A5023001564- Analytical Chemistry and Chromatography
- Mass Spectrometry Techniques and Applications
- Metabolomics and Mass Spectrometry Studies
- Advanced Chemical Sensor Technologies
- Advanced Chemical Physics Studies
- Advanced Proteomics Techniques and Applications
- Spectroscopy and Quantum Chemical Studies
- Free Radicals and Antioxidants
- Computational Drug Discovery Methods
- Molecular Junctions and Nanostructures
- Advanced Physical and Chemical Molecular Interactions
- Chemical Synthesis and Analysis
- Magnetism in coordination complexes
- Nanocluster Synthesis and Applications
- Ion-surface interactions and analysis
- Lanthanide and Transition Metal Complexes
- Chemical Thermodynamics and Molecular Structure
- Phenothiazines and Benzothiazines Synthesis and Activities
- Crystallography and molecular interactions
- Organic Electronics and Photovoltaics
- Chemical Reaction Mechanisms
- Protein Interaction Studies and Fluorescence Analysis
- X-ray Diffraction in Crystallography
- Drug Transport and Resistance Mechanisms
- CO2 Reduction Techniques and Catalysts
Material Measurement Laboratory
2014-2025
National Institute of Standards and Technology
2013-2025
University of Carabobo
2008
Central University of Venezuela
2008
National Institute of Standards
2008
Universidade de Santiago de Compostela
2006
Northwestern University
2003-2005
Center for Nanoscale Science and Technology
2005
Los Alamos National Laboratory
2003-2004
University of Chile
2000-2003
Recent progress in metabolomics and the development of increasingly sensitive analytical techniques have renewed interest global profiling, i.e., semiquantitative monitoring all chemical constituents biological fluids. In this work, we performed profiling NIST SRM 1950, "Metabolites Human Plasma", using GC-MS, LC-MS, NMR. Metabolome coverage, difficulties, reproducibility experiments on each platform are discussed. A total 353 metabolites been identified material. GC-MS provides 65 unique...
Metabolomics has a critical need for better tools mass spectral identification. Common metabolites may be identified by searching libraries of tandem spectra, which offers important advantages over other approaches to But are not nearly complete enough represent the full molecular diversity present in complex biological samples. We novel hybrid search method that can help identify library similarity compounds are. call it "hybrid" because combines conventional, direct peak matching with...
The relationship between global softness and static dipole polarizability is explored from the analogy of spherical averages defined within density functional theory. A cubic obtained that consistent with experimental observation for atoms. found to hold reasonably well similarly bonded molecules.
The validity of the minimum polarizability principle upon electronic excitation is studied as a companion that obtained by Chattaraj and Poddar in case maximum hardness principle. Twelve diatomic molecules have been selected and, both dipole for ground excited states calculated means ab initio density functional calculations using Sadlej's basis set. It has found molecule less polarizable its state than an electronically same spin multiplicity.
Electronic substituent effects may be rationalized in terms of Hammett-like linear relationships between global energy-dependent quantities and local electronic descriptors reactivity. These are framed on a hard soft acids bases (HSAB) principle accord with previous results reported by Li Evans [J. Am. Chem. Soc. 1995, 117, 7756]. Chemical substitution is indirectly assessed as responses at the active center substrate, Fukui function softness key within present approach. This model chemical...
Rationale The metabolite profiling of a NIST plasma Standard Reference Material (SRM 1950) on different liquid chromatography/mass spectrometry (LC/MS) platforms showed significant differences. Although these findings suggest caution when interpreting metabolomics results, the degree overlap both profiles allowed us to use tandem mass spectral libraries recurrent spectra evaluate what extent results are transferable across and develop cross‐platform chemical signatures. Methods Non‐targeted...
The Mass Spectrometry Data Center (MSDC) has recently started improving existing libraries and creating new ones for identifying analyzing plastics-related compounds (PRC) materials (PRM) as part of the NIST circular economy program. PRC are small molecules dissimilar chemical nature; hence, to increase coverage, we have used three types ionizations: EI, ESI, APCI. PRM solids that include polymers, polymer mixtures, commercial plastics, so pyrolysis-gas chromatography (py-GC-MS) create a...
Binding between water and models of poly(ethylene oxide), (CH2−CH2−O)n, n = 2−40, has been studied using the topographic features electrostatic potential, V(r), standard density functional theory methods. It was found that, in general, contour around minima oxygen atoms overlap forming a negative-valued spiral coiled positive-valued helix. The positive zone defines helical groove O−C−C−O units where lone pairs critical points are located. Topological analysis molecule also suggested that...
Approaches such as quantitative structure−activity relationships (QSAR) and molecular modeling are integrated with the study of complex networks to understand drug binding human serum albumin (HSA). A robust QSAR model using topological substructural descriptors/design (TOPS-MODE) approach has been derived shows good predictability interpretability in terms structural contribution HSA. perfect agreement exists between group/fragment contributions found by TOPS-MODE specific interactions...
RATIONALE Certain product ions in electrospray ionization tandem mass spectrometry are found to react with residual water the collision cell. This reaction often leads formation of that cannot be formed directly from precursor ions, and this complicates spectra may distort MRM (multiple monitoring) results. METHODS Various drugs, pesticides, metabolites, other compounds were dissolved acetonitrile/water/formic acid studied by record their MS 2 n several spectrometers (QqQ, QTOF, IT, Orbitrap...
