Molecular sensing of 3-chloro-1,2-propanediol by molecular imprinting

A covalent interaction-based molecularly imprinted polymer (MIP) material for 3-chloro-1,2-propanediol (3-MCPD), a post-testicular anti-fertility agent and possible carcinogen and mutagen in food products containing acid-hydrolyzed vegetable proteins, has been successfully fabricated using 4-vinylphenylboronic acid as the functional monomer. Rebinding assay revealed that the binding constant, K_B, for the receptor sites and non-specific sites are 1.93±0.1×10⁴ and 2.74±0.7×10² M⁻¹, respectively. The estimated number of receptor site, B_max, imprinted is 123.3±3 μmol/g of MIP. The MIP material is able to act as a potentiometric chemosensor for 3-MCPD via increase in Lewis acidity of the receptor sites upon reaction of the arylboronic acid with 3-MCPD to form the more acidic arylboronic acid esters. A simple pH glass electrode is sufficient to monitor the analyte-specific rebinding. In unbuffered aqueous media, linear potentiometric response from 0 to 350 ppm of 3-MCPD can be achieved. The MIP-based chemosensing in a soya sauce matrix has also been attempted. It is found that the dynamic range of the potentiometric chemosensing response of the MIP material is much reduced, probably due to the blocking or deactivation of receptor sites by interferents in soya sauces. Nevertheless, the present work demonstrated the feasibility of using MIP-based chemosensors as semi-quantitative analytical tools for screening purposes in quality control of food products.     

Rationally designed chromogenic chemosensor that detects cysteine in aqueous solution with remarkable selectivity

A sensing ensemble for cysteine was assembled conveniently by simply mixing N,N,N′,N′-tetra-(2-pyridylmethyl)-p-xylylenediamine (TPXD), cadmium perchlorate, and pyrocatechol violet in an 1:2:1 molar ratio in water of neutral pH. In the ensemble, [Cd₂(TPXD)]⁴⁺ formed from TPXD and cadmium perchlorate serves as the receptor, and pyrocatechol violet functions as the indicator in sensing the analyte. The detection can be made either spectroscopically from the decrease of the UV-visible absorbance at 665 nm or visually from the color change to yellow upon addition of an aqueous solution of the analyte to the solution of the ensemble. The association constant (K_ass) for the binding of the indicator to the receptor was determined with an isothermal titration calorimeter to be (2.77±0.98)×10⁵ M⁻¹ and that for the binding of cysteine to the receptor was obtained to have (1.62±0.97)×10⁷ M⁻¹ by the non-linear regression analysis of the titration curve obtained by titration of the solution of the ensemble with cysteine solution. The chemosensor showed excellent selectivity for cysteine over other amino acids including homocysteine.     

Quantification of Intracellular Thiols by HPLC-Fluorescence Detection

Biothiols, such as cysteine and glutathione, play important roles in various intracellular reactions represented by the redox equilibrium against oxidative stress. In this study, a method for intracellular thiol quantification using HPLC-fluorescence detection was developed. Thiols were derivatized with a thiol-specific fluorescence derivatization reagent, viz. ammonium 7-fluoro-2,1,3-benzoxadiazole-4-sulfonate (SBD-F), followed by reversed-phase separation on an InertSustain AQ-C18 column. Six different SBD-thiols (homocysteine, cysteine, cysteinylglycine, γ-glutamylcysteine, glutathione, and N-acetylcysteine as an internal standard) were separated within 30 min using a citric buffer (pH 3.0)/MeOH mobile phase. The calibration curves of all the SBD-thiols had strong linearity (R² > 0.999). Using this developed method, the thiol concentrations of human chronic myelogenous leukemia K562 cell samples were found to be 5.5–153 pmol/1 × 10⁶ cells. The time-dependent effect of a thiol scavenger, viz. N-ethyl maleimide, on intracellular thiol concentrations was also quantified. This method is useful for elucidating the role of intracellular sulfur metabolism.     

