Visible-Light Activated [2+2] Photocycloaddition Reaction Enabled Identification of Carbon-Carbon Double Bonds Position Isomerism in Structural Lipidomics

The photocycloaddition of olefins with carbonyls is of fundamental interest and practical importance in C=C bond location in unsaturated lipids. However, the traditional UV light activated [2+2] photocycloaddition reaction suffers side reactions and potential health damage. Here, we reported the first example of visible-light activated [2+2] photocycloaddition of anthraquinone with unsaturated lipids. This reaction showed great capability for locating the C=C bonds in various kinds of monounsaturated and polyunsaturated lipids by combining with tandem mass spectrometry (MS), such as fatty acids, phospholipids and glycerides. Based on this developed reaction, a workflow with liquid chromatography tandem MS method was developed for the global identification of unsaturated lipids in human serum, and 86 of monounsaturated and complicated polyunsaturated lipids were identified with definitive positions of C=C bonds. This approach provides new insights both on the photocycloaddition reactions and the structural lipidomics.

Visible-Light Activated [2+2] Cycloaddition Reaction Enables Pinpointing Carbon-Carbon Double Bonds in Lipids

The precise location of C=C bonds in bioactive molecules is critical for deep understanding the relationship between their structures and biological roles. However, the traditional ultraviolet light-based approaches exhibited great limitations. Here, we discovered a new type of visible-light activated [2+2] cycloaddition of carbonyl with C=C bonds. We found that carbonyl in anthraquinone showed great reactivities towards C=C bonds in lipids to form the oxetanes under the irradiation of visible-light. Combining with tandem mass spectrometry, this site-specific dissociation of oxetane enabled precisely locating the C=C bonds in various kinds of monounsaturated and polyunsaturated lipids. The proof-of-concept applicability of this new type of [2+2] photocycloaddition was validated in the global identification of unsaturated lipids in complicated human serum sample. 86 of monounsaturated and polyunsaturated lipids were identified with definitive positions of C=C bonds, includes phospholipids and fatty acids even with up to 6 C=C bonds. This study provides new insights both on the photocycloaddition reactions and the structural lipidomics.

Lipidomic characterization of extracellular vesicles in human serum

There is a wide variety of extracellular vesicles (EVs) that differ in size and cargo composition. EVs isolated from human plasma or serum carry lipid, protein, and RNA cargo that provides insights to the regulation of normal physiological processes, and to pathological states. Specific populations of EVs have been proposed to contain protein and RNA cargo that are biomarkers for neurologic and systemic diseases. Although there is a considerable amount of evidence that circulating lipids are biomarkers for multiple disease states, it not clear if these lipid biomarkers are enriched in EVs, or if specific populations of EVs are enriched for particular classes of lipid. A highly reproducible workflow for the analysis of lipid content in EVs isolated from human plasma or serum would facilitate this area of research. Here we optimized an MS/MSALL workflow for the untargeted analysis of the lipid content in EVs isolated from human serum. A simple sequential ultracentrifugation protocol isolated three distinct types of serum EVs that were identified based on size, targeted protein, and untargeted lipidomic analyses. EVs in the upper and middle fractions were approximately 140 nm in diameter, while EVs in the pellet were approximately 110 nm in diameter. EVs in the upper most buoyant fractions contained the highest concentration of lipids, were enriched with phospholipids, and immunopositive for the cytoskeletal markers actin, α-actinin, and the mitochondrial protein mitofillin, but negative for the typical EV markers CD63, TSG101, and flotillin. A central fraction of EVs was devoid of cytoskeletal and mitochondrial markers, and positive for CD63, and TSG101, but negative for flotillin. The EV pellet contained no cytoskeletal or mitochondrial markers, but was positive for CD63, TSG101, and flotillin. The EV pellet contained the lowest concentration of most lipids, but was enriched with ceramide. These results provided new insights into the lipid composition of EVs isolated from serum using a simple ultracentrifugation isolation method suitable for lipidomic analysis by mass spectrometry.

