Crystal Structure of C-(n-propyl)calix[4]resorcinarene and its Complex with Caffeine

Abstract

The crystal structures of the all-cis epimer of C-(n-propyl)calix[4]resorcinarene (1) and its caffeine complex are reported. 1 · CH₃CN · H₂O (2) crystallizes in the tetragonal space group P4, a = 14.3645(9), c = 9.3344(8) Å, V = 1926(2) ų. Refinement led to a final conventional R ₁ value of 0.047 for 3406 reflections and 236 parameters. The caffeine complex 1 · C₈H₁₀N₄O₂ · CH₃OH · H₂O (3) crystallizes in the triclinic space group P1, a = 11.2892(4), b = 13.0367(8), c = 16.9700(11) Å, α = 82.902(2), β = 79.713(3), γ = 88.053(2)°, V = 2438(2) ų. Refinement led to a final conventional R ₁ value of 0.067 for 6393 reflections and 641 parameters. The resorcinarene displays the usual bowl shape in both compounds. The caffeine molecule in 3 is hydrogen bonded to two resorcinarene and one water molecules and one of its methyl groups is included in the cavity of a third macrocycle, suggesting CH₃…π interactions. Extended hydrogen bonding patterns involving phenolic protons and solvent molecules are also present in both compounds.     

Interfacial Interaction of Polymer/Liquid Crystal Molecules and Electrooptical Properties of their Composite Systems

Polymer/liquid crystal composite films were prepared from a solution of polymer and nematic liquid crystal (LC) by a solvent casting method. The phase-separated structure of the composite film was controlled by the solvent evaporation rate. The light-scattering profile of a poly(diisopropyl fumarate)/LC: 40/60 w/w solution during solvent evaporation exhibited a periodic structure, indicating that the phase-separated structure was formed by spinodal decomposition. The aggregation structure of the composite film was investigated with a scanning electron microscope (SEM). SEM observation of the composite film suggested the presence of periodicity and dual connectivity of polymer and LC phases. The faster the solvent was evaporated, the smaller the LC channel (domain) size in the composite film. The composite film, composed of poly(methyl methacrylate) (PMMA) and a nematic LC (E44) with a positive dielectric anisotropy, exhibited remarkable and reversible light-scattering-light-transmission switching, under the modulation of an ac electric field. The light-scattering state was dependent on such optical heterogeneities as spatial distribution of the nematic directors and/or mismatching in the refractive indices of the components. The electrooptical behavior of the composite film was strongly dependent on the LC channel (domain) size in the composite film. The transmittance increased and the rise and decay response times (τ_R and τ_D), decreased and increased, respectively, with an increase in the size of the LC channel (domain).

The electrooptical switching properties for the polymer/LC composite film should be influenced by miscibility between the polymer and the LC phases. The miscibility between both phases was evaluated from a distribution of relaxation time for interfacial polarization. The anchoring effect was also investigated by measuring the nonlinearity of the dielectric constant for the composite system.     

Three‐Step Spin State Transition and Hysteretic Proton Transfer in the Crystal of an Iron(II) Hydrazone Complex

A proton–electron coupling system, exhibiting unique bistability or multistability of the protonated state, is an attractive target for developing new switchable materials based on proton dynamics. Herein, we present an iron(II) hydrazone crystalline compound, which displays the stepwise transition and bistability of proton transfer at the crystal level. These phenomena are realized through the coupling with spin transition. Although the multi‐step transition with hysteresis has been observed in various systems, the corresponding behavior of proton transfer has not been reported in crystalline systems; thus, the described iron(II) complex is the first example. Furthermore, because proton transfer occurs only in one of the two ligands and π electrons redistribute in it, the dipole moment of the iron(II) complexes changes with the proton transfer, wherein the total dipole moment in the crystal was canceled out owing to the antiferroelectric‐like arrangement.     

Permselectivity of Gramicidin A Channels Based on Single‐channel Recordings

The expression mechanism of permselectivity through a gramicidin A (gA) channel between two aqueous phases (W1 and W2) was investigated. When the concentration of CsCl or CsBr in W1 was equivalent to that in W2, the single‐channel current was proportional to the absolute value of the applied membrane potential. Although the single‐channel current linearly increased with increasing electrolyte concentration in W1 and W2 until about 0.1 M (mol dm^?3), it began to level off around 0.1 M, indicating that ion permeation across the channel pore is the rate‐determining step and that the saturation of the transporting ion within the channel pore provokes the leveling off. In the case of asymmetric composition of the electrolyte in W1 and W2, the monovalent cation and the counter anion were transported in the opposite direction through the gA channel pore or the bilayer lipid membrane around the gA channel. Finally, the experimental data was fitted using the Goldman‐Hodgkin‐Katz equation based on the relationship between the membrane potential and the single‐channel current to define the ratio of the diffusion coefficients of Cs⁺, Cl^?, and Br^? as 5.7 : 1.0 : 0.26.     

