A statistically validated protocol to identify "relevant" water molecules in protein binding sites using HINT score and a geometric descriptor termed Rank is described. In training, conservation/nonconservation was modeled for 86% of the waters. For the test set, 87% of waters were correctly classified (92% when crystallographic resolution was

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.

We explore a new in situ NMR spectroscopy method that possesses the ability to monitor the chemical evolution of supercritical CO(2) in relevant conditions for geological CO(2) sequestration. As a model, we use the fast reaction of the mineral brucite, Mg(OH)(2), with supercritical CO(2) (88 bar) in aqueous conditions at 80 °C. The in situ conversion of CO(2) into metastable and stable carbonates is observed throughout the reaction. After more than 58 h of reaction, the sample was depressurized and analyzed using in situ Raman spectroscopy, where the laser was focused on the undisturbed products through the glass reaction tube. Postreaction, ex situ analysis was performed on the extracted and dried products using Raman spectroscopy, powder X-ray diffraction, and magic-angle spinning (1)H-decoupled (13)C NMR. These separate methods of analysis confirmed a spatial dependence of products, possibly caused by a gradient of reactant availability, pH, and/or a reaction mechanism that involves first forming hydroxy-hydrated (basic, hydrated) carbonates that convert to the end-product, anhydrous magnesite. This carbonation reaction illustrates the importance of static (unmixed) reaction systems at sequestration-like conditions.

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.