Qian Tang

Photo-responsive molecularly imprinted hydrogels for the detection of melamine in aqueous media

In this paper, by combination of the specificity of a molecularly imprinted technique, the water solubility of hydrogels and the photoisomerization property of azobenzene chromophores, we report a new and quick detection method for trace melamine in aqueous media based on photo-responsive molecularly imprinted hydrogels (MIHs). The MIHs were fabricated using a water-soluble azobenzene-containing 4-[(4-methacryloyloxy)phenylazo]benzenesulfonic acid (MAPASA) as the functional monomer, 1,3,5-benzenetriol as a mimic template, and tetramethacryloyl triethylene tetramine (TTT) as the cross-linker. The MIHs show specific affinity to melamine with a binding constant of 3.20 × 104 M−1 in aqueous Tris–HCl buffer at pH 7.0. The density of the melamine-specific receptor sites in the MIHs material is 2.69 μmol g−1 MIHs. Upon alternate irradiation at 365 and 440 nm, the MIHs can quantitatively uptake and release melamine. The photoisomerization rate of MIHs is related to the concentration of melamine in the detecting solution, and therefore, a quick detection method for trace melamine is established. Analytical application of the MIHs to detect the melamine concentration in both milk and milk powder has been accomplished successfully with a simple pre-treatment of the samples.

Ultrasensitive detection of bisphenol A in aqueous media using photoresponsive surface molecular imprinting polymer microspheres

Photoresponsive surface molecular imprinting polymer (SMIP) microspheres were synthesized on silica microspheres by surface polymerization using a water-soluble azobenzene-containing 4-[(4-methacryloyloxy)phenylazo]benzenesulfonic acid as the functional monomer. The SMIP microspheres displayed good photoresponsive properties and specific affinity towards bisphenol A (BPA) with high recognition ability (maximal adsorption capacity: 6.96 μmol g−1) and fast binding kinetics (binding constant: 2.47 × 104 M−1) in aqueous media. Upon alternate irradiation at 365 and 440 nm, the SMIP microspheres could quantitatively bind and release BPA. Analytical application of the SMIP microspheres for the detection of trace BPA concentration in mineral water and tap water has been carried out successfully, and therefore a simple and quick detection method for trace BPA in the environment was established.

Photocontrolled solid-phase extraction of guanine from complex samples using a novel photoresponsive molecularly imprinted polymer

A novel photoresponsive molecularly imprinted polymer (MIP) was developed for the selective extraction of guanine from complex samples. The photoresponsive MIP was fabricated using guanine as the template, water-soluble 5-[(4-(methacryloyloxy)phenyl)diazenyl]isophthalic acid as the functional monomer, and water-soluble triethanolamine trimethacrylate as the cross-linker. The MIP displayed good selectivity toward guanine with a dissociation constant of (2.70 ± 0.16) × 10(-5) mol L(-1) in aqueous media. The density of the guanine-specific receptor sites in the MIP material was (4.49 ± 0.22)μmol g(-1). Quantitatively release and uptake of guanine by the MIP occurred with irradiation at 365 and 440 nm, respectively. The MIP could efficiently extract guanine from beer and then release it into aqueous media under photocontrol. This method could be used for selective separation and subsequent determination of a specific analytes from complex samples.

Synthesis and characterization of photo- and pH-responsive nanoparticles containing amino-substituted azobenzene

A novel dual responsive nanomaterial sensitive to both photo- and pH stimuli has been successfully developed. The polymer-based nanoparticles were fabricated from a specially designed photo- and pH-responsive amino-substituted azobenzene monomer, 4-amino-4′-methacrylatylazobenzene (AMAAB), via free radical polymerization with trimethylolpropane trimethacrylate (TRIM) cross-linkers. The trans-cis photoisomerization properties of AMAAB were retained after incorporation into the rigid three-dimensional cross-linked polymer matrix. The TRIM/AMAAB molar ratio significantly influenced the kinetics of the trans-cis photoisomerization. The nanoparticles also possessed good pH-responsive properties. The change in absorbance with media pH was monitored at 402 nm, and a “titration type” curve was obtained with a pKa value of 0.61 ± 0.06. At this transition point, the color of the nanoparticle suspension changed colour from yellow to pink. Thermogravimetric analysis (TGA) indicated that the nanoparticles were thermally stable.

Photoresponsive surface molecularly imprinted polymer on ZnO nanorods for uric acid detection in physiological fluids

A photoresponsive surface molecularly imprinted polymer for uric acid in physiological fluids was fabricated through a facile and effective method using bio-safe and biocompatible ZnO nanorods as a support. The strategy was carried out by introducing double bonds on the surface of the ZnO nanorods with 3-methacryloxypropyltrimethoxysilane. The surface molecularly imprinted polymer on ZnO nanorods was then prepared by surface polymerization using uric acid as template, water-soluble 5-[(4-(methacryloyloxy)phenyl)diazenyl]isophthalic acid as functional monomer, and triethanolamine trimethacryl ester as cross-linker. The surface molecularly imprinted polymer on ZnO nanorods showed good photoresponsive properties, high recognition ability, and fast binding kinetics toward uric acid, with a dissociation constant of 3.22×10(-5)M in aqueous NaH2PO4 buffer at pH=7.0 and a maximal adsorption capacity of 1.45μmolg(-1). Upon alternate irradiation at 365 and 440nm, the surface molecularly imprinted polymer on ZnO nanorods can quantitatively uptake and release uric acid.