Experimental and theoretical studies on inversion dynamics of dichloro(l-difluoromethionine-N,S)platinum(II) and dichloro(l-trifluoromethionine-N,S)platinum(II) complexes

Fluorinated analogues of methionine such as l-S-(difluoromethyl)homocysteine (l-difluoromethionine; DFM) and l-S-(trifluoromethyl)homocysteine (l-trifluoromethionine; TFM) have been demonstrated to be interesting analogues for incorporation into peptides and proteins. The presence of the fluorine nucleus adjacent to the sulfur atom in the side chain not only serves to alter the nucleophilicity and electron density of the sulfur atom but it can function as an important NMR spectroscopic (¹⁹F) probe. Additional information on the properties of these fluorinated amino acid analogues was obtained by studying their interactions with dipotassium tetrachloroplatinate (K₂PtCl₄). The resulting complexes, dichloro(l-difluoromethionine-N,S)platinum(II) and dichloro(l-trifluoromethionine-N,S)platinum(II) were investigated with respect to their sulfur inversion rates utilizing dynamic NMR methods. Inversion barriers for the DFM- and TFM-platinum complexes were experimentally determined to be 16.4 ± 0.2 and 18 ± 1 kcal/mol, respectively. Density functional calculations at the B3LYP/SDD level were also performed to model the structures and energies of the ground and transition states for these complexes.     

Selectivity features of molecularly imprinted polymers recognising the carbamate group

The molecular recognition properties of molecular imprinted polymers which bind the carbamate function were studied. Functional monomers potentially able to form non-covalent interactions with the model molecule N,O-dibenzylcarbamate were selected on the basis of a computational approach describing possible interactions between the template and a small library of vinylic monomers. These results were in accordance with N,O-dibenzylcarbamate batch-rebinding measurements performed on several miniMIPs prepared with the same library. From these preliminary results, four polymers were prepared by thermoinduced radical polymerization, using ethylene dimethacrylate as a cross-linker, chloroform (MIP1, MIP3) or acetonitrile (MIP2, MIP4) as porogens and methacrylic acid (MIP1, MIP2) or acrylamide (MIP3, MIP4) as functional monomers. Molecular recognition features of these materials were studied by high-performance liquid chromatography. In this manner selectivity was evaluated by considering the column retention of a library of sixteen structural analogues of dibenzylcarbamate, characterized by the transformation of the carbamate into a related function, or by the alteration of the molecular structure.The experimental results show that methacrylic acid is more efficient than acrylamide as a functional monomer (imprinting factors: MIP1 = 24.1, MIP2 = 25.6, MIP3 = 13.3, MIP4 = 2.44), and that chloroform enhances polymer selectivity. As regards structural motifs which conditionate the selectivity, the carbamate function strictly controls the presence/absence of molecular recognition, while shape and dimension of the substituents modulate the recognition itself. In particular, a marked recognition for analogs which were slightly bigger than the template was observed (N-benzyl-O-phenethylcarbamate: MIP1 α = 1.13, MIP2 α = 1.41, MIP3 α = 0.97; N-phenethyl-N-benzylcarbamate: MIP1 α = 1.61, MIP2 α = 1.17, MIP3 α = 0.81; N,O-diphenethylcarbamate: MIP1 α = 0.89, MIP2 α = 1.20, MIP3 α = 0.55).     

6-Chloro-N,N-Diethyl-1,3,5-Triazine-2,4-Diamine (Simazine) Electrochemical Sensing Chip Based on Biomimetic Recognition Utilizing a Molecularly Imprinted Polymer Layer on a Gold Chip

Abstract

Electrochemical sensing chip of 6-chloro-N,N-diethyl-1,3,5-triazine-2,4-diamine (Simazine) was developed on its reductive current. In order to give sensitivity and selectivity to the simazine sensing chip, a gold chip was modified with molecularly imprinted polymer (MIP) for simazine, which is worked as biomimetic recognition element and showed. Using simazine sensing chip, cathodic current of simazine was measured by cyclic voltammetry and the peak current depended on the concentration of simazine. The detection limit was 0.4 µM. Simazine sensing chip was 29 times more sensitive to simazine than bare gold electrode and showed selective response to simazine compared to atrazine and MCC, by the modification with Sim-MIP.     

