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A method is presented for the rapid identification of tertiary aliphatic and aromatic N-oxide functionalities in protonated analytes via ion-molecule reactions with dimethylamine (DMA) in a linear quadrupole ion trap mass spectrometer (LQIT). DMA was leaked into the trapping region of the mass spectrometer and allowed to react with protonated analytes (ionized by electrospray ionization) for 500 ms, after which all ions were detected. Protonated analytes with the tertiary N-oxide functionality react with DMA to yield exclusively product ions with m/z-values that are 45 units greater than that of the protonated analyte, corresponding to a stable DMA adduct. Collision-activated dissociation of the adduct ions suggests that formation of a hydrogen bond between DMA and the protonated analytes is responsible for the formation of the stable adduct. Hydrogen bond energies were calculated for several adducts at the B3LYP/6-31++G(d,p) level of theory (including correction for basis-set superposition error) to define the potential energy wells for the formation of [M+H+DMA]+ adduct ions. The relative enthalpies calculated for the [M+H+DMA]+ adduct ions were found to be lower than those of the products resulting from proton transfer from protonated tertiary N-oxides and one aromatic ketone, ketoprofen, to DMA. On the other hand, a protonated primary N-oxide, nitrosobenzene, exclusively reacts via proton transfer with DMA, which was calculated to be more exothermic than formation of an adduct ion. Collisional cooling was found to be crucial to the formation of an adduct ion for analytes with proton affinities lower than that of DMA. Ion-molecule reactions of protonated 4-nitro-2-picoline N-oxide (PA = 206 kcal mol−1) with DMA (PA = 222 kcal mol−1) in an FT-ICR at ultra-high vacuum with no buffer gas resulted solely in proton transfer to DMA. Finally, examination of the reactions of DMA with protonated clozapine and clozapine-4′-N-oxide demonstrated that DMA can be used to identify the N-oxide functionality in the presence of other basic functionalities. Compared to other reagents reported for the identification of tertiary N-oxide functionalities via ion-molecule reactions in a mass spectrometer, DMA is the only one volatile enough to be used in a multi-ported pulsed valve system designed for rapid introduction of several reagents, each diagnostic for a different functionality, for characterization of analytes as they elute from an HPLC.

Seven synthesized G-lignin oligomer model compounds (ranging in size from dimers to an octamer) with 5-5 and/or β-O-4 linkages, and three synthesized S-lignin model compounds (a dimer, trimer, and tetramer) with β-O-4 linkages, were evaporated and deprotonated using negative-ion mode ESI in a linear quadrupole ion trap/Fourier transform ion cyclotron resonance mass spectrometer. The collision-activated dissociation (CAD) fragmentation patterns (obtained in MS2 and MS3 experiments, respectively) for the negative ions were studied to develop a procedure for sequencing unknown lignin oligomers. On the basis of the observed fragmentation patterns, the measured elemental compositions of the most abundant fragment ions, and quantum chemical calculations, the most important reaction pathways and likely mechanisms were delineated. Many of these reactions occur via charge-remote fragmentation mechanisms. Deprotonated compounds with only β-O-4 linkages, or both 5-5 and β-O-4 linkages, showed major 1,2-eliminations ...

Isomeric O- and N-glucuronides are common drug metabolites produced in phase II of drug metabolism. Distinguishing these isomers by using common analytical techniques has proven challenging. A tandem mass spectrometric method based on gas-phase ion/molecule reactions of deprotonated glucuronide drug metabolites with trichlorosilane (HSiCl3) in a linear quadrupole ion trap mass spectrometer is reported here to readily enable differentiation of the O- and N-isomers. The major product ion observed upon reactions of HSiCl3 with deprotonated N-glucuronides is a diagnostic HSiCl(3) adduct that has lost two HCl molecules ([M − H + HSiCl3 − 2HCl]-). This product ion was not observed for deprotonated O-glucuronides. Reaction mechanisms were explored with quantum chemical calculations at the M06-2X/6-311++G(d,p) level of theory.

A chemical ionization reagent ion, ClMn2+, has been identified for the analysis of mixtures of organic compounds since it allows ionization of both polar and nonpolar analytes so that only one product ion, ClMn+ adduct of the analyte, is generated without fragmentation. The reagent ion is formed upon ionization of ClMn(CO)5 via corona discharge in an atmospheric pressure chemical ionization source of a linear quadrupole ion trap mass spectrometer. Volatile analytes were introduced into the ion trap via a reagent mixing manifold. Nonvolatile analytes were deposited on a titanium foil and desorbed using laser-induced acoustic desorption (LIAD). Formation of a ClMn+ adduct with no accompanying fragmentation was observed for all analytes, including branched saturated hydrocarbons. Calculations indicate that ClMn+ binds to saturated hydrocarbons via an agostic interaction involving the manganese center and a C H bond of the analyte. The reagent ion Mn+ was also investigated. This ion forms a stable adduct with most analytes studied. It binds fairly strongly to saturated hydrocarbons via two agostic interactions with two C H bonds instead of insertion into a C H bond. However, it was found to cause fragmentation for alcohols. ClMn(H2O)+ has been previously shown to ionize most compounds by ClMn+ adduct formation but also to yield molecular ions for amines due to their low ionization energies ( C bond cleavages for highly branched alkanes upon ionization. This was not observed for the reagent ions studied here. ClMn2+ ion is a more universal ionization reagent than Mn+ and the previously reported reagent ions due to its ability to ionize analytes with low ionization energies without electron transfer and due to the complete lack of fragmentation for all analytes. Furthermore, based on the examination of six very different analytes, it has no significant bias toward specific types of analytes.

Current biomass utilization processes do not make use of lignin beyond its heat value. Here we report on a bimetallic Zn/Pd/C catalyst that converts lignin in intact lignocellulosic biomass directly into two methoxyphenol products, leaving behind the carbohydrates as a solid residue. Genetically modified poplar enhanced in syringyl (S) monomer content yields only a single product, dihydroeugenol. Lignin-derived methoxyphenols can be deoxygenated further to propylcyclohexane. The leftover carbohydrate residue is hydrolyzed by cellulases to give glucose in 95% yield, which is comparable to lignin-free cellulose (solka floc). New conversion pathways to useful fuels and chemicals are proposed based on the efficient conversion of lignin into intact hydrocarbons.

The development of chemical methods for the direct catalytic conversion of biomass to high value organic molecules is an area of increasing interest. The plant matter component known as lignin is a polymer consisting of aromatic rings that could provide a means of obtaining aromatic materials currently derived solely from petroleum. This report describes a bimetallic Pd/C and Zn catalytic system that can perform selective hydrodeoxygenation (HDO) of monomeric lignin surrogates as well as successfully cleave the β-O-4 linkages found in dimeric lignin model complexes and synthetic lignin polymers with near quantitative conversions and yields between 80–90%. The reaction with lignin polymer was highly selective affording methoxy substituted propylphenol as the major product. These reactions were performed in a Parr reactor operating at relatively mild temperature (150 °C) and pressure (20 bar H2) using methanol as a solvent. Reaction products were characterized using high-pressure liquid chromatography coupled to a linear quadrupole ion trap mass spectrometer equipped with an electrospray ionization source using negative ion mode. Hydroxide ions were doped into the analyte solutions to encourage negative ion formation. This method ionizes all the mixture components to yield a single ion/analyte with no fragmentation. The catalyst is fully recyclable without the need for additional zinc. X-ray absorption spectroscopy (EXAFS) is consistent with Pd nanoparticles (4–5 nm) and no evidence of Pd–Zn alloy formation. A mechanistic hypothesis on the synergy between Pd and Zn is presented.