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. The calculations were done at 323 K and a total fluid pressure of 124 bars using a novel approach (constant reservoir composition molecular dynamics, CRC-MD) that uses bias forces to maintain a constant composition in the fluid external to the pore. This purely MD approach overcomes the difficulties in making stochastic particle insertion-deletion moves in dense fluids encountered in grand canonical Monte Carlo and related hybrid approaches. The results show that both the basal siloxane surfaces and protonated broken edge surfaces of montmorillonite both prefer CO2 relative to CH4 suggesting that methods of enhanced oil and gas production using CO2 will readily displace CH4 from such pores. This preference for CO2 is due to its preferred interaction with the surfaces and extends to approximately 20 Å from them.

Water dynamics in hydrated amorphous materials: a molecular dynamics study of the effects of dehydration in amorphous calcium carbonate.

Amorphous calcium carbonate (ACC) is often a critical transient phase in the formation of crystalline phases of CaCO3via dehydration of hydrated ACC. The behavior of the water molecules plays a pivotal role in this transformation. We report here the dynamics of water molecules in ACC at hydration levels from CaCO3·1H2O to CaCO3·0.25H2O using molecular dynamics (MD) simulations. Due to the presence of highly hydrophilic Ca2+ and the strong H-bond acceptor CO32-, most of the water molecules in our simulations have restricted translational and orientational dynamics. These are referred here as 'slow water'. However, a small fraction of them show high diffusivity at all hydration states and are referred here as 'fast water'. The computed diffusion coefficients of the slow waters, as extrapolated from simulation results, yield diffusion distances of the order of µm on the 1 hour time scale, consistent with rapid dehydration of ACC nano-particles in the laboratory. We correlate our fast waters with the water molecules in the percolating water-rich, Ca2+-deficient nano-pores in the structure of Goodwin et al. [Chem. Mater., 2010, 22, 3197], obtained by analysis of X-ray scattering data, and our slow waters with those in the Ca2+-rich volumes with less water in their model. The fast waters can be considered to be free rotors on the ns time scale and have orders of magnitude shorter rotational relaxation times than the slow waters.

Childhood intelligence is heritable, highly polygenic and associated with FNBP1L.

Intelligence in childhood, as measured by psychometric cognitive tests, is a strong predictor of many important life outcomes, including educational attainment, income, health and lifespan. Results from twin, family and adoption studies are consistent with general intelligence being highly heritable and genetically stable throughout the life course. No robustly associated genetic loci or variants for childhood intelligence have been reported. Here, we report the first genome-wide association study (GWAS) on childhood intelligence (age range 6-18 years) from 17,989 individuals in six discovery and three replication samples. Although no individual single-nucleotide polymorphisms (SNPs) were detected with genome-wide significance, we show that the aggregate effects of common SNPs explain 22-46% of phenotypic variation in childhood intelligence in the three largest cohorts (P=3.9 × 10(-15), 0.014 and 0.028). FNBP1L, previously reported to be the most significantly associated gene for adult intelligence, was also significantly associated with childhood intelligence (P=0.003). Polygenic prediction analyses resulted in a significant correlation between predictor and outcome in all replication cohorts. The proportion of childhood intelligence explained by the predictor reached 1.2% (P=6 × 10(-5)), 3.5% (P=10(-3)) and 0.5% (P=6 × 10(-5)) in three independent validation cohorts. Given the sample sizes, these genetic prediction results are consistent with expectations if the genetic architecture of childhood intelligence is like that of body mass index or height. Our study provides molecular support for the heritability and polygenic nature of childhood intelligence. Larger sample sizes will be required to detect individual variants with genome-wide significance.

