Simplified Electrochemically Mediated Atom Transfer Radical Polymerization using a Sacrificial Anode

Simplification of electrochemically mediated atom transfer radical polymerization was achieved efficiently under either potentiostatic or galvanostatic conditions using an aluminum wire sacrificial anode (seATRP) immersed directly into the reaction flask without separating the counter electrode. seATRP polymerizations were carried out under different applied potentials, E_apps=E_1/2, E_pc, E_pc ?40 mV, and E_pc ?80 mV. As the rate of polymerization (R_p) can be modulated by applying different E_app potentials, more reducing conditions resulted in faster R_p. The polymerization results showed similar narrow molecular‐weight distribution throughout the reactions, similar to results observed for n‐butyl acrylate (BA) polymerization under conventional eATRP. High‐molecular‐weight PBA and diblock copolymers were synthesized by seATRP with more than 90 % monomer conversion. Furthermore, galvanostatic conditions were developed for synthesizing PBA with the two‐electrode system.     

Kinetics of propane oxydehydrogenation on metals oxides and metals phosphates catalysts: Evidence of compensation effects

Kinetics of oxidative dehydrogenation of propane has been tested on three groups of catalysts; alumina‐supported metal oxides (MO) (where metal is V, Cr, Ni, Zr, Mo, or Ba), alumina‐supported rare earth metal oxides (RO) (where metal is Ce, Tb, Dy, Ho, Tm, or Yb), and metal phosphates (MP) (where metal is V, Cr, Mn, Ni, Zr, Mg, Ba, or Ce). They were found to be active and exhibited different selectivities to propylene, ethylene, and COx (CO and CO₂). The Arrhenius parameters—apparent pre‐exponential factor (lnA_app) and activation energy E_app)—were evaluated. Evidence of compensation effects was established through statistically significant linear relationship between ln A_app and E_app. The rates of propane conversions and CO_x productions on MO and MP showed common compensation line different from that of RO. When the data for rates of production of propylene and ethylene were plotted, the line for the ethylene rate on MO appeared above that of propylene rate, contrary to the observation on MP and RO. An attempt was made to associate the differences in the behaviors of the catalysts with differences in the ensembles of chemisorbed species that form the respective active centers. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 176–183, 2006     

A novel tridentate nitrogen donor as ligand in copper catalyzed ATRP of methyl methacrylate

A tridentate ligand, BPIEP: 2,6‐bis[1‐(2,6‐diisopropyl phenylimino) ethyl] pyridine, having central pyridine unit and two peripheral imine coordination sites was effectively employed in controlled/“living” radical polymerization of MMA at 90°C in toluene as solvent, Cu^IBr as catalyst, and ethyl‐2‐bromoisobutyrate (EBiB) as initiator resulting in well‐defined polymers with polydispersities M_w/M_n ≤ 1.23. The rate of polymerization follows first‐order kinetics, k_app = 3.4 × 10^?5 s^?1, indicating the presence of low radical concentration ([P*] ≤ 10^?8) throughout the reaction. The polymerization rate attains a maximum at a ligand‐to‐metal ratio of 2:1 in toluene at 90°C. The solvent concentration (v/v, with respect to monomer) has a significant effect on the polymerization kinetics. The polymerization is faster in polar solvents like, diphenylether, and anisole, as compared to toluene. Increasing the monomer concentration in toluene resulted in a better control of polymerization. The molecular weights (M_n,SEC) increased linearly with conversion and were found to be higher than predicted molecular (M_n,Cal). However, the polydispersity remained narrow, i.e., ≤1.23. The initiator efficiency at lower monomer concentration approaches a value of 0.7 in 110 min as compared to 0.5 in 330 min at higher monomer concentration. The aging of the copper salt complexed with BPIEP had a beneficial effect and resulted in polymers with narrow polydispersitities and higher conversion. PMMA obtained at room temperature in toluene (33%, v/v) gave PDI of 1.22 (M_n = 8500) in 48 h whereas, at 50°C the PDI is 1.18 (M_n = 10,300), which is achieved in 23 h. The plot of lnk_app versus 1/T gave an apparent activation energy of polymerization as (ΔE^≠_app) 58.29 KJ/mol and enthalpy of equilibrium (ΔH⁰_eq) to 28.8 KJ/mol. Reverse ATRP of MMA was successfully performed using AIBN in bulk as well as solution. The controlled nature of the polymerization reaction was established through kinetic studies and chain extension experiments. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4996–5008, 2005     

