Enantioselective Addition Reaction of Azlactones with Styrene Derivatives Catalyzed by Strong Chiral Brønsted Acids

An enantioselective intermolecular addition reaction of azlactones, as carbon nucleophiles, with styrene derivatives, as simple olefins, was demonstrated using a newly developed chiral Brønsted acid catalyst, namely, F₁₀BINOL‐derived N‐triflyl phosphoramide. Addition products having vicinal tetrasubstituted carbon centers, one of which is an all‐carbon quaternary stereogenic center, were formed in good yields with moderate to high stereoselectivities. Extremely high acidity of the new chiral Brønsted acid was confirmed by its calculated pK_a value based on DFT studies and is the key to accomplishing not only high catalytic activity but also efficient stereocontrol in the intermolecular addition.     

Visualizing Microglia with a Fluorescence Turn‐On Ugt1a7c Substrate

Microglia, the brain‐resident macrophage, are involved in brain development and contribute to the progression of neural disorders. Despite the importance of microglia, imaging of live microglia at a cellular resolution has been limited to transgenic mice. Efforts have therefore been dedicated to developing new methods for microglia detection and imaging. Using a thorough structure–activity relationships study, we developed CDr20, a high‐performance fluorogenic chemical probe that enables the visualization of microglia both in vitro and in vivo. Using a genome‐scale CRISPR‐Cas9 knockout screen, the UDP‐glucuronosyltransferase Ugt1a7c was identified as the target of CDr20. The glucuronidation of CDr20 by Ugt1a7c in microglia produces fluorescence.     

Antenna Performance of a Directly Dug Corrugated Feedhorn for the 150-GHz Band

We have developed a 150 GHz band corrugated feed horn. These corrugated feed horns have been established by a new machining method, which involves digging corrugations through a metal material. We were able to realize E plane and H plane symmetry, low side lobe level, and low cross-polarization level. Measured co-polarization beam patterns above − 35 dB were consistent with the simulated patterns within a designed frequency range. The peak levels of cross-polarization beam patterns were less than − 30 dB. And, the performances were uniform in several horns. In the present paper, we describe the corrugated horn produced by this methods.     

Evaluation of immobilized-lysozyme by means of TOF-SIMS

Evaluation of immobilized-proteins on bio-devices is important for the development of sophisticated devices. Lysozyme molecules immobilized on substrates were evaluated by means of time-of-flight secondary ion mass spectrometry (TOF-SIMS). Two types of the lysozyme-immobilized samples were prepared by controlling the binding parts, i.e., the amino groups or carboxyl groups, of the protein. The TOF-SIMS spectra of each sample were analyzed with mutual information to select fragment ions specific to each sample. According to the results, differences between the samples being immobilized in the different ways are suggested, and the surface structure of the lysozyme molecule immobilized at amino groups is determined based on three-dimensional structure of lysozyme in the Protein Data Bank.     

Scanning tunneling microscopy observation of initial growth of Sn and Ge1−xSnx layers on Ge(0 0 1) substrates

We have investigated the initial growth of Sn and Ge_1−xSn_x layers on Ge(0 0 1) surface by using scanning tunneling microscopy. After the growth of a 0.035 ML-thick Sn layer at room temperature, Sn clusters lining vertically to a dimer row was observed. In the case of the 0.035-0.018 ML-thick Sn growth at 250 °C, the characteristic surface reconstruction with the step-edge undulation like a comb was observed. In the growth of a Ge_0.994Sn_0.006 layer at 250 °C, the multilayer polynuclear growth with a lot of two-dimensional small domain was observed. These surface reconstructions should be accounted for by the large compressive stress induced in the surface layer due to the incorporation of Sn atoms.     

Water vapor: An extraordinary terahertz wave source under optical excitation

In modern terahertz (THz) sensing and imaging spectroscopy, water is considered a nemesis to be avoided due to strong absorption in the THz frequency range. Here we report the first experimental demonstration and theoretical implications of using femtosecond laser pulses to generate intense broadband THz emission from water vapor. When we focused an intense laser pulse in water vapor contained in a gas cell or injected from a gas jet nozzle, an extraordinarily strong THz field from optically excited water vapor is observed. Water vapor has more than 50% greater THz generation efficiency than dry nitrogen. It had previously been assumed that the nonlinear generation of THz waves in this manner primarily involves a free-electron plasma, but we show that the molecular structure plays an essential role in the process. In particular, we found that THz wave generation from H₂O vapor is significantly stronger than that from D₂O vapor. Vibronic activities of water cluster ions, occurring naturally in water vapor, may possibly contribute to the observed isotope effect along with rovibrational contributions from the predominant monomers.     

Preparation and ionic conductivity of transparent glass−ceramics containing a large quantity of lithium−mica

In order to crystallize a large quantity of the lithium?mica in glass?ceramics, 5.1 mass% MgF₂ was added to the starting materials of the parent glasses having chemical compositions of Li_(1+x)Mg₃AlSi_3(1+x)O_10+6.5xF₂ (x = 0.5 and 1.0). Transparent glass?ceramics, in which a large quantity of lithium?mica with particle size of <50 nm was separated, could be prepared from the MgF₂-added parent glass with x = 0.5. While the parent glass, which had a binodal phase separation structure, did not exhibit electrical conductivity, the transparent glass–ceramic was given conductivity by the formation of an interlocking structure of mica. As the separated mica formed a tighter interlocking structure, the conductivity increased and reached a value of 2.0 × 10^?3 S/cm at 600 °C. The MgF₂-added parent glass with x = 1.0 was not transparent because of coarse spinodal phase separation. The conductivity was 4.3 × 10^?4 S/cm at 600 °C but was significantly decreased by the separation of mica.     