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. (3) In systems containing both H2O and CO2, the NOM molecules adopt equilibrium positions at the H2O-CO2 interface with the more hydrophilic structural elements facing the H2O and the more hydrophobic ones facing the CO2. In systems with only CO2, NOM and Na(+) ions are pinned to the clay surface with the hydrophilic structural elements of the NOM pointed toward the clay surface. Dynamically, in systems with only CO2, Na(+) diffusion is nearly eliminated, and in systems with a thin water film on the clay surface diffusion perpendicular the surface is greatly reduced relative to the system with bulk water. Energetically, the results for the systems with only H2O show that hydration of the net charge neutral Na-NOM molecule outweighs the sum of its Coulombic and dispersive interactions with the net charge-neutral Na-clay particle and the interactions of the water molecules with the hydrophobic structural elements of the NOM. The aggregation of NOM molecules in solution appears to be driven not by Na(+) bridging between the molecules but by hydrophobic interactions between them. In contrast, for the systems with only CO2 the interaction between the Na-NOM molecules and the CO2 is outweighed by the interaction of NOM with the clay particle. With both H2O and CO2 present, the energetic interactions leading to the hydration of the Na-clay surface and the hydrophilic structural elements of the Na-NOM molecule and the hydrophobic interactions between the CO2 and the hydrophobic aromatic and aliphatic structural elements of the NOM can both be satisfied, leading to the Na-NOM molecules migrating away from the surface and residing at the H2O-CO2 interface. The MD results suggest some alternative explanations for the previously observed (23)Na NMR behavior of Na-hectorite at elevated temperatures and CO2 pressures.

Ab initio and metadynamics studies on the role of essential functional groups in biomineralization of calcium carbonate and environmental situations.

The interactions of proteins, polysaccharides and other biomolecules with Ca(2+), CO3(2-), and water are central to the understanding of biomineralization and crystallization of calcium carbonate (CaCO3), and their association with the natural organic matter (NOM) in the environment. A molecular-level investigation of how such interactions and thermodynamic forces drive the nucleation and growth of crystalline CaCO3 in living organisms remains elusive. This paper presents ab initio and metadynamics studies of the interactions of Ca(2+), CO3(2-), and water with the essential amino acids/functional groups, e.g. arginine/NH2(+), aspartate or glutamate/COO(-), aspartic or glutamic acid/COOH, and serine/OH, of protein/organic molecules that are likely to be critical to the biomineralization of CaCO3. These functional groups were modeled as guanidinium (Gdm(+)), acetate (AcO(-)), acetic acid (AcOH), and ethanol (EtOH) molecules, respectively. The Gdm(+)-Ca(2+)-CO3(2-) and AcO(-)-Ca(2+)-CO3(2-) systems were found to form stable ion-complexes irrespective of the presence of near neighbor water molecules. The strong electrostatic interactions of these functional groups with their counter-ions significantly affect the fundamental vibrational frequencies of the functional groups, mainly the NH2 stretching (str.) and degenerate (deg.) scissors modes of Gdm(+) and -C=OO, CC, and CO str. modes of AcO(-). The free-energy calculations reveal that EtOH forms weakly bound molecular complexes with the Ca(2+)-CO3(2-) ion pairs in water. However, the interaction strength of EtOH with crystalline CaCO3 can increase significantly due to combined effect of H-bond and electron donor acceptor (EDA) type of interactions. These results indicate that -NH2(+) and -COO(-) bearing molecules serve as potential nucleation sites promoting crystallization of CaCO3 phases while -OH bearing molecules are likely to control the morphology of the crystalline phases by attaching to the growing crystal surfaces.

A pilot study evaluating GSK1070806 inhibition of interleukin-18 in renal transplant delayed graft function.

INTRODUCTION: Delayed graft function (DGF) following renal transplantation is a manifestation of acute kidney injury (AKI) leading to poor long-term outcome. Current treatments have limited effectiveness in preventing DGF. Interleukin-18 (IL18), a biomarker of AKI, induces interferon-γ expression and immune activation. GSK1070806, an anti-IL18 monoclonal antibody, neutralizes activated (mature) IL18 released from damaged cells following inflammasome activation. This phase IIa, single-arm trial assessed the effect of a single dose of GSK1070806 on DGF occurrence post donation after circulatory death (DCD) kidney transplantation. METHODS: The 3 mg/kg intravenous dose was selected based on prior studies and physiologically based pharmacokinetic (PBPK) modeling, indicating the high likelihood of a rapid and high level of IL18 target engagement when administered prior to kidney allograft reperfusion. Utilization of a Bayesian sequential design with a background standard-of-care DGF rate of 50% based on literature, and confirmed via extensive registry data analyses, enabled a statistical efficacy assessment with a minimal sample size. The primary endpoint was DGF frequency, defined as dialysis requirement ≤7 days post transplantation (except for hyperkalemia). Secondary endpoints included safety, pharmacokinetics and pharmacodynamic biomarkers. RESULTS: GSK1070806 administration was associated with IL18-GSK1070806 complex detection and increased total serum IL18 levels due to IL18 half-life prolongation induced by GSK1070806 binding. Interferon-γ-induced chemokine levels declined or remained unchanged in most patients. Although the study was concluded prior to the Bayesian-defined stopping point, 4/7 enrolled patients (57%) had DGF, exceeding the 50% standard-of-care rate, and an additional two patients, although not reaching the protocol-defined DGF definition, demonstrated poor graft function. Six of seven patients experienced serious adverse events (SAEs), including two treatment-related SAEs. CONCLUSION: Overall, using a Bayesian design and extensive PBPK dose modeling with only a small sample size, it was deemed unlikely that GSK1070806 would be efficacious in preventing DGF in the enrolled DCD transplant population. TRIAL REGISTRATION: NCT02723786.

