Dehydrogenation and dehalogenation of amines in MALDI-TOF MS investigated by isotopic labeling

Formation of multiple ion types during MALDI imaging mass spectrometry analysis of Mitragyna speciosa alkaloids in dosed rat brain tissue

Mitragyna speciosa, more commonly known as kratom, has emerged as an alternative to treat chronic pain and addiction. However, the alkaloid components of kratom, which are the major contributors to kratom's pharmaceutical properties, have not yet been fully investigated. In this study, matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry was used to map the biodistribution of three alkaloids (corynantheidine, mitragynine, and speciogynine) in rat brain tissues. The alkaloids produced three main ion types during MALDI analysis: [M + H]+, [M - H]+, and [M - 3H]+. Contrary to previous reports suggesting that the [M - H]+ and [M - 3H]+ ion types form during laser ablation, these ion types can also be produced during the MALDI matrix application process. Several strategies are proposed to accurately map the biodistribution of the alkaloids. Due to differences in the relative abundances of the ions in different biological regions of the tissue, differences in ionization efficiencies of the ions, and potential overlap of the [M - H]+ and [M - 3H]+ ion types with endogenous metabolites of the same empirical formula, a matrix that mainly produces the [M + H]+ ion type is optimal for accurate mapping of the alkaloids. Alternatively, the most abundant ion type can be mapped or the intensities of all ion types can be summed together to generate a composite image. The accuracy of each of these approaches is explored and validated.

Fiber Laser-Generated Silver-109 Nanoparticles for Laser Desorption/Ionization Mass Spectrometry of Illicit Drugs

Cannabinoids and opioids are the most prominently used drugs in the world, with fentanyl being the main cause of drug overdose-related deaths. Monitoring drug use in groups as well as in individuals is an important forensic concern. Analytical methods, such as mass spectrometry (MS), have been found most useful for the identification of drug abuse on a small and large scale. Pulsed fiber laser 2D galvoscanner laser-generated nanomaterial (PFL 2D GS LGN) was obtained from monoisotopic silver-109. Nanomaterial was used for laser desorption/ionization mass spectrometry of selected illicit drug standards with standard high-resolution reflectron-based time-of-flight MALDI apparatus. Δ9-THC, 11-OH-THC, 11-COOH-THC, fentanyl, codeine, 6-monoacetylmorphine (6-MAM), heroin, tramadol, and methadone were chosen as test compounds. Illicit drugs were tested in a concentration range from 100 μg/mL to 10 pg/mL, equating to 50 μg to 50 fg per measurement spot. For all analyzed compounds, identification and quantification by silver-109-assisted laser desorption/ionization (LDI) MS was possible, with uncommon [M + 109Ag3]+ and [M - H]+ ions present for certain structures. The results of the quantitative analysis of drugs using silver-109 PFL 2D GS LGN for LDI MS are presented. Laser-generated NPs are proven to be useful for the analysis of selected drugs, with exceptionally good results for fentanyl monitoring in a broad range of concentrations.

Nitro Indole Derivatives as Novel Dual-Polarity Matrices for MALDI Mass Spectrometry and Imaging with Broad Applications

A new matrix framework is presented in this study for the improved ionization efficiency of complex mixtures by matrix-assisted laser desorption ionization (MALDI) mass spectrometry/imaging. Five nitro indole (NI) derivatives [3-methyl-4-nitro-1H-indole (3,4-MNI), 3-methyl-6-nitro-1H-indole (3,6-MNI), 2,3-dimethyl-4-nitro-1H-indole (2,3,4-DMNI), 2,3-dimethyl-6-nitro-1H-indole (2,3,6-DMNI), and 4-nitro-1H-indole (4-NI)] were synthesized and shown to produce both positive and negative ions with a broad class of analytes as MALDI matrices. NI matrices were compared to several common matrices, such as 2,5-dihydroxybenzoic acid (DHB), alpha-cyano-4-hydroxylcinnamic acid (CHCA), sinapinic acid (SA), 1,5-diaminonaphthelene (1,5-DAN), and 9-aminoacridine (9-AA), for the analysis of lipid, peptide, protein, glycan, and perfluorooctanesulfonic acid (PFOS) compounds. 3,4-MNI demonstrated the best performance among the NI matrices. This matrix resulted in reduced ion suppression and better detection sensitivity for complex mixtures, for example, egg lipids/milk proteins/PFOS in tap water, while 2,3,6-DMNI was the best matrix for blueberry tissue imaging. Several important aspects of this work are reported: (1) dual-polarity ion production with NI matrices and complex mixtures; (2) quantitative analysis of PFOS with a LOQ of 0.5 ppb in tap water and 0.05 ppb in MQ water (without solid phase extraction enrichment), with accuracy and precision within 5%; (3) MALDI imaging with 2,3,6-DMNI as a matrix for plant metabolite/lipid identification with ionization enhancement in the negative ion mode m/z 600-900 region; and (4) development of a thin film deposition under/above tissue method for MALDI imaging with a vacuum sublimation matrix on a high-vacuum MALDI instrument.

