Papers by Athula Attygalle
Journal of the American Society for Mass Spectrometry, Jul 17, 2023
Journal of Analytical Science and Technology, Nov 18, 2019
Background: Trimethylamine (TMA) is a marker used for monitoring the quality of seafood because i... more Background: Trimethylamine (TMA) is a marker used for monitoring the quality of seafood because it is the primary component of the "fishy" odor. Methods: The levels of TMA in seafood samples were directly measured by helium-plasma ionization mass spectrometry (HePI-MS). Each sample was directly exposed to the HePI source, and the intensity of the m/z 60 signal for protonated TMA was monitored by a selected-ion-recording (SIR) protocol. Using a set of TMA-spiked water standards, the TMA levels in seafood samples were quantified. Results: The signal intensity of the m/z 60 ion from shrimp samples maintained at room temperature for 2 days can be attenuated to baseline levels by adding lime juice. The amounts of TMA in samples of salmon and shrimp recovered from some sushi preparations, and in squid samples, were found to be 0.24 μg, 0.16 μg, and 17.2 μg per gram, respectively. Conclusions: HePI-MS is an efficient technique to screen and monitor the TMA content and assess the quality of seafood.
Journal of the American Society for Mass Spectrometry, Dec 6, 2021
The current IUPAC-recommended definition of the term "monoisotopic mass" of a chemical ... more The current IUPAC-recommended definition of the term "monoisotopic mass" of a chemical species is based on the most abundant isotopes of the constituent elements. It has even been proposed to constrain the definition to be based only on the atomic masses of the most abundant stable isotopes. Such an approach is flawed because in this way several elements and their compounds, in addition to isotopically enriched species, would not merit to be assigned a monoisotopic mass. Furthermore, for large molecules, such as proteins, the monoisotopic mass as currently defined loses its significance. Therefore, we propose to eliminate using the current definition altogether. Instead, the term isotopologue mass should be applied uniformly to every species denoted by a specific chemical formula.
Journal of Mass Spectrometry, May 22, 2017
In the past, Chrome Yellow (lead chromate, PbCrO 4), a bright orange-red substance, has been wide... more In the past, Chrome Yellow (lead chromate, PbCrO 4), a bright orange-red substance, has been widely used as an inorganic pigment in the production of paints, coatings, and plastics. Herein, we demonstrate that laser desorption/ionization mass spectrometry (LDI-MS) is a powerful tool for the detection of lead chromate in solid residues. In fact, lead chromate in trace amounts is easily detectable by LDI-MS even from residues left as latent prints. For example, a latent print obtained by stamping the exposed laterally cut surface of a pencil over 50 years old on an acetonitrile-moistened paper, was successfully imaged for both lead and chromate using a Synapt G2 HDMS mass spectrometer. After rastering the print with a 355 nm laser beam and recording positive-and negative-ion mass spectra over the range m/z 50-1200, we generated false-color "heat maps" (single-ion images) for 208 Pb +• (m/z 207.98) and for Cr 2 O 6-• (m/z 199.85). The heat maps matched closely with the faint visual image of the pencil imprint. Moreover, our results confirmed that lead chromate was used in the pigment coating of old pencils. Evidently, LDI-MS imaging is an efficient procedure to survey for the presence of lead and chromate in minerals and other materials.
Journal of the American Society for Mass Spectrometry, Sep 21, 2022
Journal of Mass Spectrometry, Aug 15, 2018
Results from ion-mobility (IM) separation experiments demonstrate that O- and N-protomers of p-(d... more Results from ion-mobility (IM) separation experiments demonstrate that O- and N-protomers of p-(dimethylamino)chalcone (p-DMAC) can coexist in the gas phase. The relative populations of the two protomers strongly depend on the ion-generating settings and the conditions the precursor ions experience from the point of their gas-phase inception to the time of their detection. Under relatively dry source conditions, the ratio of the gas-phase protomers generated under helium-plasma ionization (HePI) conditions is biased towards the thermodynamically favored O-protomer. However, when the humidity of the enclosed ion source was increased, the IM arrival-time distribution profile of the mass-selected protonated precursor of p-DMAC changed rapidly to one dominated by the N-protomer. Under spray-ionization conditions, the formation of the thermodynamically less favored protomer has been generally attributed to a phenomenon called kinetic trapping. Herein, we demonstrate that the population of thermodynamically less favored N-protomer can be dramatically increased simply by introducing water vapor to the HePI ion source.
