Comprehensive understanding of structure- photosensitivity relationships of photochromic [2.2]paracyclophane-bridged imidazole dimers

The photochromic [2.2]paracyclophane-bridged imidazole dimers show instantaneous coloration upon exposure to UV light and rapid fading in the dark. Experimental details for the enhancement of the photosensitivity and the unique photoisomerization of newly designed [2.2]paracyclophane-bridged imidazole dimers are demonstrated. We explored the structure-property relationships and demonstrated an efficient strategy for designing high-performance fast-photochromic molecules with increased photosensitivity to solar UVA radiation. The [2.2]paracyclophane-bridged imidazole dimer consists of two types of imidazole rings, Im1 and Im2. Im1 is characterized by a 6π electron system with an electron-donating characteristic, whereas Im2 is distinguished by a 4π electron system with an electron-withdrawing characteristic. The introduction of electron-donating substituents into the phenyl rings attached to the electron-withdrawing Im2 was proved to enhance the photosensitivity with the aid of the intramolecular charge transfer transitions. The unique photoisomerization resulting from the changes in the bonding manner between two imidazole rings was also investigated in detail.     

Photochromic properties of [2.2]paracyclophane-bridged imidazole dimer with increased photosensitivity by introducing pyrenyl moiety

The photochromic [2.2]paracyclophane-bridged imidazole dimers show instantaneous coloration upon exposure to UV light and rapid fading in the dark. A new [2.2]paracyclophane-bridged imidazole dimer, pseudogem-PPI-DPI[2.2]PC, with high photosensitivity to UVA radiation was developed. To enhance the photosensitivity, we introduced pyrenyl moieties to the [2.2]paracyclophane-bridged imidazole dimer. The localized π-π* transition of pyrenyl moieties appears in the UVA radiation region by introducing a pyrenyl moietiy on the 4-position of the imidazole rings. The expansion of the π-electron system also affects the absorption spectrum of the colored species. The broad absorption band of the colored species covers the whole range of visible light region and its absorbance is approximately equal throughout the visible light region. Thus, pseudogem-PPI-DPI[2.2]PC shows the photochromic reaction coloring black upon light irradiation and successive fast thermal bleaching following the monoexponential kinetics with a time constant of 12 ms at room temperature.     

Total Synthesis,Proof of Absolute Configuration,and Biosynthetic Origin of Stylopsal,the First Isolated Sex Pheromone of Strepsiptera

The asymmetric total synthesis of the diastereomers of stylopsal establishes the absolute configuration of the first reported sex pheromone of the twisted‐wing parasite Stylops muelleri as (3R,5R,9R)‐trimethyldodecanal. The key steps for the diastereo‐ and enantiodivergent introduction of the methyl groups are two different types of asymmetric conjugate addition reactions of organocopper reagents to α,β‐unsaturated esters, whereas the dodecanal skeleton is assembled by Wittig reactions. The structure of the natural product was confirmed by chiral gas chromatography (GC) techniques, GC/MS and GC/electroantennography (EAD) as well as field tests. An investigation into the biosynthesis of the pheromone revealed that it is likely to be produced by decarboxylation of a 4,6,10‐trimethyltridecanoic acid derivative, which was found in substantial amounts in the fat body of the female, but not in the host bee Andrena vaga. This triple‐branched fatty acid precursor thus seems to be biosynthesized de novo through a polyketide pathway with two consecutive propionate‐propionate‐acetate assemblies to form the complete skeleton. The simplified, motionless and fully host‐dependent female exploits a remarkable strategy to maximize its reproductive success by employing a relatively complex and potent sex pheromone.     

