Oxygen-rich Molecules Research Articles

Nanocavity in hollow sandwiched catalysts as substrate regulator for boosting hydrodeoxygenation of biomass-derived carbonyl compounds.

Hydrodeoxygenation of oxygen-rich molecules toward hydrocarbons is attractive yet challenging in the sustainable biomass upgrading. The typical supported metal catalysts often display unstable catalytic performances owing to the migration and aggregation of metal nanoparticles (NPs) into large sizes under harsh conditions. Here, we develop a crystal growth and post-synthetic etching method to construct hollow chromium terephthalate MIL-101 (named as HoMIL-101) with one layer of sandwiched Ru NPs as robust catalysts. Impressively, HoMIL-101@Ru@MIL-101 exhibits the excellent activity and stability for hydrodeoxygenation of biomass-derived levulinic acid to gamma-valerolactone under 50°C and 1-megapascal H2, and its activity is about six times of solid sandwich counterparts, outperforming the state-of-the-art heterogeneous catalysts. Control experiments and theoretical simulation clearly indicate that the enrichment of levulinic acid and H2 by nanocavity as substrate regulator enables self-regulating the backwash of both substrates toward Ru NPs sandwiched in MIL-101 shells for promoting reaction with respect to solid counterparts, thus leading to the substantially enhanced performance.

Hygroscopic Growth, Phase Morphology, and Optical Properties of Model Aqueous Brown Carbon Aerosol.

Brown carbon aerosol in the atmosphere contain light-absorbing chromophores that influence the optical scattering properties of the particles. These chromophores may be hydrophobic, such as PAHs, or water soluble, such as nitroaromatics, imidazoles, and other conjugated oxygen-rich molecules. Water-soluble chromophores are expected to exist in aqueous solution in the presence of sufficient water and will exhibit physical properties (e.g., size, refractive index, and phase morphology) that depend on the environmental relative humidity (RH). In this work, we characterize the RH-dependent properties of 4-nitrocatechol (4-NC) and its mixtures with ammonium sulfate, utilizing a single-particle levitation platform coupled with Mie resonance spectroscopy to probe the size, real part of the complex refractive index (RI), and phase morphology of individual micron-sized particles. We measure the hygroscopic growth properties of pure 4-NC and apply mixing rules to characterize the growth of mixtures with ammonium sulfate. We report the RI at 589 nm for these samples as a function of RH and explore the wavelength dependence of the RI at non-absorbing wavelengths. The real part of the RI at 589 nm was found to vary in the range 1.54-1.59 for pure 4-NC from 92.5 to 75% RH, with an estimated pure component RI of 1.70. The real part of the RI was also measured for mixtures of AS and 4-NC and ranged from 1.39 to 1.51 depending on the component ratio and RH. We went on to characterize phase transitions in mixed particles, identifying the onset RH of liquid-liquid phase separation (LLPS) and efflorescence transitions. Mixtures showed LLPS in the range of 85-76% RH depending on the molar ratio, while efflorescence typically fell between 22 and 42% RH. Finally, we characterized the imaginary part of the complex RI using an effective oscillator model to capture the wavelength-dependent absorption properties of the system.

Legacy Effects of Sorption Determine the Formation Efficiency of Mineral-Associated Soil Organic Matter.

Sorption of dissolved organic matter (DOM) is one major pathway in the formation of mineral-associated organic matter (MOM), but there is little information on how previous sorption events feedback to later ones by leaving their imprint on mineral surfaces and solutions ("legacy effect"). In order to conceptualize the role of legacy effects in MOM formation, we conducted sequential sorption experiments with kaolinite and gibbsite as minerals and DOM derived from forest floor materials. The MOM formation efficiency leveled off upon repeated addition of identical DOM solutions to minerals due to the retention of highly sorptive organic molecules (primarily aromatic, nitrogen-poor, hydrogen-poor, and oxygen-rich molecules), which decreased the sorption site availability and simultaneously modified the mineral surface charge. Organic-organic interactions as postulated in multilayer models played a negligible role in MOM formation. Continued exchange between DOM and MOM molecules upon repeated sorption altered the DOM composition but not the MOM formation efficiencies. Sorption-induced depletion of high-affinity compounds from solutions further decreased the MOM formation efficiencies to pristine minerals. Overall, the interplay between the differential sorptivities of DOM components and the mineral surface chemistry explains the legacy effects that contribute to the regulation of fluxes and the distribution of organic matter in the soil.

