Reactions of O−. with methyl benzoate: A negative ion chemical ionization and Fourier transform ion cyclotron resonance study

The reactions of O*- with methyl benzoate have been examined by the measurement of negative ion chemical ionization (NICI) mass spectra using a CI source, with confirmatory studies carried out on a Fourier transform ion cyclotron resonance mass spectrometer. Reaction mechanisms have been elucidated using isotopically labeled esters. Nucleophilic attack at the carbonyl carbon and the aromatic ring were important reaction pathways. Nucleophilic attack at the carbonyl carbon was followed by the production of products (C6HsCO2- and CH3OCO2-) characteristic of radical, beta-fragmentation. Using 18O-labeled methyl benzoate, the SN2 reaction was found to account for a smaller percentage, 21(+/-1)%, of the benzoate product. Aromatic ring attack resulted in formation of [M + O - H]- and [M - 2H]*- ions. Although aryl hydrogens accounted for most H2*+ abstracted by O*-, evidence for abstraction of HarylH*+alkyl and HalkylH*+alkyl was also found. Although present at much lower abundance, dehydrobenzoate, dehydrophenoxy, and C7H6*- ([M - 2H - CO2]*-) radical anions were also observed. An Haryl/Halkyl exchange associated with formation of the benzoate anion was attributed to an Halkyl abstraction that occurred within the methanol/dehydrobenzoate ion-dipole complex. The [M - 2H]*-, dehydrobenzoate, dehydrophenoxy, and [M - 2H - CO2]*- ion signals were quenched by reaction with O2. Conditions required for production of O*- spectra under NICI conditions were also examined.     

Planar-chiral cyrhetrenes for the rhodium-catalyzed asymmetric 1,4-addition and the hydrogenation of enamides

[reaction: see text] The syntheses of novel cyrhetrenes 7a-c and 8a,b are described. These planar-chiral, mono- and diphosphines have been applied as ligands in the Rh-catalyzed 1,4-addition reaction to activated olefins and in the Rh-catalyzed hydrogenation of enamide 12, giving the corresponding products with up to 97 and 93% ee, respectively.     

Role of Gold in Inflammation and Tristetraprolin Activity

The zinc finger protein tristetraprolin (TTP) regulates inflammation by downregulating cytokine mRNAs. Misregulation results in arthritis, sepsis and cancer, and there is an interest in modulating TTP activity with exogenous agents. Gold has anti-inflammatory properties and has recently been shown to modulate the signaling pathway that produces TTP, suggesting that TTP may be a target of gold. The reactivity of [Au^III(terpy)Cl]Cl₂ with TTP was investigated by UV/Vis spectroscopy, spin-filter inductively coupled plasma mass spectrometry, X-ray absorption spectroscopy and native electrospray ionization mass spectrometry. Au^III was found to replace zinc in the protein active site in the reduced Au^I form, with the Au^I ion coordinated to two cysteine residues in a linear geometry. The replacement of Zn^II with Au^I results in loss of both secondary structure and RNA binding function. In contrast, when Zn^IITTP is bound to its RNA target, no replacement of Zn^II with Au^I is observed, even in the presence of excess Au^IIIterpy. This discovery of differential reactivity of gold with TTP versus TTP/RNA offers a potential strategy for selective targeting with gold complexes to control inflammation.     

Organophotocatalytic Aerobic Oxygenation of Phenols in a Visible-Light Continuous-Flow Photoreactor

A mild photocatalytic phenol oxygenation enabled by a continuous-flow photoreactor using visible light and pressurized air is described herein. Products for wide-ranging applications, including the synthesis of vitamins, were obtained in high yields by precisely controlling principal process parameters. The reactor design permits low organophotocatalyst loadings to generate singlet oxygen. It is anticipated that the efficient aerobic phenol oxygenation to benzoquinones and p-quinols contributes to sustainable synthesis.     

The detection of red pigment-concentrating hormone (RPCH) in crustacean eyestalk tissues using matrix-assisted laser desorption/ionization-Fourier transform mass spectrometry: [M + Na]+ ion formation in dried droplet tissue preparations

Red pigment-concentrating hormone (RPCH), an octapeptide found in crustaceans and insects with the sequence pGlu-Leu-Asn-Phe-Ser-Pro-Gly-Trp-NH2, is an N- and C-terminally blocked uncharged peptide. These structural features are shared with many members of the larger adipokinetic hormone (AKH)/RPCH peptide family in insects. We have applied vacuum UV matrix-assisted laser desorption/ionization (MALDI)-Fourier transform ion cyclotron mass spectrometry (FTMS) to the direct analysis of crustacean sinus gland tissues, using 2,5-dihydroxybenzoic acid (DHB) as the MALDI matrix, and have found that RPCH is detected in the cationized, [M + Na]+, form under conditions where other peptides in the direct tissue spectra are protonated without accompanying [M + Na]+ or [M + K]+ satellite peaks. The [M + H]+ ion for RPCH is not detected in tissue samples or for an RPCH standard, even when care is taken to eliminate metal ions. This behavior is not unprecedented; however, both direct tissue spectra and SORI-CID spectra provide no clues to suggest that the ionizing agent is a metal cation. In this communication, we characterize the MALDI-FTMS ionization and SORI-CID mass spectra of the [M + Na]+ and [M + K]+ ions from RPCH, and report on the detection of this neuropeptide in sinus gland tissues from the lobster Homarus americanus and the kelp crab Pugettia producta. We describe two strategies, an on-probe extraction procedure and a salt-doping approach, that can be applied to previously analyzed MALDI tissue samples to enhance and unmask sodiated peptides that may otherwise be mistaken for novel neuropeptides.     

Infrared molecular beam depletion spectroscopy of size-selected methanol clusters

Molecular beam depletion spectroscopy has been employed to study the dissociation of small methanol clusters in the spectral region between 1000 and 1100 cm^?1 which covers thev ₈ CO stretch (1033.5 cm^?1) and thev ₇ CH₃ rock (1074.5 cm^?1) monomer vibrations. Size selection has been achieved by dispersing the (CH₃OH) _n cluster beam by a secondary He beam. Aside from the recently published CH₃OH dimer absorption bands at 1026.5 and 1051.6 cm^?1 which are assigned to the excitation of the CO stretching vibrations in the non-equivalent subunits of the hydrogen-bonded complex, a previously unobserved band was found at 1071.3 cm^?1. This absorption band is attributed to the excitation of the CH₃ rocking vibration in the dimer. It appears that this transition which is very weak in the free methanol monomer receives substantial oscillator strength due to the intermolecular interaction in the complex. A splitting of this band could not be observed. The trimer and tetramer spectra feature single peaks for the CO stretching vibration being centered at 1042.2 cm^?1 and 1044.0 cm^?1, respectively. This observation is consistent with the cyclic structures of these species. The trimer and tetramer rocking vibrations are observed near 1060.5 cm^?1 but cannot be localized exactly, due to a gap in the CO₂ laser tuning range.