Thermo‐Responsive Hydrogels with Nanodomains: Rapid Shrinking of a Nanogel‐Crosslinking Hydrogel of Poly(N‐isopropyl acrylamide)

Rapidly shrinking poly(N‐isopropyl acrylamide) (PNIPAM) hydrogels are prepared by crosslinking with self‐assembled nanogels that consist of cholesteryl‐ and methacryloyl‐substituted pullulan (CHPMA). The CHPMA nanogel (R_h = 26.4 nm) was used as a crosslinker for a hydrophilic nanodomain. Transmission electron microscopy images of the nanogel‐crosslinked PNIPAM hydrogel reveal a well‐defined nanoporous structure. The nanogel‐crosslinked PNIPAM hydrogel shows rapid shrinking based on its structure. The shrinking half‐time was ≈2 min, which is about 3 400 times faster than that of a PNIPAM hydrogel crosslinked by methylene(bisacrylamide).

     

Elucidation of Metal‐Ion Accumulation Induced by Hydrogen Bonds on Protein Surfaces by Using Porous Lysozyme Crystals Containing RhIII Ions as the Model Surfaces

Metal‐ion accumulation on protein surfaces is a crucial step in the initiation of small‐metal clusters and the formation of inorganic materials in nature. This event is expected to control the nucleation, growth, and position of the materials. There remain many unknowns, as to how proteins affect the initial process at the atomic level, although multistep assembly processes of the materials formation by both native and model systems have been clarified at the macroscopic level. Herein the cooperative effects of amino acids and hydrogen bonds promoting metal accumulation reactions are clarified by using porous hen egg white lysozyme (HEWL) crystals containing Rh^III ions, as model protein surfaces for the reactions. The experimental results reveal noteworthy implications for initiation of metal accumulation, which involve highly cooperative dynamics of amino acids and hydrogen bonds: i) Disruption of hydrogen bonds can induce conformational changes of amino‐acid residues to capture Rh^III ions. ii) Water molecules pre‐organized by hydrogen bonds can stabilize Rh^III coordination as aqua ligands. iii) Water molecules participating in hydrogen bonds with amino‐acid residues can be replaced by Rh^III ions to form polynuclear structures with the residues. iv) Rh^III aqua complexes are retained on amino‐acid residues through stabilizing hydrogen bonds even at low pH (≈2). These metal–protein interactions including hydrogen bonds may promote native metal accumulation reactions and also may be useful in the preparation of new inorganic materials that incorporate proteins.     

An improved synthesis of the C42–C52 segment of ciguatoxin 3C

In our previously reported method for the construction of the IJKLM-ring of ciguatoxin 3C (CTX3C), the lengthy synthetic process for the intermediate C42–C52 (L-ring) segment was problematic. Therefore, a new and improved procedure for the C42–C52 segment, having modified protecting groups, was developed. The new route includes a chirality transferring Ireland-Claisen rearrangement for the construction of the vicinal dimethyl branching at C47–48, a one-pot cyclization process for the establishment of the stereocenters at C45 and C46 as well as the γ-hydroxy δ-lactone framework corresponding to the L-ring, and Brown’s asymmetric crotylboration for the installation of the stereocenters at C43 and C44. The new C42–C52 segment was successfully coupled with the previously reported C32–C41 (I-ring) segment to produce the IJKLM-ring.     

Syntheses of cyclopentyl nucleoside (−)-neplanocin A through tetrazole-fragmentation from cyanophosphates

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Unveiling Latent Photoreactivity of Imines

Unlike carbonyl compounds, it has long been common understanding that excited imines show virtually no photoreactivity, and hence their properties and potential utility in chemical science remain largely unexplored. Now, a strategy is presented for eliciting latent photoreactivity of imines based on the introduction of a donor–acceptor (D‐A) structure to extend the lifetime of their photoexcited states. A series of spectroscopic analyses and density functional theory calculations reveal unique photophysical properties of the D‐A‐type imines. Furthermore, the reactivity of the D‐A‐type imines is demonstrated by using them as a photoredox catalyst for atom‐transfer radical addition. These findings illuminate a previously neglected chemical space in the field of photochemistry, which will be exploited by taking advantage of the inherent structural modularity of imines.     

