Polycatenation‐Driven Self‐Assembly of Nanoporous Frameworks Based on a 1D Ribbon of Rings: Regular Structural Evolution,Interpenetration Transformation,and Photochemical Modification

A series of nanoporous frameworks constructed by a polycatenated isoreticular 1D ribbon of rings have been developed. The orientation of catenated ribbons can be fine tuned by varying counter anions, which allows both pore size and shape to be systematically adjusted in a pre‐synthetic process. Distinct from conventional pore construction modes in which the organic linkers are alternately connected by metal nodes into a 3D periodic arrangement, the present polycatenation approach represents an alternative for constructing soft porous materials with tunable pore metrics and functions. Furthermore, these porous structures can interconvert into each other based on an anion‐exchange process, accompanied by the transformation of the interpenetrating structures in different dimensional networks, which is unusual in porous frameworks. In addition, such a porous framework can be post‐synthetically modified by a photoinduced [2+2] cycloaddition reaction, which not only achieves the surface modification (from conjugated to non‐conjugated inner surface), but also triggers the structural transformation from low dimension to high dimension. Such a post‐modification process reinforces the pore architecture through a covalent locking effect and has a great impact on the adsorption properties.     

Spontaneous curvature induced shape transformations of tubular polymersomes

The behavior of tubular polymersomes is investigated within the framework of the elastic energy model. The transition from a cylindrical tube to a chain of beads connected by small necks is studied in detail. The evolution of a polymersome shape, resulting from a change of the temperature is modeled by the shape transformations caused by a change of the spontaneous curvature. Good agreement between the experiments and the theoretical calculations is found.     

The electronic structure of nonpolyhex carbon nanotubes

Generalizing the folding method to any periodic two-dimensional planar carbon structures we have calculated the corresponding electronic structures in the framework of the one orbital one site tight-binding (Bloch-Hückel) method by solving the eigenvalue problems in a numerical way. We discussed the metallic or the nonmetallic behavior of the nanotubes by applying the folding vectors of parameters (m, n). We extended the topological coordinate method to two-dimensional periodic planar structures as well. Nearly regular hexagonal, pentagonal, and heptagonal polygons were obtained. The curvatures of the final relaxed structures can be read from the sizes of the polygons. Thus relying only on the topological information we could describe the shape of the tubular structures and their conductivity behaviors.     

Control of self-organized contact instability and patterning in soft elastic films

The surface of a soft elastic film becomes unstable and forms a labyrinth pattern when a rigid flat plate is brought into adhesive contact, without application of any external pressure. These isotropic undulations have a characteristic wavelength, lambda approximately 3H, where H is the film thickness. We present here technique of ordering, aligning, and modulating these micro-labyrinth structures by using a patterned stamp, by varying the stamp-film inter-surface distance, by a lateral confinement of the instability and even by a simple shear motion of a flat stamp. Many complex structures, such as an array of femto-liter beakers and doubly periodic channels, are generated from a simple stamp consisting of parallel channels. The elastic nature of the patterns allows an in-situ tuning, manipulation, and reconfiguration of the microstructures. Regardless of their precise morphology, the structures continue to have the elastic length scale, lambda approximately 3H. The structures can also be made permanent as required by UV-ozone-induced oxidation of the structures. The underlying principles of the elastic contact instability presented here have the potential to develop into a new soft lithography technique-elastic contact lithography (ECL), allowing a simple, rapid and large area patterning of soft solids.     

典型蛋白质折叠中阳离子-π相互作用的特异性

蛋白质中的阳离子-π相互作用是带正电荷的氨基酸(Lys、Arg)和芳香族氨基酸(Phe、Tyr、Trp)之间的一种作用力.对α/β类蛋白中两种典型折叠类型(单绕和双绕)的研究表明:(1)单绕结构中阳离子-π相互作用的分布密度大约是双绕结构中的2.6倍;(2)在单绕结构中,样本所含氨基酸残基数量与样本中阳离子-π的数量有明显的相关性,在双绕结构中没有发现类似的相关性;(3)Lys、Arg与Tyr在单绕中比在双绕中更容易形成阳离子-π相互作用;(4)Arg-Tyr组合在单绕中出现的几率较大,Arg-Phe组合在双绕中出现的几率较大;(5)阳离子-π相互作用在65%的单绕样本中形成阵列或分布在结构的首尾间.     

