Allosteric bindings of thiacalix[4]arene-based receptors with 1,3-alternate conformation having two different side arms

A novel ditopic receptor possessing two complexation sites such as crown ether and 2-pyridylmethyl groups bearing 1,3-alternate conformation based on thiacalix[4]arene was prepared. The binding behaviors with Li⁺ and Ag⁺ have been examined by ¹H NMR titration experiment. The exclusive formation of mononuclear complexes of 1,3-alternate-5 with Li⁺ and Ag⁺ was observed even though the formation of the heterogeneous dinuclear complexes was expected. The decomplexation of Li⁺ from the crown moiety of 1:1 complex 1,3-alternate-5?Li⁺ to form the Ag⁺?1,3-alternate-5 complex by addition of AgSO₃CF₃ clearly shows that pyridyl moiety works as an efficient switch-off of the recognition ability of the crown moiety. We have also developed the construction of hydrogen-bonding self-assembly heterodimeric systems based on bis(4-pyridyl) and dicarboxylic acid thiacalix[4]arene derivatives in 1,3-alternate conformation. Their supramolecular behaviors are studied by ¹H NMR titration experiments with K⁺ and Ag⁺ ions. Although the values of the dimerization constants are relatively small, the stability of the dimers is strong enough to overcome only small conformational changes upon complex formation.     

Preparation of novel fluoroalkyl end-capped oligomeric nanoparticles-encapsulated hibitane

Fluoroalkyl end-capped N-(1,1-dimethyl-3-oxobutyl)acrylamide oligomer [R_F-(DOBAA)_n-R_F] reacted with hibitane in methanol at 90 °C to afford R_F-(DOBAA)_n-R_F oligomeric nanoparticles-encapsulated hibitane in good isolated yields. These fluorinated oligomeric particles-encapsulated hibitane were nanometer size-controlled very fine particles, and were found to exhibit a good dispersibility and stability in a wide variety of traditional organic solvents including fluorinated aliphatic solvents. Each dispersed solution with fluorinated nanoparticles afforded transparent colorless solution. These fluorinated nanoparticles were also found to exhibit a good antibacterial activity, and were applied to the surface modification of traditional organic polymers such as poly(methyl methacrylate).     

Electronic transport properties of the Ising quantum Hall ferromagnet in a Si quantum well

Magnetotransport properties are investigated for a high mobility Si two-dimensional electron system in the vicinity of a Landau level crossing point. At low temperatures, the resistance peak having a strong anisotropy shows large hysteresis which is attributed to Ising quantum Hall ferromagnetism. The peak is split into two peaks in the paramagnetic regime. A mean field calculation for the peak positions indicates that electron scattering is strong when the pseudospin is partially polarized. We also study the current-voltage characteristics which exhibit a wide voltage plateau.     

Formation mechanism of one-dimensional Si islands on a H/Si(001) surface

The formation mechanism of one-dimensional Si islands on a H/Si(001)-(2x1) surface is studied using scanning tunneling microscopy/spectroscopy and first-principles calculations. We observed that one-dimensional islands that are made from dimer chains are formed at the initial growth stages similar to the bare Si(001) surface. It is found that the number of odd-numbered dimer chains is larger than that of even-numbered dimer chains. We propose the growth processes of the two types of growth edges to explain the observation.     

Synthesis, Conformations and Inclusion Properties of Hexahomotrioxacalix[3]arene Triamide Derivatives having Hydrogen-bonding Groups

The lower rim functionalizedhexahomotrioxacalix[3]arene triamide derivatives4a and 4b were synthesized from triol 1by a stepwise reaction. Extraction data for alkalimetal ions, transition metal ions, and alkyl ammoniumions from water into dichloromethane are discussed.Due to the strong intramolecular hydrogen bondingbetween the neighboring NH and CO groups, theiraffinities to metal cations were weakened.cone-4a shows a single selectivity ton-BuNH₃ ^plus while partial-cone-4aalmost has no affinity to cations. The anioncomplexation of cone-4a was studied by¹H NMR titration experiments. cone-4abinds halides through the intermolecular hydrogenbonding among the NH hydrogens of amide in a 1 : 1fashion in CDCl₃. The association constantscalculated from these changes in chemical shifts ofthe amide protons are K_a = 8520 M^-1for Cl^-1 and K_a = 1720 M^-1 forBr^-1. cone-4a shows a preference forCl^-1 complexation over Br^- complexation. Incontrast, cone-4b has good selectivity andaffinity to Ag^plus cation. A good Job plot proves1:1 coordination of cone-4b withAg^plus cation. The complexation mode of cone-4a with n-BuNH₃Cl and cone-4b with AgSO₃CF₃ were also demonstrated by ¹H NMR titration in CDCl₃.     

Reactivities of cellulases from fungi towards ribbon-type bacterial cellulose and band-shaped bacterial cellulose

We have investigated the reactivities of various cellulases onribbon-type bacterial cellulose (BC I) and band-shaped bacterial cellulose (BCII) so as to clarify the properties of different cellulases. BC I waseffectively hydrolyzed by exo-type cellulases from different fungi from twicetofour times as much as BC II, but endo-type cellulases showed little differencein reactivity on those substrates. One of the endo-type cellulases, EG II fromTrichoderma reesei, degraded BC II more rapidly thanexo-type cellulases even in the production of reducing sugars. The degree ofpolymerization (DP) of BC II was rapidly decreased by endo-type cellulases atanearly stage, while exo-type cellulases did not cause the decrease of DP atthe initial stage, though the decrease of DP was observed after an incubation of24 h. All exo-type cellulases adsorbed on BC I and BC II,whileendo-type cellulases except for EG II adsorbed slightly on both substrates. Itwas interesting to observe EG II adsorbed on BC I but not on BC II. It issuggested that the adsorption of enzyme on cellulose is important for thedegradation of BC I, but not for BC II. It is proposed that the ratio of aspecific activity of each enzyme between BC I and BC II represents thedifference in the mode of action of cellulase. Furthermore, the K _RW value, which we can calculate from thedecrease of DP/reducing sugar produced, is effective for discriminating themode of action of cellulase, especially the evaluation of randomness in thehydrolysis of cellulose by endo- and exo-type cellulases.     