Journal of Natural Products, Feb 1, 2021
Natural product congeners serve a useful role in the understanding of natural product biosynthesi... more Natural product congeners serve a useful role in the understanding of natural product biosynthesis and structure-activity relationships. A minor congener with superior activity, selectivity, and modifiable functional groups could serve as a more effective lead structure and replace even the original lead molecule that was used for medicinal chemistry modifications. Currently, no effective method exists to discover targeted congeners rapidly, specifically, and selectively from producing sources. Herein, a new method based on liquid-chromatography tandem-mass spectrometry combination is evaluated for targeted discovery of congeners of platensimycin and platencin from the extracts of Streptomyces platensis. By utilizing a precursor-ion searching protocol, tandem mass spectrometry not only confirmed the presence of known congeners but also provided unambiguous detection of many previously unknown congeners of platensimycin and platencin. This high-throughput and quantitative method can be rapidly and broadly applied for dereplication and congener discovery from a variety of producing sources, even when the targeted compounds are obscured by the presence of unrelated natural products.
Journal of Chromatography A, Mar 1, 2019
Pyrazines are an important group of natural products widely used as food additives and fragrants.... more Pyrazines are an important group of natural products widely used as food additives and fragrants. Gas chromatography-mass spectrometry (GC MS) is the most widely applied analytical technique for characterization of alkylpyrazines. However, mass spectra of many positional isomers of alkylpyrazines are very similar. Consequently, an unambiguous identification of each positional isomer by spectral interpretation or database search protocols is practically unfeasible. In fact, there are many misidentifications in literature. To identify alkylpyrazines, chemists often resort to gas chromatographic retention indices (RIs). Although there are many compilations of retention indices of alkylpyrazines, these databases are often incomplete and the values reported are sometimes inconsistent. Herein, we present retention indices of fifty-six alkylpyrazines recorded on DB-1, ZB-5MS, DB-624, and ZB-WAXplus stationary phases, and compare them with those available in the NIST-2017 MS-RI database. Furthermore, we demonstrate how RI values can be used, together with mass spectral interpretations, to identify certain alkylpyrazines unambiguously.
Halogenated anilines (haloanilines) are widely used as synthetic raw materials for the manufactur... more Halogenated anilines (haloanilines) are widely used as synthetic raw materials for the manufacture of azo dyes, agrochemicals, drugs, and other industrial chemicals. They are often discharged as industrial waste into environment or maybe formed during the metabolism of some aromatic drugs in mammals. Therefore, their unequivocal identification is vital for metabolic studies as well as for impurity assessments. For purity assessment of simple volatile molecules, gas chromatography in conjunction with electron-ionization mass spectrometry (GC/MS) is the preferred analytical procedure because of its high specificity and sensitivity. Unfortunately, electron-ionization mass spectra are not very helpful for characterizing ortho, meta, and para isomers of underivatized haloanilines since their mass spectra are virtually identical. This book describes simple derivatization procedures, which may be utilized for isomer differentiation of haloanilines. Tandem mass spectrometry and density functional theory calculations are used to study the gas-phase fragmentation pathways of haloanilines and their N-acyl derivatives.
Journal of Chemical Education, May 22, 2023
Analyst, 2022
One of the key barriers to the prostate cancer is monitor treatment response. Here we described a... more One of the key barriers to the prostate cancer is monitor treatment response. Here we described a conceptually new ‘MS-statistical analysis-metabolome’ strategy for discovery of metabolic features.
