Enantioseparation of dansyl amino acids by ultra-high pressure liquid chromatography using cationic β-cyclodextrins as chiral additives

This work reports the application of ultra-high pressure liquid chromatography (UHPLC) for reasonably fast enantiorecognition of some dansyl amino acids by employing three cationic β-cyclodextrins (β-CDs) as chiral additives. Good resolutions were obtained on an Agilent C18 column (2.1 mm i.d.; 1.8 μm; 50 mm length) with 1% (v/v) triethylammonium acetate buffered at pH 4.7 and acetonitrile as the mobile phase. Most of the analytes could be baseline resolved within 10 min. Increased cationic CD concentration or acetonitrile proportion in the mobile phase results in a decreased retention factor but accentuated selectivity. Furthermore, molecular mechanics calculation was performed and found to be consistent with the experimental results.     

Indicator approach to develop a chemosensor for the colorimetric sensing of thiol-containing water and its application for the thiol detection in plasma

A strategy for the determination of the presence of thiol-containing amino acids was successfully established by simply assembling copper chloride and xylenol orange (3,3'-bis[N,N-bis(carboxymethyl)aminomethyl]-o-cresolsulfonephthalein trisodium salt; XO) in a 1 : 1 molar ratio in quasi-physiological water solution (pH 6.0). The copper(II)-XO ensemble was highly selective for thiol species such as cysteine, homocysteine, and glutathione without interference from other amino acids and could quantitatively detect thiol in the range from 10 to 200 μM with a linear relationship having an average molar absorbance constant of 6530 L mol(-1) cm(-1) in pure water. The whole recognition process for thiol gave rise to a rapid visual color change from purple-red to yellow which can be observed simultaneously with the naked-eye.     

Communication: branching ratio measurements in the predissociation of 12C16O by time-slice velocity-map ion imaging in the vacuum ultraviolet region

The first direct branching ratio measurement of the three lowest energy dissociation channels of CO that produce C((3)P) + O((3)P), C((1)D) + O((3)P), and C((3)P) + O((1)D) is reported. Rotational resolved carbon ion yield spectra for two Π bands (W(3sσ)(1)Π (v(') = 3) at 108,012.6 cm(-1) and (1)Π(v(') = 2) at 109,017 cm(-1)) and two Σ bands ((4sσ)(1)Σ(+)(v(') = 4) at 109,452 cm(-1) and (4pσ)(1)Σ(+)(v(') = 3) at 109,485 cm(-1)) of CO were obtained. Our measurements show that the branching ratio in this energy region is strongly dependent on the electronic and vibrational energy but it is independent or just weakly dependent on the parity and rotational energy levels. To our knowledge, this is the first time that the triplet channel producing O((1)D) has been experimentally observed and this is also the first time that a direct measurement of the branching ratio for the different channels in the predissociation of CO in this energy region has been made.     

ZrO2-SiO2复合物表面酸性的调控及催化四氢呋喃聚合性能研究

采用醇-水溶液加热法制备了复合均匀的ZrO2-SiO2复合氧化物,通过调整复合物中ZrO2含量及焙烧温度对ZrO2-SiO2复合氧化物表面酸量及酸类型进行精细调控,并将其应用于催化四氢呋喃(THF)开环聚合反应.结果表明,当ZrO2含量小于30 mol%时,随着ZrO2含量的增加,复合物总酸量显著增加,且B酸与L酸酸量...     

Unexpected Adsorption Capacity of Ca-deficient Hydroxyapatite in Oil/water System

Symmetrical diynes were synthesized by ligand‐free copper‐catalyzed homocoupling reaction of 1,1‐dibromo‐1‐alkenes using a DBU/DMSO system at room temperature in good to excellent yields dot.^?1.     

Electrocatalysis Oxidation of GMP Based on Layered Double Hydroxide Functionalized with Anionic Surfactant and Room Temperature Ionic Liquid Modified Glassy Carbon Electrode

The electrocatalysis oxidation of guanosine‐5′‐monophosphate (GMP) was investigated on Mg‐Al layered double hydroxide (LDH) functionalized with sodium dodecyl sulfate (SDS) and room temperature ionic liquid (RTIL) modified glass carbon electrode (GCE). The cyclic voltammogram of GMP on the modified electrode (RTIL/ LDH‐SDS/GCE) exhibited a well defined anodic peak at 1.091 V in 0.2 mol·L^?1 pH 4.4 acetate buffer solution. The GMP oxidation was enhanced in the presence of anionic surfactant in the ?lms. The results suggest that the surfactant molecules intercalate the LDH layers to preconcentrate GMP molecules and the RTIL showed good ionic conductivity. The experimental parameters were optimized, the kinetic parameters were investigated and the probable oxidation mechanism was proposed. Under the optimized conditions, the oxidation peak current was proportional to GMP concentration in the range from 5.0×10^?7 to 1.0×10^?4 mol·L^?1 with the correlation coefficient of 0.9987 and the detection limit was 1.0×10^?7 mol·L^?1. The RTIL/LDH‐SDS/GCE showed a good electrochemical response to the oxidation of GMP and would be developed into a new biosensor.     

