Cooperative folding kinetics of BBL protein and peripheral subunit-binding domain homologues

Recent experiments claiming that Naf-BBL protein follows a global downhill folding raised an important controversy as to the folding mechanism of fast-folding proteins. Under the global downhill folding scenario, not only do proteins undergo a gradual folding, but folding events along the continuous folding pathway also could be mapped out from the equilibrium denaturation experiment. Based on the exact calculation using a free energy landscape, relaxation eigenmodes from a master equation, and Monte Carlo simulation of an extended Muñoz–Eaton model that incorporates multiscale-heterogeneous pairwise interactions between amino acids, here we show that the very nature of a two-state cooperative transition such as a bimodal distribution from an exact free energy landscape and biphasic relaxation kinetics manifest in the thermodynamics and folding–unfolding kinetics of BBL and peripheral subunit-binding domain homologues. Our results provide an unequivocal resolution to the fundamental controversy related to the global downhill folding scheme, whose applicability to other proteins should be critically reexamined.     

Scaling Law of the Disjoining Pressure Reveals 2D Structure of Polymeric Fluids

A scaling relation for the disjoining pressure of strongly confined polymer fluids is proposed for the first time, which yields directly the scaling exponent ν of the radius of gyration for polymers. To test the proposed scaling relation we performed extensive particle‐based, coarse‐grained computer simulations of polymers confined under θ‐solvent conditions and found that the value of ν agrees with the expected value for strictly two dimensional chains, ν = 4/7, which points towards the essential correctness of our scaling relation. New approaches are suggested for experimental tests of this scaling law. This work opens up the way to look for other scaling exponents that may reveal new physical regimes and it constitutes an efficient route to determine ν because the scaling exponent can be obtained with chains of a single polymerization degree by simply reducing the distance between the confining plates.

     

Partial Molar Volumes and Thermal Expansion Coefficients as an Explanation for Co‐Solvent Effect of Penetrants in Multicomponent Polymer Mixtures

Experimental mixed‐gas sorption/dilation data and mixture densities estimated by the fitted Sanchez–Lacombe equation of state have been used to estimate the partial molar volumes (PMV) of gases and polymers in multicomponent mixtures (i.e., ternary) at conditions of industrial relevance. The method developed estimates accurately the PMV and volumetric thermal expansion coefficients of various highly soluble gases and polymers in multicomponent mixtures over a wide range of temperatures, pressures, and gas phase compositions. A comparison of solubility, volumetric thermal expansion coefficients, and PMVs of the gases involved in the studied ternary mixtures reveal that, irrespective of the polymer nature, co‐solvent effect is caused by the gas with higher solubility in the polymer phase and higher thermal expansion coefficient, which provides an explanation to the occurrence of co‐solubility effects in multicomponent gases/polymer mixtures. It has also been shown that the PMV behavior of gases in the ternary mixtures with polymers is different from their PMV behavior in the corresponding binary gas/polymer mixtures, and that the PMV of a gaseous penetrant in a multicomponent system depends on its gas phase concentration.

     

Kinetic Study of D,L‐Lactide and Glycolide Homopolymerizations by Differential Scanning Calorimetry

The homopolymerizations of D ,L ‐lactide and glycolide catalyzed by ZnOct₂ were studied by DSC. The kinetic parameters obtained are compared with those obtained from conversion data of bulk polymerizations. For the glycolide, the respective values of the calculated rate constants were quite similar. For the lactide polymerization, however, the agreement between the values obtained was not so good because the kinetics is affected by thermodynamics in the DSC experiments. As a result, the kinetics can not be studied by DSC. The degree of aggregation of the catalyst, the reaction order with respect to it, and the initiator influence were determined for glycolide homopolymerization.

