Journal of the American Society for Mass Spectrometry最新文献

Mass spectrometry (MS) has become an essential tool in virtually all academic, pharmaceutical, and biopharmaceutical analytical laboratories. The specialized and bespoke area of MS research and application of high m/z ion (>m/z 6000 and high mass, >150 kDa) formation, transmission, analysis, and detection is a relatively new area of focus for MS that has seen dramatic acceleration in interest over the last two decades. Herein we delve into this exciting aspect of MS, discussing how MS instrumentation has been refined and evolved for native-MS analysis. We cover the early groundbreaking experiments showing high m/z ion formation, transmission, and preservation of protein structure in the gas phase. Additionally, we discuss specific instrument optimizations and modifications that have advanced high m/z ion generation, transmission, analysis, and detection, contributing to the research area known as gas-phase structural biology. Native-MS sample introduction methods, emerging technologies, and future perspectives are also examined. Finally, we share personal opinions, observations, and experiences that are new to the community or previously unpublished.

Ion mobility mass spectrometry (IM-MS) can assist in the identification of isobaric chemical analytes by exploiting the difference in their gas phase collision cross-section (CCS) property. In glycomics, reliable glycan characterization remains challenging, even with IM-MS, because of closely related isomeric species and the available binding arrangements of substituted monosaccharides, allowing for the formation of complex structures. Here, we present a computational procedure to obtain gas-phase structural information from the experimental IM-MS CCS data of carbohydrates. The workflow proceeds with high throughput charge modeling of glycan seed structures to determine the precise protonation or deprotonation site. The charge models were then screened by using density functional theory (DFT) to produce candidate charge states for conformation generation. An extensive conformational scoring of the glycan ions was performed quantum mechanically at the DFT D3-B3LYP/6-31G+(d,p) level for the negative mode, [M - H]^-, and at the D3-B3LYP/6-31G(d,p) level for the positive mode, [M + H]⁺. For most of our test set, the computed CCS values from the final geometry optimized structures showed good agreement with experiment. We also demonstrated the capability of characterizing configurational and constitutional isomeric species. Altogether, we believe that the method we used in this work can be used to build a reliable theoretical reference database for glycans that can be used for experimental quality control and for assigning molecular structure to experimental IM-MS CCS information.

Illicit fentanyl and fentanyl analogs are a growing concern in the United States as opioid related deaths rise. Given that fentanyl analogs are readily obtained by modifying the structure of fentanyl, illicit fentanyl analogs appearing on the black market often contain similar structures, making analogue differentiation and identification difficult. Thus, obtaining both precursor and product ion data during analysis is becoming increasingly valuable in fentanyl analog characterization. In this paper, we provide GC column retention time, precursor, and product ion mass spectrum data for 74 fentanyl analogs that were analyzed using atmospheric pressure chemical ionization-gas chromatography-mass spectrometry (APCI-GC-MS) utilizing a triple quadrupole mass analyzer. During analysis, precursor ions underwent collision induced dissociation (CID) by increasing the collision energy (10, 20, 30, 40, and 50 V) throughout a single run. Data reveal that APCI readily produces product ions of the piperidine and N-alkyl chain but rarely provides data on the acyl group. Furthermore, fentanyl analogs with greater substitution at the N-alkyl chain demonstrate a greater preference for dissociation at the N-αC and αC-βC bond, while greater substitution at the amide group leads to fragmentation at the N-C4 bond.

In this study, the formation and emission of alkali halide cluster ions in charged droplets generated by electrospray ionization (ESI) was investigated using mass spectrometry (MS). We focus on ion emission at the air-solution interface of charged droplets, distinguishing between two mechanisms: the ion evaporation model (IEM), where ions are released directly from the interface, and the charge residue model (CRM), where ions are generated after complete solvent evaporation. Using an iodide/chloride mixture, we analyzed how interfacial affinity influences the composition of the generated alkali halide cluster cations and anions. With the knowledge that iodides have much higher interfacial affinities than chlorides, a relative faction of iodide in the cluster ion enables us to distinguish between IEM and CRM. Small cluster anions and cations exclusively containing iodides are suggested to be from IEM, while the larger cluster ions containing more chlorides are expected to be from CRM. This work clarifies the distinctions between IEM and CRM in alkali halide cluster ion formation and also establishes a robust analytical approach for assessing interfacial affinities of ions using ESI-MS, which may potentially enhance our understanding of interfacial chemistry and its implications in atmospheric and analytical sciences.

