Controlled Trifluoromethylation Reactions of Alkynes through Visible‐Light Photoredox Catalysis

The control of a reaction that can form multiple products is a highly attractive and challenging concept in synthetic chemistry. A set of valuable CF₃‐containing molecules, namely trifluoromethylated alkenyl iodides, alkenes, and alkynes, were selectively generated from alkynes and CF₃I by environmentally benign and efficient visible‐light photoredox catalysis. Subtle differences in the combination of catalyst, base, and solvent enabled the control of reactivity and selectivity for the reaction between an alkyne and CF₃I.     

Development of a liquid chromatography–tandem mass spectrometry method for the determination of Grayanotoxins in rat blood and its application to toxicokinetic study

A sensitive and specific high‐performance liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method was developed for the determination of Grayanotoxin I (GTX I) and Grayanotoxin III (GTX III) in rat whole blood. Grayanotoxins (GTXs) and clindamycin as internal standard (IS) were extracted from rat blood via solid‐phase extraction using PEP solid‐phase extraction cartridges. Chromatographic separation of the analytes was achieved on a Kinetex C₁₈ (100 × 2.1 mm, 2.6 µm) reversed‐phase column using a gradient elution with the mobile phase of 1% acetic acid in water and methanol at a flow rate of 0.2 mL/min. Electrospray ionization mass spectrometry was operated in the positive ion mode with multiple reaction monitoring. The calibration curves obtained were linear over the concentration range of 1–100 ng/mL with a lower limit of quantification of 1 ng/mL for GTXs. The relative standard deviation of intra‐day and inter‐day precision was below 6.8% and accuracy ranged from 94.8 to 106.6%. The analytes were stable in the stability studies. The validated method was successfully applied to the quantification and toxicokinetic study of GTXs in rats for the first time after oral administration of 11.52 mg/kg mad honey and 0.35 mg/kg GTX III, respectively. Copyright © 2014 John Wiley & Sons, Ltd.     

Directing the Structural Features of N2‐Phobic Nanoporous Covalent Organic Polymers for CO2 Capture and Separation

A family of azo‐bridged covalent organic polymers (azo‐COPs) was synthesized through a catalyst‐free direct coupling of aromatic nitro and amine compounds under basic conditions. The azo‐COPs formed 3D nanoporous networks and exhibited surface areas up to 729.6 m² g^?1, with a CO₂‐uptake capacity as high as 2.55 mmol g^?1 at 273 K and 1 bar. Azo‐COPs showed remarkable CO₂/N₂ selectivities (95.6–165.2) at 298 K and 1 bar. Unlike any other porous material, CO₂/N₂ selectivities of azo‐COPs increase with rising temperature. It was found that azo‐COPs show less than expected affinity towards N₂ gas, thus making the framework “N₂‐phobic”, in relative terms. Our theoretical simulations indicate that the origin of this unusual behavior is associated with the larger entropic loss of N₂ gas molecules upon their interaction with azo‐groups. The effect of fused aromatic rings on the CO₂/N₂ selectivity in azo‐COPs is also demonstrated. Increasing the π‐surface area resulted in an increase in the CO₂‐philic nature of the framework, thus allowing us to reach a CO₂/N₂ selectivity value of 307.7 at 323 K and 1 bar, which is the highest value reported to date. Hence, it is possible to combine the concepts of “CO₂‐philicity” and “N₂‐phobicity” for efficient CO₂ capture and separation. Isosteric heats of CO₂ adsorption for azo‐COPs range from 24.8–32.1 kJ mol^?1 at ambient pressure. Azo‐COPs are stable up to 350 °C in air and boiling water for a week. A promising cis/trans isomerization of azo‐COPs for switchable porosity is also demonstrated, making way for a gated CO₂ uptake.     

