The right isotherms for the right reasons?: validation of generic force fields for prediction of methane adsorption in metal-organic frameworks

In recent years, the use of computational tools to aid in the evaluation, understanding and design of advanced porous materials for gas storage and separation processes has become ever-more widespread. High-performance computing facilities have become more powerful and more accessible and molecular simulation of gas adsorption has become routine, often involving the use of a number of default and commonly-used parameters as a result. In this work, we consider the application of molecular simulation in one particular field of adsorption – the prediction of methane adsorption in metal-organic frameworks in the low-loading regime – and employ a range of computational techniques to evaluate the appropriateness of many commonly chosen simulation parameters to these systems. In addition to confirming the power of relatively simple generic force fields to quickly and accurately predict methane adsorption isotherms in a range of MOFs, we demonstrate that these force fields are capable of providing detailed molecular-level information which is in very good agreement with quantum chemical predictions. We highlight a number of chemical systems in which molecular-level insight from generic force fields should be approached with a degree of caution and provide some general recommendations for best-practice in simulations of CH4 adsorption in MOFs

A Protein Preload Enhances the Glucose-Lowering Efficacy of Vildagliptin in Type 2 Diabetes

Ranking and judging political misbehaviours: the benefits of focus group approach and of quantitative method for analysing qualitative dataQualitative researches based on focus group offer valuable insights in analyzing moral conflicts. This article suggests they also prove very useful to explore citizens’ perceptions of political misbehaviours. Moral expectations regarding politicians’ behaviours are ambiguous judgements because of the various criteria that underpin their perceptions of politics. This article is based on the analysis of eight different, socio-culturally homogeneous focus groups. Collected arguments are analysed through a quantitative method examining discursive contents. The existence of a common grid for ranking political misbehaviours is emphasized. The moderating effects of collective discussion on judgements are also outlined. The article emphasizes variations in judgments, differentiating groups according to their social and occupational experiences. At last, different “repertoires of arguments” are identified relying on different principles.Les enjeux de probité publique se prêtent bien aux recherches qualitatives menées par focus group, habituellement utilisées dans l’exploration des conflits moraux et normatifs. La démarche est ici mobilisée pour explorer l’ambiguïté des jugements portés par les citoyens sur les pratiques et transgressions des élus. Elle repose sur huit groupes socio-culturellement différenciés et sur une exploitation originale à partir d’une méthode de quantification du contenu des discours recueillis. L’article montre l’existence d’une échelle homogène de qualification et de classification des pratiques politiques qui graduent les jugements de réprobation. La discussion collective favorise l’expression de formes de modération dans les jugements. L’exploitation pointe des différences liées aux caractéristiques sociales des groupes. Elle identifie des « répertoires argumentatifs », mobilisant des principes de jugement divergents

Methane adsorption in metal-organic frameworks containing nanographene linkers: a computational study

Metal-organic framework (MOF) materials are known to be amenable to expansion through elongation of the parent organic linker. For a family of model (3,24)-connected MOFs with the rht topology, in which the central part of organic linker comprises a hexabenzocoronene unit, the effect of the linker type and length on their structural and gas adsorption properties is studied computationally. The obtained results compare favourably with known MOF materials of similar structure and topology. We find that the presence of a flat nanographene-like central core increases the geometric surface area of the frameworks, sustains additional benzene rings, promotes linker elongation and the efficient occupation of the void space by guest molecules. This provides a viable linker modification method with potential for enhancement of uptake for methane and other gas molecules

Selective Gas Uptake and Rotational Dynamics in a (3,24)-Connected Metal–Organic Framework Material

The desolvated (3,24)-connected metal-organic framework (MOF) material, MFM-160a, [Cu3(L)(H2O)3] [H6L = 1,3,5-triazine-2,4,6-tris(aminophenyl-4-isophthalic acid)] exhibits excellent high pressure uptake of CO2 (110 wt% at 20 bar, 298 K) and highly selective separation of C2 hydrocarbons from CH4 at 1 bar pressure. Henry’s law selectivities of 79:1 for C2H2:CH4 and 70:1 for C2H4:CH4 at 298 K are observed, consistent with IAST predictions. Significantly, MFM-160a shows a selectivity of 16:1 for C2H2:CO2. Solid state 2H NMR spectroscopic studies on partially deuterated MFM-160-d12 shows an ultra-low barrier to rotation of the phenyl group in the activated MOF (~2 kJ mol-1), and a rotation rate five orders of magnitude slower than usually observed for solid state materials (1.4 x 106 Hz cf. 1011 - 1013 Hz). Upon introduction of CO2 and C2H2 into desolvated MFM-160a, this rate of rotation was found to increase with increas-ing gas pressure, a phenomenon attributed to the weakening of an intramolecular hydrogen bond in the triazine-containing linker upon gas binding. DFT calculations of binding energies and interactions of CO2 and C2H2 around the triazine-core are entirely consistent with the 2H NMR spectroscopic observations

