镎(Ⅳ)、镅(Ⅲ)、锔(Ⅲ)的AMBER力场参数化及评估

The radioactivity and toxicity of actinides impede experimental investigation into their chemical properties in the condensed phase. The rapid development of computational methods and computational facilities allows for alternative experimental methods, including the use of a molecular force field, to gain insight into the coordination chemistry and dynamics of actinides. The key to this method is the force fieild parameters. In the present work, we report the development and validation of the AMBER (Assisted Model Building with Energy Refinement) force field parameters for Np⁴⁺, Am³⁺, and Cm³⁺ based on the experimentally determined ion-oxygen distance (IOD). The parameter set, together with that reported for Th⁴⁺, U⁴⁺, and Pu⁴⁺, was then applied to investigate the coordination chemistry and dynamics of these six actinide ions in the aqueous phase, in the absence and presence of counterions Cl^-, NO₃^-, and CO₃^2-. The simulations showed a shorter An-O_w coordination length for An⁴⁺ than for An³⁺, and for higher atomic numbers of ions in the same valence state. Th⁴⁺ preferentially existed in a 10-coordinated state, adopting a BCASP (bicapped square antiprism) conformation, while the other ions tended to be 9-coordinated with a CASP (capped square antiprism) conformation. The only exception was Cm³⁺, which adopted a TCTP (tricapped trigonal prism) conformation. The results also showed that the water molecules around An⁴⁺ were more ordered than those around An³⁺, as indicated by the smaller angles between the An-O_w vector and the dipole direction of the water ligand. This highly ordered structure of coordinated water affected their translation and rotation, i.e., the diffusion coefficient and rotational relaxation time of the water molecules around An⁴⁺ were smaller than those in the case of An³⁺ due to the stronger electrostatic interaction between An⁴⁺ and ligating water. The hydration free energies of the targeted actinide ions were also calculated by the FEP (free energy perturbation) method. An⁴⁺ underwent a greater degree of stabilization than did An³⁺ upon hydration; among the ions in the same oxidation states, those with a higher atomic number were better stabilized. In summary, the results of the simulations were consistent with the literature data in terms of the hydration structure, coordination of counterions, and hydration free energy of the actinide ions. The ability of the parameter set to describe the dynamics of water in the vicinity of actinides remains to be verified due to the lack of reference data. We tentatively propose that it may be used to investigate the coordination chemistry of actinides both in conformational analysis and binding strength, while special care should be taken when studying the kinetics of the solvated system. This work is expected to enrich our understanding of the solution behavior of An³⁺/An⁴⁺ at the force field level.     

The surface and materials science of tin oxide

The study of tin oxide is motivated by its applications as a solid state gas sensor material, oxidation catalyst, and transparent conductor. This review describes the physical and chemical properties that make tin oxide a suitable material for these purposes. The emphasis is on surface science studies of single crystal surfaces, but selected studies on powder and polycrystalline films are also incorporated in order to provide connecting points between surface science studies with the broader field of materials science of tin oxide. The key for understanding many aspects of SnO₂ surface properties is the dual valency of Sn. The dual valency facilitates a reversible transformation of the surface composition from stoichiometric surfaces with Sn⁴⁺ surface cations into a reduced surface with Sn²⁺ surface cations depending on the oxygen chemical potential of the system. Reduction of the surface modifies the surface electronic structure by formation of Sn 5s derived surface states that lie deep within the band gap and also cause a lowering of the work function. The gas sensing mechanism appears, however, only to be indirectly influenced by the surface composition of SnO₂. Critical for triggering a gas response are not the lattice oxygen concentration but chemisorbed (or ionosorbed) oxygen and other molecules with a net electric charge. Band bending induced by charged molecules cause the increase or decrease in surface conductivity responsible for the gas response signal. In most applications tin oxide is modified by additives to either increase the charge carrier concentration by donor atoms, or to increase the gas sensitivity or the catalytic activity by metal additives. Some of the basic concepts by which additives modify the gas sensing and catalytic properties of SnO₂ are discussed and the few surface science studies of doped SnO₂ are reviewed. Epitaxial SnO₂ films may facilitate the surface science studies of doped films in the future. To this end film growth on titania, alumina, and Pt(1 1 1) is reviewed. Thin films on alumina also make promising test systems for probing gas sensing behavior. Molecular adsorption and reaction studies on SnO₂ surfaces have been hampered by the challenges of preparing well-characterized surfaces. Nevertheless some experimental and theoretical studies have been performed and are reviewed. Of particular interest in these studies was the influence of the surface composition on its chemical properties. Finally, the variety of recently synthesized tin oxide nanoscopic materials is summarized.     