Photoelectrochemical reaction and H2 generation at zero bias optimized by carrier concentration of n-type GaN

The authors studied the photoelectrochemical properties dependent on carrier concentration of n-type GaN. The photocurrent at zero bias became the maximum value at the carrier concentration of 1.7x10(17) cm-3. Using the sample optimized carrier concentration, the authors achieved H2 gas generation at a Pt counterelectrode without extra bias for the first time. The authors also discussed the mechanism of the dependence of photocurrent on the carrier concentration of GaN.     

Electronic spectra of jet-cooled calix[4]arene and its van der Waals clusters: encapsulation of a neutral atom in a molecular bowl

The encapsulation of neutral guest has been studied for calix[4]arene (C4A) by forming van der Waals clusters with Ar and Ne in supersonic jets. The electronic transitions of these clusters suggest that the first Ar (Ne) is encapsulated inside the C4A cavity, while the next atoms are bound outside.     

Synthesis of biladienone and bilatrienone by coupled oxidation of tetraarylporphyrins

Tetraarylbiladien-ab-ones bearing various substituents (R) in the para position of the phenyl groups were preprared by coupled oxidation of tetraarylporphyrin iron complexes. The yields of 5,10,15-triaryl-19-aroyl-15-hydroxybiladien-ab-ones were 74% (R=H), 85% (R=OMe), 44% (R=COOMe), and 28% (R=CN). Kinetic studies of the iron porphyrin oxidation revealed that the reaction is accelerated by an electron-withdrawing substituent with the Hammett reaction constant rho=0.295. 5,10,15-Triaryl-19-aroyl-15-hydroxybiladien-ab-ones undergo the acid-catalyzed elimination reaction either by acetic acid or by mesoporous silica to afford 5,10,15-triaryl-19-aroylbilatrien-abc-one. The elimination reaction in acetic acid is accelerated by an electron-donating substituent with the Hammett reaction constant rho=-1.48.     

Numerical study comparing RANS and LES approaches on a circulation control airfoil

A numerical study over a nominally two-dimensional circulation control airfoil is performed using a large-eddy simulation code and two Reynolds-averaged Navier–Stokes codes. Different Coanda jet blowing conditions are investigated. In addition to investigating the influence of grid density, a comparison is made between incompressible and compressible flow solvers. The incompressible equations are found to yield negligible differences from the compressible equations up to at least a jet exit Mach number of 0.64. The effects of different turbulence models are also studied. Models that do not account for streamline curvature effects tend to predict jet separation from the Coanda surface too late, and can produce non-physical solutions at high blowing rates. Three different turbulence models that account for streamline curvature are compared with each other and with large eddy simulation solutions. All three models are found to predict the Coanda jet separation location reasonably well, but one of the models predicts specific flow field details near the Coanda surface prior to separation much better than the other two. All Reynolds-averaged Navier–Stokes computations produce higher circulation than large eddy simulation computations, with different stagnation point location and greater flow acceleration around the nose onto the upper surface. The precise reasons for the higher circulation are not clear, although it is not solely a function of predicting the jet separation location correctly.     

Photoreactivity of crystals of a rhodium dithionite complex with ethyltetramethylcyclopentadienyl ligands: crystal surface morphology changes and degradation

A photoreactive rhodium dithionite complex [(RhCp(Et))(2)(μ-CH(2))(2)(μ-O(2)SSO(2))] (1(Et)) with Cp(Et) (η(5)-C(5)Me(4)Et) ligands was newly synthesized. Upon short-time irradiation with low intensity light, two kinds of stepwise surface morphology changes of the crystal 1(Et) were observed. Prolonged irradiation with high intensity light caused cracking and breaking down of the crystal.