The benefits of native mass spectrometry have led to the extensive study of proteins inside mass spectrometers in the gas phase. The expansion of native mass spectrometry requires novel tools for gaining greater insights into protein structures. Herein, we introduce a new approach utilizing gas phase ion/ion reactions, where cross-linking reagents link unprotonated lysine residues, arginine residues, and N-termini with their protonated forms. We used three lengths of linkers, determining that different length cross-linkers resulted in different residues being cross-linked, as we have previously observed for electrostatic-to-electrostatic cross-linkers. However, this new method allows for the probing of both protonated and neutral lysine and arginine residues. Native mass spectrometry often produces fewer charges than protonatable sites, allowing access to a greater number of sites on proteins using an electrostatic-to-covalent cross-linking approach. In this report, we describe the reaction phenomenology and trends at reaction sites. We envision electrostatic-to-covalent cross-linking as a useful structural tool to provide complementary information to other native MS-based measurements such as collision cross section.

The end groups of three- and four-arm star-shaped polylactides (PLA) with trimethylolpropane and pentaerythritol core structures were functionalized with acetic acid. Reaction products with different degrees of functionalization were analyzed by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Additional gradient elution liquid adsorption chromatography (GELAC) measurements were performed to determine the degree of functionalization. This technique enabled clear separation and sufficient quantification of the formed species. These chromatographic data could be used inversely to quantify mass spectrometric results, which are usually biased by the unknown ionization probabilities of different polymer end group structures. Our results showed that, in this particular case, the peak intensity in the MALDI-TOF mass spectra can be used to semiquantitatively determine the degree of functionalization in incompletely functionalized multiarm PLA.

Deamidation of asparagine and glutamine residues occurs spontaneously, is influenced by pH, temperature, and incubation time, and can be accelerated by adjacent amino acid residues. Incubation conditions used for proteolytic digestion in bottom-up proteomic studies can induce significant deamidation that affects results, either knowingly or unknowingly. This has prompted studies into modifications to common trypsin digestion protocols to minimize chemical deamidation, including shorter incubation times and specific lysis buffers. Prior work suggested ammonium acetate at pH 6 to minimize chemical deamidation, but this buffer has compatibility issues with trypsin digestion and common assays (e.g., bicinchoninic acid assays). Here, we re-evaluated former comparisons of Tris-HCl, ammonium bicarbonate, and triethylammonium bicarbonate buffers for the amount of artificial, chemically induced deamidation generated in a standard bottom-up proteomics workflow, and we added an evaluation of three commonly used and biologically compatible buffers, HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid), EPPS (3-[4-(2-Hydroxyethyl)piperazin-1-yl]propane-1-sulfonic acid), and PBS (phosphate buffered saline). Our findings show that HEPES exhibited the least amount of artificial deamidation and is a reasonable choice for general proteomic experiments, especially for studies considering N-glycosylation.

Atmospheric-pressure chemical ionization mass spectrometry (APCI-MS) is a widely used technique for the analysis of a diverse range of analytes. Under APCI conditions, a nonthermal plasma, rich in highly oxidative species such as H₂O₂, O₃, atomic O, and radicals such as HO^•, is created. These oxidants trigger unanticipated and often undesirable chemical reactions within the ion source. For example, when aniline was introduced into this environment, it initially underwent oxidative dimerization forming hydrazobenzene (m/z 185). However, with prolonged exposure, there was a marked increase in total ion abundance and the generation of additional artifact ions such as protonated azobenzene (m/z 183) and protonated azoxybenzene (m/z 199). The emergence of these artifacts was found to be highly dependent on the corona-current magnitude. Moreover, the desorption-gas temperature significantly influenced the rate of artifact generation. Recognizing and acknowledging the formation and presence of such artifacts in an ion source is paramount in conducting validated chemical analysis. The existence of artifacts can complicate mass spectral interpretation, potentially leading to erroneous conclusions and misinterpretations of both qualitative and quantitative data. Thus, understanding the intricacies of nonthermal plasma-driven artifact formation is critical for accurate analytical outcomes.

It is demonstrated here that a recently published LabView-based time-of-flight mass spectrometer (TOFMS) simulation program (named TOFSim) can accurately simulate data collected on a commercial Bruker Autoflex III matrix-assisted laser desorption/ionization (MALDI) TOFMS instrument operating in linear mode. Once the instrument distances are determined by matching measured and simulated flight times, it is shown that both overall flight times and peak widths are reproduced for data collected under both focused and slightly defocused conditions. This work confirms that TOFSim can be used not just for training new instrument operators in the principles of TOFMS but, as demonstrated here, to show how changing the voltage applied to grid G1 in the source or the delayed extraction delay time affects the focusing properties of the instrument. In the future we expect that this will also allow users to perform "what-if" experiments to investigate scenarios which may be difficult or impossible to do in a real instrument.