General sacrificial template method for the synthesis of cadmium chalcogenide hollow structures

Semiconductor CdX (X=Te, Se, S) hollow structures have been successfully prepared by using Cd(OH)Cl precursors as a sacrificial template. The hollow structures can be hollow spheres or tubes by controlling the shape of the sacrificial template. The products were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and energy-dispersive spectrometry. The obtained results showed that the hollow structures had complementary shapes and sizes of the original sacrificial templates. This is a general method for the synthesis of cadmium chalcogenide hollow structures, and the method is simpler and more practical than direct synthesis of certain hollow structures, which further widens the avenue to using those materials that have been synthesized with various shapes to fabricate specific hollow structures.     

Probing phenylalanine/adenine pi-stacking interactions in protein complexes with explicitly correlated and CCSD(T) computations

To examine the effects of pi-stacking interactions between aromatic amino acid side chains and adenine bearing ligands in crystalline protein structures, 26 toluene/(N9-methyl)adenine model configurations have been constructed from protein/ligand crystal structures. Full geometry optimizations with the MP2 method cause the 26 crystal structures to collapse to six unique structures. The complete basis set (CBS) limit of the CCSD(T) interaction energies has been determined for all 32 structures by combining explicitly correlated MP2-R12 computations with a correction for higher-order correlation effects from CCSD(T) calculations. The CCSD(T) CBS limit interaction energies of the 26 crystal structures range from -3.19 to -6.77 kcal mol (-1) and average -5.01 kcal mol (-1). The CCSD(T) CBS limit interaction energies of the optimized complexes increase by roughly 1.5 kcal mol (-1) on average to -6.54 kcal mol (-1) (ranging from -5.93 to -7.05 kcal mol (-1)). Corrections for higher-order correlation effects are extremely important for both sets of structures and are responsible for the modest increase in the interaction energy after optimization. The MP2 method overbinds the crystal structures by 2.31 kcal mol (-1) on average compared to 4.50 kcal mol (-1) for the optimized structures.     

Atomic Layer Electrodeposition of Pt on Nanoporous Au and its Application in pH Sensing

The preparation of nanoporous metal structures has received a substantial amount of attention because of the unique properties and various applications of these structures. In this work, the preparation of nanoporous Pt structures by modification of nanoporous gold (NPG) surfaces with Pt was achieved. An atomic layer electrodeposition (ALED) technique previously reported for the modification of flat Au surfaces with Pt was applied to the NPG surfaces to produce Pt‐modified NPG structures. The optimal ALED parameters, such as deposition potential, time, and number of cycles, for the preparation of Pt‐modified NPG structures were investigated. Scanning electron microscopy and energy‐dispersive X‐ray analysis confirmed the successful preparation of nanoporous Pt structures by ALED techniques. The Pt‐modified NPG performed well as a pH sensor with a Nernstian slope and negligible hysteresis. The method of preparing the nanoporous Pt structures reported in this work could be utilized in various applications such as electrocatalysis and electroanalysis.     

Evaluation of ion mobility spectroscopy for determining charge-solvated versus salt-bridge structures of protonated trimers

The cross sections of five different protonated trimers consisting of two base molecules and trifluoroacetic acid were measured by using ion mobility spectrometry. The gas-phase basicities of these five base molecules span an 8-kcal/mol range. These cross sections are compared with those determined from candidate low-energy salt-bridge and charge-solvated structures identified by using molecular mechanics calculations using three different force fields: AMBER*, MMFF, and CHARMm. With AMBER*, the charge-solvated structures are all globular and the salt-bridge structures are all linear, whereas with CHARMm, these two forms of the protonated trimers can adopt either shape. Globular structures have smaller cross sections than linear structures. Conclusions about the structure of these protonated trimers are highly dependent on the force field used to generate low-energy candidate structures. With AMBER*, all of the trimers are consistent with salt-bridge structures, whereas with MMFF the measured cross sections are more consistent with charge-solvated structures, although the assignments are ambiguous for two of the protonated trimers. Conclusions based on structures generated by using CHARMm suggest a change in structure from charge-solvated to salt-bridge structures with increasing gas-phase basicity of the constituent bases, a result that is most consistent with structural conclusions based on blackbody infrared radiative dissociation experiments for these protonated trimers and theoretical calculations on the uncharged base-acid pairs.     