Extracellular Production and Characterization of <Emphasis Type="BoldItalic">Streptomyces</Emphasis> X-prolyl Dipeptidyl Aminopeptidase

X-prolyl dipeptidyl aminopeptidases (X-PDAPs) are useful in various food industries. In this study, we performed sequence-based screening to obtain a stable X-PDAP enzyme from thermophilic Streptomyces strains. We found three genes that encoded X-PDAP from Streptomyces thermoluteus subsp. fuscus NBRC 14270 (14270 X-PDAP), Streptomyces thermocyaneoviolaceus NBRC 14271 (14271 X-PDAP), and Streptomyces thermocoerulescens NBRC 14273, which were subsequently cloned and sequenced. The deduced amino acid sequences of these genes showed high similarity, with ~80% identity with each other. The isolated X-PDAPs and an X-PDAP from Streptomyces coelicolor were expressed in Streptomyces lividans using a hyperexpression vector: pTONA5a. Among these genes, only 14270 and 14271 X-PDAPs caused overexpression and extracellular production without artificial signal peptides. We also characterized the biochemical properties of purified 14271 X-PDAP. In addition, we found that, in peptide synthesis via an aminolysis reaction, this enzyme recognized d-amino acid derivatives as acyl acceptors, similar to l-amino acid derivatives.     

Combustion wave propagation and detonation initiation in the vicinity of closed-tube end walls

There are not many studies on DDT with no obstacles and the initiation of DDT near the end of a closed tube. Therefore in the present study we experimentally investigate the mechanism of the combustion wave transition to a detonation wave when there are no obstacles. In particular, we show that a local explosion near the tube wall is necessary for the initiation of a detonation. Parameters that we varied are the wall configuration, distance between the ignition point and the wall, and initial filling pressure. The combustion waves and the compression waves are visualized using the Schlieren optical system. From the results, we found it is necessary for the combustion wave to reach four walls so that the detonation could be initiated by the local explosion. In the conditions of the present experiment, we exhibited that the local explosion did not occur in the vicinity of a single wall and four orthogonal walls; instead, the local explosion occurred in a situation with five orthogonal walls. The time of the local explosion and the detonation initiation is 2.6 ± 1.1 and 2.0 ± 0.1 times the characteristic time for the combustion wave to propagate hemispherically from an ignitor and reach the four walls.     

High-energy, broadly tunable, narrow-bandwidth mid-infrared optical parametric system pumped by quasi-phase-matched devices

We have developed a tunable, narrow-bandwidth (<2 cm(-1)) mid-infrared (MIR) optical parametric system with a large-aperture periodically poled Mg-doped LiNbO(3) (LA-PPMgLN)-based high-energy pump source. The system has a continuously tunable tuning range from 4.6 to 11.2 mum and produces a maximum output energy of 2.0 mJ at 5.1 mum. Practical use of the MIR source is demonstrated by MIR-UV double-resonance spectroscopy of jet-cooled acetanilide.     

MD simulation study of the sputtering process by high-energy gas cluster impact

We performed molecular dynamics (MD) simulations to study the characteristic sputtering process with large cluster ion impact. The statistical properties of incident Ar and sputtered Si atoms were examined using 100 different MD simulations with Ar₁₀₀₀ cluster impacting on a Si(0 0 1) target at a total acceleration energy of 50 keV. The results show that the kinetic energy distribution of Ar atoms after impact obeys the high-temperature Boltzmann distribution due to thermalization through high-density multiple collisions on the target. On the other hand, the kinetic energy distribution of sputtered target atoms demonstrates a hybrid model of thermalization and collision-cascade desorption processes.     

Peculiar ‘Reptational’ Movements of Single Synthetic Polymer Chains on Substrate Observed by AFM

Peculiar ‘reptational’ movements of isotactic PMMA chains on mica are observed by in situ AFM. The polymer molecules comprise long flexible chains that exhibit reptative, or snake‐like, motion on the substrate along the direction of the polymer chain. Intriguingly, some chains underwent forward then backward motion in which the head of the chain moved in a curvilinear manner along the previous contours of the polymer chain. No limitation in the direction of movement for the ends of the polymer chain was anticipated based on an assumed reptational mechanism. As a result, the chains recovered a conformation that had been adopted prior to the initial movement. Several factors that may affect the movement are discussed.