Pathway dependence of the efficiency of calculating free energy and entropy of solute–solute association in water

In this study we investigate two alternative pathways to compute the free energy and the entropy of small molecule association (ΔF_assoc and ΔS_assoc) in water. The first route (direct pathway) uses thermodynamic integration as function of the distance R between the solutes. The mean force and the mean covariance of the force with the energy in solution are calculated from molecular dynamics simulation followed by integration of these quantities with respect to the reaction coordinate R. The alternative approach examined (solvation pathway) would first remove the solutes from the solution using thermodynamic integration as function of a solvation coupling parameter λ, change the solute–solute distance in vacuo and then solvate back the solute pair at the new separation distance. The system studied was a pair of CH₄ molecules in water. We investigate the influence of the CH₄–water interaction strength on the obtained ΔF_assoc and ΔS_assoc values by changing van der Waals and Coulomb interaction and evaluated the accuracy and efficiency for the two pathways. We find that the direct route seems more suitable for the calculation of free energies of hydrophobic solutes while the solvation pathway performs better when calculating entropy changes for solutes that have a stronger interaction with the solvent.     

A New Non-centrosymmetric Microporous Fluorinated Iron Phosphate: Structural Elucidation,Spectroscopic Study and Hirshfeld Surface Analysis

The crystal structure of a new non-centrosymmetric microporous fluorinated iron phosphate, (H₃O)₂[Fe₄(H₂O)₂F₄(PO₄)₂(HPO₄)₂](H₂O), was determined by single crystal X-ray diffraction analysis and the result reveals that it belongs to the orthorhombic system with four molecules in the unit cell(space group P2₁2₁2₁). Thus, the complex was characterized by powder X-ray diffraction, spectroscopic techniques(Fourier transform infrared and Fourier transform Raman) and ¹⁹F MAS NMR. The elemental analysis of the sample was also carried out. The chiral inorganic sheets, which stacked along[100] showed the presence of FeF₂O₄ as well as FeF₂O₃H₂O octahedra, PO₄ besides HPO₄ tetrahedra, hydronium ions(H₃O⁺) and isolated water molecules. Hirshfeld surface analysis, especially d_nom surface and fingerprint plots, were used for decoding the intermolecular interactions in the crystal network and the contribution of component units for the construction of the 3D architecture. From the Hirshfeld surfaces and 2D fingerprint analysis, it was found that the subtle interactions, such as H…H associating the third intense interaction of all intercontacts, provide extra stabilization in addition to the presence of the strong hydrogen bonds mentioned above.     

