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The magnetic properties of all complexes were studied by variable-temperature magnetic susceptibility and magnetization measurements. The obtained parameters of J range from -33.1 to -211 cm(super -1), indicating very strong antiferromagnetic coupling between Cu(super II) ions.

A study of the solution structure of the parallel-stranded oligodeoxynucleotide (3')T8(5')-(5')C4A8(3')hairpin was presented. The study protocol involved the use of high-resolution 2-dimensional proton-proton and proton-phosphorus nuclear magnetic resonance analysis to delineate the 3-dimensional structure of the hairpin. The results gave clear proof of the existence of a reverse Watson-Crick base-pairing between adenine and thymidine. Details of the structure of the hairpin were also inferred from data on sugar ring puckering, base orientation and bacbone conformation.

Two-dimensional nuclear magnetic resonance and restrained molecular dynamics stuies of the DNA oligomer d(T8C4A8) hairpin structure were reported. Hairpin structures are of special interest because they are usually found in DNA regions with biological control functions. The studies showed that thehairpin loop formed by d(T8C4A8) is unique, because the first loop cytosine base is notstacked with the other bases but positioned outside the loop.

Metal-free atom transfer radical polymerization (ATRP) was successfully achieved in aqueous media for the first time. Polymerization of poly(ethylene oxide) methyl ether acrylate (PEGA480) was well controlled (Đ < 1.40) under visible light irradiation using tetrabromofluorescein (Eosin Y) as catalyst and pentamethyldiethylenetriamine (PMDETA) as electron donor. A validated kinetic model was developed to investigate the process of photoredox catalytic cycle via reductive quenching pathway. Experimental and simulation results showed that electron donor not only had an important influence on the ATRP activation, but also participated in the ATRP deactivation. Furthermore, the effects of water content, catalyst concentration, and degree of polymerization on the polymerization were studied thoroughly by a series of experiments. Good controllability of the polymerization regulated by light on and off confirmed the high degree of temporal control. The livingness of the chains was proved by a successful chain extension experiment. Both experimental and simulation techniques were used to study aqueous metal-free ATRP, which provided a promising method to synthesize polymers in the absence of metal and organic solvent. [ABSTRACT FROM AUTHOR]

Thermoresponsive random copolymers consisting of poly(N-isopropylacrylamide) (PNIPAM) and polymerized ionic liquid (IL) poly(1,1,3,3-tetramethylguanidine acrylate) (PTMGA) were synthesized via reversible addition-fragmentation chain transfer radical polymerization (RAFT). The reactivity ratios of NIPAM (rNIPAM = 2.11) and TMGA (rTMGA = 0.56) were determined by the extended Kelen-Tödüs method. Glass transition temperatures (Tg) of the copolymers were analyzed, which followed the Fox equation very well. The phase transition behaviors of the copolymers in aqueous solution were studied through UV-vis transmission measurements. Their lower critical solution temperature (LCST) ranged from 30.5 to 73.2 °C, depending on the hydrophilic IL content. The apparent pKa related to LCST was determined, and thus the protonation degree was calculated. The hydrophilicity of the copolymers could be regulated by gas treatments. Bubbling CO2 led to lowering the transition temperature while bubbling N2 resulted in its recovery. This CO2/N2 switchability became more profound with higher IL content. With the ability to undergo reversible protonation caused by the change of pH, the system showed good reversibility in LCST when bubbled with CO2 and N2. SO2 could also be used to lower LCST. However, a basic compound (e.g., NaOH) was required for its recovery. The pH-dependent solution phase transition behavior provided great insight into the LCST regulation mechanism. The widest LCST shifting window (~12 °C) was found between pH 5.16 and 5.96, which could be fulfilled by the CO2 regulation approach. This work provides guidance for the design and synthesis of gas-switchable thermoresponsive polymers based on ionic liquids. [ABSTRACT FROM AUTHOR]

Oil/water separation has inspired much research interest because of the damages caused to our natural environment due to oily wastewater. As a leader of advanced separation materials, electrospun polymeric fibrous mats having the properties of special surface wettability, high specific surface area, and high porosity will be a good membrane material for the separation of oily wastewater. Herein, we first prepared pH-responsive polymer poly(dimethylsiloxane)-block-poly(4-vinylpyridine) (PDMS-b-P4VP) mat using electrospinning technology. The PDMS-b-P4VP fibrous mat with a thickness of around 250 μm exhibits good pH-switchable oil/water wettability and is able to effectively separate oil or water from layered oil/water mixtures by gravity driven through adjusting the pH value. Stemming from its porous structure and pH-switchable superwettability, the electrospun PDMS-b-P4VP fibrous mat achieved controllable separations with high fluxes of approximately 9000 L h-1 m-2 for oil (hexane) and 27 000 L h-1 m-2 for water. In addition, extended studies on the polymer/silica nanoparticulate (silica NP) composite fibrous mats show that the addition of an inorganic component improves the thermal stability, pH-switchable wettability, and separation performance of the fibrous mats (approximately 9000 L h-1 m-2 for hexane and 32 000 L h-1 m-2 for water). It can be concluded from the results that both polymer fibrous mats and silica-filled composite fibrous mats are good candidates for on-demand layered oil/water mixture separation. [ABSTRACT FROM AUTHOR]

