicate that there are four stable radicals with CCC bond connectivity on the C3HS potential surface, namely, HCCCS, CCHCS, CCCHS, and (cyclo-C3H)S. Of these structures, two have been synthesized by one electron vertical oxidation of precursor anions, formed as follows: (i) CH3−CC−S−C2H5 + O-• → (HCCCS)- + H2O + C2H5• and (ii) Me3Si−CC−CH(cyclo-SCH2CH2S) + F- → -CC−CHS + Me3SiF + cyclo-SC2H4. A comparison of the -CR+ and -NR+ spectra of these two anions indicate that the neutral HCCCS is stable with a lifetime of at least 1 μs, whereas the oxidation of (CCCHS)- leads to two neutrals, CCCHS and HCCCS. Theoretical calculations indicate that the rearrangement of CCCHS to HCCCS can occur by three pathways; concerted H or S rearrangements or the stepwise H rearrangement process CCCCHS → CCHCS → (cyclo-C3H)S → HCCCS. Comparison of the -CR+ and -NR+ spectra of (CC13CHS)- indicates that at least a part of the rearrangement involves the S migration pathway. Theoretical considerations suggest that H rearrangement should compete with S rearrangement: there is no experimental evidence to confirm or refute this proposal.
02/2003;
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ABSTRACT: The stable anion [CCBO]- may be formed in the chemical ionization source of a mass spectrometer by the process F- + (CH3)3Si−CC−B(O-iso-Pr)2 → [CCBO]- + (CH3)3SiF + CH3−CHCH2. Anion [CCBO]- may be converted to stable doublet CCBO by a collision-induced vertical Franck−Condon oxidation in the first of two collision cells. Calculations at the MP4SDTQ/aug-cc-pVTZ//MP2(full)/6-31G(d) level of theory indicate that [CCBO]- and CCBO are linear species, with structures approximated by valence bond forms [:CCBO]- and ·CC−BO, respectively. Neutral CCBO may be converted to [CCBO]+ in the second collision cell by vertical ionization. Some of the [CCBO]+ cations are stable, while others are energized and undergo rearrangement to [OCCB]+. This exothermic rearrangement may occur for both the singlet and triplet forms of [CCBO]+ (the triplet form is lower in energy by only 5.2 kcal mol-1) with both rearrangements proceeding through distorted rhombic forms of [cyclo-CCBO]+.
01/2003;
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ABSTRACT: Loss of H2S is the characteristic Cys side-chain fragmentation of the [M-H]- anions of Cys-containing peptides. A combination of experiment and theory suggests that this reaction is initiated from the Cys enolate anion as follows: RNH-(-)C(CH2SH)CONHR' Ø [RNHC(=CH2)CONHR' (HS-)] Ø [RNHC(=CH2)CO-HNR'-H]-+H2S. This process is facile. Calculations at the HF/6-31G(d)//AM1 level of theory indicate that the initial anion needs only > or =20.1 kcal mol(-1) of excess energy to effect loss of H2S. Loss of CH2S is a minor process, RNHCH(CH2SH)CON(-)-R' Ø RNHCH(CH2S-)CONHR' Ø RNH -CHCONHR+CH2S, requiring an excess energy of > or =50.2 kcal mol(-1). When Cys occupies the C-terminal end of a peptide, the major fragmentation from the [M-H]- species involves loss of (H2S+CO2). A deuterium-labelling study suggests that this could either be a charge-remote reaction (a process which occurs remote from and uninfluenced by the charged centre in the molecule), or an anionic reaction initiated from the C-terminal CO2- group. These processes have barriers requiring the starting material to have an excess energy of > or =79.6 (charge-remote) or > or =67.1 (anion-directed) kcal mol(-1), respectively, at the HF/6-31G(d)//AM1 level of theory. The corresponding losses of CH2O and H2O from the [M-H]- anions of Ser-containing peptides require > or =35.6 and > or =44.4 kcal mol(-1) of excess energy (calculated at the AM1 level of theory), explaining why loss of CH2O is the characteristic side-chain loss of Ser in the negative ion mode.
Rapid Communications in Mass Spectrometry 01/2003; 17(22):2488-94. · 2.79 Impact Factor
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ABSTRACT: A recent theoretical investigation by Terzieva & Herbst of linear carbon chains, Cn where n ≥ 6, in the interstellar medium has shown that these species can undergo efficient radiative association to form the corresponding anions. An experimental study by Barckholtz, Snow & Bierbaum of these anions has demonstrated that they do not react efficiently with molecular hydrogen, leading to the possibility of detectable abundances of cumulene-type anions in dense interstellar and circumstellar environments. Here we present a series of electronic structure calculations which examine possible anionic candidates for detection in these media, namely the anion analogues of the previously identified interstellar cumulenes CnH and Cn−1CH2 and heterocumulenes CnO (where n = 2–10). The extraordinary electron affinities calculated for these molecules suggest that efficient radiative electron attachment could occur, and the large dipole moments of these simple (generally) linear molecules point to the possibility of detection by radio astronomy.
Monthly Notices of the Royal Astronomical Society 10/2001; 328(1):89 - 100. · 4.90 Impact Factor
