Versatile chromatographic method for catechin determination in development of topical formulations containing natural extracts

Catechin is found in several natural sources, as Eugenia dysenterica and Syzygium cumini extracts. Its antioxidant and UV‐protective properties suggest a potential use in cosmetic and dermatological formulations. A simple analytical method capable of giving support to experiments performed along the development of topical formulations containing this natural substance (i.e. drug assay, skin permeation and stability studies), however, is still needed. Thus, this work aimed to develop and validate a selective HPLC method for catechin determination during the development of topical formulations. Separation was achieved using an RP‐C₁₈ column (300 × 3.9 mm; 10 μm), with a mobile phase of methanol–phosphoric acid 0.01 m (15: 85, v/v), a flow rate of 0.8 mL/min, temperature set at 40°C and UV detection at 230 nm. The method was linear in a range from 0.5 to 10.0 μg/mL (r = 0.9998), precise with an overall variation coefficient of 5.5% and accurate with catechin recovery from the skin layers >85%. Additionally, the method was sensitive (limit of detection, 0.109 μg/mL; limit of quantification, 0.342 μg/mL) and selective against plant extracts, skin matrices and formulation interferents, as well as catechin degradation products. It was also robust regarding both methodology parameters and analytical stability.     

An ALE finite element method for a coupled Stefan problem and Navier–Stokes equations with free capillary surface

In this article, an ALE finite element method to simulate the partial melting of a workpiece of metal is presented. The model includes the heat transport in both the solid and liquid part, fluid flow in the liquid phase by the Navier–Stokes equations, tracking of the melt interface solid/liquid by the Stefan condition, treatment of the capillary boundary accounting for surface tension effects and a radiative boundary condition. We show that an accurate treatment of the moving boundaries is crucial to resolve their respective influences on the flow field and thus on the overall energy transport correctly. This is achieved by a mesh‐moving method, which explicitly tracks the phase boundary and makes it possible to use a sharp interface model without singularities in the boundary conditions at the triple junction. A numerical example describing the welding of a thin‐steel wire end by a laser, where all aforementioned effects have to be taken into account, proves the effectiveness of the approach.Copyright © 2012 John Wiley & Sons, Ltd.     

Towards the Rational Design of Efficient Organic Structure‐Directing Agents for Zeolite Synthesis

Zeolites are crystalline microporous materials with application in diverse fields, especially in catalysis. The ability to prepare zeolites with targeted physicochemical properties for a specific catalytic application is a matter of great interest, because it allows the efficiency of the entire chemical process to be increased (higher product yields, lower undesired by‐products, less energy consumption, and cost savings, etc). Nevertheless, directing the zeolite crystallization towards the material with the desired framework topology, crystal size, or chemical composition is not an easy task, since several variables influence the nucleation and crystallization processes. The combination of accumulated knowledge, rationalization, and innovation has allowed the synthesis of unique zeolitic structures in the last few years. This is especially true in terms of the design of organic and inorganic structure‐directing agents (SDAs). In this Minireview we will present the rationale we have followed in our studies to synthesize new zeolite structures, while putting this in perspective with the advances made by other researchers of the zeolite community.     

Silver nanoparticles immobilized onto poly(4‐vinylpyridine)‐functionalized magnetic nanoparticles: A robust magnetically recyclable catalyst for oxidant‐free alcohol dehydrogenation

A heterogeneous and recyclable catalyst with a high loading of silver nanoparticles was synthesized via the silver nanoparticles being supported onto the surface of magnetic nanoparticles coated with poly(4‐vinylpyridine). The synthesized catalyst was used in the dehydrogenation of alcohols to corresponding carbonyl compounds. A broad diversity of alcohols was converted into their corresponding carbonyl compounds in excellent yields. The catalyst was easily recovered by applying an external magnetic field and reused for seven reaction cycles without considerable loss of activity. The catalyst was fully characterized using various techniques.     

Green synthesis of supported palladium nanoparticles employing pine needles as reducing agent and carrier: New reusable heterogeneous catalyst in the Suzuki coupling reaction

A green method for the synthesis of supported Pd nanoparticles (NPs) using pine needle extract as the reducing agent and the extracted residue of pine needle (RPN) as the carrier is described. The Pd/RPN nanocomposites were characterized using Fourier transform infrared, UV–visible, inductively coupled plasma atomic emission and X‐ray photoelectron spectroscopies, transmission electron microscopy and X‐ray diffraction. The spherical Pd NPs had a mean particle size of 3.25 nm and were evenly distributed on the RPN surface. More importantly, the Pd/RPN nanocomposite, as a heterogeneous catalyst, presented superior catalytic activity for the Suzuki coupling reaction. The yield of the reaction of 4‐bromotoluene with phenylboronic acid catalyzed by Pd_0.03/RPN reached 98% with low Pd loading (0.1 mmol%) at room temperature for 30 min. In addition, the catalyst could be easily separated by centrifugation and reused at least six times without significant loss of activity.     