Palladium‐catalyzed carbonylative cyclization of β‐bromo‐α,β‐unsaturated carboxylic acids with 2,2‐dimethylhydrazine leading to 1‐(dimethylamino)‐1H‐pyrrole‐2,5‐diones

β‐Bromo‐α,β‐unsaturated carboxylic acids are carbonylatively cyclized with 2,2‐dimethylhydrazine under carbon monoxide pressure in THF in the presence of a catalytic amount of a palladium catalyst along with a base to give 1‐(dimethylamino)‐1H‐pyrrole‐2,5‐diones. Copyright © 2014 John Wiley & Sons, Ltd.     

Nanoporous block copolymer micelle/micelle multilayer films with dual optical properties

We introduce a novel and versatile approach for preparing self-assembled nanoporous multilayered films with tunable optical properties. Protonated polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and anionic polystyrene-block-poly(acrylic acid) (PS-b-PAA) block copolymer micelles (BCM) were used as building blocks for the layer-by-layer assembly of BCM multilayer films. BCM film growth is governed by electrostatic and hydrogen-bonding interactions between the opposite BCMs. Both film porosity and film thickness are dependent upon the charge density of the micelles, with the porosity of the film controlled by the solution pH and the molecular weight (M(w)) of the constituents. PS(7K)-b-P4VP(28K)/PS(2K)-b-PAA(8K) films prepared at pH 4 (for PS(7K)-b-P4VP(28K)) and pH 6 (for PS(2K)-b-PAA(8K)) are highly nanoporous and antireflective. In contrast, PS(7K)-b-P4VP(28K)/PS(2K)-b-PAA(8K) films assembled at pH 4/4 show a relatively dense surface morphology due to the decreased charge density of PS(2K)-b-PAA(8K). Films formed from BCMs with increased PS block and decreased hydrophilic block (P4VP or PAA) size (e.g., PS(36K)-b-P4VP(12K)/PS(16K)-b-PAA(4K) at pH 4/4) were also nanoporous. This is attributed to a decrease in interdigitation between the adjacent corona shells of the low M(w) BCMs, thus creating more void space between the micelles. Multilayer films with antireflective and photochromic properties were obtained by incorporating a water-insoluble photochromic dye (spiropyran) into the hydrophobic PS core of the BCMs assembled in the films. The optical properties of these films can be modulated by UV irradiation to selectively and reversibly control the transmission of light. Light transmission of higher than 99% was observed with accompanying photochromism in the (PS(7K)-b-P4VP(28K)/PS(2K)-b-PAA(8K)) multilayer films assembled at pH 4/6. Our approach highlights the potential to incorporate a range of materials, ranging from conventional hydrophilic materials with specific interactions to hydrophobic compounds, into the assembled BCMs to yield multifunctional nanoporous films.     

Metal ion sensing novel calix[4]crown fluoroionophore with a two-photon absorption property

1,3-Alternate calix[4]arene-based fluorescent chemosensors bearing two-photon absorbing chromophores have been synthesized, and their sensing behaviors toward metal ions were investigated via absorption band shifts as well as one- and two-photon fluorescence changes. Free ligands absorb the light at 461 nm and weakly emit their fluorescence at 600 nm when excited by UV-vis radiation at 461 nm, but no two-photon excited fluorescence is emitted by excitation at 780 nm. Addition of an Al(3+) or Pb(2+) ion to a solution of the ligand causes a blue-shifted absorption and enhanced fluorescence due to a declined resonance energy transfer (RET) upon excitation by one- and two-photon processes. Addition of a Pb(2+) ion to a solution of 1.K(+) results in a higher fluorescence intensity than the original 1.Pb(2+) complex regardless of one- or two-photon excitation, due to the allosteric effect induced by the complexation of K(+) with a crown loop.     

