A DFT Study of the Reactivity of Anatase TiO2 and Tetragonal ZrO2 Stepped Surfaces Compared to the Regular (101) Terraces

It is generally assumed that low‐coordinated sites at extended defects of oxide surfaces like steps or edges are more reactive than the regular, fully coordinated sites at the flat terraces. In this work we have considered the properties of stepped surfaces of anatase TiO₂ and tetragonal ZrO₂ by means of periodic DFT+U calculations. For both oxides, the stability of oxygen vacancies located near the step edges is compared to that of the same defects at the regular terraces. The capability of the steps to induce nucleation of metal nanoparticles on the surface has been evaluated by simulating the adsorption of a single ruthenium adatom. We conclude that, for anatase, step edges have no particular role in favouring the reduction of the oxide by reducing the cost for oxygen abstraction; in the same way, there is no special role of the stepped anatase surface in stabilizing adsorbed Ru atoms. On the contrary, step edges on zirconia display some capability to stabilise oxygen vacancies and ruthenium adatoms.     

环形镧系分子簇合物的组装与单分子磁体性质

由于稀土离子具有很强的磁各向异性,近年来基于单核或多核稀土化合物的单分子磁体研究得到了人们广泛的关注.环形簇合物是一类特殊的簇合物,也称分子轮或金属冠醚.设计合成环形稀土簇合物不仅可以获得新的稀土单分子磁体,而且环形簇合物中稀土离子磁偶极的涡旋分布还可以产生环形磁矩,因而在量子计算、信息存储、自旋分子器件等方面具有潜在的应用.鉴于环形稀土簇合物特别是含奇数核的环形簇合物的合成依然充满挑战,本综述将着重阐述已报道的环形稀土簇合物的组装规律、结构特点及磁性研究.     

开环聚合诱导自组装的挑战与展望

聚合诱导自组装（PISA）是一种新兴的纳米粒子制备技术,它集聚合与组装过程于一体,可在高固含量条件下进行,因此备受青睐.此外,通过改变嵌段聚合度以及固含量等参数,可以精确地控制纳米粒子的形貌,实现从球形胶束到空心囊泡的形貌转变.然而,受限于适用于PISA体系的聚合方法和单体种类,其发展也受到了一定的限制.目前,PISA主要基于可逆加成-断裂链转移聚合（RAFT）,其在聚合诱导自组装机理、形貌控制、结构表征等方面的研究成果,对于高分子化学其他领域具有重要的参考价值.然而,由于RAFT聚合诱导自组装（RAFT-PISA）体系中适用的单体往往局限于（甲基）丙烯酸酯类和苯乙烯类,导致RAFT-PISA制备的纳米粒子限于其碳-碳主链的基本结构难以生物降解,因此生物医用前景并不乐观.为了克服以上缺陷,开环聚合诱导自组装（ROPISA）应运而生,主要包括开环易位聚合诱导自组装（ROMPISA）、氨基酸-N-羧基-环内酸酐开环聚合诱导自组装（NCA-PISA）及自由基开环聚合诱导自组装（rROPISA）.由于ROMPISA体系对诸多功能性基团表现出化学惰性,从而为多功能纳米粒子的原位制备提供了新的方法;而rROPISA和NCA-PISA则使得生物可降解纳米粒子的原位制备成为可能.作为PISA领域崭新的研究方向,ROPISA不仅将新聚合方法引入了PISA体系,而且突破了以往PISA难以制备可降解纳米粒子的瓶颈,为PISA技术在生物医药领域的应用架起了桥梁.作者简要总结了ROPISA的发展现状,着重分析并提出了该领域面临的挑战,最后从机理研究、单体设计及转化应用等方面对ROPISA的发展前景进行了展望.     

