Permanganate oxidation of alkenes. Substituent and solvent effects. Difficulties with MP2 calculations

The permanganate oxidation of alkenes has been studied both experimentally and computationally. Transition state structures were located for the reaction of permanganate ion with a variety of monosubstituted alkenes at the B3LYP/6-311++G** level. Although the calculated activation energy for the reaction with ethene was reasonable, the calculated effect of substituents, based on the energies of the reactants, was much larger than that experimentally found. This was shown to be due to the formation of an intermediate charge-dipole complex which led to the transition state. Reaction field calculations found the complex to disappear in a high dielectric constant medium, and the range of activation energies for the reaction in solution became quite small. MP2 calculations were carried out in order to have a comparison with the DFT results. MP2-MP4 gave unusual results for calculations on permanganate ion as well as chromate ion and iron tetraoxide. They also gave markedly unreasonable results for the activation energy of the reaction of permanganate with ethane. CCSD/6-311++G** calculations gave satisfactory results for permanganate ion and chromate ion. At this level of theory, the reaction of permanganate with ethene was found to have a very early transition state, when the bond lengths of the reactants just began to change. The reaction was calculated to be very exothermic (-69 kcal/mol), and this was confirmed via calorimetry. The rates of permanganate oxidation of allyl alcohol and acrylonitrile were determined, and they had similar reactivities. The kinetics and the products of the reaction of permanganate with crotonate ion were examined in some detail.     

A molecular dynamics exploration of the catalytic mechanism of yeast cytosine deaminase

Yeast cytosine deaminase (yCD), a zinc metalloenzyme of significant biomedical interest, is investigated by a series of molecular dynamics simulations in its free form and complexed with its reactant (cytosine), product (uracil), several reaction intermediates, and an intermediate analogue. Quantum chemical calculations, used to construct a model for the catalytic Zn ion with its ligands (two cysteines, a histidine, and one water) show, by comparison with crystal structure data, that the cysteines are deprotonated and the histidine is monoprotonated. The simulations suggest that Glu64 plays a critical role in the catalysis by yCD. The rotation of the Glu64 side-chain carboxyl group that can be protonated or deprotonated permits it to act as a proton shuttle between the Zn-bound water and cytosine and subsequent reaction intermediates. Free energy methods are used to obtain the barriers for these rotations, and they are sufficiently small to permit rotation on a nanosecond time scale. In the course of the reaction, cytosine reorients to a geometry to favor nucleophilic attack by a Zn-bound hydroxide. A stable position for a reaction product, ammonia, was located in the active site, and the free energy of exchange with a water molecule was evaluated. The simulations also reveal small motions of the C-terminus and the loop that contains Phe114 that may be important for reactant binding and product release.     

Depth Profile Analysis on the Nanometer Scale by a Combination of Electron Probe Microanalysis (EPMA) and Focused Ion Beam Specimen Preparation (FIB)

Electron probe microanalysis (EPMA) offers high sensitivity and high accuracy in quantitative measurements of chemical compositions and mass coverages. Owing to the low detection limits of the wavelength-dispersive technique, monolayers with mass coverages of about 0.05µgcm^–2 can be detected. Assuming a density of 5gcm^–3 this corresponds to a thickness of 0.1nm. With these advantages in mind, EPMA was extended to depth profile analysis in the sub-micron range using a surface removal technique.The present paper shows how depth profile analysis can be improved by combining EPMA and the focused ion beam (FIB) technique. The focused ion beam system uses a Ga⁺ ion beam. The ion beam allows the milling of defined geometries on the nanometer scale, so that very shallow bevels with exactly defined angles in relation to the surface can be obtained. Low surface damage is expected due to low sputtering effects. Calibrated WDX measurements along the bevel deliver quantitative concentration depth profiles. First results obtained with this new combination of methods will be presented for a multilayered sample used in optical data storage.     

Nickel(II) and cobalt(II) complexes of the hydrazide of 1-naphthylacetic acid

Summary The hydrazide of 1-naphthylacetic acid forms both bis- and tris-(ligand) high-spin nickel(II) and cobalt(II) complexes possessing an octahedral configuration. The compositions of the complexes are influenced not only by the metal-ligand stoichiometry but also by the nature of the inorganic anion. A physico-chemical investigation showed that the ligand is neutral and bidentate, coordinated through amido-nitrogen and carbonyl oxygen. The compounds were characterized by elemental analysis, magnetic measurements, i.r. and diffuse-reflection spectra and molar conductivity.     

Efficient Computational Schemes of the Conjugate Gradient Method for Solving Linear Systems

The technique of the initial guess calculation for the conjugate gradient method is proposed. Computational schemes of the linear system solution with symmetrical positive definite matrices are constructed on its basis. Their efficient modifications for systems with five-diagonal matrices are proposed. The investigation of the developed methods using the problem of two-dimensional numerical simulation of bipolar transistors has been carried out. Experimental evidence of the proposed method's efficiency has been obtained.     

Electrochemically induced multicomponent ‘one-pot’ assembling benzaldehydes,N,N′-dimethylbarbituric acid,and kojic acid

Monatshefte für Chemie - Chemical Monthly - The new electrochemically induced multicomponent assembling was found: the electrocatalytic transformation of benzaldehydes,...     

Combined Newton-Kurchatov method for solving nonlinear operator equations

We investigate local and semi-local convergence of the combined Newton-Kurchatov method under the classical and generalized Lipschitz conditions for solving nonlinear equations. The convergence order of the method is examined and the uniqueness ball for the solution of the nonlinear equation is proved. Numerical experiments are conducted on test problems. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Vibrational Raman spectra of CdSx Se1‐x magic‐size nanocrystals

Resonant Raman scattering spectra of ultrasmall (<2 nm) magic‐size nanocrystals (NCs) are reported. The spectra of CdS and CdS_x Se_1‐x NCs, resonantly excited with 325 nm and 442 nm laser lines, correspondingly, reveal broad features in the range of bulk optical phonons. The relatively large width, ～50 cm^‐1, and downward shift, ～20 cm^‐1, of the Raman bands with respect to the longitudinal optical phonon in bulk crystals and large NCs are discussed based on the breaking of the translational symmetry and bond distortion in these ultrasmall NCs. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)