Gas phase synthesis and reactivity of dimethylaurate

A combination of multistage <annref idrefs="ann1">mass spectrometry</annref> experiments and DFT calculations were used to examine the synthesis and reactivity of <compname idrefs="chem1">dimethylaurate</compname>. <annref idrefs="ann2">Collision induced dissociation</annref> (<annref idrefs="ann2">CID</annref>) of [(CH<small>₃</small>CO<small>₂</small>)<small>₄</small>Au]<small>⁻</small> proceeded <em>via</em> reductive elimination of <compname idrefs="chem3">acetylperoxide</compname> to yield the <annref idrefs="ann3">diacetate</annref> [CH<small>₃</small>CO<small>₂</small>AuO<small>₂</small>CCH<small>₃</small>]<small>⁻</small>, which in turn underwent sequential <annref idrefs="ann2">CID</annref> decarboxylation reactions to yield the organoaurates [CH<small>₃</small>CO<small>₂</small>AuCH<small>₃</small>]<small>⁻</small> and [CH<small>₃</small>AuCH<small>₃</small>]<small>⁻</small>. The unimolecular chemistry of the <annref idrefs="ann3">dimethylaurate</annref> proceeds <em>via</em> a combination of bond homolysis to yield the <annref idrefs="ann4">methyl</annref> aurate <annref idrefs="ann5">radical anion</annref> [CH<small>₃</small>Au]˙<small>⁻</small> as well as formation of the <compname idrefs="chem4">gold dihydride</compname> [<compname idrefs="chem5">HAuH</compname>]<small>⁻</small>. DFT calculations reveal that the latter anion is formed <em>via</em> a 1,2-dyotropic <annref idrefs="ann6">rearrangement</annref> to yield the isomer [CH<small>₃</small>CH<small>₂</small>AuH]<small>⁻</small>, followed by a <annref idrefs="ann3">β-hydride</annref> <annref idrefs="ann7">elimination reaction</annref>. Ion-molecule reactions of [CH<small>₃</small>AuCH<small>₃</small>]<small>⁻</small> with <compname idrefs="chem6">methyl iodide</compname> did not yield any products even at relatively high concentrations of the neutral substrate and longer reaction times, indicating a reaction efficiency of less than 1 in 20 000 collisions. DFT calculations were carried out on two different potential energy surfaces (<annref idrefs="ann8">PES</annref>) for the reaction of [CH<small>₃</small>AuCH<small>₃</small>]<small>⁻</small> with CH<small>₃</small>I: (i) an S<small>_N</small>2 mechanism proceeding <em>via</em> a side-on transition state; and (ii) a stepwise mechanism proceeding <em>via</em> oxidative addition followed by reductive elimination. Both pathways have significant endothermic barriers, consistent with the lack of C–C bond coupling products being formed in the experiments. Finally, the reactivity of [CH<small>₃</small>AuCH<small>₃</small>]<small>⁻</small> is compared to the previously studied [CH<small>₃</small>AgCH<small>₃</small>]<small>⁻</small> and [CH<small>₃</small>CuCH<small>₃</small>]<small>⁻</small>, as well as condensed phase studies on <compname idrefs="chem1">dimethylaurate</compname> salts

Ambient Mass Spectrometry: Bringing Ms Into The Real World"."

Mass spectrometry has recently undergone a second contemporary revolution with the introduction of a new group of desorption/ionization (DI) techniques known collectively as ambient mass spectrometry. Performed in an open atmosphere directly on samples in their natural environments or matrices, or by using auxiliary surfaces, ambient mass spectrometry (MS) has greatly simplified and increased the speed of MS analysis. Since its debut in 2004 there has been explosive growth in the applications and variants of ambient MS, and a very comprehensive set of techniques based on different desorption and ionization mechanisms is now available. Most types of molecules with a large range of masses and polarities can be ionized with great ease and simplicity with the outstanding combination of the speed, selectivity, and sensitivity of MS detection. This review describes and compares the basis of ionization and the concepts of the most promising ambient MS techniques known to date and illustrates, via typical analytical and bioanalytical applications, how ambient MS is helping to bring MS analysis deeper than ever into the real world open atmosphere environment--to wherever MS is needed.398265-9

Fast Screening And Secure Confirmation Of Milk Powder Adulteration With Maltodextrin Via Electrospray Ionization-mass Spectrometry [esi(+)-ms] And Selective Enzymatic Hydrolysis.

