Biomimetic formation of gramicidin S by dimerization-cyclization of pentapeptide precursor on solid support

The biomimetic formation of gramicidin S, cyclo(-d-Phe-Pro-Val-Orn-Leu-)₂, by the dimerization and cyclization of pentapeptide precursor without the protection of δ-amino group of the Orn residue was examined on a solid support. The cyclization of H-d-Phe-Pro-Val-Orn-Leu-oxime on a resin with an oxime group of 0.62 mmol/g in 1,4-dioxane directly gave gramicidin S in a 50% yield. The dimerization-cyclization mode on the solid support was similar to that of the biosynthesis of gramicidin S on an enzyme.     

Vibrational spectroscopic encoding of polystyrene-based resin beads: converting the encoding peaks into barcodes

A detailed approach is described for the vibrational spectroscopic encoding of polystyrene-based resin beads by converting the infrared absorption peaks suitable for encoding (encoding peaks) into barcodes. Based on combining the FT-IR measurements and the quantum-chemical computations, the vibrational characteristics of p-tert-butylstyrene monomer, polystyrene and poly(p-tert-butylstyrene) resin beads are analyzed, which are helpful for the selection of encoding peaks. The vibrational spectroscopic encoding of polystyrene-based resin beads could be obtained by converting the wavenumber, intensity and full width at half maximum (FWHM) of the encoding peaks into barcodes automatically through a computer program designed in our laboratory.     

Solid phase extractive preconcentration of uranium(VI) using quinoline-8-ol anchored chloromethylated polymeric resin beads

A new chelating polymeric sorbent has been developed using Merrifield chloromethylated resin anchored with quinoline-8-ol (HQ). The modified polymeric resin was characterized by FT-IR spectroscopy and elemental analysis. The HQ anchored resin showed superior binding affinity for U(VI) over Th(IV) and La(III). The influence of various physicochemical parameters on the recovery of U(VI) were optimized by both static and dynamic methods. The phase exchange kinetic studies performed for U(VI) revealed that <5 min was sufficient for reaching equilibrium metal ion sorption. The maximum sorption capacity of HQ anchored resin for U(VI) was found to be 120.30 mg g⁻¹ of resin which is higher than other solid phase extraction sorbents reported so far excepting N,N-dibutyl, N′-benzoyl thiourea sorbed Amberlite XAD-16. The developed HQ anchored polymeric resin is highly selective as none of the extraneous species were found to have any deleterious effect. Solid phase extraction (SPE) studies performed using HQ anchored polymeric resin offered enrichment factor of 100 and the lowest concentration below which recoveries become non-quantitative is 5 μg l⁻¹. The accuracy of the developed SPE method in conjunction with Arsenazo III procedure was tested by analyzing marine sediment (MESS-3) and soil (IAEA–Soil 7) reference materials. Furthermore, the above procedure has been successfully employed for the analysis of real soil and sediment samples.     

Electrostatic interactions between amphoteric latex particles and proteins

The electrostatic interactions between amphoteric polymethyl methacrylate latex particles and proteins with different pI values were investigated. These latex particles possess a net positive charge at low pH, but they become negatively charged at high pH. The nature and degree of interactions between these polymer particles and proteins are primarily controlled by the electrostatic characteristics of the particles and proteins under the experimental conditions. The self-promoting adsorption process from the charge neutralization of latex particles by the proteins, which have the opposite net charge to that of the particles, leads to a rapid reduction in the zeta potential of the particles (in other words colloidal stability), and so strong flocculation occurs. On the other hand, the electrostatic repulsion forces between similarly charged latex particles and the proteins retard the adsorption of protein molecules onto the surfaces of the particles. Therefore, latex particles exhibit excellent colloidal stability over a wide range of protein concentrations. A transition from net negative charge to net positive charge, and vice versa (charge reversal), was observed when the particle surface charge density was not high enough to be predominant in the protein adsorption process.     

Preparation and characterization of bismaleimide/1,3-dicyanatobenzene modified epoxy intercrosslinked matrices

An intercrosslinked network of cyanate ester (CE)-bismaleimide (BMI) modified epoxy matrix system was made by using epoxy resin, 1,3-dicyanatobenzene and bismaleimide (N,N^′-bismaleimido-4,4^′-diphenyl methane) with diaminodiphenylmethane as curing agent. BMI-CE-epoxy matrices were characterised using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and heat deflection temperature (HDT) analysis. The matrices, in the form of castings, were characterised for their mechanical properties such as tensile strength, flexural strength and unnotched Izod impact test as per ASTM methods. Mechanical studies indicated that the introduction of cyanate ester into epoxy resin improves the toughness and flexural strength with reduction in tensile strength and glass transition temperature, whereas the incorporation of bismaleimide into epoxy resin influences the mechanical and thermal properties according to its percentage content. DSC thermograms of cyanate ester as well as BMI modified epoxy resin show an unimodal reaction exotherm. Electrical properties were studied as per ASTM method and the morphology of the BMI modified epoxy and CE-epoxy systems were studied by scanning electron microscope.     

