Imparting gas selective and pressure dependent porosity into a non-porous solid: Via coordination flexibility

Using a simple hard-soft acid-base concept we have deliberately designed gas-specific and pressure dependent porosity into a non-porous solid via coordination flexibility. This creates distinct gate-openings wherein the CO2 molecule opens-up the framework pores by rotating the ligand about the weaker hard-soft bonds (hard-soft gate control). For this, we have studied the CO2 gating behaviour of M(4-PyC)2 (M = Mg, Mn and Cu), which represent metals of varying hardness. A combination of quantum chemical calculations, molecular dynamics and Grand canonical Monte Carlo simulations were performed to examine the gate opening of the isonicotinate ligands in Mg(4-PyC)2. The simulations show that interaction of the CO2 molecules with the isonicotinate ligands at different CO2 loadings can result in pressure-dependent gate opening. Furthermore, the simulated CO2 uptake values calculated using the partially gate-opened structures at different loadings showed good agreement with the experimental uptake values. This provides an effective strategy for designing highly-stable dynamic porous solids employing rigid frameworks

Biochemical aspects of nitric oxide synthase feedback regulation by nitric oxide

Nitric oxide (NO) is a small gas molecule derived from at least three isoforms of the enzyme termed nitric oxide synthase (NOS). More than 15 years ago, the question of feedback regulation of NOS activity and expression by its own product was raised. Since then, a number of trials have verified the existence of negative feedback loop both in vitro and in vivo. NO, whether released from exogenous donors or applied in authentic NO solution, is able to inhibit NOS activity and also intervenes in NOS expression processes by its effect on transcriptional nuclear factor NF-κB. The existence of negative feedback regulation of NOS may provide a powerful tool for experimental and clinical use, especially in inflammation, when massive NOS expression may be detrimental

Computational high throughput screening of irMOFs: Proposing new materials for CO <inf>2</inf> capture

Metal organic frameworks (MOFs) are an emerging class of microporous materials which are generating considerable interest due to their high capacity for CO 2 sequestration and storage. Computational methods of studying MOF materials have recently become an important complement to synthetic work. With computation, detailed research can be carried out on aspects of a MOF which give rise to preferential adsorption, quantity adsorbed, and gas binding character. By applying well established predictive algorithms we intend to propose, in silico, novel MOFs designed to capture greenhouse gases. This study investigates the implementation of high throughput (HT) screening on isoreticular MOFs (irMOFs). The subclass of isoretcular MOFs possess the property that substituents on the organic linker molecules can be changed without altering the topology of the framework. Novel MOF materials with high CO 2 gas selectivity and absolute adsorption are screened by altering functional groups on a series of irMOFs

Idealized carbon-based materials exhibiting record deliverable capacities for vehicular methane storage

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOMaterials for vehicular methane storage have been extensively studied, although no suitable material has been found. In this work, we use molecular simulation to investigate three types of carbon-based materials, Schwarzites, layered graphenes, and carbon nanoscrolls, for use in vehicular methane storage under adsorption conditions of 65 bar and 298 K and desorption conditions of 5.8 bar and 358 K. Ten different Schwarzites were tested and found to have high adsorption with maximums at 273 V-STP/V, but middling deliverable capacities of no more than 131 V-STP/V. Layered graphene and graphene nanoscrolls were found to have extremely high CH4 adsorption capacities of 355 and 339 V-STP/V, respectively, when the interlayer distance was optimized to 11 angstrom. The deliverable capacities of perfectly layered graphene and graphene nanoscrolls were also found to be exceptional with values of 266 and 252 V-STP/V, respectively, with optimized interlayer distances. These values make idealized graphene and nanoscrolls the record holders for adsorption and deliverable capacities under vehicular methane storage conditions.123210501058FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO2013/08293-7Sem informaçãoSem informaçãoThe authors would like to thank the University of Ottawa and FAPESP for a collaborative FAPESP-CALDO grant that supported this work. This work was supported in part by the Brazilian Agencies CAPES, CNPq, and FAPESP and the Canadian Agencies of NSERC and the Canada Research Chairs program. The authors thank the Center for Computational Engineering and Sciences at Unicamp for financial support through the FAPESP/CEPID Grant #2013/08293-7. We are also grateful for computing resources provided by Canada Foundation for Innovation and Compute Canada

