A flowing afterglow study of [C3H3]− ions generated from the reactions of [OH]− with allene and propyne

Flowing afterglow studies are reported for the rates and modes of reaction of [C₃H₃]^? ions produced from allene and propyne by reaction with [OH]^? or by electron impact. Studies with methyl formate provide further evidence for the formation from propyne of two distinct stable species.     

Accurate quantification of the redox-sensitive GSH/GSSG ratios in the yeast Pichia pastoris by HILIC–MS/MS

A novel method for the simultaneous quantification of both glutathione (GSH) and its oxidized form glutathione disulfide (GSSG) by hydrophilic interaction chromatography–MS/MS has been developed and is critically discussed. Internal standardization based on isotopically labeled standards for both analytes is an absolute prerequisite for accurate quantification of this redox pair. Hence, a highly efficient and selective miniaturized procedure for the synthesis of isotopically labeled GSSG from commercially available glutathione-(glycine-¹³C₂,¹⁵N) was established using H₂O₂ as oxidant and NaI as catalyst. Moreover, a tool is presented to monitor and hence uncover artifactual GSSG formation due to oxidation of GSH during sample preparation, which is the main source of systematic error in GSSG analysis. For this purpose, we propose to monitor the oxidation product formed by reaction of naturally occurring GSH with the isotopically labeled GSH used as internal standard. For the determination of GSH/GSSG ratios in yeast, different extraction methods based on (1) hot extraction with aqueous, acidic, or organic solvents, (2) mechanical cell lysis, and (3) extraction at subambient temperature were investigated in terms of recovery, extraction efficiency, and artifactual formation of GSSG. Total combined uncertainties of as low as 25–30 % (coverage factor?=?2) for the determination of GSH/GSSG ratios without derivatization were made possible by the addition of the internal standards early in the analytical procedure (before extraction) and immediate analysis of the analytes.     

O-atom transport catalysis by atomic cations in the gas phase: reduction of N2O by CO

Atomic cations (26), M+, have been shown to lie within a thermodynamic window for O-atom transport catalysis of the reduction of N2O by CO and have been checked for catalytic activity at room temperature with kinetic measurements using an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. Only 10 of these 26 atomic cations were seen to be catalytic: Ca+, Fe+, Ge+, Sr+, Ba+, Os+, Ir+, Pt+, Eu+, and Yb+. The remaining 16 cations that lie in the thermodynamic window (Cr+, Mn+, Co+, Ni+, Cu+, Se+, Mo+, Ru+, Rh+, Sn+, Te+, Re+, Pb+, Bi+, Tm+, and Lu+) react too slowly at room temperature either in the formation of MO+ or in its reduction by CO. Many of these reactions are known to be spin forbidden and a few actually may lie outside the thermodynamic window. A new measure of efficiency is introduced for catalytic cycles that allows the discrimination between catalytic cations on the basis of the efficiencies of the two legs of the catalytic cycle. Also, a potential-energy landscape is computed for the reduction of N2O by CO catalyzed by Fe+(6D) that vividly illustrates the operation of an ionic catalyst.     

Mass spectrometric study of the dissociation of Group XI metal complexes with fatty acids and glycerolipids: Ag2H+ and Cu2H+ ion formation in the presence of a double bond

Results of mass spectrometric studies are reported for the collisional dissociation of Group XI (Cu, Ag, Au) metal ion complexes with fatty acids (palmitic, oleic, linoleic and α-linolenic) and glycerolipids. Remarkably, the formation of M₂H⁺ ions (M = Cu, Ag) is observed as a dissociation product of the ion complexes containing more than one metal cation and only if the lipid in the complex contains a double bond. Ag₂H⁺ is formed as the main dissociation channel for all three of the fatty acids containing double bonds that were investigated while Cu₂H⁺ is formed with one of the fatty acids and, although abundant, is not the dominant dissociation channel. Also, Cu(I) and Ag(I) ion complexes were observed with glycerolipids (including triacylglycerols and glycerophospholipids) containing either saturated or unsaturated fatty acid substituents. Interestingly, Ag₂H⁺ ion is formed in a major fragmentation channel with the lipids that are able to form the complex with two metal cations (triacylglycerols and glycerophosphoglycerols), while lipids containing a fixed positive charge (glycerophospocholines) complex only with a single metal cation. The formation of Ag₂H⁺ ion is a significant dissociation channel from the complex ion [Ag₂(L–H)]⁺ where L = Glycerophospholipid (GP) (18:1/18:1). Cu(I) also forms complexes of two metal cations with glycerophospholipids but these do not produce Cu₂H⁺ upon dissociation. Rather organic fragments, not containing Cu(I), are formed, perhaps due to different interactions of these metal cations with lipids resulting from the much smaller ionic radius of Cu(I) compared to Ag(I).     