Mechanism of Gold(I)‐Catalyzed Conia‐ene Reaction of β‐Ketoesters with Alkynes: A DFT Study

Density functional calculations have been performed to comparatively investigate two possible pathways of Au(I)‐catalyzed Conia‐ene reaction of β‐ketoesters with alkynes. Our studies find that, under the assistance of trifluoromethanesulfonate (TfO), the β‐ketoester is the most likely to undergo Model II to isomerize into its enol form, in which TfO plays a proton transfer role through a 6‐membered ring transition state. The coordination of the Au(I) catalyst to the alkynes triple bond can enhance the eletrophilic capability and reaction activity of the alkynes moiety, which triggers the nucleophilic addition of the enol moiety on the alkynes moiety to give a vinyl‐Au intermediate. This cycloisomerizaion step is exothermal by 21.3 kJ/mol with an energy barrier of 56.0 kJ/mol. In the whole catalytic process, the protonation of vinyl‐Au is almost spontaneous, and the formation of enol is a rate‐limiting step. The generation of enol and the activation of Au(I) catalyst on the alkynes are the key reasons why the Conia‐ene reaction can occur in mild condition. These calculations support that Au(I)‐catalyzed Conia‐ene reactions of β‐ketoesters with alkynes go through the pathway 2 proposed by Toste.     

A low dielectric constant polyimide/polyoxometalate composite

A silane‐modified mono‐lacunary Keggin‐type polyoxometalate (POM), (Bu₄N)₄[SiW₁₁O₃₉{(CH₂?CH? Si)₂O}] (SiW₁₁? CH?CH₂), was obtained by reaction of vinyltrimethoxysilane with K₈(SiW₁₁O₃₉) in acidic MeCN/H₂O mixed solutions. Then, the modified polyoxometalate was physically blended with the pyromellitic dianhydride (PMDA)‐4,4′‐oxydianiline (ODA) poly(amic acid) and the blends were thermally imidized to form polyimide/ polyoxometalate composites. The X‐ray diffraction (XRD) analysis indicates that the polyoxometalate clusters cannot form crystalline structures in the composite, suggesting that the blending leads to improved compatibility between the polymer matrix and the modified polyoxometalate. The EDS (W‐mapping) studies on the composite films reveal that the polyoxometalate clusters are well dispersed in the polyimide matrix. The physical incorporation of modified POM into polyimide remarkably reduced the dielectric constant of the latter from 3.29 to 2.05 when 20 wt% of SiW₁₁? CH?CH₂ was used. Besides, the addition of the modified POM into polyimide increased the storage modulus of polyimide without severely affecting its thermal properties. Copyright © 2009 John Wiley & Sons, Ltd.     

A novel ion‐imprinted hydrogel for recognition of potassium ions with rapid response

A novel ion‐imprinted strategy is developed for synthesizing responsive hydrogels with rapid response to potassium ions. With potassium ions as templates, ion‐imprinted poly(N‐isopropylacrylamide‐co‐benzo‐15‐crown‐5‐acrylamide) (P(NIPAM‐co‐B15C5Am)) hydrogels are synthesized with 15‐crown‐5 crown ethers mounted on the polymer networks in pairs; therefore, it is very easy and fast for the crown ethers to capture potassium ions again by their Venus flytrap action and form stable 2:1 “host–guest” complexes with potassium ions in the ion‐recognition process. As a result, the response rate of the ion‐imprinted hydrogels to potassium ions is significantly faster than that of normal P(NIPAM‐co‐B15C5Am) hydrogels in which 15‐crown‐5 crown ethers are randomly pendent on the polymeric networks. Copyright © 2010 John Wiley & Sons, Ltd.     

3,4‐Dihydroxy‐L‐phenylalanine for Preparation of Gold Nanoparticles and as Electron Transfer Promoter in H2O2 Biosensor

3,4‐Dihydroxy‐L ‐phenylalanine (dopa) and 2‐(3,4‐dihydroxyphenyl)ethylamine (dopamine) were investigated as reducing agent and stabilizer for synthesis of gold nanoparticles (AuNPs) by one‐pot heating of a solution of HAuCl₄/dopa or dopamine. AuNPs with different sizes were obtained by controlling the mass ratios of HAuCl₄/dopa or dopamine. The formation mechanism for AuNPs was also proposed. Immobilization of horseradish peroxidase (HRP) and promotion of its electron transfer by polydopa film were investigated for preparation of H₂O₂ biosensor. Alkaline dopa solution was dropped onto a gold electrode for the formation of polydopa film. HRP was immobilized on the polydopa film through interactions between heme centre of HRP and the amine and carboxyl groups in polydopa. The AuNPs embedded in the polydopa film improved the electron transfer efficiency. These two factors allowed successful development of a H₂O₂ sensor with HRP@polydopa‐AuNPs electrode. Due to its biocompatibility, the polydopa‐AuNPs film provided good retention of enzyme activity and long‐term stability of the sensor. A rapid catalytic response (3 s) and a linear range from 0.006 to 5.0 mmol L^?1 were obtained for H₂O₂. This facile preparation strategy can be extended to other enzyme‐based biosensors.