Organocatalytic asymmetric direct aldol reactions of trifluoroacetaldehyde ethyl hemiacetal with aromatic methyl ketones

The organocatalytic asymmetric direct aldol reaction of trifluoroacetaldehyde ethyl hemiacetal with aromatic methyl ketones in the presence of a catalytic amount of (S)-5-(pyrrolidin-2-yl)-1H-tetrazole in dichloroethane at 40 °C proceeds smoothly to produce (R)-4,4,4-trifluoro-1-aryl-3-hydroxy-1-butanones in high yields with up to 90% ee.     

Reversal of diastereoselectivity in reactions of the trifluoroacetaldehyde ethyl hemiacetal with enamines and imines: metal-free, complementary anti- and syn-selective synthesis of 4,4,4-trifluoro-1-aryl-3-hydroxy-2-methyl-1-butanones

A complete reversal of diastereoselectivity was observed for reactions of the trifluoroacetaldehyde ethyl hemiacetal with enamines and imines, derived from propiophenones, that produce 4,4,4-trifluoro-1-aryl-3-hydroxy-2-methyl-1-butanones. This process serves as the first reliable, metal-free, complementary anti- and syn-selective method to prepare 4,4,4-trifluoro-1-aryl-3-hydroxy-2-methyl-1-butanones.     

Synthesis of novel fatty-acyl gratisin derivatives

To find candidates with high antimicrobial and low hemolytic activities, many gratisin (GR) analogues have been designed and synthesized. In the present account, we synthesized novel derivatives of GR having both the polycationic and fatty acyl groups, cyclo{-Val(1)-Orn(2)-Leu(3)-D-Phe(4)-Pro(5)-D-Lys(6)(X)-Val(7)-Orn(8)-Leu(9)-D-Phe(10)-Pro(11)-D-Lys(12)-} {X=-CO(CH(2))(6)CH(3) (1), -Lys-CO(CH(2))(6)CH(3) (2), -(Lys)(2)-CO(CH(2))(6)CH(3) (3), and -(Lys)(3)-CO(CH(2))(6)CH(3) (4)}, and examined the biological activities. Among them, we found that 2-4 have differential ionic interaction against the prokaryotic membrane and eukaryotic membrane. In other words, the dissociation with high antimicrobial activity and low hemolytic activity is caused by the addition of D-Lys(6)-{(Lys)(n)-CO(CH(2))(6)CH(3)} residues at position 6 of [D-Lys(6,12)]-GR. Our findings should be helpful in finding drug candidates with high antimicrobial activity and low hemolytic activity that are capable of combating microbial resistance.     

Utilization and Modification of Perovskite-Type Layered Structures as Inorganic-Organic Hybrid Materials

Abstract

The aromatic ammonium-based layered halide compounds were obtained of bis(4-nitroanilinium)tetrachlorocadmate and bis(2-methyl-4-nitroanilinium) tetrachlorocadmate, aiming at a new type of inorganic-organic hybrid layered material. X-ray diffraction analyses of the single crystals revealed that both of the crystals take an alternate layered structure of the organic bilayer and the inorganic sheet. Cadmium ion and chloride anions form six-coordinated octahedra whose corner anions are shared with the neighboring octahedra for the crystal of bis(4-nitroanilinium)tetrachlorocadmate. In the case of bis(2-methyl-4-nitroanilinium) tetrachlorocadmate crystal the inorganic portion takes distorted four-coordinated tetrahedra. The structure of the inorganic portion for the latter crystal can be considered to be caused by the distortion of a perovskite-type octahedron due to the introduction of a bulky organic molecule.     

Polymerization of solid C<Subscript>60</Subscript> under C<Stack><Subscript>60</Subscript><Superscript>+</Superscript></Stack> cluster ion bombardment

The structure transformation occurring in fullerene film under bombardment by 50 keV C₆₀⁺ cluster ions is reported. The Raman spectra of the irradiated C₆₀ films reveal a new peak rising at 1458 cm⁻¹ with an increase in the ion fluence. This feature of the Raman spectra suggests linear polymerization of solid C₆₀ induced by the cluster ion impacts. The aligned C₆₀ polymeric chains composing about 5–10 fullerene molecules have been distinguished on the film surface after the high-fluence irradiation using atomic force microscopy (AFM). The surface profiling analysis of the irradiated films has revealed pronounced sputtering during the treatment. The obtained results indicate that the C₆₀ polymerization occurs in a deep layer situated more than 40 nm below the film surface. The deep location of the C₆₀ polymeric phase indirectly confirms the dominant role of shock waves in the detected C₆₀ phase transformation.     

