Ultrasound irradiation alters the spatial structure and improves the antioxidant activity of the yellow tea polysaccharide

In this study, the impact of ultrasound irradiation on the structural characteristics and antioxidant properties of yellow tea polysaccharides with different molecular weights (Mw) were investigated. Native yellow tea polysaccharide containing YTPS-3N, YTPS-5N and YTPS-7N were prepared through precipitation with ethanol at various concentrations of 30%, 50%, and 70%, respectively, and irradiated with high intensity ultrasound (20 kHz) for 55 min to yield yellow tea polysaccharide including YTPS-3U, YTPS-5U and YTPS-7U. The molecular weight (Mw) of YTPS-3N (from 37.7 to 15.1 kDa) and YTPS-5N (from 14.6 to 5.2 kDa) sharply decreased upon ultrasound irradiation, coincidentally particle size (Zavg) was also significantly reduced for YTPS-3N (40%), YTPS-5N (48%) and YTPS-7N (54%). The high-performance liquid chromatography and Fourier transform-infrared spectroscopy analysis revealed a partial degradation of native yellow tea polysaccharide treated with ultrasound, though the monosaccharide composition was not altered. Furthermore, changes in morphology and the breakdown of native yellow tea polysaccharide upon irradiation was confirmed with the circular dichroism spectrum, atomic force and scanning electron microscopy. As a consequence, irradiation of yellow tea polysaccharide increased free radical scavenging activity with YTPS-7U exhibiting the highest levels of 2, 2-diphenyl-1-picrylhydrazyl free radical, superoxide and hydroxyl radicals scavenging activity. These results suggest that the alteration of the spatial structure of yellow tea polysaccharide can enhance its antioxidant activity which is an important property for functional foods or medicines.     

“Exact” and Approximate Methods for Bayesian Inference: Stochastic Volatility Case Study

We conduct a case study in which we empirically illustrate the performance of different classes of Bayesian inference methods to estimate stochastic volatility models. In particular, we consider how different particle filtering methods affect the variance of the estimated likelihood. We review and compare particle Markov Chain Monte Carlo (MCMC), RMHMC, fixed-form variational Bayes, and integrated nested Laplace approximation to estimate the posterior distribution of the parameters. Additionally, we conduct the review from the point of view of whether these methods are (1) easily adaptable to different model specifications; (2) adaptable to higher dimensions of the model in a straightforward way; (3) feasible in the multivariate case. We show that when using the stochastic volatility model for methods comparison, various data-generating processes have to be considered to make a fair assessment of the methods. Finally, we present a challenging specification of the multivariate stochastic volatility model, which is rarely used to illustrate the methods but constitutes an important practical application.     

Closed-packed lattice model for polymer solution systems considering the chain length dependence effect: Correlating LLE,VLE, and gel swelling behaviors using identical interaction energy parameters

We propose a new Helmholtz energy of mixing equation following the original Flory–Huggins (F–H) closed-packed lattice model. Also, to overcome F–H mean-field approximation, we introduce new universal constants to consider chain length dependence of polymer in solvent and consider specific interactions to describe strongly interacting polymer systems. Our proposed model successfully describes liquid–liquid equilibria (LLE) for binary polymer–solvent systems using identical interaction parameters which do not depend on the polymer molecular weight. We also describe vapor–liquid equilibria (VLE) for polymer/solvent systems and swelling equilibria of thermosensitive hydrogel systems using the same energy parameters obtained from LLE calculations.     

Studies on novel thermally stable segmented polyurethanes based on thiourea-derivative diols

Novel thermoplastic segmented poly(urethane-thiourea)s (PURs) were synthesized via one-step polymerization from aromatic diols containing sulfur (thiourea linkage) in the main-chain, including terephthaloyl bis (3-(2-hydroxopyridyl) thiourea) (TBHPT) and terephthaloyl bis (3-(5-naphtholyl) thiourea) (TBNT), along with 1,4-phenylene diisocyanate (PDI) as hard segment and 20, 50 and 80 mol% polyethylene glycol (PEG) as a soft segment. The prepared chain extenders and polymers were characterized by conventional methods, and physical properties such as η_inh, solubility, thermal stability and thermal behavior were studied. Easily processable PURs with excellent thermal stability were obtained by incorporating 20 mol% PEG in the soft segment. Thermogravimetric analysis indicated that poly(urethane-thiourea)s were fairly stable above 500 °C and own high glass transition temperatures about 263-266 °C. These polymers also showed partially crystalline structures. Ultimately, weight average molecular weights (M_w) of PURs were up to 109 × 10³. Compared to typical polyurethanes, PURs exhibited better thermal stability and T_g’s owing to rigid hard segment structure.     

An optimized protocol for the multigram synthesis of 3-(trifluoromethyl)bicyclo[1.1.1]pent-1-ylglycine (CF3-Bpg)

An optimized procedure for the multigram synthesis of 3-(trifluoromethyl)bicyclo[1.1.1]pent-1-ylglycine (CF₃-Bpg) has been developed. The overall yield of the synthesis for the optimized up-scaling was increased from 35% to 53%. Moreover, conditions for separating the key isomeric aminonitriles 7 and 8 by crystallization were found, which greatly facilitated the isolation of 8 on a multigram scale. Following this optimized protocol, 100 g of optically pure CF₃-Bpg have been synthesized.     

