Gas-Phase Ion/Ion Reactions to Enable Radical-Directed Dissociation of Fatty Acid Ions: Application to Localization of Methyl Branching.

Methyl branching on the carbon chains of fatty acids and fatty esters is among the structural variations encountered with fatty acids and fatty esters. Branching in fatty acid/ester chains is particularly prominent in bacterial species and, for example, in vernix caseosa and sebum. The distinction of branched chains from isomeric straight-chain species and the localization of branching can be challenging to determine by mass spectrometry (MS). Condensed-phase derivatization strategies, often used in conjunction with separations, are most commonly used to address the identification and characterization of branched fatty acids. In this work, a gas-phase ion/ion strategy is presented that obviates condensed-phase derivatization and introduces a radical site into fatty acid ions to facilitate radical-directed dissociation (RDD). The gas-phase approach is also directly amenable to fatty acid anions generated via collision-induced dissociation from lipid classes that contain fatty esters. Specifically, divalent magnesium complexes bound to two terpyridine ligands that each incorporate a ((2,2,6,6-tetramethyl-1-piperidine-1-yl)oxy) (TEMPO) moiety are used to charge-invert fatty acid anions. Following the facile loss of one of the ligands and the TEMPO group of the remaining ligand, a radical site is introduced into the complex. Subsequent collision-induced dissociation (CID) of the complex exhibits preferred cleavages that localize the site(s) of branching. The approach is illustrated with iso-, anteiso-, and isoprenoid branched-chain fatty acids and an intact glycerophospholipid and is applied to a mixture of branched- and straight-chain fatty acids derived from Bacillus subtilis.

Development of mass spectrometric glycan characterization tags using acid-base chemistry and/or free radical chemistry.

Despite recent advances in glycomics, glycan characterization still remains an analytical challenge. Accordingly, numerous glycan-tagging reagents with different chemistries were developed, including those involving acid-base chemistry and/or free radical chemistry. Acid-base chemistry excels at dissociating glycans into their constituent components in a systematic and predictable manner to generate cleavages at glycosidic bonds. Glycans are also highly susceptible to depolymerization by free radical processes, which is supported by results observed from electron-activated dissociation techniques. Therefore, the free radical activated glycan sequencing (FRAGS) reagent was developed so as to possess the characteristics of both acid-base and free radical chemistry, thus generating information-rich glycosidic bond and cross-ring cleavages. Alternatively, the free radical processes can be induced via photodissociation of the specific carbon-iodine bond which gives birth to similar fragmentation patterns as the FRAGS reagent. Furthermore, the methylated-FRAGS (Me-FRAGS) reagent was developed to eliminate glycan rearrangements by way of a fixed charged as opposed to a labile proton, which would otherwise yield additional, yet unpredictable, fragmentations including internal residue losses or multiple external residue losses. Lastly, to further enhance glycan enrichment and characterization, solid-support FRAGS was developed.

Contact and Support Considerations in the Hydrogen Evolution Reaction Activity of Petaled MoS2 Electrodes.

Petaled MoS2 electrodes grown hydrothermally from Mo foils are found to have an 800 nm, intermediate, MoSxOy layer. Similar petaled MoS2 films without this intermediate layer are grown on Au. X-ray photoelectron and Raman spectroscopies and transmission electron microscopy indicate the resulting petaled multilayer MoS2 films are frayed and exhibit single-layer, 1T-MoS2 behavior at the edges. We compare the electrocatalytic hydrogen evolution reaction activity via linear sweep voltammetry with Tafel analysis as well as the impedance properties of the electrodes. We find that petaled MoS2/Au and petaled MoS2/Mo exhibit comparable overpotential to 10 mA cm(-2) at -279 vs -242 mV, respectively, and similar Tafel slopes of ∼68 mV/decade indicating a similar rate-determining step. The exchange current normalized to the geometric area of petaled MoS2/Au (0.000921 mA cm(-2)) is 3 times smaller than that of petaled MoS2/Mo (0.00290 mA cm(-2)), and is attributed to the lower petal density on the Au support. However, Au supports increase the turnover frequency per active site of petaled MoS2 to 0.48 H2 Mo(-1) s(-1) from 0.25 H2 Mo(-1) s(-1) on Mo supports. Both petaled MoS2 films have nearly ohmic contacts to their supports with uncompensated resistivity Ru of <2.5 Ω·cm(2).

A screening technique useful for testing the effectiveness of novel "self-cleaning" photocatalytic surfaces.

We describe a screening methodology that can be used to quickly determine the effectiveness of newly synthesized photocatalysts. We were particularly interested in measuring the destruction of organic molecules painted onto a photocatalytic surface by spraying, with destruction proceeding in ambient air (as a model for airborne toxin destruction). Our method can utilize photocatalysts that are synthesized as powders (such as doped and undoped titanium oxide) and which are then calcined onto a glass substrate disk at 600°C. Herein, we used UV illumination of Aeroxide P-25 TiO(2), but the method is general and can accommodate any region of the light spectrum.