A Novel Molecularly Imprinted Photoelectrochemical Sensor Based on g‐C3N4‐AuNPs for the Highly Sensitive and Selective Detection of Triclosan

A novel molecularly imprinted polymer (MIP) photoelectrochemical sensor was fabricated for the highly sensitive and selective detection of triclosan. The MIP photoelectrochemical sensor was fabricated using graphite‐like carbon nitride (g‐C₃N₄) and gold nanoparticles (AuNPs) as photoelectric materials. The MIP/g‐C₃N₄‐AuNPs sensor used photocurrent as the detection signal and was triggered by ultraviolet light (UV‐Light 365 nm). g‐C₃N₄‐AuNPs was immobilized on indium tin oxide electrodes to produce the photoelectrochemically responsive electrode of the MIP/g‐C₃N₄‐AuNPs sensor. A MIP layer of poly‐o‐phenylenediamine was electropolymerized on the g‐C₃N₄‐AuNPs‐modified electrode to act as the recognition element of the MIP/g‐C₃N₄‐AuNPs sensor and to enable the selective adsorption of triclosan to the sensor through specific binding. Under optimal experimental conditions, the designed MIP/g‐C₃N₄‐AuNPs sensor presented high sensitivity for triclosan with a linear range of 2×10⁻¹² to 8×10⁻¹⁰ M and a limit of detection of 6.01×10⁻¹³ M. Moreover, the MIP/g‐C₃N₄‐AuNPs sensor showed excellent selectivity. The sensor had been successfully applied in the analysis of toothpaste samples.     

Surface plasmon resonance sensor for lysozyme based on molecularly imprinted thin films

Molecularly imprinted polymers (MIPs) selective for lysozyme were prepared on SPR sensor chips by radical co-polymerization with acrylic acid and N,N′-methylenebisacrylamide. Gold-coated SPR sensor chips were modified with N,N′-bis(acryloyl)cystamine, on which MIP thin films were covalently conjugated. The presence of NaCl during the polymerization and the re-binding tests affected the selectivity and the optimization of NaCl concentration in the pre-polymerization mixture and the re-binding buffer could enhance the selectivity in the target protein sensing. When the lysozyme-imprinted polymer thin films were prepared in the presence of 40 mM NaCl, the selectivity factor (target protein bound/reference protein bound) of MIP in the re-binding buffer containing 20 mM NaCl was 9.8, meanwhile, that of MIP in the re-binding buffer without NaCl was 1.2. A combination of SPR sensing technology with protein-imprinted thin films is a promising tool for the construction of selective protein sensors.     

The Synthesis of Magnetic Lysozyme‐Imprinted Polymers by Means of Distillation–Precipitation Polymerization for Selective Protein Enrichment

A protein imprinting approach for the synthesis of core–shell structure nanoparticles with a magnetic core and molecularly imprinted polymer (MIP) shell was developed using a simple distillation–precipitation polymerization method. In this work, Fe₃O₄ magnetic nanoparticles were first synthesized through a solvothermal method and then were conveniently surface‐modified with 3‐(methacryloyloxy)propyltrimethoxylsilane as anchor molecules to donate vinyl groups. Next a high‐density MIP shell was coated onto the surface of the magnetic nanoparticles by the copolymerization of functional monomer acrylamide (AAm), cross‐linking agent N,N′‐methylenebisacrylamide (MBA), the initiator azodiisobutyronitrile (AIBN), and protein in acetonitrile heated at reflux. The morphology, adsorption, and recognition properties of the magnetic molecularly imprinted nanoparticles were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), and rebinding experiments. The resulting MIP showed a high adsorption capacity (104.8 mg g^?1) and specific recognition (imprinting factor=7.6) to lysozyme (Lyz). The as‐prepared Fe₃O₄@Lyz‐MIP nanoparticles with a mean diameter of 320 nm were coated with an MIP shell that was 20 nm thick, which enabled Fe₃O₄@Lyz‐MIP to easily reach adsorption equilibrium. The high magnetization saturation (40.35 emu g^?1) endows the materials with the convenience of magnetic separation under an external magnetic field and allows them to be subsequently reused. Furthermore, Fe₃O₄@Lyz‐MIP could selectively extract a target protein from real egg‐white samples under an external magnetic field.     