Ab initio study of hydrated sodium halides NaX(H2O)(1-6) (X=F, Cl, Br, and I)

We have studied the dissociation phenomena of sodium halides by water molecules. The structures, binding energies, electronic properties, and IR spectroscopic features have been investigated by using the density-functional theory, second-order Moller-Plesset perturbation theory, and coupled clusters theory with single, double, and perturbative triplet excitations. In the case that the sodium halides are hydrated by three water molecules, the most stable structures show the partial (or half) dissociation feature. The dissociated structures are first found for NaX(H2O)(n=5) for X=BrI, though these structures are slightly higher in energy than the global minimum-energy structure. In the case of hexahydrated sodium halides the global minimum-energy structures (which are different from the structures reported in any previous work) are found to be dissociated (X=F/I) or partially/half dissociated (X=Cl/Br), while other nearly isoenergetic structures are undissociated, and the dissociated cubical structures are higher in energy than the corresponding global minimum-energy structure.     

Electrical Conductivity of Films Formed by Few-Layer Graphene Structures

Current–voltage characteristics of few-layer graphene structures produced by electrochemical exfoliation of graphite in an electrolyte solution were measured. It was shown that few-layer graphene structures possess an electronic conductivity, which is indicative of the small degree of surface functionalization of the structures. The resistance of films formed by these structures grows with increasing relative humidity of the medium because of the shielding of fl akes of the few-layer graphene structures by a film of water.     

A benchtop method for the fabrication and patterning of nanoscale structures on polymers

A benchtop method for the facile production of nanoscale metal structures on polymers is demonstrated. This approach allows for the design and patterning of a wide range of metallic structures on inexpensive polymer surfaces, affording the fabrication of nanoscaled platforms for use in the design of sensors, actuators, and disposable electronic and photonic devices. Numerous structures, from simple nanowires to multilayered metallic gratings, are demonstrated, with sizes ranging from microns to the nanoscale. The process involves molding a malleable metal film deposited on a rigid substrate such as mica, by the compression of a plastic polymer stamp with the desired pattern against the metal film. While under compression, an etchant is then used to modify the metal. Upon separation of the stamp from the support, micro- to nanoscaled metallic structures are found on the stamp and/or on the substrate. The sizes of the structures formed depend on the sizes of the features on the stamp but can be fine-tuned by about 4-fold through variations in both pressure and duration of etching. Also, depending on the processing, multiple dimension metallic structures can be obtained simultaneously in a single stamping procedure. The metallic structures formed on the stamp can also be subsequently transferred to another surface allowing for the construction of multilayered materials such as band gap gratings or the application of electrical contacts. Using this approach, fabrication of both simple and complex micro- to nanoscaled structures can be accomplished by most any researcher as even the grating structure of commercial compact disks may be used as stamps, eliminating the requirement of expensive lithographic processes to form simple structures.     

仿生分级结构NiO纳米线/纳米纤维的可控制备及光催化性能

采用静电纺丝技术和"自下而上"的溶液相自组装技术, 制备了具有仿生主次分级结构的三维NiO纳米线/纳米纤维. 采用扫描电子显微镜(SEM)、 X射线衍射仪(XRD)和比表面积分析仪分别对其形貌、 晶型和孔结构进行了表征. 以水体中的有色染料亚甲基蓝为模型污染物, 研究了分级结构NiO纳米线/纳米纤维的光催化性能. 结果表明, 在180 min内, 以分级结构NiO为催化剂时, 亚甲基蓝的降解率达到了97%, 分别是以纳米纤维和纳米粒子为催化剂时的1.24倍和2.16倍.     

有机分子晶体中的局部结构无序（Ⅰ）

应用单晶Ｘ衍射法测定５个有机分子样品结构，发现晶态下部分原子存在的无序排列（占有率，位置）导致分子构象的变化。Ｘ射线衍射分析获得的是分子的平均结构，由于有机分子晶体结构中普通存在无序现象，故增加了Ｘ射线衍射分析在三维空间中测定晶体准确结构的难度。     

Tautomerism of metal complexes with 1,8-dihydroxy-3-R1-6-R2-9,10-anthraquinones

The structures of metal complexes with 1,8-dihydroxyanthraquinones studied by spectrophotometric, quantum-chemical, and correlation methods were found to be determined by tautomeric 9,10–1,10-anthraquinoid structures of the ligands and by the degree of the ligand ionization. Complex formation is accompanied by the shifts in tautomeric equilibria influencing both excited and ground states of the ligands. The 1,10-anthraquinoid forms of complexes are the most characteristic. The known complexes are classified in accordance with the ligand structures.     

