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1.
Chemistry ; 29(5): e202203052, 2023 Jan 24.
Artículo en Inglés | MEDLINE | ID: mdl-36411247

RESUMEN

Nesquehonite is a magnesium carbonate mineral relevant to carbon sequestration envisioned for carbon capture and storage of CO2 . Its chemical formula remains controversial today, assigned as either a hydrated magnesium carbonate [MgCO3 ⋅ 3H2 O], or a hydroxy- hydrated- magnesium bicarbonate [Mg(HCO3 )OH ⋅ 2H2 O]. The resolution of this controversy is central to understanding this material's thermodynamic, phase, and chemical behavior. In an NMR crystallography study, using rotational-echo double-resonance 13 C{1 H} (REDOR), 13 C-1 H distances are determined with precision, and the combination of 13 C static NMR lineshapes and density functional theory (DFT) calculations are used to model different H atomic coordinates. [MgCO3 ⋅ 3H2 O] is found to be accurate, and evidence from neutron powder diffraction bolsters these assignments. Refined H positions can help understand how H-bonding stabilizes this structure against dehydration to MgCO3 . More broadly, these results illustrate the power of NMR crystallography as a technique for resolving questions where X-ray diffraction is inconclusive.


Asunto(s)
Magnesio , Difracción de Neutrones , Magnesio/química , Cristalografía , Minerales/química , Cristalografía por Rayos X
2.
Chemistry ; 28(54): e202201497, 2022 Sep 27.
Artículo en Inglés | MEDLINE | ID: mdl-35726630

RESUMEN

Organometallic molecules offer some of the most promising scaffolds for interaction with G-quadruplex nucleic acids. We report the efficient synthesis of a family of organoplatinum(II) complexes, featuring a 2-([2,2'-bipyridin]-6-yl)phenyl tridentate (N∧ N∧ C) ligand, that incorporates peripheral side-chains aiming at enhancing and diversifying its interaction capabilities. These include a di-isopropyl carbamoyl amide, a morpholine ethylenamide, two enantiomeric proline imides and an oxazole. The binding affinities of the Pt-complexes were evaluated via UV-vis and fluorescence titrations, against 5 topologically-distinct DNA structures, including c-myc G-quadruplex, two telomeric (22AG) G-quadruplexes, a duplex (ds26) and a single-stranded (polyT) DNA. All compounds exhibited binding selectivity in favour of c-myc, with association constants (Ka ) in the range of 2-5×105  M-1 , lower affinity for both folds of 22AG and for ds26 and negligible affinity for polyT. Remarkable emission enhancements (up to 200-fold) upon addition of excess DNA were demonstrated by a subset of the compounds with c-myc, providing a basis for optical selectivity, since optical response to all other tested DNAs was low. A c-myc DNA-melting experiment showed significant stabilizing abilities for all compounds, with the most potent binder, the morpholine-Pt-complex, exhibiting a ΔTm >30 °C, at 1 : 5 DNA-to-ligand molar ratio. The same study implied contributions of the diverse side-chains to helix stabilization. To gain direct evidence of the nature of the interactions, mixtures of c-myc with the four most promising compounds were studied via UV Resonance Raman (UVRR) spectroscopy, which revealed end-stacking binding mode, combined with interactions of side-chains with loop nucleobase residues. Docking simulations were conducted to provide insights into the binding modes for the same four Pt-compounds, suggesting that the binding preference for two alternative orientations of the c-myc G-quadruplex thymine 'cap' ('open' vs. 'closed'), as well as the relative contributions to affinity from end-stacking and H-bonding, are highly dependent on the nature of the interacting Pt-complex side-chain.


Asunto(s)
G-Cuádruplex , Fármacos Sensibilizantes a Radiaciones , Amidas , ADN/química , Genes myc , Imidas , Ligandos , Morfolinas , Oxazoles , Compuestos de Platino , Prolina , Proteínas Proto-Oncogénicas c-myc/química , Proteínas Proto-Oncogénicas c-myc/genética , Timina
3.
J Phys Chem A ; 125(45): 9802-9818, 2021 Nov 18.
Artículo en Inglés | MEDLINE | ID: mdl-34748350

