Synthesis of oxime phosphoranes from reaction between triphenylphosphine and acetylenic esters in the presence of oxime derivatives

A new one-pot, simple and effective procedure is presented for the preparation of O-containing phosphorus ylides by the Michael addition reaction of N-methylpyrrole-2-carbaldehydoxime, pyridin-2-carbaldehydoxime or acetophenonoxime with acetylenic esters.     

Novel ferrocene-based ionic liquid supported on silica nanoparticles as efficient catalyst for synthesis of naphthopyran derivatives

We report synthesis of silica nanospheres containing ferrocene-tagged imidazolium acetate (SiO₂@Im-Fc[OAc]) as efficient heterogeneous nanocatalyst for synthesis of naphthopyran derivatives under solvent-free conditions, based on modification of nano SiO₂ by ionic liquid with ferrocene tags and subsequent anion metathesis reaction. The synthesized novel nanocatalyst (SiO₂@Im-Fc[OAc]) was systematically characterized using Fourier-transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, and field-emission scanning electron microscopy. The catalytic activity of (SiO₂@Im-Fc[OAc]) was tested in one-pot three-component reaction of aromatic aldehydes, malononitrile, and 2-naphthol for facile synthesis of naphthopyran derivatives. To achieve high catalytic efficacy, the effects of various reaction parameters such as temperature, amount of catalyst, type of solvent, etc. were investigated. Furthermore, recovery and reuse of the nanocatalyst several times was demonstrated without appreciable loss in catalytic activity. The presented protocol offers several advantages, including green and ecofriendly nature, operational simplicity, higher yield, and easy recovery and reuse of the nanostructured catalyst. The workup of these very clean reactions involves only recrystallization of the product from ethanol and recovery of the catalyst by filtration.     

Characterization and High Level Expression of Acidic Endoglucanase in Pichia pastoris

Bioconversion of cellulosic material into glucose needs cellulase enzymes. One of the most important organisms that produces cellulases is Trichoderma reesei, whose cellulose enzymes are probably the most widely used in the industry. However, these enzymes are not stable enough at high pH and temperatures. The optimized synthetic endoglucanase II gene with Pichia pastoris codon preferences was secretary expressed in P. pastoris. Recombinant enzyme characterization showed maximum activity at pH 4.8 and temperature 75 °C, and it demonstrated increasing thermal stability in high temperature. The enzyme maintained its activity in a wide pH range from 3.5 to 6.5. The optimization of fermentation medium was carried out in shaking flasks. Recombinant protein expression at optimum conditions (pH 7, temperature 25 °C, and 1 % methanol induction) for 72 h demonstrated 2,358.8 U/ml endoglucanase activity units. To our knowledge, this is the highest acidic thermophilic endoglucanase activity that is reported in crude intracellular medium in P. pastoris. We conclude that P. pastoris is an appropriate host for high-level expression of optimized endoglucanase gene with improved thermal stability.     

Electrospinning of nylon-6,6 solutions into nanofibers: Rheology and morphology relationships

The relationship between the rheological properties of nylon-6,6 solutions and the morphology of their electrospun nanofibers was established. The viscosity of nylon-6,6 in formic acid(90%) was measured in the concentration range of 5 wt%-25 wt% using a programmable viscometer. Electrospinning of nylon-6,6 solutions was carried out under controlled parameters. The chemical structure, morphology and thermal properties of the obtained nanofibers were investigated using Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy(SEM) and differential scanning calorimetry(DSC), respectively. Entanglement concentration(ce) was found to be 15 wt% and a power law relationship between specific viscosity and solution concentration was observed with exponents of 2.0 and 3.3 for semi-dilute unentangled(c ce) and semi-dilute entangled(c ce) regimes, respectively. The diameter and uniformity of the nanofibers were found to be dependent on the viscosity. Moreover, the average diameter of electrospun nanofibers was found to be dependent on zero shear rate viscosity and normalized concentration(c/ce) in a power law relationship with exponents of 0.298 and 0.816, respectively. For nylon-6,6 solutions, the entanglement concentration(ce = 15 wt%) provides the threshold viscosity required for the formation of a stable polymeric jet during electrospinning and producing uniform beadless fibers. For concentrations less than ce, beaded fibers with some irregularities are formed. DSC analysis showed an increase in crystallinity of all electrospun samples compared to original polymer. Furthermore, Based on FTIR spectroscopy, α phase is dominant in electrospun nanofibers and minor amount of β and γ phases is also available.     

