Theoretical study of the adsorption of analgesic environmental pollutants on pristine and nitrogen-doped graphene nanosheets.

Interactions of the analgesic medications dextropropoxyphene (DPP, opioid), paracetamol (PCL, nonnarcotic), tramadol (TDL, nonnarcotic), ibuprofen (IBN, nonsteroidal anti-inflammatory drug (NSAID)), and naproxen (NPX, NSAID) with pristine graphene (GN) and nitrogen-doped GN (NGN; containing only graphitic N atoms) nanosheets were explored using density functional theory (DFT) in the gas and aqueous phases. Calculations in the aqueous phase were performed using the integral equation formalism polarized continuum model (IEFPCM). Calculated geometry-optimized structures, partial atomic charges (determined using Natural Bond Orbital analysis), highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gaps, work functions (determined using time-dependent DFT), and molecular electrostatic potential plots showed that the adsorption process is physical in nature (viz. physisorption), primarily due to noncovalent π-π and van der Waals interactions. In addition, calculated adsorption energies (ΔEad) were exergonic, indicating that formation of the analgesic/GN and analgesic/NGN complexes is thermodynamically favorable in the gas (ΔEad values for analgesic/GN and analgesic/NGN were in the range of -66.56 kJ mol-1 to -106.78 kJ mol-1) and aqueous phases (ΔEad values for analgesic/GN and analgesic/NGN complexes were in the range of -58.75 kJ mol-1 to -100.46 kJ mol-1). Generally, for GN and NGN, adsorption was more endergonic in the aqueous phase by as much as +10.41 kJ mol-1. Calculated solvation energies (ΔEsolvation) were exergonic for all analgesic/GN complexes (ΔEsolvation values were in the range of -56.50 kJ mol-1 to -66.17 kJ mol-1) and analgesic/NGN complexes (ΔEsolvation values were in the range of -77.26 kJ mol-1 to -87.96 kJ mol-1), with analgesic/NGN complexes exhibiting greater stability in aqueous solutions (∼20 kJ mol-1 more stable). In summary, the results of this theoretical study demonstrate that the adsorption and solvation of analgesics on GN and NGN nanosheets is thermodynamically favorable. In addition, generally, analgesic/NGN complexes exhibit higher adsorption affinities and solvation energies in the gas and aqueous phases. Therefore, GN and NGN nanosheets are potential adsorbents for extracting analgesic contaminants from aqueous environments such as aquatic ecosystems.

Identification of lipid biomarkers of metastatic potential and gene expression (HER2/p53) in human breast cancer cell cultures using ambient mass spectrometry.

In breast cancer, overexpression of human epidermal growth factor receptor 2 (HER2) correlates with overactivation of lipogenesis, mutation of tumor suppressor p53, and increased metastatic potential. The mechanisms through which lipids mediate p53, HER2, and metastatic potential are largely unknown. We have developed a desorption electrospray ionization mass spectrometry (DESI-MS) method to identify lipid biomarkers of HER2/p53 expression, metastatic potential, and disease state (viz. cancer vs. non-cancerous) in monolayer and suspension breast cancer cell cultures (metastatic potential: MCF-7, T-47D, MDA-MB-231; HER2/p53: HCC2218 (HER2+++/p53+), HCC1599 (HER2-/p53-), HCC202 (HER2++/p53-), HCC1419 (HER2+++/p53-) HCC70 (HER2-/p53+++); non-cancerous: MCF-10A). Unsupervised principal component analysis (PCA) of DESI-MS spectra enabled identification of twelve lipid biomarkers of metastatic potential and disease state, as well as ten lipids that distinguish cell lines based on HER2/p53 expression levels (> 200 lipids were identified per cell line). In addition, we developed a DESI-MS imaging (DESI-MSI) method for mapping the spatial distribution of lipids in metastatic spheroids (MDA-MB-231). Of the twelve lipids that correlate with changes in the metastatic potential of monolayer cell cultures, three were localized to the necrotic core of spheroids, indicating a potential role in promoting cancer cell survival in nutrient-deficient environments. One lipid species, which was not detected in monolayer MDA-MB-231 cultures, was spatially localized to the periphery of the spheroid, suggesting a potential role in invasion and/or proliferation. These results demonstrate that combining DESI-MS/PCA of monolayer and suspension cell cultures with DESI-MSI of spheroids is a promising approach for identifying lipid biomarkers of specific genotypes and phenotypes, as well as elucidating the potential function of these biomarkers in breast cancer. Graphical Absract.

