Headspace solid-phase microextraction of menthol using a sol–gel titania-based coating along with multiwalled carbon nanotubes on the surface of stainless steel fiber

Sol–gel coating technology for the preparation of solid-phase microextraction fibers involves a single-step procedure and allows for in situ creation of chemically bonded coatings which are characterized by high thermal and solvent stabilities. A novel titania sol–gel coating was prepared for the first time on a stainless steel fiber and applied for the headspace solid-phase microextraction (HS-SPME) of menthol with gas chromatography and flame ionization detection. Important parameters influencing the efficiency of SPME process, such as extraction time, extraction temperature and ionic strength, were optimized by central composite design. An extraction time of 40 min at 60 °C gave maximum extraction efficiency, when NaCl (10% w/v) was added to the aqueous sample. The analytical characteristics of the proposed method were comparable with other reported fibers. Under optimized conditions, the linearity was between 0.05 and 100 µg mL^??1. The relative standard deviations (RSDs) determined at 0.5 µg mL^??1 concentration level (n?=?5) were as follows: intra-day RSD 7.26%; inter-day RSD 10.87%; fiber-to-fiber RSD 9.05%. The relative recoveries determined after spiking a mint distillate sample at three concentration levels from 0.067 to 50.0 µg mL^??1 varied from 86 to 102%. The proposed method was successfully applied for the analysis of menthol in peppermint samples.     

Atom transfer radical polymerization of (meth)acrylates and their novel block copolymers with vinyl acetate

Homopolymerization of methyl acrylate (MA) and methyl methacrylate (MMA) by atom transfer radical polymerization (ATRP) were carried out at 90 °C using methyl-2-bromopropionate (MBP) as initiator, copper halide (CuX, X=Cl, Br) as catalyst, 2,2^′-bipyridine (bpy) or N,N,N^′,N^′,N^″-pentamethyldiethylenetriamine (PMDETA) as ligand in 1-butanol (less polar and containing OH) and acetonitrile (more polar) solvents. It was found that with CuCl/bpy catalyst ATRP of MA and MMA in 1-butanol proceeded faster than that in acetonitrile. The rate of ATRP of MA and MMA in acetonitrile and 1-butanol was comparable when CuCl/PMDETA used as catalyst system. The number-average molecular weights increased with conversion and polydispersities were low . The ATRP of MA and MMA with vinyl acetate telomer having trichloromethyl end group (PVAc-CCl₃) were also used to synthesize new block copolymers. The structures and molecular weight of synthesized PVAc-b-PMA and PVAc-b-PMMA were characterized by ¹H NMR, FTIR spectroscopy and gel permeation chromatography (GPC) and shown that the block copolymers were novel.     

Wrapped branes as qubits

Recent work has established a correspondence between the tripartite entanglement measure of three qubits and the macroscopic entropy of the four-dimensional 8-charge STU black hole of supergravity. Here we consider the configurations of intersecting D3-branes, whose wrapping around the six compact dimensions T6 provides the microscopic string-theoretic interpretation of the charges, and associate the three-qubit basis vectors |ABC>, (A, B, C=0 or 1) with the corresponding 8 wrapping cycles. In particular, we relate a well-known fact of quantum information theory, that the most general real three-qubit state can be parameterized by four real numbers and an angle, to a well-known fact of string theory, that the most general STU black hole can be described by four D3-branes intersecting at an angle.     

无溶剂条件下锰 (Ⅲ)-席夫碱配合物催化过氧化氢氧化醇

 Aliphatic and aromatic alcohols are efficiently oxidized to ketones or carboxylic acids using aqueous hydrogen peroxide as an oxidant in the presence of a Mn(III) Schiff-base complex as a catalyst under solvent-free conditions. The oxidation of alcohols occurred at 50 °C to give the corresponding ketones or carboxylic acids with a yield higher than 60%.     

Synthesis of Pyranopyrazoles Using Magnetically Recyclable Heterogeneous Iron Oxide‐silica Core‐shell Nanocatalyst

The Fe₃O₄@SiO₂ core‐shell nanocatalyst were prepared and efficiently used for four‐component coupling reaction of aromatic aldehydes, malononitrile, ethyl acetoacetate and hydrazine hydrate in water/ethanol mixture. Various aromatic aldehydes possessing electron‐withdrawing and electron‐donating groups in different positions on the ring were successfully transformed to substituted pyranopyrazoles in high yields in short time. The nanocatalyst was easily recovered, and reused five times without significant loss in cata‐ lytic activity and performance. The structure, size and morphology of the nanosized catalyst were studied by various techniques such as Fourier transform infrared spectroscopy, powder X‐ray diffraction, dynamic light scattering and transmission electron microscopy.     

