Response Of Aqueous Solutions Research Articles

Recycling of UO22+ expanded by metal-organic framework bearing pyrazinoquinoxaline tetracarboxylic acid: pH fluorescence sensing and photocatalytic activity

With the wide application of nuclear energy, the recycling of uranium resources and environmental protection have become the focus of scientific research and industrial attention. Uranyl ions have better electronic configurations and optical properties, but poor energy utilization and recycling as ionic states. Drawing on the structural features of Metal-Organic Frameworks (MOFs), the combination of UO22+ nodes with photoactive ligands should be able to effectively regulate the energy level matching between metal nodes and conjugated ligands, improve the electronic configuration and energy band structure, and thus produce better photoresponsive functional properties. In the present work, an example of a novel two-dimensional layered U-MOF was constructed by self-assembly, which utilizes pyrazinoquinoxaline tetracarboxylic acid. Due to the stable coordination structure, matched energy levels and synergistic photoresponsive behavior of UO22+ with pyrazinoquinoxaline ligands, U-MOF enables fluorescence sensing response in aqueous solution at pH=2–5, 9.5–12 and fluorescence quenching detection of a wide range of substrates. Theoretical calculations reveal that the interaction of the hydrogen ion with pyrazinozinoquinoxaline moiety extends the degree of conjugation of the moiety. Meanwhile, the interaction of hydroxide ions with pyrazinozinoquinoxaline groups elevates the highest occupied molecular orbital (HOMO) energy level, which significantly affects the photoelectric properties of U-MOF. In addition, U-MOF can be used as a photocatalyst to realize the conversion of benzylamine to N-benzylbenzylideneimine by oxidation under mild conditions. The effective electron transfer between uranyl ions and ligands ensured the photogenerated electron-hole separation efficiency and enhanced the energy utilization. Therefore, the related results of U-MOFs illustrate the practicality of introducing UO22+ nodes into MOFs to construct novel photoresponsive materials, which provides a new way for the efficient recycling and utilization of uranium resources.

Structural study of two polymer chains of poly(2-methoxyethyl glycidyl ether)-b-poly(2-ethoxyethyl glycidyl ether) thermoresponsive block copolymers using molecular dynamics simulations

Block copolymers are expected to be applied in a wide variety of fields due to the property of self-assembly. Our group has reported that poly(glycidyl ether) block copolymers exhibited complex temperature response in aqueous solution. In this study, we investigated the two chains of the block copolymer structure and configurations at different temperatures by using MD simulation. The results showed that at low temperatures, the polymer structure is linear and can form micelles, but above a certain temperature, the polymer structure changes to a U-shape and the micelle structure would be destroyed, which is responsible for the complex temperature response.

Electrochemical reactions of highly active nitroxyl radicals with thiol compounds.

Nitroxyl radicals are known to electrochemically oxidize thiols as well as alcohols and amines. In this study, a preliminary investigation of the electrochemical reaction of thiols with 9-azabicyclo[3.3.1]nonane N-oxyl (ABNO), 2-azaadamantane N-oxyl (AZADO), and nortropine N-oxyl (NNO), which are highly active due to their bicyclo structures, for use in electrochemical analysis was performed and the results were compared with those for a typical nitroxyl radical compound, 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO). Mercaptopropane sulfonic acid (MPS) was used as a model compound to investigate the electrochemical response in aqueous solution. In addition, electrochemical detection of glutathione, a biological thiol molecule, was performed.

Probing the Ni2+ -selective Response of Fluorescent Probe NiSensor-1 with the NiCast Photocaged Complex.

CTEA (N,N-bis[2-(carboxylmethyl)thioethyl]amine) is a mixed donor ligand that has been incorporated into multiple fluorescent sensors such as NiSensor-1 that was reported to be selective for Ni2+ . Other metal ions such as Zn2+ do not produce an emission response in aqueous solution. To investigate the coordination chemistry and selectivity of this receptor, we prepared NiCast, a photocage containing the CTEA receptor. Cast photocages undergo a photoreaction that decreases electron density on a metal-bound aniline nitrogen atom, which shifts the binding equilibrium toward unbound metal ion. The unique selectivity of CTEA was examined by measuring the binding affinity of NiCast and the CTEA receptor for Ni2+ , Zn2+ , Cd2+ and Cu2+ under different conditions. In aqueous solution, Ni2+ binds more strongly to the aniline nitrogen atom than Cd2+ ; however, in CH3 CN, the change in affinity virtually disappears. The crystal structure of [Cu(CTEA)], which exhibits a Jahn-Teller-distorted square pyramidal structure, was also analyzed to gain more insight into the underlying coordination chemistry. These studies suggest that the fluorescence selectivity of NiSensor-1 in aqueous solution is due to a stronger interaction between the aniline nitrogen atom and Ni2+ compared to other divalent metal ions except Cu2+ .

