Synthetic application and structural elucidation of axially chiral dicarboxylic acid: asymmetric Mannich-type reaction with diazoacetate, (diazomethyl)phosphonate, and (diazomethyl)sulfone

The past decade has witnessed the burgeoning research fields of chiral Br?nsted acid catalysis. However, carboxylic acids, arguably the most general acids in organic chemistry, have rarely been used as chiral Br?nsted acid catalysts. In this context, we developed axially chiral dicarboxylic acid and evaluated its catalytic activity in asymmetric Mannich-type reaction of aromatic aldehyde-derived N-Boc imines and tert-butyl diazoacetate. To demonstrate the remarkable generality of this catalytic system, tert-butyl diazoacetate was replaced with its phosphorus and sulfur analogues, (diazomethyl)phosphonate and (diazomethyl)sulfone, by which synthetically valuable chiral β-amino phosphonates and β-amino sulfones could be obtained with high enantioselectivities under identical reaction conditions. X-ray crystallographic analysis of axially chiral dicarboxylic acid complexed with a pyridine derivative revealed its unique internal hydrogen bonding, a property that serves as a basis for its distinctive acidity and chiral scaffold.     

Uniaxial strain orientation dependence of superconducting transition temperature (Tc) and critical superconducting pressure (Pc) in β-(BDA-TTP)2I3

Dependence of the superconducting transition temperature (T(c)) and critial superconducting pressure (P(c)) of the pressure-induced superconductor β-(BDA-TTP)(2)I(3) [BDA-TTP = 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene] on the orientation of uniaxial strain has been investigated. On the basis of the overlap between the upper and lower bands in the energy dispersion curve, the pressure orientation is thought to change the half-filled band to the quarter-filled one. The observed variations in T(c) and P(c) are explained by considering the degree of application of the pressure and the degree of contribution of the effective electronic correlation at uniaxial strains with different orientations parallel to the conducting donor layer.     

Finite size effect of proton-conductivity of amorphous silicate thin films based on mesoscopic fluctuation of glass network

The finite size effect of proton conductivity of amorphous silicate thin films, a-M(0.1)Si(0.9)O(x) (M = Al, Ga, Hf, Ti, Ta, and La), was investigated. The proton conductivity across films, σ, was measured in dry air by changing the thickness in the range of 10-1000 nm. σ of the films with M = Al, Ga, and Ta was elevated in a power law by decreasing thickness into less than a few hundred nanometers, and the increment was saturated at a thickness of several 10's of nanometers. On the other hand, σ of the films with M = Hf, Ti, and La was not related to the decrease of the thickness in the range of >10 nm. Thickness-dependent conductivity of the former could be numerically simulated by a percolative resistor network model that involves the randomly distributed array of two kinds of resistors R(1) and R(2) (R(1) > R(2)) in the form of a simple cubic-type lattice. High-resolution TEM clarified that a-M(0.1)Si(0.9)O(x) films involved heterogeneous microstructures made of the condensed domain and the surrounding uncondensed matrix due to the fluctuation of glass networks on the nanometer scale. The condensed domain had a wormlike shape with an average length of several 10's of nanometers and performed the role of the proton conduction pathway penetrating through the poorly conducting matrix. It was concluded that the thickness-dependent conductivity could be identical to finite-size scaling of the percolative network of the interconnected domains in the nanometer range.     

Fabrication of super-oil-repellent dual pillar surfaces with optimized pillar intervals

Hierarchical dual pillar surfaces with optimized pillar intervals are fabricated by a novel combined process of the oblique angle magnetron sputtering deposition of Al-Nb alloys and their anodizing. The pillar intervals are controlled by the deposition angle and cell size of a scalloped substrate for oblique angle deposition. Anodizing of the deposited pillar surfaces develops a nanopillar oxide layer, producing the hierarchical dual pillar surfaces. After being coated with a fluoroalkyl phosphate layer to reduce the surface free energy, hierarchical surfaces with submicrometer pillar intervals greater than 400 nm show super liquid repellency even for hexadecane with a low surface tension of 27.5 mN m(-1), although the submicrometer pillar surfaces with smaller submicrometer pillar intervals and without nanopillars were not super-oil-repellent. In contrast, the dual pillar surfaces show superhydrophobicity regardless of the submicrometer pillar intervals. Thus, the present study demonstrates the importance of the pillar intervals (gap size between pillars) to realize the superoleophobicity.     

