Molecularly imprinted electrochemiluminescence sensor based on a novel luminol derivative for detection of human serum albumin via click reaction.

A novel luminol derivative of N-(1,4-dioxo-1,2,3,4-tetrahydrophthalazin-5-yl)acrylamide (DTA) with excellent luminescence efficiency was designed and synthesized. Furthermore, a molecularly imprinted electrochemiluminescence sensor (MIECLS) was fabricated to detect ultratrace levels of human serum albumin (HSA) with high sensitivity and selectivity via a click reaction. The molecularly imprinted polymers (MIPs) were formed on the electrode surface via electropolymerization with HSA as a template molecule and catechol as a monomer. In the detection process, the -SH group of HSA on the electrode and the C = C bond of acryloyl group in DTA formed a new C-S bond via the Michael addition reaction to construct the MIECLS. The higher the concentration of HSA, the greater electrochemiluminescence (ECL) intensity measured. Taking advantage of MIECLS for ECL detection (scanning potential, - 0.4 to 0.5 V), there was a good linear relationship between ECL intensity and the logarithm of HSA concentration in the range 5 × 10-9 to 1 × 10-13 mg mL-1. The limit of detection (LOD) of the sensor was 1.05 × 10-15 mg mL-1. The sensor exhibited outstanding selectivity and stability. The sensor was applied to detect HSA in human serum with good recoveries of 97.7-105.2%. The concentration of HSA was detected by electrochemical method using the gating effect of MIP.

Magnetic MXene-based molecularly imprinted electrochemical sensor for methylmalonic acid.

A novel magnetic Ti3C2Tx-MXene/Fe3O4 composite was prepared from Ti3C2Tx and magnetic Fe3O4. The characterizations by electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) exhibited that the Ti3C2Tx/Fe3O4 nanomaterial presented an outstanding conductivity and a large specific area, which could improve the electron transfer rate, leading to the amplification of the sensor's signal. Furthermore, an ultrasensitive molecularly imprinted electrochemical sensor based on MXene/Fe3O4 composites was fabricated for detecting methylmalonic acid (MMA) with high selectivity. The current intensity of differential pulse voltammetry of the sensor presented a good linear relationship with the logarithm of MMA concentration ranging from 9 × 10-15 mol L-1 to 9 × 10-13 mol L-1. The detection limit of the sensor was 2.33 × 10-16 mol L-1. The fabricated sensor was utilized for detecting MMA in human serum samples with excellent recoveries. Therefore, this method significantly improved the sensitivity of detection, and constitutes an  affordable sensing platform for trace detection of organic carboxylic acid.

Diverse and chemoselective sigmatropic shift rearrangements of multisubstituted N,O-diarylhydroxylamines.

N,O-Diarylhydroxylamines generally favor the [3,3] sigmatropic shift rearrangement. Possible N/O[1,3] sigmatropic shift rearrangements of multisubstituted N,O-diarylhydroxylamines were investigated experimentally with rationally designed substrates, which were generally in situ prepared from suitable nitroaryl halides and N-arylhydroxylamines via aromatic nucleophilic substitution. The results indicate that both N- and O-(2,4,6-trimethylphenyl)hydroxylamines still favor the [3,3] sigmatropic shift followed by tautomerization rather than N[1,3] and O[1,3] sigmatropic shifts and the rearranged products of N-(2,4,6-trimethylphenyl)hydroxylamines further undergo an intramolecular nucleophilic addition to afford dibenzo[b,d]furan-4a(9bH)-amine derivatives, while N-(4-mono- and 3,5-disubstituted phenyl)-O-(2,4,6-trinitrophenyl)hydroxylamines favorably first undergo the O[1,3] sigmatropic shift followed by tandem Smiles rearrangement and amide/ester exchange reactions, generating 2-arylaminoaryl benzoate derivatives. N-Phenyl-O-(2,4,6-trinitrophenyl)hydroxylamines undergo tandem double O[1,3] sigmatropic shift rearrangement to produce formal O[1,5] shift products. However, O-(2,6-dinitrophenyl)-N-(4-substituted phenyl)hydroxylamines undergo tandem O[1,3] and double [3,3] sigmatropic shift rearrangements to give formal 3,5-shift products. The proposed mechanism is rationalized by density functional theory (DFT) calculations. The current investigation provides not only a comprehensive understanding of the chemoselective sigmatropic shift rearrangements of N,O-diarylhydroxylamines, but also some novel synthetic strategies for dibenzo[b,d]furanamines, diarylamines, diaryl ethers, 2'-amino-[1,1'-biphenyl]-2(1H)-one, and 2'-amino-[1,1'-biaryl]-4-ol derivatives.