液滴在超疏水植物叶面的沉积：实验和分子动力学模拟

农药液滴在靶标植物叶面的动态沉积对于提高农药利用率具有重要的意义,特别是在超疏水植物叶面的动态沉积。在本文中,我们利用生物基表面活性剂和甘油之间的氢键作用来增强液滴在超疏水植物叶面的有效沉积。在较低浓度的山梨醇-烷基胺表面活性剂溶液中,添加0.001%的甘油,可有效抑制液滴在不同超疏水/疏水植物叶片表面的弹跳和飞溅行为。结果表明,甘油的加入并没有显著改变山梨醇-烷基胺表面活性剂溶液的表面张力、粘度和聚集体的形态。核磁共振波谱(DOSY)显示,甘油加速了山梨醇-烷基胺表面活性剂分子的扩散速度。利用分子动力学模拟,对山梨醇-烷基胺表面活性剂/甘油体系的能量演化及表面活性剂相对于固体表面距离的分布进行了研究。这项目工作不仅为抑制液滴在植物叶面的弹跳飞溅提供了一种建设性的方法,而且为选择农用表面活性剂提供了理论基础。     

K~+、Na~+、Ca~(2+)、Mg~(2+)对胜利褐煤平衡复吸水的影响

以胜利褐煤为研究对象,利用FT-IR等手段,用灰分、不同湿度下的平衡复吸水含量等,系统研究了不同相对湿度下K+、Na+、Ca2+、Mg2+的水合作用对胜利褐煤平衡复吸水含量的影响。结果表明,相同浓度不同类型的金属离子与煤样的交换能力的趋势为Ca2+Na+K+Mg2+。金属离子对胜利褐煤平衡复吸水含量影响力的顺序为Mg2+Ca2+Na+≈K+。相对湿度高时,平衡复吸水含量的主要控制因素为游离水分子之间的分子作用力;相对湿度中等时,平衡复吸水含量的主要控制因素为金属水簇与毛细管之间的毛细管作用力;相对湿度低时,平衡复吸水含量的主要控制因素为金属离子的水合作用。     

Adsorption of bacterial surface polysaccharides on mineral oxides is mediated by hydrogen bonds

Adhesion of bacterial cells to solid surfaces is often largely affected by bacterial surface polymers. In this study, we investigated the adsorption of three different O-antigens isolated from bacterial lipopolysaccharides on TiO₂, Al₂O₃, and SiO₂. The O-antigens of Escherichia coli 08 DSM 46243 and Citrobacter freundii PCM 1487 had high affinity for TiO₂ and low affinity for Al₂O₃, whereas the O-antigens of Stenotrophomonas maltophilia 70401 had low affinities for both surfaces. Adsorption on SiO₂ was low for all polysaccharides. The dependence of the adsorption on the molecular mass of polysaccharides was investigated with dextrans of various chain lengths. The affinity increased with the molecular mass. The affinity of the dextrans was reduced compared with the O-antigen of E. coli, which had similar chemical composition and molecular mass. The adsorption of the E. coli and C. freundii O-antigens on Al₂O₃ and TiO₂ was irreversible, whereas for the S. maltophilia O-antigen it was partially reversible. The reversibility of dextran adsorption decreased with increasing molecular mass.

Infrared spectroscopy showed that all bacterial O-antigens and the dextrans formed hydrogen bonds with surface hydroxyl groups or interacted with surface-bound water of TiO₂, Al₂O₃, and SiO₂. A concentration-dependent mechanism of adsorption was observed with TiO₂. At low polysaccharide concentrations, the surface water molecules ware replaced by the polysaccharides, and at increased concentration the surface hydroxyl groups were involved in the formation of hydrogen bonds. At higher surface coverages, the adsorbed polysaccharides formed loops between the few adsorbed units.     

三维化合物[Ni2(BDC)2(m-bix)(H2O)3·3H2O]n的合成、结构和性质

水热条件下,合成了一个三维配位聚合物[Ni₂(BDC)₂(m-bix)(H₂O)₃·3H₂O]_n(1)[BDC=对苯二甲酸,m-bix=1,3-双(咪唑基-1-甲基)-苯],并通过红外,热重和X-射线单晶衍射进行了表征。X射线衍射结果表明化合物含有类似配位环境的金属2个Ni²⁺离子,2个BDC^2-配体,1个m-bix分子,3个配位水分子和3个游离的溶剂水分子。两个Ni²⁺离子分别采用八面体构型,通过桥联水分子形成双核单元,然后通过全部脱质子的BDC形成三维孔洞结构,m-bix配体通过连接两类双核金属原子形成三维框架,游离水分子存在于框架之中。有趣的是,化合物的结构是单一六节点,具有自穿插特征。而且对化合物的红外和热重性质进行了表征。     