RESUMEN

An extensive correlated molecular orbital theory study of the reactions of CO2 with a range of substituted amines and H2O in the gas phase and aqueous solution was performed at the G3(MP2) level with a self-consistent reaction field approach. The G3(MP2) calculations were benchmarked at the CCSD(T)/CBS level for NH3 reactions. A catalytic NH3 reduces the energy barrier more than a catalytic H2O for the formation of H2NCOOH and H2CO3. In aqueous solution, the barriers to form both H2NCOOH and H2CO3 are reduced, with HCO3- formation possible with one amine present and H2NCOO- formation possible only with two amines. Further reactions of H2NCOOH to form HNCO and urea via the Bazarov reaction have high barriers and are unlikely in both the gas phase and aqueous solution. Reaction coordinates for CH3NH2, CH3CH2NH2, (CH3)2NH, CH3CH2CH2NH2, (CH3)3N, and DMAP were also calculated. The barrier for proton transfer correlates with amine basicity for alkylammonium carbamate (ΔG‡aq < 15 kcal/mol) and alkylammonium bicarbonate (ΔG‡aq < 30 kcal/mol) formation. In aqueous solution, carbamic acids, carbamates, and bicarbonates can all form in small amounts with ammonium carbamates dominating for primary and secondary alkylamines. These results have implications for CO2 capture by amines in both the gas phase and aqueous solution as well as in the solid state, if enough water is present.

4.
Mol Ecol ; 29(24): 4970-4984, 2020 12.
Artículo en Inglés | MEDLINE | ID: mdl-33058329

RESUMEN

It has long been of interest to identify the phenotypic traits that mediate reproductive isolation between related species, and more recently, the genes that underpin them. Much work has focused on identifying genes associated with animal colour, with the candidate gene CYP2J19 identified in laboratory studies as the ketolase converting yellow dietary carotenoids to red ketocarotenoids in birds with red pigments. However, evidence that CYP2J19 explains variation between red and yellow feather coloration in wild populations of birds is lacking. Hybrid zones provide the opportunity to identify genes associated with specific traits. Here we investigate genomic regions associated with colour in red-fronted and yellow-fronted tinkerbirds across a hybrid zone in southern Africa. We sampled 85 individuals, measuring spectral reflectance of forecrown feathers and scoring colours from photographs, while testing for carotenoid presence with Raman spectroscopy. We performed a genome-wide association study to identify associations with carotenoid-based coloration, using double-digest RAD sequencing aligned to a short-read whole genome of a Pogoniulus tinkerbird. Admixture mapping using 104,933 single nucleotide polymorphisms (SNPs) identified a region of chromosome 8 that includes CYP2J19 as the only locus with more than two SNPs significantly associated with both crown hue and crown score, while Raman spectra provided evidence of ketocarotenoids in red feathers. Asymmetric backcrossing in the hybrid zone suggests that yellow-fronted females mate more often with red-fronted males than vice versa. Female red-fronted tinkerbirds mating assortatively with red-crowned males is consistent with the hypothesis that converted carotenoids are an honest signal of quality.


Asunto(s)
Carotenoides , Estudio de Asociación del Genoma Completo , África Austral , Animales , Aves/genética , Color , Femenino , Masculino , Pigmentación/genética
5.
Phys Chem Chem Phys ; 21(33): 18300-18309, 2019 Aug 21.
Artículo en Inglés | MEDLINE | ID: mdl-31396614

RESUMEN

Perylene bisimides (PBIs) are dyes known for combining high absorption and emission in the visible region with thermal and photochemical stability. H-bond-directed aggregation driven by free imide groups has been reported to promote the uncommon J-type aggregate formation of PBIs. J-aggregates are highly desired thanks to their bathochromically shifted narrow absorption and fluorescence due to excitonic coupling, together with hyperchromicity and superradiance compared to the monomer. Herein we present the water soluble MEG-PBI showing interesting aggregation in water and in the solid state. Unlike its hydrophobic counterparts, MEG-PBI aggregates in water with increasing temperature, indicating entropy-driven self-assembly. Temperature-dependent Resonance Raman (RR) spectroscopy was employed for the structural characterization of MEG-PBI in aqueous solution versus toluene and in aggregated thin films, employing excitation at different wavelengths to probe the contribution of various chromophores to the supramolecular structure of the aggregate. We find that the perylene core distorts upon aggregation, where the bonds along the perylene long N-N axis lengthen and the ones perpendicular to that shorten, suggesting a head-to-tail arrangement due to H-bonding between neighboring units.

