Temperature-dependent molecular-recognizable membranes based on poly(N-isopropylacrylamide) and β-cyclodextrin

A novel temperature-dependent molecular-recognizable membrane, poly(N-isopropylacylamide-co-glycidyl methacrylate/cyclodextrin)-grafted-polyethylene terephthalate (P(NIPAM-co-GMA/CD)-g-PET) membrane, is prepared by the combination of plasma-induced pore-filling grafting polymerization and chemical reaction. Scanning electron microscope (SEM) images show that the surfaces and cross-sections of the prepared membranes are uniformly grafted by polymeric layer. Fourier transform infrared (FT-IR) results show that CDs are successfully induced onto the P(NIPAM-co-GMA) grafted chains through reaction with epoxy groups. When the environmental temperature increases from 25 °C to 45 °C, the contact angle of prepared P(NIPAM-co-GMA/CD)-g-PET membrane increases from 65° to 76.9°; whereas, that of substrate membrane decreases from 84.8° to 77.1°. During the dynamic adsorption experiments, the guest 8-anilino-1-naphthalenesulfonic acid ammonium salt (ANS) molecules are adsorbed onto the P(NIPAM-co-GMA/CD)-g-PET membrane at lower temperature (25 °C) and desorbed from it at higher temperature (40 °C) with good repeatability. This phenomenon of adsorption at low temperature and desorption at high temperature of the P(NIPAM-co-GMA/CD)-g-PET membrane is attributable to both the “swollen–shrunken” configuration change of P(NIPAM-co-GMA) grafted chains and the molecular recognition of CD toward ANS. The P(NIPAM-co-GMA/CD)-g-PET membrane show both good thermo-responsibility and temperature-dependent molecular-recognizable characteristics toward guest molecules, which is highly potential to be applied in temperature-controlled affinity separations.     

Fluorescence “turn-on” chemosensor for the selective detection of zinc ion based on Schiff-base derivative

N,N′-phenylenebis(salicylideaminato) (L) has been used to detect trace amounts of zinc ion in acetonitrile–water solution by fluorescence spectroscopy. The fluorescent probe undergoes fluorescent emission intensity enhancement upon binding to zinc ions in MeCN/H₂O (1:1, v/v) solution. The fluorescence enhancement of L is attributed to the 1:1 complex formation between L and Zn(II), which has been utilized as the basis for selective detection of Zn(II). The linear response range for Zn(II) covers a concentration range of 1.6 × 10^?7 to 1.0 × 10^?5 mol/L, and the detection limit is 1.5 × 10^?7 mol/L. The fluorescent probe exhibits high selectivity over other common metal ions, and the proposed fluorescent sensor was applied to determine zinc in water samples and waste water.     

The CGC enantiomer separation of 2-arylcarboxylic acid esters by using β-cyclodextrin derivatives as chiral stationary phases

Chiral 2-arylcarboxylic acid esters are important intermediates in preparation of enantioenriched 2-arylpropionic acids type Non-steroidal anti-inflammatory drugs (NSAIDs). Enantiomer separation of 2-arylcarboxylic acid esters is crucial for evaluation of the asymmetric synthesis efficiency and the enantiomer excess of chiral 2-arylcarboxylic acid derivatives. The capillary gas chromatography (CGC) enantiomer separation of 17 pairs of 2-arylcarboxylic acid esters enantiomers was conducted by using seven different β-cyclodextrin derivatives (CDs) as chiral stationary phases. It was found that for the 7 pairs of 2-phenylpropionates enantiomers, CDs with both alkyl and acyl substituents especially 2,6-di-O-pentyl-3-O-butyryl-β-cyclodextrin exhibited better enantiomer separation abilities than the other CDs examined. For the 7 pairs of 2-(4-substituted phenyl)propionates enantiomers, 2,3,6-tri-O-methyl-β-cyclodextrin possessed better enantiomer separation abilities than the other CDs. Among the 3 pairs of 2-phenylbutyrates enantiomers examined, only methyl 2-phenylbutyrate enantiomers could be separated by three CDs among the 7 CDs tested, while enantiomers of ethyl 2-phenylbutyrate and isopropyl 2-phenylbutyrate couldn't be separated by any of the 7 CDs tested. Besides the structures of CDs, the structures of 2-arylcarboxylic acid esters including different ester moieties, substituents of phenyl, and different carboxylic acids moieties in 2-arylcarboxylic acid esters also affected the enantiomer separation results greatly. The CGC enantiomer separation results of 2-arylcarboxylic acid esters on different CDs are useful for solving the enantiomer separation problem of 2-arylcarboxylic acid esters.     

