Catalysis of enantiomeric ester hydrolysis in polymer domains: Catalytic effects of N-decanoyl-histidine and of dipeptide derivatives containing a histidyl residue

The catalytic activities of N-decanoyl-L -histidine and its methyl ester and of dipeptide derivatives containing an L -histidine residue toward the stereoselective hydrolysis of enantiomeric substrates have been studied at pH 7.30 (in 0.01M Bis-tris buffer) and 25°C in the presence of poly(ethyleneimine) derivatives. The dipeptide catalyst revealed greatest stereoselectivity in a quaternized poly(ethyleneimine) derivative. A comparison of catalytic effects on both the rate constants and stereoselectivities of N-decanoyl-L -histidine and its methyl ester elucidates the cooperative effects of carboxyl groups in the polymer domains. The structure of the substrates influenced both the rate constants and stereoselectivities in polymer domains.     

直链醇对反胶束体系中木素过氧化物酶催化活性的影响

根据研究发现, 在有醇作助表面活性剂的CTAB反胶束中木素过氧化物酶(LiP)不能表现活力, 而在水介质中CTAB对LiP的催化活性影响又不是很大. 为了揭示其中醇的影响, 本工作就不同碳链长度的醇对LiP酶催化性能的影响进行了研究. 由于CTAB反胶束体系中醇浓度较高, 且碳原子数大于4的直链醇在水中的溶解度又很小, 为此采用了LiP可在其中显示催化活性的CTAB正胶束、AOT反胶束和Brij30反胶束作介质, 通过研究这些介质中不同链长的醇对LiP催化活力的影响, 来探讨CTAB反胶束中木素过氧化物酶(LiP)不能表现活力的原因. 结果表明, 不管表面活性剂聚集体的结构、电性质及反胶束大小如何, 只要醇的浓度超过500 mmol•L^－1 (丁醇≥1200 mmol•L^－1), LiP在上述原本可显示活力的介质中均无催化活性. 据此推测CTAB反胶束中木素过氧化物酶(LiP)不能表现活力的原因主要是由助表面活性剂醇造成的.     

Nanosized mixed aggregates of alkylated <Emphasis Type="Italic">p</Emphasis>-sulfonatocalix[<Emphasis Type="Italic">n</Emphasis>]arenes and cetyltrimethylammonium bromide: self-organization and catalytic activity

Self-organization and catalytic activity of supramolecular systems based on a series of O-alkylated p-sulfonatocalix[n]arenes (SCA: n = 4, 6, 8; R = Bu, Oct, Dod (Oct is octyl, Dod is dodecyl)) and cetyltrimethylammonium bromide (CTAB) were studied by dynamic light scattering, tensimetry, and spectrophotometry. In aqueous solutions containing SCA (10^-6-10^-4 mol L^-1) and CTAB (10^-2-10^-12 mol L^-1), mixed associates and SCA—CTAB micelles are formed in a wide concentration range. Their sizes (100–300 nm), properties, and reactivity depend mainly on the structure and concentration of the starting components, as well as on the nature of their associates in solutions. A relationship between the nonlinear concentration dependences of the sizes of SCA—CTAB micelles (SCA: n = 4, 6, 8; R = Dod) and their catalytic activity in the hydrolysis of _O-ethyl _O-(4-nitrophenyl) chloromethylphosphonate was established. The study of the physiological effect on plant cells in solutions of SCA (n = 6; R = Dod), CTAB, and their mixtures showed that SCA and CTAB exerted opposite effects on the energy exchange in the wheat root cells, while a mixed solution of these substances (1: 1) has almost no effect on the physiological state of the roots, which is due to the formation of stable CTAB—SCA aggregates that protect the biosystem from the action of the starting components.     