Metal cation complexation with natural organic matter in aqueous solutions: molecular dynamics simulations and potentials of mean force.

Natural organic matter (NOM, or humic substance) has a known tendency to form colloidal aggregates in aqueous environments, with the composition and concentration of cationic species in solution, pH, temperature, and the composition of the NOM itself playing important roles. Strong interaction of carboxylic groups of NOM with dissolved metal cations is thought to be the leading chemical interaction in NOM supramolecular aggregation. Computational molecular dynamics (MD) study of the interactions of Na(+), Mg(2+), and Ca(2+) with the carboxylic groups of a model NOM fragment and acetate anions in aqueous solutions provides new quantitative insight into the structure, energetics, and dynamics of the interactions of carboxylic groups with metal cations, their association, and the effects of cations on the colloidal aggregation of NOM molecules. Potentials of mean force and the equilibrium constants describing overall ion association and the distribution of metal cations between contact ion pairs and solvent-separated ions pairs were computed from free MD simulations and restrained umbrella sampling calculations. The results provide insight into the local structural environments of metal-carboxylate association and the dynamics of exchange among these sites. All three cations prefer contact ion pair to solvent-separated ion pair coordination, and Na(+) and Ca(2+) show a strong preference for bidentate contact ion pair formation. The average residence time of a Ca(2+) ion in a contact ion pair with the carboxylic groups is of the order of 0.5 ns, whereas the corresponding residence time of a Na(+) ion is only between 0.02 and 0.05 ns. The average residence times of a Ca(2+) ion in a bidentate coordinated contact ion pair vs a monodentate coordinated contact ion pair are about 0.5 and 0.08 ns, respectively. On the 10 ns time scale of our simulations, aggregation of the NOM molecules occurs in the presence of Ca(2+) but not Na(+) or Mg(2+). These results agree with previous experimental observations and are explained by both Ca(2+) ion bridging between NOM molecules and decreased repulsion between the NOM molecules due to the reduced net charge of the NOM-metal complexes. Simulations on a larger scale are needed to further explore the relative importance of the different aggregation mechanisms and the stability of NOM aggregates.

Killing tigers to save them: fallacies of the farming argument.

The lucrative, illegal trade in tigers (Panthera tigris) remains a major conservation problem. Tiger farming has been proposed as a potential solution, with farmed tigers substituting for wild tigers. At first glance, this argument's logic seems simple: farming will increase the supply of tigers, prices will fall, and poaching will no longer be profitable. We contend, however, that this supply-side argument relies on mistaken assumptions. First, tiger markets are imperfect, meaning they are dominated by a few producers who control price. Second, consumers prefer wild tigers to farmed tigers and therefore the two are not pure substitutes. In economic terms, products from wild tigers are luxury goods, commanding a price premium. Third, there is no evidence that farmed tigers can be produced or sold more cheaply than wild tigers. In sum, it is unlikely that farming will drive down the price of wild-caught tigers or decrease profitability for tiger poachers. Rather, tiger farming is more likely to increase aggregate demand for tiger products and stimulate higher levels of poaching.

High-resolution nuclear magnetic resonance of inorganic solids.