Twisted Orlicz algebras,II

Let G be a locally compact group, let be a 2‐cocycle, and let () be a complementary pair of strictly increasing continuous Young functions. We continue our investigation in [14] of the algebraic properties of the Orlicz space with respect to the twisted convolution ? coming from Ω. We show that the twisted Orlicz algebra posses a bounded approximate identity if and only if it is unital if and only if G is discrete. On the other hand, under suitable condition on Ω, becomes an Arens regular, dual Banach algebra. We also look into certain cohomological properties of , namely amenability and Connes‐amenability, and show that they rarely happen. We apply our methods to compactly generated group of polynomial growth and demonstrate that our results could be applied to variety of cases.     

Selective Catalytic Chemistry at Rhodium(II) Nodes in Bimetallic Metal–Organic Frameworks

We report the first study of a gas‐phase reaction catalyzed by highly dispersed sites at the metal nodes of a crystalline metal–organic framework (MOF). Specifically, CuRhBTC (BTC^3?=benzenetricarboxylate) exhibited hydrogenation activity, while other isostructural monometallic and bimetallic MOFs did not. Our multi‐technique characterization identifies the oxidation state of Rh in CuRhBTC as +2, which is a Rh oxidation state that has not previously been observed for crystalline MOF metal nodes. These Rh²⁺ sites are active for the catalytic hydrogenation of propylene to propane at room temperature, and the MOF structure stabilizes the Rh²⁺ oxidation state under reaction conditions. Density functional theory calculations suggest a mechanism in which hydrogen dissociation and propylene adsorption occur at the Rh²⁺ sites. The ability to tailor the geometry and ensemble size of the metal nodes in MOFs allows for unprecedented control of the active sites and could lead to significant advances in rational catalyst design.     

Novel isocyanide-based four-component reaction: a facile synthesis of fully substituted 3,4-dihydrocoumarin derivatives

A novel isocyanide-based four-component reaction between a 2-hydroxybenzaldehyde, Meldrum's acid, an isocyanide, and an aromatic or an aliphatic alcohol efficiently provide 3,4-dihydrocoumarin derivatives in good to excellent yields without using any catalyst or activation. The reaction can be carried out as a simple one-pot protocol at room temperature.     

An improved three-dimensional model for interface pressure calculations in free-surface flows

A three-dimensional method for the calculation of interface pressure in the computational modeling of free surfaces and interfaces is developed. The methodology is based on the calculation of the pressure force at the interfacial cell faces and is mainly designed for volume of fluid (VOF) interface capturing approach. The pressure forces at the interfacial cell faces are calculated according to the pressure imposed by each fluid on the portion of the cell face that is occupied by that fluid. Special formulations for the pressure in the interfacial cells are derived for different orientations of an interface. The present method, referred to as pressure calculation based on the interface location (PCIL), is applied to both static and dynamic cases. First, a three-dimensional motionless drop of liquid in an initially stagnant fluid with no gravity force is simulated as the static case and then two different small air bubbles in water are simulated as dynamic cases. A two-fluid, piecewise linear interface calculation VOF method is used for numerical simulation of the interfacial flow. For the static case, both the continuum surface force (CSF) and the continuum surface stress (CSS) methods are used for surface tension calculations. A wide range of Ohnesorge numbers and density and viscosity ratios of the two fluids are tested. It is shown that the presence of spurious currents (artificial velocities present in case of considerable capillary forces) is mainly due to the inaccurate calculation of pressure forces in the interfacial computational cells. The PCIL model reduces the spurious currents up to more than two orders of magnitude for the cases tested.

Also for the dynamic bubble rise case, it is shown that using the numerical solver employed here, without PCIL, the magnitude of spurious currents is so high that it is not possible to simulate this type of surface tension dominated flows, while using PCIL, we are able to simulate bubble rise and obtain results in close agreement with the experimental data.