Zein film as a novel natural biopolymer membrane in electrochemical detections

Permselective modifier films are very important in preparing highly sensitive electrochemical sensors. In this work, for the first time, the behavior of gold and glassy carbon electrodes coated with biocompatible zein film as a permselective membrane for the electrochemical detection of various compounds has been investigated. For this purpose, several electroactive cationic (methylene blue, brilliant green, and thionine) and anionic (potassium ferricyanide, alizarin red S, and riboflavin-5’-phosphate) compounds have been used as model. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) showed that zein membranes prepared from casting solution containing 1% zein in ethanol/water have porous structures with high nanometric roughness. The capacitance values of electrical double layers of electrodes modified with zein film were very high for hydrophilic ions in comparison with hydrophobic ions. Point of zero charge pH (pHpzc) of zein membrane was 4.8. The results of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) as well as pHpzc study indicated that zein permselective membrane acts as ion exchanger film for selected cationic compounds with fast electrochemical kinetics responses in aqueous solution (pH=7). This behavior was confirmed by circulating solutions containing model compounds from homemade continuous cell equipped with polyamide membranes modified with zein film.

Colorimetric chemosensor based on a Ni2+ complex of a pyridylazo dye for detection of citrate in aqueous solution

We developed a colorimetric naked-eye chemosensor based on the complex between a pyridylazo dye and Ni2+ in a 2:1 stoichiometric ratio (BrPSAA2-Ni2+) for the selective detection of citrate in a pure aqueous solution via the indicator displacement assay. Upon the addition of citrate, BrPSAA2-Ni2+ exhibited a naked-eye detectable color change from red to orange over other anions including dicarboxylates with a blue shift in absorption spectra due to the regeneration of BrPSAA by the interaction of citrate with Ni2+. Furthermore, the citrate detection process was not significantly influenced by other coexisting anions. Therefore, BrPSAA2-Ni2+ can be utilized as a simple and practical colorimetric chemosensor for citrate with selectivity and fast response in aqueous solution.

Ruthenium-based phosphorescent probe for selective and naked-eye detection of cyanide in aqueous media

A simple molecular phosphorescent Ru(II) probe P1 has been synthesized by the reaction of 5-aldehyde-2,2′-bipyridine with ruthenium(II) chlorides under mild conditions. The probe upon interaction with different cation and anion showed high selectivity and sensitivity for cyanide ion (CN‒) through phosphorescence “turn-on” response in aqueous solution (60% water) with a detection limit of 0.75 μM. The significant phosphorescence enhancement (~ 30-fold) is attributed to the nucleophilic addition of cyanide ion to the aldehyde groups of the ruthenium complex in 3 : 1 stoichiometry, in which a naked-eye sensitive orange red color of solution changed to a yellow. The generation of cyanohydrin species through nucleophilic addition has been confirmed by 1H NMR, FT-IR and mass spectra. Based on the color change of the solution, a visual colorimetric strip was prepared, which also showed good detection performance on cyanide ion with quick response time. The prominent efficiency of the Ru(II) probe proved the potential possibility of application in biosystems relating with cyanide ion.

An aggregation-induced emission (AIE) fluorescent chemosensor for the detection of Al(III) in aqueous solution

A novel fluorescent chemosensor (2) for the detection of Al(III) was designed based on the strategy of aggregation-induced emission (AIE), which was synthesized by introducing carboxyl group to tetraphenylethylene structure. 2 can bind with Al(III) to form chelate polymers with AIE characteristic, giving rise to an intense “turn-on” response in aqueous solution at pH 7.0. The binding stoichiometry of 2 toward Al(III) was in 1:1. High sensitivity and selectivity to Al(III) were achieved. A detection limit of 1.96 μmol L−1 and a linear rang of 0.0–50.0 μmol L−1 were obtained. Furthermore, 2 was successfully applied in detecting Al(III) in real water samples, which showed satisfactory recovery and accuracy.

A Fluorescent Chemosensor with a Hybridized Local and Charge Transfer Nature and Aggregation‐Induced Emission Effect for the Detection of Picric Acid

AbstractA novel fluorescent molecule TPA‐CO, which exhibited a hybridized local and charge transfer (HLCT) nature and aggregation‐induced emission (AIE) effect, was developed and utilized as a chemosensor for the detection of picric acid (PA) in both organic solution and water. It was found that TPA‐CO exhibited apparent fluorescent quenching along with the color change to yellow upon the addition of PA. Notably, more sensitive detection was achieved in the H2O: THF (9:1) medium, with the LOD almost two third lower than that in pure THF. Such more sensitive response in aqueous solution was accomplished by the synergy of HLCT and AIE effects in TPA‐CO nanoparticles, which facilitated both highly efficient fluorescence in the absence of PA and rapid quenching rate in the presence of PA, respectively. Therefore, it is proposed an effective design strategy by integrating HLCT and AIE effects for developing PA chemosensors.

