Intramolecular interactions and the neutral loss of ammonia from collisionally activated, protonated ω-aminoalkyl-3-hydroxyfurazans.

Gas phase fragmentation reactions of monoprotonated 4-(3-aminopropyl)- and 4-(4-aminobutyl)-3-hydroxyfurazan were investigated to examine potential interactions between functional groups. The two heterocyclic alkyl amines were ionized by electrospray ionization (ESI, positive mode) and fragmented using tandem mass spectrometry (MS/MS). The fragmentation pathways were characterized using pseudo MS3 experiments, precursor-ion scans, and density functional computations. For both heterocyclic ions, loss of ammonia was the only fragmentation process observed at low collision energies. Computational analysis indicated that the most feasible mechanism was intramolecular nucleophilic displacement of ammonia from the protonated ω-aminoalkyl side chain by N5 of the furazan ring. The alkylated nitrogen in the resulting bicyclic product ion facilitated N-O bond cleavage; subsequent neutral losses of nitric oxide (NO) and carbon monoxide (CO) occurred by homolytic bond cleavages. Next in the multistep sequence, neutral loss of ethylene from a radical cation was observed. A less favorable, competing fragmentation pathway of protonated 4-(3-aminopropyl)-3-hydroxyfurazan was consistent with cleavage of the 3-hydroxyfurazan ring and losses of NO and CO. Overall, the similar fragmentation behavior found for protonated 4-(3-aminopropyl)- and 4-(4-aminobutyl)-3-hydroxyfurazan differed from that previously characterized for furazan analogs with shorter alkyl chains. These observations demonstrate that a small change in the structure of multifunctional, heterocyclic alkyl amines may significantly influence interactions between distinct functional groups and the nature of the fragmentation process.

Fragmentation reactions of protonated α,ω-diamino carboxylic acids: The importance of functional group interactions.

Protonated members of a homologous series of biologically significant α,ω-diamino carboxylic acids were subjected to collision induced dissociation (CID). The resulting fragmentation patterns were studied using isotopic labeling, quantum mechanical computations, and pseudo MS3 experiments conducted primarily on an ion trap mass spectrometer. Each protonated α,ω-diamino acid showed a primary neutral loss of either ammonia or water; a clear explanation was developed for the observed variation of the two losses within the series. Protonated 2,3-diaminopropanoic acid, 2,4-diaminobutanoic acid, and 2,7-diaminoheptanoic acid gave secondary losses of water, carbon monoxide, and a loss of water plus carbon monoxide, respectively. In the parallel pathways characterized for the fragmentations of protonated ornithine and lysine, the α-nitrogen of the diamino acid was maintained in the cyclic iminium product formed by successive losses of NH3 and (H2 O + CO), whereas the side-chain nitrogen was retained by consecutive losses of H2 O and (CO, NH3 ). The 1-piperideine ion from protonated lysine was fragmented further, losing ethylene from carbons 4 and 5. Protonated 2,6-diaminopimelic acid fragmented by analogous reactions. Detailed mechanistic schemes for the fragmentation of both protonated 2,3-diaminopropanoic and ornithine were generated from MP2/DFT computations. This work highlights the participation of the side-chain amino group, which distinguishes the gas-phase chemistry of protonated α,ω-diamino acids from the well-documented fragmentation reactions of protonated α-amino acids bearing a hydrogen atom or an alkyl side chain. In general, the results further illustrate the importance of intramolecular separations affecting the specific interactions between functional groups leading to the fragmentation of multifunctional ions.

Fragmentation Pathways of Cationized, Saturated, Short-Chain Triacylglycerols: Lithiated and Sodiated Tripropanoyl- and Trihexanoylglycerol.