A Hydrogen Peroxide Biosensor Based on Room Temperature Ionic Liquid Functionalized Graphene Modified Carbon Ceramic Electrode

A room temperature ionic liquid (IL) 1‐butyl‐3‐methylimidazolium hexafluorophosphate functionalized graphene (GE) was prepared and a hydrogen peroxide (H₂O₂) biosensor was fabricated by immobilizing hemoglobin (Hb) into the IL‐GE composite film. UV‐visible and Fourier transform infrared spectra of the composite film indicated that Hb retained its native structure in the film. Electrochemical investigation of the biosensor showed a pair of well‐defined, quasi‐reversible redox peaks with E_pa=?0.209 V and E_pc= ?0.302 V (vs. SCE) in pH 7.0 phosphate buffer solution at the scan rate of 100 mV/s. To the reduction of H₂O₂, the biosensor had a good linear range from 8.0×10^?7 to 1.8×10^?4 mol/L with a detection limit of 3.0×10^?7 mol/L. The apparent Michaelis‐Menten constant K^app_M was estimated to be 3.4×10^?5 mol/L.     

Effect of temperature on the number of active sites and propagation rate constant at ethylene polymerization over supported bis(imino)pyridine iron catalysts

The inhibition of ethylene polymerization with radioactive carbon monoxide (¹⁴CO) was used to obtain data on the number of active sites (C_P) and propagation rate constant (k_P) at ethylene polymerization in the temperature range of 35–70 °C over supported catalysts LFeCl₂/Al₂O₃, LFeCl₂/SiO₂, and LFeCl₂/MgCl₂ (L: 2,6‐(2,6‐(Me)₂C₆H₃N = CMe)₂C₅H₃N) with activator Al(i‐Bu)₃. The values of effective activation energy (E_eff), activation energy of propagation reaction (E_P), and temperature coefficients of variation of the number of active sites (E_Cp = E_eff ? E_P) were determined. The activation energies of propagation reaction for catalysts LFeCl₂/Al₂O₃, LFeCl₂/SiO₂, and LFeCl₂/MgCl₂ were found to be quite similar (5.2–5.7 kcal/mol). The number of active sites diminished considerably as the polymerization temperature decreased, the E_Cp value being 5.2–6.2 kcal/mol for these catalysts at polymerization in the presence of hydrogen. The reactions of reversible transformations of active centers to the surface hydride species at polymerization in the presence and absence of hydrogen are proposed as the derivation of E_Cp. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6621–6629, 2008     

Electrochemistry and Electrocatalysis of a Nafion/Nano‐CaCO3/Hb Film Modified Carbon Ionic Liquid Electrode Using BMIMPF6 as Binder

In this paper a room temperature ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆) was used as binder for the construction of carbon ionic liquid electrode (CILE) and a new electrochemical biosensor was developed for determination of H₂O₂ by immobilization of hemoglobin (Hb) in the composite film of Nafion/nano‐CaCO₃ on the surface of CILE. The Hb modified electrode showed a pair of well‐defined, quasi‐reversible redox peaks with E_pa and E_pc as ?0.265 V and ?0.470 V (vs. SCE). The formal potential (E°′) was got by the midpoint of E_pa and E_pc as ?0.368 V, which was the characteristic of Hb Fe(III)/Fe(II) redox couples. The peak to peak separation was 205 mV in pH 7.0 Britton–Robinson (B–R) buffer solution at the scan rate of 100 mV/s. The direct electrochemistry of Hb in the film was carefully investigated and the electrochemical parameters of Hb on the modified electrode were calculated as α=0.487 and k_s=0.128 s^?1. The Nafion/nano‐CaCO₃/Hb film electrode showed good electrocatalysis to the reduction of H₂O₂ in the linear range from 8.0 to 240.0 μmol/L and the detection limit as 5.0 μmol/L (3σ). The apparent Michaelis–Menten constant (K_M^app) was estimated to be 65.7 μmol/L. UV‐vis absorption spectroscopy and FT‐IR spectroscopy showed that Hb in the Nafion/nano‐CaCO₃ composite film could retain its native structure.     

