Cluster shape anisotropy in irreversibly aggregating particulate systems

The results for cluster shape anisotropy over a broad range (10)(-3)-10(-1)) of monomer volume fractions, fv values, are presented for both two- (2d) and three-dimensional (3d) simulations of diffusion-limited (DLCA), ballistic-limited (BLCA), and reaction-limited (RLCA) cluster-cluster aggregation classes. We find that all three aggregation classes have different dilute-limit shape anisotropies, with the diffusion-limited model having the largest value of anisotropy and the reaction-limited model having the smallest. The simulation result for the cluster shape anisotropy for each of the three aggregation classes is slightly less than the corresponding prediction of the hierarchial model. In addition, we find excellent agreement between the 2d DLCA simulation results and experimental measurements of shape anisotropy. At late times, shape anisotropy decreases from the dilute-limit value.     

Influence of EDTA on the Morphology of Barium Carbonate Using High Gravity Technology

The superfine BaCO3 particles were synthesized by high gravity technology with BaCl2·2H2O and Na2CO3 as the raw materials. The changes of particle size and morphology were studied by adding different amount of EDTA, and rod-like, near-spherical and cylindrical shape BaCO3 were prepared. The BaCO3 particles were analyzed and characterized by TG/SDAT, SEM, XRD and FT-IR. The results indicated that the crystal transformation temperature and decomposition temperature of BaCO3 had increased because of EDTA addition. With the increase of EDTA amount, the shape of BaCO3 changed from irregular rod-like to near-spherical then to cylindrical shape. All different shape BaCO3 adopts orthorhombic crystal systems.     

Performance evaluation of 2D fingerprint and 3D shape similarity methods in virtual screening

Virtual screening (VS) can be accomplished in either ligand- or structure-based methods. In recent times, an increasing number of 2D fingerprint and 3D shape similarity methods have been used in ligand-based VS. To evaluate the performance of these ligand-based methods, retrospective VS was performed on a tailored directory of useful decoys (DUD). The VS performances of 14 2D fingerprints and four 3D shape similarity methods were compared. The results revealed that 2D fingerprints ECFP_2 and FCFP_4 yielded better performance than the 3D Phase Shape methods. These ligand-based methods were also compared with structure-based methods, such as Glide docking and Prime molecular mechanics generalized Born surface area rescoring, which demonstrated that both 2D fingerprint and 3D shape similarity methods could yield higher enrichment during early retrieval of active compounds. The results demonstrated the superiority of ligand-based methods over the docking-based screening in terms of both speed and hit enrichment. Therefore, considering ligand-based methods first in any VS workflow would be a wise option.     

Vibrational delocalization in ammonia aerosol particles

The present contribution investigates shape effects and surface effects in the infrared spectra of pure (NH(3)) and mixed (NH(3)-CO(2) and NH(3)-NH(2)D-NHD(2)-ND(3)) ammonia particles with sizes between about 1 and 50 nm. The particles investigated have been generated in a collisional cooling cell as aerosols at temperatures between 20 and 80 K. The contribution reveals that only the combination with a microscopic model leads to a comprehensive understanding of the various features observed in the experimental infrared spectra. As one of the major results, the corresponding exciton model explains why pronounced shape effects observed for pure particles only play a minor role in the case of mixed particles.     

High resolution gas phase photoabsorption spectra of SiCl4 and Si(CH3)4 at the silicon l edges: characterization and assignment of resonances

High resolution gas phase photoabsorption spectra of SiCl₄, and Si(CH₃)₄ have been measured using synchrotron radiation in the 100–225 eV photon energy range. This range encompasses the Si 2p, Si 2s and Cl 2p edges. Comparison with previous spectra shows that the high resolution is essential for characterizing all Si 2p features - both the narrow intense pre-edge features, and the broader above edge shape resonances. The Si 2s spectra, along with MS Xα calculations, enable assignment of the more complex Si 2p shape resonances. There is good agreement between theory and experiment for the Si 2p and Si 2s SiCl₄ shape resonance positions. The general shape of the shape resonance structure above the Si 2p and Si 2s edges of Si(CH₃)₄ is well reproduced by the Xα calculations.     