Many methods, often depending on tandem mass spectrometry, have been developed for analysis of complex mixtures of triacylglycerols (TAGs), especially in clinical diagnostics and food authentication. Understanding the fragmentation mechanisms of cationized TAGs has proved problematic. To obtain a better understanding of viable mechanisms, detailed studies including double- and triple-stage tandem mass spectrometry were made using electrospray ionization on lithiated and sodiated tripropanoyl- and trihexanoylglycerols. Density functional theory computations, including a functional parameterized for van der Waals interactions, were used to correlate computed energies with mass spectra. Losses of both a neutral salt and a neutral acid corresponding to a glycerol side chain were observed as major product ions in MS2 experiments. Signal intensities at low collision energies correlated well with computed energies. However, an important difference between the lithiated and sodiated ions was the appearance of the sodium cation as a major fragmentation product. Computations on the product ions resulting from the loss of a neutral acid indicated multiple structures for the lithiated ions but mainly a single structure for the sodiated ions. The lithiated product ions could be fragmented further (pseudo-MS3) to give additional structural information, whereas the sodiated ions gave only m/z 23. The longer chain TAG, while giving a much less intense mass spectrum than the shorter chain TAG, gave comparable MS2 and MS3 product ion spectra. Taken together, the spectral and computational work described herein offer a new and detailed pathway for collision-induced fragmentation of lithiated and sodiated saturated TAGs.

Fragmentation pathways arising from protonation at different sites in aminoalkyl-substituted 3-hydroxy-1,2,5-oxadiazoles (3-hydroxyfurazans).

RATIONALE: The gas-phase fragmentation chemistry of multifunctional cations is highly influenced by the site of protonation. Possible relationships between protonation site and fragmentation processes were studied using 4-aminoalkyl-3-hydroxyfurazans. For these heterocyclic amines, the starting points for competing fragmentation pathways varied with protonation at multiple sites in two tautomers. METHODS: Mass spectra were acquired using electrospray ionization (positive mode) coupled to triple quadrupole and ion trap mass spectrometers; precursor-product ion relationships were studied by collision-induced dissociation. Quantum mechanical computations were performed at the MP2/6-311++G(2d,p)//ωB97X-D/6-311+G(d) level of theory. RESULTS: Prominent successive losses of NO and CO and competing losses of CH2 =NH or NH3 were observed as fragmentation processes. The lowest barrier computed for the initial step in a fragmentation pathway was associated with the [M + H]+ ion protonated at N5 in the heterocyclic ring, whereas an alternative ring cleavage leading to complementary product ions was initiated by protonation of the ring at N2. Side-chain protonation led to loss of NH3 without cleavage of the 3-hydroxyfurazan ring. CONCLUSIONS: The product ions obtained by the competing fragmentation processes varied with the site of protonation. Interestingly, the most abundant product ions observed at low collision energies were formed by cleavage of protonated molecules possessing more internal energy than other isomers.

Competing fragmentation processes of ß-substituted propanoate ions upon collision-induced dissociation.

RATIONALE: When subjected to collisional activation, gas-phase carboxylate ions typically undergo decarboxylation. However, alternative fragmentation processes dominate when the carboxylate group is located within certain structural motifs. In this work, the fragmentation processes of ß-substituted carboxylate ions are characterized to improve correlations between reactivity and structure. METHODS: Mass spectra were collected using both ion trap and triple quadrupole mass spectrometers operating in the negative ion mode; collision-induced dissociation (CID) of ions was used to study the relationship between product ions and the structures of their precursor ions. Quantum mechanical computations were performed on a full range of reaction geometries at the MP2/6-311++G(2d,p)//B3LYP/6-31++G(2d,p) level of theory. RESULTS: For a series of ß-substituted carboxylate ions, a product ion corresponding to the anion of the ß-substituent was obtained upon CID. Detailed computations indicated that decarboxylative elimination and at least one other fragmentation mechanism had feasible energetics for the formation of substituent anions differing in their gas-phase basicities. Predicted energetics for anti- and synperiplanar alignments in the transition structures for decarboxylative elimination correlated with the positions of crossover points in breakdown curves acquired for conformationally constrained ions. CONCLUSIONS: The feasibility of more than one mechanism was established for the fragmentation of ß-substituted propanoates. The contribution of each mechanistic pathway to the formation of the substituent anion was influenced by structural variations and conformational constraints, but mostly depended on the nature of the substituent. Copyright © 2016 John Wiley & Sons, Ltd.

Identification of polymorphism in ethylone hydrochloride: synthesis and characterization.