Density functional study of H2 molecule and H atom adsorption on α‐U(001) surface

Density functional theory method has been employed to investigate the adsorption of H₂ molecule and H atom on α‐U(001) surface. There exist four initial sites [top (A), triangle‐center (B), long‐bridge (C), and short‐bridge (D)] for H₂ and H atom adsorptions on α‐U(001) surface. The E_ads (adsorption energy) values on the top sites of H₂‐U(001) configurations are around ?0.666 eV, and H₂ molecule has been elongated but not broken into H atoms. For the other three sites, the E_ads values are around ?1.521 eV. The long‐bridge site is the most reactive site for H₂ decomposing. For the H‐U(001) configurations, the E_ads are around ?2.904 eV. Top site and short‐bridge site are the most reactive sites for the H atom react on the α‐U(001) surface. Our work reveals that the different reactive sites play discrepant effects on hydrogenation process. Geometric deformations, diffusion paths, and partial density of states of H₂‐U(001) and H‐U(001) configurations have also been analyzed. Copyright © 2016 John Wiley & Sons, Ltd.     

Magnetism and crystal structure of an N3O3‐coordinated iron(II) complex

The reaction of [FeL(MeOH)₂] {where L is the tetradentate N₂O₂‐coordinating Schiff base‐like ligand (E,E)‐diethyl 2,2′‐[1,2‐phenylenebis(nitrilomethylidyne)]bis(3‐oxobutanoate)(2−) and MeOH is methanol} with 3‐aminopyridine (3‐apy) in methanol results in the formation of the octahedral complex (3‐aminopyridine‐κN¹){(E,E)‐diethyl 2,2′‐[1,2‐phenylenebis(nitrilomethylidyne)]bis(3‐oxobutanoato)(2−)‐κ⁴O³,N,N′,O^3′}(methanol‐κO)iron(II), [Fe(C₂₀H₂₂N₂O₆)(C₅H₆N₂)(CH₄O)] or [FeL(3‐apy)(MeOH)], in which the Fe^II ion is centered in an N₃O₃ coordination environment with two different axial ligands. This is the first example of an octahedral complex of this multidentate ligand type with two different axial ligands, and the title compound can be considered as a precursor for a new class of complexes with potential spin‐crossover behavior. An infinite two‐dimensional hydrogen‐bond network is formed, involving the amine NH group, the methanol OH group and the carbonyl O atoms of the equatorial ligand. T‐dependent susceptibility measurements revealed that the complex remains in the high‐spin state over the entire temperature range investigated.     

Steric Demand and Rate‐determining Step for Photoenolization of Di‐ortho‐substituted Acetophenone Derivatives

Laser flash photolysis of ketone 1 in argon‐saturated methanol yields triplet biradical 1BR (τ = 63 ns) that intersystem crosses to form photoenols Z‐1P (λ_max = 350 nm, τ ~ 10 μs) and E‐1P (λ_max = 350 nm, τ > 6 ms). The activation barrier for Z‐1P re‐forming ketone 1 through a 1,5‐H shift was determined as 7.7 ± 0.3 kcal mol^?1. In contrast, for ketone 2, which has a less sterically hindered carbonyl moiety, laser flash photolysis in argon‐saturated methanol revealed the formation of biradical 2BR (λ_max = 330 nm, τ ~ 303 ns) that intersystem crosses to form photoenol E‐2P (λ_max = 350 nm, τ > 42 μs), but photoenol Z‐2P was not detected. However, in more viscous basic H‐bond acceptor (BHA) solvent, such as hexamethylphosphoramide, triplet 2BR intersystem crosses to form both Z‐2P (λ_max = 370 nm, τ ~ 1.5 μs) and E‐2P. Thus, laser flash photolysis of ketone 2 in methanol reveals that intersystem crossing from 2BR to form Z‐2P is slower than the 1,5‐H shift of Z‐2P, whereas in viscous BHA solvents, the 1,5‐H shift becomes slower than the intersystem crossing from 2BR to Z‐2P. Density functional theory and coupled cluster calculations were performed to support the reaction mechanisms for photoenolization of ketones 1 and 2 .     