Detection of a transient FeV(O)(OH) species involved in olefin oxidation by a bio-inspired non-haem iron catalyst.

The Fe(TPA) (TPA = tris(pyridyl-2-methyl)amine) class of non-haem Fe catalysts is proposed to carry out selective hydrocarbon oxidations through the generation of high-valent iron species. Using ambient mass spectrometry, we obtain direct evidence for the formation of an FeV(O)(OH) species under catalytic conditions. In addition, 18O-labelling suggests that this FeV(O)(OH) species serves as the active oxidant in hydrocarbon oxidation catalysis.

Systematic review and meta-analysis: the effects of fermented milk with Bifidobacterium lactis CNCM I-2494 and lactic acid bacteria on gastrointestinal discomfort in the general adult population.

BACKGROUND: It has been suggested that probiotics may improve gastrointestinal discomfort. Not all probiotics exhibit the same effects and consequently meta-analyses on probiotics should be confined to well-defined strains or strain combinations. The aim of this study was to evaluate the effectiveness of a probiotic fermented milk (PFM) that includes Bifidobacterium lactis (B. lactis) CNCM I-2494 and lactic acid bacteria on gastrointestinal discomfort in the general adult population. METHODS: Double-blind randomized controlled trials in the general adult population comparing PFM with a control dairy product for at least 4 weeks were searched from multiple literature databases (up to February 2015). Meta-analyses using random-effects models, with individual participant data were undertaken to calculate an odds ratio (OR) or standard mean difference (SMD), with a 95% confidence interval (CI). RESULTS: The search strategy identified 12,439 documents. Overall, three trials with a total of 598 adults (female = 96.5%) met the inclusion criteria. Consumption of the PFM product was associated with a significant improvement in overall gastrointestinal discomfort compared with the control product (OR = 1.48; 95% CI 1.07-2.05), with a number needed to treat (NNT) of 10.24 (95% CI 5.64-55.93). PFM was also superior to the control in reducing digestive symptoms, as measured using a composite score (SMD = -0.21; 95% CI -0.37 to -0.05). Sensitivity analyses produced similar results, and the heterogeneity between studies was minimal. CONCLUSIONS: This meta-analysis shows that the consumption of PFM with B. lactis CNCM I-2494 and lactic acid bacteria is associated with a modest but consistent and significant improvement of outcomes related to gastrointestinal discomfort in healthy adults.

Synchronized Desorption Electrospray Ionization Mass Spectrometry Imaging.

Desorption electrospray ionization (DESI) has emerged as a powerful technique for mass spectral analysis and imaging under ambient conditions. Synchronization of DESI (sDESI) with the ion injection period (IT)of low-duty cycle mass spectrometers has been previously shown to improve sensitivity and reduce the amount of sample depleted during the acquisition of each spectrum (viz. MS scan time). In this report, we describe the development and characterization of an sDESI mass spectrometry imaging source (sDESI-MSI). Our results show that synchronization of DESI with the IT of an LTQ Orbitrap-XL mass spectrometer improves spatial resolution by factors of ∼4-6. In addition, under certain experimental conditions, synchronization was essential to acquire distinct MS images of low-intensity endogenous FAs (< 5% relative intensity) in fingermarks at high sampling frequencies (step sizes ≤ 75 µm). The magnitudes of these improvements in performance depend on the properties of the microdroplet spray, sample, and surface. Simulations that model analyte movement during desorption and the "washing effect" replicate the experimental results with the washing parameter having the greatest impact on performance. Thus, synchronization improves spatial resolution and sensitivity by decreasing the percentage of the total MS scan time that analytes are influenced by the "washing effect". Generally, synchronization of DESI with IT improves performance and expands the range of analytes, surfaces, and experimental conditions amenable to DESI-MSI, especially for analytes that are weakly attached to a surface.

