Single-step synthesis and interface tuning of core–shell metal–organic framework nanoparticles

Control over the spatial distribution of components in metal–organic frameworks has potential to unlock improved performance and new behaviour in separations, sensing and catalysis. We report an unprecedented single-step synthesis of multi-component metal–organic framework (MOF) nanoparticles based on the canonical ZIF-8 (Zn) system and its Cd analogue, which form with a core–shell structure whose internal interface can be systematically tuned. We use scanning transmission electron microscopy, X-ray energy dispersive spectroscopy and a new composition gradient model to fit high-resolution X-ray diffraction data to show how core–shell composition and interface characteristics are intricately controlled by synthesis temperature and reaction composition. Particle formation is investigated by in situ X-ray diffraction, which reveals that the spatial distribution of components evolves with time and is determined by the interplay of phase stability, crystallisation kinetics and diffusion. This work opens up new possibilities for the control and characterisation of functionality, component distribution and interfaces in MOF-based materials.

Core–shell metal–organic framework nanoparticles have been synthesised in which the internal interface and distribution of components is found to be highly tunable using simple variations in reaction conditions.     

Synthesis of two hyaluronan trisaccharides

[formula: see text] The synthesis of two hyaluronan trisaccharides, methyl O-(beta-D-glucopyranosyluronic acid)-(1,3)-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-(1,4)-O-beta-D- glucopyranosiduronic acid and methyl O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-(1,4)-O-beta- D-glycopyranosyluronic acid)-(1,3)-O-(2-acetamido-2-deoxy-beta-D-glucopyranoside, are described. Construction of the target molecules was achieved though a combination of the phenyl sulfoxide and trichloroacetimidate glycosylation methodologies. This is the first report on the synthesis of the beta-methyl derivatives, which represent the smallest fragments that incorporate all the structural features of polymeric hyaluronan.     

Syntheses of C1-symmetric bidentate ligands having pyridyl and 1,3-Thiazolyl, 1-methylimidazolyl or pyrazinyl donor groups for enantioselective palladium-catalyzed allylic substitution and copper-catalyzed cyclopropanation

New chiral C₁-symmetric bidentate ligands, which possess two different nitrogen heterocycles, 1,3-thiazolyl, 1-methylimidazolyl or pyrazinyl and one pyridyl group, were prepared by Kröhnke condensation in 36-59% overall yield. Stable Pd(II)-allyl and Cu(II) chloride complexes formed by some of the ligands were obtained in 60-65% yields. X-ray crystal structure analysis of a copper(II) complex having 1-methylimidazolyl group indicated that it is a μ-chloro bridge dimer. The Pd(II)-allyl complexes were found to be active catalysts in the asymmetric allylic substitution of 1,3-diphenylprop-2-enyl acetate. The best result observed was 85% e.e. and 99% isolated yield. In addition, the in situ generated Cu(OTf)₂ complexes were found to be active catalysts in cyclopropanation of styrene with ethyl diazoacetate.     

Metabolic Studies of Clostebol Acetate in Horses

Clostebol acetate (4-chlorotestosterone acetate) is a synthetic anabolic steroid which may be used to enhance performance in racehorses. Studies on the in vitro biotransformation of clostebol acetate with horse liver microsomes were carried out. Six metabolites (C1 – C6) were detected. They were 4-chlorotestosterone (C1), 4-chloroandrost-4-en-3-ol-17-one (C2), 4-chloroandrost-4-ene-3,17-diol (C3), 4-chloroandrost-4-ene-3,17-dione (C4), 4-chloroandrost-4-en-6-ol-3,17-dione (C5) and 6-hydroxy-4-chlorotestosterone (C6). Clostebol acetate (350 mg) was administered orally to 2 thoroughbred geldings. The parent drug was not detected in post-administration urine, and only three metabolites C1, C3, and 4-chloroandrostane-3,17-diol (C7) were observed. The metabolic pathway for clostebol acetate is postulated. These studies have shown that metabolites C3 and C7 could be used as potential screening targets for controlling the abuse or misuse of clostebol acetate in racehorses.     

Capillary-based fully integrated and automated system for nanoliter polymerase chain reaction analysis directly from cheek cells

A miniaturized, integrated and automated system based on capillary fluidics has been developed for nanoliter DNA analysis directly from cheek cells. All steps for DNA analysis, including injecting aqueous reagents and DNA samples, mixing the solutions together, thermal cell lysis, polymerase chain reaction (PCR), transfer and injection of PCR product, separation, sizing and detection of those products are performed in a capillary-based integrated system. A small amount of cheek cells collected by a plastic toothpick is directly dissolved in the PCR cocktail in a plastic vial or mixed on-line with a small volume of PCR cocktail (125 nl) in the capillary. After thermal cell lysis and PCR in a microthermal cycler, the DNA fragments are mixed with DNA size standards and transferred to a micro-cross for injection and separation by capillary gel electrophoresis. Programmable syringe pumps, switching valves, multiposition and freeze-thaw valves are used for microfluidic control in the entire system. This work establishes the feasibility of performing all the steps of DNA analysis from real samples in a capillary-based nanoliter integrated system.     

Miniaturized Injection Method Using Silver-Coated Capillaries in DNA Sequencing by Multiplexed Capillary Electrophoresis

Silver-coated capillaries were used for direct sample injection in multiplexed capillary electrophoresis. The absence of an additional electrode simplifies mechanical alignment, reduces contamination, and decreases the amount of sample needed. Capillaries were coated by a silver paint which is a suspension of silver particles in an organic solvent. To provide electrical contact, the upper part of the capillary and a platinum wire were wound together by a copper wire. Electrical resistance from the platinum wire to the tip of the capillary was small enough (7 ω to 50 ω) to inject large amounts of DNA samples. Electrokinetic injection from eight separate sample vials to eight capillaries was demonstrated for DNA sequencing by multiplexed capillary electrophoresis. Signal-to-noise ratio and resolution were good enough to call up to 350 base pairs.     

Very Ampleness of Line Bundles and Canonical Embedding of Coverings of Manifolds

Let L be an ample line bundle on a Kähler manifolds of nonpositive sectional curvature with K as the canonical line bundle. We give an estimate of m such that K+mL is very ample in terms of the injectivity radius. This implies that m can be chosen arbitrarily small once we go deep enough into a tower of covering of the manifold. The same argument gives an effective Kodaira Embedding Theorem for compact Kähler manifolds in terms of sectional curvature and the injectivity radius. In case of locally Hermitian symmetric space of noncompact type or if the sectional curvature is strictly negative, we prove that K itself is very ample on a large covering of the manifold.     

Feedback Solution of a Class of Differential Games with Endogenous Horizons

In this paper, we consider a class of differential games in which the game ends when a subset of its state variables reaches a certain target at the terminal time. A special feature of the game is that its horizon is not fixed at the outset, but is determined endogenously by the actions of the players; conditions characterizing a feedback Nash equilibrium (FNE) solution of the game are derived for the first time. Extensions and illustrations of the derivation of FNE solutions of the game are provided.