Control of the Alternating Sequence for N-Isopropylacrylamide (NIPAM) and Methacrylic Acid Units in a Copolymer by Cyclopolymerization and Transformation of the Cyclopendant Group.

An alternating copolymer of methacrylic acid and N-isopropyl acrylamide (NIPAM) was synthesized by selective cyclopolymerization of a special divinyl monomer and transformation of repeating cyclo-units in the resultant cyclopolymer. Crucial to the breakthrough is the monomer design in view of two types of cleavable bonds (3° ester and activated ester) in the pendant group of the monomer and the lower reactivity ratio of the two double bonds (methacrylate and electron-poor acrylate) for the polymerizable groups. The thus-obtained cyclopolymer was transformed into the alternating copolymer by transformation of the activated ester into amide by isopropyl amine and cleavage of the 3° ester by trifluoroacetic acid. The resultant copolymer showed thermal and pH response in aqueous solution that was different from the 1:1 random copolymer as well as the homopolymers.

Control of the Alternating Sequence for N‐Isopropylacrylamide (NIPAM) and Methacrylic Acid Units in a Copolymer by Cyclopolymerization and Transformation of the Cyclopendant Group

AbstractAn alternating copolymer of methacrylic acid and N‐isopropyl acrylamide (NIPAM) was synthesized by selective cyclopolymerization of a special divinyl monomer and transformation of repeating cyclo‐units in the resultant cyclopolymer. Crucial to the breakthrough is the monomer design in view of two types of cleavable bonds (3° ester and activated ester) in the pendant group of the monomer and the lower reactivity ratio of the two double bonds (methacrylate and electron‐poor acrylate) for the polymerizable groups. The thus‐obtained cyclopolymer was transformed into the alternating copolymer by transformation of the activated ester into amide by isopropyl amine and cleavage of the 3° ester by trifluoroacetic acid. The resultant copolymer showed thermal and pH response in aqueous solution that was different from the 1:1 random copolymer as well as the homopolymers.

A novel fluorescence chemodosimeter for fluoride anions in aqueous solution based on siloxane-aurone moiety

A novel siloxane-aurone compound, 4′-cyano-4-tert-butyldiphenylsiloxane-aurone (named as TBDCN), was synthesized. The compound exhibits high sensitivity, fast response rate and high selectivity for fluoride anions recognition with obvious absorption and fluorescence response in aqueous solution, which is more sensitive than the traditionally type of chemodosimeters based on F−-triggered cleavage. The detection limits of TBDCN for F− are determined to be 1.9μM and 0.0017μM with absorption and fluorescence as detected signal, respectively, which satisfy the requirement from U.S. Environmental Protection Agency. The recognition mechanism is the F−-promoted dissociation of silicon-oxygen bond based on in situ mass spectra and 1H NMR spectra analysis.

FERROCENYL ALKYLAMMONIUM N-SUBSTITUTED POLYPYRROLE CONTAINING Pt AND Pd AND ITS APPLICATION ON ELECTROANALYSIS OF ARSENITE

Arsenic occurs in a variety of forms and oxidation states and is a very toxic element. The main inorganic arsenic species present in natural waters are arsenate (oxidation state V) and arsenite ions (oxidation state III). Arsenite is more toxic and mobile than arsenate. Therefore, it is important the development of new materials for analysis and control of these toxic species. This research proves that polymer-metal composite electrode materials synthesized by incorporation of Pt0 and Pd0 nanoparticles into a poly(pyrrole-ferrocenyl alkylammonium) matrix present electrocatalytic properties towards the oxidation of arsenite to arsenate. The polymer films displayed a stable electrochemical response in aqueous solution. However, when the polymer film modified electrode were transferred to aqueous solution in presence of arsenite anions, the CV curves for polymer films were deeply modified by the decrease in the electroactivity of the film. It can be concluded that the cationic polymer films present a strong affinity toward arsenite anions. The composite films containing Pt0 or Pd0 showed catalytic activity towards oxidation of As(III) to As(V) due to the presence of metal catalyst particles into the polymer films.