CO分子在不同类型Al2O3表面的吸附构型和电子结构

采用基于赝势平面波基组的密度泛函理论方法对CO分子在α-Al₂O₃（0001）以及γ-Al₂O₃的（100）、（110C）、（110D）表面上的吸附构型和电子结构进行系统研究.计算结果表明,CO倾向于选取C端吸附在表层Al原子上,并主要通过其5σ轨道与表面发生作用,吸附后部分电子从CO转移到底物,导致各Al₂O₃表面功函均发生不同程度的下降,与气相相比,吸附后CO分子的C-O伸缩振动频率均发生蓝移.通过对比CO在各表面上的吸附情况,可以看出CO可作为检测Al₂O₂不同类型表面活性中心的有效探针分子.     

Preparation and characterization of hydrophobic calcium hydroxyapatite particles grafting oleylphosphate groups

Grafting of oleylphosphate (OP) molecules to the surface of calcium hydroxyapatite particles (HAP) was carried out by a coprecipitation method with a Ca(OH)₂–H₃PO₄ system in the presence of disodium oleylphosphate (DSOP). All the particles exhibited a single-crystal nature with rod-like shape and were elongated along c-axis from 36 to 122 nm in particle length with an increase in the concentration of DSOP. It was suggested that 084% of the phosphate ions exposed on the ac or bc faces of the HAP particles are exchanged with phosphate ions of DSOP molecules directing oleyl groups outward. The hydrophobicity of OP-grafted HAP particles was enhanced with an increase in the DSOP concentration. This high surface hydrophobicity was further confirmed by water adsorption experiments. The materials with the surface oleyl groups adsorbed much less water than the HAP particles produced without DSOP.     

The interaction of H2, CO, CO2, H2O and NH3 on ZnO surfaces: an Oniom Study

We have used the Oniom method with three layers in order to study the interaction of CO, H₂, H₂O, NH₃ and CO₂ molecules with the ZnO surfaces using a (ZnO)₃₄₈ cluster model. The layers are divided into the high layer at the CCSD level, the medium layer at the RHF level and the low level layer using the UFF force field method. The orbital and binding energies of the adsorbed molecules, Mulliken and ChelpG charges as well as geometrical parameters were analyzed and compared with the available experimental and theoretical data.     

大分子振动的一般价力场力常数计算方法的研究

本文基于力常数矩阵F_s从UBFF到GVFF的可迁性,提出了一个“由UBFF力常数来限定GVFF力常数”的方法;其次,对“运动学确定力常数法”中Λ矩阵元排序的规则作了进一步研究。     

客体预嵌策略提升水系锌离子电池正极材料电化学性能

随着人们对电子通讯器件、新能源汽车以及电网级储能技术的需求日益增长,开发安全、高效且兼具环保、低成本等优点的二次电池显得至关重要。近年来,水系锌离子电池因其高安全性、高容量、低成本以及环境友好等优点受到了广泛关注。在与锌负极相匹配的众多正极材料中,具有多电子转移特性的钒基和锰基材料表现出了广阔的应用前景。然而这些正极材料在电池循环过程通常面临着结构坍塌、组分溶解、衍生副反应、反应动力学缓慢等问题,严重制约了其商业化进程。近年来,大量研究表明,客体离子或分子预嵌正极宿主结构可以有效缓解上述问题,提升水系锌离子电池正极材料的电化学性能。本文综述了客体预嵌策略应用于水系锌离子电池钒、锰基正极材料的研究进展,对该策略所解决的问题以及其局限性进行了讨论和总结,并对未来水系锌离子电池钒基和锰基正极材料的研究发展方向进行了展望。     