A twofold interpenetrating framework based on the α-metatungstates

A new compound based on polyoxometalates, [Cu(bbi)]₅H[H₂W₁₂O₄₀] (1) (bbi=1,1′-(1,4-butanediyl)bis(imidazole)), has been hydrothermally synthesized and characterized by elemental analyses, IR spectroscopy, thermogravimetric analyses, and single X-ray diffraction. Compound 1 shows a twofold 3D+3D topology, and it represents the first interpenetrating network based on the isopolytungstate. The electrochemical property of compound 1 modified carbon paste electrode (1−CPE) was investigated in 1 M H₂SO₄ solution, and the results indicate that 1−CPE exhibits the electrocatalytic activity toward the reduction of bromate and nitrite. Further, the non-isothermal kinetics of the thermal decomposition of compound 1 provides the dynamic parameters E (activation energy) and A (pre-exponential factor) for the pyrolytic reaction of the organic ligands.     

Enantioselective α-chlorination of β-keto esters and amides catalyzed by chiral imidodiphosphoric acids

Chiral imidodiphosphoric acids were employed as catalysts for the enantioselective α-chlorination of β-keto esters and amides using NCS as the chlorine source, providing a series of optically active products with good to high enantioselectivities (74–95% ee) and excellent yields (92–99%). This represents the first report of the Brønsted acid catalyzed enantioselective α-chlorination of cyclic β-keto derivatives.     

A dual chemosensor for Cu2+ and Fe3+ based on π-extend tetrathiafulvalene derivative

A new dual chemosensor (TTF-PBA) for Fe³⁺ and Cu²⁺ in different signal pathways was designed and synthesized. The absorption spectrum, fluorescence spectrum and cyclic voltammograms changed in the presence of Cu²⁺ and Fe³⁺. The optical color changed within 5 s from yellow to orange upon the addition of Cu²⁺, and it changed to dark yellow when Fe³⁺ existed. The cyclic voltammogram of Cu²⁺/TTF-PBA changed from E_ox = 0.50 V, E_red = 0.32 V to E_ox = 0.64 V, E_red = 0.80 V (vs Ag/AgCl) upon the addition of 2.0 equiv. Cu²⁺. As for Fe³⁺/TTF-PBA, its oxidation wave disappeared, and its reduction wave appeared at E_red = ?0.59 V (vs Ag/AgCl) upon the addition of 4.0 equv. Fe³⁺. The sensor displayed high selectivity for Cu²⁺ and Fe³⁺ over other ions including Pb²⁺, Zn²⁺, Ni²⁺, Ag⁺, Cr³⁺, Mn²⁺, Al³⁺, Co²⁺, Pd²⁺, Hg²⁺, Fe^2+, Cd²⁺, Ce³⁺, Bi³⁺ and Au³⁺, the detection limits for Cu²⁺ and Fe³⁺ ion reached as low as 5.33 × 10^?7 mol/L and 5.34 × 10^?7 mol/L, respectively. Furthermore, when Fe³⁺ existed, Cu²⁺ can be detected sequentially by the sensor through the absorption spectrum and the color change observed by naked-eyes.     