Polymerization-induced self-assembly of metallo-polyelectrolyte block copolymers

Cobaltocenium-containing polyelectrolyte block copolymer nanoparticles were prepared via polymerization-induced self-assembly (PISA) using aqueous dispersion RAFT polymerization. The cationic steric stabilizer was a macromolecular chain-transfer agent (macro-CTA) based on poly(2-cobaltocenium amidoethyl methacrylate chloride) (PCoAEMACl), and the core-forming block was poly(2-hydroxypropyl methacrylate) (PHPMA). Stable cationic spherical nanoparticles were formed in aqueous solution with low dispersity without adding any salts. The chain extension of macro-CTA with HPMA was efficient and fast. The effects of block copolymer compositions, solid content, charge density, and addition of salts were studied. It was found that the degree of polymerization of both the stabilizer PCoAEMACl and the core-forming PHPMA had a strong influence on the size of nanoparticles. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 77–83     

Supramolecular Metallacycles and Their Binding of Fullerenes

The synthesis of a new triaminoguanidinium-based ligand with three tris-chelating [NNO]-binding pockets and C₃ symmetry is described. The reaction of tris-(2-pyridinylene-N-oxide)triaminoguanidinium salts with zinc(II) formate leads to the formation of cyclic supramolecular coordination compounds which in solution bind fullerenes in their spherical cavities. The rapid encapsulation of C₆₀ can be observed by NMR spectroscopy and single-crystal X-ray diffraction and is verified using computation.     

Modeling the Reaction of Carboxylic Acids and Isonitriles in a Self-Assembled Capsule

Quantum chemical calculations were used to study the reaction of carboxylic acids with isonitriles inside a resorcinarene-based self-assembled capsule. Experimentally, it has been shown that the reactions between p-tolylacetic acid and n-butyl isonitrile or isopropyl isonitrile behave differently in the presence of the capsule compared both with each other and also with their solution counterparts. Herein, the reasons for these divergent behaviors are addressed by comparing the detailed energy profiles for the reactions of the two isonitriles inside and outside the capsule. An energy decomposition analysis was conducted to quantify the different factors affecting the reactivity. The calculations reproduce the experimental findings very well. Thus, encapsulation leads to lowering of the energy barrier for the first step of the reaction, the concerted α-addition and proton transfer, which in solution is rate-determining, and this explains the rate acceleration observed in the presence of the capsule. The barrier for the final step of the reaction, the 1,3 O→N acyl transfer, is calculated to be higher with the isopropyl substituent inside the capsule compared with n-butyl. With the isopropyl substituent, the transition state and the product of this step are significantly shorter than the preceding intermediate, and this results in energetically unfavorable empty spaces inside the capsule, which cause a higher barrier. With the n-butyl substituent, on the other hand, the carbon chain can untwine and hence uphold an appropriate guest length.     

Dynamics of Hydrogen Bonding in Three-Component Nanorotors

The dynamics of hydrogen bonding do not only play an important role in many biochemical processes but also in Nature's multicomponent machines. Here, a three-component nanorotor is presented where both the self-assembly and rotational dynamics are guided by hydrogen bonding. In the rate-limiting step of the rotational exchange, two phenolic O-H–N,N_{(phenanthroline)} hydrogen bonds are cleaved, a process that was followed by variable-temperature ¹H NMR spectroscopy. Activation data (ΔG^≠₂₉₈=46.7 kJ mol⁻¹ at 298 K, ΔH^≠=55.3 kJ mol⁻¹, and ΔS^≠=28.8 J mol⁻¹ K⁻¹) were determined, furnishing a rotational exchange frequency of k₂₉₈=40.0 kHz. Fully reversible disassembly/assembly of the nanorotor was achieved by addition of 5.0 equivalents of trifluoroacetic acid (TFA)/1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) over three cycles.     