C:N:P stoichiometry and nutrient limitation of the soil microbial biomass in a grazed grassland site under experimental P limitation or excess

peer-reviewedIntroduction: The availability of essential nutrients, such as nitrogen (N) and phosphorus (P), can feedback on soil carbon (C) and the soil microbial biomass. Natural cycles can be supplemented by agricultural fertiliser addition, and we determined whether the stoichiometry and nutrient limitation of the microbial biomass could be affected by an unbalanced nutrient supply. Methods: Samples were taken from a long-term trial (in effect since 1968) with annual applications of 0, 15 and 30 kg P ha−1 with constant N and potassium. Soil and microbial biomass CNP contents were measured and nutrient limitation assessed by substrate-induced respiration. Linear regression and discriminant analyses were used to identify the variables explaining nutrient limitation. Results: Soil and biomass CNP increased with increasing P fertiliser, and there was a significant, positive, correlation between microbial biomass P and biomass C, apart from at the highest level of P fertilisation when the microbial biomass was over-saturated with P. The molar ratios of C:N:P in the microbial biomass remained constant (homeostatic) despite large changes in the soil nutrient ratios. Microbial growth was generally limited by C and N, except in soil with no added P when C and P were the main limiting nutrients. C, N and P, however, did not explain all the growth limitation on the soils with no added P. Conclusions: Increased soil C and N were probably due to increased net primary production. Our results confirm that C:N:P ratios within the microbial biomass were constrained (i.e. homeostatic) under near optimum soil conditions. Soils with no added P were characterised by strong microbial P limitation and soils under high P by over-saturation of microorganisms with P. Relative changes in biomass C:P can be indicative of nutrient limitation within a site

Sugar Acetonides are a Superior Motif for Addressing the Large, Solvent Exposed Ribose 33 Pocket of tRNA Guanine Transglycosylase

The intestinal disease shigellosis caused by Shigellabacteria affects over 120 million people annually. There isan urgent demand for new drugs as resistance againstcommon antibiotics emerges. Bacterial tRNA-guanine transglycosylase(TGT) is a druggable target and controls thepathogenicity of Shigella flexneri. We report the synthesis ofsugar-functionalized lin-benzoguanines addressing theribose-33 pocket of TGT from Zymomonas mobilis. Ligandbinding was analyzed by isothermal titration calorimetry andX-ray crystallography. Pocket occupancy was optimized byvariation of size and protective groups of the sugars. Theparticipation of a polycyclic water-cluster in the recognitionof the sugar moiety was revealed. Acetonide-protected riboandpsicofuranosyl derivatives are highly potent, benefitingfrom structural rigidity, good solubility, and metabolic stability.We conclude that sugar acetonides have a significant butnot yet broadly recognized value in drug development

Density Functional Theory Study of the Adsorption of Hydrazine on the Perfect and Defective Copper (100), (110), and (111) Surfaces

We have calculated the adsorption of the reducing agent hydrazine (N2H4) on copper surfaces using density functional theory calculations with a correction for the long-range interactions (DFT-D2). We have modeled the perfect and a number of defective Cu(100), (110), and (111) surfaces, which are found in the experimentally produced structures of copper nanoparticles. We have studied adsorption of hydrazine at three types of defects in the surfaces, i.e., monatomic steps, Cu adatoms, and Cu vacancies. Several low-energy adsorption structures for hydrazine on each perfect and defective surface have been identified and compared. Our calculations reveal that hydrazine bridges surface copper atoms, with the molecule twisted from the gauche toward an eclipsed conformation, except on the adatom (100) and vacancy-containing (100) and (110) surfaces, where it adsorbs through one nitrogen atom in gauche and trans conformations, respectively. The strongest adsorption energy is found on the stepped (110) surface, where hydrazine bridges between the copper atoms on the step edge and the terrace, as it stabilizes the low-coordinated copper atoms. Our results show that, although the (110) surface contains a number of low-coordinated atoms that enhance the surface-molecule interactions, the addition of defects on the more stable (111) and (100) surfaces provides sites that enable hydrazine binding to almost the same extent. This study also confirms general observations of surface adsorption trends in terms of d-band center and binding energy as a function of coordination number, i.e., the stronger the molecular adsorption, the higher the d-band shifts at low-coordinated sites