Surfactant-induced electroosmotic flow in microfluidic capillaries

Control of EOF in microfluidic devices is essential in applications such as protein/DNA sizing and high‐throughput drug screening. With the growing popularity of poly(methyl methacrylate) (PMMA) as the substrate for polymeric‐based microfludics, it is important to understand the effect of surfactants on EOF in these devices. In this article, we present an extensive investigation exploring changes in EOF rate induced by SDS, polyoxyethylene lauryl ether (Brij35) and CTAB in PMMA microfluidic capillaries. In a standard protein buffer (Tris‐Glycine), PMMA capillaries exhibited a cathodic EOF with measured mobility of 1.54 ± 0.1 (× 10^?4 cm²/V.s). In the presence of surfactant below a critical concentration, EOF was independent of surfactant concentration. At high concentrations of surfactants, the electroosmotic mobility was found to linearly increase/decrease as the logarithm of concentration before reaching a constant value. With SDS, the EOF increased by 257% (compared to buffer), while it was decreased by 238% with CTAB. In the case of Brij35, the electroosmotic mobility was reduced by 70%. In a binary surfactant system of SDS/CTAB and SDS/Brij35, addition of oppositely charged CTAB reduced the SDS‐induced EOF more effectively compared to nonionic Brij35. We propose possible mechanisms that explain the observed changes in EOF and zeta potential values. Use of neutral polymer coatings in combination with SDS resulted in 50% reduction in the electroosmotic mobility with 0.1% hydroxypropyl methyl cellulose (HPMC), while including 2% poly (N,N‐dimethylacrylamide) (PDMA) had no effect. These results will potentially contribute to the development of PMMA‐based microfluidic devices.     

Phosphorylation of polyethylene imines in chloroform in the presence of calix[4]resorcinarenes

Kinetics of the reaction of alkylated polyethylene imines with 4-nitrophenyl bis(chloromethyl)-phosphinate in chloroform in the absence and in the presence of substituted calix[4]resorcinarenes were studied by UV spectrophotometry. It was shown that calixarenes forming mixed aggregates with polyethylene imines have a catalytic effect on the polymer phosphorylation process. The catalytic effect depends on the structure of polyethylene imine and the component ratio in the system.     

Water soluble gold-polyaniline nanocomposite: A substrate for surface enhanced Raman scattering and catalyst for dye degradation

In this work, a water-soluble gold nanoparticle-encapsulated polyaniline nanocomposite (AuNP-PANI) was prepared in the presence of an ionic surfactant such as cetyltrimethylammonium bromide (CTAB) using versatile two steps method. The prepared nanoparticles (AuNPs) were characterized by UV–Visible spectroscopy, Transmission Electron Microscope (TEM) and Dynamic Light Scattering (DLS). The nanocomposite (AuNP-PANI) were initially characterized using UV–Visible spectroscopy, Transmission Electron Microscope (TEM), Scanning Transmission Electron Microscope (STEM) and DLS. The structure and composition of AuNP-PANI further characterized using Fourier Transmission Infrared Spectroscopy (FTIR), X-ray diffraction study (XRD), Energy Dispersive X-ray Spectroscopy (EDS) and Thermogravimetric analysis (TGA). Electrochemical properties of AuNP-PANI were studied using Cyclic Voltammetry (CV). The prepared nanocomposite exhibited good surface enhanced Raman scattering (SERS) of 4-amino thiophenol (4-ATP) and 4- (dimethyl amino) pyridine (4-DMAP) for which the enhancement factor (EF) were found to be1.95 × 10⁵ and 2.016 × 10⁵, respectively. The nanocomposite also showed excellent catalytic activity for the chemical degradation of Congo red (CR) and methylene blue (MB) as evidenced from the calculated rate constants which were determined to be 0.30 s⁻¹ and 0.33 s⁻¹, respectively.     

Phosphorylation of heptafluorobutanol in the presence of metal chloride-ether catalytic systems

Catalytic activity of complex catalysts based on Li, Na, K, and Cs chlorides and polydentate ligands, viz., dibenzo-18-crown-6, mono-, di-, and tetraglymes, and poly(ethylene glycols) PEG-600 and PEG-1000 was examined in the phosphorylation of heptafluorobutanol with phosphorus oxychloride. The introduction of an organic ligand into a catalytic system leads to improvement in solubility of the salt used as a catalyst and to an increase in the reaction rate by a factor of 1.3—2.8. The catalytic systems based on LiCl and poly(ethylene glycols) proved to be most efficient.     

