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1.
Anal Chem ; 91(24): 15652-15660, 2019 12 17.
Article in English | MEDLINE | ID: mdl-31702133

ABSTRACT

Gas-phase ion/molecule reactions have been used extensively for the structural elucidation of organic compounds in tandem mass spectrometry. Reagents for ion/molecule reactions can be introduced into a mass spectrometer via a continuous flow apparatus or through a pulsed inlet system. However, most of these approaches enable the use of only a single reagent at a time. In this work, a multichannel pulsed-valve inlet system was developed for the rapid consecutive introduction of up to nine different reagents or reagent systems into a linear quadrupole ion trap mass spectrometer for diagnostic gas-phase ion/molecule reactions. Automated triggering of the pulsed valves enabled these experiments to be performed on the high-performance liquid chromatography (HPLC) time scale. This enables high-throughput screening of several functionalities in analytes as they elute from an HPLC column.

2.
Anal Chem ; 90(15): 9426-9433, 2018 08 07.
Article in English | MEDLINE | ID: mdl-29984992

ABSTRACT

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 HSiCl3 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.


Subject(s)
Glucuronides/metabolism , Pharmaceutical Preparations/metabolism , Tandem Mass Spectrometry/methods , Chromatography, High Pressure Liquid/methods , Glucuronides/chemistry , Isomerism , Pharmaceutical Preparations/chemistry , Protons , Silanes/chemistry , Silanes/metabolism
3.
Anal Chem ; 89(24): 13089-13096, 2017 12 19.
Article in English | MEDLINE | ID: mdl-29116757

ABSTRACT

Seven synthesized G-lignin oligomer model compounds (ranging in size from dimers to an octamer) with 5-5 and/or ß-O-4 linkages, and three synthesized S-lignin model compounds (a dimer, trimer, and tetramer) with ß-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 ß-O-4 linkages, or both 5-5 and ß-O-4 linkages, showed major 1,2-eliminations of neutral compounds containing one, two, or three aromatic rings. The most likely mechanisms for these reactions are charge-remote Maccoll and retro-ene eliminations resulting in the cleavage of a ß-O-4 linkage. Facile losses of H2O and CH2O were also observed for all deprotonated model compounds, which involve a previously published charge-driven mechanism. Characteristic "ion groups" and "key ions" were identified that, when combined with their CAD products (MS3 experiments), can be used to sequence unknown oligomers.

4.
Chirality ; 29(12): 854-864, 2017 Dec.
Article in English | MEDLINE | ID: mdl-28981965

ABSTRACT

The absolute configurations of the separated enantiomers of fluralaner, a racemic animal health product used to prevent fleas and ticks, have been assigned using vibrational circular dichroism (VCD). The crystallographic structure of the active enantiomer (+)-fluralaner has previously been shown to have the (S) configuration using small molecule crystallography. We sought a faster analytical method to determine the absolute configuration of the separated enantiomers. When comparing the measured IR (infrared) and VCD spectra, it is apparent that the amide carbonyl groups appear in the IR but are nearly absent in the VCD. Computational work to calculate the VCD and IR using in vacuo models, implicit solvation, and explicitly solvated complexes has implicated conformational averaging of the carbonyl VCD intensities.


Subject(s)
Amides/chemistry , Isoxazoles/chemistry , Circular Dichroism , Molecular Conformation , Stereoisomerism , Vibration
5.
J Am Soc Mass Spectrom ; 28(6): 1091-1098, 2017 06.
Article in English | MEDLINE | ID: mdl-28500583

ABSTRACT

Laser-induced acoustic desorption (LIAD) allows for desorption of neutral nonvolatile compounds independent of their volatility or thermal stability. Many different ionization methods have been coupled with LIAD. Hence, this setup provides a better control over the types of ions formed than other mass spectrometry evaporation/ionization methods commonly used to characterize biomolecules, such as ESI or MALDI. In this study, the utility of LIAD coupled with electron ionization (EI) was tested for the analysis of common amino acids with no derivatization. The results compared favorably with previously reported EI mass spectra obtained using thermal desorption/EI. Further, LIAD/EI mass spectra collected for hydrochloride salts of two amino acids were found to be similar to those measured for the neutral amino acids with the exception of the appearance of an HCl+● ion. However, the hydrochloride salt of arginine showed a distinctly different LIAD/EI mass spectrum than the previously published literature EI mass spectrum, likely due to its highly basic side chain that makes a specific zwitterionic form particularly favorable. Finally, EI mass spectra were measured for seven small peptides, including di-, tri-, and tetrapeptides. These mass spectra show a variety of ion types. However, an type ions are prevalent. Also, electron-induced dissociation (EID) of protonated peptides has been reported to form primarily an type ions. In addition, the loss of small neutral molecules and side-chain cleavages were observed that are reminiscent of other high-energy fragmentation methods, such as EID. Finally, the isomeric dipeptides LG and IG were found to produce drastically different EI mass spectra, thus allowing differentiation of the leucine and isoleucine amino acids in these dipeptides. Graphical Abstract ᅟ.