How Nature Adapts Chemical Structures to Curved Surfaces

Guided by the symmetry in a natural way, periodic potential surfaces partition the space in solid crystalline compounds. The arrangement of atoms, clusters and molecules obviously follows the (in general) curved shape of these ‘space partitioners’. In structures, the atoms therefore choose only a very limited subset of the infinite set of possible positions. In collective structures the periodic surfaces separate areas of different interactions between atoms, clusters, and molecules. In a certain sense, they can be considered as inner surfaces, a knowledge of which reveals insights into the organization of crystalline matter. There are many good indications that the weakly bonded electrons in the highest occupied orbitals are preferably localized in the region of the space partitioners. Dynamic processes as well can be correlated to the shape of the periodic surfaces. Moreover, the surfaces are didactically very helpful in making accessible the complicated three-dimensional relations in collective structures because the main features are projected onto (although curved) two-dimensional creations. The application of periodic potential surfaces to such a variety of compounds as quartz, brass and alpha-amylose underscores their general significance. Simple qualitative considerations already reveal the manifold relations to animate and inanimate nature through to mathematics, art and architecture. It appears that, in a very universal sense, the adaption of structures to a collective order finds a natural solution through curvature.     

苯二胺双电荷离子的电荷分离和电子捕获诱导解离谱研究

本工作用电荷分离(CS)谱和电子捕获诱导解离(ECID)谱研究了三种苯二胺异构体的双电荷分子离子在气相中的结构和反应。三种异构体双电荷离子的电荷分离反应和电子捕获诱导解离反应有相同的反应通道。通过测量不同反应通道的动能释放, 推测出了双电荷离子解反应过渡状态的结构。另外, 三种异构体可用ECID谱来区分。     

Gas-Phase Structure of Amyloid-β (12 – 28) Peptide Investigated by Infrared Spectroscopy, Electron Capture Dissociation and Ion Mobility Mass Spectrometry

The gas-phase structures of doubly and triply protonated Amyloid-β_12-28 peptides have been investigated through the combination of ion mobility (IM), electron capture dissociation (ECD) mass spectrometry, and infrared multi-photon dissociation (IRMPD) spectroscopy together with theoretical modeling. Replica-exchange molecular dynamics simulations were conducted to explore the conformational space of these protonated peptides, from which several classes of structures were found. Among the low-lying conformers, those with predicted diffusion cross-sections consistent with the ion mobility experiment were further selected and their IR spectra simulated using a hybrid quantum mechanical/semiempirical method at the ONIOM DFT/B3LYP/6-31 g(d)/AM1 level. In ECD mass spectrometry, the c/z product ion abundance (PIA) has been analyzed for the two charge states and revealed drastic differences. For the doubly protonated species, N – C_α bond cleavage occurs only on the N and C terminal parts, while a periodic distribution of PIA is clearly observed for the triply charged peptides. These PIA distributions have been rationalized by comparison with the inverse of the distances from the protonated sites to the carbonyl oxygens for the conformations suggested from IR and IM experiments. Structural assignment for the amyloid peptide is then made possible by the combination of these three experimental techniques that provide complementary information on the possible secondary structure adopted by peptides. Although globular conformations are favored for the doubly protonated peptide, incrementing the charge state leads to a conformational transition towards extended structures with 3₁₀- and α-helix motifs.      

A study of the effect of network angle of fabrics on kinetics of impregnation upon molding of articles made from carbon plastics

The permittivity coefficient, volume, and porosity of an elementary cell of fabric filler have been calculated. Two types of fabric structures have been considered using the example of carbon fabric: standard, in which filament yarn is cylindrical, and spread, it which it has a rectangular shape. A reflector of a mirror space antenna has been considered characterized by the presence of doubly curved surfaces is used as the object of study. Modeling of the kinetics of impregnation of reflector for two types of fabric structures has been carried out using the RAM–RTM program. In the work, the effect of the network angle on the duration of impregnation process has also been investigated. Based on the results of calculation, reflector samples have been made and their quality has been evaluated. Theoretical and experimental results have been compared.     

