Switchable Plasmonic Metasurface Utilizing the Electro-Optic Kerr Effect of a Blue Phase Liquid Crystal

A switchable metasurface composed of plasmonic split ring resonators and a polymer-stabilized liquid crystal blue phase is developed. Owing to field-induced birefringence (electro-optic Kerr effect), the state of polarization of the incident near infrared radiation changes, when a voltage is applied to the liquid crystal. Thus, different resonant modes of the split ring resonators can be addressed and the transmission spectrum changes accordingly. In comparison with other liquid crystal phases, blue phases have several advantages. For example, they are optically isotropic in the field-off state, so that no alignment layer is required. The results of the present study indicate that the advantages of these mesophases can be utilized for switchable metasurfaces.     

Enantioselective Reduction of Citral Isomers in NCR Ene Reductase: Analysis of an Active‐Site Mutant Library

A deeper understanding of the >99 % S‐selective reduction of both isomers of citral catalyzed by NCR ene reductase was achieved by active‐site mutational studies and docking simulation. Though structurally similar, the E/Z isomers of citral showed a significantly varying selectivity response to introduced mutations. Although it was possible to invert (E)‐citral reduction enantioselectivity to ee 46 % (R) by introducing mutation W66A, for (Z)‐citral it remained ≥88 % (S) for all single‐residue variants. Residue 66 seems to act as a lever for opposite binding modes. This was underlined by a W66A‐based double‐mutant library that enhanced the (E)‐citral derived enantioselectivity to 63 % (R) and significantly lowered the S selectivity for (Z)‐citral to 44 % (S). Formation of (R)‐citronellal from an (E/Z)‐citral mixture is a desire in industrial (?)‐menthol synthesis. Our findings pave the way for a rational enzyme engineering solution.     

Biocatalytic Asymmetric Phosphorylation Catalyzed by Recombinant Glycerate‐2‐Kinase

The efficient synthesis of pure d ‐glycerate‐2‐phosphate is of great interest due to its importance as an enzyme substrate and metabolite. Therefore, we investigated a straightforward one‐step biocatalytic phosphorylation of glyceric acid. Glycerate‐2‐kinase from Thermotoga maritima was expressed in Escherichia coli, allowing easy purification. The selective glycerate‐2‐kinase‐catalyzed phosphorylation was followed by ³¹P NMR and showed excellent enantioselectivity towards phosphorylation of the d ‐enantiomer of glyceric acid. This straightforward phosphorylation reaction and subsequent product isolation enabled the preparation of enantiomerically pure d ‐glycerate 2‐phosphate. This phosphorylation reaction, using recombinant glycerate‐2‐kinase, yielded d ‐glycerate 2‐phosphate in fewer reaction steps and with higher purity than chemical routes.     

Enzymatic Addition of Alcohols to Terpenes by Squalene Hopene Cyclase Variants

Squalene–hopene cyclases (SHCs) catalyze the polycyclization of squalene into a mixture of hopene and hopanol. Recently, amino-acid residues lining the catalytic cavity of the SHC from Alicyclobacillus acidocaldarius were replaced by small and large hydrophobic amino acids. The alteration of leucine 607 to phenylalanine resulted in increased enzymatic activity towards the formation of an intermolecular farnesyl–farnesyl ether product from farnesol. Furthermore, the addition of small-chain alcohols acting as nucleophiles led to the formation of non-natural ether-linked terpenoids and, thus, to significant alteration of the product pattern relative to that obtained with the wild type. It is proposed that the mutation of leucine at position 607 may facilitate premature quenching of the intermediate by small alcohol nucleophiles. This mutagenesis-based study opens the field for further intermolecular bond-forming reactions and the generation of non-natural products.     

Organometallic DNA–B12 Conjugates as Potential Oligonucleotide Vectors: Synthesis and Structural and Binding Studies with Human Cobalamin-Transport Proteins

The synthesis and structural characterization of Co-(dN)₂₅-Cbl (Cbl: cobalamin; dN: deoxynucleotide) and Co-(dN)₃₉-Cbl, which are organometallic DNA–B₁₂ conjugates with single DNA strands consisting of 25 and 39 deoxynucleotides, respectively, and binding studies of these two DNA–Cbl conjugates to three homologous human Cbl transporting proteins, transcobalamin (TC), intrinsic factor (IF), and haptocorrin (HC), are reported. This investigation tests the suitability of such DNA–Cbls for the task of eventual in vivo oligonucleotide delivery. The binding of DNA–Cbl to TC, IF, and HC was investigated in competition with either a fluorescent Cbl derivative and Co-(dN)₂₅-Cbl, or radiolabeled vitamin B₁₂ (⁵⁷Co-CNCbl) and Co-(dN)₂₅-Cbl or Co-(dN)₃₉-Cbl. Binding of the new DNA–Cbl conjugates was fast and tight with TC, but poorer with HC and IF, which extends a similar original finding with the simpler DNA–Cbl, Co-(dN)₁₈-Cbl. The contrasting affinities of TC versus IF and HC for the DNA–Cbl conjugates are rationalized herein by a stepwise mechanism of Cbl binding. Critical contributions to overall affinity result from gradual conformational adaptations of the Cbl-binding proteins to the DNA–Cbl, which is first bound to the respective β domains. This transition is fast with TC, but slow with IF and HC, with which weaker binding results. The invariably tight interaction of the DNA–Cbl conjugates with TC makes the Cbl moiety a potential natural vector for the specific delivery of oligonucleotide loads from the blood into cells.     