High-performance liquid chromatographic enantioseparation of cyclic β-aminohydroxamic acids on zwitterionic chiral stationary phases based on Cinchona alkaloids

Cyclic β-aminohydroxamic acid enantiomer pairs were stereoselectively separated by high-performance liquid chromatography on the recently developed Cinchona alkaloid-based zwitterionic chiral stationary phases Chiralpak ZWIX(+)™, ZWIX(−)™, ZWIX(+A) and ZWIX(−A). The results of variation of the applied chromatographic conditions, such as the bulk solvent composition, the concentrations and ratio of the acid and base additives, the presence of water as mobile phase additive and the counter-ion concentration furnished a better understanding of the retention mechanism. A thermodynamic study in the temperature range 5–50 °C revealed enthalpy-controlled enantiodiscrimination in all cases. The structure–selectivity relationships clearly indicated the importance of the strereochemistry of the functional groups. From an enantiorecognition aspect, the diexo position of the functional groups always proved more favorable than the diendo position. The elution sequence was determined in all cases and was found to reversed when ZWIX(+)™ was changed to ZWIX(−)™ or ZWIX(+A) to ZWIX(−A).     

Spectroscopic and electrochemical studies on the interaction of an inclusion complex of β-cyclodextrin/fullerene with bovine serum albumin in aqueous solution

The potential effect of human exposure to carbonaceous nanomaterials (e.g., fullerenes or their derivatives) in the environment has become a concern. In the current study, we report the interaction of one water-soluble fullerene with bovine serum albumin using spectroscopic and electrochemical methods under aqueous solutions. The novel supramolecular inclusion complex of the water-soluble fullerene (β-CD)₂/C₆₀ was synthesized and characterized. In the mechanism discussed, the spectroscopic methods such as fluorescence quenching and ultraviolet-visible absorption, proved that the fluorescence quenching of BSA by (β-CD)₂/C₆₀ was the result of the formation of (β-CD)₂/C₆₀-BSA complex and that the mechanism of quenching might be a static quenching procedure. The binding constants K_a, the number of binding sites n, and the corresponding thermodynamic parameters ΔG, ΔH, and ΔS at different temperatures were calculated through fluorescence spectroscopy, then as an auxiliary method, the electrochemical impedance spectroscopy (EIS) experiments confirmed this conclusion. The results indicated that the electrostatic interactions play a major role in (β-CD)₂/C₆₀-BSA association. The circular dichroism spectra show the conformation change of the effect of (β-CD)₂/C₆₀ on the conformation of BSA, which was confirmed by the results of the three-dimensional fluorescence spectra. Site marker competitive experiments indicate that the binding of (β-CD)₂/C₆₀ to BSA primarily took place in site I. The distance r between donor (BSA) and acceptor ((β-CD)₂/C₆₀) was obtained according to fluorescence resonance energy transfer (FRET). This work aims to demonstrate the mechanisms of the formation of the complex between water-soluble fullerene and protein under physiological conditions, as well as the remediation for the possible unwarranted biological effects of water-soluble fullerene.     

Li⁺ selective podand-type fluoroionophore based on a diphenyl sulfoxide derivative bearing two pyrene groups

New podand-type fluoroionophores having two pyrene moieties: 2,2′-bis(1-pyrenylacetyloxy)diphenyl sulfide (3), 2,2′-bis(1-pyrenylacetyloxy)diphenyl sulfoxide (4), and 2,2′-bis(1-pyrenylacetyloxy)diphenyl sulfone (5), have been synthesized by connecting two 1-pyrenecarbonylmethyl groups with the two hydroxy groups of 2,2′-dihydroxydiphenyl sulfide, sulfoxide, and sulfone, respectively. Their complexation behavior toward alkali metal ions was examined by fluorescence spectroscopy. Among these fluoroionophores, compound 4, having a sulfinyl group, showed high selectivity toward Li?.     