Conformational transitions of cyclic D,L-peptides

Conformational transitions of cyclic D,L-hexapeptides have been studied by first-principles calculations. Geometry optimizations for 20 types of homoresidue cyclic D,L-hexapeptide revealed that the cyclic peptides have two types of energetically stable backbone (extended (E) and bound (B) types); and for each type, the amino acid side chains have two orientations (equatorial and axial). Among the four types of isomer [E-type equatorial (E(eq)), B-type equatorial (B(eq)), E-type axial (E(ax)), and B-type axial (B(ax))], B(ax) is the energetically most preferred by most of the 20 encoded amino acid residues, whereas E(ax) is the least preferred. A search for transition states indicated that six types of conformational transition are possible between the isomers of the cyclic peptide, i.e., the backbone-backbone conversions (E(eq)-B(eq) and E(ax)-B(ax) transitions), the side chain-side chain conversions (E(eq)-E(ax) and B(eq)-B(ax) transitions), and the simultaneous conversions of the backbone and the side-chain orientation (E(eq)-B(ax) and E(ax)-B(eq) transitions). All the six transitions proceed with the breaking of the high molecular symmetry (S(6)) and go through the triangular (C(3)) intermediate structure with either equatorial or axial side-chain orientation.     

Search for anomalous top–gluon couplings at LHC revisited

Through top-quark pair productions at LHC, we study possible effects of nonstandard top–gluon couplings yielded by SU(3)×SU(2)×U(1) invariant dimension-6 effective operators. We calculate the total cross section and also some distributions for $pp\to t\bar{t}X$ as functions of two anomalous-coupling parameters, i.e., the chromoelectric and chromomagnetic moments of the top, which are constrained by the total cross section $\sigma(p\bar{p}\to t\bar{t}X)$ measured at Tevatron. We find that LHC might give us some chances to observe sizable effects induced by those new couplings.     

Odd-frequency superconductivity on the Hubbard model using the FLEX approximation

It is an important issue to clarify whether the odd-frequency superconducting state can be derived from microscopic Hamiltonian or not, where gap function has an odd-parity in frequency. We study the instability of following four superconducting states: (1) even-frequency spin-singlet, (2) even-frequency spin-triplet, (3) odd-frequency spin-singlet and (4) odd-frequency spin-triplet. By using the fluctuation exchange (FLEX) approximation on a triangular and square lattice, we find that the odd-frequency spin-triplet pairing can become dominant at a certain region where the suppression of the antiferromagnetic fluctuation due to a geometric frustration becomes prominent.     

Rate of homogeneous nucleation in alkali disilicate glasses

Rates of crystal nucleation in alkali disilicate glasses were measured by counting the number of crystals under an optical microscope. The viscosities of these glasses were measured by the method of beam-bending and penetration. Using the data of rate of nucleation and viscosity obtained in the present study and the data of free energy measured by Takahashi and Yoshio, crystal-glass interfacial energies for alkali disilicate systems were estimated on the basis of homogeneous nucleation theory as follows: 196 erg/cm² for Li₂O·2SiO₂, 126–144 erg/cm² for Na₂O·2SiO₂ and 88–104 erg/cm² for K₂O·2SiO₂. The effects of the viscosity of glass, the free energy difference between crystal and glass and crystal-glass interfacial energy on the rate of nucleation were discussed, and the remarkably higher rate of crystal nucleation in the Li₂O·2SiO₂ glass was attributed to the larger free energy difference.     

Mechanofluorochromic Materials Based on Aggregation‐Induced Emission‐Active Boron Ketoiminates: Regulation of the Direction of the Emission Color Changes

We report a series of mechanofluorochromic (MFC) compounds based on organoboron complexes with aggregation‐induced emission (AIE) characteristics. We synthesized a variety of boron ketoiminates and investigated the effect of the substituents on the optical properties by altering the end groups in the compounds. The synthesized boron ketoiminates showed AIE properties and MFC behavior. Interestingly, the hypsochromic and bathochromic shifts of the emission bands individually observed for boron ketoiminates depended on the chemical structures of the end groups. From the X‐ray diffraction and differential scanning calorimetry analyses, it was confirmed that the MFC property of boron ketoiminates should be derived from a phase transition between crystalline and amorphous states. In addition, the direction of the peak shifts of the emission bands was controlled by the degree of steric hindrance of the end group.