Ethylone, a synthetic cathinone with psychoactive properties, is a designer drug which has appeared on the recreational drug market in recent years. Since 2012, illicit shipments of ethylone hydrochloride have been intercepted with increasing frequency at the Canadian border. Analysis has revealed that ethylone hydrochloride exists as two distinct polymorphs. In addition, several minor impurities were detected in some seized exhibits. In this study, the two conformational polymorphs of ethylone hydrochloride have been synthesized and fully characterized by FTIR, FT-Raman, powder XRD, GC-MS, ESI-MS/MS and NMR ((13) C CPMAS, (1) H, (13) C). The two polymorphs can be distinguished by vibrational spectroscopy, solid-state nuclear magnetic resonance spectroscopy and X-ray diffraction. The FTIR data are applied to the identification of both polymorphs of ethylone hydrochloride (mixed with methylone hydrochloride) in a laboratory submission labelled as 'Ocean Snow Ultra'. The data presented in this study will assist forensic scientists in the differentiation of the two ethylone hydrochloride polymorphs. This report, alongside our recent article on the single crystal X-ray structure of a second polymorph of this synthetic cathinone, is the first to confirm polymorphism in ethylone hydrochloride. © 2015 Canada Border Services Agency. Drug Testing and Analysis published by John Wiley & Sons, Ltd. © 2015 Canada Border Services Agency. Drug Testing and Analysis published by John Wiley & Sons, Ltd.

Heterocyclic ring cleavage upon collision-induced dissociation of deprotonated 3-hydroxy-1,2,5-oxadiazoles (3-hydroxyfurazans).

A series of 4-substituted 3-hydroxyfurazans were subjected to electrospray ionization tandem mass spectrometry. At low collision energy, oxyisocyanate ([O=C=N-O](-), m/z 58) was formed as the predominant product ion from each deprotonated 3-hydroxyfurazan, indicating cleavage of the heterocyclic ring. The facile energetics of this characteristic fragmentation process was confirmed by density functional computations.

Phenyl group participation in rearrangements during collision-induced dissociation of deprotonated phenoxyacetic acid.

RATIONALE: The identification of trace constituents in biological and environmental samples is frequently based on the fragmentation patterns resulting from the collision-induced dissociation (CID) of gas-phase ions. Credible mechanistic characterization of fragmentation processes, including rearrangements, is required to make reliable assignments for structures of precursor and product ions. METHODS: Mass spectra were collected using both ion trap and triple quadrupole mass spectrometers operating in the negative ion mode. Precursor ion scans and CID of ions generated in-source were used to establish precursor-product ion relationships. Density functional theory (DFT) computations were performed at the MP2/6-311++G(2d,p)//B3LYP/6-31++G(2d,p) level of theory. RESULTS: Product ions at m/z 93 and 107 obtained upon CID of phenoxyacetate were attributed to phenoxide and o-methylphenoxide, respectively. An isotopic labeling experiment and computations showed that the phenoxide ion was formed by intramolecular displacement with formation of an α-lactone and also by a Smiles rearrangement. Rearrangement of phenoxyacetate via the ion-neutral complex formed in the α-lactone displacement pathway gave the isomeric o-hydroxyphenylacetate ion which yielded o-methylphenoxide upon decarboxylation. Computations provided feasible energetics for these pathways. CONCLUSIONS: Previously unrecognized and energetically favorable rearrangements during the collision-induced fragmentation of phenoxyacetate have been characterized using isotopic labeling and DFT computations. Notably, the phenyl substituent plays an indispensable role in each rearrangement process resulting in multiple pathways for the fragmentation of phenoxyacetate.

Inversion twinning in a second polymorph of the hydrochloride salt of the recreational drug ethylone.