Electrochemical sensor based on Ti3C2 membrane doped with UIO-66-NH2 for dopamine.

A Ti3C2 membrane was prepared by doping UIO-66-NH2 with Ti3C2 through hydrogen bonds. When the doping mass ratio of Ti3C2 and UIO-66-NH2 was 6:1, the electrochemical performance was optimal. Characterization was done by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS) which exhibited hierarchical cave-like physiognomy, large specific area, outstanding electronic conductive network, and excellent film-forming property. Moreover, the Ti3C2 film was analyzed via atomic force microscopy (AFM), which displayed good mechanical properties and rough surface morphology. The fabricated Ti3C2 membrane/GCE sensor was applied to the detection of dopamine (working potential of + 0.264 V vs. Ag/AgCl) with LOD of 0.81 fM and a sensitivity of 14.72 µA fM-1 cm-2. It was demonstrated that the Ti3C2 membrane can be used to construct nonenzymatic sensors with excellent performance. The fabricated sensor has high selectivity and stability and has good practicability with recoveries of 101.2-103.5% and a relative standard deviation (RSD) of 1.2-2.4%.

A novel symmetrical imidazole-containing framework as a fluorescence sensor for selectively detecting silver ions.

In this study, a novel and highly efficient "turn-off" fluorescence imidazole-based sensor (BIB) with a symmetric structure was synthesized by a four-step reaction, from o-phenylenediamine, 6-bromo-2-pyridinecarboxaldehyde, and 1-bromohexane. The sensing mechanism was confirmed via fluorescence titration, HRMS, and 1HNMR techiniques. The results showed that the binding ratio of BIB and Ag+ was 1 : 1 in a DMF-HEPES (pH 7.4) solution (9 : 1, v/v). The fluorescence response of BIB exhibited a good linear response within the Ag+ concentration ranging from 2 × 10-7 to 8 × 10-6 mol L-1, and the limit of detection was calculated to be 4.591 × 10-8 mol L-1. BIB was successfully applied to the detection of Ag+ in water samples with recoveries of 97.25-109.50% and relative standard deviations (RSD) of 1.14-2.45%. In addition, BIB can successfully be applied to qualitatively and quantitatively identify Ag+ in water by test paper strips of BIB, which is fast and convenient. This provides a possible potential for the rapid monitoring of metal ions by sensors in environmental research.

Chiral Synthesis of McGeachin-Type Bisaminals.

Bridged [3.3.1]-bisaminal structures, namely 6,12-epiminodibenzo[b,f][1,5]diazocines, are herein named McGeachin-type bisaminals. The TsOH-catalyzed chiral synthesis of McGeachin-type bisaminals is first developed by condensation of two molecules of 2-(methylamino)benzaldehyde and one molecule of chiral amines. Two chiral diastereomers are generated simultaneously and are isolated by column chromatography in a total yield of up to 99%. The absolute structure of one stereoisomer was determined by X-ray crystallography.

Theoretical calculation studies on the rearrangement mechanisms of arenesulfenanilides to generate o- and p-aminodiphenyl sulfides.