Development of an efficient, one-pot, multicomponent protocol for synthesis of 8-hydroxy-4-phenyl-1,2-dihydroquinoline derivatives

A one-pot quick and efficient multicomponent reaction has been developed for the synthesis of a new series of functionalized 8-hydroxy-4-phenyl-1,2-dihydroquinoline derivatives using 30 mol% ammonium acetate in ethanol as solvent. This economical protocol run smoothly to give variety of quinoline derivatives in 55% to 98% yield from inexpensive reagents and catalyst in mild reaction conditions. Various spectroscopic techniques like FTIR, 1H NMR and 13C NMR, MALDI-TOF-MS, and EI-MS were used to study and confirm their structure.

7-Hydroxy-4-phenyl-1, 2-dihydroquinoline derivatives: synthesis via one-pot, three-component reaction and structure elucidation

We have developed a new and facile one pot three component protocol catalyzed by ammonium acetate for construction of new functionalized 7-hydroxy-4-phenyl-1,2-dihydroquinoline derivatives. A variety of quinoline derivatives were obtained in good to excellent yield from inexpensive reagents and catalyst in mild reaction conditions that provide atom economy and cost efficacy. Various spectroscopic techniques like FTIR, ¹HNMR and ¹³CNMR were employed to study their structure while mass of the synthesized compounds were confirmed through MALDI-TOF-MS and EI mass spectrometry.

Analysis of low molecular weight compounds using MALDI- and LDI-TOF-MS: Direct detection of active pharmaceutical ingredients in different formulations

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a high throughput, easy to use analytical technique. The simple sample preparation of this technique and its tolerance to the presence of contaminants are among its advantages. In contrast, depending on the matrix used, MALDI can ionize and generates ions in the low m/z range that complicate the interpretation of the spectra of low molecular weight compounds. To address this issue, one can envisage the use of tunable ionic matrices that can reduce the low m/z interferents. In this work, the ionic matrices triethylammonium α-cyano-4-hydroxycinnamate and diisopropylammonium α-cyano-4-hydroxycinnamate were used to directly analyze 14 pharmaceutical drugs in different formulations (coated tablets, noncoated tablets, capsules, and solutions). This methodology enabled the detection of their active compounds with minimum sample preparation, thus providing a straightforward approach for the forensic analysis of pharmaceutical drugs in the quest for detecting counterfeits. LDI-MS experiments were also performed, and the active ingredient in all of the medicines analyzed were detected. However, MALDI-MS spectra for the medicines analyzed herein showed less or no fragmentation than LDI-MS, which makes the analysis easier.

The formation of [M-H]+ ions in N-alkyl-substituted thieno[3,4-c]-pyrrole-4,6-dione derivatives during atmospheric pressure photoionization mass spectrometry

RATIONALE

The formation of ions during atmospheric pressure photoionization (APPI) mass spectrometry in the positive mode usually provides radical cations and/or protonated species. Intriguingly, during the analysis of some N-alkyl-substituted thieno[3,4-c]pyrrole-4,6-dione (TPD) derivatives synthesized in our laboratory, unusual [M-H](+) ion peaks were observed. In this work we investigate the formation of [M-H](+) ions observed under APPI conditions.

METHODS

Multiple experimental parameters, including the type of ionization source, the composition of the solvent, the type of dopant, the infusion flow rate, and the length of the alkyl side chain were investigated to determine their effects on the formation of [M-H](+) ions. In addition, a comparison study of the gas-phase tandem mass spectrometric (MS/MS) fragmentation of [M + H](+) vs [M-H](+) ions and computational approaches were used.

RESULTS

[M-H](+) ions were observed under APPI conditions. The type of dopant and the length of the alkyl chain affected the formation of these ions. MS/MS fragmentation of [M-H](+) and [M + H](+) ions exhibited completely different patterns. Theoretical calculations revealed that the loss of hydrogen molecules from the [M + H](+) ions is the most favourable condition under which to form [M-H](+) ions.

CONCLUSIONS

[M-H](+) ions were detected in all the TPD derivatives studied here under the special experimental conditions during APPI, using a halogenated benzene dopant, and TPD containing substituted N-alkyl side chains with a minimum of four carbon atoms. Density functional theory calculations showed that for [M-H](+) ions to be formed under these conditions, the loss of hydrogen molecules from the [M + H](+)  ions is proposed to be necessary.

The unexpected formation of [M - H]+ species during MALDI and dopant-free APPI MS analysis of novel antineoplastic curcumin analogues

Unusual ionization behavior was observed with novel antineoplastic curcumin analogues during the positive ion mode of matrix-assisted laser desorption ionization (MALDI) and dopant-free atmospheric pressure photoionization (APPI). The tested compounds produced an unusual significant peak designated as [M - H](+) ion along with the expected [M + H](+) species. In contrast, electrospray ionization, atmospheric pressure chemical ionization and the dopant-mediated APPI (dopant-APPI) showed only the expected [M + H](+) peak. The [M - H](+) ion was detected with all evaluated curcumin analogues including phosphoramidates, secondary amines, amides and mixed amines/amides. Our experiments revealed that photon energy triggers the ionization of the curcumin analogues even in the absence of any ionization enhancer such as matrix, solvent or dopant. The possible mechanisms for the formation of both [M - H](+) and [M + H](+) ions are discussed in this paper. In particular, three proposed mechanisms for the formation of [M - H](+) were evaluated. The first mechanism involves the loss of H2 from the protonated [M + H](+) species. The other two mechanisms include hydrogen transfer from the analyte radical cation or hydride abstraction from the neutral analyte molecule.