A second polymorph of the hydrochloride salt of the recreational drug ethylone, C12H16NO3(+)·Cl(-), is reported [systematic name: (±)-2-ethylammonio-1-(3,4-methylenedioxyphenyl)propane-1-one chloride]. This polymorph, denoted form (A), appears in crystallizations performed above 308 K. The originally reported form (B) [Wood et al. (2015). Acta Cryst. C71, 32-38] crystallizes preferentially at room temperature. The conformations of the cations in the two forms differ by a 180° rotation about the C-C bond linking the side chain to the aromatic ring. Hydrogen bonding links the cations and anions in both forms into similar extended chains in which any one chain contains only a single enantiomer of the chiral cation, but the packing of the ions is different. In form (A), the aromatic rings of adjacent chains interleave, but pack equally well if neighbouring chains contain the same or opposite enantiomorph of the cation. The consequence of this is then near perfect inversion twinning in the structure. In form (B), neighbouring chains are always inverted, leading to a centrosymmetric space group. The question as to why the polymorphs crystallize at slightly different temperatures has been examined by density functional theory (DFT) and lattice energy calculations and a consideration of packing compactness. The free energy (ΔG) of the crystal lattice for polymorph (A) lies some 52 kJ mol(-1) above that of polymorph (B).

Studying the chemistry of cationized triacylglycerols using electrospray ionization mass spectrometry and density functional theory computations.

Analysis of triacylglycerols (TAGs), found as complex mixtures in living organisms, is typically accomplished using liquid chromatography, often coupled to mass spectrometry. TAGs, weak bases not protonated using electrospray ionization, are usually ionized by adduct formation with a cation, including those present in the solvent (e.g., Na(+)). There are relatively few reports on the binding of TAGs with cations or on the mechanisms by which cationized TAGs fragment. This work examines binding efficiencies, determined by mass spectrometry and computations, for the complexation of TAGs to a range of cations (Na(+), Li(+), K(+), Ag(+), NH4(+)). While most cations bind to oxygen, Ag(+) binding to unsaturation in the acid side chains is significant. The importance of dimer formation, [2TAG + M](+) was demonstrated using several different types of mass spectrometers. From breakdown curves, it became apparent that two or three acid side chains must be attached to glycerol for strong cationization. Possible mechanisms for fragmentation of lithiated TAGs were modeled by computations on tripropionylglycerol. Viable pathways were found for losses of neutral acids and lithium salts of acids from different positions on the glycerol moiety. Novel lactone structures were proposed for the loss of a neutral acid from one position of the glycerol moiety. These were studied further using triple-stage mass spectrometry (MS(3)). These lactones can account for all the major product ions in the MS(3) spectra in both this work and the literature, which should allow for new insights into the challenging analytical methods needed for naturally occurring TAGs.

Characterization of multiple fragmentation pathways initiated by collision-induced dissociation of multifunctional anions formed by deprotonation of 2-nitrobenzenesulfonylglycine.

The correlation of anion structure with the fragmentation behavior of deprotonated nitrobenzenesulfonylamino acids was investigated using tandem mass spectrometry, isotopic labeling and computational methods. Four distinct fragmentation pathways resulting from the collision-induced dissociation (CID) of deprotonated 2-nitrobenzenesulfonylglycine (NsGly) were characterized. The unusual loss of the aryl nitro substituent as HONO was the lowest energy process. Subsequent successive losses of CO, HCN and SO2 indicated that an ortho cyclization reaction had accompanied loss of HONO. Other pathways involving rearrangement of the ionized sulfonamide group, dual bond cleavage and intramolecular nucleophilic displacement were proposed to account for the formation of phenoxide, arylsulfinate and arylsulfonamide product ions at higher collision energies. The four distinct fragmentation pathways were consistent with precursor-product relationships established by CID experiments, isotopic labeling results and the formation of analogous product ions from 2,4-dinitrobenzenesulfonylglycine and the Ns derivatives of alanine and 2-aminoisobutyric acid. The computations confirmed a low barrier for ortho cyclization with loss of HONO and feasible energetics for each reaction step in the four pathways. Computations also indicated that three of the fragmentation pathways started from NsGly ionized at the carboxyl group. Overall, the pathways identified for the fragmentation of the NsGly anion differed from processes reported for anions containing a single functional group, demonstrating the importance of functional group interactions in the fragmentation pathways of multifunctional anions.

Rearrangements leading to fragmentations of hydrocinnamate and analogous nitrogen-containing anions upon collision-induced dissociation.