氧化还原对Lindqvist型多金属氧簇复合物自组装的动态调控

Dynamic regulation of self-assembly is of vital importance in chemistry, biology and material science thanks to its great potential for development of smart materials and devices. Polyoxometalates (POMs) are a class of functional inorganic nanoclusters, which has become one of the excellent building blocks for supramolecular self-assemblies, especially when covalently or non-covalently modified by organic species. As typical stimuli-responsive functional clusters, the POMs could be photochemically or electrochemically reduced to mixed-valence states, of which the structural integrity remains even after encountering stepwise multi-electron redox process. The intriguing photochromism of the POMs in different states exhibits distinct photophysical properties, which motivates us to exploit the dynamic self-assemblies of POM-based complexes. The divalent Lindqvist-type hexamolybdate cluster [Mo₆O₁₉]^2- is one of the least negative-charged POMs, which is the ideal building blocks to construct novel assembly structures. Based on this motivation, herein, a single chain surfactant-encapsulated polyoxometalate (POM) complex (ODTA)₂[Mo₆O₁₉] was prepared by simple counterion replacement of Lindqvist-type (TBA)₂[Mo₆O₁₉] with octadecyltrimethylammonium (ODTA) in acetonitrile solution. The structure of the POM complex was confirmed by ¹H nuclear magnetic resonance (NMR), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and elemental analysis. The solution of complex (ODTA)₂[Mo₆O₁₉] in the mixed solvents of acetonitrile and isopropanol with the volume ration of 4 to 1 exhibited reversible photochromism upon alternate UV light irradiation and air exposure. Upon UV light irradiation, the light yellow transparent solution of (ODTA)₂[Mo₆O₁₉] turned into blue quickly. The new broad absorption band appearing at ca.751 nm assigned to the Mo^V → Mo^VI intervalence charge-transfer (IVCT) transition, indicated the formation of reduced POM, as revealed by UV-Vis absorption spectra. After exposed to air, the blue solution was bleached. The alternate photochromism could be conducted for multiple cycles. Helical self-assembled morphology of (ODTA)₂[Mo₆O₁₉] was formed in acetonitrile/isopropanol, characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) methods. More interestingly, morphology transformation of the complex from helical strips to spherical assemblies occurred accompanied by photochromism occurrence. The morphology evolution during the photochromism process experienced from shortened helical strips through sea urchin-like aggregates to spherical assemblies. Most significantly, the helical assemblies could be recovered again after air oxidation, implying the reversible morphology transformation driven by redox stimulus. The redox-modulated reversible self-assembly is driven by the variation of electrostatic attraction between organic cations and inorganic anions as well as the electrostatic repulsion between inorganic ionic clusters, proved by X-ray photoelectron spectroscopy (XPS) and ¹H NMR spectra. The results will contribute to better understanding the mechanism of dynamic assemblies and inspire the precise fabrication of advanced smart materials.     

聚合物纳米组装体修饰丝网印刷电极构建过氧化氢传感器

通过在聚合物结构中同时引入生物亲和单体和电活性单体,使得聚合物组装体在修饰丝网印刷电极时兼具提高比表面积、保持酶活和促进电子转移功能,从而发展了一种简单、高效构建电化学传感器的方法。 以苯乙烯(St)、丙烯酸(AA)、N-乙烯基咔唑(VCz)和甲基丙烯酸二甲氨基乙酯(DMAEMA)为单体自由基聚合合成双亲性无规共聚物Poly(St-co-AA-co-VCz-co-DMAEMA)(PSACD),将聚合物在选择性混合溶剂DMF/H₂O中自组装得到聚合物纳米粒子PSACD NPs。 利用纳米粒度分析仪、扫描电子显微镜(SEM)对其进行表征。 依次将PSACD NPs水分散液、辣根过氧化物酶(HRP)溶液和全氟磺酸-聚四氟乙烯共聚物(Nafion,NF)溶液滴涂在丝网印刷碳电极(SPCE)上,制备得到过氧化氢生物传感器。 通过计时电流法对传感器性能进行研究,表明该传感器对H₂O₂在0.02~7.48 mmol/L有良好的线性响应,且响应时间短(<2 s),具有良好的选择性和稳定性。     

On-Surface Assembly of Hydrogen- and Halogen-Bonded Supramolecular Graphyne-Like Networks

Demonstrated here is a supramolecular approach to fabricate highly ordered monolayered hydrogen- and halogen-bonded graphyne-like two-dimensional (2D) materials from triethynyltriazine derivatives on Au(111) and Ag(111). The 2D networks are stabilized by N⋅⋅⋅H−C(sp) bonds and N⋅⋅⋅Br−C(sp) bonds to the triazine core. The structural properties and the binding energies of the supramolecular graphynes have been investigated by scanning tunneling microscopy in combination with density-functional theory calculations. It is revealed that the N⋅⋅⋅Br−C(sp) bonds lead to significantly stronger bonded networks compared to the hydrogen-bonded networks. A systematic analysis of the binding energies of triethynyltriazine and triethynylbenzene derivatives further demonstrates that the X₃-synthon, which is commonly observed for bromobenzene derivatives, is weaker than the X₆-synthon for our bromotriethynyl derivatives.