A Convenient Synthesis of 2, 3 - DI- O - Acetyl-1, 6 - Anhydro- β - D – Glucopyranose

Abstract

1, 2, 3-Tri-O-acetyl-6-O-benzyl-4-O-chloroacetyl-α- and -β-D-glucopyranose (4α β)were derived from 1, 2, 3-tri-O-acetyl-4, 6- O -benzyl-idehe-β-D-giucopyranose (1) in two steps. Compound 1, 1, 2, 3-tri-O -acetyl-β-D-glucopyranose (2), and 4α,β were subjected to the cyclization reaction using Lewis acids ( SnCl₄ and BF₃-etherate), to give corresponding 1, 6-anhydro derivatives.     

Glycosylation Using Methylthioglycosides of N-Acetylneuraminic Acid and Dimethyl(Methylthio)Sulfonium Triflate

Abstract

Recently, great interest has been focussed on the synthesis of oligosaccharides containing N-acetylneuraminic acid (Neu5Ac) because of its important roles in a variety of biological recognitions.² However, many difficulties in the synthesis of naturally occurring α-glycosides still remained.³ We have recently reported the stereo-selective synthesis of a series of α- and β-2-thio-neuraminyl glycosides.^1-4

In the meantime, the utility of thioglycosides in oligosaccharide synthesis has been widely developed.⁵ Particularly noteworthy is the dimethyl(methylthio)sulfonium triflate (DMTST) promoted glyco-sylation method^5k.1 because excellent yields are achieved due to the high thiophilicity of this reagent.     

Cyclophane-lectin Conjugates as a New Class of Water-soluble Host

A conjugate composed of tetraaza[6.1.6.1]paracyclophane bearing carboxylic acids and lectin, a carbohydrate binding protein, was prepared. The specific saccharide-binding abilities as well as the secondary structural features of the lectin were not disturbed, when the cyclophane were covalently bound to the lectin. The conjugate was found to act as a water-soluble host for inclusion of anionic guest molecules such as 6-p-toluidino-naphthalene-2-sulfonate (TNS) and 8-anilinonaphthalene-1-sulfonate (ANS) in aqueous acetate buffer (pH 4.0) with binding constants of 4.2 × 10⁴ and 1.5 × 10⁴ dm³ mol⁻¹, respectively. The obtained binding constants were much larger than those by untethered water-soluble cyclophane. A highly desolvated microenvironment was provided by the cyclophane cavity on the protein surfaces so that the tight host–guest interaction, which brought about the marked motional repression of the entrapped guests, became effective. The conjugate also showed molecular discrimination capabilities toward the anionic guests through electrostatic repulsion mechanism originating from acid-dissociation equilibrium of carboxylic acids of the cyclophane branches.     

Investigation of proton diffusion in Nafion®117 membrane by electrical conductivity and NMR

The proton dynamics in Nafion ^®117 is investigated by comparison of the diffusion coefficient D_NMR estimated from PFG-NMR with that of D_σ estimated from electrical conductivity. At high water content region, D_σ is about two times higher than D_NMR as a result of Grotthuss mechanism. At low water content region, D_σ and D_NMR are in good agreement with each other. Both of the diffusion coefficients decrease steeply at low water content region. It can be explained as a result of the percolation transition due to the isolation of ion clusters, which is suggested by the recent small angle X-ray scattering data.     

First experimental result with fluorescent X‐ray CT based on sheet‐beam geometry

Fluorescent X‐ray computed tomography (FXCT) enables us to reveal the cross‐sectional distribution of very low concentration of specific elements, e.g. I, Gd, or Au, in biomedical samples at a spatial resolution of several hundred micrometers, and it has been used to evaluate the states of cerebral perfusion and fatty acid metabolic function of small animals in vivo and ex vivo. However, since the current system employs the data‐acquisition scheme of the first‐generation type of CT, it requires a huge amount of time to obtain a whole set of projections. In order to overcome the problem, we propose a novel imaging geometry using a sheet incident beam. We performed a proof‐of‐concept experiment using a preliminary imaging system constructed at beam line BLNE‐5A, KEK. The efficacy of the proposed method is demonstrated by the reconstructed images of a physical phantom containing various concentrations of iodine solution and a mouse brain that is extracted after intravenous injection of ¹²⁷I‐IMP for observing the cerebral perfusion and then fixed with formalin. Copyright © 2009 John Wiley & Sons, Ltd.     

Range Technique in Scattering Medium Using a Needle-Fiber Optical Coherence Tomography System

A needle-fiber optical coherence tomography (OCT) system designed for guiding epidural anesthesia to a target is presented. In the preliminary experiment, a desired target in tofu as a strong scattering medium can be monitored over a sufficient range of several millimeters within a short measuring time. The axial resolution is 21 μm. In order to investigate the ranging performance, the relation between background noise levels and focus-scattering properties in a confocal optical system is numerically studied by use of Monte Carlo technique. Numerical results indicate that an appropriate focal length of the lens attached to the fiber should be used to separate the OCT signal from strong noise in strongly scattered medium.