6.
Angew Chem Int Ed Engl ; 58(13): 4210-4216, 2019 Mar 22.
Artículo en Inglés | MEDLINE | ID: mdl-30672073

RESUMEN

Solid-state NMR measurements coupled with density functional theory (DFT) calculations demonstrate how hydrogen positions can be refined in a crystalline system. The precision afforded by rotational-echo double-resonance (REDOR) NMR to interrogate 13 C-1 H distances is exploited along with DFT determinations of the 13 C tensor of carbonates (CO3 2- ). Nearby 1 H nuclei perturb the axial symmetry of the carbonate sites in the hydrated carbonate mineral, hydromagnesite [4 MgCO3 ⋅Mg(OH)2 ⋅4 H2 O]. A match between the calculated structure and solid-state NMR was found by testing multiple semi-local and dispersion-corrected DFT functionals and applying them to optimize atom positions, starting from X-ray diffraction (XRD)-determined atomic coordinates. This was validated by comparing calculated to experimental 13 C{1 H} REDOR and 13 C chemical shift anisotropy (CSA) tensor values. The results show that the combination of solid-state NMR, XRD, and DFT can improve structure refinement for hydrated materials.

7.
J Am Chem Soc ; 140(29): 9148-9153, 2018 07 25.
Artículo en Inglés | MEDLINE | ID: mdl-29920076

RESUMEN

The conventional synthesis of metal-organic frameworks (MOFs) through soluble metal-salt precursors provides little control over the growth of MOF crystals. The use of alternative metal precursors would provide a more flexible and cost-effective strategy for direction- and shape-controlled MOF synthesis. Here, we demonstrate for the first time the use of insoluble metal-carbon matrices to foster directed growth of MOFs. Aluminum carbide was implemented as both the metal precursor and growth-directing agent for the generation of MIL-53(Al). A unique needle-like morphology of the MOF was grown parallel to the bulk surface in a layer-by-layer manner. Importantly, the synthesis scheme was found to be transferrable to the production of different linker analogues of the MOF and other topologies. Given the variety of metal carbides available, these findings can be used as a blueprint for controlled, efficient, and economical MOF syntheses and set a new milestone toward the industrial use of MOFs at large-scale.

8.
J Am Chem Soc ; 140(28): 8648-8651, 2018 07 18.
Artículo en Inglés | MEDLINE | ID: mdl-29947515

RESUMEN

We have identified a hydrated bicarbonate formed by chemisorption of 13CO2 on both dimethylaminopropylsilane (DMAPS) and aminopropylsilane (APS) pendant molecules grafted on SBA-15 mesoporous silica. The most commonly used sequence in solid-state NMR, 13C CPMAS, failed to detect bicarbonate in these solid amine sorbent samples; here, we have employed a Bloch decay ("pulse-acquire") sequence (with 1H decoupling) to detect such species. The water that is present contributes to the dynamic motion of the bicarbonate product, thwarting CPMAS but enabling direct 13C detection by shortening the spin-lattice relaxation time. Since solid-state NMR plays a major role in characterizing chemisorption reactions, these new insights that allow for the routine detection of previously elusive bicarbonate species (which are also challenging to observe in IR spectroscopy) represent an important advance. We note that employing this straightforward NMR technique can reveal the presence of bicarbonate that has often otherwise been overlooked, as demonstrated in APS, that has been thought to only contain adsorbed CO2 as carbamate and carbamic acid species. As in other systems (e.g., proteins), dynamic species that sample multiple environments tend to broaden as their motion is frozen out. Here, we show two distinct bicarbonate species upon freezing, and coupling to different protons is shown through preliminary 13C-1H HETCOR measurements. This work demonstrates that bicarbonates have likely been formed in the presence of water but have gone unobserved by NMR due to the nature of the experiments most routinely employed, a perspective that will transform the way the sorption community will view CO2 capture by amines.


