Absolute Asymmetric Synthesis of a Tetrahedral Silver Complex

Even though the isolation of tetrahedral stereoisomers usually presents a synthetic challenge, a highly enantioenriched tetrahedral silver complex could be easily accessed by either crystallization or Viedma ripening. The overall preparation may be regarded as an example of absolute asymmetric synthesis. Experimental results indicate that both crystallization and Viedma ripening follow a similar cluster‐controlled mechanism.     

The rigid movable inclusion in elastostatics and elastodynamics

The problem of a single rigid movable inclusion is solved both for elastostatics and elastodynamic, using the null field approach. It is also shown how the solution can be obtained as the limit of the solution for an elastic inclusion. Numerical results for scattering by a superspheroidal inclusion are given.     

Enzymes immobilized in mesoporous silica: A physical–chemical perspective

Mesoporous materials as support for immobilized enzymes have been explored extensively during the last two decades, primarily not only for biocatalysis applications, but also for biosensing, biofuels and enzyme-controlled drug delivery. The activity of the immobilized enzymes inside the pores is often different compared to that of the free enzymes, and an important challenge is to understand how the immobilization affects the enzymes in order to design immobilization conditions that lead to optimal enzyme activity. This review summarizes methods that can be used to understand how material properties can be linked to changes in enzyme activity. Real-time monitoring of the immobilization process and techniques that demonstrate that the enzymes are located inside the pores is discussed by contrasting them to the common practice of indirectly measuring the depletion of the protein concentration or enzyme activity in the surrounding bulk phase. We propose that pore filling (pore volume fraction occupied by proteins) is the best standard for comparing the amount of immobilized enzymes at the molecular level, and present equations to calculate pore filling from the more commonly reported immobilized mass. Methods to detect changes in enzyme structure upon immobilization and to study the microenvironment inside the pores are discussed in detail. Combining the knowledge generated from these methodologies should aid in rationally designing biocatalyst based on enzymes immobilized in mesoporous materials.     

Multicomponent analysis of drinking water by a voltammetric electronic tongue

A voltammetric electronic tongue is described that was used for multicomponent analysis of drinking water. Measurements were performed on drinking water from a tap and injections of the compounds NaCl, NaN₃, NaHSO₃, ascorbic acid, NaOCl and yeast suspensions could be identified by use of principal component analysis (PCA). A model based on partial least square (PLS) was developed for the simultaneously prediction of identification and concentration of the compounds NaCl, NaHSO₃ and NaOCl. By utilizing this type of non-selective sensor technique for water quality surveillance, it will be feasible to detect a plurality of events without the need of a specific sensor for each type of event.     

Non-uniqueness of time-domain reflection from 3D planar elastic layers

Recently, some explicit results were obtained regarding non-uniqueness for the traction to displacement maps of bounded elastic bodies in 2D and 3D, under the assumption of an internal kinematic constraint. The approach utilized is that of transformation optics. As the approach could, under the usual continuum assumptions, handle all frequencies without resorting to active materials, it could potentially be directly applied also to time domain problems. In the present paper we cover the extension to the time domain of these recent results in the case of reflection from a composite slab of rather general anisotropy, and derive the required material properties of different slabs with identical reflection properties. In particular we describe how homogeneous and inhomogeneous slabs of very different thicknesses may be indistinguishable with respect to elastic wave reflection properties. It should be noted that the approach retains both the minor and major symmetries of the stiffness tensor, and does not require an anisotropic mass density tensor to be used.     

Hyperfine structure in the 6p5d configuration and isotope shifts in transitions between the 6s5d and the 6p5d configurations in Ba I

High-resolution laser fluorescence spectroscopy, using a single-mode dye laser acting on a collimated atomic beam, has been performed to determine the hyperfine-structure (hfs) constants in six states of the 6p 5d configuration of¹³⁵Ba and¹³⁷Ba. Isotope shifts (IS) for eleven transitions between the 6s 5d and the 6p 5d configurations have also been measured. From an analysis of the energy levels, intermediate angular wavefunctions have been deduced. The wavefunctions are used to evaluate experimental hyperfine parameters from the experimental hfs constants. The parameters are, for the magnetic-dipole interaction compared with theoretical values, and for the electricquadrupole interaction used to estimate the nuclear quadrupole moments for the odd isotopes. The IS in the measured transitions are analysed using a King-plot, with the first resonance line in Ba II as the reference. Specific mass and field shifts are evaluated for the measured transitions. The field shifts have been used to determine the change in mean-square radius between the natural abundant Ba-isotopes.     

Hyperfine-structure and isotope-shift measurements in the 6s 5d↔6p 5d transitions of Ba I in the far-red spectral region

Measurements of the hyperfine structures in the 6p5d ¹ D ₂,³ D ₁ and³ F _{2, 3, 4} states of¹³⁵Ba and¹³⁷Ba, and isotope-shifts in several far-red transitions between the 6s 5d and 6p 5d configurations, as well as the transition 6s ^{2 1} S ₀→6s6p ³ P ₁ at 7,911 Å have been performed using high-resolution laser spectroscopy on a collimated atomic beam of natural barium. An analysis of the magnetic-dipole interaction in the 6p 5d configuration using effective one- and two-body hyperfine operators is presented. In particular the contact interaction was studied with respect to the correlation between the two valence electrons. Effects of strong configuration interaction were found. From a King-plot analysis of the isotope shift term- andJ-dependence of the field shift have been evaluated for the transitions between the 6s 5d and 6p 5d configurations. Relativistic Hartree-Fock (RHF) calculations have been performed of electron densities at the nucleus for six different configurations in Ba I and Ba II. The RHF calculations reproduce the experimental King-plot slopes quite well, while the absolute values, of the changes in electron density at the nucleus for the studied transitions, are found to be 9% lower than the results derived from a muonic experiment.