Determination of S-nitrosoglutathione and other nitrosothiols by p-hydroxymercurybenzoate derivatization and reverse phase chromatography coupled with chemical vapor generation atomic fluorescence detection

S-Nitrosoglutathione (GSNO) reacts with the organic mercurial probe, p-hydroxymercury benzoate (PHMB, HO-Hg-(C₆H₄)-COO⁻Na⁺) giving the complex GS-Hg(C₆H₄)COOH (GS-PHMB). This reaction has been studied by UV measurements at 334 nm also in the presence of ascorbic acid and the product of reaction, the GS-PHMB complex, characterized by Electrospray Ionization Mass Spectrometry (ESI-MS) and by Reversed Phase Chromatography (RPLC) coupled on-line and sequentially with a UV-visible diode array detector (DAD) followed by a cold vapor generation atomic fluorescence spectrometer (CVGAFS). The simultaneous presence of PHMB and ascorbate produced a synergistic effect on GSNO decomposition rate that can be observed only above a given concentration threshold of ascorbate (ascorbate/GSNO molar ratio ≥ 180). The results indicated that the formation of GS-PHMB, both in the presence and the absence of ascorbic acid, does not involve the formation of free thiolic species but it takes place through a more complex mechanism. The PHMB derivatives of GSH and GSNO obtained by the present method were found to be identical by ESI-MS. GSSG did not interfere because it was not reduced and derivatized to GS-PHMB. Once complexed by the alkylating agent N-ethylmaleimide (NEM), GSH did not interfere with the derivatization reaction. This ensured a good selectivity of the developed PHMB derivatization system for RSNO determination. Thus, we have optimized the operating conditions for the selective reaction of PHMB with GSNO and other nitrosothiols (RSNOs) in order to determinate RSNOs in human plasma. LODc for RSNOs in plasma ultrafiltrate was 30 nM (injected concentration, 50 μL loop), the DLR ranged between 0.08 and 50 μM and the CV% was 6.5% at 300 nM concentration level. Reduced and oxidized thiols spiked to plasma did not interfere with the measurement of RSNOs. We found that the sampling procedure was critical for the recovery of endogenous and spiked RSNOs. The ultrafiltrate samples of plasma of 8 healthy humans contained 1460 ± 310 CysNO, 1000 ± 330 nM HCysNO and 320 ± 60 nM GSNO if blood was sampled in a mixture NEM/ethylendiaminotetracetic acid (EDTA)/serine-borate complex (SBC), where serine-borate complex is a potent inhibitor of γ-glutamyltransferase, an enzyme involved in the conversion of GSNO into CysGlyNO. In the absence of SBC during the sampling of blood GSNO concentration found in the ultrafiltrate was lower (at level of the determination limit in plasma ultrafiltrate, i.e. 75 nM) and the peak of CysGlyNO appeared, which corresponded to a concentration of 200 ± 60 nM (N = 4 blood samples).     

Molecularly imprinted polymer based potentiometric sensor for the determination of hydroxyzine in tablets and biological fluids

Molecular imprinting is a useful technique for the preparation of functional materials with molecular recognition properties. In this work, a biomimetic potentiometric sensor, based on a non-covalent imprinted polymer, was fabricated for the recognition and determination of hydroxyzine in tablets and biological fluids. The molecularly imprinted polymer (MIP) was synthesized by precipitation polymerization, using hydroxyzine dihydrochloride as a template molecule, methacrylic acid (MAA) as a functional monomer and ethylene glycol dimethacrylat (EGDMA) as a cross-linking agent. The sensor showed a high selectivity and a sensitive response to the template in aqueous system. The MIP-modified electrode exhibited a Nernstian response (29.4 ± 1.0 mV decade⁻¹) in a wide concentration range of 1.0 × 10⁻⁶ to 1.0 × 10⁻¹ M with a lower detection limit of 7.0 × 10⁻⁷ M. The electrode demonstrated a response time of ∼15 s, a high performance and a satisfactory long-term stability (more than 5 months). The method has the requisite accuracy, sensitivity and precision to assay hydroxyzine in tablets and biological fluids.     