Direct measurement of hydrophobic particle–bubble interactions in aqueous solutions by atomic force microscopy: Effect of particle hydrophobicity

Direct measurements of the interaction forces between a spherical silica particle and a small air bubble have been conducted in aqueous electrolyte solutions by using an atomic force microscope (AFM). The silica particle was hydrophobized with a silanating reagent, and the interaction forces were measured by using several particles with different surface hydrophobicities. In the measured force curves, a repulsive force was observed at large separation distances as the particle moved towards the bubble. The origin of the repulsive force was attributed to an electrostatic double-layer force because both the particle and bubble were negatively charged. After the repulsive force, an extremely long-range attractive force acted between the surfaces. These results indicate that the intervening thin water film between the particle and bubble rapidly collapsed, resulting in the particle penetrating the bubble.

The instability of the thin water film between the surfaces suggests the existence of an additional attractive force. By comparing the repulsive forces of the obtained force curves with the DLVO theory, the rupture thickness was estimated. The hydrophobicity of the particle did not significantly change the rupture thickness, whereas the pH of the solution is considered to be a critical factor.     

胜利褐煤Ca~(2+)负载量对其平衡复吸水含量的影响

以胜利褐煤为研究对象,利用XRF、FT-IR等手段,采用灰分、pH值、不同相对蒸气压下的复吸水含量等参数,研究了Ca2+的离子效应对褐煤在不同相对蒸气压下复吸水含量的影响。研究结果表明,煤中Ca2+的负载量随用于交换的钙离子溶液浓度的增大而增加。煤中Ca2+的负载量对煤样的平衡复吸水含量影响较大,Ca2+负载量越大,煤样的平衡复吸水含量越大。相对蒸气压高于92%平衡复吸水含量的主要控制因素为游离水分子与游离水分子之间的相互作用力。相对蒸气压在11%~92%平衡复吸水含量的主要控制因素为金属水簇Ca+(H2O)n与毛细管之间的毛细管作用力。     

AFM surface force measurements conducted with silica in CnTACl solutions: Effect of chain length on hydrophobic force

Surface forces were measured using an AFM with silica surfaces immersed in C_nTACl (n = 12–18) solutions in the absence of added salt. The results showed long-range attractive forces that cannot be explained by the DLVO theory. The long-range attractions increased with increasing surfactant concentration, reaching a maximum at the point of charge neutralization (p.c.n.) and then decreased. The long-range forces decayed exponentially, with the decay lengths increasing from 3 to 32 nm as the chain length of the surfactants increased from C-12 to C-18. The measured forces can be fitted to the charged-patch model of Miklavic et al. [S.J. Miklavic, D.Y.C. Chan, L.R. White, T.W. Healy, J. Phys. Chem. 98 (1994) 9022–9032] by assuming patch sizes that are much larger than the values reported in the literature.

It was found that the decay length decreases linearly with the effective concentration of the CH₂/CH₃ groups of the C_nTACl homologues raised to the power of −1/2, which is in line with the Eriksson et al.'s hydrophobic force model derived using a mean-field approach. It appears, therefore, that the long-range attractions observed in the present work are hydrophobic forces originating from changes in water structure across the thin surfactant solution film between the silica surfaces. It is conceivable that hydrocarbon chains in solution disrupt the surface-induced water structure and cause a decrease in hydrophobic force. This observation may also provide an explanation for the very long-range forces observed with silylated, LB-deposited, and thiol-coated surfaces.     

A theoretical study of water adsorption on (10-10) and (0001) ZnO surfaces: molecular cluster, basis set and effective core potential dependence

The adsorption of water molecule and hydroxyl ions on the (10-10) and (0001) ZnO surfaces has been studied for (ZnO)₄, (ZnO)₅ and (ZnO)₆ cluster models. Different representations for the atomic basis sets and the effective core potential (ECP) approximations have been employed and the effects of cluster size, conformation and basis sets are analyzed and discussed.     