Paper-Based Electrochemical Cell Coupled to Mass Spectrometry.

On-line coupling of electrochemistry (EC) to mass spectrometry (MS) is a powerful approach for identifying intermediates and products of EC reactions in situ. In addition, EC transformations have been used to increase ionization efficiency and derivatize analytes prior to MS, improving sensitivity and chemical specificity. Recently, there has been significant interest in developing paper-based electroanalytical devices as they offer convenience, low cost, versatility, and simplicity. This report describes the development of tubular and planar paper-based electrochemical cells (P-EC) coupled to sonic spray ionization (SSI) mass spectrometry (P-EC/SSI-MS). The EC cells are composed of paper sandwiched between two mesh stainless steel electrodes. Analytes and reagents can be added directly to the paper substrate along with electrolyte, or delivered via the SSI microdroplet spray. The EC cells are decoupled from the SSI source, allowing independent control of electrical and chemical parameters. We utilized P-EC/SSI-MS to characterize various EC reactions such as oxidations of cysteine, dopamine, polycyclic aromatic hydrocarbons, and diphenyl sulfide. Our results show that P-EC/SSI-MS has the ability to increase ionization efficiency, to perform online EC transformations, and to capture intermediates of EC reactions with a response time on the order of hundreds of milliseconds. The short response time allowed detection of a deprotonated diphenyl sulfide intermediate, which experimentally confirms a previously proposed mechanism for EC oxidation of diphenyl sulfide to pseudodimer sulfonium ion. This report introduces paper-based EC/MS via development of two device configurations (tubular and planar electrodes), as well as discusses the capabilities, performance, and limitations of the technique.

Multistage Reactive Transmission-Mode Desorption Electrospray Ionization Mass Spectrometry.

Elucidating reaction mechanisms is important for advancing many areas of science such as catalyst development. It is often difficult to probe fast reactions at ambient conditions with high temporal resolution. In addition, systems involving reagents that cross-react require analytical methods that can minimize interaction time and specify their order of introduction into the reacting system. Here, we explore the utility of transmission mode desorption electrospray ionization (TM-DESI) for reaction monitoring by directing a microdroplet spray towards a series of meshes with micrometer-sized openings coated with reagents, an approach we call multistage reactive TM-DESI (TM (n) -DESI, where n refers to the number of meshes; n = 2 in this report). Various stages of the reaction are initiated at each mesh surface, generating intermediates and products in microdroplet reaction vessels traveling towards the mass spectrometer. Using this method, we investigated the reactivity of iron porphyrin catalytic hydroxylation of propranolol and other substrates. Our experimental results indicate that TM (n) -DESI provides the ability to spatially separate reagents and control their order of introduction into the reacting system, thereby minimizing unwanted reactions that lead to catalyst deactivation and degradation products. In addition, comparison with DESI-MS analyses (the Zare and Latour laboratories published results suggesting accessible reaction times <1 ms) of the reduction of dichlorophenolindophenol by L-ascorbic acid suggest that TM (1) -DESI can access reaction times less than 1 ms. Multiple meshes allow sequential stages of desorption/ionization per MS scan, increasing the number of analytes and reactions that can be characterized in a single experiment.

Estimating vaccine efficacy using animal efficacy data.

Animal models are used to predict the effect of an intervention in humans. An example is the prediction of the efficacy of a vaccine when it is considered unethical or infeasible to challenge humans with the target disease to assess the effect of the vaccine on the disease in humans directly. In such cases, data from animal studies are used to develop models relating antibody level to protection probability in the animal, and then data from a study or studies in human subjects vaccinated with the proposed vaccine regimen are used in combination with the relevant animal models to predict protection in humans, and hence estimate vaccine efficacy. We explain the statistical techniques required to provide an estimate of vaccine efficacy and its precision. We present simulated examples showing that precise estimation of the relationship between antibody levels and protection in animals, at levels likely to be induced in humans by the vaccine regimen, is key to precise estimation of the vaccine efficacy. Because the confidence interval for the estimate of vaccine efficacy cannot be expressed in analytical form, but must be estimated from resampling, or bootstrapping, it is not possible to design studies with required power analytically. Therefore we propose that a simulation-based design of experiments approach using preliminary data is used to maximise the power of further studies and thus minimise the human and animal experimentation required.