Acs Symposium Series, 2013
Journal of the American Society for Mass Spectrometry, Apr 10, 2017
The gas-phase-ion generation technique and specific ion-source settings of a mass spectrometer in... more The gas-phase-ion generation technique and specific ion-source settings of a mass spectrometer influence heavily the protonation processes of molecules and the abundance ratio of the generated protomers. Hitherto that has been attributed primarily to the nature of the solvent and the pH. By utilizing electrospray ionization and ion-mobility mass spectrometry (IM-MS), we demonstrate, even in the seemingly trivial case of protonated aniline, that the protomer ratio strongly depends on the source conditions. Under low in-source ion activation, nearly 100% of the N-protomer of aniline is produced, and it can be subsequently converted to the C-protomer by collisional activation effected by increasing the electrical potential difference between the entrance and exit orifices of the first vacuum region. This activation and transformation process takes place even before the ion is mass-selected and subjected to IM separation. Despite the apparent simplicity of the problem, the preferred protonation site of aniline in the gas phase-the amino group or the aromatic ring-has been a topic of controversy. Our results not only provide unambiguous evidence that ring-and nitrogen-protonated aniline can coexist and be interconverted in the gas phase, but also that the ratio of the protomers depends on the internal energy of the original ion. There are many dynamic ion-transformation and fragmentation processes that take place in the different physical compartments of a Synapt G2 HDMS instrument. Such processes can dramatically change the very identity even of small ions, and therefore should be taken into account when interpreting production mass spectra.
Journal of Chromatography & Separation Techniques, Aug 10, 2015
Journal of Chemical Ecology, 2021
Journal of Chromatography & Separation Techniques, 2016
F fatty acids (FFAs) including omega-3 and omega-6 polyunsaturated fatty acidswere major derived ... more F fatty acids (FFAs) including omega-3 and omega-6 polyunsaturated fatty acidswere major derived from arachidonic acid (AA) and eicosapentaenoic acid (EPA), which plays important roles in many physiological processes, especially inflammation. Assessment of eicosanoids is important for understanding their homeostatic and pathophysiological roles in inflammatory disease. A new analytical approach focus on polyunsaturated fatty acidsmetabolome was established using isotope dilution, solid phase extraction and 2D nano liquid chromatography-nanospray ionization-time of flight-mass spectrometry (2D nano LC-NSI-Q-TOF/MS). Within 35 min, 58 FFAs, including free fatty acids, prostaglandins, lipoxins, resolvins, leukotrienes, thromboxans, maresins, hydroxyeicosatetraenoic acids as well as epoxyeicosatrienoic acids were quantified along with seven corresponding isotope dilution internal standards. The limits of quantification were between 0.008 and 20 pg per injection for 1′L. The efficiency o...
The Science of Nature, 2020
Bombardier beetles are well-known for their remarkable defensive mechanism. Their defensive appar... more Bombardier beetles are well-known for their remarkable defensive mechanism. Their defensive apparatus consists of two compartments known as the reservoir and the reaction chamber. When challenged, muscles surrounding the reservoir contract sending chemical precursors into the reaction chamber where they mix with enzymes resulting in an explosive discharge of a hot noxious chemical spray containing two major quinones: 1,4-benzoquinone and 2-methyl-1,4-benzoquinone (toluquinone). Previously, it has been speculated that the biosynthesis of all benzoquinones originates from one core precursor, 1,4-hydroquinone. Careful ligation of the base of the reservoir chamber enabled us to prevent the explosive reaction and sample untransformed reservoir fluid, which showed that it accumulates significant quantities of 1,4-hydroquinone and 2-methyl-1,4-hydroquinone. We investigated the biosynthetic mechanisms leading to quinone formation by injecting or feeding Brachinus elongatulus beetles with stable-isotope-labeled precursors. Chemical analysis of defensive secretion samples obtained from 1,4-hydroquinone-d 6administered beetles demonstrated that it underwent conversion specifically to 1,4-benzoquinone. Analogously, results from mcresol-d 8 injected or fed beetles confirmed that m-cresol is metabolized to 2-methyl-1,4-hydroquinone, which is then oxidized to 2-methyl-1,4-benzoquinone in the hot spray. Our results refute the previous claim that 1,4-hydroquinone is the precursor of all substituted benzoquinones in bombardier beetles and reveal that they are biosynthetic products of two independent pathways. Most likely, the aforementioned biosynthetic channel of hydroxylation of appropriate phenolic precursors and subsequent oxidation is not restricted to bombardier beetles; it could well be a general pathway that leads to the formation of all congeners of benzoquinones, one of the most widely distributed groups of defensive compounds in arthropods.