Impaired insulin sensitivity is associated with worsening cognition in HIV-infected patients

Objective: To determine the association of insulin sensitivity and metabolic status with declining cognition in HIV-infected individuals. Methods: We conducted targeted clinical and metabolic measures in longitudinal plasma samples obtained from HIV-infected patients enrolled in the Central Nervous System HIV Anti-Retroviral Therapy Effects Research Study (CHARTER). Findings were validated with plasma samples from the Multicenter AIDS Cohort Study (MACS). Patients were grouped according to longitudinally and serially assessed cognitive performance as having stably normal or declining cognition. Results: Patients with declining cognition exhibited baseline hyperinsulinemia and elevated plasma c-peptide levels with normal c-peptide/insulin ratios, suggesting that insulin production was increased, but insulin clearance was normal. The association of hyperinsulinemia with worsening cognition was further supported by low high-density lipoprotein (HDL), high low-density lipoprotein/HDL ratio, and elevated cholesterol/HDL ratio compared to patients with stably normal cognition. Conclusions: These findings suggest that hyperinsulinemia and impaired insulin sensitivity are associated with cognitive decline in antiretroviral therapy–treated HIV-infected patients.

Mass spectrometry imaging of the in situ drug release from nanocarriers

It is crucial but of a great challenge to study in vivo and in situ drug release of nanocarriers when developing a nanomaterial-based drug delivery platform. We developed a new label-free laser desorption/ionization mass spectrometry (MS) imaging strategy that enabled visualization and quantification of the in situ drug release in tissues by monitoring intrinsic MS signal intensity ratio of loaded drug over the nanocarriers. The proof of concept was demonstrated by investigating the doxorubicin (DOX)/polyethylene glycol–MoS2 nanosheets drug delivery system in tumor mouse models. The results revealed a tissue-dependent release behavior of DOX during circulation with the highest dissociation in tumor and lowest dissociation in liver tissues. The drug-loaded MoS2 nanocarriers are predominantly distributed in lung, spleen, and liver tissues, whereas the accumulation in the tumor was unexpectedly lower than in normal tissues. This new strategy could also be extended to other drug-carrier systems, such as carbon nanotubes and black phosphorus nanosheets, and opened a new path to evaluate the drug release of nanocarriers in the suborgan level.

An integrated mass spectrometry platform enables picomole-scale real-time electrosynthetic reaction screening and discovery

The identification of new electrosynthetic pathways enables environmentally friendly synthetic applications. However, the development of miniaturized screening procedures/platforms to expedite the discovery of electrooxidation reactions remains challenging. Herein, we developed an integrated system that serves as a reactor and ion source in a single experimental step using only picomole-scale reactants to monitor electrooxidation in real-time. This reaction screening platform utilizes the intrinsic electrochemical capabilities of nano-electrospray ionization mass spectrometry. We validated the feasibility of this method by reproducing three known electrochemical reactions. We also discovered two new electroorganic reaction pathways: (i) C–N dehydrodimerization of 8-methyl-1,2,3,4-tetrahydroquinoline to construct a novel quinoline skeleton, and (ii) TEMPO-mediated accelerated electrooxidative dehydrogenation of tetrahydroisoquinolines. Moreover, the radical cations and key intermediates captured by this screening platform provided direct evidence for the mechanism of these novel electrochemical reactions.

Characterization of organic aerosol in Beijing by laser desorption ionization coupled with Fourier Transform Ion Cyclotron Resonance Mass spectrometry

Review of matrix-assisted laser desorption/ionization mass spectrometry in analysis and imaging of small molecules

Picomole‐Scale Real‐Time Photoreaction Screening: Discovery of the Visible‐Light‐Promoted Dehydrogenation of Tetrahydroquinolines under Ambient Conditions

Mass Spectrometry for Paper-Based Immunoassays: Toward On-Demand Diagnosis

Current analytical methods, either point-of-care or centralized detection, are not able to meet recent demands of patient-friendly testing and increased reliability of results. Here, we describe a two-point separation on-demand diagnostic strategy based on a paper-based mass spectrometry immunoassay platform that adopts stable and cleavable ionic probes as mass reporter; these probes make possible sensitive, interruptible, storable, and restorable on-demand detection. In addition, a new touch paper spray method was developed for on-chip, sensitive, and cost-effective analyte detection. This concept is successfully demonstrated via (i) the detection of Plasmodium falciparum histidine-rich protein 2 antigen and (ii) multiplexed and simultaneous detection of cancer antigen 125 and carcinoembryonic antigen.