An EPR method for probing surface magnetic fields, dipolar distances, and magnetization fluctuations in single molecule magnets

We outline a spectroscopic method for probing the effective magnetic field B on the surface of crystals of the single molecule magnet (SMM) [(C6H15N3)6Fe8(mu3-O)2(mu2-OH)12]Br7(H2O)Br.H2O, (Fe8Br8). This technique utilizes the line shape changes in the EPR spectra of the organic radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) (g = 2.0036, single peak) adsorbed onto the sample. The temperature dependence of the EPR line shifts scale with the sample's magnetization as measured by a SQUID magnetometer. Analysis of the line shape in terms of dipolar coupling between the DPPH and the SMM molecules on the surface, yields their average dipolar distance. The method's potential for measuring the magnetization fluctuation dynamics is briefly pointed out using the SMM [Mn12O12(CH3COO)16(H2O)4].2CH3COOH.4H2O (Mn12-acetate).     

固定化无机结合肽AG4(NPSSLFRYLPSD)仿生制备银微晶体

摘要利用固定化的AG4进行了离体仿生制备银微晶的研究. 受静电力推动, 正离子化的PET-N(CH₃)₂膜表面吸附了AG4, AG4/ PET-N⁺⁽CH₃)₂膜经AgNO3溶液浸泡后, 用SEM观测发现了大小为1~2 μm的银微晶体, 其多数呈三角形和正方形. 经XPS检测, 银微晶体的Ag3d结合能为368.1 eV(Ag⁰的Ag_3d结合能标准值为368.2 eV), 同时还测得硝酸银的Ag_3d结合能为368.6 eV. 由此推断, 固定化后的AG4在离体条件下能将AgNO₃溶液中的Ag⁺还原为Ag⁰. 对Ag⁺在AG4/ PET-N(CH₃)₂膜上还原并形成微晶体的机理进行了初步分析和探讨.     

Shape-controlled synthesis and shape-induced texture of MnFe2O4 nanoparticles

Monodisperse MnFe2O4 nanoparticles with cubelike and polyhedron shapes were synthesized by reaction of Fe(acac)3 and Mn(acac)2 with 1,2-hexadecanediol, oleic acid, and oleylamine. Controlled evaporation of the particle dispersion led to nanoparticle superlattices. The crystal orientation of the particle in the assembly depends on the shape of the particles, with particles in a cubelike shape showing (100) texture and those in the polyhedron shape exhibiting (110) texture.     

二氧化三氮(N3O2)中性分子和离子的一些重要反应过程的理论研究

二重态的N3O2中性分子作为中间体, 在N3O2阴离子的光解离反应和NO+N2O←→N2+NO2反应中均起重要作用. 在CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)+ZPE的水平上, 对这两个反应进行了理论计算. 结果表明, 在N3O2阴离子的光解离反应中, 该阴离子先在光照下解离为与其具有相同的W构型的中性分子和一个电子, 这个中性分子是一个过渡态, 它将打破C2v构型变成具有Cs对称性的W型中间异构体, 然后再经过一个过渡态, 裂解成N2O+NO两个小分子. 这个裂解过程的能垒非常低(5.96 kJ/mol), 因此在实验中很难检测到W型的中间异构体. 在另一个重要的[N3O2]体系的反应(NO+N2O←→N2+NO2)中, 找到了两条反应通道, 其中不经过中间异构体的一步转化通道更为可行.     

