Zhangfa Tong

Analytical equation of state based on the Ornstein-Zernike equation

A new two-Yukawa function is found to mimic very closely the Lennard-Jones potential. Simple analytical expressions are developed for the structure and thermodynamic properties of the Lennard-Jones fluid, utilizing the new function. The results from the expressions developed are satisfactorily compared with the Monte Carlo simulation data, the theory of Weeks et al. and the latest 33-parameter equation of state (EOS). The phase diagram of the Lennard-Jones fluid is also well predicted by the new EOS. The properties of four real fluids (argon, methane, oxygen and nitrogen) are calculated using the present EOS. Some noticeable improvements over the Peng-Robinson EOS are found for the calculation of saturated liquid densities and second virial coefficients.

Thermal degradation kinetics study of curcumin with nonlinear methods

The results of TG/DTG when curcumin was used as the food colouring agent indicated that the processing temperature of the food should not exceed 190°C. The decomposition process of curcumin involved two stages. The results of Eα values, determined by an advanced isoconversional method, showed that the two stages were both single-step processes. The most probable mechanisms of the two stages were estimated by using comparative and nonlinear model-fitting methods. The mechanisms obtained from the two methods are the same, which are the assumed random nucleation and its subsequent growth for stage I and one-dimensional diffusion for stage II, respectively. The values of pre-exponential factor A for both stages were obtained on the basis of Ea and g(α). Besides, some thermodynamic functions (ΔS(≠), ΔH(≠) and ΔG(≠)) of the transition state complexes for the two stages were also calculated.

Rapid purification and characterization of angiotensin converting enzyme inhibitory peptides from lizard fish protein hydrolysates with magnetic affinity separation

In this study, angiotensin converting enzyme (ACE) inhibitory peptides from lizard fish protein hydrolysate with neutral protease were purified through magnetic affinity separation. Magnetic agarose microsphere was prepared by reverse-phase microemulsion method, and its surface was modified with epoxy groups to immobilize ACE as a magnetic affinity medium (MAM-ACE) and then mixed with lizard fish ultrafiltration hydrolysate (<5 kDa). The MAM-ACE was recovered by a magnet. The bound peptides were released by 1M NaCl and further purified by reverse-phase high-performance liquid chromatography. The amino acid sequence of the peptide with the highest ACE inhibitory activity was identified as Gly-Met-Lys-Cys-Ala-Phe, and its IC50 was 45.7 ± 1.1 μM. The result indicates that MAM-ACE is a faster and more efficient method for purifying micro-bioactive peptides from food protein complex mixtures compared with ion exchange and gel chromatography.

Optimization of Hydrolysis Conditions for the Production of Angiotensin-I Converting Enzyme-Inhibitory Peptides and Isolation of a Novel Peptide from Lizard Fish (Saurida elongata) Muscle Protein Hydrolysate

Lizard fish (Saurida elongata) muscle protein was hydrolyzed using neutral protease to produce protein hydrolysate (LFPH), and the hydrolysis conditions were investigated using response-surface methodology. The optimum conditions for producing peptides with the highest angiotensin-I converting enzyme (ACE)-inhibitory activity were the following: enzyme-to-substrate ratio of 10,000 U/g, temperature of 48 °C, pH 7.0, and hydrolysis time of 2 h. Under these conditions, the ACE-inhibitory activity of LFPH and the degree of hydrolysis were 84% and 24%, respectively. A novel ACE-inhibitory peptide was isolated from LFPH using ultrafiltration, Sephadex G-15, and high-performance liquid chromatography. The amino acid sequence of the ACE-inhibitory peptide was identified as Ser-Pro-Arg-Cys-Arg (SPRCR), and its IC50 was 41 ± 1 µM.

Excess molar enthalpies of ternary mixtures of an n-alkane, ethanol and methyl 1,1-dimethylpropyl ether

Abstract Excess molar enthalpies, measured at 298.15 K in a flow microcalorimeter, are reported for x1CH3(CH2)yCH3 + x2C2H5OH + x3C2H5C(CH3)2OCH3, where v is 5 and 8. Smooth representations of the results are presented and used to construct constant excess molar enthalpy contours on Roozeboom diagrams.