Controlled one-dimensional nanostructures in poly(3-hexylthiophene) thin film for high-performance organic field-effect transistors

With the aim of improving the field-effect mobilities in poly(3-hexylthiophene) (P3HT) thin film transistors, we controlled the nanostructures of P3HT thin film by changing the solvent vapor pressure in a spin-coating chamber during solidification. The transistors with P3HT thin films spin-coated under a high solvent vapor pressure (56.5 KPa), showing the one-dimensional nanowire morphologies, resulted in the relatively high field-effect mobilities (0.02 cm2/(V.s)) that are typically more than 1 order of magnitude higher than those prepared under ambient conditions, showing the featureless morphologies. This can be attributed to the higher solvent vapor pressure during film formation, providing the solvent is allowed to evaporate slowly and the degree of ordering within the P3HT crystalline domains is dramatically improved.     

Formation of superhydrophobic surfaces by biomimetic silicification and fluorination

The amazing water repellency of many biological surfaces, exemplified by lotus leaves, has recently received a great deal of interest. These surfaces, called superhydrophobic surfaces, exhibit water contact angles larger than 150 degrees and a low contact angle hysteresis because of both their low surface energy and heterogeneously rough structures. In this paper, we suggest a biomimetic method, "biosilicification", for generating heterogeneously rough structures and fabricating superhydrophobic surfaces. The superhydrophobic surface was prepared by a combination of the formation of heterogeneously rough, nanosphere-like silica structures through biosilicification and the formation of self-assembled monolayers of fluorosilane on the surface. The resulting surface exhibited the water contact angle of 160.1 degrees and the very low water contact angle hysteresis of only 2.3 degrees, which are definite characteristics of superhydrophobic surfaces. The superhydrophobic property of our system probably resulted from the air trapped in the rough surface. The wetting behavior on the surface was in the heterogeneous regime, which was totally supported by Cassie-Baxter equation.     

Infrared spectra and density functional calculations of CH2 = MHX and CH[triple bond]MH2X complexes prepared in reactions of methyl halides with Mo and W atoms

The simple methylidene and methylidyne complexes (CH2=MHX and CH[triple bond]MH2X; X = F, Cl, Br, and I) are prepared in reactions of laser-ablated Mo and W atoms with the methyl halides and investigated by matrix infrared spectroscopy and density functional theory calculations. These complex structures are photoreversible: visible irradiation converts the methylidene complex to the methylidyne complex, and UV irradiation reverses this effect via alpha-hydrogen migration. While the higher oxidation state complexes are readily formed regardless of halogen size, the Mo methylidyne complex is relatively less favored with increasing halogen size, and the W complex shows the opposite tendency. The group 6 metal methylidenes are predicted to have the most agostically distorted structures among the early transition-metal methylidenes. The computed carbon-metal bond shortens with increasing halogen size for both the methylidene and methylidyne complexes. Harmonic and anharmonic frequencies computed by DFT converge on the experimental values and thus provide support for the identification of these new Mo and W complexes.     

Single‐step multiresidue determination of ten multiclass veterinary drugs in pork,milk, and eggs using liquid chromatography with tandem mass spectrometry

A multiclass, multiresidue determination method is reported for the detection of ten veterinary drugs, including scopolamine, metoclopramide, acriflavine, berberine, tripelennamine, diphenhydramine, acrinol, triamcinolone, loperamide, and roxithromycin in pork, milk, and eggs. The method involves a simple extraction using 0.1% formic acid in acetonitrile, followed by defatting with n‐hexane, centrifugation, and filtration prior to liquid chromatography with tandem mass spectrometric analysis. As ion suppression and enhancement effects are reported, matrix‐matched calibrations are used for quantification, with determination coefficients ≥0.9765. For the majority of the tested analytes, the intra‐ and interday accuracy (expressed as recovery %) range from 70.6 to 94.6% and from 70.1 to 93.3%, respectively, and the precision (expressed as relative standard deviation) ranges from 0.5 to 19.8% and from 2.8 to 18.4% in all matrices. The limits of quantification range between 0.5 and 10 ng/g. The validated tandem mass spectrometry method is successfully applied to market samples; the target analytes are not detected in any of the tested samples. In terms of accuracy, no extract cleanup is deemed necessary. The developed method is feasible for the simultaneous detection of the tested analytes in pork, milk, and eggs.