Synthesis and crystal structures of fluorescent receptors for 9-butyladenine

Two pyrene containing fluorescent receptors, 2-(1-pyrenyl)benzoic acid (FR-1) and 8-(1-pyrenyl)-1-naphthoic acid (FR-2), have been designed and synthesized to mimic a pyrene dinucleotide for molecular recognition of 9-butyladenine (9-BuA). The X-ray crystal structures of the receptors FR-1 and FR-2 along with the binding substrate 9-BuA have been determined. FR-1 has the carboxyl group in the same plane as the phenyl group whereas the pyrenyl group is perpendicular to the phenyl group. However, both carboxyl and pyrenyl groups in FR-2 are parallel to each other but perpendicular to the naphthyl group. The binding constant for FR-2 to 9-BuA was found to be 7896±2187 M⁻¹, which is 8.3-fold greater than that for FR-1 (953±129 M⁻¹). The results indicate that the complex of 9-BuA with FR-2 is more stable than that with FR-1 by 1.2 kcal/mol. In addition, the molecular recognition of 9-BuA with the receptors can also be observed using fluorescence spectroscopy.     

Biomimetic sensor based on MnMn complex as manganese peroxidase mimetic for determination of rutin

A novel biomimetic sensor for rutin determination based on a dinuclear complex [Mn^IIIMn^II(Ldtb)(μ-OAc)₂]BPh₄ containing an unsymmetrical dinucleating ligand, 2-[N,N-bis(2-pyridylmethyl)-aminomethyl]-6-[N-(3,5-di-tert-butyl-2-oxidoben-zyl)-N-(2-pyridylamino)aminomethyl]-4-methylphenol (H₂Ldtb), as a manganese peroxidase mimetic was developed. Several parameters were investigated to evaluate the performance of the biomimetic sensor obtained after the incorporation of the dinuclear complex in a carbon paste. The best performance was obtained in 75:15:10% (w/w/w) of the graphite powder:Nujol:Mn^IIIMn^II complex, 0.1 mol L⁻¹ phosphate buffer solution (pH 6.0) and 4.0 × 10⁻⁵ mol L⁻¹ hydrogen peroxide. The response of the sensor towards rutin concentration was linear using square wave voltammetry in the range of 9.99 × 10⁻⁷ to 6.54 × 10⁻⁵ mol L⁻¹ (r = 0.9998) with a detection limit of 1.75 × 10⁻⁷ mol L⁻¹. The recovery study performed with pharmaceuticals ranged from 96.6% to 103.2% and the relative standard deviation was 1.85% for a solution containing 1.0 × 10⁻³ mol L⁻¹ rutin (n = 6). The lifetime of this biomimetic sensor was 200 days (at least 750 determinations). The results obtained for rutin in pharmaceuticals using the biomimetic sensor and those obtained with the official method are in agreement at the 95% confidence level.     

GC-MS Discrimination of Citrulline from Ornithine and Homocitrulline from Lysine by Chemical Derivatization: Evidence of Formation of N5-Carboxy-ornithine and N6-Carboxy-lysine