Asunto(s)
Aminas/química , Bicarbonatos/análisis , Dióxido de Carbono/química , Silanos/química , Dióxido de Silicio/química , Adsorción , Espectroscopía de Resonancia Magnética , Metilación , Modelos Moleculares , Agua/química
9.
Langmuir ; 34(41): 12279-12292, 2018 10 16.
Artículo en Inglés | MEDLINE | ID: mdl-30244578

RESUMEN

Most studies exploring the capture of CO2 on solid-supported amines have focused on unhindered amines or alkylimine polymers. It has been observed in extensive solution studies that another class of amines, namely sterically hindered amines, can exhibit enhanced CO2 capacity when compared to their unhindered counterparts. In contrast to solution studies, there has been limited research conducted on sterically hindered amines on solid supports. In this work, one hindered primary amine and two hindered secondary amines are grafted onto mesoporous silica at similar amine coverages, and their adsorption performances are investigated through fixed bed breakthrough experiments and thermogravimetric analysis. Furthermore, chemisorbed CO2 species formed on the sorbents under dry and humid conditions are elucidated using in situ Fourier-transform infrared spectroscopy. Ammonium bicarbonate formation and enhancement of CO2 adsorption capacity is observed for all supported hindered amines under humid conditions. Our experiments in this study also suggest that chemisorbed CO2 species formed on supported hindered amines are weakly bound, which may lead to reduced energy costs associated with regeneration if such materials were deployed in a practical separation process. However, overall CO2 uptake capacities of the solid supported hindered amines are modest compared to their solution counterparts. The oxidative and thermal stabilities of the supported hindered amine sorbents are also assessed to give insight into their operational lifetimes.

10.
Environ Sci Technol ; 52(3): 1488-1495, 2018 02 06.
Artículo en Inglés | MEDLINE | ID: mdl-29257887

RESUMEN

Materials composed of high-porosity solid supports, such as SBA-15, containing amine-bearing moieties inside the pores, such as 3-aminopropylsilane (APS), are envisioned for carbon dioxide capture; solid-state 15N NMR can be highly informative for studying chemisorption reactions. Two 15N-enriched samples with different APS loadings were studied to probe the identity of the pendant molecules and structure of the chemisorbed CO2 species. 15N cross-polarization magic-angle spinning NMR provides unique information about the amines, whether they are rigid or dynamic, by measuring contact time curves and rotating frame, T1ρ(15N), relaxation. Both carbamate and carbamic acid are formed; carbamic acid is shown to be less stable than carbamate. After desorption, a steady state for the chemisorbed reaction product is reached, leaving behind carbamate. 15N NMR monitors the evolution of the species over time. During desorption, APS is regenerated, but the ammonium propylsilane intensity does not change, leading us to conclude that carbamic acid desorbs, while carbamate (to which ammonium propylsilane is ion paired) persists. A secondary ditehtered amine present does not react with CO2, and we posit this may be due to its rigidity. These findings demonstrate the versatility of solid-state NMR to provide information about these complex CO2 reactions with solid amine sorbents.


Asunto(s)
Carbono , Dióxido de Silicio , Adsorción , Aminas , Dióxido de Carbono
11.
J Am Chem Soc ; 139(11): 3930-3933, 2017 03 22.
Artículo en Inglés | MEDLINE | ID: mdl-28256125

RESUMEN

We have measured the 75As signals arising from the interface region of single-crystal semi-insulating GaAs that has been coated and passivated with an aluminum oxide film deposited by atomic layer deposition (ALD) with optically pumped NMR (OPNMR). Using wavelength-selective optical pumping, the laser restricts the volume from which OPNMR signals are collected. Here, OPNMR signals were obtained from the interface region and distinguished from signals arising from the bulk. The interface region is highlighted by interactions that disrupt the cubic symmetry of the GaAs lattice, resulting in quadrupolar satellites for nuclear [Formula: see text] isotopes, whereas NMR of the "bulk" lattice is nominally unsplit. Quadrupolar splitting at the interface arises from strain based on lattice mismatch between the GaAs and ALD-deposited aluminum oxide due to their different coefficients of thermal expansion. Such spectroscopic evidence of strain can be useful for measuring lattice distortions at heterojunction boundaries and interfaces.

12.
Nat Mater ; 15(7): 746-53, 2016 07.
Artículo en Inglés | MEDLINE | ID: mdl-27183327

RESUMEN

The specific optical absorption of an organic semiconductor is critical to the performance of organic optoelectronic devices. For example, higher light-harvesting efficiency can lead to higher photocurrent in solar cells that are limited by sub-optimal electrical transport. Here, we compare over 40 conjugated polymers, and find that many different chemical structures share an apparent maximum in their extinction coefficients. However, a diketopyrrolopyrrole-thienothiophene copolymer shows remarkably high optical absorption at relatively low photon energies. By investigating its backbone structure and conformation with measurements and quantum chemical calculations, we find that the high optical absorption can be explained by the high persistence length of the polymer. Accordingly, we demonstrate high absorption in other polymers with high theoretical persistence length. Visible light harvesting may be enhanced in other conjugated polymers through judicious design of the structure.

