Lipidomics is an emerging field, where the structures, functions and dynamic changes of lipids in cells, tissues or body fluids are investigated. Due to the vital roles of lipids in human ...physiological and pathological processes, lipidomics is attracting more and more attentions. However, because of the diversity and complexity of lipids, lipid analysis is still full of challenges. The recent development of methods for lipid extraction and analysis and the combination with bioinformatics technology greatly push forward the study of lipidomics. Among them, mass spectrometry (MS) is the most important technology for lipid analysis. In this review, the methodology based on MS for lipid analysis was introduced. It is believed that along with the rapid development of MS and its further applications to lipid analysis, more functional lipids will be identified as biomarkers and therapeutic targets and for the study of the mechanisms of disease.
The endless molecular topology endows cyclic polymers with fascinating physical properties and applications. As a powerful strategy for the preparation of well-defined cyclic polymers, the current ...ring-closure methods have an inherent disadvantage of low production efficiency under the classic batch reaction conditions due to the requirement of ultralow reaction concentration for ring-closing linear polymer precursors. Assisted by the continuous-flow technique, we developed an efficient and practical way to ingeniously solve this essential problem and successfully produce cyclic polymers on a large scale by a light-induced ring-closure method for the first time. In addition, due to the large surface-to-volume ratio of the flow reactor, the continuous-flow technique provides the light-induced ring-closing reaction with more uniform light irradiation and transmission, resulting in a significantly increased reaction efficiency compared to that from the classic batch reaction conditions.
An efficient metal-free bimolecular homodifunctional ring-closure method was developed specifically for preparing well-defined cyclic polymers from unconjugated vinyl monomers. In this approach, ...well-defined homodifunctional linear polymers with azide terminals were prepared by using the reversible addition chain transfer polymerization/macromolecular design by interchange of xanthates (RAFT/MADIX) to polymerize unconjugated vinyl monomers in the presence of a diazide xanthate chain transfer agent. The self-accelerating double strain-promoted azide-alkyne cycloaddition (DSPAAC) reaction was then applied to ring-close the linear polymer precursors with sym-dibenzo-1,5-cyclooctadiene-3,7-diyne (DBA) as small linkers, leading to the formation of corresponding cyclic polymers. By virtue of the self-accelerating property of DSPAAC ring-closing reaction, this novel method smartly eliminated the requirement of equimolar amounts of the telechelic polymers and small linkers in the traditional bimolecular ring-closure methods for pure cyclic polymers. More importantly, the usage of excess DBA small linkers could significantly enhance the preparation efficiency of cyclic polymers. Moreover, the cyclic polymers resulted from this novel method could be conveniently cleaved back to linear polymers by a mild aminolysis of the S-C(S) bond within the cyclic polymer backbone.
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•Metal-free homodifunctional bimolecular ring-closure method for cyclic polymers from unconjugated vinyl monomers.•Self-accelerating ring-closing reaction requires no stoichiometry between linear polymers and small molecule linkers.•Aminolysis can cleave cyclic polymers back to their linear polymer counterparts.
Small organic matrixes are still the most commonly used ones in matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) because of their advantages of high sensitivity, convenience, ...and cost-effectiveness. However, due to the matrix interference in the low mass region, the direct analysis of low molecular weight amines in complex surroundings with conventional organic matrixes remains a challenge. Here, a new Brønsted–Lowry acid compound 2,3,4,5-tetrakis(3′,4′-dihydroxylphenyl)thiophene (DHPT) was designed, synthesized, and applied as a matrix for analysis of low molecular weight amines by MALDI-TOF MS. DHPT displays good selectivity in the analysis of amines without matrix-related interference and the low picomole/femtomole limit-of-detection was obtained in positive ion mode. With DHPT, the metabolites including creatinine, glycine, alloxan, allantoin, and 3-hydroxyhippuric acid in human urine were directly analyzed by MALDI-TOF MS. The identity of these metabolites was confirmed by tandem mass spectrometry. Furthermore, the urine creatinine was quantitatively determined using isotope-labeled internal standard. This DHPT-assisted LDI MS method provides a general approach for both qualitative and quantitative analysis of low molecular weight amines.
The biogenic elements concentrations in a coastal bay/estuary are strongly influenced not only by riverine input but also by submarine groundwater discharge (SGD) which has been identified as a ...typical process of land/ocean interactions in coastal zones. To assess the role of SGD in nutrient fluxes in the Southern Yellow Sea (SYS), 228Ra activities were measured in seawater collected in May 2014. Analyzing the sources and sinks of 228Ra, the flux of excess 228Ra through SGD was estimated to be (2.2 ± 1.0) ×1015 dpm yr−1. Based on the 228Ra mass balance model, we estimated the average SGD flux to be approximately (1.3 ± 0.87) ×1012 m3 yr−1 over the entire SYS, which is at least 3.3 times the estimated annual delivery from the Changjiang River into the SYS (∼1.3 × 1011 m3 yr−1). The SGD‐derived biogenic elements loads (dissolved inorganic nitrogen (DIN), phosphorus (DIP) and silicon (DSi)) were estimated as (487 ± 384) × 109 mol yr−1, (2.8 ± 2.2) × 109 mol yr−1, and (313 ± 259) × 109 mol yr−1, respectively, which are approximately 18 times, 7 times and 13 times the riverine input from both mainland China and Korea. The accumulation nutrient fluxes derived by SGD may play one of the most important roles in the green tide bloom that originated from the Subei Shoal zone in the SYS. Additionally, DIN and DIP via SGD can provide the necessary amounts of nutrient for recovering nutrient concentrations to normal levels after the green tide bloom is terminated.
