Teaching and assessing undergraduate collaboration skills scaffolded through the biochemistry curriculum using collaboration rubrics and student learning contracts.

The Department of Chemistry and Biochemistry at St. Mary's College of Maryland has scaffolded collaboration skills throughout the Biochemistry curriculum and developed several assessment tools to evaluate these skills. Biochemistry I and II have used team contracts at the beginning of extensive team projects where students identify their strengths, review expectations, and plan for group communication.

Chemistry and Dynamics of Supercritical Carbon Dioxide and Methane in the Slit Pores of Layered Silicates.

ConspectusIn the mid 2010s, high-pressure diffraction and spectroscopic tools opened a window into the molecular-scale behavior of fluids under the conditions of many CO sequestration and shale/tight gas reservoirs, conditions where CO and CH are present as variably wet supercritical fluids. Integrating high-pressure spectroscopy and diffraction with molecular modeling has revealed much about the ways that supercritical CO and CH behave in reservoir components, particularly in the slit-shaped micro- and mesopores of layered silicates (phyllosilicates) abundant in caprocks and shales. This Account summarizes how supercritical CO and CH behave in the slit pores of swelling phyllosilicates as functions of the HO activity, framework structural features, and charge-balancing cation properties at 90 bar and 323 K, conditions similar to a reservoir at ∼1 km depth.

Interlayer Cation Polarizability Affects Supercritical Carbon Dioxide Adsorption by Swelling Clays.

Several strategies for mitigating the build-up of atmospheric carbon dioxide (CO) bring wet supercritical CO (scCO) in contact with phyllosilicates such as illites and smectites. While some work has examined the role of the charge-balancing cation and smectite framework features on CO/smectite interactions, to our knowledge no one has examined how the polarizability of the charge-balancing cation influences these behaviors. In this paper, the scCO adsorption properties of Pb, Rb, and NH saturated smectite clays at variable relative humidity are studied by integrating in situ high-pressure X-ray diffraction (XRD), infrared spectroscopic titrations, and magic angle spinning nuclear magnetic resonance (MAS NMR) methods.

A Mechanistic Exploration of Natural Organic Matter Aggregation and Surface Complexation in Smectite Mesopores.

Soil minerals and organic matter play critical roles in nutrient cycling and other life-essential biogeochemical processes, yet the structural and dynamical details of natural organic matter (NOM) film formation on smectites are not fully understood on the molecular scale. XRD of Suwannee River NOM-hectorite (a smectite clay) complexes shows that the humic and fulvic components of NOM bind predominantly at the external surfaces of packets of smectite platelets rather than in the interlayer slit pores, suggesting that the key behavior governing smectite-NOM interactions takes place in mesopores between smectite particles. New molecular dynamics modeling of a ∼110 Å HO-saturated smectite mesopore at near-neutral pH shows that model NOM molecules initially form small clusters of 2-3 NOM molecules near the center of the pore fluid.

Temperature dependent structure and dynamics in smectite interlayers: Na MAS NMR spectroscopy of Na-hectorite.

Na MAS NMR spectroscopy of the smectite mineral hectorite acquired at temperatures from -120 °C to 40 °C in combination with the results from computational molecular dynamics (MD) simulations show the presence of complex dynamical processes in the interlayer galleries that depend significantly on their hydration state. The results indicate that site exchange occurs within individual interlayers that contain coexisting 1 and 2 water layer hydrates in different places. We suggest that the observed dynamical averaging may be due to motion of water volumes comparable to the dripplons recently proposed to occur in hydrated graphene interlayers (Yoshida , 2018, , 1496).

Understanding methane/carbon dioxide partitioning in clay nano- and meso-pores with constant reservoir composition molecular dynamics modeling.

The interactions among fluid species such as H2O, CO2, and CH4 confined in nano- and meso-pores in shales and other rocks is of central concern to understanding the chemical behavior and transport properties of these species in the earth's subsurface and is of special concern to geological C-sequestration and enhanced production of oil and natural gas. The behavior of CO2, and CH4 is less well understood than that of H2O. This paper presents the results of a computational modeling study of the partitioning of CO2 and CH4 between bulk fluid and nano- and meso-pores bounded by the common clay mineral montmorillonite.

Tipping Point for Expansion of Layered Aluminosilicates in Weakly Polar Solvents: Supercritical CO.

Layered aluminosilicates play a dominant role in the mechanical and gas storage properties of the subsurface, are used in diverse industrial applications, and serve as model materials for understanding solvent-ion-support systems. Although expansion in the presence of HO is well-known to be systematically correlated with the hydration free energy of the interlayer cation, particularly in environments dominated by nonpolar solvents (i.e.

Molecular dynamics modeling of carbon dioxide, water and natural organic matter in Na-hectorite.

Molecular dynamics (MD) modeling of systems containing a Na-exchanged smectite clay (hectorite) and model natural organic matter (NOM) molecules along with pure H2O, pure CO2, or a mixture of H2O and CO2 provides significant new insight into the molecular scale interactions among silicate surfaces, dissolved cations and organic molecules, H2O and CO2 relevant to geological C-sequestration strategies. The simulations for systems containing H2O show the following results; (1) Na(+) does not bridge between NOM molecules and the clay surface at protonation states comparable to near neutral pH conditions. (2) In systems without CO2 the NOM molecules retain charge balancing cations and drift away from the silicate surface.

Cation exchange at the mineral-water interface: H3O+/K+ competition at the surface of nano-muscovite.

This article describes a (39)K nuclear magnetic resonance (NMR) spectroscopic study of K+ displacement at the muscovite/water interface as a function of aqueous phase pH. (39)K NMR spectra and T 2 relaxation data for nanocrystalline muscovite wet with a solid/solution weight ratio of 1 at pH 1, 3, and 5.5 show substantial liquid-like K+ only at pH 1.

High-field (75)As NMR study of arsenic oxysalts.

Arsenic is an important environmental hazard, but there have been few NMR investigations of its molecular scale structure and dynamics, due principally to the large quadrupole moment of (75)As and consequent large quadrupole couplings. We examine here the potential of existing, single-field solid-state NMR technology to investigate solids containing arsenate and arsenite oxyanions. The results show that current techniques have significant potential for arsenates that do not contain both protonated H(x)AsO4-(3-x) groups and structural water molecules, but that the quadrupole couplings for the arsenites examined here are large enough that interpretation of the spectra is difficult, even at 21.

NMR study of strontium binding by a micaceous mineral.

The nature of strontium binding by soil minerals directly affects the transport and sequestration/remediation of radioactive strontium species released from leaking high-level nuclear waste storage tanks. However, the molecular-level structure of strontium binding sites has seldom been explored in phyllosilicate minerals by direct spectroscopic means and is not well-understood. In this work, we use solid-state NMR to analyze strontium directly and indirectly in a fully strontium-exchanged synthetic mica of nominal composition Na(4)Mg(6)Al(4)Si(4)O(20)F(4).

High-field QCPMG NMR of strontium nuclei in natural minerals.

The only stable NMR-active isotope of strontium, (87)Sr, is a spin-9/2 quadrupolar nucleus that has a low gyromagnetic ratio, a low natural abundance, and a large nuclear electric quadrupole moment. In this work, we utilize the quadrupolar Carr-Purcell-Meiboom-Gill (QCPMG) pulse sequence and a 21.14 T NMR spectrometer at the Pacific Northwest National Laboratory to characterize the strontium sites in the natural minerals strontianite (SrCO(3)) and celestine (SrSO(4)).