Effects of microsolvation and aqueous solvation on the tautomers of histidine: a computational study on energy, structure and IR spectrum

Microsolvation and combined microsolvation-continuum approaches are employed to investigate the structures and energies of canonical and zwitterionic histidine conformers. The effect of hydration on the relative conformational stability is examined. The strategy of exploring singly and doubly hydrated structures and the possible microsolvation patterns are described. We find that bonding water molecule may significantly change the relative conformational stabilities. In gas phase, the singly and doubly hydrated canonical forms are more stable than their zwitterionic counterparts. In solution, the continuum solvent model shows that bare zwitterionic form is more stable than bare canonical form by 1.1 kcal/mol. This energy separation is increased to 2.2 and 3.4 kcal/mol with inclusion of one and two explicit water molecules, respectively. We have also observed that the doubly hydrated structures obtained by combining two water molecules simultaneously to the solute molecule are preferred over the stepwise hydration. Hydrogen bond energies for the most stable hydrated histidine tautomers are determined by the atoms in molecules theory. The infrared (IR) spectra for the most stable singly and doubly hydrated structures of both histidine tautomers in gas phase are characterized. The stretching frequencies for NH of imidazole ring and OH of COOH are red shifted due to the hydrations. The IR spectra for the most stable zwitterionic tautomers in solution are also presented and discussed in connection with the comparison to the experiments. The pKa values obtained for the ring protonated zwitterions with two explicit water molecules appear to be in good agreement with the experiments.     

Self-assembly of DNA double-double crossover complexes into high-density, doubly connected, planar structures

We designed a molecular complex, the double-double crossover, consisting of four DNA double helices connected by six reciprocal exchanges. Atomic force micrographs suggest that double-double crossover complexes self-assemble into high-density, doubly connected, two-dimensional, planar structures. Such structures may be suitable as substrates for the deposition of nanomaterials in the creation of high-density electrical and quantum devices. We speculate about a modified double-double crossover complex that might self-assemble into high-density, doubly connected, three-dimensional structures.     

Calculating the number of isomers and coding for condensed polycyclic systems: Enumeration of the polybenzenes

A method is proposed for constructing a linear canonical code for planar condensed polycyclic hydrocarbons whose molecules consist of rings identical in size. The code reflects the shape of the skeleton. A constructive enumeration is performed for the structures of the isocyclic and isoperimetric polybenzenes containing up to 24 rings and 34 perimeter bonds in the molecule with allowance for structures that give rise to nonplanar molecules on account of steric hindrance.Translated from Teoreticheskaya i Éxperimental'naya Khimiya, Vol. 23, No. 1, pp. 54–61, January–February, 1987.     

Bottom-up Synthesis and Thread-in-Bead Structures of Finite (n,0)-Zigzag Single-Wall Carbon Nanotubes

The last remaining synthetic target of finite single-wall carbon nanotube models, the zigzag nanotube, has been accomplished through bottom-up chemical synthesis. The zigzag nanotube was synthetically accessible without constructing long-sought yet elusive cyclacene structures but with a cycloarylene structure by devising its cutout positions. The persistent tubular shape was also perfected in this last model by cyclization of zigzag-shaped aromatic molecules with a synchronous topological arrangement. The crystal structure of this nanotube further revealed an entangled supramolecular assembly, which showed a novel way to align nanotube molecules by utilizing their open-end functional groups in a thread-in-bead molecular assembly.     

Time‐dependent density functional theory study on the electronic excited‐state geometric structure,infrared spectra,and hydrogen bonding of a doubly hydrogen‐bonded complex

The geometric structures and infrared (IR) spectra in the electronically excited state of a novel doubly hydrogen‐bonded complex formed by fluorenone and alcohols, which has been observed by IR spectra in experimental study, are investigated by the time‐dependent density functional theory (TDDFT) method. The geometric structures and IR spectra in both ground state and the S₁ state of this doubly hydrogen‐bonded FN‐2MeOH complex are calculated using the DFT and TDDFT methods, respectively. Two intermolecular hydrogen bonds are formed between FN and methanol molecules in the doubly hydrogen‐bonded FN‐2MeOH complex. Moreover, the formation of the second intermolecular hydrogen bond can make the first intermolecular hydrogen bond become slightly weak. Furthermore, it is confirmed that the spectral shoulder at around 1700 cm^?1 observed in the IR spectra should be assigned as the doubly hydrogen‐bonded FN‐2MeOH complex from our calculated results. The electronic excited‐state hydrogen bonding dynamics is also studied by monitoring some vibraitonal modes related to the formation of hydrogen bonds in different electronic states. As a result, both the two intermolecular hydrogen bonds are significantly strengthened in the S₁ state of the doubly hydrogen‐bonded FN‐2MeOH complex. The hydrogen bond strengthening in the electronically excited state is similar to the previous study on the singly hydrogen‐bonded FN‐MeOH complex and play important role on the photophysics of fluorenone in solutions. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009     

Doubly charged ion mass spectra. 2—aromatic hydrocarbons

Doubly charged ion mass spectra for 15 aromatic hydrocarbons have been obtained using a Nier-Johnson geometry, Hitachi RMU-7L mass spectrometer operating at 1.6 kV accelerating voltage. The doubly charged ion spectra have features that are characteristic of the individual compounds. Unsaturated aromatic molecules show intense molecular ions in contrast to saturated, substituted or heteroatom compounds which undergo extensive fragmentation. Ionization energies for forming doubly charged molecular ions and appearance energies for the prominent doubly charged fragment ions have been measured. Calculations of the SCF energies and structures of various doubly charged ions have been carried out. Measured and calculated ionization/appearance energies are in reasonable accord and lend support to the suggested ion structures.     