Ferrocene and its derivatives and nickelocene undergo facile ionization when exposed directly to ... more Ferrocene and its derivatives and nickelocene undergo facile ionization when exposed directly to the ionizing plasma of a helium-plasma ionization (HePI) source. Mass spectra recorded from such samples under ambient positive-ion-generating conditions show intense peaks for the respective molecular ions [M+•] and protonated species [(M + H)+]. The protonation process occurs most efficiently when traces of water are present in the heated nitrogen used as the "heating gas." In fact, the relative population of the two categories of ions generated in this way can be manipulated by regulating the heating-gas flow. Moreover, rapid and highly efficient gas-phase hydrogen-deuterium exchange (HDX) reactions can be performed in the ion source by passing the heating gas through a vial with D2O before it reaches the HePI source. Moreover, the ionized species generated in this way can be subjected to in-source CID fragmentation in the QDa-HePI source very efficiently by varying the sampling-cone voltage. By this procedure, ions generated from ferrocene and nickelocene could be stripped so far as to ultimately generate the bare-metal cation. Other typical fragment-ions produced from protonated metallocenes included the M(cp)1+ ions (M = Fe or Ni), by elimination of a cyclopentadiene molecule, or the molecular cation, by loss of a H• radical. Moreover, H/D exchanges and subsequent tandem mass spectrometric analysis indicated that the central metal core participates in the initial protonation process of ferrocene under HePI conditions. However, in compounds such as ferrocene carboxaldehyde and ferrocene boronic acid, the protonation takes place at the peripheral functional group.
Journal of Chemical Ecology, 2020
Hydrocyanic acid (HCN) is a well-known defensive allomone in the chemical arsenal of millipedes i... more Hydrocyanic acid (HCN) is a well-known defensive allomone in the chemical arsenal of millipedes in the order Polydesmida. The presence of HCN in the headspace vapor of adult Xystocheir dissecta (Wood, 1867), a common millipede from the San Francisco Bay Area, was traced by laser desorption/ionization-mass spectrometry (LDI-MS). To accomplish this, the headspace vapor surrounding caged, live millipedes was allowed to diffuse passively over gold-nanoparticle (AuNP) deposits placed at various distances from the emitting source. The stainless steel plates with AuNP deposits were removed and irradiated by a 355nm laser. The gaseous ions generated in this way were detected by time-of-flight mass spectrometry. The intensity of the mass spectrometric peak detected at m/z 249 for the Au(CN) 2 − complex anion was compared to that of the residual Au − signal (m/z 197). Using this procedure, HCN vapors produced by the live millipedes could be detected up to 50 cm away from the source. Furthermore, the addition of H 2 O 2 , as an internal oxygen source for the gold cyanidation reaction that takes place in the AuNP deposits, significantly increased the detection sensitivity. Using the modified H 2 O 2 addition procedure, HCN could now be detected at 80 cm from the source. Moreover, we found a decreasing intensity ratio of the Au(CN) 2 − /Au − signals as the distance from the emitting source increased, following an exponential-decay distribution as predicted by Fick's law of diffusion. Keywords Millipedes. Allomones. Hydrogen cyanide (HCN). Gold nanoparticles (AuNP). Laser desorption/ionization (LDI). Hydrogen peroxide (H 2 O 2). Polydesmida Dedication: This work is respectfully dedicated to the memory of Professor Jerrold Meinwald.
Journal of Analytical Science and Technology, 2020
Aminoglycosides are broad-spectrum antibiotics often employed to combat Gram-negative bacterial i... more Aminoglycosides are broad-spectrum antibiotics often employed to combat Gram-negative bacterial infections. A technique based on electrospray-ionization mass spectrometry (ESI-MS) was developed for rapid determination of aminoglycosides. This method, which does not require prior chromatographic separation, or derivatization and extensive sample preparation steps, was deployed to estimate gentamicin, tobramycin, and amikacin in pharmaceutical formulations. Upon gas-phase collisional activation, protonated gentamicin, tobramycin, and amikacin undergo a facile loss of their respective “C” ring moiety to produce characteristic ions of m/z 322, 324, and 425, respectively. The mass spectral peak intensities for these specific product ions were monitored either by a flow-injection analysis selected-ion monitoring (FIA-SIM) time-intensity method or by a mass spectrometric internal-standard method. The linear dynamic ranges of detection for both methods were evaluated to be 10–1000 ng/mL for...
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Papers by Athula Attygalle