1,721,036 research outputs found
The adsorption of glucose at the surface of anatase: A computational study
No full textAb initio computational methods are used to study the interaction of a-D-glucose with the (1 0 1) surface of anatase. Both mono- and bi-dentate Ti--OðglucoseÞ adsorption models are considered. The geometry, energetics and electronic structure of the resulting systems are analyzed and possible implications in the glucose photoreforming process are suggested. The adsorption process is energetically favored in all cases, molecular being preferred over dissociative adsorption. In most cases, the highest occupied elec- tronic state is localized almost exclusively on the adsorbed glucose, which offers an explanation for the experimentally observed ability of glucose to act as an efficient hole scavenger for photoexcited titania nanoparticles
Electrochemical Investigation of Dioxygen Interaction with Two Cobalt Chelates in Solution and at the Electrode Surface
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The four-member square scheme in cyclic voltammetry: general solution for nernstian electron transfers
No full textA general solution of the four-member square scheme under cyclic voltammetric conditions is presented. The diffusional problem is converted into a system of integral equations, which can be solved numerically, giving 'individual' currents. The heterogeneous electron transfer steps are assumed to be nernstian, while no limitations on the magnitude of the kinetic constants of the homogeneous chemical reactions are imposed
N1s and C1s NEXAFS spectra of model systems for pyridine on Si(100) surface: a DFT simulation
No full textAdsorption of organic molecules on semiconductor surfaces has been attracting a growing attention for its importance in emerging technologies. Since the properties of the resulting materials are largely dependent on the organic/semiconductor interface, fundamental research on the covalent bonding of molecules with the surface can provide useful information. Problems that have been addressed include the structure of the resulting systems and spectroscopic measurements often in concert with theoretical calculations can assess the orientation and geometry of the molecular adsorbate. In this respect NEXAFS spectroscopy represents a powerful technique to investigate the interaction of molecules with a surface. The theoretical simulation of NEXAFS spectra of molecules adsorbed on a surface represents a significant challenge both for a proper modelling of the adsorbate system as well as for the size of system which needs theoretical methods capable to fulfill requirements of accuracy and computational economy. Here we present DFT simulations of NEXAFS spectra of pyridine adsorbed on a regular Si (100) surface, considering several adsorption models.1 The surface and the adsorbate models have been previously optimized through periodic calculations, then suitable finite clusters have been be cut out from the optimized periodic structures and used for the simulation of the angle resolved NEXAFS spectra of the adsorbed molecule. The spectra have been calculated employing a molecular DFT methodology based on the transition potential scheme in order to include the core hole relaxation effect.2 Both the N1s and C1s adsorption edges of the adsorbed pyridine have been investigated. The results show that a careful analysis of the calculated polarized spectra can provide important information on specific details of the adsorbtion geometries; the reliability of the computational strategy is proved by the comparison of the theoretical results with the experimental data.1,3 The periodic optimization of the molecules adsorbed on the surface plays a fundamental role in the design of clusters which correctly model the adsorbed system
New Cationic and Neutral Ru(II)- and Os(II)-dmso carbonyl Compounds
No full textThe preparation and structural characterization of three cationic Ru(II)-dmso carbonyls and of four neutral mono- and dicarbonyl Os(II)-dmso derivatives is reported. The two monocarbonyl species fac-[Ru(CO)(dmso-O)3 (dmso-S)2][PF6]2 (11) and cis,cis,cis-[RuCl(CO)(dmso-O)2(dmso-S)2][PF6] (12) were obtained from the neutral monocarbonyl precursor cis,trans,cis-[RuCl2(CO)(dmso-O)(dmso-S)2] (3) upon stepwise replacement of the chlorides with dmso, that binds in each case through the oxygen atom. The dicarbonyl cationic complex cis,cis,trans-[Ru(CO)2(dmso-O)2(dmso-S)Cl][PF6] (13) was instead obtained upon treatment of the neutral tricarbonyl
precursor fac-[RuCl2(CO)3(dmso-O)] (8) with AgPF6 in the presence of DMSO: replacement of a Cl− with a dmso-O impliedalso the substitution of one CO ligand by another dmso (that binds through S trans to Cl). The Os(II) carbonyls trans,trans,trans-[OsCl2(CO)(dmso-O)(dmso-S)2] (17), trans,cis,cis-[OsCl2(CO)2(dmso-O)2] (18), cis,mer-[OsCl2(CO)(dmso-S)3] (19), and cis,trans,cis-[OsCl2(CO)(dmso-O)(dmso-S)2] (20) were obtained by treatment of the Os(II)-dmso precursors trans-[OsCl2(dmso-S)4] (14) and cis,fac-[OsCl2(dmso-O)(dmso-S)3] (15) with CO. Each one of them is structurally similar to an already known Ru(II) analog, even though - in agreement with the expected greater inertness of Os(II) - more forcing reaction conditions were required for their preparation. Interestingly, compound 20 could not be isolated in pure form, but only as a 1:1 cocrystallized mixture with its precursor 15. The dmso ligand is always bound through the oxygen atom when trans to CO. We are con fi dent that the new Ru(II)- and Os(II)-dmso carbonyl species described here represent a contribution to expand the pool of complexes bearing some easily replaceable dmso ligands to be used as well-behaved precursors in inorganic synthesis
Electrochemistry of Iridium Chelates with Phenanthroline or Substituted Phenanthroline and Cyclooctadiene
No full textAn irresolute linker: separation, and structural and spectroscopic characterization of the two linkage isomers of a Ru(ii)-(2-(2′-pyridyl)pyrimidine-4-carboxylic acid) complex
No full textFor the fi rst time the two linkage isomers of a Ru( II ) complex with 2-(2 ’ -pyridyl)pyrimidine-4-carboxylic acid (cppH) – that form in comparable amounts – have been fully characterized individually. The X-ray structure of each isomer is related to its NMR spectrum in solution
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