Recent improvements in instrumentation and technique now permit the observation of high-resolution nuclear magnetic resonance spectra of many nuclei in inorganic solids. The application of nuclear magnetic resonance to the study of the structures of materials of interest in chemistry, earth science, and materials science are discussed together with a prognosis for future work.

Hydrogen-bonding structure and dynamics of aqueous carbonate species from car-parrinello molecular dynamics simulations.

A comprehensive Car-Parrinello molecular dynamics (CP-MD) study of aqueous solutions of carbonic acid (H(2)CO(3)), bicarbonate (HCO(3)(-)), carbonate (CO(3)(2-)), and carbon dioxide (CO(2)) provides new quantitative insight into the structural and dynamic aspects of the hydrogen-bonding environments for these important aqueous species and their effects on the structure, H-bonding, and dynamical behavior of the surrounding water molecules. The hydration structures of the different carbonate species depend on their ability to accept and donate H-bonds with H(2)O. The H-bonds donated by the C-O-H sites of the carbonate species to water molecules are generally stronger and longer-lived than those accepted by these sites from water molecules. The structural relaxation among the water molecules is dominated by diffusional (translational) motion of H(2)O, whereas the H-bond reorganization is dominated by the librational motion of the water molecules and the carbonate species. The rates of structural relaxation of the H(2)O molecules and the rates of H-bond reorganization among them are slower in systems containing carbonate species, consistent with previous studies of simple salt solutions. The strengths and lifetimes of H-bonds involving the carbonate species positively correlate with the total negative charge on the species. H-bond donation from H(2)O to CO(2) is weak, but the presence of CO(2) noticeably affects the structure and structural relaxation of the surrounding H-bonding network leading to generally stronger H-bonds and slower relaxation rates, the behavior typical of a hydrophobic solute.

A multistate empirical valence bond model for solvation and transport simulations of OH- in aqueous solutions.

We describe a new multistate empirical valence bond (MS-EVB) model of OH(-) in aqueous solutions. This model is based on the recently proposed "charged ring" parameterization for the intermolecular interaction of hydroxyl ion with water [Ufimtsev, et al., Chem. Phys. Lett., 2007, 442, 128] and is suitable for classical molecular simulations of OH(-) solvation and transport. The model reproduces the hydration structure of OH(-)(aq) in good agreement with experimental data and the results of ab initio molecular dynamics simulations. It also accurately captures the major structural, energetic, and dynamic aspects of the proton transfer processes involving OH(-) (aq). The model predicts an approximately two-fold increase of the OH(-) mobility due to proton exchange reactions.

The antimicrobial mechanism of electrochemically activated water against Pseudomonas aeruginosa and Escherichia coli as determined by SDS-PAGE analysis.

AIMS: To expose bacteria to anolyte and subsequently investigate the effect of anolyte on the protein profiles of treated bacteria. METHODS AND RESULTS: Proteins were extracted from bacteria treated with different concentrations of anolyte and analysed using SDS-PAGE. Fewer and more faint protein bands were observed for concentrated halide anolyte treated bacteria when compared to untreated bacteria while extra protein bands were observed for bacteria exposed to dilute concentrations. CONCLUSIONS: The undiluted and the 10(-1) dilution of halide derived anolyte was effective in killing the test bacteria. Anolyte caused bacterial death by complete destruction of proteins or by causing oxidative stress which resulted in protein fragmentation. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of this study provide information on the antimicrobial mechanism of anolyte on other bacteria for which the information is currently unavailable.

Temperature dependent structure and dynamics in smectite interlayers: 23Na MAS NMR spectroscopy of Na-hectorite.

23Na 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 et al. Nat. Commun., 2018, 9, 1496). Such motion would cause rippling of the T-O-T structure of the clay layers at frequencies greater than ∼25 kHz. For samples exposed to 0% relative humidity (R.H.), the 23Na spectra show the presence of two Na+ sites (probably 6 and 9 coordinated by basal oxygen atoms) that do not undergo dynamical averaging at any temperature from -120 °C to 40 °C. For samples exposed to R.H.s from 29% to 100% the spectra show the presence of three hydrated Na+ sites that undergo dynamical averaging beginning at -60 °C. These sites have different numbers of H2O molecules coordinating the Na+, and diffusion calculations indicate that they probably occur within the same individual interlayer. The average hydration state of Na+ increases with increasing R.H. and water content of the clay.