Derivatization of amino acids by 2 M HCl/CH₃OH (60 min, 80 °C) followed by derivatization of the intermediate methyl esters with pentafluoropropionic anhydride (PFPA) in ethyl acetate (30 min, 65 °C) is a useful two-step derivatization procedure (procedure A) for their quantitative measurement in biological samples by gas chromatography-mass spectrometry (GC-MS) as methyl ester pentafluoropropionic (PFP) derivatives, (Me)_m-(PFP)_n. This procedure allows in situ preparation of trideutero-methyl esters PFP derivatives, (d₃Me)_m-(PFP)_n, from synthetic amino acids and 2 M HCl/CD₃OD for use as internal standards. However, procedure A converts citrulline (Cit) to ornithine (Orn) and homocitrulline (hCit) to lysine (Lys) due to the instability of their carbamide groups under the acidic conditions of the esterification step. In the present study, we investigated whether reversing the order of the two-step derivatization may allow discrimination and simultaneous analysis of these amino acids. Pentafluoropropionylation (30 min, 65 °C) and subsequent methyl esterification (30 min, 80 °C), i.e., procedure B, of Cit resulted in the formation of six open and cyclic reaction products. The most abundant product is likely to be N⁵-Carboxy-Orn. The second most abundant product was confirmed to be Orn. The most abundant reaction product of hCit was confirmed to be Lys, with the minor reaction product likely being N⁶-Carboxy-Lys. Mechanisms are proposed for the formation of the reaction products of Cit and hCit via procedure B. It is assumed that at the first derivatization step, amino acids form (N,O)-PFP derivatives including mixed anhydrides. At the second derivatization step, the Cit-(PFP)₄ and hCit-(PFP)₄ are esterified on their C¹-Carboxylic groups and on their activated N^ureido groups. Procedure B also allows in situ preparation of (d₃Me)_m-(PFP)_n from synthetic amino acids for use as internal standards. It is demonstrated that the derivatization procedure B enables discrimination between Cit and Orn, and between hCit and Lys. The utility of procedure B to measure simultaneously these amino acids in biological samples such as plasma and urine remains to be demonstrated. Further work is required to optimize the derivatization conditions of procedure B for biological amino acids.     

An efficient route to disymmetrically substituted calix[6]arenes. Synthesis of novel ligands presenting a N2S or N3CO2 binding core

The C_3v tris-methoxy calix[6]arene was selectively mono-alkylated by dibromoethane yielding a key intermediate for the design of disymmetrically O-substituted calix[6]arenes. Indeed, subsequent reactions with various functional groups afforded novel calix[6]arene-based biomimetic ligands that present a mixed donor N₂S or N₃CO₂⁻ environment in an efficient way.     

H, C, and F NMR studies of phencyclone adducts of N-(polyhalophenyl)maleimides: evidence for dynamic NMR in maleamic acids: Ab initio calculations for optimized structures

NMR methods, including one- and two-dimensional techniques (at 7.05 T) for ¹H, ¹³C and ¹⁹F, have been applied to studies of hindered rotations and magnetic anisotropy in some crowded Diels-Alder adducts of phencyclone (1). Symmetrically substituted N-aryl maleimides (2) bearing numerous halogens on the N-aryl ring, were employed as dienophiles to form the target adducts (3). The maleimides included: N-(4-bromo-2,6-difluorophenyl)maleimide (2a); N-(2,3,5,6-tetrafluorophenyl)maleimide (2b); N-(4-bromo-2,3,5,6-tetrafluorophenyl)maleimide (2c); N-(2,3,4,5,6-pentachlorophenyl)maleimide (2d); and N-(2,4,6-tribromophenyl)maleimide (2e). Maleimides (2a-2c) were prepared from the precursor N-aryl maleamic acids (5a-5c). Ambient temperature fluorine-19 NMR of these maleamic acids in d₆-acetone showed substantial unusual peak broadening consistent with intermediate exchange rate processes, which may correspond to the N-aryl rotation process. Maleimides (2d) and (2e) were produced in one step from pentachloroaniline or 2,4,6-tribromoaniline, respectively, and maleic anhydride with anhydrous ZnCl₂ at ca. 200 °C. For the adducts (3), we observed slow exchange limit spectra on the ¹H, ¹³C, [and ¹⁹F, for (3a-3c)] NMR timescales for the rotation of the unsubstituted bridgehead phenyls about the C(sp³)C(sp²) bonds, and for the rotations of the N-aryl rings about the N(sp²)C(aryl sp²) bonds. Ab initio calculations for geometry optimizations at the Hartree-Fock level with 6-31G* (or LACVP*) basis sets were performed for the adducts. We believe that this is the first report of detailed ¹H, ¹³C, and ¹⁹F NMR data for a substantial collection of N-aryl maleamic acids, maleimides and their phencyclone adducts bearing multiple fluorines or other halogens directly on the N-aryl ring, together with complementary quantitative geometric parameters from high-level HF/6-31G* (or LACVP*) calculations.     

