Methanolysis of poly(lactic acid) (PLA) catalyzed by ionic liquids

Poly(lactic acid) (PLA) was depolymerized by methanol in the presence of a novel catalyst: ionic liquids. It was found that the purification method of the main products in the methanolysis catalyzed by ionic liquids was simpler than that of traditional compounds, such as sulfuric acid. Qualitative analysis indicated that the main product in the methanolysis process was methyl lactate. The influences of experimental parameters, such as the amount of ionic liquids, methanolysis time, reaction temperature, and dosages of methanol on the conversion of PLA, yield of methyl lactate were investigated. Under the optimum conditions, using ionic liquid 1-butyl-3-methylimidazolium acetate ([Bmim][Ac]) as catalyst, results showed that the ionic liquid could be reused up to 6 times without apparent decrease in the conversion of PLA and yield of methyl lactate. The kinetics of the reaction was also investigated. The results indicated that the methanolysis of PLA was a first-order kinetic reaction with activation energy of 38.29 kJ/mol. In addition, a possible catalysis mechanism of the methanolysis of PLA was proposed.     

An efficient strategy for unmodified nucleotide-mediated dispersion of magnetic nanoparticles,leading to a highly sensitive MRI-based mercury ion assay

It is highly attractive to develop a detection system that is not only sensitive and selective but also simple, rapid, practical and cost-effective in operation. Here, we report an interesting observation that single-stranded oligonucleotide (ssDNA) can adsorb efficiently on carboxylic acid-functionalized magnetic nanoparticles (CAMNPs) and stabilize the nanoparticles against aggregation in weakly acidic solution. The adsorbing rate closely correlates with the pH of the solution, the temperature and the sequence length of ssDNA. On the basis of this observation, we have designed a highly sensitive, non-sandwich type magnetic relaxation-based detection system for quantitatively probing mercury ion. The assay is independent of the sample's optical properties, requires no covalent modification of the ssDNA or the CAMNPs surfaces, and can be used for high-throughput analysis. By varying the concentration of CAMNPs, four orders of dynamic response range and a detection limit of 0.3 nM for Hg²⁺ are achieved. Moreover, we developed a multi-sample assay to detect Hg²⁺ in real environmental samples with high sensitivity, selectivity and efficiency.     

Synthesis of original spherical α-Ni(OH)2 architectures by microwave-assisted hydrothermal method and their in situ thermal convention to NiO

The original spherical α-Ni(OH)₂ architectures with many cubic particles growing from the surface were successfully synthesized by a microwave-assisted hydrothermal method using urea as hydrolysis-controlling agent and polyethylene glycol (PEG) as surfactant. The NiO architectures with similar morphology were obtained by simple thermal decomposition of the precursor α-Ni(OH)₂. The as-obtained products were well characterized by XRD, FTIR, TGA, SEM, TEM, UV–Vis and CVs. The experimental results showed that the diameter of spherical α-Ni(OH)₂ architectures was in the range of 2–4 μm. The side length of the cubic particles was uniform about 200 nm. The cyclic voltammetric results showed that the reversible behavior of NiO electrode change better with the increasing of the cycle index. The original NiO we have prepared are expected to have good electrochemical behavior.     

Dynamics analysis of a delayed viral infection model with logistic growth and immune impairment

In this paper, the dynamics behavior of a delayed viral infection model with logistic growth and immune impairment is studied. It is shown that there exist three equilibria. By analyzing the characteristic equations, the local stability of the infection-free equilibrium and the immune-exhausted equilibrium of the model are established. By using suitable Lyapunov functional and LaSalle invariant principle, it is proved that the two equilibria are globally asymptotically stable. In the following, the stability of the positive equilibrium is investigated. Furthermore, we investigate the existence of Hopf bifurcation by using a delay as a bifurcation parameter. Finally, numerical simulations are carried out to explain the mathematical conclusions.     

微孔中简单流体混合物扩散系数的分子动力学模拟与关联

为了了解简单流体混合物在微孔介质中的流动和传递性质 ,对微孔中氩和氪流体混合物的扩散系数进行了计算机模拟和关联模型研究 .运用平衡分子动力学方法模拟了宏量条件下饱和氩流体的扩散系数和恒温氪流体的扩散系数 ,模拟值与文献实验值符合良好 ,从而程序的正确性得到验证 .然后 ,采用类似Bitsanis等人的方法模拟了平板湿壁微孔中氩和氪等摩尔流体混合物在不同对比温度、不同对比密度以及不同对比孔径条件下的扩散系数 ,发现孔径很小的时候扩散系数会急剧的增大 .同时基于这些模拟值 ,参考CE理论和Heyes关系式 ,以对比温度、对比密度以及对比孔径为变量 ,关联出两个简单流体等摩尔混合物在微孔中扩散系数的计算模型 .模型的计算结果与计算机模拟值能够较好地吻合     

Investigation on isobaric vapor liquid equilibrium for acetic acid + water + (n-propyl acetate or iso-butyl acetate)

Isobaric vapor-liquid equilibrium (VLE) data for acetic acid + water, acetic acid + n-propyl acetate, acetic acid + iso-butyl acetate, acetic acid + water + n-propyl acetate, acetic acid + water + iso-butyl acetate are measured at 101.33 kPa with a modified Rose still. The nonideal behavior in vapor phase caused by the association of acetic acid are corrected by the chemical theory and Hayden-O’Connell method, and analyzed by calculating the second virial coefficients and apparent fugacity coefficients. The VLE data for acetic acid + water, acetic acid + n-propyl acetate, and acetic acid + iso-butyl acetate are correlated through the NRTL and UNIQUAC models using the nonlinear least square method. The obtained NRTL model parameters are used to predict the ternary VLE data. The ternary predicted values obtained in this way agree well with the experimental values.