Incorporation of large amounts of gentamicin sulphate into acrylic bone cement: effect on handling and mechanical properties, antibiotic release, and biofilm formation.

Bacterial infection remains a significant complication following total joint replacement. If infection is suspected when revision surgery is being performed, a large dose of antibiotic, usually gentamicin sulphate, is often blended with the acrylic bone cement powder in an attempt to reduce the risk of recurrent infection. In this in-vitro study the effect of small and large doses of gentamicin sulphate on the handling and mechanical properties of the cement, gentamicin release from the cement, and in-vitro biofilm formation by clinical Staphylococcus spp. isolates on the cement was determined. An increase in gentamicin loading of 1, 2, 3, or 4 g, in a cement powder mass of 40 g, resulted in a significant decrease in the compressive and four-point bending strength, but a significant increase in the amount of gentamicin released over a 72h period. When overt infection was modelled, using Staphylococcus spp. clinical isolates at an inoculum of 1 x 10(7) colony-forming units/ml, an increase in the amount of gentamicin (1, 2, 3, or 4 g) added to 40 g of poly(methyl methacrylate) cement resulted in an initial decrease in bacterial colonization but this beneficial effect was no longer apparent by 72 h, with the bacterial strains forming biofilms on the cements despite the release of high levels of gentamicin. The findings suggest that orthopaedic surgeons should carefully consider the clinical consequences of blending large doses (1 g or more per 40 g of poly(methyl methacrylate)) of gentamicin into Palacos R bone cement for use in revision surgery as the increased gentamicin loading does not prevent bacterial biofilm formation and the effect on the mechanical properties could be important to the longevity of the prosthetic joint.

The use of electrochemically activated saline as a uterine instillation in pony mares.

Twelve pony mares were randomly assigned to either a control or a treatment group and inseminated with fresh, raw semen from a single stallion of known fertility in a cross-over trial design. Pregnancy was diagnosed by transrectal ultrasound 12-14 days post-ovulation and then terminated by administration of a luteolytic dose of cloprostenol. Treatment mares received a uterine instillation of 100 ml of electrochemically activated (ECA) saline 4-12 hours post-insemination. Control mares received no treatment post-insemination. Per cycle pregnancy rate was 58.3 % in the control group and 50 % in the treatment group. There was no statistical difference (P = 1.000) in pregnancy rate between the 2 groups. The principles of ECA and applications of ECA saline are discussed.

Validation of masks for determination of V̇O2 max in horses exercising at high intensity.

BACKGROUND: The need for a horse to be ridden while wearing a measurement device that allows unrestricted ventilation and gas exchange has hampered accurate measurement of its maximal oxygen consumption (V̇O2 max) under field conditions. OBJECTIVES: Design and validate a facemask with the potential to measure V̇O2 max accurately in the field. STUDY DESIGN: Experiment with 6 × 6 Latin square design. METHODS: Two variations of a mask and associated electronic control module (ECM) were designed to enable breath-by-breath measurement of airflows through two 7.8 cm diameter pneumotachometers located 7.5 cm in front of each narus. The ECM was comprised of an analogue-to-digital converter and a lithium-ion battery that provided power and signal filtering to the pneumotachometers and an oxygen sensing cell, and powered a pump connected to gas sampling ports between the nares and pneumotachometers. Airflow and oxygen content of inspired and expired gases were recorded through the ECM and electronically transferred to a notebook. V̇O2 was determined from these recordings using a customised software program. Mask B encased the lower jaw. Mask R left the jaw free so the horse could wear a bit if ridden. V̇O2 max and arterial blood gases were measured in 6 horses during multiple treadmill tests. Each mask was worn twice and results compared to those from an established open flow-through system (O) by ANOVA-RM (P<0.05). System utility was evaluated using the intraclass correlation coefficient of 4 independent raters. RESULTS: Blood gases and V̇O2 max (151.9±7.0 [mean±s.d.; O], 151.5±9.6 [B], 149.5±7.5 [R] ml/[kg.min]) were not different between masks. V̇O2 max measures were reproducible for each mask. Intraclass correlation coefficient between raters = 0.99. MAIN LIMITATIONS: Some rebreathing of expired air from mask dead space. CONCLUSION: Masks capable of measuring V̇O2 max during treadmill exercise were developed, tested and found to be accurate. Mask R has potential application to measurement of V̇O2 max under field conditions.