Key Points
Large excess 228Ra was observed in the Southern Yellow Sea
SGD and its derived nutrient fluxes are dominant
SGD may contribute to massive green tide bloom in the Southern Yellow Sea
As the most straightforward synthetic strategy for cyclic polymers in theory, the traditional homodifunctional bimolecular ring-closure methods showed limited success for preparing pure cyclic ...polymers in practice even after several decades of development. A breakthrough was achieved in this paper to develop a successful homodifunctional bimolecular ring-closure method using a self-accelerating double strain-promoted azide–alkyne click reaction as the intermolecular and subsequent intramolecular coupling reactions. Because of the self-accelerating property of coupling reaction, this novel approach eliminated the usage of equimolar quantities between telechelic polymers and small molecule linkers, which was the prerequisite of traditional homodifunctional bimolecular ring-closure methods for pure cyclic polymers. More importantly, this approach could use an excess amount of small linkers to increase the intermolecular coupling reaction rate, further resulting in a significantly enhanced preparation efficiency of cyclic polymers.
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Co and N doped porous carbon (Co-NC) material, which is derived from a coordination compound, can simultaneously act as adsorbent of volatile compounds and as matrix of MALDI MS, to ...provide the capability of MALDI MS to analyze volatile compounds. Moreover, Co-NC is available for both positive and negative ionization modes without background interferences in the low-mass region (<500 Da) in MALDI MS, which tremendously extends the application of MALDI MS.
Traditional matrix does not allow matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) to analyze volatile compounds, because volatile analytes may vaporize during the sample preparation process or in the high vacuum circumstance of ion source. Herein, we reported a Co and N doped porous carbon material (Co-NC) which were synthesized by pyrolysis of a Schiff base coordination compound. Co-NC could simultaneously act as adsorbent of volatile compounds and as matrix of MALDI MS, to provide the capability of MALDI MS to analyze volatile compounds. As adsorbent, Co-NC could strongly adsorb and enrich the volatile compounds in perfume and herbs, and hold them even in the high vacuum circumstance. On the other hand, Co-NC could absorb the energy of the laser, and then transfer the energy to the analyte for desorption and ionization of analyte in both negative and positive ionization modes. Additionally, the background interferences were avoided in the low-mass region (< 500 Da) when using Co-NC as matrix, overcoming the challenges of MALDI MS analysis of small molecule compounds. In summary, Co-NC as matrix tremendously extended the application of MALDI MS.
A self-accelerating double-strain-promoted azide–alkyne cycloaddition reaction (DSPAAC) was employed for the formation of periodic polymers with ultrahigh molecular weights or a cyclic topology. ...DSPAAC-based stoichiometric imbalance-promoted step-growth polymerization was introduced to copolymerize sym -dibenzo-1,5-cyclooctadiene-3,7-diyne (DIBOD) and encoded bis-azide monomers (N 3 –R–N 3 ) from a multicomponent reaction. With excess molar amounts of DIBOD to N 3 –R–N 3 , this novel step-growth polymerization produced the periodic polymers with absolute molecular weights above 6 × 10 5 g mol −1 . This value is much higher than that (usually less than 5 × 10 4 g mol −1 ) of the periodic polymers obtained by traditional step-growth polymerization reported in the literature. With excess molar amounts of encoded N 3 –R–N 3 to DIBOD, periodic telechelic polymers with azide terminals and relatively low molecular weights were prepared. They were then efficiently ring-closed in a highly dilute solution in the presence of excess molar amounts of DIBOD to produce the corresponding periodic cyclic polymers with high purity.
This study proposes a new strategy for achieving rapid volumetric heating of moldable low-dielectric-loss glass over a wide temperature range using only microwave sources. As a proof of concept, both ...multi-physics modeling and experimental demonstration of microwave heating (MWH) of Pyrex 7740 glass are performed. The results reveal that there is an activation threshold of 400 °C for this glass, i.e., below this threshold the glass is mainly heated by SiC molds through interfacial heat transfer, while above it the glass can be directly heated by 2.45-GHz MWs through volumetric dielectric loss. As a result, the glass preform can attain an internal temperature of 727 °C (well above its transition point) within a short MWH process (130 s), at a low level of specific energy consumption (6.43 kW h/kg). The average volumetric heating rate of the glass is estimated as 5.44 °C/s, which outperforms the reported rates (2.00−3.60 °C/s) in previous precision glass molding (PGM) studies. Furthermore, the temperature difference in the entire glass can be minimized through MWH combined with post-annealing. With the demonstrated capabilities of instantaneous, volumetric, and selective heating, the proposed MWH strategy holds great promise in PGM and many other glass thermoforming sectors.
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A very uniform 2,5-dihydroxybenzoic acid (DHB) layer was for the first time constructed and used as a matrix for matrix-assisted laser desorption ionization Fourier transform ion cyclotron resonance ...mass spectrometry (MALDI-FTICR MS) for quickly exploring the changes in lipids within biological systems. Lipid extracts from biological samples were dissolved in chloroform and deposited onto the DHB layer. Benefiting from the insolubility of DHB in chloroform, the uniform matrix crystals were still maintained, and more importantly, the lipid analytes were distributed homogeneously on the layer, which significantly increased the reproducibility of analysis using MALDI-FTICR MS. Taking advantage of the benefit of high resolution of FTICR MS and the fragment ions obtained by MS/MS, lots of lipids were identified. This method was used for exploring the changes of lipids in drug-resistant tumor cells compared with paired drug-sensitive tumor cells. The principal component analysis (PCA) and partial least-squares discriminant analysis (PLS-DA) were employed for discovery of the changed lipids. This method, characterized by the simplicity and the speediness, demonstrated a new and promising approach for lipidomics study.
A very uniform 2,5-dihydroxybenzoic acid (DHB)-analyte co-crystal was skillfully constructed for lipidomics study by MALDI-FTICR MS.
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