On the Reaction Mechanism of the Complete Intermolecular O2 Transfer between Mononuclear Nickel and Manganese Complexes with Macrocyclic Ligands

The recently described intermolecular O₂ transfer between the side‐on Ni‐O₂ complex [(12‐TMC)Ni‐O₂]⁺ and the manganese complex [(14‐TMC)Mn]²⁺, where 12‐TMC and 14‐TMC are 12‐ and 14‐membered macrocyclic ligands, 12‐TMC=1,4,7,10‐tetramethyl‐1,4,7,10‐tetraazacyclododecane and 14‐TMC=1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane, is studied by means of DFT methods. B3LYP calculations including long‐range corrections and solvent effects are performed to elucidate the mechanism. The potential energy surfaces (PESs) compatible with different electronic states of the reactants have been analyzed. The calculations confirm a two‐step reaction, with a first rate‐determining bimolecular step and predict the exothermic character of the global process. The relative stability of the products and the reverse barrier are in line with the fact that no reverse reaction is experimentally observed. An intermediate with a μ‐η¹:η¹‐O₂ coordination and two transition states are identified on the triplet PES, slightly below the corresponding stationary points of the quintet PES, suggesting an intersystem crossing before the first transition state. The calculated activation parameters and the relative energies of the two transition sates and the products are in very good agreement with the experimental data. The calculations suggest that a superoxide anion is transferred during the reaction.     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

Theoretical Investigation of the Stepwise Hydrolysis of the [Re3(μ‐Cl)3Cl9]3‐ Anion

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.     

Time‐dependent flow across a step: the slip with friction boundary condition

The paper studies numerically the slip with friction boundary condition in the time‐dependent incompressible Navier–Stokes equations. Numerical tests on two‐ and three‐dimensional channel flows across a step using this boundary condition on the bottom wall are performed. The influence of the friction parameter on the flow field is studied and the results are explained according to the physics of the flow. Due to the stretching and tilting of vortices, the three‐dimensional results differ in many respects from the two‐dimensional ones. Copyright © 2005 John Wiley & Sons, Ltd.     

Towards ultra-responsive biodegradable polysaccharide humidity sensors

Sodium alginate is a biodegradable natural polymer that is derived from algae and is water soluble. Upon immersion in a CaCl₂ solution, a sodium alginate water solution is cross-linked to form water-insoluble calcium alginate. When the sodium alginate water solution is immersed in the CaCl₂ bath via a syringe pump, calcium alginate fibers are produced. By changing the CaCl₂ concentration, calcium alginate fibers with different degrees of cross-linking can be produced. Such fibers were found to differ in mechanical and morphological properties, and more interestingly, were found to possess humidity sensing and conductive properties. Interestingly, the higher the CaCl₂ concentration, the lower the degree of cross-linking, which produced softer fibers with better humidity sensing and conductive properties. The fibers were able to trap water in their structures, and a higher water content increased the conductivity due to the presence of an electrolyte salt in the fiber and due to the polyelectrolyte nature of the fiber itself. The cross-linking and percent shrinking degree, morphology and mechanical properties of the fibers were found to create significant changes in the conductivity and humidity sensing properties of the fibers. High humidity environments led to an increase in the conductivity of the fibers, whereas dry environments led to a decrease in the conductivity. The fibers, especially those with the highest CaCl₂ concentration, were determined to be ultra-responsive to humidity changes and exhibited very good repetition in humidity cycles. These tailored fibers are proposed as novel biodegradable conductive materials for various humidity sensing, robotic and bio-robotic applications.     

关于K个复相关矩阵相等的检验

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Theoretical elucidation of a classic reaction: protonation of the quadruple bond of the octachlorodimolybdate(II,II) [Mo2Cl8]4- anion

The protonation reaction of the unbridged quadruple metal-metal bond of [Mo(2)Cl(8)](4-) anion producing the triply bonded hydride [Mo(2)(μ-H)(μ-Cl)(2)Cl(6)](3-) is studied by accurate Density Functional Theory computations. The reactant, product, stable intermediates, and transition states are located on the potential energy surface. The water solvent is explicitly included in the calculations. Full reaction profiles are calculated and compared to experimental data. The mechanism of the reaction is fully elucidated. This involves two steps. The first is a proton transfer from an oxonium ion to the quadruple bond, being rate determining. The second, involves the internal rearrangement of chlorine atoms and is much faster. Activation energies with a mean value of 19 kcal/mol are calculated, in excellent agreement with experimental values.     

Mechanical reinforcement and water repellency induced to cellulose sheets by a polymer treatment

The present study reports a simple method to control the mechanical and surface properties of cellulose fiber networks and to protect them from humidity, without altering their initial morphology. This is achieved by dip coating the fiber networks in solutions containing different amounts of ethyl cyanoacrylate monomer (ECA). Under ambient humidity and due to the presence of the -OH groups of the cellulose, the ECA polymerizes around each individual cellulosic fiber forming a thin poly(ethyl cyanoacrylate) (PECA) shell. PECA was found to interact with the cellulose surface via hydrogen bonding as evidenced by Fourier transform infrared spectroscopy and thermogravimetric analysis measurements. The detailed surface characterization reveals that only 3.5 wt% of ECA in solution is sufficient to form compact PECA cladding around every cellulose fiber. After the proposed treatment the cellulose sheets become hydrophobic, well protected from the environmental humidity and with increased Young’s modulus.     

Protein-ligand interaction energies with dispersion corrected density functional theory and high-level wave function based methods

With dispersion-corrected density functional theory (DFT-D3) intermolecular interaction energies for a diverse set of noncovalently bound protein-ligand complexes from the Protein Data Bank are calculated. The focus is on major contacts occurring between the drug molecule and the binding site. Generalized gradient approximation (GGA), meta-GGA, and hybrid functionals are used. DFT-D3 interaction energies are benchmarked against the best available wave function based results that are provided by the estimated complete basis set (CBS) limit of the local pair natural orbital coupled-electron pair approximation (LPNO-CEPA/1) and compared to MP2 and semiempirical data. The size of the complexes and their interaction energies (ΔE(PL)) varies between 50 and 300 atoms and from -1 to -65 kcal/mol, respectively. Basis set effects are considered by applying extended sets of triple- to quadruple-ζ quality. Computed total ΔE(PL) values show a good correlation with the dispersion contribution despite the fact that the protein-ligand complexes contain many hydrogen bonds. It is concluded that an adequate, for example, asymptotically correct, treatment of dispersion interactions is necessary for the realistic modeling of protein-ligand binding. Inclusion of the dispersion correction drastically reduces the dependence of the computed interaction energies on the density functional compared to uncorrected DFT results. DFT-D3 methods provide results that are consistent with LPNO-CEPA/1 and MP2, the differences of about 1-2 kcal/mol on average (<5% of ΔE(PL)) being on the order of their accuracy, while dispersion-corrected semiempirical AM1 and PM3 approaches show a deviating behavior. The DFT-D3 results are found to depend insignificantly on the choice of the short-range damping model. We propose to use DFT-D3 as an essential ingredient in a QM/MM approach for advanced virtual screening approaches of protein-ligand interactions to be combined with similarly "first-principle" accounts for the estimation of solvation and entropic effects.