Synthesis and characterization of novel electrochromic and photoresponsive materials based on azobenzene-4,4′-dicarboxylic acid dialkyl ester

Novel electrochromic and photoresponsive materials based on azobenzene-4,4′-dicarboxylic acid dialkyl ester derivatives (ADDEDs) were successfully prepared and characterized through nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and high-performance liquid chromatography-mass spectrometry. The electrochromic behavior, electrochromic mechanism, electro-optical properties, and photoresponsive properties of ADDEDs were investigated through cyclic voltammetry and ultraviolet-visible absorption spectra. ADDEDs displayed not only outstanding electrochromic behavior but also good and reversible photoisomerization properties even under electrochromic conditions. Electrochromic devices (ECDs) based on ADDEDs were fabricated, and their electrochromic performance was analyzed. The ECDs presented a color change from colorless to magenta between 0.0 V (bleached state) and ±3.0 V (colored state). In addition, the ECDs exhibited fast switching times, reasonable contrast, satisfactory optical memories, and redox stability. The novel redox-active azobenzene derivatives are promising candidates for full-color EC display devices, electronic paper, smart windows, optical memory devices, dual-stimuli-responsive systems, as well as other potential new applications.

The preparation and characterization of photo-responsive sol-gel materials for 2,4-dichlorophenoxyacetic acid by surface imprinting

The primary objective of this work is to develop a photo-responsive surface molecularly imprinted polymer (SMIP) for 2,4-dichlorophenoxyacetic acid (2,4-D) to overcome the shortcomings of conventional molecularly imprinted polymers. A photo-responsive functional monomer was firstly prepared by covalent connecting azobenzene and 2,4-D. The photo-responsive SMIP was then prepared on SiO2 nanoparticles via sol–gel process, and 2,4-D was removed via hydrolysis in acid. The SMIP shows specific affinity to 2,4-D and reversible uptake and release of 2,4-D upon alternate irradiation at 365 and 440xa0nm, respectively. The favorable binding strength of the imprinted receptor sites in the SMIP for 2,4-D is found to be 2.51xa0×xa0104xa0M−1. Density of receptor sites in the SMIP material is 10.59xa0μmol/g SMIP. The SMIP requires a shorter time to reach equilibrium than does the conventional molecularly imprinted polymer. The well-defined core-shell structure was clearly visualized by high resolution transmission electron microscopy.Graphical Abstract

Facile one-pot fabrication of magnetic nanoparticles (MNPs)-supported organocatalysts using phosphonate as an anchor point through direct co-precipitation method

In this paper, a novel type of efficient, magnetically recoverable magnetic nanoparticles (MNPs)-supported 9-amino-9-deoxy-epicinchonidine organocatalysts were prepared through a facile co-precipitation method using phosphonic acid (–PO3H2) as an anchor point. These MNPs-supported organocatalysts possessed the high and tunable loading capacities of an organocatalyst (0.18–0.52 mmol g−1), 2–25 nm regular mesopores and 10.6–44.06 emu g−1 saturated magnetization. In the catalytic asymmetric aldol reactions of cyclohexanone with various o, m and p-substituted benzaldehydes in water, the aromatic aldehydes with electron-withdrawing substituents including-NO2, X and –CN afforded the relevant aldol adducts in excellent yields (86–100%) and steroselectivities (anti/syn = 82–98/18–2 and 93–98%ee anti). Moderate to good yields (36–97%) and steroselectivities (anti/syn = 82–96/18–4 and 75–97%ee anti) for the aromatic aldehydes with strong electron-donating substituents (–CH3 and –OCH3) were also satisfactorily achieved. Futhermore, these MNPs-supported organocatalysts could be quantitatively recovered from the reaction mixture using an external magnet, and reused six times with excellent catalytic performance (93%, anti/syn = 89/11 and 96%ee anti). Meanwhile, MNPs-supported organocatalysts, prepared by the surface-modification method, were investigated in detail as comparative samples.

Colorimetric test paper for cyanide ion determination in real-time

A colorimetric cyanide ion (CN−) sensor 4-[(1E)-2-(2-hydroxyphenyl)ethenyl]-1-allylpyridinium bromide (2-HPEAPB) was synthesized via condensation and N-alkylation reactions using 4-methylpyridine and salicylaldehyde as the starting materials. 2-HPEAPB displayed good selectivity, fast response, and high sensitivity toward CN− over other competing anions in acetonitrile–water (95:5, v/v) with a limit of detection of 8.0 × 10−6 mol L−1 by the naked eye. The sensing mechanism and the influence of pH and temperature on sensing properties were investigated. Colorimetric test paper for CN− was prepared by absorption of 2-HPEAPB to a chromatography paper, which could be used to detect CN− directly and quickly. Analytical application of measuring CN− concentration in an electroplating wastewater in real-time was conducted successfully.

Organosoluble zirconium phosphonate nanocomposites and their supported chiral ruthenium catalysts: The first example of homogenization of inorganic-supported catalyst in asymmetric hydrogenation

In this article, we report the synthesis, structure, morphologies, and asymmetric catalytic properties of a series of novel organosoluble zirconium phosphonate nanocomposites and their supported chiral ruthenium catalysts, which have a good organosolubility (0.1-0.5 g mL(-1)) in various solvents and mesoporous, filiform, and layered structures. Due to the organosoluble properties in various organic solvents, the first homogenization of zirconium phosphonate-supported catalyst was realized in the field of catalysis. In the asymmetric hydrogenation of substituted α-ketoesters, enantioselectivities (74.3-84.7% ee) and isolated yields (86.7-93.6%) were higher than the corresponding homogeneous Ru(p-cymene)(S-BINAP)Cl(2) due to the confinement effect caused by the remaining mesopores in the backbone of the zirconium phosphonate. After completing the reaction, the supported catalyst can be readily recovered in quantitative yield by adding cyclohexane and centrifugation, and reused for five consecutive runs without significant loss in catalytic activity.