Fluorographene nanosheets: a new carbon-based matrix for the detection of small molecules by MALDI-TOF MS

Fluorographene nanosheets (FG) was synthesized and applied as matrix for analysis of small molecules with clear background, good compatibility and homogeneity.

Electrospray soft-landing for the construction of non-covalent molecular nanostructures using charged droplets under ambient conditions

An ambient electrospray soft-landing apparatus was designed to create surface-confined networks on highly oriented pyrolytic graphite through ion/surface interactions.

Rapidly Probing Antibacterial Activity of Graphene Oxide by Mass Spectrometry-based Metabolite Fingerprinting

Picomole-Scale Real-Time Photoreaction Screening: Discovery of the Visible-Light-Promoted Dehydrogenation of Tetrahydroquinolines under Ambient Conditions

The identification of new photocatalytic pathways expands our knowledge of chemical reactivity and enables new environmentally friendly synthetic applications. However, the development of miniaturized screening procedures/platforms to expedite the discovery of photochemical reactions remains challenging. Herein, we describe a picomole‐scale, real‐time photoreaction screening platform in which a handheld laser source is coupled with nano‐electrospray ionization mass spectrometry. By using this method, we discovered an accelerated dehydrogenation pathway for the conversion of tetrahydroquinolines into the corresponding quinolines. This transformation is readily promoted by an off‐the‐shelf [Ru(bpy)3]Cl2⋅6 H2O complex in air at ambient temperature in direct sunlight, or with the aid of an energy‐saving lamp. Moreover, radical cations and trans‐dihydride intermediates captured by the screening platform provided direct evidence for the mechanism of the photoredox reaction.

Mass spectrometry imaging reveals the sub-organ distribution of carbon nanomaterials

Label and label-free methods to image carbon-based nanomaterials exist. However, label-based approaches are limited by the risk of tag detachment over time, and label-free spectroscopic methods have slow imaging speeds, weak photoluminescence signals and strong backgrounds. Here, we present a label-free mass spectrometry imaging method to detect carbon nanotubes, graphene oxide and carbon nanodots in mice. The large molecular weights of nanoparticles are difficult to detect using conventional mass spectrometers, but our method overcomes this problem by using the intrinsic carbon cluster fingerprint signal of the nanomaterials. We mapped and quantified the sub-organ distribution of the nanomaterials in mice. Our results showed that most carbon nanotubes and nanodots were found in the outer parenchyma of the kidney, and all three materials were seen in the red pulp of the spleen. The highest concentrations of nanotubes in the spleen were found within the marginal zone.

A Theoretical Method for Characterizing Nonlinear Effects in Paul Traps with Added Octopole Field

Plasma-based ambient sampling/ionization/transmission integrated source for mass spectrometry

MALDI-TOF MS Imaging of Metabolites with a N-(1-Naphthyl) Ethylenediamine Dihydrochloride Matrix and Its Application to Colorectal Cancer Liver Metastasis

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) is a label-free technique for identifying multiplex metabolites and determining both their distribution and relative abundance in situ. Our previous study showed that N-(1-naphthyl) ethylenediamine dihydrochloride (NEDC) could act as a matrix for laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF MS) detection of oligosaccharides in solution. In the present study, NEDC-assisted LDI-TOF MSI yielded many more endogenous compound peaks between m/z 60 and m/z 1600 than 9-aminoacridine (9-AA). Our results show that NEDC-assisted LDI-TOF MSI is especially well-suited for examining distributions of glycerophospholipids (GPs) in addition to low molecular weight metabolites below m/z 400. Particularly, NEDC matrix allowed the LDI-TOF MSI of glucose in animal tissue. Furthermore, NEDC-assisted LDI-TOF MSI was applied to a mouse model of colorectal cancer liver metastasis. We revealed the distinct spatio-molecular signatures of many detected compounds in tumor or tumor-bearing liver, and we found that taurine, glucose, and some GPs decreased in tumor-bearing liver as the tumor developed in liver. Importantly, we also found a glucose gradient in metastatic tumor foci for the first time, which further confirms the energy competition between tumors and liver remnant due to the Warburg effect. Our results suggest that NEDC-assisted LDI MSI provides an in situ label-free analysis of multiple glycerophospholipids and low molecular weight metabolites (including glucose) with abundant peaks and high spatial resolution. This will allow future application to in situ definition of biomarkers, signaling pathways, and disease mechanisms.