Tandem mass spectrometry (MS/MS) confirmed decarboxylation as the major collision-induced dissociation (CID) pathway of deprotonated hydrocinnamic acid (C6H5CH2CH2CO2H), N-phenylglycine (C6H5NHCH2CO2H) and 3-pyridin-2-ylpropanoic acid (C5H4NCH2CH2CO2H). The structure and stability of isomeric precursor and product anions were examined using density functional theory and ab initio methods. Geometry optimizations and frequency calculations were performed using the B3LYP/6-31++G(2d,p) level of theory and basis set with additional single point energies calculated at the MP2/6-311++G(2d,p) level. The formation of a delocalized product anion by carboxyl group-mediated migration of a benzylic proton to the ortho position of the ring and subsequent Cα-CO2(-) bond cleavage was energetically more favorable than direct decarboxylation and rearrangements of anions within ion-neutral complexes with carbon dioxide. The energy barrier for rearrangement of the delocalized product anion to the more stable benzylic anion was lowest in the fragmentation pathway of 3-pyridin-2-ylpropanoate. More energetically demanding fragmentation processes were indicated by the formation of other product anions at higher collision energy. Computations supported the feasibility of the formation of hydroxycarbonyl, styrene, and phenide ions from the benzylic anion of hydrocinnamate and the corresponding product anions from the nitrogen-containing analogues. The loss of dihydrogen from decarboxylated 3-pyridin-2-ylpropanoate was characterized computationally as hydride abstraction of an aryl proton. Overall, the results highlight the importance of exploring rearrangements in the fragmentation pathways of ions formed by electrospray ionization (ESI).

Correlations of ion structure with multiple fragmentation pathways arising from collision-induced dissociations of selected α-hydroxycarboxylic acid anions.

Under conditions of collision-induced dissociation (CID), anions of α-hydroxycarboxylic acids usually fragment to yield the distinctive hydroxycarbonyl anion (m/z 45) and/or the complementary product anion formed by neutral loss of formic acid (46 u). Further support for the known two-step mechanism, involving an ion-neutral complex for the formation of the hydroxycarbonyl anion from the carboxyl group, is herein provided by tandem mass spectrometric results and density functional theory computations on the glycolate, lactate and 3-phenyllactate ions. A fourth, structurally related α-hydroxycarboxylate ion, obtained by deprotonation of mandelic acid, showed only loss of carbon dioxide upon CID. Density functional theory computations on the mandelate ion indicated that similar energy inputs were required for a direct, phenyl-assisted decarboxylation and a postulated novel rearrangement to a carbonate ester, which yielded the benzyl oxide ion upon loss of CO2. Rearrangement of the glycolate ion led to expulsion of carbon monoxide, whereas the 3-phenyllactate ion showed the loss of water and formation of the benzyl anion and the benzyl radical as competing processes. The fragmentation pathways proposed for lactate and 3-phenyllactate are supported by isotopic labeling. The relative computed energies of saddle points and product ions for all proposed fragmentation pathways are consistent with the energies supplied during CID experiments and the observed relative intensities of product ions. The diverse reaction pathways characterized for this set of four α-hydroxycarboxylate ions demonstrate that it is crucial to understand the effects of structural variations when attempting to predict the gas-phase reactivity and CID spectra of carboxylate ions.

Fragmentation pathways of some benzothiophene radical cations formed by atmospheric pressure chemical ionisation.

Polycyclic aromatic sulfur-containing compounds (PASHs) are commonly found in fossil fuels and are of considerable importance in environmental studies. This work presents detailed studies on the fragmentation patterns of radical cations formed from four representative PASHs, benzo[b]thiophene, dibenzothiophene, 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene, using tandem atmospheric pressure chemical ionization mass spectrometry (APCI-MS/MS). Understanding these fragmentation patterns can be a useful aid in the analysis of PASHs employing APCI or electron ionization (EI-MS/MS), either alone or in conjunction with liquid or gas chromatography.

Quantitative aspects of and ionization mechanisms in positive-ion atmospheric pressure chemical ionization mass spectrometry.

