化学最新文献

One of the great triumphs of mass spectrometry-based peptide and protein characterization is the characterization of their modifications as most modifications have a characteristic mass shift. What happens when the modification does not change the mass of the peptide? Here, the characterization of several peptide and proteins modifications that do not involve a mass shift are highlighted. Protein and peptide synthesis on ribosomes involves L-amino acids; however, posttranslational modifications (PTMs) can convert these L-amino acids into their D-isomers. As another example, nonenzymatic PTM of aspartate leads to the formation of three different isomers, with isoaspartate being the most prevalent. Both modifications do not alter the mass of the peptide and yet can have profound impact on the physicochemical characteristics of the peptide. Several MS and ion mobility techniques are highlighted, as are other methods such as chromatography, enzymatic enrichment, and labeling. The challenges inherent to these analytical methods and prospective developments in bioinformatics and computational strategies are discussed for these zero-dalton PTMs.

Mass spectrometry (MS) is a powerful analytical technique that typically involves sample preparation and online analytical separation before MS detection. Traditional methods often face bottlenecks in sample preparation and analytical separation, despite the rapid detection capabilities of MS. This review explores the integration of electrokinetic manipulations directly with the ionization step to enhance MS performance, focusing on methods that eliminate or simplify sample preparation and separation processes. Techniques such as paper spray, electrophoresis in nanoelectrospray ionization (nESI) emitters, induced nESI, counterflow gradient electrofocusing, and in-syringe electrokinetics are highlighted for their ability to combine extraction and ionization in a single step, significantly improving throughput. The review delves into the use of electric fields during sample preparation and separations for these methods, demonstrating the efficiency of electrophoretic methods in driving extractions, crude separations, desalting, and enhanced sensitivity. The integration of these methods directly with MS ionization aims to enhance the analytical capabilities of mass spectrometry, while reducing costs and increasing throughput relative to traditional approaches.

Cancer is the leading cause of death worldwide characterized by patient heterogeneity and complex tumor microenvironment. While the genomics-based testing has transformed modern medicine, the challenge of diverse clinical outcomes highlights unmet needs for precision oncology. As functional molecules regulating cellular processes, proteins hold great promise as biomarkers and drug targets. Mass spectrometry (MS)-based clinical proteomics has illuminated the molecular features of cancers and facilitated discovery of biomarkers or therapeutic targets, paving the way for innovative strategies that enhance the precision of personalized treatment. In this article, we introduced the tools and current achievements of MS-based proteomics, choice of discovery and targeted MS from discovery to validation phases, profiling sensitivity from bulk samples to single-cell level and tissue to liquid biopsy specimens, current regulatory landscape of MS-based protein laboratory-developed tests (LDTs). The challenges, success and future perspectives in translating research MS assay into clinical applications are also discussed. With well-designed validation studies to demonstrate clinical benefits and meet the regulatory requirements for both analytical and clinical performance, the future of MS-based assays is promising with numerous opportunities to improve cancer diagnosis, treatment, and monitoring.

Mass spectrometry imaging (MSI) technologies are widely used today to study the in situ spatial distributions for a variety of analytes. As these technologies advance, the pursuit of higher resolution in MSI has intensified. The limitation of direct desorption/ionization is its insufficient ionization, posing a constraint on the advancement of high-resolution MSI technologies. The introduction of postionization process compensates the low ionization efficiency caused by sacrificing the desorption area while pursuing high spatial resolution, resolving the conflict between high spatial resolution and high sensitivity in direct desorption/ionization method. Here, we discuss the sampling and ionization steps of MSI separately, and review the postionization methods in MSI according to three different sampling modes: laser sampling, probe sampling, and ion beam sampling. Postionization technology excels in enhancing ionization efficiency, boosting sensitivity, mitigating discrimination effect, simplifying sample preparation, and expanding the scope of applicability. These advantages position postionization technology as a promising tool for biomedical sciences, materials sciences, forensic analysis and other fields.

Secondary electrospray ionization (SESI) and extractive electrospray ionization (EESI), as derivative technologies of electrospray ionization (ESI), have empowered the real-time analysis of trace compounds residing in gases and aerosols. Over the past three decades, SESI and EESI have demonstrated remarkable potential in a wide spectrum of applications, spanning disease diagnosis, drug detection, food safety, and environmental surveillance. Concurrently, the strides made in deciphering the ionization mechanisms of SESI and EESI have spurred the creation of diverse ion source configurations that are characterized by enhanced sensitivity and diminished background noise. This comprehensive review encapsulates the ionization mechanisms inherent in SESI and EESI processes, with particular emphasis on the impact of analyte characteristics (such as proton affinity, dipole moment, polarizability, and solubility) and ion source operational parameters (encompassing temperature, humidity, voltage, flow rate and electrospray composition) on ionization efficiency. Additionally, it delves into the progression of SESI and EESI sources, highlights recent breakthroughs, and probes into future trajectories, furnishing novel perspectives for the development of both technologies and the associated instruments.

Ionization and fragmentation are at the core of mass spectrometry. But they are not necessarily separated in space, as in-source fragmentation can also occur. Here, we survey the literature published since our 2005 review on the internal energy and fragmentation in electrospray ionization sources. We present new thermometer molecules to diagnose and quantify source heating, provide tables of recommended threshold (E₀) and appearance energies (E_app) for the survival yield method, and attempt to compare the softness of a variety of ambient pressure ionization sources. The droplet size distribution and desolvation dynamics play a major role: lower average internal energies are obtained when the ions remain protected by a solvation shell and spend less time nakedly exposed to activating conditions in the transfer interface. Methods based on small droplet formation without charging can thus be softer than electrospray. New dielectric barrier discharge sources can gas-phase ionize small molecules while conferring barely more internal energy than electrospray ionization. However, the tuning of the entire source interface often has an even greater influence on ion internal energies and fragmentation than on the ionization process itself. We hope that this review will facilitate further research to control and standardize in-source ion activation conditions, and to ensure the transferability of data and research results in mass spectrometry.

Monosaccharides play a central role in metabolic networks and in the biosynthesis of glycomolecules, which perform essential functions across all domains of life. Thus, identifying and quantifying these building blocks is crucial in both research and industry. Routine methods have been established to facilitate the analysis of common monosaccharides. However, despite the presence of common metabolites, most organisms utilize distinct sets of monosaccharides and derivatives. These molecules therefore display a large diversity, potentially numbering in the hundreds or thousands, with many still unknown. This complexity presents significant challenges in the study of glycomolecules, particularly in microbes, including pathogens and those with the potential to serve as novel model organisms. This review discusses mass spectrometric techniques for the isomer-sensitive analysis of monosaccharides, their derivatives, and activated forms. Although mass spectrometry allows for untargeted analysis and sensitive detection in complex matrices, the presence of stereoisomers and extensive modifications necessitates the integration of advanced chromatographic, electrophoretic, ion mobility, or ion spectroscopic methods. Furthermore, stable-isotope incorporation studies are critical in elucidating biosynthetic routes in novel organisms.