A new approach to fabricate agarose microstructures

Agarose hydrogels find wide applications in different fields such as biological sciences, tissue engineering and food industry, and its use has been investigated in many fields ranging from electronics to crystallography. Usually, agarose structures are made by casting, and more recently some attempts have been made to build agarose structures by additive manufacturing. All of the fabrication methods are based on thermo‐reversible gelling properties of agarose gel. A new method to fabricate agarose microstructures in a binary solvent composed of water and dimethyl sulfoxide is presented and modelled in this paper. This new method allows building agarose structures by an additive layer‐by‐layer approach using a modified inkjet printer. The fabrication method and printing device are described in detail. Furthermore, finite‐element model simulations, which predict with high confidence the final line width of the printed structures, are discussed and analysed. Mechanical properties of printed gel structures are comparable with those obtained by gel casting, as demonstrated by tensile testing. The presented results demonstrate the feasibility of this approach to fabricate agarose structures with more complex shapes that can be done by casting. Copyright © 2013 John Wiley & Sons, Ltd.     

Phase segregation of a symmetric diblock copolymer in constrained space with a square-pillar array

In this study, we apply a self-consistent field theory of polymers to study the structures of a symmetric diblock copolymer in parallel substrates filled with square-pillar arrays in which the substrates and pillars exhibit a weak preference for one block of the copolymer. Three classes of structures, i.e., lamellae, perpendicular cylinders, and bicontinuous structures, are achieved by varying the polymer film thickness, the pillar pitch (the distance between two centers of the nearest neighboring pillars), the gap and rotation of the pillars. Because of the confinement along horizontal directions imposed by the pillar array, eight novel types of perpendicular lamellar structures and eight novel types of cylindrical structures with various shapes and distributions occur. In the hybridization states of the parallel and perpendicular lamellar structures, several novel bicontinuous structures such as the double-cylinder network, pseudo-lamellae, and perforated lamellar structure are also found. By comparing the free energies of the various possible structures, the antisymmetric parallel lamellae are observed to be stable with the larger pillar gap at a certain film thickness. The structural transformations between the alternating cylindrical structures (alternating cross-shaped, square-shaped, and octagonal perpendicular cylinders) and parallel lamellae with increasing film thickness or pillar gap are well explained by the modified strong separation theory. Our results indicate that array confinement can be an effective method to prepare novel polymeric nanopattern structures.     

Au-induced polyvinylpyrrolidone aggregates with bound water for the highly shape-selective synthesis of silica nanostructures

Novel Au-induced polyvinylpyrrolidone (PVP) aggregates with bound water (PVP-water) were created for the highly shape-selective synthesis of distinctive silica nanostructures, such as core-shell spheres, rods, snakes, tubes, capsules, thornlike, and dendritic morphologies. A water/PVP/n-pentanol system was first designed to bind water to PVP, and then Au nanoparticles were used to induce the PVP-water species to aggregate into distinctive soft structures by exploiting the interplay between PVP and gold. This was confirmed by the IR absorption spectra. The bound water in the soft structures was consumed during the hydrolysis of tetraethylorthosilicate and the target silica nanostructures were obtained. The soft structures, and therefore, the silica morphologies, can be readily tuned by adjusting the experimental parameters. The tunable Au-induced PVP-water soft structures reported herein open up new dimensions for the synthesis of distinctive nanomaterials (other than silica) that have new physicochemical properties and applications. These soft structures were also successfully extended to synthesize ZnO and SnO(2) particles with remarkable shapes, such as spheres, leaves, T-shaped structures, and dendritic morphologies.     

GenIce: Hydrogen‐Disordered Ice Generator

GenIce is an efficient and user‐friendly tool to generate hydrogen‐disordered ice structures. It makes ice and clathrate hydrate structures in various file formats. More than 100 kinds of structures are preset. Users can install their own crystal structures, guest molecules, and file formats as plugins. The algorithm certifies that the generated structures are completely randomized hydrogen‐disordered networks obeying the ice rule with zero net polarization. © 2017 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.     

The stability of the closest packings of Lennard-Jones particles with vacancy sublattices at negative pressures

The stability conditions were analyzed for two-and three-dimensional closely packed crystal structures including regular vacancy sublattices. The interaction of particles was described by the Lennard-Jones potential. The limiting negative pressure at which structures lost stability was calculated for the examples considered. The enthalpies of the structures in the region of their existence were compared. It was shown that the structures with vacancy or vacancy cluster sublattices could be stabler than ideal structures under certain conditions. A defect lattice became stabler than ideal if the concentration of defects did not exceed some threshold value. The results obtained contribute to the understanding of the special features of the behavior of crystals under dilatation conditions.     