Electrooxidation of alcohols catalyzed by amino alcohol ligated ruthenium complexes.

Ruthenium transfer hydrogenation catalysts physisorbed onto edge-plane graphite electrodes are active electrocatalysts for the oxidation of alcohols. Electrooxidation of CH3OH (1.23 M) in a buffered aqueous solution at pH 11.5 with [(η(6)-p-cymene)(η(2)-N,O-(1R,2S)-cis-1-amino-2-indanol)]Ru(II)Cl (2) on edge-plane graphite exhibits an onset current at 560 mV vs NHE. Koutecky-Levich analysis at 750 mV reveals a four-electron oxidation of methanol with a rate of 1.35 M(-1) s(-1). Mechanistic investigations by (1)H NMR, cyclic voltammetry, and desorption electrospray ionization mass spectrometry indicate that the electroxidation of methanol to generate formate is mediated by surface-supported Ru-oxo complexes.

Characterization of MYC-induced tumorigenesis by in situ lipid profiling.

We apply desorption electrospray ionization mass spectrometry imaging (DESI-MSI) to provide an in situ lipidomic profile of genetically modified tissues from a conditional transgenic mouse model of MYC-induced hepatocellular carcinoma (HCC). This unique, label-free approach of combining DESI-MSI with the ability to turn specific genes on and off has led to the discovery of highly specific lipid molecules associated with MYC-induced tumor onset. We are able to distinguish normal from MYC-induced malignant cells. Our approach provides a strategy to define a precise molecular picture at a resolution of about 200 µm that may be useful in identifying lipid molecules that define how the MYC oncogene initiates and maintains tumorigenesis.

Capturing fleeting intermediates in a catalytic C-H amination reaction cycle.

We have applied an ambient ionization technique, desorption electrospray ionization MS, to identify transient reactive species of an archetypal C-H amination reaction catalyzed by a dirhodium tetracarboxylate complex. Using this analytical method, we have detected previously proposed short-lived reaction intermediates, including two nitrenoid complexes that differ in oxidation state. Our findings suggest that an Rh-nitrene oxidant can react with hydrocarbon substrates through a hydrogen atom abstraction pathway and raise the intriguing possibility that two catalytic C-H amination pathways may be operative in a typical bulk solution reaction. As highlighted by these results, desorption electrospray ionization MS should have broad applicability for the mechanistic study of catalytic processes.

Transient Ru-methyl formate intermediates generated with bifunctional transfer hydrogenation catalysts.

Desorption electrospray ionization (DESI) coupled to high-resolution Orbitrap mass spectrometry (MS) was used to study the reactivity of a (ß-amino alcohol)(arene)RuCl transfer hydrogenation catalytic precursor in methanol (CH(3)OH). By placing [(p-cymene)RuCl(2)](2) on a surface and spraying a solution of ß-amino alcohol in methanol, two unique transient intermediates having lifetimes in the submillisecond to millisecond range were detected. These intermediates were identified as Ru (II) and Ru (IV) complexes incorporating methyl formate (HCOOCH(3)). The Ru (IV) intermediate is not observed when the DESI spray solution is sparged with Ar gas, indicating that O(2) dissolved in the solvent is necessary for oxidizing Ru (II) to Ru (IV). These proposed intermediates are supported by high-resolution and high mass accuracy measurements and by comparing experimental to calculated isotope profiles. Additionally, analyzing the bulk reaction mixture using gas chromatography-MS and nuclear magnetic resonance spectroscopy confirms the formation of HCOOCH(3). These results represent an example that species generated from the (ß-amino alcohol)(arene)RuCl (II) catalytic precursor can selectively oxidize CH(3)OH to HCOOCH(3). This observation leads us to propose a pathway that can compete with the hydrogen transfer catalytic cycle. Although bifunctional hydrogen transfer with Ru catalysts has been well-studied, the ability of DESI to intercept intermediates formed in the first few milliseconds of a chemical reaction allowed identification of previously unrecognized intermediates and reaction pathways in this catalytic system.