Three-dimensional grids based on graphene oxide and 3,3’,4,4’-tetraaminodiphenyl oxide for supercapacitor electrodes

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Pressure-induced transformations in α- and β-Ge3N4: in situ studies by synchrotron X-ray diffraction

Metastable high-pressure transformations in germanium nitride (α- and β-Ge₃N₄ polymorphs) have been studied by energy- and angle-dispersive synchrotron X-ray diffraction at high pressures in a diamond anvil cell. Between P=22 and 25 GPa, the phenacite-structured β-Ge₃N₄ phase (P6₃/m) undergoes a 7% reduction in unit-cell volume. The densification is primarily concerned with the a-axis parameter, in a plane normal to the hexagonal c-axis. Based on results of previous LDA calculations and Raman spectroscopic studies, we propose that the structural collapse is due to transformation into a new metastable polymorph (δ-Ge₃N₄) that has a unit-cell symmetry based upon P3, that is related to the low-pressure β-Ge₃N₄ phase by concerted displacements of N atoms away from special symmetry sites in the plane normal to the c-axis. No such transformation occurs for α-Ge₃N₄, due to the different stacking of linked GeN₄ layers. All three polymorphs (α-, β- and δ-Ge₃N₄) are based on tetrahedrally coordinated Ge atoms, unlike the spinel-structured γ-Ge₃N₄ phase, that contains octahedrally coordinated Ge⁴⁺. Experimentally determined bulk modulus values for α-Ge₃N₄ (K₀=165(10) GPa, K₀′=3.7(4)) and β-Ge₃N₄ (K₀=185(7) GPa, K₀′=4.4(5)) are in excellent agreement with theoretical predictions. The bulk modulus for the new δ-Ge₃N₄ polymorph is only determined above the β-δ transition pressure (P=24 GPa); K=161(20) GPa, assuming K′=4. Above 45 GPa, both α- and δ-Ge₃N₄ polymorphs become amorphous, as determined by X-ray diffraction and Raman scattering.     

An access to α, β-unsaturated ketones via dual cooperative catalysis

A dual cooperative organocatalytic approach for the synthesis of α, β-unsaturated ketones is described. This one pot transformation is realized via a domino Knoevenagel-Michael-retro Michael reaction sequence. Various aliphatic ketones reacted smoothly with aromatic as well as aliphatic aldehydes in presence catalytic amount of Meldrum’s acid and bifunctional amine. The highlights of this protocol are the easy availability of catalysts, high selectivity, and functional group tolerance. The reaction proved to highly E-selective with no side products emanating from self-condensation, unlike the base-mediated reactions.     

Phase transition induced by lithium insertion in αI- and αII-VOPO4

Lithium insertion in α_I-VOPO₄ and α_II-VOPO₄, either by chemical or electrochemical route, leads to the same new compound: α_I-LiVOPO₄ (space group P4/nmm). The structure, resolved by neutron and synchrotron diffraction, is made up of planes of corner-connected PO₄ and VO₅ polyhedra, whereas lithium atoms are located between the layers. The reversal of the short vanadyl bond that corresponds to the insertion-induced α_II-α_I transition finds an explanation in terms of lattice energy. It favors the migration of lithium ions in the (0 0 1) interlayer planes, a key parameter for the electrochemical performance as electrode material in Li-ion batteries.     

Ab-initio structure determination of β-La2WO6

The structure of the low-temperature form of β-La₂WO₆ has been determined from laboratory X-ray, neutron time-of-flight and electron diffraction data. This tungstate crystallizes in the non-centrosymmetric orthorhombic space group (no. 19) P2₁2₁2₁, with Z=8, a=7.5196(1) Å, b=10.3476(1) Å, c=12.7944(2) Å, and a measured density 7.37(1) g cm⁻³. The structure consists of tungsten [WO₆] octahedra and tetrahedral [OLa₄]. Tungsten polyhedra are connected such that [W₂O₁₁]¹⁰⁻ units are formed.     