Bis(4‐pyridylamino)triazine‐stabilized magnetite nanoparticles: preparation,characterization and application as a retrievable catalyst for the green synthesis of 4H‐pyran, 4H‐thiopyran and 1,4‐dihydropyridine derivatives

Synthesis of bis(4‐pyridylamino)triazine stabilized on silica‐coated nano‐Fe₃O₄ particles, and their feasibility as a reusable heterogeneous basic catalyst are reported. The catalytic performance of this novel material was studied for the green synthesis of highly functionalized 4H ‐pyran, 4H ‐thiopyran and 1,4‐dihydropyridine derivatives via one‐pot multicomponent reactions. Eco‐friendly method, high yield and purity of desired products, short reaction time along with ease of workup procedure outline the advantages of these new methodologies over earlier ones. Surface and magnetic properties of the core–shell hybrid nanoparticles were characterized via transmission and scanning electron microscopies, X‐ray diffraction, energy‐dispersive X‐ray and Fourier transform infrared spectroscopies and vibrating sample magnetometry. Copyright © 2016 John Wiley & Sons, Ltd.     

The Cambridge Structural Database in Retrospect and Prospect

The Cambridge Crystallographic Data Centre (CCDC) was established in 1965 to record numerical, chemical and bibliographic data relating to published organic and metal–organic crystal structures. The Cambridge Structural Database (CSD) now stores data for nearly 700 000 structures and is a comprehensive and fully retrospective historical archive of small‐molecule crystallography. Nearly 40 000 new structures are added each year. As X‐ray crystallography celebrates its centenary as a subject, and the CCDC approaches its own 50th year, this article traces the origins of the CCDC as a publicly funded organization and its onward development into a self‐financing charitable institution. Principally, however, we describe the growth of the CSD and its extensive associated software system, and summarize its impact and value as a basis for research in structural chemistry, materials science and the life sciences, including drug discovery and drug development. Finally, the article considers the CCDC’s funding model in relation to open access and open data paradigms.     

Synthesis,characterization and application of alumina/ vanadium pentoxide nanocomposit by sol–gel method

In this work, we report the preparation of Al₂O₃/V₂O₅ nanocomposit using vanadium and aluminum nitrate by sol–gel method. Characterization of nanocomposit was carried out by powder X‐ray diffractometry (XRD), Fourier transform infrared (FT‐IR), scanning electron microscopy (SEM), Energy‐Dispersive X‐ray (EDX) and UV spectroscopy. Then, applicability of the synthesized nanocomposit was tested as a nanocatalyst for the synthesis of diindolyl oxindole derivatives, an important class of potentially bioactive compounds. The products were obtained in good to high yields from one‐pot three‐component condensation of isatin with indole. Also, this nanocatalyst has been reused several times, without observable loss of activity.     

Determination of the inhibitory effect of green tea extract on glucose‐6‐phosphate dehydrogenase based on multilayer capillary enzyme microreactor

Natural herbal medicines are an important source of enzyme inhibitors for the discovery of new drugs. A number of natural extracts such as green tea have been used in prevention and treatment of diseases due to their low‐cost, low toxicity and good performance. The present study reports an online assay of the activity and inhibition of the green tea extract of the Glucose 6‐phosphate dehydrogenase (G6PDH) enzyme using multilayer capillary electrophoresis based immobilized enzyme microreactors (CE‐IMERs). The multilayer CE‐IMERs were produced with layer‐by‐layer electrostatic assembly, which can easily enhance the enzyme loading capacity of the microreactor. The activity of the G6PDH enzyme was determined and the enzyme inhibition by the inhibitors from green tea extract was investigated using online assay of the multilayer CE‐IMERs. The Michaelis constant (K_m) of the enzyme, the IC₅₀ and K_i values of the inhibitors were achieved and found to agree with those obtained using offline assays. The results show a competitive inhibition of green tea extract on the G6PDH enzyme. The present study provides an efficient and easy‐to‐operate approach for determining G6PDH enzyme reaction and the inhibition of green tea extract, which may be beneficial in research and the development of natural herbal medicines. Copyright © 2016 John Wiley & Sons, Ltd.