Effects of mussel-inspired co-deposition of 2-hydroxymethyl methacrylate and poly (2-methoxyethyl acrylate) on the hydrophilicity and binding tendency of common hemodialysis membranes: Molecular dynamics simulations and molecular docking studies

Despite advances in the field, hemoincompatibility remains a critical issue for hemodialysis (HD) as interactions between various human blood constituents and the polymeric structure of HD membranes results in complications such as activation of immune system cascades. Adding hydrophilic polymer structures to the membranes is one modification approach that can decrease the extent of protein adsorption. This study conducted molecular dynamics (MD) simulations to understand the interactions between three human serum proteins (fibrinogen [FB], human serum albumin, and transferrin) and common HD membranes in untreated and modified forms. Poly(aryl ether sulfone) (PAES) and cellulose triacetate were used as the common dialyzer polymers, and membrane modifications were performed with 2-hydroxymethyl methacrylate (HEMA) and poly (2-methoxyethyl acrylate) (PMEA), using polydopamine-assisted co-deposition. The MD simulations were used as the framework for binding energy simulations, and molecular docking simulations were also performed to conduct molecular-level investigations between the two modifying polymers (HEMA and PMEA) and FB. Each of the three proteins acted differently with the membranes due to their unique nature and surface chemistry. The simulations show PMEA binds less intensively to FB with a higher number of hydrogen bonds, which reflects PMEA's superior performance compared to HEMA. The simulations suggest PAES membranes could be used in modified forms for blood-contact applications as they reflect the lowest binding energy to blood proteins.     

RDX分子内振动能量重分配的动力学研究

基于从头算分子动力学(Born-oppenheimer molecular dynamics, BOMD)模拟, 构建了环硝胺六氢-1,3,5-三硝基-1,3,5-三嗪(RDX)单分子不同振动模式之间的耦合矩阵, 并计算了在不同加载能量下从低频振动模式到高频振动模式的最优能量传输路径. 结果表明, RDX单分子中—NNO₂基团更有利于能量局域化, 振动模式v₃和v₄在从低频振动模式到高频振动模式的能量传输过程中扮演着重要角色. 通过对v₃和v₄两个振动模式的进一步分析发现, 加载能量的不同会导致RDX单分子能量传输路径的不同. 当加载能量较低时, RDX单分子倾向于从低频振动模式到中频振动模式再到高频振动模式的能量传输路径; 当加载能量较高时, 能量更倾向于从低频振动模式直接传输到高频振动模式上. 揭示了RDX分子内振动耦合能量转移的微观机制, 为进一步探索RDX将“机械能”转化为“化学能”的微观过程提供了理论基础.     

Macrocycle Dynamics in a Branched [8]Catenane Controlled by Three Different Stimuli in Three Different Regions

A branched [8]catenane from an efficient one-pot synthesis (72 % HPLC yield, 59 % isolated yield) featuring the simultaneous use of three kinds of templates and cucurbit[6]uril-mediated azide–alkyne cycloaddition (CBAAC) for ring-closing is reported. Design and assembly of the [8]catenane precursors are unexpectedly complex that can involve cooperating, competing and non-influencing interactions. Due to the branched structure, dynamics of the [8]catenane can be modulated in different extent by rigidifying/loosening the mechanical bonds at different regions by using solvent polarity, acid-base and metal ions as the stimuli. This work not only highlights the importance of understanding the delicate interplay of the weak and non-obvious supramolecular interactions in the synthesis of high-order [n]catenane, but also demonstrates a complex control of dynamics and flexibility for exploiting [n]catenanes applications.     

Effects of ball-to-powder diameter ratio and powder particle shape on EDEM simulation in a planetary ball mill

The effects of the ball-to-powder diameter ratio (BPDR) and the shape of the powder particles on EDEM simulation results and time in the planetary ball mill was investigated. BPDR was varied from 1 to 40/3 by changing the powder particle diameter from 8 to 0.6 ?mm. The size and shape of the powder particles do not give a significant change in both the ball motion pattern and simulation results when BPDR is over 20/3. It can be assumed that the kinetic energy of the ball has nothing to do with the size and shape of the powder particle. The simulation time and data size increase exponentially as BPDR increases. The effect of change of the powder particle shape on the calculated data size is not significant, but the more complicated its shape, the longer the simulation time, which is linearly related to the number of spheres composing a particle.     