Diffusion and reactions of interstitial oxygen species in amorphous SiO2: A review

This article briefly summarizes the diffusion and reactions of interstitial oxygen species in amorphous SiO₂ (a-SiO₂). The most common form of interstitial oxygen species is oxygen molecule (O₂), which is sensitively detectable via its characteristic infrared photoluminescence (PL) at 1272 nm. The PL observation of interstitial O₂ provides key data to verify various processes related to interstitial oxygen species: the dominant role of interstitial O₂ in long-range oxygen transport in a-SiO₂; formation of the Frenkel defect pair (Si–Si bond and interstitial oxygen atom, O⁰) by dense electronic excitation; efficient photolysis of interstitial O₂ into O⁰ with F₂ laser light (λ = 157 nm, hν = 7.9 eV); and creation of interstitial ozone molecule via reaction of interstitial O₂ with photogenerated O⁰. The efficient formation of interstitial O⁰ by F₂ laser photolysis makes it possible to investigate the mobility, optical absorption, and chemical reactions of interstitial O⁰. The observed properties of O⁰ are consistent with the model that O⁰ takes the configuration of Si–O–O–Si bond. Interstitial O₂ and O⁰ react with dangling bonds, oxygen vacancies, and chloride groups in a-SiO₂. Reactions of interstitial O₂ and O⁰ with mobile interstitial hydrogen species produce interstitial water molecules and hydroperoxy radicals. Interstitial hydroxyl radicals are formed by F₂ laser photolysis of interstitial water molecules.     

Theory of chemical bonds in metalloenzymes XXI. Possible mechanisms of water oxidation in oxygen evolving complex of photosystem II

ABSTRACT

Possible mechanisms for water cleavage in oxygen evolving complex (OEC) of photosystem II (PSII) have been investigated based on broken-symmetry (BS) hybrid DFT (HDFT)/def2 TZVP calculations in combination with available XRD, XFEL, EXAFS, XES and EPR results. The BS HDFT and the experimental results have provided basic concepts for understanding of chemical bonds of the CaMn₄O₅ cluster in the catalytic site of OEC of PSII for elucidation of the mechanism of photosynthetic water cleavage. Scope and applicability of the hybrid DFT (HDFT) methods have been examined in relation to relative stabilities of possible nine intermediates such as Mn-hydroxide, Mn-oxo, Mn-peroxo, Mn-superoxo, etc., in order to understand the O–O (O–OH) bond formation in the S₃ and/or S₄ states of OEC of PSII. The relative stabilities among these intermediates are variable, depending on the weight of the Hartree–Fock exchange term of HDFT. The Mn-hydroxide, Mn-oxo and Mn-superoxo intermediates are found to be preferable in the weak, intermediate and strong electron correlation regimes, respectively. Recent different serial femtosecond X-ray (SFX) results in the S₃ state are investigated based on the proposed basic concepts under the assumption of different water-insertion steps for water cleavage in the Kok cycle. The observation of water insertion in the S₃ state is compatible with previous large-scale QM/MM results and previous theoretical proposal for the chemical equilibrium mechanism in the S₃ state . On the other hand, the no detection of water insertion in the S₃ state based on other SFX results is consistent with previous proposal of the O–OH (or O–O) bond formation in the S₄ state . Radical coupling and non-adiabatic one-electron transfer (NA-OET) mechanisms for the OO-bond formation are examined using the energy diagrams by QM calculations and by QM(UB3LYP)/MM calculations . Possible reaction pathways for the O–O and O–OH bond formations are also investigated based on two water-inlet pathways for oxygen evolution in OEC of PSII. Future perspectives are discussed in relation to post HDFT calculations of the energy diagrams for elucidation of the mechanism of water oxidation in OEC of PSII.     

Improved sound absorption performance of three-dimensional MPP space sound absorbers by filling with porous materials

Because microperforated panels (MPPs), which can be made from various materials, provide wide-band sound absorption, they are recognized as one of the next-generation absorption materials. Although MPPs are typically placed in front of rigid walls, MPP space sound absorbers without a backing structure, including three-dimensional cylindrical MPP space absorbers (CMSAs) and rectangular MPP space absorbers (RMSAs), are proposed to extend their design flexibility and easy-to-use properties. On the other hand, improving the absorption performance by filling the back cavity of typical MPP absorbers with porous materials has been shown theoretically, and three-dimensional MPP space absorbers should display similar improvements. Herein the effects of porous materials inserted into the cavities of CMSAs and RMSAs are experimentally investigated and a numerical prediction method using the two-dimensional boundary element method is proposed. Consequently, CMSAs and RMSAs with improved absorption performances are illustrated based on the experimental results, and the applicability of the proposed prediction method as a design tool is confirmed by comparing the experimental and numerical results.