Synthesis and binding properties of a macrocycle with two binding subcavities

A large, covalent macrocycle that can be served as an artificial allosteric model was prepared in a reasonable yield (36%) through the template-directed synthesis. The macrocycle contains two topologically discrete subcavities, each of which consists of four amide NHs of pyridine-2,6-dicarboxamide units. The macrocycle strongly binds two molecules of N,N,N′,N′-tetramethylterephthalamide in positive cooperative manner by hydrogen-bonding interactions. The association constants were calculated to be K₁ = 1480 ± 90 and K₂ = 5580 ± 150 M⁻¹ with the Hill coefficient (h) of 1.6 at 25 °C in CDCl₃.     

Studies of silicon-containing maleimide polymers: 1. Synthesis and characteristics of model compounds

A series of the (N-maleimido phenoxy)silane monomers were synthesized by a two-step reaction for using as the application of flame retardant, functional modifier, or a photoresist material in deep-UV region. All of the monomers with maleimide ring were polymerized by radical polymerization in toluene solution using 2,2′-azobisisobutyronitrile (AIBN) as initiator so as to prepare homopolymers. The structures of the maleimide monomers were identified by ¹H, ¹³C, ²⁹Si NMR and element analysis. The chemical structures of polymers were identified by Fourier transform infrared reflection (FT-IR) spectroscopy. The molecular weight distributions of polymers were measured by gel permeation chromatography (GPC) equipment. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to analyze the thermal properties of the polymers. The degree of polymerization in silicon-containing maleimide polymers should be affected by side chains. The introduction of alkylsilane into a side chain of maleimide polymer may reduce the glass transition temperature (T_g) and thermal stability, but increase char yield of solid residue as an excellent flame retardant.     

A microvolume molecularly imprinted polymer modified fiber-optic evanescent wave sensor for bisphenol A determination

A fiber-optic evanescent wave sensor for bisphenol A (BPA) determination based on a molecularly imprinted polymer (MIP)-modified fiber column was developed. MIP film immobilized with BPA was synthesized on the fiber column, and the sensor was then constructed by inserting the optical fiber prepared into a transparent capillary. A microchannel (about 2.0 μL) formed between the fiber and the capillary acted as a flow cell. BPA can be selectively adsorbed online by the MIP film and excited to produce fluorescence by the evanescent wave produced on the fiber core surface. The conditions for BPA enrichment, elution, and fluorescence detection are discussed in detail. The analytical measurements were made at 276 nm/306 nm (λ _ex/λ _em), and linearity of 3?×?10^?9–5?×?10^?6 g mL^?1 BPA, a limit of detection of 1.7?×?10^?9 g mL^?1 BPA (3σ), and a relative standard deviation of 2.4 % (n?=?5) were obtained. The sensor selectivity and MIP binding measurement were also evaluated. The results indicated that the selectivity and sensitivity of the proposed fiber-optic sensor could be greatly improved by using MIP as a recognition and enrichment element. Further, by modification of the sensing and detection elements on the optical fiber, the proposed sensor showed the advantages of easy fabrication and low cost. The novel sensor configuration provided a platform for monitoring other species by simply changing the light source and sensing elements. The sensor presented has been successfully applied to determine BPA released from plastic products treated at different temperatures.

Thermodynamic studies of monuron

Monuron (C₉H₁₁ClN₂O; N,N-dimethyl-N′-(4-chlorophenyl) urea, CAS 150-68-5) was synthesized and the heat capacities of the compound were measured in the temperature range from 79 to 385 K with a high precision automated adiabatic calorimeter. No phase transition or thermal anomaly was observed in this range. The enthalpy and entropy data of the compound relative to the reference temperature 298.15 K were derived based on the heat capacity data. The thermodynamic properties of the compound were further investigated through DSC and TG analysis. The melting point, the molar enthalpy, and entropy of fusion were determined to be 447.6±0.1 K, 29.3±0.2 kJ mol⁻¹, and 65.4 J K⁻¹ mol⁻¹, respectively.