Semi-Interpenetrating Hydrogels of Polyelectrolytes,Polymer-Metal Complexes and Polymer-Protected Palladium Nanoparticles

Summary: Semi-interpenetrating hydrogels (SIHs) of polyelectrolytes consisting of poly(acrylamide) hydrogel (PAAH) as matrix and sodium poly(styrenesulfonate) (NaPSS), poly(N,N′-dimethyl-N,N′-diallylammonium chloride) (PDMDAAC), stoichiometric interpolyelectrolyte complex of NaPSS-PDMDAAC, and linear polyethyleneimine-metal complexes (PMC) as well as polymer-protected palladium nanoparticles were prepared by in situ polymerization, e.g. crosslinked acrylamide chains were formed in aqueous solutions of NaPSS, PDMDAAC, NaPSS-PDMDAAC (1:1 mol/mol), PMC and palladium nanoparticles protected by poly(N-vinylpyrrolidone) (PVP), poly-(vinyl alcohol) (PVA), poly(acrylic acid) (PAA), and linear poly(ethyleneimine) (LPEI) respectively in the presence of N,N′-methylenebisacrylamide. For each system the equilibrium swelling degree α and the parameters n and k describing the mechanism of water transport into SIHs volume was determined. Catalytic properties of SIHs were studied in allyl alcohol hydrogenation and cyclohexane oxidation reactions.     

Shape‐memory effect in hyperbranched poly(ethyleneimine)‐modified epoxy thermosets

A series of shape‐memory epoxy thermosets were synthesized by crosslinking diglycidyl ether of bisphenol A with mixtures of commercially available hyperbranched poly(ethyleneimine) and polyetheramine. Thermal, mechanical and shape‐memory properties were studied and the effect on them of the content and structure of the hyperbranched polymer was discussed. Measurements showed that the glass transition temperature can be tailored from 60 °C to 117 °C depending on the hyperbranched polymer content, and all formulations showed an appropriate glassy/rubbery storage modulus ratio. Shape‐memory programming was carried out at TgE′ given the excellent mechanical properties of the materials, with maximum stress and failure strain up to 15 MPa and 60%, respectively. The resulting shape‐memory behavior was excellent, with maximum shape recovery and shape fixity of 98% as well as a fast shape‐recovery rate of 22%/min. The results show that hyperbranched poly(ethyleneimine) as a crosslinking agent can be used to enhance mechanical and shape‐memory properties with different effects depending on the crosslinking density. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 924–933     

MICELLAR CATALYSIS OF COMPOSITE REACTIONS I MICELLAR EFFECT ON THE CONSECUTIVE FIRST ORDER REACTION

The micellar catalytic model (or the consecutive first order reaction has been proposed in this paper. It was applied to the alkaline hydrolysis of dimethyl phthalate in micellar solutions of surfactants (CTAB, SDS and Triton X-100), and the alkaline hydrolysis of bis (2,4-dinitrophenyl) posphate in CTAB micellar solution. Rate constants obtained in micellar phase indicate that the two steps of alkaline hydrolysis of dimethyl phthalate are both inhibited by all of the surfactants investigated. CTAB micelle exhibits a greater catalytic effect on the alkaline hydrolysis of bis (2, 4-dinitrophenyl) phosphate. this may be arised from the local concentration effect of hydroxide ion in CTAB micellar phase. Nevertheless. the second order rate constant of bis-(2, 4-dinitrophenyl) phosphate in the micellar phase is smaller than that in the bulk phase.     