13.
Environ Sci Technol ; 51(11): 6553-6559, 2017 Jun 06.
Artículo en Inglés | MEDLINE | ID: mdl-28460168

RESUMEN

Multiple chemisorption products are found from the interaction of CO2 with the solid-amine sorbent, 3-aminopropyl silane (APS), bound to mesoporous silica (SBA15) using solid-state NMR and FTIR spectroscopy. We employed a combination of both 15N{13C} rotational-echo double-resonance (REDOR) NMR and 13C{15N} REDOR to determine the chemical identity of these products. 15N{13C} REDOR measurements are consistent with a single 13C-15N pair and distance of 1.45 Å. In contrast, both 13C{15N} REDOR and 13C CPMAS are consistent with multiple 13C products. 13C CPMAS shows two neighboring resonances, whose chemical shifts are consistent with carbamate (at 165 ppm) and carbamic acid. The 13C{15N} REDOR experiments resonant at 165 ppm show an incomplete buildup of the REDOR data to ∼90% of the expected maximum. We conclude this 10% missing intensity corresponds to a 13C NMR species that resonates at the identical chemical shift but that is not in dipolar contact with 15N. These data are consistent with the presence of bicarbonate, HCO3-, since it is commonly observed at ∼165 ppm and lacks 15N for dipolar coupling.


Asunto(s)
Dióxido de Carbono , Dióxido de Silicio , Imagen por Resonancia Magnética , Espectroscopía de Resonancia Magnética
14.
Phys Chem Chem Phys ; 19(42): 28853-28866, 2017 Nov 01.
Artículo en Inglés | MEDLINE | ID: mdl-29057414

RESUMEN

We report here the photophysical properties of a water-soluble conjugated polythiophene with cationic side-chains. When dissolved in aqueous buffer solution (PBS, phosphate buffered saline), there is ordering of the polymer chains due to the presence of the salts, in contrast to pure water, where a random-coil conformation is adopted at room temperature. The ordering leads to a pronounced colour change of the solution (the absorption maximum shifts from 400 nm to 525 nm). Combining resonance Raman spectroscopy with density functional theory computations, we show a significant backbone planarization in the ordered phase. Moreover, the ratio of ordered phase to random-coil phase in PBS solution, as well as the extent of intermolecular interactions in the ordered phase, can be tuned by varying the temperature. Femtosecond transient absorption spectroscopy reveals that the excited-state behaviour of the polyelectrolyte is strongly affected by the degree of ordering. While triplet state formation is favoured in the random-coil chains, the ordered chains show a weak yield of polarons, related to interchain interactions. The investigated polyelectrolyte has been previously used as a biological DNA sensor, based on optical transduction when the conformation of the polyelectrolyte changes during assembly with the biomolecule. Therefore, our results, by correlating the photophysical properties of the polyelectrolyte to backbone and intermolecular conformation in a biologically relevant buffer, provide a significant step forward in understanding the mechanism of the biological sensing.

15.
Environ Sci Technol ; 49(3): 1631-8, 2015 Feb 03.
Artículo en Inglés | MEDLINE | ID: mdl-25588145

RESUMEN

We have developed an approach for determining pH at elevated pressures and temperatures by using (13)C NMR measurements of inorganic carbon species together with a geochemical equilibrium model. The approach can determine in situ pH with precision better than 0.1 pH units at pressures, temperatures, and ionic strengths typical of geologic carbon sequestration systems. A custom-built high pressure NMR probe was used to collect (13)C NMR spectra of (13)C-labeled CO2 reactions with NaOH solutions and Mg(OH)2 suspensions at pressures up to 107 bar and temperatures of 80 °C. The quantitative nature of NMR spectroscopy allows the concentration ratio [CO2]/[HCO3(-)] to be experimentally determined. This ratio is then used with equilibrium constants calculated for the specific pressure and temperature conditions and appropriate activity coefficients for the solutes to calculate the in situ pH. The experimentally determined [CO2]/[HCO3(-)] ratios agree well with the predicted values for experiments performed with three different concentrations of NaOH and equilibration with multiple pressures of CO2. The approach was then applied to experiments with Mg(OH)2 slurries in which the change in pH could track the dissolution of CO2 into solution, rapid initial Mg(OH)2 dissolution, and onset of magnesium carbonate precipitation.