Direct-infusion electrospray ionization-mass spectrometry [ESI(+)-MS] of several milk powder samples, confiscated by the Brazilian Federal Police, showed ions accounting for sodiated and potassiated molecules of disaccharides (m/z 365 and 381) as well as trisaccharides (m/z 527 and 543), whereas monosaccharide ions were not detected. The trisaccharide ions were not detected in samples of genuine milk powder, raising the suspicion that their presence indicates adulteration by the addition of maltodextrin. In control samples, maltose and maltotriose were hydrolyzed by alpha-glucosidase and not beta-galactosidase, whereas lactose was resistant to alpha-glucosidase but was hydrolyzed with beta-galactosidase. Samples suspected of being adulterated behaved in the same fashion, confirming the presence of maltose and maltotriose or maltodextrin. Direct-infusion ESI-MS is shown therefore to provide rapid screening of milk powder for adulteration with maltodextrin, whereas its combination with selective enzymatic hydrolysis provides highly reliable confirmation for unambiguous results.589407-1

Separation Of Isomeric Disaccharides By Traveling Wave Ion Mobility Mass Spectrometry Using Co2 As Drift Gas.

The use of CO(2) as a massive and polarizable drift gas is shown to greatly improve peak-to-peak resolution (R(p-p) ), as compared with N(2) , for the separation of disaccharides in a Synapt G2 traveling wave ion mobility cell. Near or baseline R(p-p) was achieved for three pairs of sodiated molecules of disaccharide isomers, that is, cellobiose and sucrose (R(p-p)  = 0.76), maltose and sucrose (R(p-p)  = 1.04), and maltose and lactose (R(p-p)  = 0.74). Ion mobility mass spectrometry using CO(2) as the drift gas offers therefore an attractive alternative for fast and efficient separation of isomeric disaccharides.471643-

Fingerprinting And Aging Of Ink By Easy Ambient Sonic-spray Ionization Mass Spectrometry.

Using easy ambient sonic-spray ionization mass spectrometry (EASI-MS), fast and non-destructive fingerprinting identification and aging of ballpoint pen ink writings have been performed directly from paper surfaces under ordinary ambient conditions. EASI-MS data obtained directly from the ink lines showed that pens from different brands provide typical ink chemical profiles. Accelerated ink aging has also been monitored by EASI-MS revealing contrasting degradation behaviors for six different common ink dyes. As demonstrated for Basic Violet 3, some dyes display a cascade of degradation products whose abundances increase linearly with time thus functioning as 'chemical clocks' for ink aging. Analysis of questionable documents has confirmed the ink aging capabilities of EASI-MS. The order of superimposition at a crossing point has also been determined by EASI-MS. For two superimposed ink lines, continuous EASI-MS analysis has also shown that the EASI spray is able to penetrate through the layers and therefore both ink layers could be characterized.135745-5

Instantaneous Chemical Profiles Of Banknotes By Ambient Mass Spectrometry.

Using two desorption/ionization techniques (DESI and EASI) and Brazilian real, US$ dollar, and euro bills as proof-of-principle techniques and samples, direct analysis by ambient mass spectrometry is shown to function as an instantaneous, reproducible, and non-destructive method for chemical analysis of banknotes. Characteristic chemical profiles were observed for the authentic bills and for the counterfeit bills made using different printing processes (inkjet, laserjet, phaser and off-set printers). Detection of real-world counterfeit bills and identification of the counterfeiting method has also been demonstrated. Chemically selective 2D imaging of banknotes has also been used to confirm counterfeiting. The nature of some key diagnostic ions has also been investigated via high accuracy FTMS measurements. The general applicability of ambient MS analysis for anti-counterfeiting strategies particularly via the use of invisible ink markers is discussed.1352533-

Single embryo and oocyte lipid fingerprinting by mass spectrometry[S]

Methods used for lipid analysis in embryos and oocytes usually involve selective lipid extraction from a pool of many samples followed by chemical manipulation, separation and characterization of individual components by chromatographic techniques. Herein we report direct analysis by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) of single and intact embryos or oocytes from various species. Biological samples were simply moisturized with the matrix solution and characteristic lipid (represented by phosphatidylcholines, sphingomyelins and triacylglycerols) profiles were obtained via MALDI-MS. As representative examples, human, bovine, sheep and fish oocytes, as well as bovine and insect embryos were analyzed. MALDI-MS is shown to be capable of providing characteristic lipid profiles of gametes and embryos and also to respond to modifications due to developmental stages and in vitro culture conditions of bovine embryos. Investigation in developmental biology of the biological roles of structural and reserve lipids in embryos and oocytes should therefore benefit from these rapid MALDI-MS profiles from single and intact species