Two‐step Synthesis of New γ‐Lactones via Cyclization of 7‐Chloro‐2‐(methoxycarbonyl)‐4‐6‐dimethylocta‐(2E,4E,6E)‐trienoic acid

A new rapid synthesis of γ‐lactones, cis fused with a cyclopentenic ring by thermal cyclization of 7‐chloro‐2‐(methoxycarbonyl)‐4‐6‐dimethylocta‐7‐phenyl (or methyl) (2E,4E,6E)‐trienoic acids was reported. The key step implicates an intramolecular cyclization to a cyclopentenyl cation, according to an electrocyclic π_2s + π_2a conrotatory process, published in a recent paper (from the corresponding diacids). We have investigated the thermal behavior of the corresponding half‐esters since; if the cyclization obeys to the proposed mechanism, the diacids, half‐esters must also cyclize in a similar manner. Saponification of these led to γ‐dilactones via intermediary cyclopropanes. Mechanistic pathways were investigated.     

Copolymerization of methacrylic acid with methyl methacrylate by SET‐LRP

Single‐electron transfer living radical polymerization (SET‐LRP) has developed as a reliable, robust and straight forward method for the construction well‐defined polymers. To span an even larger variety of functional monomers, we investigated the copolymerization of methyl methacrylate with methacrylic acid by SET‐LRP. Copolymerizations were catalyzed by Cu(0)/Me₆‐TREN and performed in MeOH/H₂O mixtures at 50 °C. The SET‐LRP copolymerizations of varying methacrylic acid content were evaluated by kinetic experiments. At low (2.5%) and moderate (10%) MAA loadings, the copolymerizations obeyed perfect first order kinetics (k_p^app = 0.008 min^?1 and k_p^app = 0.006 min^?1) and exhibited a linear increase in molecular weights with conversion providing narrow molecular weight distributions. The SET‐LRP of MMA/25%‐MAA was found to be significantly slower (k_p^app = 0.0035 min^?1). However, a reasonable first‐order kinetics in monomer consumption was maintained, and the control of the polymerization process was preserved since the molecular weight increased linearly with conversion and could therefore be adjusted. This work demonstrates that the copolymerization of methacrylic acid by SET‐LRP is feasible and the design of well‐defined macromolecules comprising acidic functionality can be achieved. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

A phase separation fluoroimmunoassay of estradiol

A competitive indirect fluoroimmunoassay of free estradiol (E₂) was established based on the thermal sensitivity of hydrogel–‐poly‐N‐isopropylacrylamide. Free estradiol was covalently bound to bovine serum albumin (BSA) to form complete antigen (E₂‐BSA), which was in turn labeled by fluorescein isothiocyanate (FTTC) as the fluorescence probe. The anti‐ E₂ monoclonal antibody (McAb) was prepared by an in vivo method, and coupled with N‐isopropylacrylamide (NIPA) to make an immune copolymer, poly‐N‐isopropylacylamidemonoclonal antibody (pNIPA‐McAb), for the determination of free E₂. The immunoassay method was based on the competitive binding of free E₂ and fluoresceinated antigen (E₂‐BSA‐FTTC) with limited amount of pNIPA‐McAb. When the immunological reaction was over, precipitation and centrifugal procedures were carried out to separate pNIPA‐McAb‐E₂‐BSA‐FTTC from other constituents in solution. The precipitate pNIPA‐McAb‐E₂‐BSA‐FTTC was dissolved in solution and then the fluorescence intensity was measured. The calibration curve covered a range of 78–500 ng/mL for free E₂. The recoveries were 91.2–107.2%.     