Highly Fluorescent Carbon Dots as a Potential Fluorescence Probe for Selective Sensing of Ferric Ions in Aqueous Solution

This paper’s emphasis is on the development of a fluorescent chemosensor for Fe3+ ions in an aqueous solution, using hydrophilic carbon dots (O-CDs). A simple, cost-effective, and environmentally friendly one-step hydrothermal synthesis method was used to synthesize fluorescent hydrophilic O-CDs from Oxalis corniculata (Family; Oxalidaceae). The graphitic structure and size distribution of the O-CDs was verified by X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy studies. The resulting O-CDs had a near-spherical shape and an adequate degree of graphitization at the core, with an average diameter of 4.5 nm. X-ray photoelectron and Fourier transform infrared spectroscopy methods revealed the presence of several hydrophilic groups (carbonyl, amine, carboxyl, and hydroxyl, along with nitrogen and oxygen-rich molecules) on the surface of O-CDs. The synthesized hydrophilic O-CDs with excitation wavelength-dependent emission fluorescence characteristics showed a high quantum yield of about 20%. Besides this, the hydrophilic O-CDs exhibited a bright and controllable fluorescence with prolonged stability and photo-stability. These fluorescent hydrophilic O-CDs were used as a nanoprobe for the fluorometric identification of Fe3+ ions in an aqueous solution, with high sensitivity and selectivity. By quenching the blue emission fluorescence of this nanosensor, a highly sensitive Fe3+ ion in the range of 10–50 µM with a minimum detection limit of 0.73 µM was achieved. In addition, the developed nanosensor can be used to sense intracellular Fe3+ ions with high biocompatibility and cellular imaging capacity, and it has a lot of potential in biomedical applications.

The Stratified Distribution of Dissolved Organic Matter in an AMD Lake Revealed by Multi-sample Evaluation Procedure.

As a typical extreme environment, acid mine drainage (AMD) has been extensively studied for its biogeochemical cycle, but little is known about the quality of dissolved organic matter (DOM) in AMD. In this study, DOM molecules in an AMD lake were detected with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and the change of DOM molecules in the stratified water column was analyzed with a multi-sample evaluation procedure. The results demonstrate that DOM quality is highly stratified and can be linked with severe biogeochemical gradients. In the surface layer, DOM molecules can be distinguished by low quantities and intensities, as well as potential photodegradation products. Oxygen-poor and oxygen-rich molecules alternately dominate the chemocline, which can be explained by the redox-dependent adsorption/desorption of DOM on metastable secondary minerals. A rich and abundant DOM pool with a high proportion of heteroatoms exists at the bottom which can be significantly influenced by material exchange with sediments. These findings emphasize the active role of DOM in extreme AMD environments and expand the understanding of the carbon cycle in the hydrosphere.

Non-target and suspect screening strategies for electrodialytic soil remediation evaluation: Assessing changes in the molecular fingerprints and per- and polyfluoroalkyl substances (PFASs)