Comparative study on the enzymatic polymerization of N‐substituted aniline derivatives

A series of water‐soluble N‐substituted poly(alkylanilines) (PNAAs) have been enzymatically synthesized with a variety of groups, from methyl to n‐butyl, such as poly(N‐methylaniline), poly(N‐ethylaniline), poly(N‐butylaniline) and poly(N‐phenylethanolamine). The syntheses were made in the presence of poly(4‐sodium styrene sulfonate) (SPS) as a template and horseradish peroxidase (HRP) as a catalyst. The size and type of the groups have a great effect on the properties of the final polymers. UV‐vis spectroscopy and cyclic voltammetry measurements confirmed that for enzymatically synthesized PNAAs/SPS complexes, the electroactivity increased with the bulkiness of the substituents. These polymers have been studied in the doped and undoped states by FT‐IR and UV‐vis spectroscopy. Also these polymers show multiple and reversible optical transitions that can be ascribed to the formation of polaron and bipolaron states. Copyright © 2005 John Wiley & Sons, Ltd.     

PNPP Cleavage Catalyzed by Schiff Base Mn(III) Complexes Containing Polyether Side Chains in CTAB Micellar Solutions

Two Schiff base Mn(III) complexes containing polyether side chain were synthesized and characterized. The catalytic hydrolysis of p‐nitrophenyl picolinate (PNPP) by the two complexes in the buffered CTAB micellar solution in the pH range of 6.60–8.20 was investigated kinetically in this study. The influences of acidity, temperature, and structure of complex on the catalytic cleavage of PNPP were also studied. The mechanism of PNPP hydrolysis catalyzed by Schiff base manganese(III) complexes in CTAB micellar solution was proposed. The relative kinetic and thermodynamic parameters were determined. Comparied with the pseudo‐first‐order rate constant (k ₀) of PNPP spontaneous hydrolysis in water, the pseudo‐first‐order rate constants (k _obsd) of PNPP catalytic hydrolysis are 1.93×10³ fold for MnL¹ ₂Cl and 1.06×10³ fold for MnL² ₂Cl in CTAB micellar solution at pH=7.00, T=25°C, and [S]=2.0×10^?4mol · dm^?3, respectively. Furthermore, comparing the k _obsd of PNPP catalytic hydrolysis by metallomicelles with that of PNPP hydrolysis catalyzed only by metal complexes or CTAB micelle at the above‐mentioned condition, metallomicelles of MnL₂(L=L¹, L²) Cl/CTAB exhibit notable catalytic activities for promoting PNPP hydrolysis, and MnL¹ ₂Cl/CTAB system is superior in promoting cleavage of PNPP relative to MnL² ₂Cl/CTAB system under the same experimental conditions. The results indicate that the rate of PNPP catalytic cleavage is influenced by the structures of the two complexes, the acidity of reaction systems, and the solubilization of PNPP in CTAB micelles.     

水热合成Co3O4的制备参数调变及其催化分解N2O性能

以十六烷基三甲基溴化胺（CTAB）为模板剂,通过调变CTAB浓度水热合成了氧化钴前驱体,焙烧制得棒状形貌的Co₃O₄,在其表面浸渍K₂CO₃溶液制得K改性的Co₃O₄催化剂,用于N₂O分解。用X射线衍射（XRD）、N₂物理吸附（BET）、扫描电镜（SEM）、X射线光电子能谱（XPS）、H₂程序升温还原（H₂-TPR）和O₂程序升温脱附（O₂-TPD）等技术对催化剂进行了表征,考察了CTAB/钴及尿素/钴物质的量比等制备参数对Co₃O₄催化分解N₂O活性的影响。结果表明,CTAB浓度为0.05 mol/L、CTAB/钴离子物质的量比为1、尿素/钴离子物质的量比为4时,所制备的Co₃O₄催化剂具有较高的N₂O分解活性,而K改性可以进一步提升其催化性能。K改性的Co₃O₄在有氧有水气氛中400℃下进行N₂O分解反应,50 h后N₂O转化率仍保持在91%以上。     

Amperometric Sensor for Detection of the Reduced Form of Nicotinamide Adenine Dinucleotide Using a Poly(pyronin B) Film Modified Electrode