A Novel Chemiluminescence Immunoassay Using Solid‐Phase Antigen for Free 17β‐Estradiol in Human Serum

A high‐performance chemiluminescence immunoassay, with long‐term durability, good precision and time‐saving, was proposed for the detection of free 17β‐estradiol (E₂) in human serum. Ninety‐six microplates were coated with bovine serum albumin conjugated E₂ antigen as solid phase for the immunoassay. The E₂‐BSA antigen coated on the microplate and the E₂ antigen in the sample competed for the binding sites on the horseradish peroxidase (HRP) labeled anti‐E₂ antibody. Chemiluminescence reaction was subsequently carried out by HRP catalyzing luminol‐H₂O₂ substrates, and the chemiluminescence intensity was inversely proportional to the amount of analyte in human sera samples. The concentration of immunoreagents, immunoreaction time, and other relevant variable conditions upon the immunoassay were studied and optimized. The proposed method exhibited detection limit as low as 5.94×10^?3 µg·L^?1 in a linear detection range from 0.01 to 1.00 µg·L^?1, good recoveries between 105% and 108%, and high precision with intra‐ and inter‐assay coefficients between 7.9% and 14.3%.     

Kinetics and quantification of the electrophilic reactivities of substituted thiophenes and structure‐reactivity relationships

Second‐order rate constants (k₁) have been measured spectrophotometrically for reactions of 2‐methoxy‐3‐X‐5‐nitrothiophene 1a‐c (X = NO₂, CN, and COCH₃) with secondary cyclic amines (pyrrolidine 2a , piperidine 2b , and morpholine 2 c ) in CH₃CN and 91:9 (v/v) CH₃OH/CH₃CN at 20°C. The experimental data show that the rate constants (k₁) values exhibit good correlation with the parameters of nucphilicity (N) of the amines 2a‐c and are consistent with the Mayr's relationship log k (20°C) = s(E + N). We have shown that the electrophilicity parameters E derived for 1a–c and those reported previously for the thiophenes 1d‐g (X = SO₂CH₃, CO₂CH₃, CONH₂, and H) are linearly related to the pK_a values for their gem‐dimethoxy complexes in methanol. Using this correlation, we successfully evaluated the electrophilicity E values of 12 structurally diverse electrophiles in methanol for the first time. In addition, a satisfactory linear correlation (r² = 0.9726) between the experimental (log k_exp) and the calculated (log k_calcd) values for the σ‐complexation reactions of these 12 electrophiles with methoxide ion in methanol has been observed and discussed.     

Inclusion complexes of 2-phenoxyethanol and alkoxyethanols in cyclodextrins: an 1H NMR study

The association in aqueous solutions of small amphiphilic molecules [2-phenoxyethanol, PhE₁, and some α-n-alkyl-ω-hydroxyoligo(oxiethylenes], C₄E₁, C₄E₂ and C₆E₂) with β-cyclodextrin (βCD), heptakis(2,6-di-O-methyl)-β-cyclodextrin (DIMEB) and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TRIMEB) was investigated by ¹H NMR spectroscopy. The upfield shifts observed for the H3 and H5 NMR signals due to anisotropic shielding confirm that the host–guest associations are of inclusion type. The stoichiometries and the apparent inclusion constants, K _app, were determined by ¹H NMR spectroscopy using the H5 and H3 signals. The relative differences in the K _app values for βCD inclusion complexes seem to reflect the hydrophobic/hydrophilic balance of the guests. The K _app values for the PhE₁ inclusion complexes can be related to the degree of methylation and hydrophobicity variation within the considered hosts. In addition, a comparative study between βCD and TRIMEB inclusion complexes using 2D ROESY (Rotating-frame Overhauser Enhancement SpectroscopY) NMR spectra provides structural features for these complexes which are inaccessible by other experimental methods.     