A large fraction of ions observed in electrospray liquid chromatography–mass spectrometry (LC–ESI-MS) experiments biological samples remain unidentified. One the main reasons for this is that spectral libraries pure compounds fail to account complexity metabolite profiling complex materials. Recently, NIST Mass Spectrometry Data Center has been developing a novel type searchable mass library includes all recurrent unidentified spectra found sample profile. These libraries, conjunction with...
We present a simple model to describe the induction of magnetic behavior on gold clusters upon chemisorption one organic molecule with different chemical linkers. In particular, we address problem stability lowest lying singlet and show that for some linkers there exists spin symmetry-breaking lowers energy leads preferential density localization atoms neighboring site. The is basically an adaptation Stoner itinerant electron ferromagnetism finite it may have important implications our...
Selected reaction monitoring (SRM) of quinolone drugs showed different sensitivities in aqueous solution vs. biological extract. The authors suggested formation two singly protonated molecules with behavior, one undergoing loss H(2)O and the other CO(2), so that SRM transitions might depend on ratios these forms generated by electrospray. These surprising results prompted us to re-examine several some simpler compounds further elucidate mechanisms. We find relative contributions CO(2) tandem...
The tandem mass spectra of many compounds contained peaks which could not have arisen from the precursor ion. Such were found to be due reaction arylium ions with N2 in collision cell. Therefore, this was studied detail representative compounds.Various classes dissolved acetonitrile/water/formic acid and by electrospray ionization spectrometry record their MS(2) pseudo-MS(3) a QqQ spectrometer accurate m/z values an Orbitrap Elite instrument. Arylium react confirmed studies, comparison...
Reference spectral library searching, while widely used to identify compounds in other areas of mass spectrometry, is not commonly glycomics. Building on a study by Cotter and coworkers analysis sialylated oligosaccharides using atmospheric pressure-matrix-assisted laser-induced tandem spectrometry (MS/MS), we show that search methods enable the automated differentiation such oligosaccharide isomers MS/MS derived from electrospray collision-induced dissociation ion trap beam-type...
In this work, the topology of electrostatic potential using density functional theory for periodic systems was used to study nature interaction water with laponite surfaces; an uncharged sheet model also used. The topological analysis predicts that surfaces adsorption mode is such molecules are adsorbed almost parallel surface. For surfaces, where there a net charge, involves repulsion between negative lone pairs on and ones surface oxygen atoms. As consequence, bind in perpendicular tilted...
A prominent dissociation path for electrospray generated tryptic peptide ions is the of bond linking second and third residues from amino-terminus. The formation resulting b(2) y(n-2) fragments has been rationalized by specific facile mechanisms. An examination spectral libraries shows that this predominates in diprotonated peptides composed 12 or fewer residues, with notable exception containing glutamine glutamic acid at N-terminus. To elucidate mechanism which these amino acids affect...
Electrospray ionization mass spectrometry (ESI-MS) of many protonated aldehydes shows loss CO as a major fragmentation pathway. However, we find that certain undergo H2 followed by reaction with water in the collision cell. This complicates interpretation tandem (MS/MS) spectra and affects multiple monitoring (MRM) results.3-Formylchromone other were dissolved acetonitrile/water/formic acid studied ESI-MS to record their MS(2) MS(n) several spectrometers (QqQ, QTOF, ion trap (IT), Orbitrap...
Basic principles: The use of simple topological principles permits the design small molecules with very high proton affinities. According to DFT calculations, 3,6,7,8-tetraazatricyclo[3.1.1.12,4]octane and its analogues behave as superbases, show important structural deviations from known sponges. Their electrostatic potential maps a characteristic compact region at protonation site (blue regions in picture).
There is a lack of experimental reference materials and standards for metabolomics measurements, such as urine, plasma, other human fluid samples. Reasons include difficulties with supply, distribution, dissemination information about the materials. Additionally, there long lead time because need their compositions to be fully characterized uncertainty, labor-intensive process material containing thousands relevant compounds. Furthermore, data analysis can hampered by different methods using...
Various density functionals have been tested in calculating atomic and molecular dipole polarizabilities. For atoms, it has found that the results are not competitive with more sophisticated ab initio methods. Exchange correlation effects analyzed separately to show main cause of errors lies exchange functional models. Strong numerical evidence is given support idea a right asymptotic behavior potential essential obtain reliable values for In this sense, hybrid method proposed by Becke (J....
We present a simple methodology to study trends in conductance of molecule−metal junctions based on Density Functional Theory calculations modified quasimolecular Green functions capacitor-like electric field. The approach is series assumptions about the voltage spatial profile and molecule−surface chemisorptive coupling metal−molecule interfaces that seem be validated for number junctions. method assumes drops entirely at junction can approximately factorized as product contact molecular...
The energy dependence of fragmentation in a collision cell was measured for 2400 protonated peptide ions derived from the digestion 24 proteins. voltage at which sum fragment ion abundances equal to remaining parent (V(1/2)) principal measure effectiveness. Each class peptides characterized by linear relation between V(1/2) and m/z whose slope depended on and, with little adjustment, intersected origin. Peptide where number protons is no greater than arginine residues show greatest slope,...
While analyzing tandem mass spectra of tryptic tripeptides, intense unassigned peaks were observed, corresponding to neutral loss 45 Da from a(2) ions. This process was confirmed by MS(3) experiments. Based on exact analysis, the ascribed (NH(3) + CO) or formamide. The proposed mechanism involves a cyclic form structure - ions their fragmentation in Loss occurs competition with other paths, such as H(2)O formation immonium However, if ion contains methionine, 48 (ascribed CH(3)SH)...