Optical rotation of achiral pentaerythritol

The optical rotatory power of achiral crystals of achiral pentaerythritol molecules was measured. The maximum rotations were found to be +/-6 degrees /mm. The quantum mechanically computed rotation of pentaerythritol molecules using linear response theory was 6 times larger although the experimental and theoretical tensors were similarly oriented to within 5 degrees .     

Spectroscopic studies of the corrinoid/iron-sulfur protein from Moorella thermoacetica

Methyl transfer reactions are important in a number of biochemical pathways. An important class of methyltransferases uses the cobalt cofactor cobalamin, which receives a methyl group from an appropriate methyl donor protein to form an intermediate organometallic methyl-Co bond that subsequently is cleaved by a methyl acceptor. Control of the axial ligation state of cobalamin influences both the mode (i.e., homolytic vs heterolytic) and the rate of Co-C bond cleavage. Here we have studied the axial ligation of a corrinoid iron-sulfur protein (CFeSP) that plays a key role in energy generation and cell carbon synthesis by anaerobic microbes, such as methanogenic archaea and acetogenic bacteria. This protein accepts a methyl group from methyltetrahydrofolate forming Me-Co(3+)CFeSP that then donates a methyl cation (Me) from Me-Co(3+)CFeSP to a nickel site on acetyl-CoA synthase. To unambiguously establish the binding scheme of the corrinoid cofactor in the CFeSP, we have combined resonance Raman, magnetic circular dichroism, and EPR spectroscopic methods with computational chemistry. Our results clearly demonstrate that the Me-Co3+ and Co2+ states of the CFeSP have an axial water ligand like the free MeCbi+ and Co(2+)Cbi+ cofactors; however, the Co-OH2 bond length is lengthened by about 0.2 angstroms for the protein-bound cofactor. Elongation of the Co-OH2 bond of the CFeSP-bound cofactor is proposed to make the cobalt center more "Co1+-like", a requirement to facilitate heterolytic Co-C bond cleavage.     

Influence of the organic compounds on the ecotoxicity in the treatment of foundry sludge and olive mill waste

The study of the ecotoxicity in two industrial waste materials and the relationships with the organic parameters has been conducted. Foundry sludge and olive mill waste have been used as industrial waste materials with organic or mixed character. Stabilisation/solidification (S/S) and advanced oxidation (AOP) processes have been carried out in order to treat both foundry sludge and olive mill waste. Analysis of ecotoxicity, total organic carbon, COD and phenol index have been evaluated in the untreated waste and end-products. The results of the treated samples allow obtaining the best formulations in both processes. The best formulations in the immobilisation process have been obtained with Portland cement and black carbon, activated carbon or foundry sand ashes. In the AOP process, ozone concentrations above 35 mg/l and reaction times equal to 120 minutes have been the optimal variables. The relationships between the organic parameters and the ecotoxicity of the samples have been studied in this paper. Furthermore, the global organic parameters have been studied in relation to the phenolic compounds. Lineal and logarithmic expressions have been obtained between the total organic carbon and phenol index and the ecotoxicity of the samples related to the organic parameters, respectively. Ecotoxicity of the samples with Vibrio fischeri is recommended as a very promising biotest for the study of the characterisation and the evaluation of the treatment of organic and mixed character waste and total organic carbon is recommended as global organic parameter in the treatment of foundry sludge.     

Pyrazine as a building block for molecular architectures with PtII

A series of pyrazine (pz) complexes containing cis-(NH(3))(2)Pt(II), (tmeda)Pt(II) (tmeda = N,N,N',N'-tetramethylethylenediamine), and trans-(NH(3))(2)Pt(II) entities have been prepared and characterized by X-ray crystallography and/or 1H NMR spectroscopy. In these compounds, the pz ligands act as monodentate (1-3) or bidentate bridging ligands (4-7). Three variants of the latter case are described: a dinuclear complex [Pt(II)]2 (4b), a cyclic tetranuclear [Pt(II)](4) complex (5), and a trinuclear mixed-metal complex [Pt2Ag] (7). Mono- and bidentate binding modes are readily differentiated by 1H NMR spectroscopy, and the assignment of pz protons in the case of monodentate coordination is aided by the observation of (195)Pt satellites. Formation of the open molecular box cis-[{(NH3)2Pt(pz)}4](NO3)8.3.67H2O (5) from cis-(NH3)2Pt(II) and pz follows expectations of the "molecular library approach" for the generation of a cyclic tetramer.     