A fast isocratic liquid chromatography method for the quantification of xanthophylls and their stereoisomers

A fast isocratic liquid chromatography method was developed for the simultaneous quantification of eight xanthophylls (13‐Z‐lutein, 13’‐Z‐lutein, 13‐Z‐zeaxanthin, all‐E‐lutein, all‐E‐zeaxanthin, all‐E‐canthaxanthin, all‐E‐β‐apo‐8’‐carotenoic acid ethyl ester and all‐E‐β‐apo‐8’‐carotenal) within 12 min, compared to 90 min by the conventional high‐performance liquid chromatography method. The separation was achieved on a YMC C₃₀ reversed‐phase column (100 mm x 2.0 mm; 3 μm) operated at 20°C using a methanol/tert‐butyl methyl ether/water solvent system at a flow rate of 0.8 mL/min. The method was successfully applied to quantify lutein and zeaxanthin stereoisomers in egg yolk, raw and cooked spinach, and a dietary supplement. The method can be used for the rapid analysis of xanthophyll isomers in different food products and for quality control purposes.     

SET‐LRP of acrylonitrile in ionic liquids without any ligand

Use of ionic liquids as reaction media was investigated in the design of an environmentally friendly single electron transfer‐living radical polymerization (SET‐LRP) for acrylonitrile (AN) without any ligand by using Fe(0) wire as catalyst and 2‐bromopropionitrile as initiator. 1‐Methylimidazolium acetate ([mim][AT]), 1‐methylimidazolium propionate ([mim][PT]), and 1‐methylimidazolium valerate ([mim][VT]) were applied in this study. First‐order kinetics of polymerization with respect to the monomer concentration, linear increase of the molecular weight, and narrow polydispersity with monomer conversion showed the controlled/living radical polymerization characters. The sequence of the apparent polymerization rate constant of SET‐LRP of AN was k_app ([mim][AT]) > k_app ([mim][PT]) > k_app ([mim][VT]). The living feature of the polymerization was also confirmed by chain extensions of polyacrylonitrile with methyl methacrylate. All three ionic liquids were recycled and reused and had no obvious effect on the controlled/living nature of SET‐LRP of AN. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Quantitative evaluation of stress distribution in bulk polymer samples through the comparison of mechanical behaviors between giant single‐crystal and semicrystalline samples of poly(trans‐1,4‐diethyl muconate)

The Raman shift and crystallite modulus were measured under the application of tensile force for a giant single crystal and a series of uniaxially oriented semicrystalline samples of poly(trans‐1,4‐diethyl muconate) (polyEMU). The apparent Raman shift factor α^app or a vibrational frequency shift per 1 GPa tensile stress was higher for the semicrystalline samples with lower crystallinity or lower bulk modulus. The apparent crystallite modulus E or Young's modulus along the chain axis in the crystalline region was not constant but varied remarkably between the giant single crystal and semicrystalline samples. A systematic change in α^app and E among the polyEMU samples with different preparation history could be interpreted quantitatively on the basis of a mechanical series parallel model consisting of crystalline and amorphous phases. The origin of different E and α^app was speculated to be a stress concentration on the taut‐tie chain contained as a parallel crystalline component in the mechanical model. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 444–453, 2003     

Electrochemical Sensing of NADH and Glutamate Based on Meldola Blue in 1,2‐Diaminobenzene and 3,4‐Ethylenedioxythiophene Polymer Films

The redox mediator Meldola blue (MB) was entrapped into two polymers, poly‐1,2‐diaminobenzene (p‐DAB) and poly‐3,4‐ethylenedioxythiophene (p‐EDOT) by potential cycling and films were applied to NADH oxidation with subsequent glutamate detection using immobilized glutamate dehydrogenase. Both polymer films were tested for electrocatalysis of NADH using amperometry at E_app=0.1 V vs. Ag/AgCl and similar response characteristics were obtained with sensitivity values of 6.1 nA μM^?1, linear range up to 0.5 mM (R²=0.9972) and LOD of 50 μM. Subsequent amperometric determination of glutamate resulted in sensitivity 0.7 nA μM^?1, linearity 0–100 μM and detection limit of 2 μM glutamate.