Fabrication of polyaniline with hierarchical structures in alkaline solution

Nanosheet- or nanorod-based microspheres and nanorod-based microrods of polyaniline (PANI) with hierarchical structures were successfully prepared by oxidation polymerization of aniline in alkaline solution. Temperature was found to have important influence on the morphology of PANI hierarchical structures and their building blocks. The concentration of alkali (NaOH) could be used to guide the morphological evolution of PANI, from leaf-like structures to nanosheet-based particles, and to nanorod-based microspheres and nanorod-based microrods with increasing concentration of NaOH in synthesis. The chemical structures of product were characterized by FTIR, UV-vis spectra and XRD, and its solubility was also studied in this report.     

分级结构纳米材料的液相合成策略

由于具有多层次、多维度、多组分的耦合和协同效应,分级结构纳米材料的设计合成近年来吸引了广泛的关注.本文从分级结构的三种实现方式,即核壳结构、节型结构和分支结构,分别介绍其液相合成方法进展,并侧重从晶体成核生长和反应动力学等角度对分级结构的形成原理和影响因素进行阐述.总的来说,分级结构材料的构筑主要涉及次级结构材料在初级结构材料上的异质成核生长或两种材料之间的成分交换.其中,材料之间的晶格匹配度、次级结构材料的过饱和度及化学成键情况等是影响二次相成核位点及方式的重要因素,而对晶面能的调控是调节二次相材料生长行为的重要途径.对基于成分交换的合成策略来讲,一个重要的前提条件是两种材料具有相同的阴离子或阳离子.     

Atom accurate structure determination of alprazolam/cyclodextrin inclusion complexes by ROESY and computational approaches

A lot of interest has been seen in computational methods that provide reliable atom accurate structures of different molecular systems. In this article, we describe the complexation of alprazolam (ALP) with three cyclodextrins, i.e., α-, β- and γ-CD. ROESY spectra showed that no complex was formed between ALP and α-CD however, ring A of ALP formed ICs with β- and γ-CD. Therefore, structures of ALP/β-CD and ALP/γ-CD were obtained by a combination of NMR (2D-ROESY) and computational methods by a quantitative ROESY approach. Here we determined the structures of CD ICs by a method recently used in our laboratory and then the structures were obtained independently by DFT (B3LYP functional and def2-TZVP basis set). The structures obtained by both methods were compared with each other. Results demonstrated that our method provides reasonable structures comparable to DFT, and can be used to obtain highly atom accurate structures of CD inclusion complexes. Quantitative ROESY analysis of MM and MD structures consume less time and are cheap as compared to DFT, which is highly CPU demanding and time taking. Negative values of binding energy showed that the process of inclusion was spontaneous and complexes formed were stable. The large negative value of binding energy for ALP/β-CD as compared to ALP/γ-CD showed a higher binding affinity of ALP towards β-CD. FMO studies also revealed the higher HOMO-LOUMO gap for inclusion complexes as compared to pure ALP. Intermolecular H-bonds formed in both the complexes are also one of the forces responsible for inclusion complex formation.     

Design of three-dimensional, millimeter-scale models for molecular folding.

This communication describes the fabrication of three-dimensional structures of organic polymers using principles of design inspired by protein folding. The structures consist of rigid polyhedral components with dimensions of a few millimeters ("microdomains"), representing alpha-helical and beta-sheet secondary structures, connected with flexible linkers representing loops or turns. These structures were fabricated from polyurethane using photolithographic and soft lithographic techniques. The surfaces of the microdomains were patterned into hydrophobic and hydrophilic regions, and a hydrophobic photocurable liquid (serving both as lubricant and adhesive) was selectively precipitated onto the hydrophobic areas. The unfolded structures were suspended in water and agitated by tumbling. Self-assembly occurred through coalescence of the thin films of hydrophobic liquid, and was caused by minimization of the free energy of the interface between the liquid adhesive and the water. The self-assembled structures were locked in place by curing the adhesive with UV light. These results demonstrate the use of concepts abstracted from the study of proteins-including attractive hydrophobic interactions, shape complementarity, and conformational constraint-in the self-assembly of complex, three-dimensional structures on the millimeter scale.     

Self-assembly and chemical processing of block copolymers: A roadmap towards a diverse array of block copolymer nanostructures

Block copolymers can yield a diverse array of nanostructures.Their assembly structures are influenced by their inherent structures,and the wide variety of structures that can be prepared especially becomes apparent when one considers the number of routes available to prepare block copolymer assemblies.Some examples include self-assembly,directed assembly,coupling,as well as hierarchical assembly,which can yield assemblies having even higher structural order.These assembly routes can also be complemented by processing techniques such as selective crosslinking and etching,the former technique leading to permanent structures,the latter towards sculpted and the combination of the two towards permanent sculpted structures.The combination of these pathways provides extremely versatile routes towards an exciting variety of architectures.This review will attempt to highlight destinations reached by LIU Guojun and coworkers following these pathways.