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 21.1T. Compounds that contain both structural H(2)O molecules and protonated arsenate groups do not yield resolvable signal, likely a result of T(2) effects related to a combination of strong quadrupolar interactions and proton exchange. Spin-echo experiments at 11.7 and 14.1T were effective for Li(3)AsO(4) and CsH(2)AsO(4), as were whole-pattern spikelet experiments for arsenate oxide (As(2)O(5)) at 17.6 and 21.1T. The central transition resonance of Ca(3)(AsO(4))(2).8H(2)O is approximately 6 MHz broad and required a non-conventional, histogram-style spikelet method at high field to improve acquisition efficiency. This approach reduces the acquisition time due to the sensitivity enhancement of the spikelet sequence and a reduction in the number of frequency increments required to map the resonance. Despite the large quadrupole couplings, we have identified a correlation between the (75)As isotropic chemical shift and the electronegativity of the next-nearest neighbor cation in arsenate compounds.

Tipping Point for Expansion of Layered Aluminosilicates in Weakly Polar Solvents: Supercritical CO2.

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 H2O 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., CO2), uptake into the interlayer is not well-understood. Using novel high-pressure capabilities, we investigated the interaction of dry supercritical CO2 with Na-, NH4-, and Cs-saturated montmorillonite, comparing results with predictions from molecular dynamics simulations. Despite the known trend in H2O and that cation solvation energies in CO2 suggest a stronger interaction with Na, both the NH4- and Cs-clays readily absorbed CO2 and expanded, while the Na-clay did not. The apparent inertness of the Na-clay was not due to kinetics, as experiments seeking a stable expanded state showed that none exists. Molecular dynamics simulations revealed a large endothermicity to CO2 intercalation in the Na-clay but little or no energy barrier for the NH4- and Cs-clays. Indeed, the combination of experiment and theory clearly demonstrate that CO2 intercalation of Na-montmorillonite clays is prohibited in the absence of H2O. Consequently, we have shown for the first time that in the presence of a low dielectric constant, gas swelling depends more on the strength of the interaction between the interlayer cation and aluminosilicate sheets and less on that with solvent. The finding suggests a distinct regime in layered aluminosilicate swelling behavior triggered by low solvent polarizability, with important implications in geomechanics, storage, and retention of volatile gases, and across industrial uses in gelling, decoloring, heterogeneous catalysis, and semipermeable reactive barriers.

Hydration, swelling, interlayer structure, and hydrogen bonding in organolayered double hydroxides: insights from molecular dynamics simulation of citrate-intercalated hydrotalcite.

Molecular dynamics (MD) simulation of the Mg/Al (3:1) layered double hydroxide (LDH), hydrotalcite (HT), containing citrate, C6H5O7(3-), as the charge balancing interlayer anion provides new molecular scale insight into the interlayer structure, hydrogen bonding, and energetics of the hydration and consequent swelling of LDH compounds containing organic and biomolecules. Citrate-HT exhibits affinity for water up to very high hydration levels, in contrast to the preferred low hydration states of most LDHs intercalated with small, inorganic anions. This result is consistent with the recent experimental observation of the delamination of lactate-HT. The high water affinity is rationalized in terms of the preference of citrate ion for hydrogen bonds (H-bonds) donated from water molecules rather than from the hydroxyl groups of the metal hydroxide layer and the need to develop an integrated interlayer H-bond network among the citrate ions, water, and -OH groups of the hydroxide layers. The changes in the orientation of citrate molecules with progressive hydration are also intimately related to its preference to accept hydrogen bonds from water.

Diurnal variation of rat liver enzymes catalyzing bile acid conjugation and sulfation.

This study investigated the diurnal variation in the activity of the hepatic enzymes catalyzing conjugation and sulfation of bile acids. A circadian rhythm was noted in cholic acid : CoA ligase and glycolithocholate sulfotransferase activity. There was no diurnal variation in lithocholate sulfotransferase activity raising the possibility of multiple bile acid sulfotransferases in liver.