Contamination of soils with organic pollutants is an increasing global problem, so novel soil remediation techniques are urgently needed. One such technique is electrokinetic remediation, in which an electric field is applied over the soil to extract contaminants. Previous evaluations of the technique have been limited to a few specific compounds. In this study, we integrated the latest advances in high-resolution mass spectrometry (HRMS) to identify molecular fingerprints, and used the results to improve the mechanistic understanding necessary for successful remediation. A laboratory-scale 0.38 mA cm−2 electrodialytic treatment was applied for 21 days to a contaminated soil from a firefighter training facility in Sweden. Non-target analysis allowed generic evaluation of changes in the soil organic fraction by tentatively determining the elemental composition of compounds present. The results showed that smaller oxygen-rich molecules were significantly transported to the anode by electromigration, while larger hydrogen-saturated molecules were transported to the cathode by electroosmotic flow. Wide suspect screening with >3000 per- and polyfluoroalkyl substances (PFASs) tentatively identified seven new PFASs in the test soil, including perfluoroheptanesulfonic acid (PFHpS), and PFASs with butoxy, ethoxy, ethanol, and ethylcyclohexanesulfonate functional groups.

The Importance of Iron Testing for D3 Cross Country Runners

PURPOSE: Iron is an important mineral carried throughout the body, which helps carry oxygen rich molecules via hemoglobin. For endurance athletes, blood iron levels may be an important predictor of performance. Previous research has shown that iron absorption rates are lower in athletes in comparison to sedentary individuals. The purpose of the current investigation was twofold: first, to measure pre-season blood iron levels in division III collegiate cross country runners to determine if iron deficiency existed, and secondly, improve blood iron levels with a five week nutrition intervention for subjects classified as low. METHODS: Capillary puncture was utilized to measure blood iron levels during the week of pre-season practice in division III male (N=26) & female (N=20) cross country runners. Athletes were classified as low iron if the males were below 13.0mg/dL, and 12.0mg/dL for the females. If subjects were classified as low, they received a nutritional pamphlet as an intervention, and were retested five weeks later. RESULTS: The researchers classified 26.92% of males as iron deficient, and 5.00% of females as deficient. After retesting the deficient subjects, a paired t-test was utilized to determine if significant improvements in blood iron occurred following the five week intervention. A p-value of 0.002 (2-tail) was yielded showing a significant improvement in hemoglobin levels from preseason in comparison to 5 weeks following the intervention (12.28 +/- 1.09, 13.94 +/- 0.25 respectively). CONCLUSIONS: After a five week intervention, iron levels in those previously deficient, were significantly improved. Iron is a significant mineral for athletes, especially runners who are greatly dependent on oxygen for their performance. Thus, making sure cross country runners are educated on good nutritional habits, allowing them to maintain the said desirable blood iron levels is key to optimize their performance. Lastly, meeting the recommended guidelines for iron is vastly important, and educating athletes can result in a substantial improvement in blood iron levels.

Insight into visible light spectrum changes with increasing reflectance in bituminite and inertinite macerals

White Light Reflectance Spectrometry (WLRS) allows the wavelength dispersion of reflectance (Ro) values to be measured and recorded. Previous studies have extensively evaluated the wavelength dispersion of macerals in various coal ranks and types. This study examines the wavelength dispersion of recycled vitrinite and inertinite macerals as well as bituminite macerals in an immature oil shale with the objective of studying the variation in wavelength dispersion associated with changes in Ro due to bacterial degradation of bituminite macerals and recycling of vitrinite macerals.Four samples were measured from the thermally immature zone of the Upper Cretaceous Second White Specks Formation in Central Alberta. These samples were analyzed geochemically (using Rock-Eval) and petrographically for reflectance and using WLRS. Red/green wavelength reflectance ratios in bituminite macerals demonstrate a drop off in variation due to bacterial degradation at Ro of approximately 0.55%, which is close to the onset of maturity. This dropoff suggests that the transformation of the organic matter (OM) leading to the liberation of hydrogen and oxygen rich molecules not only increases Ro but also results in a shift in the R/G ratio of the measured maceral. Wavelength dispersion trends in recycled vitrinite/inertinite macerals follows similar trends to those observed previously in coals, with a gradual decrease in reflectance toward lower wavelengths.Results indicate that the wavelength dispersion trends of recycled vitrinite/inertinite macerals in an organic rich mud rock closely follow the trends previously observed in coals. Determination of unaltered macerals is a difficult but important step in characterizing the organic matter of the oil shale and in calculating its source rock potential. This study demonstrates that the WLRS method can be used in conjunction with Ro by observing the R/G variability dropoff in order to distinguish the best preserved primary OM population from OM that has been bacterially or thermally degraded or altered.

A Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA) study of oleate adsorbed on magnetite nano-particle surface

Magnetite nano-particles were coated with sodium oleate and the spectral behaviour of the coating layer was studied by FTIR spectroscopy after the particles had been heated in air and argon. Magnetite was synthesized by controlled co-precipitation and subsequently coated with sodium oleate. Thermal analysis in combination with mass spectroscopy was carried out to support the FTIR spectroscopic interpretations, but also to monitor the decomposition and surface reaction of oleate adsorbed on the magnetite surface. It was deduced from FTIR and TGA results that the oleate molecules are bonded to iron atoms by a bidentate mononuclear complex and form essentially a single layer with a distance between oleate molecules of ∼36 Å 2. It was shown by IR as well as Raman spectroscopy that oleic acid, when heated in air, undergoes decomposition implying that new carbon–oxygen bonds are formed. Heating the iron oxide–oleate system in air also implies oxidation of the double bond at the C:9 position of the alkyl chain and formation of intermediate oxygen-rich molecules. An enthalpy change of Δ H = 49.86 J/g was obtained for oleate desorption/decomposition at ∼350 °C under argon atmosphere and a carbonaceous graphitic species resulted from this decomposition.

Molecular characterization of dissolved organic matter (DOM) along a river to ocean transect of the lower Chesapeake Bay by ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

In this study, electrospray ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) is utilized to molecularly characterize DOM as it is transported along a river to estuary to ocean transect of the lower Chesapeake Bay system. The ultrahigh resolving power (greater than 500,000) and mass accuracy of FTICR-MS allow for the resolution of the thousands of components in a single DOM sample, and can therefore elucidate the molecular-level changes that occur during DOM transformation from a terrestrial location to the marine environment. An important feature of FTICR-MS is that its sensitivity allows for direct analysis of low salinity samples without employing the traditional concentration approaches involving C 18 extraction or ultrafiltration. To evaluate the advantages of using direct analysis, a C 18 extract of riverine water is compared to its whole, unfractionated water, and it was determined that the C 18 extraction is selective in that it eliminates two major series of compounds. One group is aliphatic amines/amides that are not adsorbed to the C 18 disk because they exist as positive ions prior to extraction. The second group is tannin-like compounds with higher oxygen contents and a more polar quality that also allow them not to be adsorbed to the C 18 disk. This direct approach could not be used for brackish/saline waters, so the C 18 method is resorted to for those samples. Along the subject transect, a significant difference is observed in the molecular composition of DOM, as determined from assigned molecular formulas. The DOM tends to become more aliphatic and contain lower abundances of oxygen-rich molecules as one progresses from inshore to the offshore. A considerable amount of molecular formula overlap does exist between samples from sites along the transect. This can be explained as either the presence of refractory material that persists throughout the transect, due to its resistance to degradation, or that the assigned molecular formulas are the same but the chemical structures are different. ESI-FTICR-MS is a powerful technique for the investigation of DOM and has the ability to detect compositional variations along the river to ocean transect. Visualization tools such as two dimensional and three dimensional van Krevelen diagrams greatly assist in highlighting the shift from the more aromatic, terrestrial DOM to the more aliphatic, marine DOM.

