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Energetic Stability (energetic + stability)

Distribution by Scientific Domains

Chemistry	75%

Selected Abstracts

Energetic stability of boron nitride nanostructures doped with one carbon atom

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 9 2010
Rebeca D. Gonçalves
Abstract We have investigated, using first-principles calculations, the role of a substitutional carbon atom on the geometric stability of boron nitride monolayers, nanotubes, and nanocones. It is shown that the formation of energy depends on the number of atoms for the monolayers and on the diameter for the tubes. It is also found, for the carbon-doped boron nitride nanotubes, that the value for the strain energy approaches the one obtained for nondoped tubes with increasing diameter. For the structural stability, we have verified that the doping, which introduces an excess of nitrogen or boron, makes each structure more favorable in its reverse atmosphere, i.e., excess of nitrogen is more stable in a boron-rich growth environment, whereas excess of boron is preferred in a nitrogen-rich condition. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source]

The function of D1-H332 in Photosystem II electron transport studied by thermoluminescence and chlorophyll fluorescence in site-directed mutants of Synechocystis 6803

FEBS JOURNAL, Issue 17 2004
Yagut Allahverdiyeva
The His332 residue of the D1 protein has been identified as the likely ligand of the catalytic Mn ions in the water oxidizing complex (Ferreira, K.N., Iverson, T.M., Maghlaoui, K., Barber, J. & Iwata, S. (2004) Science 303, 1831,1838). However, its function has not been fully clarified. Here we used thermoluminescence and flash-induced chlorophyll fluorescence measurements to characterize the effect of the D1-H333E, D1-H332D and D1-H332S mutations on the electron transport of Photosystem II in intact cells of the cyanobacterium Synechocystis 6803. Although the mutants are not photoautotrophic they all show flash-induced thermoluminescence and chlorophyll fluorescence, which originate from the S2QA, and S2QB, recombinations demonstrating that charge stabilization takes place in the water oxidizing complex. However, the conversion of S2 to higher S states is inhibited and the energetic stability of the S2QA, charge pair is increased by 75, 50 and 7 mV in the D1-H332D, D1-H332E and D1-H332S mutants, respectively. This is most probably caused by a decrease of Em(S2/S1). Concomitantly, the rate of electron donation from Mn to Tyr-Z, during the S1 to S2 transition is slowed down, relative to the wild type, 350- and 60-fold in the D1-H332E and D1-H332D mutants, respectively, but remains essentially unaffected in D1-H332S. A further effect of the D1-H332E and D1-H332D mutations is the retardation of the QA to QB electron transfer step as an indirect consequence of the donor side modification. Our data show that although the His residue in the D1-332 position can be substituted by other metal binding residues for binding photo-oxidisable Mn it is required for controlling the functional redox energetics of the Mn cluster. [source]

First-principles study of the structural stability and electronic structures of TaN

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2008
C. L. Cao
Abstract Using the plane-wave pseudopotential method within the generalized gradient approximation, we have studied the structural stability and electronic structures for several TaN phases. Our results show CoSn is the calculated ground-state structure of TaN among the five crystallographic structures that have been studied. The order of energetic stability of phase structures of TaN from low to high is: CsCl < ZnS-B3 < NaCl < WC < CoSn. The higher stability of TaN in the CoSn and WC structures is due to the formation of pseudogap around the Fermi level and the stronger hybridization between N-2p states and Ta-5d states. TaN in all structures studied has a metallic nature. The calculated bulk modulus indicates that TaN in the WC structure may be a less compressible material. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Nb and Ta Adducts: Connecting d0 Metal Chlorides and Phosphorus Sulfide Cages

CHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2009
Diana Hoppe Dr.
Abstract Phosphorus sulfide cages ,-P4S4, ,-P4S5, ,-P4S5, and ,-P4S6 and transition-metal chlorides TaCl5 and NbCl5 form molecular adducts in CS2/n -hexane. The crystal structures of the adducts (TaCl5)(,-P4S4), (TaCl5)(,-P4S5), (TaCl5)(,-P4S5), (NbCl5)(,-P4S5), and (TaCl5)(,-P4S6) are reported and their conformation and energetic stability are discussed on the basis of ab initio electronic structure calculations. Furthermore bond lengths of coordinated and noncoordinated phosphorus sulfide cages obtained from experiment and theory are compared, emphasizing the changes within the cages that emerge upon coordination. [source]