Preparation of a solid-state ion-selective electrode based on polypyrrole conducting polymer for magnesium ion

In this study, a potentiometric sensor based on a pencil graphite electrode (PGE) coated with polypyrrole doped with Titan yellow dye (PPy/TY) was prepared for potentiometric determination of magnesium ion in aqueous solutions. The structural characteristics of magnesium sensor electrode (PGE/PPy/TYMg) were studied using scanning electron microscopy and Fourier transform infrared along with energy-dispersive spectroscopy. Under the optimal conditions, the electrode reveals a good Nernstian behavior with slope of 28.27 ± 0.40 mV per decade over the concentration range of 1.0 × 10^?5–5.0 × 10^?2 M and a detection limit of 6.28 × 10^?6 M. The potentiometric response of fabricated electrode toward magnesium ion was found to be independent of the pH of the test solution in the pH range of 4.5–8.0. The electrode showed fast response time (<10 s) and good shelf lifetime (>2 months). The prepared magnesium sensor electrode can also be used as an indicator electrode in potentiometric titration of Mg²⁺ with EDTA with distinguished end point. The electrode revealed good selectivity with respect to many cations including alkali, alkaline earth, transition and heavy metal ions. The introduced magnesium electrode was used for measurement of Mg²⁺ ion in real samples without any serious interferences from other ions.     

Effect of block lengths on the association behavior of poly(l-lactic acid)/poly(ethylene glycol) (PLA–PEG–PLA) micelles in aqueous solution

A series of poly(l-lactic acid)/poly(ethylene glycol) triblock copolymers with a PLA–PEG–PLA architecture were synthesized by a ring-opening polymerization (ROP) process. The copolymers were characterized by ¹H NMR and GPC. The total number average molecular weights were in the range of 4,700–50,000, whereas the degrees of polymerization of the PLA and PEG blocks varied from 15 to 359 and from 68 to 136, respectively. The self-association of these copolymers in aqueous environment was studied by emission fluorescence spectroscopy of anilinonaphthalene probe and the critical association concentration (CAC) of the copolymers was measured. It was found that the micellization process of these copolymers was mainly determined by the length of the hydrophobic LA block, while the length of the hydrophilic PEG block had little effect. Furthermore, the low CAC values of the copolymers suggest that the copolymers form stable supramolecular structures in aqueous solutions.     

Morphology of polyaniline nanofibers synthesized under different conditions

Polyaniline nanofibers are readily synthesized by bulk polymerization; ammonium per sulphate (APS) is used as oxidizing agent and hydrochloric acid as dopant without any hard or soft templates. A detailed study was conducted on the effect of a variety of synthetic conditions on the size and morphology of the polyaniline nanostructure. These conditions include the concentration of dopant, and the APS-to-aniline and acid-to-aniline molar ratios. The morphology of the nanofibers was confirmed by SEM and TEM. XRD and FT-IR and UV–visible spectroscopy were used for structural characterization of nanofibers. The results showed that not only the microstructure of the polyaniline product, but also other characteristics, for example conductivity, crystallinity, and, more importantly, the efficiency of the process are strongly affected by the synthetic conditions.     

Influence of polymeric coating on capillary electrophoresis of iron oxide nanoparticles

In this work, electrophoresis was successfully used to separate three different polymer-coated magnetic iron oxide nanoparticles with similar sizes (nominally 50 nm) using high-pH borate buffer system. The coating polymers were dextran, polyethylene glycol, or carboxymethyl dextran. The results showed that the migration time of carboxymethyl dextran coated nanoparticles is the longest due to relatively more negative surface charges. Investigation of the effects of buffer concentration, pH, electric field strength and the capillary temperature, on electrophoretic properties of samples was also carried out. The results showed that pH, electric field strength and the capillary temperature had indirect relations with both of the migration time and the separation resolution of three different polymer-coated nanoparticles while the buffer concentration had a direct relation.     

Synthesis and application of a thermosensitive tri-block copolymer as an efficient sample treatment technique for preconcentration and ultra-trace detection of lead ions

We have designed and synthesized a thermosensitive tri-block copolymer for selective trace extraction of Pb(II) ions from biological and food samples. The polymer was characterized by Fourier transform IR and NMR spectroscopy, and by gel permeation chromatography. The critical aggregation concentration and lower critical solution temperature were determined via fluorescence and UV spectrophotometry, respectively. The effects of solution pH value, amount of copolymer, of the temperature on extraction and on phase separation, and of the matrix on the extraction of Pb(II) were optimized. Pb(II) ions were then quantified by FAAS. The use of this copolymer resulted in excellent figures of merit including a calibration plot extending from 0.5 to 160 μg L^?1 (with an R² of >0.99), a limit of detection (LOD) as low as 90 pg L^?1, an extraction efficiency of >98 %, and relative standard deviations of <4 % for eight separate extraction experiments.