Kinematics and Chemistry of the Hot Molecular Core in G34.26+0.15 at High Resolution

(abridged) We present high angular resolution (~ 1") multi-tracer spectral line observations toward the hot core associated with G34.26+0.15 between 87--109 GHz. We have mapped emission from (i) complex nitrogen- and oxygen-rich molecules like CH3OH, HC3N, C2H5CN, NH2CHO, CH3OCH3, HCOOCH3; (ii) sulfur-bearing molecules like OCS, SO and SO2; and (iii) the recombination line H53 beta. The high angular resolution enables us to directly probe the hot molecular core associated with G34.26+0.15 at spatial scales of 0.018 pc. At this resolution we find no evidence for the hot core being internally heated. The continuum peak detected at lambda=2.8 mm is consistent with the free-free emission from component C of the ultracompact H II region. Velocity structure and morphology outlined by the different tracers suggest that the hot core is primarily energized by component C. Emission from the N- and O-bearing molecules peak at different positions within the innermost regions of the core; none is coincident with the continuum peak. Based on the brightness temperatures of optically thick lines in our sample, we estimate the kinetic temperature of the inner regions of the HMC to be 160+-30 K. Comparison of the observed abundances of the different species in G34.26+0.15 with existing models does not produce a consistent picture.

Biodegradable dissolved organic matter in a temperate and a tropical stream determined from ultra-high resolution mass spectrometry

We investigated dissolved organic matter (DOM) metabolism by employing plug-flow biofilm reactors and ultra‐ high resolution mass spectrometry of DOM isolated by C18 extraction in two forested stream ecosystems, a low DOM tropical stream sampled at baseflow and a higher DOM temperate stream sampled during a storm. On passage through the bioreactors, DOM concentrations in the tropical stream sample declined by 22%, whereas they declined by 42% in the temperate stream sample. The extracted DOM was subjected to electrospray ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry to obtain information on molecular weight distributions and elemental compositions for the thousands of compounds whose masses are calculated with sufficient accuracy to allow calculation of unique elemental formulas. In both streams, metabolism modifies DOM to lower molecular weight molecules, and oxygen-rich molecules are selectively biodegraded. Applying van Krevelen analyses for the unique elemental formulas of DOM constituents revealed that hydrogen-deficient molecules with low H : C ratios (assigned to black carbon‐derived molecules) are present and generally not metabolized. Black carbon molecules are refractory to biodegradation compared with other components of DOM, supporting the suggestion that black carbon molecules in DOM flow to the ocean without experiencing significant microbial degradation.

Production of oxygen by electronically induced dissociations in ice

A solid-state chemical model is given for the production of O2 by electronic excitation of ice, a process that occurs on icy bodies in the outer solar system. Based on a review of the relevant available laboratory data, we propose that a trapped oxygen atom-water complex is the principal precursor for the formation of molecular oxygen in low-temperature ice at low fluences. Oxygen formation then occurs through direct excitation of this complex or by its reaction with a freshly produced, nonthermal O from an another excitation event. We describe a model for the latter process that includes competition with precursor destruction and the effect of sample structure. This allows us to put the ultraviolet photon, low-energy electron, and fast-ion experiments on a common footing for the first time. The formation of the trapped oxygen atom precursor is favored by the preferential loss of molecular hydrogen and is quenched by reactions with mobile H. The presence of impurity scavengers can limit the trapping of O, leading to the formation of oxygen-rich molecules in ice. Rate equations that include these reactions are given and integrated to obtain an analytic approximation for describing the experimental results on the production and loss of molecular oxygen from ice samples. In the proposed model, the loss rate varies, roughly, inversely with solid-state defect density at low temperatures, leading to a yield that increases with increasing temperature as observed. Cross sections obtained from fits of the model to laboratory data are evaluated in light of the proposed solid-state chemistry.

Oxochromium(V) species formed with 2,3-dehydro-2-deoxy-N-acetylneuraminic or N-acetylneuraminic (sialic) acids: an in vitro model system of oxochromium(V) species potentially stabilized in the respiratory tract upon inhalation of carcinogenic chromium(VI) compounds.