Cyclization of 4‐Phenylthiosemicarbazide with Phenacylbromide Revisited. Formation of 1,3,4‐Thiadiazines and of Isomeric 1,3‐Thiazoles

The cyclization of 4‐phenylthiosemicarbazide with phenacylbromide, carried out in refluxing ethanol, afforded 1,3,4‐thiadiazine 1 as the major product. In contrast to a previous report, 2‐phenylimino‐4‐phenyl‐2,3‐dihydro‐1,3‐thiazol‐3‐amine ( 2 ) and not 2‐hydrazono‐3,4‐diphenyl‐2,3‐dihydro‐1,3‐thiazole ( 8 ) was formed as a side‐product. This product is the main product when the reaction is carried out in concentrated hydrochloric acid. Our findings were independently confirmed by independent syntheses of the isomeric products and by a thorough study of their reactivity. It is important to note that the product distribution of the cyclization of thiosemicarbazides with haloketones strongly depends on the substitution pattern and on the reaction conditions.     

Generation and dissociation of oxygen‐ and chloride‐bridged iron(III) and manganese(III) tetraphenylporphyrin dimer ions in the gas phase

Electrospray ionization mass spectrometry (ESI/MS) has allowed the discovery of novel dimer ions emerging from solutions of metalloporphyrin salts and their investigation by collision‐induced dissociation (CID) with N₂ molecules. ESI mass spectra have been recorded for the formation of the oxygen or chloride‐bridged dimer ions [(FeTPP)₂OH]⁺, [(MnTPP)₂OH]⁺, [(FeTPP)₂Cl]⁺ and [(MnTPP)₂Cl]⁺ derived from various solutions of FeTPPCl and MnTPPCl salts. The CID of [(FeTPP)₂OH]⁺ proceeds mainly by neutral loss of (FeTPP)OH to form [FeTPP]⁺ and, to a minor extent, to form the charge‐reversed products. The CID of [(MnTPP)₂OH]⁺ exhibits exclusively the product ion [MnTPP]⁺ by loss of neutral (MnTPP)OH. [(FeTPP)₂Cl]⁺ and [(MnTPP)₂Cl]⁺ dissociate by loss of (Fe/MnTPP)Cl to give rise to [Fe/MnTPP]⁺. [(FeTPP)₂O]⁺ and [(FeTPP)₂OH]⁺ were generated from a solution of the dimer, (FeTPP)₂O. Dissociation of [(FeTPP)₂O]⁺ yields two product ions, [FeTPP]⁺ and [(FeTPP)O]⁺, with higher onsets compared to the equivalent fragments formed from [(FeTPP)₂OH]⁺. Copyright © 2009 John Wiley & Sons, Ltd.     

Existence of doubly charged lead monohydrate: experimental evidence and theoretical examination

Despite reports to the contrary, doubly charged lead monohydrate is a stable species against both proton and charge transfers. [Pb(H(2)O)](2+) has been observed as a minor product in the ligand-exchange reaction of [Pb(CH(3)CN)](2+) with H(2)O after collisional activation. Density functional theory has been used to examine reaction profiles of [Pb(H(2)O)(n)](2+) where n = 1, 2, and 3.     

Synthesis of 2‐Unsubstituted 1,3‐Selenazoles by Cyclization of Selenoformamide with α‐Bromocarbonyl Compounds

2‐Unsubstituted 1,3‐selenazoles were prepared by cyclization of selenoformamide with α‐bromoacetophenones. Parent 1,3‐selenazole was prepared by cyclization of selenoformamide with α‐bromoacetaldehyde.