Periodic orbits in atomic hydrogen exposed to circularly polarised laser light

Exact circular periodic orbits for a hydrogen atom in a strong circularly polarised laser field are derived. A stability analysis shows one orbit to be stable or unstable depending on the laser parameters, whereas the other orbit is always unstable. These orbits are expected to manifest themselves as resonances in laser assistede ^? ?H ⁺ scattering. The binding mechanism for these resonances is provided by the trapping of the quantum mechanical wave function onto the neighbourhood of a classical periodic orbit. This mechanism is analogous to that for a Wannier ridge resonance in a doubly excited two-electron atom.     

Double‐Shell Vesicles,Strings of Vesicles and Filaments Found in Crosslinked Micellar Solutions of Poly(1,2‐butadiene)‐block‐poly(ethylene oxide) Diblock Copolymers

Micellar structures of amphiphilic poly(1,2‐butadiene)‐block‐poly(ethylene oxide) diblock copolymers have been crosslinked in aqueous solution by γ‐irradiation. By transmission electron microscopy (TEM) of negatively stained specimens it is shown that the predominant structures present are copolymer vesicles (which appear to be double‐layered). These fixed vesicles are stable with respect to their shape and can be transferred from water into a good solvent for both blocks, such as tetrahydrofuran, thus demonstrating the effectiveness of the crosslinking. In addition to the vesicles, a small number of flexible cylindrical/filamentous structures, sequentially fused vesicles/strings of vesicles and giant sheet‐like vesicles are also visible after cross‐linking. The vesicle chains seem to be formed by fusion of the double‐layered vesicles; the outer layer of the vesicles apparently fuses sequentially, whereas the inner shell remains intact, creating periodic linear thickenings.     

Homogeneous crystallization of the Lennard-Jones liquid. Structural analysis based on Delaunay simplices method

The crystallization process of a simple liquid upon slow cooling has been modeled by the Monte-Carlo method. The model contains 10,000 Lennard-Jones atoms in the model box with periodic boundary conditions. The model structure is investigated at different stages of crystallization using Delaunay simplices. The simplex belonging to one or another particular crystal structure was determined by the shape of the given simplex taking into account the shape of its neighboring simplices. Simplices typical of the fcc and hcp crystal structures, as well as of polytetrahedral aggregates, not typical of crystals, were studied. The analysis has shown that the “precursors” of a hcp structure are strongly dominating over the “precursors” of a fcc structure in liquid phase before the beginning of crystallization. When crystallization starts, small embryos of the fcc structure are observed; the simplices peculiar to hcp are present at that in great amount, but they are distributed over the sample more uniformly. As crystallization proceeds, the portion of the fcc phase grows faster than hcp. However, no unified crystal appears in our case of slow cooling of the model. A complex polycrystalline structure containing crystalline regions with multiple twinning, pentagonal prisms and elements of icosahedral structures arises instead.     

Coupling infrared multiphoton dissociation spectroscopy, mass-spectrometry and ion mobility spectrometry for the determination of structures of angiotensin II cations

Gas-phase structures of mass-selected singly- and doubly charged angiotensin ions have been determined by means of infrared multiple photon dissociation (IRMPD) spectroscopy and ion mobility spectrometry. Simulation of IRMPD spectra at the DFT level provides the location of the proton on the Arg side-chain in the case of the singly charged species. Interpretation of the ion mobility data suggests that the structures of singly- and doubly charged species are rather similar except for an internal proton transfer.     

氯代甲苯双电荷离子的单分子解离反应研究

研究了在70 eV电子轰击电离条件下，氯代甲苯及氯化苄产生的双电荷离子[C_7H_7Cl]~(2＋)、[C_7H_6Cl]~(2＋·)和[C_7H_5Cl]~(2＋)为母体的两种类型单分子解离反应．主要讨论了亚稳双电荷离子的异构化反应、失H解高的“偶电子规则”以及单分子电荷分离过渡态的结构．