化学最新文献

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.

Lignin is an attractive feedstock for a wide variety of applications ranging from aromatic chemicals and transportation fuels to resins and coatings. Emerging biorefinery concepts, like the organosolv process, enable the separation of all the lignocellulose components, and moreover, produce lignins of high quality and purity susceptible to valorisation by depolymerisation. In this work, we focus on the depolymerisation of lignins obtained by γ-valerolactone (GVL) organosolv fractionation of four biomass feedstocks, eucalyptus, white birch, sugarcane bagasse and Scots pine. We demonstrate that lignins extracted with the GVL process are depolymerised using unsupported molybdenum-based catalysts under reductive conditions in supercritical ethanol. As a result, over 90% yields of low-molecular-weight lignin oils are obtained with minimal char formation, yields of the aromatic monomers being 7-16 wt%. Furthermore, the design of experiments method is used to analyse the effect of depolymerisation conditions, catalyst, hydrogen loading and temperature, on the yields and properties of the product fractions. Notably, we show that the properties of the lignin oils and monoaromatics can be tuned towards the targeted application by modifying the depolymerisation conditions.

In zero-gap saltwater electrolysis, ion transport is influenced by convective forces, but their effects have not been examined when using thin-film composite (TFC) membranes with advective flow through the membrane. In this study, we adapted a one-dimensional solution-friction transport model for a zero-gap electrolyzer to incorporate measured water flux across a TFC membrane. Open-circuit or electrolysis (20 mA cm^-2) experiments quantified ion transport with and without electrochemical reactions. Water velocity, estimated from volume changes in the anolyte and the catholyte, was used to infer convective contributions to ion transport. Ion-specific friction coefficients were determined using open-circuit data. Using the fitted friction factors and incorporating water flux, the modeled ion crossover concentration showed good agreement with electrolysis data, including changes caused by reversing the membrane orientation. Removing the convective flux from the model showed up to a 740% change in predicted ion crossover and worsened agreement with experimental data. The strong correlation between the fraction of charge carried by major salt ions and the measured water flux suggests that electroosmotic drag could be one of the main mechanisms responsible for the observed water flux. These results highlight the importance of incorporating solution convection when modeling ion behavior in zero-gap systems using TFC membranes.

Lignin (L)-stabilized emulsions have gained interest as sustainable systems. Despite their advantages, the interaction of lignin derivatives with oil and water in emulsion systems remains unclear. In this work, we verified a hypothesis that different modification strategies would generate lignin derivatives with different emulsifying performances, even if lignin is anionically charged to a similar degree. To verify this hypothesis, we generated sulfoethylated lignin (SL) and carboxyethylated lignin (CL) softwood kraft lignin (L) as functional emulsifiers for soybean water emulsion systems. It was observed that lignin derivatives with a more negative zeta potential (ζ-potential) and smaller oil particles resulted in more stable emulsions at alkaline pH due to enhanced electrostatic repulsion. Due to well-dispersed oil droplets and a strong electrostatic system, the viscosity of emulsions was lower at alkaline conditions. It was also noted that SL and CL generated Pickering emulsions via depositing on oil droplets and developing steric hindrance with oil droplet sizes of 436 and 452 nm at acidic pH. However, such systems had shorter lifespans under acidic environments, indirectly implying that steric hindrance was insufficient to generate emulsions with long-term stability. These findings verified the involvement of different mechanisms for stabilizing oil emulsions at various pH levels.

This work focuses on improving the sustainability of electrolytes for sodium-ion capacitors (SICs). Through the combination of a low-fluorinated salt, namely sodium difluoro(oxalato)borate (NaDFOB), and the bio-based solvent γ-Valerolactone (GVL), a new electrolyte formulation (1 mol L^-1 NaDFOB in GVL) is being studied for application in SICs. Remarkably, the performance of the SIC full-cells is very comparable to the most commonly used formulation of sodium hexafluorophosphate in ethylene carbonate:propylene carbonate (1 mol L^-1 NaPF₆ in EC:PC). Furthermore, presodiation strategies were compared for the novel electrolyte system. The in situ oxidation of a sacrificial salt (sodium squarate, Na₂C₄O₄) incorporated into the positive electrode yielded comparable results to the ex situ electrochemical approach. X-ray photoelectron spectroscopy studies revealed that depending on the presodiation strategy, the solid-electrolyte-interphase composition varies significantly.

The spectroscopic and photophysical properties of novel 10-hydroxybenzo[h]quinoline (HBq) derivatives with various para-substituted phenyl groups at the 7- and 9-positions (1R; R = –NMe₂, –OMe, –Me, –H, –F, –Cl, –CF₃, –CN, and –NO₂) were evaluated by the electron-donating and electron-withdrawing ability of the substituent R in terms of the Hammett substituent constant. The electronic nature of the substituents controlled the excited-state properties. In particular, 1NO₂ exhibited a larger nonfluorescence rate constant than that predicted from the energy gap dependence, and the fluorescence from 1NO₂ was solvent-dependent, distinct from that of the other derivatives. The TD-DFT calculations revealed that the excited-state derivatives except for 1NO₂ adopted the keto-form structures generated by ESIPT, whereas 1NO₂ exhibited non-ESIPT excited-state geometry. The difference originates from the variation in the charge-transfer characters: in the former, charge transfer occurs within the HBq moiety, whereas in the latter, charge transfer proceeds from the HBq moiety to the 4-nitrophenyl groups. The systematic tuning of the electronic transition demonstrated control of the excited-state geometry of HBq derivatives and provided important insights into proton transfer in the excited state. The introduction of 4-substituted phenyl groups also controlled the basicity of the derivatives in the ground states and, notably, 1NMe₂ exhibited pronounced fluorescence color variations, ranging from the near-infrared to the blue region, as a function of the concentration of trifluoroacetic acid.