An Efficient and Environment Friendly Procedure for the Synthesis of Arylmethylenemalononitrile Catalyzed by Strong Base Anion‐Exchange Resin in Water

Abstract

Knoevenagel condensation of malononitrile with aromatic aldehydes catalyzed by strong base anion‐exchange resin in water results arylmethylenemalononitrile in 74–98% yield at room temperature.     

静电纺丝法制备酚醛纤维研究进展

酚醛树脂是一种广泛使用的合成树脂,包括热固性和热塑性两类,具有良好的阻燃性、耐热性和耐腐蚀性。酚醛纤维是由酚醛树脂所制成的交联纤维,传统的酚醛纤维制备方法有熔融纺丝法和湿法纺丝法,后来出现了静电纺丝法。本文根据酚醛树脂的种类分别介绍了热固性、热塑性和热塑/热固混合酚醛树脂三类材料静电纺丝的研究进展。在改善酚醛纤维特性方面,综述了四种优化措施,包括加入无机盐、微波辐射辅助固化、非匀速阶梯式加热固化、氧化石墨烯修饰的静电纺丝法等。此外,对本实验室制备酚醛纤维的研究也进行了概述,阐述了酚醛纤维当前存在的问题及未来发展方向。     

Methylol‐functional benzoxazines as precursors for high‐performance thermoset polymers: Unique simultaneous addition and condensation polymerization behavior

A new class of high‐performance resins of combined molecular structure of both traditional phenolics and benzoxazines has been developed. The monomers termed as methylol‐functional benzoxazines were synthesized through Mannich condensation reaction of methylol‐functional phenols and aromatic amines, including methylenedianiline (4,4′‐diaminodiphenylmethane) and oxydianiline (4,4′‐diaminodiphenyl ether), in the presence of paraformaldehyde. For comparison, other series of benzoxazine monomers were prepared from phenol, corresponding aromatic amines, and paraformaldehyde. The as‐synthesized monomers are characterized by their high purity as judged from ¹H NMR and Fourier transform infrared spectra. Differential scanning calorimetric thermograms of the novel monomers show two exothermic peaks associated with condensation reaction of methylol groups and ring‐opening polymerization of benzoxazines. The position of methylol group relative to benzoxazine structure plays a significant role in accelerating polymerization. Viscoelastic and thermogravimetric analyses of the crosslinked polymers reveal high T_g (274–343 °C) and excellent thermal stability when compared with the traditional polybenzoxazines. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Preparation and characterization of novel organic chelating resin and its application in recovery of Zn(II) from aqueous solutions

An organic polymeric resin was synthesized by anchoring p ‐aminobenzoic acid onto macroporous chloromethylated polystyrene beads, and was used for Zn(II) removal from aqueous solutions. The resin exhibited an initially rapid adsorption property for Zn(II) with equilibrium time of 10 h and the maximum adsorption capability approached 184.5 mg g⁻¹. Optimum pH was 4.5. The mechanism of adsorption was investigated using kinetic, isotherm and thermodynamic models. The adsorption kinetic data were described well by a pseudo second‐order model with R ² of 0.997. There was a negative ΔG (−17.98 kJ mol⁻¹) and positive ΔH (13.58 kJ mol⁻¹). HCl solution (1.0 mol l⁻¹) could achieve an elution rate of 100%. The experimental data were well fitted by the Thomas model with R ² of 0.9826. Copyright © 2016 John Wiley & Sons, Ltd.     

含氟嵌段聚合物改性环氧树脂性能研究

用AGET ATRP法制备含环氧基的含氟嵌段聚合物聚甲基丙烯酸六氟丁酯-b-聚甲基丙烯酸缩水甘油酯(PHFMA-b-PGMA),将其用于双酚A型环氧树脂改性.表面性能测试表明,PHFMA-b-PGMA改性环氧涂膜的表面疏水疏油性优于纯环氧,且经长时间水浸泡、丁酮浸泡或高温热处理后,其表面稳定性仍表现优良.热性能测试表明,PHFMA-b-PGMA改性环氧的热稳定性优于纯环氧.机械性能测试结果表明,用PHFMA-bPGMA改性环氧有助于韧性提高,与断裂面SEM测试结果相吻合.