Preparation and catalytic activity of P4VP–Cu(II) complex supported on silica gel

Micron-sized silica gel particles were chemically modified on their surfaces with the coupling agent, γ-methacryloxypropyl trimethoxysilane (MPS), double bond was introduced onto the surfaces of silica gel particles, and the modified particles MPS–SiO₂ were obtained. Then, poly(4-vinylpyridine) (P4VP) was grafted from the silica gel surfaces, and grafting particles P4VP/SiO₂ was prepared. Finally, the coordination between grafted P4VP and cupric ions Cu²⁺ was performed, and the supported complex Cu(II)–P4VP/SiO₂ was obtained. The grafting particles P4VP/SiO₂ and the supported complex Cu(II)–P4VP/SiO₂ were characterized with infrared spectra (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). Cu(II)–P4VP/SiO₂ was used as a catalyst for the oxidation of ethyl benzene into acetophenone with molecular oxygen under ordinary pressure. The experimental results show that the supported complex Cu(II)–P4VP/SiO₂ can be successfully prepared via grafting polymerization of 4VP and coordination between the grafted P4VP and cupric ions Cu²⁺. In oxidation of ethyl benzene into acetophenone by molecular oxygen under ordinary pressure, the supported complex Cu(II)–P4VP/SiO₂ displayed high catalytic activity and excellent catalytic selectivity up to more than 98% for the transformation of ethyl benzene to acetophenone.     

原位透射电子显微镜观察电荷驱动的氧化物纳米颗粒水中自组装

以四氧化三钴Co_3O_4纳米棒为研究对象,我们利用液体环境透射电子显微镜,原位观察了四氧化三钴纳米棒在水中的自组装过程。研究发现在电子束辐照的水环境下,四氧化三钴纳米棒的晶面存在互补式自组装现象。随着纳米棒之间的距离越来越近,纳米棒之间的相对运动速率逐渐增加,纳米棒之间的相互作用力逐渐增加。通过进一步分析纳米棒的形貌发现,纳米棒的暴露晶面大多数为{100}、{110}以及{111}晶面,而Co_3O_4属于极性氧化物,这些晶面往往会带有一定的电荷。在液体环境下,正是由于这些易暴露面都带有不同大小的电荷,在晶面电荷的驱动下,电荷属性相反的四氧化三钴纳米棒会互相吸引,形貌结构上进行互补,实现快速驱动的纳米棒之间自组装。     

二维金属-六亚氨基苯框架材料的气体吸附效应

利用密度泛函理论研究了气体分子(NH₃, H₂O, H₂S, NO₂)吸附在二维M₃(HIB)₂(M=Ni, Cu; HIB为六亚氨基苯)薄膜上体系的几何结构和电子结构的变化. 结果表明, 2种薄膜对气体分子的响应不同. 其中NH₃, H₂O和H₂S在M₃(HIB)₂薄膜表面的吸附较弱, 主要与薄膜的亚氨基形成氢键, 吸附能均小于-0.36 eV, 吸附对体系电子性质的影响很小. 但是 NO₂分子在薄膜表面形成化学吸附, 吸附能在-0.65~-1.72 eV范围内. 吸附NO₂分子使其电子结构发生明显改变, 如Cu₃(HIB)₂在费米能级处打开带隙, 由金属性质转变为半导体性质. 这是由于NO₂分子的p_z轨道与金属原子$d_{z}^{2}$ 轨道发生了强烈的轨道杂化. 此外, 研究发现高浓度的NO₂分子吸附能够使Ni₃(HIB)₂薄膜由非磁性变为磁性体系, 由普通金属性质变为半金属性质; 而高浓度的NO₂分子使Cu₃(HIB)₂薄膜由金属性质变为半导体性质, 薄膜电导率降低.