An electrochemical method for the preparation of poly(pyronin B) film was proposed in this paper. A poly(pyronin B) (poly(PyB)) film modified glassy carbon electrode (GCE) has been fabricated via an electrochemical oxidation procedure and applied to the electrocatalytic oxidation of reduced form of nicotinamide adenine dinucleotide (NADH). The poly(PyB) film modified electrode surface has been characterized by atomic force microscope (AFM), scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS), UV‐visible absorption spectrophotometry (UV‐vis) and cyclic voltammetry (CV). These studies have been used to investigate the poly(PyB) film, which demonstrates the formation of the polymer film and the excellent electroactivity of poly(PyB) in neutral and even in alkaline media. Due to its potent catalytic effects towards the electrooxidation of NADH at lower potential (0.0 V), poly(PyB) film modified electrode can be used for the selective determination of NADH in real samples because of dopamine, ascorbic acid and uric acid oxidation can be avoided at this potential. The catalytic peak currents are linearly dependent on the concentrations of NADH in the range of 1.0×10^?6 to 5.0×10^?4 mol/L with correlation coefficients of 0.999. The detection limits for NADH is 0.5×10^?6 mol/L. Poly(PyB) modified electrode also shows good stability and reproducibility due to the irreversible attachment of polymer film at GCE surface.     

Copper Schiff base complex immobilized on magnetic graphene oxide: Efficient heterogeneous nanocatalyst for treating environmental pollutants and synthesis of chromenes

Herein, a new Cu(II) Schiff base complex was immobilized onto the magnetic graphene oxide surface through a stepwise procedure. The as-synthesized nanostructure (GO/Fe₃O₄/CuL) was characterized by various techniques including Fourier transform infrared (FT-IR), Raman spectroscopies, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), energy-dispersive X-ray (EDX) and inductively coupled plasma (ICP) spectroscopies, N₂ adsorption–desorption analysis, vibrating sample magnetometry (VSM), and X-ray diffraction (XRD). The catalytic activity of the synthesized nanocatalyst was examined in 4-nitrophenol (4-NP), Congo red (CR), and methylene blue (MB) reduction using NaBH₄ in an aqueous solution at room temperature. The reaction progress was monitored by UV–Vis spectroscopy. Also, the synthesized nanostructure was evaluated as an efficient catalyst for the synthesis of 2-amino-4H-benzopyrans via three-component reactions of 1-naphthol, malononitrile, and various aldehydes in ethanol/water at 50°C. The use of green solvents, the short reaction time, the high product yield, and easy separation from the reaction environment are the main benefits of this catalytic system. By covalent grafting of the complex on the graphene oxide surface, its catalytic performance significantly increased compared with graphene oxide; this is probably related to the chemical change of the graphene oxide surface. The results show the high chemical stability and the improved reusability of the synthesized nanocatalyst (six times) without significant loss in the catalytic activity of GO/Fe₃O₄/CuL nanocomposite.     

Selective Interaction Between Proteins and the Outermost Surface of Polyelectrolyte Multilayers: Influence of the Polyanion Type,pH and Salt

Protein adsorption was studied by in-situ ATR-FT-IR spectroscopy of consecutively deposited polyelectrolyte multilayer systems terminated either with poly(ethyleneimine) (PEI) or polyanions, such as poly-(acrylic acid) (PAC), poly(maleic acid-co-propylene) (PMA-P) or poly(vinyl sulfate) (PVS). The influence of the polyanion type, pH and ionic strength was investigated. Negatively charged human serum albumin (HSA) was strongly repelled by multilayers terminated with weak polyanions (PAC, PMA-P), whereas moderate attraction was observed for those terminated with the strong polyanion PVS. Changing the pH from 7.4 to 5 resulted in enhanced HSA adsorption onto PAC-terminated multilayers. An increase in ionic strength diminished the attractive HSA adsorption onto PEI-terminated multilayers. For the PEI/PAC system, the biomedically relevant adsorption of human fibrinogen (FGN) is determined via its isoelectric point in accordance with three other proteins.     