     

中药四性研究现状与设想

根据近十年发表的国内外文献,结合自已的科研工作和体会,分析了目前中药四性研究现状及存在的问题,提出应根据热力学第一定律,Hess定律,建立生物热焓状态数学模型进行生物热力学研究,以阐明中药的四性问题。     

阴离子交换树脂与双氯芬酸钠的交换反应特性

目的研究阴离子交换树脂与双氯芬酸钠的交换反应特性。方法以双氯芬酸钠为模型药物,以强碱性阴离子交换树脂(201 ×7)为载体,采用静态法制备药物树脂,考察了阴离子交换树脂不同类型(OH-和Cl-)、树脂粒径以及反应温度对交换过程的影响,并对交换动力学曲线进行了拟合,考察了离子交换反应速率常数、活化能和选择性系数,同时考察了交换反应热力学参数吉布斯自由能变化,反应焓变化和反应熵变化。结果Cl-型OH-型阴离子交换树脂对双氯芬酸钠的载药能力相同。树脂粒径越小,反应温度越高,则反应速率越快。药物树脂间的交换反应符合一级动力学反应,反应活化能约为60·68 kJ·mol-1。在303K、313K和323K三种温度下得到的热力学参数都满足于ΔrGθm<0,ΔrHmθ>0 andΔrSmθ>0。结论药物与树脂的交换过程主要受树脂粒径和反应温度的影响,而且该离子交换反应是吸热反应,即升高温度有助于反应正向自发进行。     

中药药性研究概论

当今中药药性研究热潮越来越高.在回顾原有研究的基础上,对中药药性研究存在的问题进行反思,指出中药药性研究在近期内要取得重大突破,应进一步凝练研究目标,理清研究思路,规范研究方法.寒热药性可作为首要突破口;建立寒热药性的客观评价方法,阐明寒热药性的客观真实性将是中药药性理论研究的首要关键科学问题之一.首次提出并建立了基于还原整合和热力学表达的中药药性研究模式和方法.     

Polymer Brushes by Grafting to Reaction in Melt: New Insights into the Mechanism

Ultrathin films of end-tethered polymers, generally indicated as polymer brushes, have gained great interest for their ability to modify the surface interaction with the surrounding environment. One of the most common strategies to obtain polymer brushes is based on the reaction of end-functional polymers with the substrate surface, in a process defined as grafting to. The two advantages of grafting to reactions are i) the functional polymer is prepared before the grafting reaction and therefore can be fully characterized and ii) the reaction has a self-limiting nature, meaning that the number of grafted chains converges to a plateau value after a sufficiently long reaction time. The limit value of grafted chains is governed by the molecular weight of the employed polymer, thus allowing a fine control of the brush thickness. In this work, the origin of the self-limiting nature of the grafting to reaction is discussed comparing theoretical models with experimental data. Furthermore, the kinetics of the process is discussed, considering both polymer diffusion and end-group reactivity as the main drivers of the grafting to process. Finally, the effect of molecular weight dispersity on the brush characteristics is highlighted.     

Effect of Ionic Strength and Anion Identity on Rare-Earth Element Chelation by Poly(acrylic acid)

Rare-earth elements (REEs) are critical components of many modern technologies, but their efficient separation and purification continue to pose significant challenges. Metal-binding polymers may enable the development of promising alternative approaches to conventional separation techniques (e.g., solvent extraction), and insights into the interactions between the metal ions and polymers in solution are crucial to such development. In this work,  the effect of ionic strength on the chelation of REEs by poly(acrylic acid) is investigated using isothermal titration calorimetry (ITC) to measure the metal-binding thermodynamics. ITC experiments revealed that when ionic strength increases from increasing the sodium acetate buffer strength, polymer-REE binding becomes increasingly disfavored. However, when ionic strength is increased by the addition of sodium chloride, binding again becomes increasingly disfavored, but to a lesser extent than when ionic strength increases from increasing the buffer strength. Additionally, the reduction in binding affinity is enthalpically driven when ionic strength is raised with sodium chloride, while it is entropically driven when raised with sodium acetate buffer, suggesting competive binding by the acetate ions. These results highlight the importance of ionic strength in polymer-metal binding thermodynamics and will guide the development of new processes for the purification of critical metals.