Effects of Sustained Treatment With Lixisenatide on Gastric Emptying and Postprandial Glucose Metabolism in Type 2 Diabetes: A Randomized Controlled Trial

Objective: Tachyphylaxis for slowing of gastric emptying is seen with continuous exposure to glucagon-like peptide 1 (GLP-1). We therefore aimed to establish whether prolonged use of a "short-acting" GLP-1 receptor agonist, lixisenatide, achieves sustained slowing of gastric emptying and reduction in postprandial glycemia. Research design and methods: A total of 30 patients with metformin-treated type 2 diabetes underwent assessment of gastric emptying (scintigraphy) and glucose metabolism (dual tracer technique) after a 75-g glucose drink, before and after 8 weeks' treatment with lixisenatide (20 μg subcutaneously daily) or placebo, in a double-blind randomized parallel design. Results: Gastric retention of the glucose drink was markedly increased after lixisenatide versus placebo (ratio of adjusted geometric means for area under curve [AUC] over 240 min of 2.19 [95% CI 1.82, 2.64; P < 0.001]), associated with substantial reductions in the rate of systemic appearance of oral glucose (P < 0.001) and incremental AUC for blood glucose (P < 0.001). Lixisenatide suppressed both glucagon (P = 0.003) and insulin (P = 0.032), but not endogenous glucose production, over 120 min after oral glucose intake. Postprandial glucose lowering over 240 min was strongly related to the magnitude of slowing of gastric emptying by lixisenatide (r = -0.74, P = 0.002) and to the baseline rate of emptying (r = 0.52, P = 0.048) but unrelated to β-cell function (assessed by β-cell glucose sensitivity). Conclusions: Eight weeks' treatment with lixisenatide is associated with sustained slowing of gastric emptying and marked reductions in postprandial glycemia and appearance of ingested glucose. Short-acting GLP-1 receptor agonists therefore potentially represent an effective long-term therapy for specifically targeting postprandial glucose excursions

Effects of taurocholic acid on glycemic, glucagon-like peptide-1, and insulin responses to small intestinal glucose infusion in healthy humans

CONTEXT: In vitro and animal studies suggest that bile acids have the capacity to reduce blood glucose by stimulating glucagon-like peptide-1 (GLP-1) and, thereby, insulin. OBJECTIVE: This study evaluated the effects of intrajejunal taurocholic acid (TCA) on blood glucose, GLP-1, and insulin responses to jejunal glucose infusion in healthy men. PARTICIPANTS AND DESIGN: Ten healthy men were each studied on 2 days in a double-blind, randomized order. After the subjects fasted overnight, a jejunal catheter was positioned and a balloon inflated 30 cm beyond the pylorus with aspiration of endogenous bile. Two grams TCA in saline, or saline control, was infused beyond the balloon over 30 minutes, followed by 2 g TCA or control, together with 60 g glucose, over the next 120 minutes. Blood was sampled frequently for the measurements of blood glucose, total GLP-1, insulin, C-peptide, and glucagon. RESULTS: Intrajejunal infusion of TCA alone (t = −30 to 0 minutes) had no effect on blood glucose, GLP-1, insulin, C-peptide, or glucagon concentrations. During intrajejunal glucose infusion (t = 0 to 120 minutes), blood glucose concentrations were lower (P < .001), and plasma GLP-1 (P < .001) and the C-peptide/glucose ratio (P = .008) were both greater, whereas plasma insulin, C-peptide, and glucagon levels were not significantly different after TCA than after control. CONCLUSIONS: In healthy humans, small intestinal infusion of TCA potently reduces the glycemic response to small intestinal glucose, associated with an increase in GLP-1 and C-peptide/glucose ratio. These observations indicate the potential for bile acid-based therapy in type 2 diabetes.Tongzhi Wu, Michelle J. Bound, Scott D. Standfield, Karen L. Jones, Michael Horowitz, and Christopher K. Rayne