Asunto(s)
Espectroscopía de Resonancia Magnética con Carbono-13/métodos , Dióxido de Carbono/química , Secuestro de Carbono , Geología/métodos , Concentración de Iones de Hidrógeno , Magnesio/química , Presión , Temperatura
16.
Environ Sci Technol ; 49(22): 13684-91, 2015 Nov 17.
Artículo en Inglés | MEDLINE | ID: mdl-26477882

RESUMEN

Hyperbranched amine polymers (HAS) grown from the mesoporous silica SBA-15 (hereafter "SBA-15-HAS") exhibit large capacities for CO2 adsorption. We have used static in situ and magic-angle spinning (MAS) ex situ (13)C nuclear magnetic resonance (NMR) to examine the adsorption of CO2 by SBA-15-HAS. (13)C NMR distinguishes the signal of gas-phase (13)CO2 from that of the chemisorbed species. HAS polymers possess primary, secondary, and tertiary amines, leading to multiple chemisorption reaction outcomes, including carbamate (RnNCOO(-)), carbamic acid (RnNCOOH), and bicarbonate (HCO3(-)) moieties. Carbamates and bicarbonate fall within a small (13)C chemical shift range (162-166 ppm), and a mixture was observed including carbamic acid and carbamate, the former disappearing upon evacuation of the sample. By examining the (13)C-(14)N dipolar coupling through low-field (B0 = 3 T) (13)C{(1)H} cross-polarization MAS NMR, carbamate is confirmed through splitting of the (13)C resonance. A third species that is either bicarbonate or a second carbamate is evident from bimodal T2 decay times of the ∼163 ppm peak, indicating the presence of two species comprising that single resonance. The mixture of products suggests that (1) the presence of amines and water leads to bicarbonate being present and/or (2) the multiple types of amine sites in HAS permit formation of chemically distinct carbamates.


Asunto(s)
Dióxido de Carbono/química , Espectroscopía de Resonancia Magnética/métodos , Polímeros/química , Adsorción , Aminas/química , Carbamatos/química , Isótopos de Carbono , Dióxido de Silicio , Agua/química
17.
Environ Sci Technol ; 49(1): 657-64, 2015 Jan 06.
Artículo en Inglés | MEDLINE | ID: mdl-25437754

RESUMEN

In the conversion of CO2 to mineral carbonates for the permanent geosequestration of CO2, there are multiple magnesium carbonate phases that are potential reaction products. Solid-state (13)C NMR is demonstrated as an effective tool for distinguishing magnesium carbonate phases and quantitatively characterizing magnesium carbonate mixtures. Several of these mineral phases include magnesite, hydromagnesite, dypingite, and nesquehonite, which differ in composition by the number of waters of hydration or the number of crystallographic hydroxyl groups. These carbonates often form in mixtures with nearly overlapping (13)C NMR resonances which makes their identification and analysis difficult. In this study, these phases have been investigated with solid-state (13)C NMR spectroscopy, including both static and magic-angle spinning (MAS) experiments. Static spectra yield chemical shift anisotropy (CSA) lineshapes that are indicative of the site-symmetry variations of the carbon environments. MAS spectra yield isotropic chemical shifts for each crystallographically inequivalent carbon and spin-lattice relaxation times, T1, yield characteristic information that assist in species discrimination. These detailed parameters, and the combination of static and MAS analyses, can aid investigations of mixed carbonates by (13)C NMR.


Asunto(s)
Espectroscopía de Resonancia Magnética con Carbono-13 , Magnesio/análisis , Minerales/análisis , Anisotropía , Protones , Factores de Tiempo
18.
Environ Sci Technol ; 48(24): 14344-51, 2014 Dec 16.
Artículo en Inglés | MEDLINE | ID: mdl-25420634

RESUMEN

Reactions of CO2 with magnesium silicate minerals to precipitate magnesium carbonates can result in stable carbon sequestration. This process can be employed in ex situ reactors or during geologic carbon sequestration in magnesium-rich formations. The reaction of aqueous CO2 with the magnesium silicate mineral forsterite was studied in systems with transport controlled by diffusion. The approach integrated bench-scale experiments, an in situ spectroscopic technique, and reactive transport modeling. Experiments were performed using a tube packed with forsterite and open at one end to a CO2-rich solution. The location and amounts of carbonate minerals that formed were determined by postexperiment characterization of the solids. Complementing this ex situ characterization, (13)C NMR spectroscopy tracked the inorganic carbon transport and speciation in situ. The data were compared with the output of reactive transport simulations that accounted for diffusive transport processes, aqueous speciation, and the forsterite dissolution rate. All three approaches found that the onset of magnesium carbonate precipitation was spatially localized about 1 cm from the opening of the forsterite bed. Magnesite was the dominant reaction product. Geochemical gradients that developed in the diffusion-limited zones led to locally supersaturated conditions at specific locations even while the volume-averaged properties of the system remained undersaturated.


