Facile Preparation and Molecular Structure of a Novel Metacyclophane

Abstract

A novel 1,1,10,10,19,19-hexamethyl-5,14,23-trimethoxy[3.3.3]metacyclophane (2) was prepared in 25% yield by Friedel–Crafts cyclization of 4-(2-methoxyphenyl)-2-methylbutan-2-ol (1) at ? 78 °C using TiCl₄ as Lewis acid catalyst in anhydrous dichloromethane. The structure of cyclophane 2 was determined by single-crystal X-ray diffraction, and the impact of substrate concentration on the yield of macrocycle 2 was also examined. The study on the effect of substituents at the phenyl ring showed that the methoxy group in 1 is crucial for its trimerization to give the hexamethyl[3.3.3]metacyclophane derivative. Demethylation of 2 with BBr₃ gave 1,1,10,10,19,19-hexamethyl-5,14,23-trihydroxy[3.3.3]metacyclophane (4) in 96% yield, and its three hydroxyl groups provide the possible modification sites for further construction of supramolecular assemblies.     

Stereoselective Synthesis of 1,3-Dienes from Propargylic Alcohols by LiAlH4/AlCl3

Herein we report that LiAlH₄/AlCl₃ is a very efficient reagent for the reductive dehydration of aryl propargylic alcohols in tetrahydrofuran solvent at reflux to give 1,3-dienes with good yields and high E selection. The reaction conditions are mild and easy to operate, and a variety of aryl functional groups, such as bromo, fluoro, butyl, and methoxyl groups, are tolerated. With our protocol, useful (E,E)-1,3-dienes can be synthesized.

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Fibrous Networks with Incorporated Macrocycles: A Chiral Stimuli‐Responsive Supramolecular Supergelator and Its Application to Biocatalysis in Organic Media

A new and versatile, crown ether appended, chiral supergelator has been designed and synthesized based on the bis‐urea motif. The introduction of a stereogenic center improved its gelation ability significantly relative to its achiral analogue. This low‐molecular‐weight gelator forms supramolecular gels in a variety of organic solvents. It is sensitive to multiple chemical stimuli and the sol–gel phase transitions can be reversibly triggered by host–guest interactions. The gel can be used to trap enzymes and release them on demand by chemical stimuli. It stabilizes the microparticles in Pickering emulsions so that enzyme‐catalyzed organic reactions can take place in the polar phase inside the microparticles, the organic reactants diffusing through the biphasic interface from the surrounding organic phase. Because of the higher interface area between the organic and polar phases, enzyme activity is enhanced in comparison with simple biphasic systems.     

Osteopontin: A Uranium Phosphorylated Binding‐Site Characterization

Herein, we describe the structural investigation of one possible uranyl binding site inside a nonstructured protein. This approach couples spectroscopy, thermodynamics, and theoretical calculations (DFT) and studies the interaction of uranyl ions with a phosphopeptide, thus mimicking a possible osteopontin (OPN) hydroxyapatite growth‐inhibition site. Although thermodynamical aspects were investigated by using time‐resolved laser fluorescence spectroscopy (TRLFS) and isothermal titration calorimetry (ITC), structural characterization was performed by extended X‐ray absorption fine structure (EXAFS) at the U L_III‐edge combined with attenuated total reflection Fourier transform infrared (ATR‐FTIR) spectroscopy. From the vibrational and fluorescence spectra, several structural models of a UO₂²⁺/peptide complex were developed and subsequently refined by using theoretical calculations to fit the experimental EXAFS obtained. The structural effect of the pH value was also considered under acidic to moderately acidic conditions (pH 1.5–5.5). Most importantly, the uranyl/peptide coordination environment was similar to that of the native protein.     

Dispersion of Graphene Sheets in Aqueous Solution by Oligodeoxynucleotides

Applications of graphene sheets in the fields of biosensors and biomedical devices are limited by their insolubility in water. Consequently, understanding the dispersion mechanism of graphene in water and exploring an effective way to prepare stable dispersions of graphene sheets in water is of vital importance for their application in biomaterials, biosensors, biomedical devices, and drug delivery. Herein, a method for stable dispersion of graphene sheets in water by single‐stranded oligodeoxynucleotides (ssODNs) is studied. Owing to van der Waals interactions between graphene sheets, they undergo layer‐to‐layer (LtL) aggregation in water. Molecular dynamics simulations show that, by disrupting van der Waals interaction of graphene sheets with ssODNs, LtL aggregation of graphene sheets is prevented, and water molecules can be distributed stably between graphene sheets. Thus, graphene sheets are dispersed stably in water in the presence of ssODNs. The effects of size and molarity of ssODNs and noncovalent modification of graphene sheets are also discussed.     

Reflective mode of deformed-helix ferroelectric liquid crystal cells for sensing applications

We present a detailed theoretical and experimental study of the reflectance response of a deformed-helix ferroelectric (DHF) liquid crystal (LC) cell to an applied voltage under cross-polarisers. Using a model based on the effective dielectric tensor approximation, we derive simple analytical formulas to design a LC cell with maximum modulation depth and optimal linearity of the electro-optical response intensity versus the electric field. Our experimental results show that the cell works at frequencies up to 10 kHz and exhibits excellent linearity, with a total harmonic distortion as low as ?70 dB. These findings suggest that DHF-LCs can be exploited to develop simple and accurate optical sensors.     

Fast switching beam steering based on ferroelectric liquid crystal phase shutter and polarisation grating

We report on fast-switching and high-efficient optical beam steering based on a polymerisable liquid crystal polarisation grating (PG) in combination with ferroelectric liquid crystal (FLC) phase shutter. The PG was fabricated in a convenient single-step holographic exposure process using photo-sensitive azo-dye material as alignment layer for liquid crystal (LC) director. A binary electro-optical FLC was employed for circular polarisation selection, which enables the electro-tunable steering of the combined system. The efficiency of 95.7% with 82 μs switching time is obtained for 1064 nm laser. This work provides a versatile candidate for non-mechanical beam steering devices.     

Properties of Aqueous Polyurethane Dispersion Modified by Epoxide Resin and Their Use as Adhesive

The aqueous polyurethane hybrid dispersion modified by the epoxy resin were synthesized using 1,4-butanediol ( BDO ) and dimethylolpropionic(DMPA) as chain extenders. A kind of automobile interior decoration adhesive was made by the modified hybrid dispersions. Effects of the content and the kinds of epoxide resin on the properties of dispersions and dispersion-cast films such as appearance, pot life, viscosity, particle size, molecular mass, hardness, swelling in water, contact angle, strength of stress, elongation at break, and other mechanical properties were studied. At the same time the effect of the E20 content on the peel strength of the adhesive for several automobile interior decoration substrates such as rubber/wood, poly(vinyl chloride)/wood; leather/wood, sponge/wood was investigated. The experimental results show that when the epoxy resin E20 content was 8%, the modified polyurethane hybrid dispersions possess better properties and the adhesive made by the modified dispersions posses better adhesion for automobile interior decoration substrates. The stress-strain curve of the modified aqueous polyurethane hybrid dispersions films shows the modified aqueous cast films possess better rigidity and toughness.