Mechanism study on inorganic oxidants induced inhibition of Ru(bpy)₃²+ electrochemiluminescence and its application for sensitive determination of some inorganic oxidants

Inhibited Ru(bpy)₃²⁺ electrochemiluminescence by inorganic oxidants is investigated. Results showed that a number of inorganic oxidants can quench the ECL of Ru(bpy)₃²⁺/tri-n-propylamine (TPrA) system, and the logarithm of the decrease in ECL intensity (ΔI) was proportional to the logarithm of analyte concentrations. Based on which, a sensitive approach for detection of these inorganic oxidants was established, e.g. the log-log plots of ΔI versus the concentration of MnO₄⁻, Cr₂O₇²⁻ and Fe(CN)₆³⁻ are linear in the range of 1 × 10⁻⁷ to 3 × 10⁻⁴ M for MnO₄⁻ and Cr₂O₇²⁻, and 1 × 10⁻⁷ to 1 × 10⁻⁴ M for Fe(CN)₆³⁻, with the limit of detection (LOD) of 8.0 × 10⁻⁸ M, 2 × 10⁻⁸ M, and 1 × 10⁻⁸ M, respectively. A series of experiments such as a comparison of the inhibitory effect of different compounds on Ru(bpy)₃²⁺/TPrA ECL, ECL emission spectra, UV-Vis absorption spectra etc. were investigated in order to discover how these inorganic analytes quench the ECL of Ru(bpy)₃²⁺/TPrA system. A mechanism based on consumption of TPrA intermediate (TPrA^·) by inorganic oxidants was proposed.     

Enantioselective analysis of melagatran via an LSPR biosensor integrated with a microfluidic chip

The impact of chiral compounds on pharmacological and biological processes is well known. With the increasing need for enantiomerically pure compounds, effective strategies for enantioseparation and chiral discrimination are in great demand. Herein we report a simple but efficient approach for the enantioselective determination of chiral compounds based on a localized surface plasmon resonance (LSPR) biosensor integrated with a microfluidic chip. A glass microfluidic chip with an effective volume of ～0.75 μL was fabricated for this application. Gold nanorods (AuNRs) with an aspect ratio of ～2.6 were self-assembled onto the surface of the inner wall of the chip to serve as LSPR transducers, which would translate the analyte binding events into quantitative concentration information. Human α-thrombin was immobilized onto the AuNR surface for enantioselective sensing of the enantiomers of melagatran. The proposed sensor was found to be highly selective for RS-melagatran, while the binding of its enantiomer, SR-melagatran, to the sensor was inactive. Under optimal conditions, the limit of detection of this sensor for RS-melagatran was found to be 0.9 nM, whereas the presence of 10?000-fold amounts of SR-melagatran did not interfere with the detection. To the best of our knowledge, this is the first demonstration of an LSPR-based enantioselective biosensor.     

PHOTOCHEMISTRY OF ARYLMETHYL ESTERS ADSORBED ON ZSM-5 ZEOLITE──SIZE/SHAPE SELECTIVITY

本文研究了对甲基苯乙酸苄基酯(BCO₂A)及苯乙酸1-萘基酯(ACO₂N)在ZSM-5沸石中的光化学反应。研究发现,光解BCO₂A在ZSM-5沸石中主要生成BA,而光解ACO₂N只生成AA及NN.两种酯的产物分布和在乙腈溶液中的光解完全不同。这些结果是由ZSM-5沸石孔腔对底物分子的尺寸及形状具有选择性而引起的。     

Determination of glucose by using fluorescent silicon nanoparticles and an inner filter caused by peroxidase-induced oxidation of o-phenylenediamine by hydrogen peroxide

Microchimica Acta - The authors describe a new kind of enzymatic glucose assay. The strategy involves three processes: (a) Generation of H2O2 via glucose oxidase catalyzed oxidation of glucose; (b)...     

Application of graphene-modified electrode for selective detection of dopamine

Graphene was synthesized chemically by Hummers and Offeman method and the graphene-modified electrode was applied in selective determination of dopamine with a linear range from 5 μM to 200 μM in a large excess of ascorbic acid. Selective detection was realized in completely eliminating ascorbic acid, different from the methods based on the potential separations. π–π stacking interaction between dopamine and graphene surface may accelerate the electron transfer whereas weaken the ascorbic acid oxidation on this graphene-modified electrode. The resulted graphene-modified electrode also showed a better performance than multi-walled carbon nanotubes-modified electrode. The phenomena were considered from the elusive two-dimensional structure and unique electronic properties of graphene.     

Carboxylic Acids Promoted Speier’S Catalyst for the Hydrosilylation of Styrene with Triethoxysilane: Activity,Selectivity, and Mechanism

Abstract

Catalytic performances of Speier's catalyst with carboxylic acids were studied in the hydrosilylation reaction of styrene with triethoxysilane. The effect of carboxylic acids (RCOOH) with different pKa values and size was investigated, and the temperature and n(COOH)/n(Pt) ratios were also studied. The catalytic activity of the hydrosilylation reaction is related to the acid strength of the carboxylic acid, temperature, and n(COOH)/n(Pt) ratio, while the selectivity for the β-adduct is related to the size of carboxylic acid and the n(COOH)/n(Pt) ratio. Moreover, the influence of carboxylic acid on the hydrosilylation reaction was explained with the help of density functional theory calculations, and a reasonable mechanism was proposed.     

