Are the anions MeO(CO)n- (n = 1 and 2) methoxide anion donors in the gas phase? A theoretical investigation.

1. The anions CH(3)O-(-)CO and CH(3)OCO-(-)CO are both methoxide anion donors. The processes CH(3)O-(-)CO --> CH(3)O(-) + CO and CH(3)OCO-CO --> CH(3)O(-) + 2CO have DeltaG values of +8 and -68 kJ mol(-1), respectively, at the CCSD(T)/6-311++G(2d, 2p)//B3LYP/6-311++G(2d,2p) level of theory.

How does energized NCCCCCN lose carbon in the gas phase? A joint experimental and theoretical study.

Neutral NCCCCCN may be prepared in a collision cell of a VG ZAB 2HF mass spectrometer by charge stripping of (NCCCCCN)(*-), formed in the ion source by the process NCCCCH(OEt)(CN) + HO(-) --> H(2)O + NCCCC(-)(OEt)(CN) --> (NCCCCCN)(*-) + EtO(*). A comparison of the neutralization/reionization ((-)NR(+)) and charge reversal ((-)CR(+)) spectra of (NCCCCCN)(*-) indicate that some neutrals NCCCCCN are energized and rearrange to an isomer which decomposes by loss of carbon. An ab initio study at the CCSD(T)/cc-pVTZ//B3LYP/6-311+G(3df) level of theory indicates that (i) triplet NCCCCCN is the ground state with a T/S energy gap of -14.

Anions [N(CH2)3]- and [ON(CH2)2]- are stable in the gas phase, but can they be charge stripped to form the radicals N(CH2)3 and ON(CH2)2? A joint experimental and theoretical study.

Collision-induced activation of deprotonated trimethylamine N-oxide yields the two anions [N(CH(2))(3)](-) and [ON(CH(2))(2)](-) following losses of H(2)O and CH(4), respectively. These two anions decompose by minor losses of H(*) and H(2) when collisionally activated: no other fragmentations are noted. Calculations at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31+G(d) level of theory indicate that these trigonal anions are stable, and should not rearrange following collisional activation.

Is the hypothiocyanite anion (OSCN)- the major product in the peroxidase catalyzed oxidation of the thiocyanate anion (SCN)-? A joint experimental and theoretical study.

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)(-).

One-electron oxidation of [CCOCC]-* in the gas phase forms stable and decomposing forms of CCCCO.

The radical anion [CCOCC]-* may be made in the source of a VG ZAB 2HF mass spectrometer by the reaction between F-(from SF6) and (CH3)3SiC[triple bond]COC[triple bond]CSi(CH3)3. Vertical (Franck-Condon) one-electron oxidation of [CCOCC]-* in the first collision cell produces both singlet and triplet CCOCC. A combination of experiment and molecular modelling (at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G* level of theory) gives data which are consistent with the CCOCC neutrals rearranging over small barriers to form singlet and triplet CCCCO in exothermic reactions.

Generation of transient neutrals in the gas phase from anionic precursors. Does energised CNCCO rearrange to NCCCO?

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)).

The formation of RCCCO and CCC(O)R (R = Me, Ph) neutral radicals from ionic precursors in the gas phase: the rearrangement of CCC(O)Ph.

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.

Gas phase generation of the neutrals H2CCCCO, HCCCCDO and CCCHCHO from anionic precursors. Rearrangements of HCCCCDO and CCCHCHO. A joint experimental and theoretical study.

The reaction between O-. and MeO-CH2-C identical to C-CDO in the ion source of a VG ZAB 2HF mass spectrometer gives a number of product anions including [H2CCCCO]-. and [HCCCCDO]-.

Generation of neutrals from ionic precursors in the gas phase. The rearrangement of CCCCCHO to HCCCCCO.

The neutrals HCCCCCO and CCCCCHO have been studied by experiment and by molecular modelling at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory. Neutral HCCCCCO has been made by one-electron reduction of [HCCCCCO]+ in the dual collision cell of a VG ZAB 2HF mass spectrometer. The isomer CCCCCHO is also formed in the dual collision cell, but this time by one-electron oxidation of the anion [CCCCCHO]-.

Formation of neutral molecules of potential stellar interest by neutralisation of negative ions in a mass spectrometer. The application of experiment and molecular modelling in concert.

This paper is a modified version of a lecture which describes the synthesis, structure and reactivity of some neutral molecules of stellar significance. The neutrals are formed in the collision cell of a mass spectrometer following vertical Franck-Condon one electron oxidation of anions of known bond connectivity. Neutrals are characterised by conversion to positive ions and by extensive theoretical studies at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory.

Collision-induced fragmentations of the (M-H)- parent anions of underivatized peptides: an aid to structure determination and some unusual negative ion cleavages.

This article describes the fundamental cleavage reactions of (M-H)(-) anions of underivatized peptides that contain up to 25 amino acid residues. The experimental observations of these cleavages have been backed up by molecular modeling, generally at the AM1 level of theory. The basic cleavages are the ubiquitous alpha- and beta-backbone cleavage reactions, which provide information similar to that of the B and Y + 2 cleavages of MH(+) ions of peptides.

Backbone cleavages of [M - H](-) anions of peptides. Cyclisation of citropin 1 peptides involving reactions between the C-terminal [CONH](-) residue and backbone amide carbonyl groups. A new type of beta cleavage: a joint experimental and theoretical study.

This paper reports the study of backbone cleavages in the collision-induced negative-ion mass spectra of the [M - H](-) anions of some synthetic modifications of the bioactive amphibian peptide citropin 1 (GLFDVIKKVASVIGGL-NH(2)). The peptides chosen for study contain no amino acid residues which could effect facile side-chain cleavage, i.e.