Diastereospecific and diastereoselective syntheses of Ruthenium(II) complexes using N,N' bidentate ligands aryl-pyridin-2-ylmethyl-amine ArNH-CH2-2-C5H4N and their oxidation to imine ligands

Coordination of N,N' bidentate ligands aryl-pyridin-2-ylmethyl-amine ArNH-CH2-2-C5H4N 1 (Ar = 4-CH3-C6H4, 1a; 4-CH3O-C6H4, 1b; 2,6-(CH3)2-C6H3, 1c; 4-CF3-C6H4, 1d) to the moieties [Ru(bipy)2]2+, [Ru(eta5-C5H5)L]+ (L = CH3CN, CO), or [Ru(eta6-arene)Cl]2+ (arene = benzene, p-cymene) occurs under diastereoselective or diastereospecific conditions. Detailed stereochemical analysis of the new complexes is included. The coordination of these secondary amine ligands activates their oxidation to imines by molecular oxygen in a base-catalyzed reaction and hydrogen peroxide was detected as byproduct. The amine-to-imine oxidation was also observed under the experimental conditions of cyclic voltammetry measurements. Deprotonation of the coordinated amine ligands afforded isolatable amido complexes only for the ligand (1-methyl-1-pyridin-2-yl-ethyl)-p-tolyl-amine, 1e, which doesn't contain hydrogen atoms in a beta position relative to the N-H bond. The structures of [Ru(2,2'-bipyridine)2(1b)](PF6)2, 2b; [Ru(2,2'-bipyridine)(2)(1c)](PF6)2, 2c; trans-[RuCl2(COD)(1a)], 3; and [RuCl2(eta6-C6H6)(1a)]PF6, 4a, have been confirmed by X-ray diffraction studies.     

Unravelling the origin of the high-catalytic activity of supported Au: a density-functional theory-based interpretation

Using first principles DF calculations we have studied the structural and catalytic properties of Au supported on TiOx-Mo(112) films. Our theoretical models are consistent with an initial (8 x 2) Mo(112)-Ti2O3 pattern which after Au deposition gives rise to ordered Au films that completely wet the surface. The oxidation of CO on model surfaces at coverage 1, 4/3, and 5/2 ML has been analyzed. The oxidation proceeds through a peroxo-like complex in which molecular oxygen is simultaneously bound to the CO and the surface. The energy barrier computed for a Au coverage of 4/3 ML is found significantly lower in agreement with the unusual high activity observed for this catalyst. The detailed analysis of the geometry and electronic structure provides a fundamental understanding of the reaction.     

The constrained space orbital variation analysis for periodic ab initio calculations

The constrained space orbital variation (CSOV) method for the analysis of the interaction energy has been implemented in the periodic ab initio CRYSTAL03 code. The method allows for the partition of the energy of two interacting chemical entities, represented in turn by periodic models, into contributions which account for electrostatic effects, mutual polarization and charge transfer. The implementation permits one to carry out the analysis both at the Hartree-Fock and density functional theory levels, where in the latter the most popular exchange-correlation functionals can be used. As an illustrating example, the analysis of the interaction between CO and the MgO (001) surface has been considered. As expected by the almost fully ionic character of the support, our periodic CSOV results, in general agree with those previously obtained using the embedded cluster approach, showing the reliability of the present implementation.     

Path integral ground state study of finite-size systems: application to small (parahydrogen)N (N=2-20) clusters

We use the path integral ground state method to study the energetic and structural properties of small para-H2 clusters of sizes ranging from 2 to 20 molecules. A fourth order formula is used to approximate the short imaginary-time propagator and two interaction potentials are considered. Our results are compared to those of exact basis set calculations and other quantum Monte Carlo methods when available. We find that for all cluster sizes considered, our results show a lower ground state energy than literature values obtained by diffusion Monte Carlo and variational Monte Carlo. For the dimer and trimer, ground state energies are in good agreement with exact results obtained using the discrete variable representation. Structural properties are found to be insensitive to the choice of interaction potential. We explore the use of Pekeris coordinates to analyze the importance of linear arrangement in trimers and for trimers within clusters of larger size.     

Critical point estimation of the Lennard-Jones pure fluid and binary mixtures

The apparent critical point of the pure fluid and binary mixtures interacting with the Lennard-Jones potential has been calculated using Monte Carlo histogram reweighting techniques combined with either a fourth order cumulant calculation (Binder parameter) or a mixed-field study. By extrapolating these finite system size results through a finite size scaling analysis we estimate the infinite system size critical point. Excellent agreement is found between all methodologies as well as previous works, both for the pure fluid and the binary mixture studied. The combination of the proposed cumulant method with the use of finite size scaling is found to present advantages with respect to the mixed-field analysis since no matching to the Ising universal distribution is required while maintaining the same statistical efficiency. In addition, the accurate estimation of the finite critical point becomes straightforward while the scaling of density and composition is also possible and allows for the estimation of the line of critical points for a Lennard-Jones mixture.