In situ assembly, regeneration and plasmonic immunosensing of a Au nanorod monolayer in a closed-surface flow channel

Herein, a simple and effective approach is reported for the in situ generation and regeneration of a Au nanorod (AuNR) monolayer inside a glass/silica-based, closed-surface flow channel. The density of the AuNR monolayer in the flow channel can be easily modified by varying the concentration of the AuNR and the cetyltrimethylammonium bromide as well as the incubation time. The fabricated AuNR monolayer in the flow channels was stable under harsh conditions, such as in extreme pH, organic solvents and at a fast flow rate. In addition, the flow channel could be reused by removing the immobilized AuNRs via the injection of diluted aqua regia or potassium iodide; the AuNR monolayer can subsequently be regenerated. The AuNRs in the closed flow channel were further exploited as a label-free detection method for a clinical biomarker, neutrophil gelatinase-associated lipocalin (NGAL), based on single-nanoparticle plasmonic assay. The corresponding limit of detection for NGAL was measured to be 8.5 ng mL(-1) (~340 pM) based on a signal-to-noise ratio of 3. The estimated recovery of NGAL in human serum and urine was higher than 80%, which indicates that this technique could potentially be used for the diagnosis of acute kidney injury.     

Study on interaction between a new fluorescent probe 2-methylbenzo[b][1,10]phenanthrolin-7(12H)-one and BSA

A new fluorescence reagent, 2-methylbenzo[b][1,10]phenanthrolin-7(12H)-one (mBPO), synthesized in our laboratory was used as the probe for protein and its interaction with Bovine Serum Albumin (BSA) was investigated in detail in this paper. It was found that BSA had the ability to quench the fluorescence of mBPO at 411 nm (λ(ex) = 286 nm), and the quenched intensity of fluorescence was proportional to the concentration of BSA. Based on this fact, mBPO has been used as a fluorescence probe for the detection of BSA. Under the optimal conditions, the calibration graph is linear up to 0.5 mg L(-1) for BSA and the limit of detection (LOD) was 0.06 mg L(-1). The regression equation is y = 1048.8x + 7.2093 with R(2) = 0.9913. The mechanism for the interaction of mBPO with BSA was also studied, while the binding constant and the number of binding sites were calculated. According to the thermodynamics parameter, the binding mode between mBPO and BSA was deduced. The results suggested the interaction between mBPO and BSA to be hydrophobic force in nature. It also proved that the fluorescence quenching reaction was affected by the tryptophan residue of BSA. For there are two tryptophan (Trp) residues, in site 134 and site 212 of BSA, and mBPO maybe has interaction with them respectively.     

The reaction mechanisms of boron amidinate and small molecules: a density function theory study

Density functional theory calculations have been carried out to explore the reaction mechanisms for the reactions of “frustrated Lewis pairs” (FLPs) with small molecules. Four reactions were studied in the present investigation. A new N-heterocyclic carbene borane, boron amidinate compound HC(iPrN)₂B(C₆F₅)₂ (1), classified as FLPs, was chosen as the common reactant of these reactions. It was used to react with CO₂, CO, and two terminal alkynes, methylacetylene and phenylacetylene. The reactions of 1 with CO₂ and CO can both be regarded as the concerted addition mechanisms. In these reactions, the formations of the C2–N2 and B–O1 bonds take place simultaneously. For the reactions of 1 and methylacetylene or phenylacetylene, our calculations indicated that a deprotonation pathway and the connection between B atoms and terminal alkyne C atoms occur by a concerted manner simultaneously, together with the connection between N2 and hydrogen atoms. We also investigated the reaction mechanisms according to the frontier molecular orbital (FMO) theory and carried out electric charge analyses, finding that the two results were consistent with each other perfectly. Electric charges transfer from HOMO of 1_OPEN to LUMO of CO₂ or CO. In contrast, electric charges transfer from HOMO of methylacetylene or phenylacetylene to LUMO of 1_OPEN.     

A Ratiometric Fluorescence Probe for Selective Detection of ex vivo Methylglyoxal in Diabetic Mice

Accurate monitoring of methylglyoxal (MGO) at cell and living level was crucial to reveal its role in the pathogenesis of diabetes since MGO was closely related to diabetes. Herein, a ratiometric fluorescence strategy was constructed based on the capture probe 2,3-diaminonaphthalene (DAN) for the specific detection of MGO. Compared to the fluorescent probes with a single emission wavelength, the ratiometric mode by monitoring two emissions can effectively avoid the interference from the biological background, and provided additional self-calibration ability, which can realize accurate detection of MGO. The proposed method showed a good linear relationship in the range of 0–75 μm for MGO detection, and the limit of detection was 0.33 μm . DAN responded to MGO with good specificity and was successfully applied for detecting the ex vivo MGO level in plasma of KK−Ay mice as a type II diabetes model. Besides, the prepared DAN test strip can be visualized for rapid semi-quantitative analysis of MGO using the naked eye. Furthermore, human skin fibroblasts and HeLa cells were utilized for exogenous MGO imaging, and ex vivo MGO imaging was performed on tissues of KK−Ay mice. All results indicated that the DAN-based ratiometric fluorescence probe can be used as a potential method to detect the level of MGO, thus enabling indications for the occurrence of diabetes and its complications.