Subject(s)
Amino Acids/chemistry , Lasers , Mass Spectrometry/methods , Peptides/chemistry , Acoustics , Electrons , Spectrometry, Mass, Electrospray Ionization/methods
7.
ChemSusChem ; 9(24): 3513-3526, 2016 Dec 20.
Article in English | MEDLINE | ID: mdl-27896945

ABSTRACT

The collision-activated fragmentation pathways and reaction mechanisms of 34 deprotonated model compounds representative of lignin degradation products were explored experimentally and computationally. The compounds were evaporated and ionized by using negative-ion mode electrospray ionization doped with NaOH to produce abundant deprotonated molecules. The ions were isolated and subjected to collision-activated dissociation (CAD). Their fragment ions were then isolated and also subjected to CAD. This was repeated until no further fragmentation was observed (up to MS6 ). This approach enabled the identification of characteristic reaction pathways and delineation of reasonable fragmentation mechanisms for deprotonated molecules containing various functional groups. The varying fragmentation patterns observed for different types of compounds allow for the identification of the functionalities in these compounds. This information was utilized to identify the presence of specific functionalities and their combinations in molecules in an organosolv lignin sample.


Subject(s)
Lignin/chemistry , Protons , Tandem Mass Spectrometry , Aldehydes/chemistry , Carboxylic Acids/chemistry , Esters/chemistry , Phenols/chemistry
8.
J Am Soc Mass Spectrom ; 27(11): 1813-1823, 2016 11.
Article in English | MEDLINE | ID: mdl-27553243

ABSTRACT

Conversion of lignin into smaller molecules provides a promising alternate and sustainable source for the valuable chemicals currently derived from crude oil. Better understanding of the chemical composition of the resulting product mixtures is essential for the optimization of such conversion processes. However, these mixtures are complex and contain isomeric molecules with a wide variety of functionalities, which makes their characterization challenging. Tandem mass spectrometry based on ion-molecule reactions has proven to be a powerful tool in functional group identification and isomer differentiation for previously unknown compounds. This study demonstrates that the identification of the phenol functionality, the most commonly observed functionality in lignin degradation products, can be achieved via ion-molecule reactions between diethylmethoxyborane (DEMB) and the deprotonated analyte in the absence of strongly electron-withdrawing substituents in the ortho- and para-positions. Either a stable DEMB adduct or an adduct that has lost a methanol molecule (DEMB adduct-MeOH) is formed for these ions. Deprotonated phenols with an adjacent phenol or hydroxymethyl functionality or a conjugated carboxylic acid functionality can be identified based on the formation of DEMB adduct-MeOH. Deprotonated compounds not containing the phenol functionality and phenols containing an electron-withdrawing ortho- or para-substituent were found to be unreactive toward diethylmethoxyborane. Hence, certain deprotonated isomeric compounds with phenol and carboxylic acid, aldehyde, carboxylic acid ester, or nitro functionalities can be differentiated via these reactions. The above mass spectrometry method was successfully coupled with high-performance liquid chromatography for the analysis of a complex biomass degradation mixture. Graphical Abstract ᅟ.

9.
Anal Chem ; 85(23): 11284-90, 2013 Dec 03.
Article in English | MEDLINE | ID: mdl-24171553

ABSTRACT

A novel differentially pumped dual linear quadrupole ion trap (DLQIT) mass spectrometer was designed and built to facilitate tandem MS experiments free from interfering reactions. The instrument consists of two differentially pumped Thermo Scientific linear quadrupole ion trap (LQIT) systems that have been connected via an ion transfer octupole encased in a machined manifold. Tandem MS experiments can be performed in the front trap and then the resulting product ions can be transferred via axial ejection into the back trap for further, independent tandem MS experiments in a differentially pumped area. This approach allows the examination of consecutive collision-activated dissociation (CAD) and ion-molecule reactions without unwanted side reactions that often occur when CAD and ion-molecule reactions are examined in the same space. Hence, it greatly facilitates investigations of ion structures. In addition, the overall lower pressure of the DLQIT, as compared to commercial LQIT instruments, results in a reduction of unwanted side reactions with atmospheric contaminants, such as water and oxygen, in CAD and ion-molecule experiments.


Subject(s)
Particle Accelerators , Tandem Mass Spectrometry/methods , Ion Exchange , Mass Spectrometry/methods
10.
Anal Chem ; 84(14): 6000-7, 2012 Jul 17.
Article in English | MEDLINE | ID: mdl-22746183

ABSTRACT

In the search for a replacement for fossil fuel and the valuable chemicals currently obtained from crude oil, lignocellulosic biomass has become a promising candidate as an alternative biorenewable source for crude oil. Hence, many research efforts focus on the extraction, degradation, and catalytic transformation of lignin, hemicellulose, and cellulose. Unfortunately, these processes result in the production of very complex mixtures. Further, while methods have been developed for the analysis of mixtures of oligosaccharides, this is not true for the complex mixtures generated upon degradation of lignin. For example, high-performance liquid chromatography/multiple stage tandem mass spectrometry (HPLC/MS(n)), a tool proven to be invaluable in the analysis of complex mixtures derived from many other biopolymers, such as proteins and DNA, has not been implemented for lignin degradation products. In this study, we have developed an HPLC separation method for lignin degradation products that is amenable to negative-ion-mode electrospray ionization (ESI doped with NaOH), the best method identified thus far for ionization of lignin-related model compounds without fragmentation. The separated and ionized compounds are then analyzed by MS(3) experiments to obtain detailed structural information while simultaneously performing high-resolution measurements to determine their elemental compositions in the two parts of a commercial linear quadrupole ion trap/Fourier-transform ion cyclotron resonance mass spectrometer. A lignin degradation product mixture was analyzed using this method, and molecular structures were proposed for some components. This methodology significantly improves the ability to analyze complex product mixtures that result from degraded lignin.


Subject(s)
Chromatography, High Pressure Liquid/methods , Hydroxides/chemistry , Lignin/chemistry , Spectrometry, Mass, Electrospray Ionization/methods , Tandem Mass Spectrometry/methods , Limit of Detection , Solvents/chemistry
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