Unraveling the properties of octamethylcyclotetrasiloxane under nanoscale confinement: atomistic view of the liquidlike state from molecular dynamics simulation

We developed an atomistic model of octamethylcyclotetrasiloxane (OMCTS) liquid confined within the nanospace between two flat mica surfaces. Molecular dynamics simulation was carried out for the liquidlike state where OMCTS liquid is not frozen, while forming molecular layers parallel to the surface. With the aid of a layer by layer analysis of the intra- and interlayer microscopic structures and the dynamics, it is found that the difference in the properties of the inner layers and the bulk liquid are relatively small in spite of the clear differences in the structure. This leads to the conclusion that the layered structure itself is an appearance of the microscopic structure that already exists in the bulk liquid. The most striking difference from the bulk liquid is mainly seen in the contact layer, where characteristic molecular orientations that are not seen in the crystalline phase appeared, and the dynamics of the liquid becomes 2-3 orders of magnitude slower than that of the bulk.     

Benzo[e]pyrene skeleton dipyrylium dication with a strong donor-acceptor-donor interaction, and its two-electron reduced molecule

The donor-acceptor-donor (D-A-D) conjugated molecules 1,4-bis(diarylaminophenylethynyl)anthraquinone (1,4-Am(2)Aq) and 1,4-bis(ferrocenylethynyl)anthraquinone (1,4-Fc(2)Aq), undergo a double proton cyclization reaction with bis(trifluoromethanesulfone)imide acid (TFSIH) to yield 1,4-bis(diarylaminophenyl or ferrocenyl) dipyrylium salts [1,4-R(2)Pyl(2)](TFSI)(2) (R=Am or Fc) with novel planar pentacyclic structures similar to the aromatic benzo[e]pyrene-type skeleton. [1,4-Am(2)Pyl(2)](TFSI)(2) could be reduced to give the neutral molecule [1,4-Am(2)Pyl(2)](0), which is stable and maintains the benzo[e]pyrene-type skeleton. To the best of our knowledge, this is the first oxygen-atom-containing polycyclic aromatic hydrocarbon with 22 (4n+2) π-electrons. The obtained condensed-ring benzo[e]pyrene-type skeleton compounds show physical and chemical properties that are significantly different from those of [1,5-Am(2)Pyl(2)](TFSI)(2), which has a perylene-type skeleton.     

A facile synthesis of 2-[1-(dialkylamino)alkyl]-4H-3,1-benzoxazin-4-ones by the reaction of 1,1-dimethylethyl 2-isocyanobenzoates with N,N-dialkyliminium iodides

A convenient synthetic approach to 2-[1-(dialkylamino)alkyl]-4H-3,1-benzoxazin-4-ones has been developed. Thus, 1,1-dimethylethyl 2-isocyanobenzoates, which can be readily prepared from 2-nitrobenzoic acids by a simple four-step sequence, react with N,N-dialkyliminium iodides without using any catalysts under mild conditions to give the desired products in generally fair-to-good yields.     

Synthesis of modified pyrimidine nucleosides via Vorbrüggen-type N-glycosylation catalyzed by 2-methyl-5-phenylbenzoxazolium perchlorate

Several acidic azolium salts prepared from oxazole, thiazole, and imidazole derivatives were investigated as catalysts in N-glycosylation reaction using a silylated modified pyrimidine and an acylated ribose or glucose to afford the corresponding pyrimidine nucleoside. Among the salts, 2-methyl-5-phenylbenzoxazolium perchlorate showed the highest catalytic activity. This salt is a nonhygroscopic crystalline compound that shows higher activity than the frequently used trimethylsilyl triflate. Reactions with this salt can be conducted in gram scales.     

Effect of Brønsted acid co-catalyst in asymmetric conjugate addition of 3-aryloxindoles to maleimide under base-free phase-transfer conditions

Highly diastereo- and enantioselective conjugate addition of 3-aryloxindoles to maleimide was accomplished under base-free phase-transfer conditions. The effect of Brønsted acid co-catalyst was examined, and we found that the use of a phenol derivative as co-catalyst was effective for obtaining the target conjugate adduct in good yield with high stereoselectivity.     

Dose–dependent biodistribution of prenatal exposure to rutile-type titanium dioxide nanoparticles on mouse testis

Au@TiO₂/graphene (Gr) composite with visible-light response was fabricated. The prepared samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscope, and diffuse reflection spectroscopy, respectively. The results indicated that metallic Au nanoparticles with round shape and about 10 nm in size were loaded on TiO₂ particles uniformly, and Au@TiO₂ was grafted on Gr shaped in thin and big sheets. Photocatalytic degradation of 2,4-dichlorophenol (2,4-DCP) was conducted under the visible-light irradiation (>420 nm) in order to evaluate the activity of photocatalysts. The light absorption spectrum of TiO₂ was extended to visible-light region by loading Au nanoparticles with plasmonic effect and 2,4-DCP could be degraded with Au@TiO₂ and Au@TiO₂/Gr by photocatalysis under visible light. Compared to that with Au@TiO₂, the elimination rate of 2,4-DCP was increased with Au@TiO₂/Gr. This enhanced photocatalytic performance was attributed to the concentration effect due to the improved adsorption performance introduced by Gr.