Environmental Molecular Sciences Laboratory

About: Environmental Molecular Sciences Laboratory is a facility organization based out in Richland, Washington, United States. It is known for research contribution in the topics: Mass spectrometry & Ion. The organization has 1471 authors who have published 3010 publications receiving 169961 citations.

Reactivity of liquid and semisolid secondary organic carbon with chloride and nitrate in atmospheric aerosols.

Abstract: Constituents of secondary organic carbon (SOC) in atmospheric aerosols are often mixed with inorganic components and compose a significant mass fraction of fine particulate matter in the atmosphere. Interactions between SOC and other condensed-phase species are not well understood. Here, we investigate the reactions of liquid-like and semisolid SOC from ozonolysis of limonene (LSOC) and α-pinene (PSOC) with NaCl using a set of complementary microspectroscopic analyses. These reactions result in chloride depletion in the condensed phase, release of gaseous HCl, and formation of organic salts. The reactions attributed to acid displacement by SOC acidic components are driven by the high volatility of HCl. Similar reactions can take place in SOC/NaNO3 particles. The results show that an increase in SOC mass fraction in the internally mixed SOC/NaCl particles leads to higher chloride depletion. Glass transition temperatures and viscosity of PSOC were estimated for atmospherically relevant conditions. Data show that the reaction extent depends on SOC composition, particle phase state and viscosity, mixing state, temperature, relative humidity (RH), and reaction time. LSOC shows slightly higher potential to deplete chloride than PSOC. Higher particle viscosity at low temperatures and RH can hinder these acid displacement reactions. Formation of organic salts from these overlooked reactions can alter particle physiochemical properties and may affect their reactivity and ability to act as cloud condensation and ice nuclei. The release and potential recycling of HCl and HNO3 from reacted aerosol particles may have important implications for atmospheric chemistry.

Comprehensive Metabolite Identification Strategy Using Multiple Two-Dimensional NMR Spectra of a Complex Mixture Implemented in the COLMARm Web Server.

Abstract: Identification of metabolites in complex mixtures represents a key step in metabolomics. A new strategy is introduced, which is implemented in a new public web server, COLMARm, that permits the coanalysis of up to three two-dimensional (2D) NMR spectra, namely, 13C–1H HSQC (heteronuclear single quantum coherence spectroscopy), 1H–1H TOCSY (total correlation spectroscopy), and 13C–1H HSQC-TOCSY, for the comprehensive, accurate, and efficient performance of this task. The highly versatile and interactive nature of COLMARm permits its application to a wide range of metabolomics samples independent of the magnetic field. Database query is performed using the HSQC spectrum, and the top metabolite hits are then validated against the TOCSY-type experiment(s) by superimposing the expected cross-peaks on the mixture spectrum. In this way the user can directly accept or reject candidate metabolites by taking advantage of the complementary spectral information offered by these experiments and their different sensiti...

Design and performance of an ESI interface for selective external ion accumulation coupled to a Fourier transform ion cyclotron mass spectrometer.

Abstract: The coupling of Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) with electrospray ionization has advanced the analysis of large biopolymers and provided the basis for high-throughput protein characterization (e.g., for rapid "proteome" analyses). In this work, the combination of high-performance capillary liquid chromatography with FTICR mass spectrometry and external ion accumulation has been shown to increase both sensitivity and analysis duty cycle. Instrument versatility is further improved by ion preselection followed by ion accumulation in an external linear quadrupole ion trap. The interface was tested with a 3.5-T FTICR mass spectrometer and evaluated with a number of peptides and proteins whose molecular weights ranged from 500 to 66000. A significant increase in the sensitivity, duty cycle, and dynamic range over that of the previously used accumulated trapping was achieved, exhibiting a detection limit of approximately 10 zmol (approximately 6000 molecules) for smaller proteins such as cytochrome c. Capillary LC external accumulation interface with FTICR was successfully applied for the study of whole-proteome mouse tryptic digests.

Charge-Transfer Versus Charge-Transfer-Like Excitations Revisited⊥

Abstract: Criteria to assess charge-transfer (CT) and CT-like character of electronic excitations are examined. Time-dependent density functional theory (TDDFT) calculations with non-hybrid, hybrid, and tuned long-range corrected (LC) functionals are compared with coupled-cluster (CC) benchmarks. The test set comprises an organic CT complex, two push-pull donor-acceptor chromophores, a cyanine dye, and several polycyclic aromatic hydrocarbons. Proper CT is easily identified. Excitations with significant density changes upon excitation within regions of close spatial proximity can also be diagnosed. For such excitations, the use of LC functionals in TDDFT sometimes leads to dramatic improvements of the singlet energies, similar to proper CT. It is shown that such CT-like excitations do not have the characteristics of physical charge transfer, and improvements with LC functionals may not be obtained for the right reasons. The TDDFT triplet excitation energies are underestimated for all systems, often severely. For the CT-like candidates, the singlet-triplet (S/T) separation changes from negative with a non-hybrid functional to positive with a tuned LC functional. For the cyanine, the S/T separation is systematically too large with TDDFT, leading to better error compensation for the singlet energy with a non-hybrid functional.

Integration of capillary isoelectric focusing with capillary reversed-phase liquid chromatography for two-dimensional proteomics separation.

Abstract: On-line combination of capillary isoelectric focusing (CIEF) with capillary reversed-phase liquid chromatography (CRPLC) is developed using a microinjector as the interface for performing two-dimensional (2-D) protein/peptide separations of complex protein mixtures. The focusing effect of CIEF not only contributes to a high-resolution protein/peptide separation, but also may permit the analysis of low-abundance proteins with a typical concentration factor of 50-100 times. The preparative capabilities of CIEF are much larger than most of capillary-based electrokinetic separation techniques since the entire capillary is initially filled with a solution containing proteins/peptides and carrier ampholytes for the creation of a pH gradient inside the capillary. The focused peptides which have a similar pI are coinjected into the second separation dimension and further resolved by their differences in hydrophobicity. The resolving power of combined CIEF-CRPLC system is demonstrated using the soluble fraction of Drosophila salivary glands taken from a period beginning before steroid-triggered programmed cell death and extending to its completion. The separation mechanisms of CIEF and CRPLC are completely orthogonal and the overall peak capacity is estimated to be around approximately 1800 over a run time of less than 8 h. Significant enhancement in the separation peak capacity can be realized by further increasing the number of CIEF fractions and/or slowing the solvent gradient in CRPLC, however, at the expense of overall analysis time. The results of our preliminary studies display significant differences in the separation profiles of peptide samples obtained from salivary glands of animals staged at the 6 and 12 h following puparium formation.