A comprehensive Monte Carlo simulation of styrene atom transfer radical polymerization

<正>An optimized and high-performance Monte Carlo simulation is developed to take thorough account of four different cases of termination in styrene ATRP.According to the simulation results,the bimolecular termination rate constant sharply drops throughout the polymerization when either chain-length dependency of termination rate constant,gel effect,or both together is applied to the simulation.In addition,as expected,the initiator is quickly decomposed at the early stages of the polymerization.The concentration of the catalyst in lower oxidation state decreases at first and then plateaus at higher conversion;furthermore,the steady concentration of M_t~nY/L in the polymerization is the highest when the chain-length-dependent diffusion-controlled termination rate constant is employed in the simulation.The rates of deactivation and chain end degradation reactions are also smaller in this case.Therefore,the fraction of dormant chains is higher throughout the reaction and consequently the portion of dead polymers decreases.Besides,molecular weight increases linearly with conversion;however,when neither gel effect nor chain-length dependency of termination rate constant is considered,the molecular weight deviates from linearity at the end of the reaction.The peak of chain length distribution shifts toward higher molecular weight too during the reaction.Finally,the molecular weight distribution broadens at higher conversion;however, the chain length distribution of polymers produced under conditions of applying chain-length-dependent diffusion-controlled termination rate constant is narrower.     

菌类多糖链构象及其表征方法研究进展 （专题报道）

 概述了菌类多糖在溶液中链构象及其表征方法的研究进展.主要报道从各种真菌（香菇、茯苓、灵芝、木耳、黄单胞菌、裂褶菌等）中提取的多糖在溶液中的分子量、分子形态和尺寸,即链构象.同时介绍多糖链构象对生物活性的影响,并且指出多糖刚性链带电基团及适量分子量有利于促进它与免疫细胞上受体结合,从而抑制肿瘤细胞增殖.由此表明,多糖链构象的研究对弄清其生物功能和推动生命科学发展十分重要.多糖在溶液中主要以无规线团、双螺旋、三螺旋、蠕虫状、棒状链以及聚集体构象存在,它取决于单糖组成、糖苷键、支链结构以及分子内和分子间作用力.测定链构象的方法主要包括光散射、黏度、显微技术（透射电镜,扫描电镜以及原子力显微镜）、微量热法和小角X-射线散射等.此外,介绍了多糖溶液理论以及计算链构象参数的表达式.     

VDF/CTFE共聚物原子转移自由基反应法氢化制备VDF/TrFE/CTFE三元共聚物的研究

报道了一种用于偏氟乙烯-三氟氯乙烯共聚物(VDF/CTFE共聚物)制备偏氟乙烯/三氟乙烯/三氟氯乙烯共聚物(VDF/TrFE/CTFE共聚物)的新方法,该方法以CuCl与2′,2-Bpy的配合物为催化剂,N-甲基吡咯烷酮(NMP)为溶剂,异丙苯(丙酮、2,6-二叔丁基-4-甲基苯酚)为链转移剂,通过原子转移法在VDF/CTFE共聚物上产生自由基,进而利用自由基链转移反应将VDF/CTFE共聚物上部分Cl原子用H原子取代以制备VDF/TrFE/CTFE三元共聚物.对该体系的反应机理及其影响因素进行研究发现,随着实验温度的升高(80～140℃),反应时间的延长,氢化量增加,产物中TrFE含量增加;反应温度越高,初始反应速度越快,完全氢化时间越短;催化剂与氢化量的比例基本为1:1,通过控制催化剂的量可以定量控制氢化率;新的反应体系不会对产物的分子量产生大的影响.     

由对苯二甲酰胺二醇合成聚酯酰胺及其扩链反应的研究

以N,N′-二(2-羟乙基)对苯二甲酰胺与己二酸及丁二醇缩聚,合成了同时带有端羧基与端羟基的聚酯酰胺预聚体,研究了不同扩链剂的扩链反应,获得了特性黏度达1.05 dL/g的聚酯酰胺.对预聚体及扩链后聚合物进行了红外与核磁表征,研究了聚合物的结构,并对聚合物进行了DSC与TG分析.     

Structure factor of ferrofluids with chain aggregates: Theory and computer simulations

In this paper we present theoretical and simulation results on the structure factor of mono- and bidisperse ferrofluids with chain aggregates, both with and without an applied external magnetic field. Chain distribution is obtained by the density functional theory (DFT). The radial distribution function (RDF) is calculated directly on the basis of the chain distribution and Fourier transformed to calculate the structure factor. An extensive comparison of the theoretical predictions to the results of the molecular dynamics computer simulations is provided. The proposed combined approach allows to elucidate the connection between experimentally observed small angle neutron scattering (SANS) images and the ferrofluid microstructure.