Search results for "Ash"
showing 10 items of 1718 documents
Self-enforcing international environmental agreements with a stock pollutant
2005
In this paper the stability of an International Environmental Agreement (IEA) among N identical countries that emit a pollutant are studied using a two-stage game. In the first stage each country decides noncooperatively whether or not to join an IEA, and in the second stage signatories jointly against nonsignatories determine their emissions in a dynamic setting defined in continuous time. For this second stage we have studied both the open-loop Nash equilibrium and the feedback Nash equilibrium. A numerical simulation shows that a bilateral coalition is the unique self-enforcing IEA independently of the gains coming from cooperation and the kind of strategies played by the agents (open-lo…
Effect of pH on compressive strength of some modification of mineral trioxide aggregate
2013
Objectives: Recently, it was shown that NanoMTA improved the setting time and promoted a better hydration process which prevents washout and the dislodgment of this novel biomaterial in comparison with WTMA. This study analyzed the compressive strength of ProRoot WMTA (Dentsply), a NanoWMTA (Kamal Asgar Research Center), and Bioaggregate (Innovative Bioceramix) after its exposure to a range of environmental pH conditions during hydration. Study Design: After mixing the cements under aseptic condition and based on the manufacturers' recommendations, the cements were condensed with moderate force using plugger into 9 × 6 mm split molds. Each type of cement was then randomly divided into three…
Scavenging of sulphur, halogens and trace metals by volcanic ash: The 2010 Eyjafjallajökull eruption
2013
The Eyjafjallajökull volcanic eruption in 2010 released considerable amounts of ash into the high troposphere-low stratosphere, leading to unprecedented disruption of air traffic over Europe. The role of such fine-grained tephra in adsorbing, and therefore rapidly scavenging, volcanogenic volatile elements such as sulphur and halogens, is explored here. We report on results (major to trace element chemistry) of leaching experiments carried out on 20 volcanic ash samples, taken from the deposits of the main phases of the eruption (March–April 2010), or directly while falling (5–9 May 2010). Ash leachate solutions from Eyjafjallajökull are dominated – among cations – by Ca and Na, and display…
Internal dynamics and protein-matrix coupling in trehalose-coated proteins.
2005
Abstract We review recent studies on the role played by non-liquid, water-containing matrices on the dynamics and structure of embedded proteins. Two proteins were studied, in water–trehalose matrices: a water-soluble protein (carboxy derivative of horse heart myoglobin) and a membrane protein (reaction centre from Rhodobacter sphaeroides ). Several experimental techniques were used: Mossbauer spectroscopy, elastic neutron scattering, FTIR spectroscopy, CO recombination after flash photolysis in carboxy-myoglobin, kinetic optical absorption spectroscopy following pulsed and continuous photoexcitation in Q B containing or Q B deprived reaction centre from R. sphaeroides . Experimental result…
A New Heterogeneous Catalyst Obtained via Supramolecular Decoration of Graphene with a Pd2+ Azamacrocyclic Complex
2019
A new G-(H2L)-Pd heterogeneous catalyst has been prepared via a self-assembly process consisting in the spontaneous adsorption, in water at room temperature, of a macrocyclic H2L ligand on graphene (G) (G + H2L = G-(H2L)), followed by decoration of the macrocycle with Pd2+ ions (G-(H2L) + Pd2+ = G-(H2L)-Pd) under the same mild conditions. This supramolecular approach is a sustainable (green) procedure that preserves the special characteristics of graphene and furnishes an efficient catalyst for the Cu-free Sonogashira cross coupling reaction between iodobenzene and phenylacetylene. Indeed, G-(H2L)-Pd shows an excellent conversion (90%) of reactants into diphenylacetylene under mild conditio…
New concepts in multidentate ligand chemistry: effects of multidentarity on catalytic and spectroscopic properties of ferrocenyl polyphosphines.
2008
This tutorial review devoted to ligand chemistry deals with the design and properties of ferrocenyl polyphosphines, an original class of multidentate ligands. The development of a varied library of ferrocenyl tetra-, tri- and diphosphine ligands is reviewed. The multidentate nature of these species has led to unique spectroscopic and catalytic properties, in which the spatial proximity of phosphorus atoms is crucial. Regarding their catalytic applications, the key issues of catalyst longevity and ultralow catalyst loadings are discussed. Another part is concerned with fundamental advances gained in physical chemistry for structure elucidation by the study of the intriguing “through-space” N…
Photodynamics in stable complexes composed of a zinc porphyrin tripod and pyridyl porphyrins assembled by multiple coordination bonds
2010
A tripod zinc porphyrin (TPZn(3)) forms a stable 1:1 complex with gold(III) tetra(4-pyridyl)porphyrin (AuTPyP(+)) and free-base tris(4-pyridyl)porphyrin (2H-Py(3)P) in nonpolar solvents. The strong binding of TPZn(3) with AuTPyP(+) or 2H-Py(3)P results from the encapsulation of AuTPyP(+) or 2H-Py(3)P inside the cavity of TPZn(3) through multiple coordination bonds, as indicated by UV-vis-NIR, ESI-MS, (1)H NMR, electrochemistry and computational studies. The binding constants of monomer zinc porphyrin (MPZn) with AuTPyP(+) and 2H-Py(3)P drastically decrease as compared with TPZn(3). Detailed photophysical studies have been carried out on these composites using laser flash photolysis as well …
The Monod-Wyman-Changeux allosteric model accounts for the quaternary transition dynamics in wild type and a recombinant mutant human hemoglobin
2012
International audience; The acknowledged success of the Monod-Wyman-Changeux (MWC) allosteric model stems from its efficacy in accounting for the functional behavior of many complex proteins starting with hemoglobin (the paradigmatic case) and extending to channels and receptors. The kinetic aspects of the allosteric model, however, have been often neglected, with the exception of hemoglobin and a few other proteins where conformational relaxations can be triggered by a short and intense laser pulse, and monitored by time-resolved optical spectroscopy. Only recently the application of time-resolved wide-angle X-ray scattering (TR-WAXS), a direct structurally sensitive technique, unveiled th…
Electrostatic control of the photoisomerization efficiency and optical properties in visual pigments: on the role of counterion quenching.
2009
Hybrid QM(CASPT2//CASSCF/6-31G*)/MM(Amber) computations have been used to map the photoisomerization path of the retinal chromophore in Rhodopsin and explore the reasons behind the photoactivity efficiency and spectral control in the visual pigments. It is shown that while the electrostatic environment plays a central role in properly tuning the optical properties of the chromophore, it is also critical in biasing the ultrafast photochemical event: it controls the slope of the photoisomerization channel as well as the accessibility of the S(1)/S(0) crossing space triggering the ultrafast decay. The roles of the E113 counterion, the E181 residue, and the other amino acids of the protein pock…
High Pressure Enhances Hexacoordination in Neuroglobin and Other Globins
2005
The techniques of high applied pressure and flash photolysis have been combined to study ligand rebinding to neuroglobin (Ngb) and tomato Hb, globins that may display a His-Fe-His hexacoordination in the absence of external ligands. High pressure induces a moderate decrease in the His association rate and a large decrease in His dissociation rate, thus leading to an enhancement of the overall His affinity. The overall structural difference between penta- and hexacoordinated globins may be rather small and can be overcome by external modifications such as high pressure. Over the pressure range 0.1-700 MPa (7 kbar), the globins may show a loss of over a factor of 100 in the amplitude of the b…