Superelectrophilic activation of 4-heterocyclohexanones. Implications for polymer synthesis. A theoretical study

The stability and the reactivity of mono- and diprotonated 4-heterocyclohexanones as well as cyclohexanone in triflic acid have been studied at the PBE0/aug-cc-pvtz//PBE0/6-31+G** level of theory. In all cases the first protonation is an exergonic process occurring at a carbonyl oxygen except for 4-piperidone where a nitrogen atom is protonated fist. Second protonation is only slightly endergonic for all studied molecules except for cyclohexanone where the second protonation is very unfavorable thermodynamically. According to calculations, diprotonated 4-heterocyclohexanones are much more active in the reactions of triflic acid mediated polyalkoxyalkylation with aromatic hydrocarbons compared to monoprotonated ones. The increase of the reactivity of diprotonated 4-heterocyclohexanones is due to inductive effect rather than through space electrostatic influence as follows from the electronic structure analysis of dications. Moreover, the second protonation reduces the possibility of an aldol condensation side reaction, reducing the enol electrophilicity rendering heterocyclohexanones as promising monomers for superacid mediated polyhydroxyalkylation.     

The critical temperature for the BCS equation at weak coupling

For the BCS equation with local two-body interaction λV(x), we give a rigorous analysis of the asymptotic behavior of the critical temperature as γ»0. We derive necessary and sufficient conditions onV(x) for the existence of a nontrivial solution for all values of γ>0.     

Free-base tripyrrins

The hitherto unavailable free-base tripyrrins HTrpy have been prepared by cyanide promoted demetallation of a nickel(ii) tripyrrin and by acid-induced condensation of a diformylpyrrole and an alkylpyrrole with a sterically shielded alpha-position.     

Characterization of nanoporous gold electrodes for bioelectrochemical applications

The high surface areas of nanostructured electrodes can provide for significantly enhanced surface loadings of electroactive materials. The fabrication and characterization of nanoporous gold (np-Au) substrates as electrodes for bioelectrochemical applications is described. Robust np-Au electrodes were prepared by sputtering a gold-silver alloy onto a glass support and subsequent dealloying of the silver component. Alloy layers were prepared with either a uniform or nonuniform distribution of silver and, post dealloying, showed clear differences in morphology on characterization with scanning electron microscopy. Redox reactions under kinetic control, in particular measurement of the charge required to strip a gold oxide layer, provided the most accurate measurements of the total electrochemically addressable electrode surface area, A(real). Values of A(real) up to 28 times that of the geometric electrode surface area, A(geo), were obtained. For diffusion-controlled reactions, overlapping diffusion zones between adjacent nanopores established limiting semi-infinite linear diffusion fields where the maximum current density was dependent on A(geo). The importance of measuring the surface area available for the immobilization was determined using the redox protein, cyt c. The area accessible to modification by a biological macromolecule, A(macro), such as cyt c was reduced by up to 40% compared to A(real), demonstrating that the confines of some nanopores were inaccessible to large macromolecules due to steric hindrances. Preliminary studies on the preparation of np-Au electrodes modified with osmium redox polymer hydrogels and Myrothecium verrucaria bilirubin oxidase (MvBOD) as a biocathode were performed; current densities of 500 μA cm(-2) were obtained in unstirred solutions.     

ChemInform Abstract: Pressure‐Induced Formation of Molecular B2X4(μ‐X)2 (X: Cl,Br, I) Species.

Gas‐phase formation and decomposition of the boron(III) halides of title is explored by CCSD(T) and MP2 ab initio calculations.     

Asymptotic analysis of 3D thin anisotropic plates with a piezoelectric patch

We consider a thin elastic plate with piezo patches mounted on top of it. Electrodes are located on the upper and, depending on the devices, at the lower surface of the patches. This piezo actuator is coupled to an elastic body. We develop an asymptotic procedure to derive a two‐dimensional approximation of the entire structure. As a result, we obtain an inhomogeneous fourth‐order plate equation with piecewise smooth coefficients for the vertical displacement coupled to a second‐order in‐plane problem. The analysis and the resulting asymptotic limits help clarifying the modeling issue concerning active piezo devices in multidimensional smart structures. Copyright © 2012 John Wiley & Sons, Ltd.     

Asymptotics for estimation of quantile regressions with truncated infinite-dimensional processes

Many processes can be represented in a simple form as infinite-order linear series. In such cases, an approximate model is often derived as a truncation of the infinite-order process, for estimation on the finite sample. The literature contains a number of asymptotic distributional results for least squares estimation of such finite truncations, but for quantile estimation, results are not available at a level of generality that accommodates time series models used as finite approximations to processes of potentially unbounded order. Here we establish consistency and asymptotic normality for conditional quantile estimation of truncations of such infinite-order linear models, with the truncation order increasing in sample size. We focus on estimation of the model at a given quantile. The proofs use the generalized functions approach and allow for a wide range of time series models as well as other forms of regression model. The results are illustrated with both analytical and simulation examples.     

Distance sensing using dynamic speckles formed by micro-electro-mechanical-systems deflector

We present a novel architecture of dynamic-speckles distance sensors with a micro-electro-mechanical system (MEMS) deflecting mirror for surface scanning. Since the MEMS mirror deflects the beam sinusoidally, the speed of scanning varies during the scan leading to sufficient variations in the signal frequency which is used to evaluate the distance to the object. Nevertheless, this feature does not affect the accuracy of range measurements when the distance is estimated from zero-crossing counts of the signal during a specially chosen time window within the scan. Experimental results indicate that a single 1 ms scan yields 70 μm accuracy of distance measurement. Averaging data from multiple scans of different surface areas during a 1-s measurement can provide approximately 2 mm of accuracy. Precision of the measurements can be further improved by optimization of the optical system. The compactness of the MEMS deflector and simplicity of the suggested signal processing provides a good basis for practical applications of this distance sensor.     

Graphene Nanobelts,Möbius and Higher Order Möbius Strips Formed from Graphene. A Combined CASSCF/DFT Study

Russian Journal of Physical Chemistry A - Twisted graphene nanoribbons with linking numbers (Lk) of 2 and 3 have been studied at hybrid DFT and CASSCF levels. CASSCF calculations demonstrated...     

Push–pull hyperbranched molecules. A theoretical study

The electronic properties of the ground state, unrelaxed and relaxed first excited states of push–pull hyperbranched molecules bearing amino and nitro terminal groups have been studied at BB1K/cc‐pvdz//HF/6‐31g(d), TD‐BB1K/cc‐pvdz//HF/6‐31g(d) and TD‐BB1K/cc‐pvdz//CIS/6‐31g(d) levels of theory, respectively. It was demonstrated that dendritic architecture of push–pull molecules favours the charge transfer in the excited state compared to linear molecules. The possibility of adopting a plane conformation is an important condition for the charge transfer in an excited state. According to the calculations 1:1 ratio of donor and acceptor groups is another important precondition for the manifestation of strong charge separation in the excited state. In case of excess of nitro groups over the amino, some of the excitations participating in the S0 → S1 transition favour the charge transfer in the excited state in the opposite directions, thus decreasing the charge separation. Copyright © 2008 John Wiley & Sons, Ltd.