Nonlinear Effects in Paul Traps Operated in the Second Stability Region: Analytical Analysis and Numerical Verification

1,5-Diaminonaphthalene Hydrochloride Assisted Laser Desorption/Ionization Mass Spectrometry Imaging of Small Molecules in Tissues Following Focal Cerebral Ischemia

Lysosomal pH Rise during Heat Shock Monitored by a Lysosome-Targeting Near-Infrared Ratiometric Fluorescent Probe

Quantitative Assessment of Protein Adsorption on Microparticles with Particle Mass Spectrometry

Synthesis of graphene nanosheet powder with layer number control via a soluble salt-assisted route

Organic salt NEDC (N-naphthylethylenediamine dihydrochloride) assisted laser desorption ionization mass spectrometry for identification of metal ions in real samples

Organic salt NEDC has qualified as a good matrix for the MALDI MS analysis of metal ions.

Differentiation of Chinese liquors by using ambient glow discharge ionization mass spectrometry

Induced Dual-Nanospray: A Novel Internal Calibration Method for Convenient and Accurate Mass Measurement

1-Naphthylhydrazine hydrochloride: A new matrix for the quantification of glucose and homogentisic acid in real samples by MALDI-TOF MS

Carbon Nanodots As a Matrix for the Analysis of Low-Molecular-Weight Molecules in Both Positive- and Negative-Ion Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry and Quantification of Glucose and Uric Acid in Real Samples

Carbon nanodots were applied for the first time as a new matrix for the analysis of low-molecular-weight compounds by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) in both positive- and negative-ion modes. A wide range of small molecules including amino acids, peptides, fatty acids, as well as β-agonists and neutral oligosaccharides were analyzed by MALDI MS with carbon nanodots as the matrix, and the lowest 0.2 fmol limits-of-detection were obtained for octadecanoic acid. Clear sodium and potassium adducts and deprotonated signals were produced in positive- and negative-ion modes. Furthermore, the glucose and uric acid in real samples were quantitatively determined by the internal standard method with the linear range of 0.5–9 mM and 0.1–1.8 mM (R2 > 0.999), respectively. This work gives new insight into the application of carbon nanodots and provides a general approach for rapid analysis of low-molecular-weight compounds.

2,3,4,5-Tetrakis(3′,4′-dihydroxylphenyl)thiophene: A New Matrix for the Selective Analysis of Low Molecular Weight Amines and Direct Determination of Creatinine in Urine by MALDI-TOF MS

N-(1-Naphthyl) Ethylenediamine Dinitrate: A New Matrix for Negative Ion MALDI-TOF MS Analysis of Small Molecules

Spectroscopic Response of Ferrocene Derivatives Bearing a BODIPY Moiety to Water: A New Dissociation Reaction

Rhodamine B Piperazinoacetohydrazine: A Water-Soluble Spectroscopic Reagent for Pyruvic Acid Labeling

A near-infrared fluorescent probe for monitoring tyrosinase activity

A highly specific ferrocene-based fluorescent probe for hypochlorous acid and its application to cell imaging

New Approach for Local Structure Analysis of the Tyrosine Domain in Proteins by Using a Site-Specific and Polarity-Sensitive Fluorescent Probe

Analysis of local structure of Arg10 domain in apo-α-lactalbumin with a polarity-sensitive arginine-specific fluorescent probe

N-Terminal Specific Fluorescence Labeling and its Use in Local Structure Analysis of Proteins (Invited Review)

Molecularly imprinted solid-phase extraction combined with electrochemical oxidation fluorimetry for the determination of methotrexate in human serum and urine

Molecularly imprinted on-line solid-phase extraction combined with chemiluminescence for the determination of pazufloxacin mesilate

Flow-injection–electrochemical oxidation fluorimetry for determination of methotrexate