Interfacing capillary-based separations to mass spectrometry using desorption electrospray ionization.

The powerful hybrid analysis method of capillary-based separations followed by mass spectrometric analysis gives substantial chemical identity and structural information. It is usually carried out using electrospray ionization. However, the salts and detergents used in the mobile phase for electrokinetic separations suppress ionization efficiencies and contaminate the inlet of the mass spectrometer. This report describes a new method that uses desorption electrospray ionization (DESI) to overcome these limitations. Effluent from capillary columns is deposited on a rotating Teflon disk that is covered with paper. As the surface rotates, the temporal separation of the eluting analytes (i.e., the electropherogram) is spatially encoded on the surface. Then, using DESI, surface-deposited analytes are preferentially ionized, reducing the effects of ion suppression and inlet contamination on signal. With the use of this novel approach, two capillary-based separations were performed: a mixture of the rhodamine dyes at milligram/milliliter levels in a 10 mM sodium borate solution was separated by capillary electrophoresis, and a mixture of three cardiac drugs at milligram/milliliter levels in a 12.5 mM sodium borate and 12.5 mM sodium dodecyl sulfate solution was separated by micellar electrokinetic chromatography. In both experiments, the negative effects of detergents and salts on the MS analyses were minimized.

Trace detection of non-uniformly distributed analytes on surfaces using mass transfer and large-area desorption electrospray ionization (DESI) mass spectrometry.

Ambient ionization methods such as desorption electrospray ionization (DESI) allow the analysis of chemicals adsorbed at surfaces without the need for sample (or surface) pretreatment. A limitation of current implementations of these ionization sources is the small size of the area that can be sampled. This makes examination of surfaces of large areas time-consuming because of the need to raster across the surface. This paper describes a DESI source that produces a spray plume with an effective desorption/ionization area of 3.6 cm(2), some 200 times larger than given by conventional DESI sources. Rhodamine 6G and several drugs of abuse (codeine, heroin and diazepam) were used to demonstrate the ability to use large-area DESI MS to perform rapid (a few seconds) representative sampling of areas of the order of several square centimetres without scanning the probe across the surface. The large area ion source displayed high sensitivity (limits of detection in the high nanogram range) and high reproducibility (approximately 20 to 35% relative standard deviation). The rapid analysis of even larger surfaces (hundreds of cm(2)) for traces of explosives is possible using a sorbent surface wipe followed by large-area DESI interrogation performed directly on the wipe material. The performance of this mass transfer dry wipe method was examined by determination of the limits of detection of several explosives. Surfaces with different topographies and compositions were also tested. Using this method, absolute limits of detection observed for HMX and RDX from plastic surfaces and skin were found to be as low as 10 ng cm(-2). The concentration of residue from large surface areas in this technique allowed the detection of 100 ng of explosives from surfaces with areas ranging from 1.00 x 10(3) cm(2) to 1.40 x 10(4) cm(2).

Hand-held mass spectrometer for environmentally relevant analytes using a variety of sampling and ionization methods.

A recently developed hand-held, rectilinear ion trap mass spectrometer, capable of performing in situ analysis, has been evaluated for a variety of environmentally relevant analytes. Different sampling and ionization methods were implemented, demonstrating the considerable versatility of this instrument. A discontinuous (viz. pulsed) atmospheric pressure inlet (DAPI) was used to introduce externally-generated analyte ions. Nitro compounds were ionized by electrosonic spray ionization (ESSI) yielding the protonated and sodiated forms of the molecular ion, as well as fragment ions. The amines 2,2,6,6-tetramethylpiperidine, triethylamine and 2,6-diphenylpyridine showed low parts per billion (ppb) detection limits. Vapor phase external ionization was used to examine the chemical warfare simulant dimethyl methylphosphonate and the insect repellant N,N-diethyl-m-toluamide. Membrane introduction mass spectrometry (MIMS) was used as the introduction system for hydrophobic analytes using a selectively permeable (polydimethylsiloxane) membrane placed within the vacuum manifold with subsequent ionization of the thermally desorbed neutral compounds inside the ion trap. MIMS allowed the quantitation of trace levels (a few ppb) of fluorinated compounds in the vapor phase. MIMS was also applied to the quantitation of aqueous polycyclic aromatic hydrocarbons (PAH's) with limits of detection again in the low ppb range for naphthalene, acenaphthene, anthracene and phenanthrene.