Structural Studies on Saturated Aqueous Solutions of Manganese(II), Cobalt(II), and Nickel(II) Chlorides by X-ray Diffraction

As a part of our studies on crystallization processes of electrolytes, the structure of aqueous solutions of MCl₂ (M = Mn, Co, Ni) equilibrated with hydrate crystals, MCl₂ · mH₂O (m = 6, 4, 2), was investigated by means of X-ray diffraction at 25, 40, 55, and 70°C. The complexes formed in MnCl₂ solutions, were found to be mixed–ligand chloroaqua octahedral complexes of M²⁺ ions with the Mn—O and Mn—Cl distances of about 220 and 251 pm, respectively. The average number of Mn—Cl and Mn—O interactions increased from 1.2 to 1.9 and decreased from 4.8 to 4.1, respectively, with changing MnCl₂ solutions from Mn25 (MnCl₂ solution at 25°C) to Mn70 (MnCl₂ solution at 70°C). In the octahedral species of Co²⁺, the Co—O and Co—Cl distances were found to be about 211 and 240 pm, respectively. With an increase in the saturated concentration by changing temperature from 25 to 70°C, the average coordination number of the Co—Cl contact per Co²⁺ increased from 0.5 to 1.2, and the average number of Co—O interactions decreased from 5.5 to 4.8. The structural analysis was carried out by taking into consideration the existence of the tetrahedral species in the solutions saturated at 40, 55, and 70°C, on the assumption of the existence of [CoCl₄]^2–. The Co—Cl distance was found to be 228 pm, while the number of Co—Cl interactions in the [CoCl₄] complex was calculated to be 3.7 by the least-squares calculations. The Ni—O and Ni—Cl distances were estimated to be about 206 and 237 pm, respectively. The frequency factor n of the Ni—O and Ni—Cl interactions decreased monotonously from 5.6 to 5.0 and increased from 0.4 to 1.0, respectively, with increasing NiCl₂ concentration. The n values of the Co—Cl and Ni—Cl interactions of the octahedral complexes increased sharply with concentration at higher concentrations. Comparing structures of the complexes in the saturated solutions and the hydrate crystals of these metal ions, we discussed a role of the complexing species on crystallization of the hydrates.     

Two-Dimensional Multi-Lens Array with Circular Aperture Spherical Lens for Flat-Top Irradiation of Inertial Confinement Fusion Target

A two-dimensional multi-lens array 350 mm in diameter with spherical element lenses has been tested to improve the irradiation uniformity of a high power glass laser for inertial confinement fusion (ICF). A circular shape for the element lens aperture is chosen to eliminate azimuthally asymmetric intensity distribution. An approximate flat-top intensity distribution is obtained with a lens array of 37 lenses. Beam patterns of a coherent laser and partially coherent light (PCL) with the random phase plate (RPP) and the multi-lens array (MLA) are measured in a GEKKO XII glass laser system. Spherical mode structure of the irradiation nonuniformity of 5.6% with MLA is estimated with cos3 θ distribution of absorption coefficient in the target plasma.     

Molecular dynamics simulation of trp-repressor/operator complex: analysis of hydrogen bond patterns of protein–DNA interaction

Molecular dynamics simulation of Escherichia coli trp-repressor/operator complex was performed to elucidate protein–DNA interactions in solution for 800 ps on special-purpose computer MD-GRAPE. The Ewald summation method was employed to treat the electrostatic interaction without cutoff. DNA kept stable conformation in comparison with the result of the conventional cutoff method. Thus, the trajectories obtained were used to analyze the protein–DNA interaction and to understand the role of dynamics of water molecules forming sequence specific recognition interface. The dynamical cross-correlation map showed a significant positive correlation between the helix-turn-helix DNA-binding motifs and the major grooves of operator DNA. The extensive contact surface was stable during the simulation. Most of the contacts consisted of direct interactions between phosphates of DNA and the protein, but several water-mediated polar contacts were also observed. These water-mediated interactions, which were also seen in the crystal structure (Z. Otwinowski, et al., Nature, 335 (1998) 321) emerged spontaneously from the randomized initial configuration of the solvent. This result suggests the importance of the water-mediated interaction in specific recognition of DNA by the trp-repressor, consistent with X-ray structural information.     

Soluble polyphenol

Soluble polyphenol was synthesized for the first time by enzymatic oxidative polymerization of phenol using peroxidase and hydrogen peroxide as catalyst and oxidizing agent, respectively. A mixed solvent of alcohol and buffer improved the polymer solubility toward N,N-dimethylformamide (DMF). The resulting polymer was composed of a mixture of phenylene and oxyphenylene units. Changing the solvent composition could control the molecular weight and regioselectivity of the polymer. The polymer was found to possess relatively high thermal stability.