A reversible colourimetric and selective fluorescent chemosensor for the cascade recognition of Cu2+ and H2PO4− in aqueous solution

This report describes a reversible colourimetric and on–off–on module of fluorescent chemosensor for selective cascade recognition of Cu2+ and with unique output optical response in aqueous solution. On the other hand, F−, Cl−, Br−, I−, CH3COO−, HSO4−, ClO4−, CN− and SCN− did not induce significant changes in fluorescence. Moreover, the colour change in chemosensor LH by response of this colourimetric chemosensor can be visualised by naked eye. These fluctuations in spectral response, under electronic behaviour, can be viewed to mimic as IMPLICATION logic gate.

A fluorescent chemosensor for Al3+ based on julolidine and tryptophan moieties

A new and simple fluorescent chemosensor 1, based on julolidine and tryptophan moieties, has been synthesized and characterized. The sensor 1 displayed a selective and sensitive detecting ability for aluminum (III) ion by ‘OFF–ON’ fluorescent response in aqueous solution. This sensing mechanism might be due to the inhibition of CN isomerization, and the activation of chelation enhanced fluorescence (CHEF). This sensing mechanism of 1 for Al3+ was supported by theoretical calculations. Moreover, sensor 1 had a low detection limit (6.4 μM), which is below than the WHO recommendation level (7.41 μM) for drinking water. Importantly, the chemosensor 1 could be applied to living cells to detect Al3+. Therefore, the sensor 1 can be employed as a practical fluorescent chemosensor for recognition of Al3+ in aqueous solution.

A new fluorescent probe based on quinoline for detection of Al3+ and Fe3+ with “off–on–off” response in aqueous solution

A new quinoline-based fluorescent probe has been designed and synthesized. It showed highly selective relay recognition of Al3+ and Fe3+via a fluorescence “off–on–off” mechanism by central metal displacement.

DNA detection by THz pumping

DNA semiconductor detection and sequencing is considered to be the most promising approach for future discoveries in genome and proteome research which is dramatically dependent on the challenges faced by semiconductor nanotechnologies. DNA pH-sensing with ion-sensitive field effect transistor (ISFET) is well-known to be a successfully applied electronic platform for genetic research. However this method lacks fundamentally in chemical specificity. Here we develop the first ever silicon nanosandwich pump device, which provides both the excitation of DNA fragments’ self-resonant modes and the feedback for current-voltage measurements at room temperature. This device allows direct detection of singlestranded label-free oligonucleotides by measuring their THz frequency response in aqueous solution. These results provide a new insight into the nanobioelectronics for the future real-time technologies of direct gene observations.

Two fluorescence turn-on Schiff׳s base chemosensors for Cu2+ ions

Two new salicylaldehyde Schiff base chemosensors have been synthesized. Their crystal structures, photophysical properties as well as recognition properties for Cu2+ ions have also been examined. Their absorption peaks exhibit obvious blue shift upon the addition of Cu2+ to a HEPES buffer–methanol (3:7, v/v) solution of the compounds. The compounds are found to be able to recognize Cu2+ ions with fluorescence turn-on response in aqueous solution owing to the hydrolysis of the hydrazone bond in the Schiff׳s base compounds induced by Cu2+ ions.

Transient Response in Aqueous Solution of an Anions Porous Silicon Based Sensor

A porous silicon based sensor has been developed to detect anions in a salt solution by the application of DC pulses on a Semiconductor/Electrolyte system. The sensor performance can be explained invoking a model where charge accumulation in the semiconductor surface states directly affects their geometric capacitances. By varying anions concentrations in salt solution, the results show a fairly constant value of substrate resistance, whereas variations in those geometric capacitances depend on the anion concentration. The constancy of substrate resistance and variability of geometric capacitance constitute key points for the development of an anion solution sensor.

Luminescence response of an osmium(II) complex to macromolecular polyanions for the detection of heparin and chondroitin sulfate in biomedical preparations

Heparin, dextran sulfate (DS), chondroitin sulfate (CS), and carrageenan are found to enhance the luminescence intensity of an osmium(II) carbonyl complex with phenanthroline (phen) and 4-phenylpyridine (4-phpy) ligands in aqueous and ethanol solutions. The enhancing effect of the polyanions on the luminescence of the complex is heavily dependent on the sulfate content and other factors such as structure, solubility, and counter ions of the polyanion. The highly sulfated dextran and ι-carrageenan have the most profound effect, while the low charged κ-carrageenan and CS have the least response in aqueous solution. All polyanions exhibited enhanced luminescence intensity of the complex in ethanol solutions, and even the low charged CS and κ-carrageenan enhanced the luminescence more than 4 times. DS contamination of the sodium heparin at 5% can show a significant increase in luminescence response. The osmium complex is found to be highly successful in the fast and sensitive detection of heparin in commercial injectable samples with various backgrounds as well as the detection of CS in over the counter food supplement tablets.