Reorganization Energy for Internal Electron Transfer in Multicopper Oxidases.

We have calculated the reorganization energy for the intramolecular electron transfer between the reduced type 1 copper site and the peroxy intermediate of the trinuclear cluster in the multicopper oxidase CueO. The calculations are performed at the combined quantum mechanics and molecular mechanics (QM/MM) level, based on molecular dynamics simulations with tailored potentials for the two copper sites. We obtain a reorganization energy of 91-133 kJ/mol, depending on the theoretical treatment. The two Cu sites contribute by 12 and 22 kJ/mol to this energy, whereas the solvent contribution is 34 kJ/mol. The rest comes from the protein, involving small contributions from many residues. We have also estimated the energy difference between the two electron-transfer states and show that the reduction of the peroxy intermediate is exergonic by 43-87 kJ/mol, depending on the theoretical method. Both the solvent and the protein contribute to this energy difference, especially charged residues close to the two Cu sites. We compare these estimates with energies obtained from QM/MM optimizations and QM calculations in a vacuum and discuss differences between the results obtained at various levels of theory

Illustrationen als Paratext beim Ubersetzen : Mit Beispielen aus einem Werk von O. Preusler

Purpose: The authors tested associations between (a) parent-reported temporary vs. persistent vocabulary delay and (b) parent-reported behavioral/emotional problems in a sample of 5,497 young Dutch children participating in a prospective population-based study. Method: Mothers completed the MacArthur Communicative Development Inventory-Netherlands (Zink & Lejaegere, 2003) at age 18 months and the Language Development Survey (Rescorla, 1989) at age 30 months, with expressive vocabulary delay defined as scores in the lowest 15th age-and gender-specific percentiles. The Child Behavior Checklist (Achenbach & Rescorla, 2000) was completed by mothers when their children were age 18 months and by both parents when their children were age 36 months, from which Internalizing Problems and Externalizing Problems scores were analyzed. Results: All analyses were adjusted for covariates. Expressive vocabulary delay at age 18 months was weakly related to Internalizing Problems scores at age 18 months as well as mother-reported Externalizing and Internalizing Problems scores at age 36 months (the latter for boys only). Expressive vocabulary delay at age 30 months was weakly associated with mother-reported Externalizing and Internalizing Problems scores (the latter for boys only) and father-reported Internalizing Problems scores. Persistent expressive vocabulary delay predicted the highest risk of mother-reported internalizing and externalizing problems at age 36 months. Conclusion: This population-based study showed modest associations between vocabulary delay and behavioral/emotional problems detectable from 18 months onward

Filling a niche in “ligand space” with bulky, electron-poor phosphorus (III) alkoxides

The chemistry of phosphorus(III) ligands, which are of key importance in coordination chemistry, organometallic chemistry and catalysis, is dominated by relatively electron-rich species. Many of the electron-poor P(III) ligands that are readily available have relatively small steric profiles. As such, there is a significant gap in “ligand space” where more sterically bulky, electron-poor P(III) ligands are needed. This contribution discusses the coordination chemistry, steric and electronic properties of P(III) ligands bearing highly fluorinated alkoxide groups of the general form PRn(ORF)3-n, where R = Ph, RF = C(H)(CF3)2 and C(CF3)3; n = 1-3. These ligands are simple to synthesize and a range of experimental and theoretical methods suggest that their steric and electronic properties can be “tuned” by modification of their substituents, making them excellent candidates for large, electron-poor ligands

Potential energy function and vibrational states of HN3 and DN3

International audienceEight different six-dimensional potential energy functions for the electronic ground state of the HN3 have been generated by the CCSD(T) method and various density functional approaches. The potentials in their analytic forms have been used in variational calculations of the vibrational states (J = 0). The calculated anharmonic wavenumbers for the fundamentals agree with the known experimental values to within 7 cm(-1)(HN3) and 16 cm(-1)(DN,) for the CCSD(T) potential. The best density functional approach (B3LYP) yields fundamentals which are within 10 cm(-1)(HN3) and 44 cm(-1)(DN3), with the exception of the upsilon(2) which is in error by 43 cm(-1)(HN3) and 95 cm(-1)(DN3). Also the experimental isotope shifts for N-15 substituted species are very well reproduced for HN3. The barrier to linearity of the HN2 moiety has been calculated to be 11 578 cm(-1)(CCSD(T)). Due to the near-linearity of the NNN group, for which a barrier of only 327 cm(-1) has been calculated, the overtones and combination levels of the in-plane upsilon(5) and the out-of-plane upsilon(6) bending states fall in clusters in higher excited states. The vibrational energies for all states up to the NH(ND) stretching wavenumbers and their assignments are given

Hydrogen generation from alcohols catalyzed by ruthenium-triphenylphosphine complexes : multiple reaction pathways

We report a comprehensive density functional theory (DFT) study of the mechanism of the methanol dehydrogenation reaction catalyzed by [RuH2(H2)(PPh3)3]. Using the B97-D dispersion-corrected functional, four pathways have been fully characterized, which differ in the way the critical beta-hydrogen transfer step is brought about (e.g., by prior dissociation of one PPh3 ligand). All these pathways are found to be competitive (Delta G double dagger = 27.0-32.1 kcal/mol at 150 degrees C) and strongly interlocked. The reaction can thus follow multiple reaction channels, a feature which is expected to be at the origin of the good kinetics of this system. Our results also point to the active role of PPh3 ligands, which undergo significant conformational changes as the reaction occurs, and provide insights into the role of the base, which acts as a "co-catalyst" by facilitating proton transfers within active species. Activation barriers decrease on going from methanol to ethanol and 2-propanol substrates, in accord with experiment.PostprintPeer reviewe