The human respiratory tract is rich in sialoglycoconjugates. These polyfunctional, oxygen-rich molecules stabilize potentially genotoxic oxoCr(V) species, which has relevance to the metabolic fate of carcinogenic Cr(VI) compounds when inhaled as dusts, mists, and fumes during occupational exposure. A series of oxoCr(V) species formed from solutions of Cr(VI) and the reductant, glutathione (GSH), in the presence of an excess of small molecule ligands that model sialoglycoconjugates, either 2,3-dehydro-2-deoxy-N-acetylneuraminic acid (I) or N-acetylneuraminic acid (II), have been characterized as a function of pH value, using electron paramagnetic resonance (EPR) spectroscopy (Cr(V) = d(1)). Where [I] or [II] is in large excess of [Cr(V)-GSH], oxoCr(V)-I or -II species form (g(iso) = 1.97-1.98) via ligand-exchange reactions in which oxygen donor atoms from the carboxylic acid (I), tert-2-hydroxycarboxylato(2-) (II), and/or diolato(2-) groups (I, II) feature in the oxoCr(V) coordination sphere. At pH approximately 7.1 (where [Cr(V)-GSH]:[II] << 1), the oxoCr(V)-II complexes remain EPR active for 24 h (with t(1/2) approximately 380 min). The parent EPR spectrum from oxoCr(V)-I or -II solutions represents the sum of spectra from individual linkage isomers; using EPR spectral simulation procedures, coupled with empirical EPR spectroscopic data for previously characterized oxoCr(V)-hydroxycarboxylato and -diolato species, a signature EPR spectrum has been predicted for each oxoCr(V)-I or -II linkage isomer, with defining g(iso) and (1)H a(iso) values and signal multiplicities. At pH values > 7.0, the major EPR signal (g(iso) approximately 1.980) is a septet, indicating the presence of oxoCr(V)-I or oxoCr(V)-II species with coordination from two O(8),O(9)-diolato(2-) chelates, with six magnetically equivalent protons ((1)H a(iso) approximately 0.7 x 10(-)(4) cm(-)(1)). At pH values < 7.0, where carboxylato binding competes with diolato binding, the species (g(iso) approximately 1.979) most likely feature mixed binding modes from one diolato(2-) and one tert-2-hydroxycarboxylato(2-) chelate (oxoCr(V)-II) or one diolato(2-) chelate, one monodentate carboxylato(1-) group, and aqua and/or hydroxo oxygen donors (oxoCr(V)-I). In I and II, the relative concentration of the oxoCr(V) linkage isomer featuring donation via the O(7),O(8) diolato group is about 1 order of magnitude smaller than the concentration of the O(8),O(9) linkage isomer. The dominance of oxoCr(V)-I or -II linkage isomers with O(8),O(9) donation correlates with the dihedral angle in these isomers (O(9)-C(9)-C(8)-O(8) approximately 65 degrees ) being more favorably disposed toward metal binding, as compared to the O(7),O(8) analogue (O(7)-C(7)-C(8)-O(8) approximately 163 degrees ). These results have important implications with respect to the nature of the oxoCr(V) species that may potentially form in the sialoglycoconjugate-rich environment of the human respiratory tract upon inhalation of carcinogenic Cr(VI) compounds.

Hydrogen Trioxide Anion: A Possible Atmospheric Intermediate and Path to Oxygen-Rich Molecules

The structure of the HO3- anion has been studied theoretically using many theoretical methods. We found two metastable isomers for HO3-. The most stable isomer has a structure reminiscent to its neutral HOOO and cationic HOOO+ relatives. However, the central O−O bond in the anion was found to be unusually long (1.79 Å) compared to the same bond in the cation (1.40 Å) and in the neutral molecule (1.56 Å). Careful analysis reveals that the long O−O bond in the anion is a true chemical bond, but the bond order is only 0.75, which is the reason for its extreme length. We believe that the HO3- anion may play a role in atmospheric processes and its unusual long bond can expand our view of chemical bonding in oxygen-rich molecules.