Bifidobacterium longum l-Arabinose Isomerase—Overexpression in Lactococcus lactis, Purification, and Characterization

Bifidobacterium longum NRRL B-41409 l-arabinose isomerase (l-AI) was cloned and overexpressed in Lactococcus lactis using a phosphate-depletion-inducible expression system. The purified B. longum l-AI was characterized using d-galactose and l-arabinose as the substrates. The enzyme was active and stable at acidic pH with an optimum at pH 6.0?C6.5. The enzyme showed the highest activity at 55?°C during a 20-min incubation at pH 6.5. The K _m value was 120?mM for l-arabinose and 590?mM for d-galactose. The V _max was 42?U mg^?1 with l-arabinose and 7.7?U mg^?1 with d-galactose as the substrates. The enzyme had very low requirement for metal ions for catalytic activity, but it was stabilized by divalent metal ions (Mg²⁺, Mn²⁺). The enzyme bound the metal ions so tightly that they could not be fully removed from the active site by EDTA treatment. Using purified B. longum l-AI as the catalyst at 35?°C, equilibrium yields of 36?% d-tagatose and 11?% l-ribulose with 1.67?M d-galactose and l-arabinose, respectively, as the substrates were reached.     

A unified framework for a posteriori error estimation for the Stokes problem

In this paper, a unified framework for a posteriori error estimation for the Stokes problem is developed. It is based on $[H^1_0(\Omega )]^d$ -conforming velocity reconstruction and $\underline{\varvec{H}}(\mathrm{div},\Omega )$ -conforming, locally conservative flux (stress) reconstruction. It?gives guaranteed, fully computable global upper bounds as well as local lower bounds on the energy error. In order to apply this framework to a given numerical method, two simple conditions need to be checked. We show how to do this for various conforming and conforming stabilized finite element methods, the discontinuous Galerkin method, the Crouzeix–Raviart nonconforming finite element method, the mixed finite element method, and a general class of finite volume methods. The tools developed and used include a new simple equilibration on dual meshes and the solution of local Poisson-type Neumann problems by the mixed finite element method. Numerical experiments illustrate the theoretical developments.     

The maximum angle condition is not necessary for convergence of the finite element method

We show that the famous maximum angle condition in the finite element analysis is not necessary to achieve the optimal convergence rate when simplicial finite elements are used to solve elliptic problems. This condition is only sufficient. In fact, finite element approximations may converge even though some dihedral angles of simplicial elements tend to π.     

Pyrogallarenes as alkali metal receptors: the role of cation-pi interactions in complexation

Crystallization studies of C-methyl pyrogallarene with potassium, rubidium and caesium bromides or chlorides resulted in a hydrogen bonded molecular cage in which the alkali metal cations are eta6 coordinated to aromatic rings via strong cation-pi interactions.     

Amino-functionalization of large-pore mesoscopically ordered silica by a one-step hyperbranching polymerization of a surface-grown polyethyleneimine

A simple method for surface functionalization of large-pore mesoporous silica by hyperbranching polymerization resulting in a high loading of amine groups is presented.     

Discrete maximum principle for FE solutions of the diffusion-reaction problem on prismatic meshes

In this paper we analyse the discrete maximum principle (DMP) for a stationary diffusion-reaction problem solved by means of prismatic finite elements. We derive geometric conditions on the shape parameters of the prismatic partitions which guarantee validity of the DMP. The presented numerical tests show the sharpness of the obtained conditions.     

A Computational Study on Closed-Shell Molecular Hexafluorides MF6 (M=S,Se, Te,Po, Xe,Rn, Cr,Mo, W,U) – Molecular Structure,Anharmonic Frequency Calculations,and Prediction of the NdF6 Molecule

Quantum chemical methods were used to study the molecular structure and anharmonic IR spectra of the experimentally known closed-shell molecular hexafluorides MF₆ (M=S, Se, Te, Xe, Mo, W, U). First, the molecular structures and harmonic frequencies were investigated using Density Functional Theory (DFT) with all-electron basis sets and explicitly considering the influence of spin-orbit coupling. Second, anharmonic frequencies and IR intensities were calculated with the CCSD(T) coupled cluster method and compared, where available, with IR spectra recorded by us. These comparisons showed satisfactory results. The anharmonic IR spectra provide means for identifying experimentally too little studied or unknown MF₆ molecules with M=Cr, Po, Rn. To the best of our knowledge, we predict the NdF₆ molecule for the first time and show it to be a true local minimum on the potential energy surface. We used intrinsic bond orbital (IBO) analyses to characterize the bonding situation in comparison with the UF₆ molecule.     

ChemInform Abstract: Icosahedral Au72: A Predicted Chiral and Spherically Aromatic Golden Fullerene

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 of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Lithium-ion Mobility in Li6B18(Li3N) and Li Vacancy Tuning in the Solid Solution Li6B18(Li3N)1−x(Li2O)x

All-solid-state batteries are promising candidates for safe energy-storage systems due to non-flammable solid electrolytes and the possibility to use metallic lithium as an anode. Thus, there is a challenge to design new solid electrolytes and to understand the principles of ion conduction on an atomic scale. We report on a new concept for compounds with high lithium ion mobility based on a rigid open-framework boron structure. The host–guest structure Li₆B₁₈(Li₃N) comprises large hexagonal pores filled with Li₇N] strands that represent a perfect cutout from the structure of α-Li₃N. Variable-temperature ⁷Li NMR spectroscopy reveals a very high Li mobility in the template phase with a remarkably low activation energy below 19 kJ mol⁻¹ and thus much lower than pristine Li₃N. The formation of the solid solution of Li₆B₁₈(Li₃N) and Li₆B₁₈(Li₂O) over the complete compositional range allows the tuning of lithium defects in the template structure that is not possible for pristine Li₃N and Li₂O.