Control of porosity geometry in amino acid derived nanoporous materials

Substitution of the pillaring ligand in the homochiral open-framework [Ni(2)(L-asp)(2)(bipy)] by extended bipy-type ligands leads to a family of layer-structured, homochiral metal-organic frameworks. The 1D channel topology can be modified by the nature of the organic linker, with shape, cross-section and the chemical functionality tuneable. In addition, the volume of these channels can be increased by up to 36 % compared to the parent [Ni(2)(L-asp)(2)(bipy)]. The linker 1,4-dipyridylbenzene (3rbp) gives access to a new layered homochiral framework [Ni(2)(L-asp)(2)(3rbp)] with channels of a different shape. In specific cases, non-porous analogues with the linker also present as a guest can be activated to give porous materials after sublimation. Their CO(2) uptake shows an increase of up to 30 % with respect to the parent [Ni(2)(L-asp)(2)(bipy)] framework.     

水热法制备纳米TiO2及其在水相介质中分散性的研究

以硫酸法钛白粉生产工艺的中间体偏钛酸为原料,采用水热法制备了纳米TiO2粉体。研究了磷酸、硫酸、反应温度及反应时间对TiO2粉体的晶型、粒径及形貌的影响,考察了其在水相介质中的分散性。并借助XRD、SEM、动态激光粒度分析仪和动电位及静态激光粒度分析仪对其进行了表征。     

Variational approach to wetting problems: Calculation of a shape of sessile liquid drop deposited on a solid substrate in external field

Analysis of the shape of sessile drops pinned to a solid substrate and exposed to the external potential is presented. Explicit expressions describing the drops’ shape are obtained with a calculus of variations for 2D and 3D wetting problems. The presented approach is applicable for analysis of electrowetting problems, the study of vibrated and centrifuged drops.     

Shape resonances in photoionization of diatomic molecules: An example in thed inner shell ionization of the hydrogen halides

A classification of the shape resonances in the photoionization of diatomic molecules into two types is proposed: the well known molecular shape resonances which appear in the σ _u channel for the photoionization of the σ _g shells of light molecules like 3σ _g in N₂ or in O₂, and the atomic-like shape resonances. To illustrate this last class of shape resonances, calculations in the frozen core static exchange approximation of thed inner shell photoionization cross sections, σ, and of the angular distribution parameters, β, are performed for both HBr and HI. In our model, the σ and β curves look roughly like that of the isoelectronic Kr and Xe rare gases, but in order to obtain quantitative agreement with experiment, an approach including interchannel interactions, i.e. similar to that used for the halogen atoms would be probably necessary.     

Spherical shape complementarity as an overriding motif in the molecular recognition of noncharged organic guests by p-sulfonatocalix[4]arene: complexation of bicyclic azoalkanes

[reaction: see text] The complexation of p-sulfonatocalix[4]arene (CX4) with 2,3-diazabicyclo[2.2.1]hept-2-ene (1), 2,3-diazabicyclo[2.2.2]oct-2-ene (2), 2,3-diazabicyclo[3.2.2]non-2-ene (3), 1-methyl-4-isopropyl-2,3-diazabicyclo[2.2.2]oct-2-ene (4), and 1-phenyl-2,3-diazabicyclo[2.2.2]oct-2-ene (5) was studied in D2O at pD 7.4 by 1H NMR spectroscopy. The formation of deep inclusion complexes was indicated by large upfield 1H NMR shifts of the guest protons (up to 2.6 ppm), which were also used to assign, in combination with 2D ROESY spectra, a preferential inclusion of the isopropyl group of 4 and a dominant inclusion of the azo bicyclic residue for 5. The bicyclic azoalkanes 1-3 showed exceptionally high binding constants on the order of 1000 M(-1), 1-2 orders of magnitude larger than for previously investigated noncharged organic guest molecules. The strong binding was attributed to the spherical shape complementarity between the guest and the conical cavity offered by CX4. Interestingly, although the derivatives 4 and 5 are more hydrophobic, they showed a 2-3 times weaker binding, which was again attributed to the deviation from spherical shape in these bridgehead-substituted derivatives. The preferential inclusion of the hydrophilic but spherical bicyclic residue of 5 rather than the hydrophobic aromatic phenyl group provides a unique observation in aqueous host-guest chemistry and corroborates the pronounced spherical shape affinity of CX4.     

