Engineered C–N Lyase: Enantioselective Synthesis of Chiral Synthons for Artificial Dipeptide Sweeteners

Aspartic acid derivatives with branched N‐alkyl or N‐arylalkyl substituents are valuable precursors to artificial dipeptide sweeteners such as neotame and advantame. The development of a biocatalyst to synthesize these compounds in a single asymmetric step is an as yet unmet challenge. Reported here is an enantioselective biocatalytic synthesis of various difficult N‐substituted aspartic acids, including N‐(3,3‐dimethylbutyl)‐l ‐aspartic acid and N‐[3‐(3‐hydroxy‐4‐methoxyphenyl)propyl]‐l ‐aspartic acid, precursors to neotame and advantame, respectively, using an engineered variant of ethylenediamine‐N,N′‐disuccinic acid (EDDS) lyase from Chelativorans sp. BNC1. This engineered C–N lyase (mutant D290M/Y320M) displayed a remarkable 1140‐fold increase in activity for the selective hydroamination of fumarate compared to that of the wild‐type enzyme. These results present new opportunities to develop practical multienzymatic processes for the more sustainable and step‐economic synthesis of an important class of food additives.     

Supply chain modelling and its analytical evaluation

A model-based analysis of supply chains (SCs) is proposed as a means of estimating performance measures like lead times and resource utilisations. SCs are regarded as discrete event dynamic systems (DEDS), described as process chains in an application-specific formalism, and analysed by state-of-the-art techniques developed for queueing networks (QNs) and Petri nets (PNs). The theoretical approach is accompanied by a toolset that provides automatic translations between a process-chain-specification front end and analysis engines for QN and PN models. In addition, the analysis technique also supports a hybrid approach, in which dedicated sub-models are mapped into a PN model, numerically analysed, and replaced with an aggregate. Finally, the resulting QN models may be analysed using analytical as well as simulative techniques. As an example application, we investigate the impact of an additional SC channel between a manufacturer and web-consumers on the overall performance of an SC. The example was inspired by the trend towards retail trade via the internet and illustrates the new challenges of electronic commerce for SC management.     

Infinite tensor products of Banach spaces I

In this paper we construct a new class of infinite tensor product Banach spaces. We call them spaces of type v since they are constructed in a manner which closely parallels von Neumanns construction of infinite tensor products of Hilbert spaces. We use these spaces to present results on infinite tensor products of semigroups of operators.     

Organic zeolites from a diolefinic monomer

Submicrometer particles of diethyl p-phenylenediacrylate (EPA) with tunable molecular adsorption characteristics were produced by solid-state photopolymerization in the presence of template molecules. EPA monomer particles were produced by rapid expansion of supercritical solutions (RESS), and deposited directly onto surface acoustic wave (SAW) resonators. The EPA particles were photopolymerized directly on the SAW devices in the presence of molecular templates, and dynamic sorption isotherms of C1- through C9-alkanes were studied to characterize the particle-vapor interaction. The mass increase due to vapor uptake into the particulate coatings was measured by monitoring the SAW resonance frequency during vapor sorption. The vapor selectivity and molecular porosity of the particulate coatings were studied in situ on the piezoelectric substrate by measuring sorption isotherms. A gradual exclusion of smaller alkane molecules from the molecularly imprinted particulate coatings was observed with decreasing template molecule size. The observed selective and reversible adsorption of alkane analytes with different molecular sizes suggest that these imprinted polymers may be categorized as organic analogues of zeolites.     

Unidirectional redox-stimulated movement around a C-C single bond

A remarkable challenge for the design of molecular machines is the realization of a synchronized and unidirectional movement caused by an external stimulus. Such a movement can be achieved by a unidirectionally controlled change of the conformation or the configuration. Biphenol derivatives are one possibility to realize a redox-driven unidirectional molecular switch. For this reason, a 4,4'-biphenol derivative was fixed to a chiral cyclopeptidic scaffold and stimulated by chemical oxidants and reduction agents. The conformation of the switch was determined by DFT calculations by using B3LYP and the 6-31G* basis set. The switching process was observed by UV and circular dichroism (CD) spectroscopic measurements. Several oxidation agents and various conditions were tested, among which (diacetoxy)iodobenzene (DAIB) in methanol proved to be the best. In this way it was possible to synthesize a redox-stimulated molecular switch with a movement that is part of a rotation around a biaryl binding axis.     

Surface structure of cubic ionic crystals studied by optical second-harmonic generation

Polarization and azimuthal dependencies of optical second-harmonic generation at the surface of cubic ionic crystals have been measured on polished surfaces of BaF₂ (111) and (100), CaF₂ (111) and NaCl (111), using a fundamental wavelength of 532 nm. The results are interpreted in terms of available theory, which shows that for transparent cubic media only the dipolar surface contribution depends on the crystal orientation. For BaF₂ (111) and NaCl (111) the crystallineC _3vgeometry could be identified but not for CaF₂ (111). Although the nature of the electronic surface structure giving rise to a dipolar polarizability remains undetermined, the experimental result suggests that it may be due to impurity or defect states in the band gap at the surface.     

Approximation to linear functionals on H1 by point evaluations

The degree of approximation to a bounded linear functional on H¹ having a smooth kernel by finite sums of point evaluations is shown to depend on the smoothness of that kernel. Use is made of a Jackson-Bernstein type theorem concerning the approximation of continuous unimodular functions by finite Blaschke products.     

Canonical Proper-Time Dirac Theory

In this paper, we report on a new approach to relativistic quantum theory. The classical theory is derived from a new implementation of the first two postulates of Einstein, which fixes the proper-time of the physical system of interest for all observers. This approach leads to a new group that we call the proper-time group. We then construct a canonical contact transformation on extended phase space to identify the canonical Hamiltonian associated with the proper-time variable. On quantization we get a new relativistic wave equation for spin 1/2 particles that generalizes the Dirac theory. The Hamiltonian is positive definite so we naturally interpret antiparticles as particles with their proper-time reversed. We show that for the hydrogen atom problem, we get the same fine structure separation. When the proton spin magnetic moment is taken into account, we get the standard hyperfine splitting terms of the Pauli approximation and two additional terms. The first term is small in p-states. It diverges in s-states, and provides more than enough to account for the Lamb-shift when the proton radius is used as a cut off. The last term promises to provide a correction to the hyperfine splitting term. Although incomplete, the general approach offers hope of completely accounting for the hydrogen spectrum as an eigenvalue problem.     

Quick assessment methodology for reliability of solder joints in ball grid array (BGA) assembly—Part II: Reliability experiment and numerical simulation

In the present study, a facility, i.e., a mechanical deflection system (MDS), was established and applied to assess the long-term reliability of the solder joints in plastic ball grid array (BGA) assembly. It was found that the MDS not only quickly assesses the long-term reliability of solder joints within days, but can also mimic similar failure mechanisms in accelerated thermal cycling (ATC) tests. Based on the MDS and ATC reliability experiments, the acceleration factors (AF) were obtained for different reliability testing conditions. Furthermore, by using the creep constitutive relation and fatigue life model developed in part I, a numerical approach was established for the purpose of virtual life prediction of solder joints. The simulation results were found to be in good agreement with the test results from the MDS. As a result, a new reliability assessment methodology was established as an alternative to ATC for the evaluation of long-term reliability of plastic BGA assembly. The project supported by the National Natural Science Foundation of China (59705008)