The thermal and acid-catalyzed rearrangement mechanisms of arenesulfenanilides were investigated theoretically via density functional theory (DFT) calculations. The results indicate that the o-aminodiphenyl sulfide rearrangement involves a novel S[1,3]-sigmatropic shift followed by tautomerization, while the p-aminodiphenyl sulfide rearrangement proceeds via tandem [3,3]- and [3,3]-sigmatropic shifts followed by tautomerization under thermal conditions. Furthermore, computational studies reveal that water assists the proton shift more efficiently than anilines during tautomerization. Moreover, under the acid-catalyzed conditions, the o-aminodiphenyl sulfide rearrangement involves an S[1,3]-sigmatropic shift similar to that under the thermal conditions, while the p-aminodiphenyl sulfide rearrangement proceeds via cascade S[1,3]- and S[1,3]-sigmatropic shifts followed by water-aided tautomerization. The current theoretical studies provide new insights into the formation mechanism of o/p-aminodiphenyl sulfides in the arenesulfenanilide rearrangement and support the unprecedented suprafacial symmetry-allowed S[1,3]-sigmatropic shift with an inversion of the configuration in the migrating sulfur atom. The mechanism is affected by the reaction medium. Disproportionation of arenesulfenanilides into diaryl disulfides and azobenzenes is a competitive radical pathway during the arenesulfenanilide rearrangements.

N[1,3]-Sigmatropic shift in the benzidine rearrangement: experimental and theoretical investigation.

The N[1,3]-sigmatropic shift in the benzidine rearrangement has been studied in depth experimentally with the aid of density functional theory (DFT) calculations. The designed substituted N,N'-diaryl hydrazines rearrange exclusively to the expected o/p-semidines and diphenylines. Intercrossing experiments support the intramolecular rearrangement process. Radical trapping experiments exclude the intermediacy of biradicals in the rearrangements. Computational results demonstrate that the o-semidine rearrangement involves a novel N[1,3]-sigmatropic shift and the p-semidine rearrangement proceeds via tandem N[1,3]/N[1,3]-sigmatropic shifts, while the diphenyline rearrangement occurs through cascade N[1,3]/[3,3]-sigmatropic shifts. The proposed mechanism involving the key N[1,3]-sigmatropic shift as the rate-limiting step is in good agreement with reported kinetic isotope measurements. The combined methods provide new insight into the formation mechanism of o/p-semidines and diphenylines in the benzidine rearrangement and support the unprecedented suprafacial symmetry allowed N[1,3]-sigmatropic shift with an inversion of the configuration in the migrating nitrogen atom.

A molecularly imprinted sensor for single-molecule detection of pesticide metabolite at the amol/L level sensitized by water-soluble luminol derivative encapsulated liposome via click reaction.

A novel luminol derivative, 4-[(1,4-dioxo-1,2,3,4-tetrahydrophthalazin-5-yl)amino]-4-oxobut-2-enoic acid (ALD) with electrochemiluminescence intensity and stability characteristics similar to luminol, but higher solubility in near neutral solution, was designed and synthesized in this study. Using this derivative, a molecular imprinted electrochemiluminescence sensor (MIECLS) was prepared for the sensitive and selective determination of 2-amino-5-mercapto-1,3,4-thiadiazole (AMT), a metabolite of bismerthiazol, thiediazole copper, thiazole zinc, and other pesticides. The ALD probes encapsulated in liposomes are immobilized on the molecularly imprinted film by light-triggered click reaction, and the concurrent release of multiple probes allows for highly sensitive detection. In the AMT concentration range of 1.00 × 10-18 - 5.00 × 10-13 mol/L, the relation between ECL response and log AMT concentration is linear. With a detection limit of 5.25 × 10-19 mol/L (about 4 - 6 molecules in 10 µL of the sample), the sensor allows for high sensitivity analysis of ultra-trace amounts of small organic compounds. In general, the ECL-based single-molecule detection technique proposed herein might be a promising alternative to fluorescence single-molecule detection.

Mechanistic insight into the formal [1,3]-migration in the thermal Claisen rearrangement.

The thermal formal [1,3]-sigmatropic shift of allyl aryl ethers has been studied in depth experimentally with the aid of the density functional theory (DFT) calculations of the B3LYP function. Three mechanistic possibilities, referred to as the radical, ionic, and concerted mechanisms, have previously been put forth to explain the thermal [1,3]-rearrangement process. However, the intercrossing and radical trapping experiments indicate the rearrangement is an intramolecular process. The computational studies reveal that the concerted C[1,3]-sigmatropic shift suffered from a higher energetic barrier to allow the rearrangement to proceed under the conditions used. However, a tandem O[1,3]-sigmatropic shift with a configuration inversion of the oxygen atom and [3,3]-sigmatropic shift (the Claisen rearrangement) is the most likely pathway for the formal [1,3] rearrangement. Furthermore, the rearrangement experiments with a designed optically active substrate and O[1,3]-sigmatropic shift examples verify the new cascade rearrangement. In addition, computational and experimental studies indicate that water molecule assists the proton shift during the isomerization. The combined methods provide the new insight into the mechanism of the thermal formal [1,3]-migration in the Claisen rearrangement and the novel O[1,3]-sigmatropic shift as well.