A two-point calibration method for quantifying organic binary mixtures using secondary ion mass spectrometry in the presence of matrix effects

Quantification of the composition of binary mixtures in secondary ion mass spectrometry (SIMS) is required in the analyses of technological materials from organic electronics to drug delivery systems. In some instances, it is found that there is a linear dependence between the composition, expressed as a ratio of component volumes, and the secondary ion intensities, expressed as a ratio of intensities of ions from each component. However, this ideal relationship fails in the presence of matrix effects and linearity is observed only over small compositional ranges, particularly in the dilute limits. In this paper, we assess an empirical method, which introduces a power law dependence between the intensity ratio and the volume fraction ratio. A previously published physical model of the organic matrix effect is employed to test the limits of the method and a mixed system of 3,3′-bis(9-carbazolyl) biphenyl and tris(2-phenylpyridinato)iridium (III) is used to demonstrate the method. This paper introduces a two-point calibration, which determines both the exponent in the power law and the sensitivity factor for the conversion of ion intensity ratio into volume fraction ratio. We demonstrate that this provides significantly improved accuracy, compared with a one-point calibration, over a wide compositional range in SIMS quantification and with a weak dependence on matrix effects. Because the method enables the use of clearly identifiable secondary ions for quantitative purposes and mitigates commonly observed matrix effects in organic materials, the two-point calibration method could be of significant benefit to SIMS analysts.     

多组件学习器实现有机分子沸点的精准预测

沸点(BP)是有机分子液体的基本物理化学量, 也是化学工业生产中的重要参数. 有机分子的沸点由分子结构决定, 呈现复杂的结构-沸点关系, 函数法(Function Method)、基团贡献法(Group Contribution Method)等传统方法无法应对复杂多样有机分子结构的预测, 应用范围狭窄, 预测精度低. 本研究中, 我们利用基于人工神经网络(ANN)和支持向量机(SVM)的多组件学习器实现有机分子沸点的精准预测. 我们构建了基于可解释性描述符的ANN、基于相关性描述符的ANN及基于复合分子指纹的SVM三个异质模型, 并通过包含4550个各种类别的有机分子沸点的数据集进行训练得到了三个异质性学习器, 最后集成三个学习器对有机分子沸点进行预测. 相比于传统方法和此前的定量结构性质关系(QSPR)模型, 多组件模型结合了三种模型的优点, 展现出很好的预测精度和泛化能力以及低的过拟合, 实现了对多种类型有机分子的沸点的有效预测.     

纳米孔缺陷导致单层黑磷电荷局域极大抑制非辐射电子-空穴复合的时域模拟

通常认为缺陷加速黑磷的非辐射电子-空穴复合,阻碍器件性能的持续提高。实验打破了这一认识。采用含时密度泛函理论结合非绝热分子动力学,我们发现P-P伸缩振动驱动非辐射电子-空穴复合,使纳米孔修饰的单层黑磷的激发态寿命比完美体系延长了约5.5倍。这主要归因于三个因素。一,纳米孔结构不但没有在禁带中引入深能级缺陷,而且由于价带顶下移使带隙增加了0.22 eV。二,除了带隙增加,纳米孔减小了电子和空穴波函数重叠,并抑制了原子核热运动,从而使非绝热耦合降低至完美体系的约1/2。三,退相干时间比完美体系延长了1.5倍。前两个因素战胜了第三个因素,使纳米孔结构激发态寿命延长至2.74 ns,而其在完美体系中约为480 ps。我们的研究表明可以制造合理数量和形貌的缺陷,如纳米孔,降低黑磷非辐射电子-空穴复合,提高光电器件效率。这一研究对于理解和调控黑磷和其它二维材料的激发态性质有重要意义。     

A Chemically Fuelled Molecular Automaton Displaying Programmed Migration of Zn2+ Between Alternative Binding Sites

A molecular system comprising a cationic zinc complex and an amino acid-derived ambident ligand having phosphate and carboxylate binding sites undergoes a series of rearrangements in which the metal cation migrates autonomously from one site to another. The location of the metal is identified by the circular dichroism spectrum of a ligated bis(2-quinolylmethyl)-(2-pyridylmethyl)amine (BQPA) chromophore, which takes a characteristic shape at each binding site. Migration is fuelled by the decomposition of trichloroacetic acid to CO₂ and CHCl₃, which progressively neutralises the acidity of the system as a function of time, revealing in sequence binding sites of increasing basicity. The migration rate responds to control by variation of the temperature, water content and triethylamine concentration, while an excess of fuel controls the duration of an induction period before the migration event.