A multi-functional fluorescent sensor for Zn2+ and HSO4− based on a new diarylethene derivative

A new photochromic diarylethene derivative with a hydralazine unit was designed and synthesized. It was not only acted as a Zn²⁺ sensor with the fluorescent color change from dark blue to bright orange, but also acted as a fluorescent sensor for HSO₄^? with the fluorescent color change from dark blue to bright blue. Furthermore, the derivative also exhibits multi-addressable switching properties by the stimulations of lights and chemical reagents. Based on these characteristics, two combinational logic circuits were constructed with the emission intensity as the output signals, and the UV/vis lights, chemical species as the input signals.     

Pseudo-template molecularly imprinted polymer for selective screening of trace β-lactam antibiotics in river and tap water

To assess the potential risks associated with the environmental exposure of β-lactam antibiotics (BLAs), the monitoring of the occurrence, distribution, and fate of these emerging contaminants in the environment is required. Herein, we demonstrate a molecularly imprinted solid-phase extraction (MISPE) method for selective and reliable screening of trace BLAs in river and tap water. By developing a low-temperature photopolymerization, highly selective molecularly imprinted polymers (MIPs) for five BLAs (penicillin G, amoxicillin, ampicillin, nafcillin and mezlocillin) were synthesized. Nafcillin was chosen as a pseudo template to make the MIP sorbent (Nafc-MIP), which was used in pseudo-template MISPE for preconcentration of the other four BLAs from river and tap water. The application of pseudo-template MISPE overcomes the template bleeding, which significantly elevates the sample background and restricts the application of MIP for detection of the target BLA below 2 μg/L. The average recoveries of BLAs are in the range of 60–90% when Nafc-MIP was adopted as the selective MISPE sorbent. The developed method was validated, and applied to the screening of trace β-lactam antibiotics in river and tap water. The linearity of the calibration curve for each BLA was observed over the range of 0.1–20 μg/L (r > 0.998). The β-lactam antibiotics were found within the range of 0–9.56 μg/L in river water at the downstream of antibiotics manufacturers, and none were detected in the tap water.     

Raman characterization of α- and β-LiFe5O8 prepared through a solid-state reaction pathway

Lithium ferrite, a mixed-inverse spinel of type A_xB_y[A_1−xB_1−y]O₄ was produced through solid state synthesis by calcining a Li₂CO₃/Fe₂O₃ mixture at 900 °C. The presence of both the ordered α-phase and disordered β-phase of LiFe₅O₈ was confirmed by XRD analysis, while formation of the latter was achieved by air quenching from high temperature. Laser Raman analysis was performed on both the α-LiFe₅O₈ and β-LiFe₅O₈ powders in order to achieve a reference set of Raman shifts for the spinel. The strongest, characteristic Raman peaks were determined to be 493, 382, 358, 300, and 263 cm⁻¹ for both phases while smaller peaks at 202 and 236 cm⁻¹ present in the α-phase were diminishing in intensity when the β-phase was present, thus providing unique identifiers for the presence of the disordered ferrite structure. SEM images taken of the synthesized LiFe₅O₈ powders showed particle sizes of less than 300 nm and an even particle size distribution.     

Critical β-values of all coil planet centrifuges

I-type, J-type and non-synchronous centrifuges are all coil planet centrifuges. Analysing the motion of I-type and J-type centrifuges has advanced the understanding of how to manufacture and use these centrifuges. This paper analyses the motion of non-synchronous centrifuges producing equations of motion that can be applied to all coil planet centrifuges. This has also produced simple equations to determine the critical β-values for any coil planet centrifuge. This paper also demonstrates that I-type centrifuges also have 2 critical β-values when it was thought that β-value did not influence the understanding of the processes within I-type centrifuges. For the I-type instrument both of these critical values are at bobbin radii approaching infinity. In practice this means all I-types function within one β-value range hence the unilateral distribution and type/effectiveness of the mixing is consistent. Finally the paper shows the influence that the tangential velocity has on the Archimedean screw effect and thus the unilateral distribution of the upper and lower phases in the columns of coil planet centrifuges. This explains why the maximum stationary phase retention in an I-type centrifuge is limited to 50%.