Oxidation of Hydroquinone By (N-Vinylpyrrolidone)-(4-Vinylpyridine) Block and Graft Copolymers

ABSTRACT

A-B Type block copolymer of N-vinylpyrrolidone (NVP) and 4-vinylpyridine (VPy) [poly(NVP-b-VPy) and graft copolymers of VPy onto copolymers of NVP with 4-vinylbenzyl N,N-diethyldithiocarbamate (VBDC) [poly(NVP-g-VPy) were synthesized by the iniferter method. the compatibility between NVP and VPy units in the copolymers was evaluated from the glass transition temperature of these copolymers. Hydroquinone was then oxidized by the synthesized NVP-VPy copolymers-Cu(II) complex catalysts. the influence of the distribution of each monomer unit in copolymers on the catalytic activity was studied by comparing the activity of these copolymers. the catalytic activity of these copolymers increased in the order: NVP-VPy blend polymer, poly(NVP-b-VPy), poly(NVP-g-VPy), random copolymer [poly(NVP-ran-VPy)]. This order parallels the compatibility between NVP units and VPy units in these copolymers.     

Sol–gel encapsulation of cresol red in presence of surfactants

Cresol Red (CR) pH indicator was encapsulated into silica network using the sol–gel process. Transparent monolithic disks of entrapped CR were obtained in the presence of cetyl trimethyl ammonium bromide (CTAB) or dodecyl dimethyl amino oxide (Genaminox LA,GLA) alkyl hydroxyethyl dimethyl ammonium chloride (HY, R = 12–14) and TX-100 surfactants. UV/VIS spectra showed that the encapsulated CR retains its structure in terms of its response to pH. At the neutral conditions it is found that the HY surfactant is considered as proton donor as favor the cationic form of the indicator, while CTAB surfactant favor the neutral, however GLA surfactant, the anionic form of CR is more favored because GLA has a zwitterionic head. The surfactant GLA with TEOS has shifted the equilibrium to the ionized form of CR due to the electrostatic interaction between the surfactant and the CR anion. Therefore their pH range is dependent on the nature of a surfactant used. It is found that the HY surfactant is more efficient as far as loading of CR is concern and it widened the working pH range.     

Network structure and thermomechanical properties of hybrid DGEBA networks cured with 1‐methylimidazole and hyperbranched poly(ethyleneimine)s

The use of commercially available hyperbranched poly(ethyleneimine)s (Lupasol?, BASF) as polymeric modifiers in diglycidyl ether of bisphenol A thermosetting formulations using 1‐methylimidazole (MI) as anionic initiator has been studied. Poly(ethyleneimine)s can get incorporated into the network structure by condensation of amine and epoxy groups. The excess, over‐stoichiometric epoxy groups can undergo anionic homopolymerization initiated by MI. The thermal, dynamomechanical, and mechanical properties of the resulting materials have been determined using DSC, thermomechanical analysis (TMA), dynamomechanical analysis (DMA), and mechanical testing. The effect of the different amine modifiers on the MI networks, determined by their structure, is complex. Low initiator content and high molecular weight modifiers create significant mobility restrictions, which have a strong effect on the glass transition temperature and the apparent crosslinking density of the cured materials. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Gold-doped ceria–lanthana solid solution: surfactant assisted preparation,nanostructural and catalytic properties

The effect of preparation methods on the formation of gold doped ceria–lanthana solid solution (Au-CLSS) nanoparticles (NPs) was studied. The nanoparticles were prepared by surfactant assisted precipitation methods viz., co-precipitation (CP) and deposition precipitation (DP) in the presence of cetyltrimethylammonium bromide (CTAB). The as prepared nanoparticles were characterized using BET, FESEM, EDS, Raman, TEM, XRD and UV–Vis. spectroscopic techniques to investigate the preferred method for the preparation of nanoparticles for catalytic applications. The cubic fluorite phase formation of nanoparticles was confirmed by XRD analysis and the average crystallite size was calculated to be around 7–10 nm. Surface area studies revealed that the NPs formed by CTAB assisted method have higher surface area. The morphology of NPs formed by both methods was flaky. Raman studies confirmed that the samples prepared by DP method generated increased oxygen vacancies than those prepared by CP method. In the present work, catalytic oxidation efficiency of the catalysts studied with toluene vapours showed maximum efficiency for Au-CLSS at low temperatures (450 K) as compared to undoped CLSS.