Asunto(s)
Dióxido de Carbono/química , Silicatos de Magnesio/química , Magnesio/química , Compuestos de Silicona/química , Secuestro de Carbono , Carbonatos/química , Precipitación Química , Difusión , Presión , Temperatura , Agua/química
19.
J Chem Phys ; 140(1): 014301, 2014 Jan 07.
Artículo en Inglés | MEDLINE | ID: mdl-24410223

RESUMEN

A detailed analysis of the resonance Raman depolarization ratio dispersion curve for the N-O symmetric stretch of nitryl chloride in methanol at excitation wavelengths spanning the D absorption band is presented. The depolarization ratios are modeled using the time-dependent formalism for Raman scattering with contributions from two excited states (2(1)A1 and 3(1)B1), which are taken as linearly dissociative along the Cl-N coordinate. The analysis focuses on the interplay between different types of broadening revealing the importance of inhomogenous broadening in determining the relative contributions of the two electronic transitions. We find that the transition dipole moment (M) for 2(1)A1 is greater than for 3(1)B1, in agreement with gas phase calculations in the literature [A. Lesar, M. Hdoscek, M. Muhlhauser, and S. D. Peyerimhoff, Chem. Phys. Lett. 383, 84 (2004)]. However, we find that the polarity of the solvent influences the excited state energetics, leading to a reversal in the ordering of these two states with 3(1)B1 shifting to lower energies. Molecular dynamics simulations along with linear response and ab initio calculations support the evidence extracted from resonance Raman intensity analysis, providing insights on ClNO2 electronic structure, solvation effects in methanol, and the source of broadening, emphasizing the importance of a contribution from inhomogeneous linewidth.

20.
JAMA Netw Open ; 7(2): e2356121, 2024 Feb 05.
Artículo en Inglés | MEDLINE | ID: mdl-38358740

RESUMEN

Importance: Publicly available, US Census-based composite measures of socioeconomic disadvantage are increasingly being used in a wide range of clinical outcomes and health services research. Area Deprivation Index (ADI) and Social Vulnerability Index (SVI) are 2 of the most commonly used measures. There is also early interest in incorporating area-level measures to create more equitable alternative payment models. Objective: To review the evidence on the association of ADI and SVI with health care spending, including claims-based spending and patient-reported barriers to care due to cost. Evidence Review: A systematic search for English-language articles and abstracts was performed in the PubMed, Web of Science, Embase, and Cochrane databases (from inception to March 1, 2023). Peer-reviewed articles and abstracts using a cross-sectional, case-control, or cohort study design and based in the US were identified. Data analysis was performed in March 2023. Findings: This review included 24 articles and abstracts that used a cross-sectional, case-control, or cohort study design. In 20 of 24 studies (83%), ADI and SVI were associated with increased health care spending. No association was observed in the 4 remaining studies, mostly with smaller sample sizes from single centers. In adjusted models, the increase in spending associated with higher ADI or SVI residence was $574 to $1811 for index surgical hospitalizations, $3003 to $24 075 for 30- and 90-day episodes of care, and $3519 for total annual spending for Medicare beneficiaries. In the studies that explored mechanisms, postoperative complications, readmission risk, and poor primary care access emerged as health care system-related drivers of increased spending. Conclusions and Relevance: The findings of this systematic review suggest that both ADI and SVI can play important roles in efforts to understand drivers of health care spending and in the design of payment and care delivery programs that capture aspects of social risk. At the health care system level, higher health care spending and poor care access associated with ADI or SVI may represent opportunities to codesign interventions with patients from high ADI or SVI areas to improve access to high-value health care and health promotion more broadly.


Asunto(s)
Gastos en Salud , Medicare , Estados Unidos , Humanos , Anciano , Estudios de Cohortes , Estudios Transversales , Disparidades Socioeconómicas en Salud
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