Porous silicon bulk acoustic wave resonator with integrated transducer

ABSTRACT: : We report that porous silicon acoustic Bragg reflectors and AlN-based transducers can be successfully combined and processed in a commercial solidly mounted resonator production line. The resulting device takes advantage of the unique acoustic properties of porous silicon in order to form a monolithically integrated bulk acoustic wave resonator.     

Porous silicon nanocrystals in a silica aerogel matrix

ABSTRACT: Silicon nanoparticles of three types (oxide-terminated silicon nanospheres, micron-sized hydrogen-terminated porous silicon grains and micron-size oxide-terminated porous silicon grains) were incorporated into silica aerogels at the gel preparation stage. Samples with a wide range of concentrations were prepared, resulting in aerogels that were translucent (but weakly coloured) through to completely opaque for visible light over sample thicknesses of several millimetres. The photoluminescence of these composite materials and of silica aerogel without silicon inclusions was studied in vacuum and in the presence of molecular oxygen in order to determine whether there is any evidence for non-radiative energy transfer from the silicon triplet exciton state to molecular oxygen adsorbed at the silicon surface. No sensitivity to oxygen was observed from the nanoparticles which had partially H-terminated surfaces before incorporation and so we conclude that the silicon surface has become substantially oxidised. Finally, the FTIR and Raman scattering spectra of the composites were studied in order to establish the presence of crystalline silicon; by taking the ratio of intensities of the silicon and aerogel Raman bands, we were able to obtain a quantitative measure of the silicon nanoparticle concentration independent of the degree of optical attenuation.     

A comparative study of high resolution cone beam X-ray tomography and synchrotron tomography applied to Fe- and Al-alloys

X-ray computed tomography (XCT) has become a very important method for non-destructive 3D-characterization and evaluation of materials. Due to measurement speed and quality, XCT systems with cone beam geometry and matrix detectors have gained general acceptance. Continuous improvements in the quality and performance of X-ray tubes and XCT devices have led to cone beam CT systems that can now achieve spatial resolutions down to 1 μm and even below. However, the polychromatic nature of the source, limited photon flux and cone beam artefacts mean that there are limits to the quality of the CT-data achievable; these limits are particularly pronounced with materials of higher density like metals. Synchrotron radiation offers significant advantages by its monochromatic and parallel beam of high brilliance. These advantages usually cause fewer artefacts, improved contrast and resolution.Tomography data of a steel sample and of two multi-phase Al-samples (AlSi12Ni1, AlMg5Si7) are recorded by advanced cone beam XCT-systems with a μ-focus (μXCT) and a sub-μm (nano-focus, sub-μXCT) X-ray source with voxel dimensions between 0.4 and 3.5 μm and are compared with synchrotron computed tomography (sXCT) with 0.3 μm/voxel. CT data features like beam hardening and ring artefacts, detection of details, sharpness, contrast, signal-to-noise ratio and the grey value histogram are systematically compared. In all cases μXCT displayed the lowest performance. Sub-μXCT gives excellent results in the detection of details, spatial and contrast resolution, which are comparable to synchrotron-XCT recordings. The signal-to-noise ratio is usually significantly lower for sub-μXCT compared with the two other methods. With regard to measurement costs “for industrial users”, scanning volume, accessibility and user-friendliness sub-μXCT has significant advantages in comparison to synchrotron-XCT.     

New Aromatic Azapentalenes: 3H‐ and 2H‐Imidazo[1,2‐d]tetrazoles

A number of title compounds ( 3a,c,4a—c ) were prepared by cyclization of 5‐aminotetrazolium salts having ketonic substituents ( 1,2 ). The following procedures were applied: a) for 3a, 4a,b : heating of 1a, 2a,b with acetic anhydride‐ base; b) for 3c,4c : heating of 1b,2b in a buffer solution of pH 6.5 (Tschitschibabin reaction). The proclivity for ring closure was more pronounced with the salts 2 . The 6‐unsubstituted representatives 3c and 4c underwent S_E‐reactions, the 2H‐isomer 4c being slightly more reactive; this was confirmed by AM1 calculations. The nitroso product 4g exists predominantly as the valence‐isomeric nitrile oxide 6 .