Direct analysis of Stevia leaves for diterpene glycosides by desorption electrospray ionization mass spectrometry.

The analysis of Stevia leaves has been demonstrated without any sample preparation using desorption electrospray ionization (DESI) mass spectrometry. Direct rapid analysis was achieved using minimal amounts of sample ( approximately 0.15 cm x 0.15 cm leaf fragment). Characteristic constituents of the Stevia plant are observed in both the positive and negative ion modes including a series of diterpene 'sweet' glycosides. The presence of the glycosides was confirmed via tandem mass spectrometry analysis using collision-induced dissociation and further supported by exact mass measurements using an LTQ-Orbitrap. The analysis of both untreated and hexane-extracted dry leaves proved that DESI can be successfully used to analyze untreated leaf fragments as identical profiles were obtained from both types of samples. Characterization and semi-quantitative determination of the glycosides was achieved based on the glycoside profile within the full mass spectrum. In addition, the presence of characteristic glycosides in an all-natural commercial Stevia dietary supplement was confirmed. This study provides an example of the application of DESI to direct screening of plant materials, in this case diterpene glycosides.

Rephasing ion packets in the Orbitrap mass analyzer to improve resolution and peak shape.

A method is described to improve resolution and peak shape in the Orbitrap under certain experimental conditions. In these experiments, an asymmetric anharmonic axial potential was first produced in the Orbitrap by detuning the voltage on the compensator electrode, which results in broad and multiply split mass spectral peaks. An AC waveform applied to the outer electrode, 180 degrees out of phase with ion axial motion and resonant with the frequency of ion axial motion, caused ions of a given m/z to be de-excited to the equator (z = 0) and then immediately re-excited. This process, termed "rephasing," leaves the ion packet with a narrower axial spatial extent and frequency distribution. For example, when the Orbitrap axial potential is thus anharmonically de-tuned, a resolution of 124,000 to 171,000 is obtained, a 2- to 3-fold improvement over the resolution of 40,000 to 60,000 without rephasing, at 10 ng/microL reserpine concentration. Such a rephasing capability may ultimately prove useful in implementing tandem mass spectrometry (MS/MS) in the Orbitrap, bringing the Orbitrap's high mass accuracy and resolution to bear on both the precursor and product ions in the same MS/MS scan and making available the collision energy regime of the Orbitrap, approximately 1500 eV.

Pharmaceutical cleaning validation using non-proximate large-area desorption electrospray ionization mass spectrometry.

Desorption electrospray ionization (DESI) is a droplet-based ionization method that is applied to samples in the ambient environment with little or no sample preparation. Its utility for industrial applications is explored here for the case of pharmaceutical cleaning validation. A non-proximate large-area DESI system was built to examine representative areas of the surfaces of reaction vessels used in active product ingredient (API) manufacturing. A large-area sprayer capable of sampling an area of approximately 2.5 cm(2) was coupled with a transport tube to allow sensitive, representative sampling of APIs from a stainless steel surface 1 m away from the mass spectrometer. The system was used to detect the APIs neostigmine, acebutolol, amiloride, amiodarone, ibuprofen, montelukast, potassium clavulanate, and beta-estradiol, at levels as low as 30-10 ng/cm(2), easily satisfying the general acceptable limits set by the pharmaceutical industry. These levels were achieved from surfaces resembling the equipment used in API manufacturing processes at a rate of 30 s per analysis.