Liposomes: Preparation, Characteristics, and Application Strategies in Analytical Chemistry.

In recent years, the application of liposomes in the field of analytical chemistry has attracted more and more attention. In this paper, the preparation and characterization of liposomes are briefly summarized, and the research and application of liposomes in organic and biological substances analysis are mainly reviewed, including immobilized liposome chromatography, liposome capillary electrophoresis, liposome application in electrochemical analysis, and optical analysis. The future developments of liposomes in the assay are also prospected.

Imidazole Compounds: Synthesis, Characterization and Application in Optical Analysis.

Imidazole is a five-membered heterocyclic ring containing three carbon atoms, two nitrogen atoms, and two double bonds. Among two nitrogen atoms, one of which carries with a hydrogen atom is a pyrrole-type nitrogen atom, another is a pyridine type nitrogen atom. Hence, the imidazole ring belongs to the π electron-rich aromatic ring and can accept strong suction to the electronic group. Moreover, the nitrogen atom of the imidazole ring is coordinated with metal ions to form metal-organic frameworks. In recent years, because of imidazole compounds' unique optical properties, their applications have attracted more and more attention in optical analysis. Thus, this review has summarized the synthesis, characterization, and application with emphasis on the research progress of imidazole compounds in optical analysis, including fluorescence probe, colorimetric probe, electrochemiluminescence sensor, fiber optical sensor, surface plasmon resonance, etc. This paper will suggest the direction for the development of imidazole-containing sensors with high sensitivity and selectivity.

MXene-based enzymatic sensor for highly sensitive and selective detection of cholesterol.

In this work, the synthesized MXene (Ti3C2Tx) exhibited large specific area, biocompatibility, excellent electronic conductivity, and good dispersion in aqueous phase. The Chit/ChOx/Ti3C2Tx nanocomposite was prepared through the continuous self-assembled process. Its structure is characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). Moreover, the biosensor for cholesterol detection was fabricated via a one-step dip-coating method. Chit andTi3C2Tx act as a support matrix to immobilize ChOx enzyme, and also play a role in increasing the electrical conductivity. Meanwhile, the addition of redox mediator (Fe(CN)63-/4-) facilitates the electron transport from the analyte to the modified electrode in the oxidation of cholesterol. The DPV response exhibited an increase in current with increasing cholesterol concentration. Under the optimum conditions, the DPV response of the biosensor indicated a good linear relationship with the concentration of cholesterol ranging from 0.3 to 4.5 nM with a low detection limit of 0.11 nM, and a high sensitivity of 132.66 µA nM-1 cm-2. In addition, with favorable selectivity and stability, the biosensor has been used to detect cholesterol in real samples and the results demonstrate that the biosensor has excellent practicability.

Facile synthesis of an aggregation-induced emission (AIE) active imidazoles for sensitive detection of trifluralin.

A novel imidazoles fluorescent probe (2) was synthesized from vanillin, o-phenylenediamine, and N,N-diphenylcarbamyl chloride. Its structure was characterized by fluorescence spectra, UV-Vis spectra, 1H NMR, 13C NMR, and high-resolution mass spectrometry (HRMS). Moreover, its aggregation-induced emission (AIE) feature was investigated in THF/MeOH solution. Furthermore, the fluorescence quenching experimental results suggest that compound 2 is the potential fluorescent probe of small organic molecules showing high selectivity and sensitivity for nitroaromatic compounds. In addition, the probe could be applied in the determination of trifluralin with fast response and stability. The fluorescence response of the probe exhibited a good linear correlation with the concentration of trifluralin ranging from 10 to 100 µM, and the limit of detection (LOD) was as low as 5.066 µM. Finally, the probe was successfully utilized to determine the amount of trifluralin in real samples, and the recoveries were 91.1% to 111.2%, indicating the applicability and reliability of the probe.