The behavior in atmospheric pressure chemical ionization of selected model polycyclic aromatic compounds, pyrene, dibenzothiophene, carbazole, and fluorenone, was studied in the solvents acetonitrile, methanol, and toluene. Relative ionization efficiency and sensitivity were highest in toluene and lowest in methanol, a mixture of molecular ions and protonated molecules was observed in most instances, and interferences between analytes were detected at higher concentrations. Such interferences were assumed to be caused by a competition among analyte molecules for a limited number of reagent ions in the plasma. The presence of both molecular ions and protonated analyte molecules can be attributed to charge-transfer from solvent radical cations and proton transfer from protonated solvent molecules, respectively. The order of ionization efficiency could be explained by incorporating the effect of solvation in the ionization reactions. Thermodynamic data, both experimental and calculated theoretically, are presented to support the proposed ionization mechanisms. The analytical implications of the results are that using acetonitrile (compared with methanol) as solvent will provide better sensitivity with fewer interferences (at low concentrations), except for analytes having high gas-phase basicities.

The influence of structural features on facile McLafferty-type, even-electron rearrangements in tandem mass spectra of carboxylate anions.

In contrast to the well-described McLafferty rearrangement in odd-electron cations, relatively little has been reported on comparable rearrangements in even-electron ions, especially negative ions. This work reports a systematic study using tandem mass spectrometry (MS/MS) fragment ion spectra of carboxylate anions having a suitably acidic proton in the gamma position. The rearrangement process was studied in both ion trap and triple quadrupole mass spectrometers; characteristic enolate anions and stable neutral products were formed at low collision energies. The process has diagnostic and analytical potential in, for example, the analysis of peptides having C-terminal serine residues and of 3-hydroxy- or 3-aminocarboxylic acids in complex mixtures.

The importance of both charge exchange and proton transfer in the analysis of polycyclic aromatic compounds using atmospheric pressure chemical ionization mass spectrometry.

The response of atmospheric pressure chemical ionization (APCI) mass spectrometry to selected polycyclic aromatic compounds (PACs) was examined in a Micromass Quattro atmospheric pressure ion source as a function of both solvents and source gases. Typical PACs found in petroleum samples were represented by mixtures of naphthalene, fluorene, phenanthrene, pyrene, fluoranthene, chrysene, triphenylene, perylene, carbazole, dibenzothiophene, and 9-phenanthrol. A large range of different gases in the APCI source was studied, with emphasis on nitrogen, air, and carbon dioxide. Solvents used included water-acetonitrile, acetonitrile, dichloromethane, and hexanes. The signal responses were dependent on both the gases and solvents used, as was the ionization mechanism, as indicated by the degree of protonation with respect to the level of charge exchange. The combination of carbon dioxide in the nebulizer gas stream with nitrogen in the other streams gave a three- to fourfold better sensitivity than using nitrogen alone for both test mixtures and for complex samples.

Studies on the positive-ion mass spectra from atmospheric pressure chemical ionization of gases and solvents used in liquid chromatography and direct liquid injection.

Detailed studies have been made using different source gases and solvents in a Micromass Quattro mass spectrometer under positive ion atmospheric pressure chemical ionization conditions. The major background ions from nitrogen, air, or carbon dioxide were investigated by tandem mass spectrometry, followed by similar studies on solvents commonly employed in normal- and reversed-phase high-performance liquid chromatography, namely, water-acetonitrile, acetonitrile, and dichloromethane, with nitrogen, air, or carbon dioxide; hydrocarbon solvents were studied using nitrogen. Spectra were interpreted in terms of the gases, solvents, and their impurities. The acetonitrile spectra provided clear evidence for both charge exchange and proton transfer, the former being facilitated by the introduction of some air into a flow of nitrogen. Radical cations of acetonitrile dimers, trimers, and tetramers were observed, as were protonated dimer and trimer species. Examination of the analytical response of four polycyclic aromatic hydrocarbons in various hydrocarbon solvents, with nitrogen gas, showed that the sensitivity of detection for an analyte and its ionization mechanism are dependent on both the analyte structure and the solvent, with pyrene showing the highest sensitivity, phenanthrene and fluorene being intermediate, and naphthalene having the lowest sensitivity. The degree of protonation followed the same trend. Signal intensity and degree of protonation were dependent on the alkane solvent used, with isooctane providing the best overall sensitivity for the sum of protonated molecules and molecular ions. The ions observed in these studies appeared to be the most stable ions formed under equilibrium conditions in the source.