Recent progress of synthesis and applications in polyoxometalate and nanogold hybrid materials

The role of polyoxometalates (POMs) in the synthesis and stabilization of gold nanoparticles (Au NPs) is reviewed in light of many of the recent developments. The vitality of these hybrid materials is discussed with many examples of POMs and different synthesis techniques. Also, applications of these newly emerging hybrid materials in numerous fields such as electrocatalysis, photocatalysis, biomass catalysis, oxidation of alkenes, bio-sensing, and medicinal use are highlighted. Limitations in these applications are indicated, and areas of future applications that could be explored in these vast ranging hybrid materials are described.

A FLUORESCENCE QUENCHING METHOD FOR DETERMINATION OF COPPER IONS WITH CDTE QUANTUM DOTS

ABSTRACT CdTe quantum dots (QDs) were synthesized in aqueous medium by employing L-cysteine as a stabilizer. They exhibited high stability and moderate fluorescence quantum yield (12.5%), and were characterized by UV-vis absorption, fluorescence spectra, Fourier transform infrared spectrometry. Based upon the fact that the fluorescence of the QDs could be quenched by Cu 2+ , a simple and rapid method for Cu 2+ detection was proposed using L-cysteine-capped CdTe QDs as fluorescent probes. Under optimum conditions, the response showed linear proportion to the concentration of Cu 2+ between 20 to 300μg·L -1 . The detection limit was 9.3μg·L -1 . This method was successfully applied to the determination of trace copper in real samples. Keywords: CdTe, Quantum dots, Fluorescence quenching, Copper ions INTRODUCTION Luminescent semiconductor quantum dots (QDs) is a novel fluorescence nano-material, which have gained increasing attention in the past decades. Compared with conventional organic dyes, QDs have some unique optical and electronic properties, such as broad excitation spectra, narrow, tunable and symmetric emission spectra, and highly stability against photobleaching

Modeling of Esterification in a Batch Reactor Coupled with Pervaporation for Production of n-Butyl Acetate

Abstract A mathematical model for esterification in a batch reactor coupled with pervaporation to describe a simultaneous reaction and water removal from the reactor was developed. The permeation of all components in the reaction mixture and their non-ideal thermodynamic behavior were taken into account. The esterification of acetic acid with n -butanol for the production of n -butyl acetate integrated with a poly(vinyl alcohol) pervaporation membrane was selected as the model system for this study. The validity of the model was tested by comparing the calculated results with experimental data reported in the literature. The results show that the esterification is facilitated by water removal using pervaporation, which accelerates the rate of ester formation. A parametric study was carried out to evaluate the effects of operating conditions on the performance of the pervaporation-coupled esterification reactor and this included temperature, initial composition of the reactants, membrane area relative to the reactors size, and catalyst concentration. Based on these results, suitable operating conditions for the membrane-integrated reaction process are discussed.

UV-H2O2 degradation of methyl orange catalysed by H3PW12O40/activated clay.

A catalyst consisting of phosphotungstic acid (H3PW12O40) combined with activated clay was prepared by the impregnation method, and an experiment was carried out to evaluate the catalytic activity of the H3PW12O40/activated clay for the degradation of methyl orange (MO) in the UV–H2O2 process. The degradation ratio of MO can be affected by H2O2 concentration, reaction time, catalyst dosage, pH and temperature. The reaction temperature should be controlled at less than 70 °C, and the catalyst has a wide applicable pH range in the UV–H2O2 process. Hydroxyl radicals were generated in the UV–H2O2 system under the action of H3PW12O40/activated clay, and MO was degraded by hydroxyl radicals. Compared with traditional catalysts used in UV–H2O2 systems, H3PW12O40/activated clay has certain advantages for its practical application.

Boron Nitride Nanowires Produced on Commercial Stainless Steel foil

Abstract Chemical vapor deposition growth of one-dimensional nanomaterials usually demands substrates that have been coated with a layer of catalyst film. In this study, a green process to synthesize boron nitride (BN) nanowires directly on commercial stainless steel foils was proposed by heating boron and zinc oxide powders under a mixture gas flow of N2 and 15% H2 at 1100°C, and a large quantities of pure h-BN nanowires have been produced directly on commercial stainless steel foil. The stainless steel foils not only acted as the substrate but also the catalyst for the nanowire growth. The synthesized BN nanowires were characterized by X-ray diffraction, scanning and transmission electron microscopes, X-ray energy dispersive spectrometer and photoluminescence spectroscopy. The nanowires also possess strong PL emission bands at 515, 535, and 728 nm.