In this work, a photoinduced iron(III)-based atom transfer radical polymerization (ATRP) without any reducing agents and additional initiators was suggested. In addition, detailed kinetic studies, including the effects of ligand and catalyst concentrations on polymerization kinetics, and the polymerization behaviors using various solvents and monomer types were evaluated for this new polymerization technique. Results showed that photoinduced iron(III)-mediated ATRP using 5000 ppm catalyst loading with 1 equiv of ligand in N,N-dimethylformamide (DMF) produced poly(methyl methacrylate) with low molecular weight distribution (Mw/Mn < 1.45) and that the evolution of molecular weight (Mn) was linearly related to monomer conversion. ¹H NMR analysis confirmed that the resulting polymer prepared through photoinduced ATRP in the present work was initiated by methyl 2,3-dichloroisobutyrate. Facile temporal control and the successful chain extension highlighted the good chain-end functionality of the resulting polymers. In short, this work provided a study on additional alkyl halides initiator-free ATRP and its application in the synthesis of methacrylate polymers with narrow Mw/Mn. [ABSTRACT FROM AUTHOR]

An iron- and methyl methacrylate (MMA)-based electrochemically mediated atom transfer radical polymerization (eATRP) system was developed for the first time. Kinetic behaviors, including the effect of applied potential and catalyst loading, were systematically investigated. Results indicated that with more negative electrode potential, the polymerization rate increased until the mass transport limitation was reached. However, reduction of the catalyst loading had adverse effects on polymerization behaviors, such as decreased polymerization rate and increased molecular weight distributions (Mw/Mn). In addition, a kinetic model based on the method of moments was also constructed to explain the mismatch in Mn and Mn,theo. Simulation results showed that slow initiation significantly influenced on the kinetic behaviors in this system. Iron(II) bromide-catalyzed normal ATRP, iron(III) bromide-catalyzed eATRP, and copper(II) bromide-catalyzed eATRP were conducted to compare and elucidate their respective polymerization reaction kinetic characteristics qualitatively. This work expanded the scope of eATRP from a copper-based system to an iron-based system in terms of polymerization kinetics, with the hope of promoting the widespread application of this method. [ABSTRACT FROM AUTHOR]

While living systems have developed highly efficient ways to convert chemical energy (e.g., ATP hydrolysis) to mechanical motion (e.g., movement of muscle), it remains a challenge to build muscle-like biomimetic systems to generate mechanical force directly from chemical reactions. Here we show that a continuous flow of reactant solution leads to by far the largest volume change to date in autonomous active gels driven by the Belousov-Zhabotinsky reaction. These results demonstrate that microfluidics offers a useful and facile experimental approach to optimize the conditions (e.g., fabrication methods, counterions, flow rates, concentrations of reagents) for chemomechanical transduction in active materials. This work thus provides much needed insights and methods for the development of chemomechanically active systems based on combining soft materials and microfluidic systems. [ABSTRACT FROM AUTHOR]

We have developed a new ternary polymeric system, poly(ethylene-alt-propylene) (PEP)/poly(butylene oxide) (PBO)/PEP−PBO, to study the complex phase behavior near the bicontinuous microemulsion phase channel. The molecular weights of the PEP and PBO homopolymers are 2600 and 3050 g/mol, respectively, and the copolymer is 23.4 kg/mol with volume fraction composition fPBO = 0.49. A combination of small-angle neutron scattering, small-angle X-ray scattering, rheology, optical microscopy, and visual oil bath measurements was employed to map out the phase diagrams at five fixed homopolymer PBO/PEP ratios, ranging from 40/60 to 60/40 by volume, with copolymer concentrations ranging from 0 to 100%. It was found that the bicontinuous microemulsion channel is consistently cut off at low temperature by a hexagonal phase. We attribute this phenomenon to the effect of the conformational asymmetry between the PEP and PBO species, whereby the more flexible PBO component induces a spontaneous curvature toward the PBO domains. These findings complement previous descriptions of the isopleth phase diagrams for A/B/A−B systems and identify a new design variable for preparing bicontinuous phases. [ABSTRACT FROM AUTHOR]

An isoflavone conjugates hydrolyzing beta-glucosidase (ICHG) from endophytic bacterium, Pseudomonas ZD-8 was purified to homogeneity by successive ammonium sulfate precipitation, gel filtration on SephadexG-100, DEAE-sephrose CL-6B and DEAE-Sephacel chromatography. The enzyme was a monomeric protein with an apparent molecular mass of 33 kDa as determined by SDS-PAGE and gel filtration. It was optimally active at pH 6.0 and 40 degrees C and had a specific activity of 1485 U mg of protein(-1) against genistin. The ICHG readily hydrolyzed rho-nitrophenyl-beta-glucoside, rho-nitrophenyl-beta-galactoside, genistin, daidzin, with Km values of 1.64, 1.87, 0.012, 0.014 mM, respectively. The ICHG showed a pronounced specificity for glucose in the 7-position of isoflavone and flavone conjugates and hydrolyzed effectively malonyl isoflavone glucosides as well as isoflavone glucosides with similar kinetics. Glucose and glucono-delta-lactone inhibited the enzyme competitively with Ki values of 84 mM and 23 mM, respectively. The enzyme did not require divalent cations for activity, and its activity was strongly inhibited by Hg2+, Ag+, rho-chloromercuribenzoate, iodoacetic acid, and N-ethylmaleimide while reducing agents such as beta-mercaptoethanol, dithiothreitol, dithioerythritol, glutathione slightly activated the enzyme.