Geometrically active atomic states and the formation of molecules in their normal shapes

We present a theory of molecular formation according to which the shape of polyhedral or coordination compounds is fixed to a very good approximation by the shape of a particular state (or states) of the central atom, which is activated by spin and spacial coupling of optimal strength between this state, called the geometrically active atomic state (GAAS) and the state of the ligands. For a molecule with a central atom, spacial coupling of optimal strength, means that the shape of the GAAS fixes the position of the ligands according to the maximum overlap principle of the Heitler–London, Slater, and Pauling theory of covalent bonding, whereby much of the energy lowering from the free atom limit is obtained by the maximization of the contribution of the exchange integrals. Hence, a direct causal relationship between the shape of the GAAS and the shape of the molecular state at equilibrium seems to exist. This relationship implies a picture of diabatic connection between the geometrically asymptotic region and the equilibrium region, which is driven by the coupled GAAS and provides the “why” of molecular shape. Since the latter is fixed by the shape of the GAAS (in cases of electronic complexity or of molecular instability it is possible that more than one GAAS contribute simultaneously), prediction of the shape of certain large systems can be made based on the a priori recognition of the corresponding GAAS. The concept of the shape of atomic states defined and computed quantum mechanically from the probability distribution ϱ(cos θ₁₂) of the angle θ₁₂ that the position vectors of two electrons form in the given atomic state. Specifically, it is deduced from the distribution's maxima which provide the most probable values of θ₁₂. As shown previously [Y. Komninos and C. A. Nicolaides, Phys. Rev. A 50 , 3782 (1994)], ϱ(cos θ₁₂) is obtainable directly from the state-specific expression for the Coulomb interaction, where the R^k integrals are replaced by Legendre polynomials P_k, multiplied by normalization constants and radial overlaps. The theory is demonstrated by explaining the shape of BeH₂, BH₂, CH₄, SiH₄, H₂O, H₂S, NH₃, PH₃, SF₆, and TiH₄ in terms of the shapes of the following GAAS. Be: 2s2p ³P⁰, B: 2s2p^{2 4}P, C: 2s2p^{3 5}S⁰, Si: 3s3p^{3 5}S⁰, O: 2s2p^{5 3}P⁰, S: 3s²3p³3d ³P⁰, N: 2s2p^{4 4}P, P: 3s3p³3d ⁴P⁰, S: 3s3p³3d^{2 7}F⁰, and Ti: 3d²4s4p ⁵G⁰. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 321–328, 1998     

2H nuclear magnetic resonance study of the molecular motion in cyanoadamantane. I. Supercooled plastically crystalline phase

The supercooled plastically crystalline phase (glassy crystal) of cyanoadamantane was investigated by multidimensional 2H NMR (T>Tg). Although the orientationally disordered crystalline phase always coexisted with the orientationally ordered crystalline phase, we were able to single out the signal from the glassy crystal by selective excitation and it was possible to carry out line shape measurements and two-dimensional (2D) experiments (in frequency and time domain). The latter directly reveal sixfold jumps with an reorientation of the molecular C3 axis via 90 degrees angles, thus reflecting the symmetry of the lattice. The motion around the C3 axis is found to be always fast. We can reproduce the line shape by random walk simulations properly taking into account these molecular motions. Both methods (line shape and 2D experiments) yield time constants which agree with those reported by other techniques. Refining the analysis a narrow distribution of correlation times is introduced to account for a weak stretching of the correlation function. We did not find any indication of a small angle process usually found in structural glasses. Thus, the motional process in the glassy crystal appears to be simple and quite different from that in structural glasses.     

Preparation of body-temperature-triggered shape-memory polyurethane with biocompatibility using isosorbide and castor oil

Shape memory polyurethanes (SMPUs) have attracted much attention in the biomedical field because they can easily control the transition temperature (T_trans) to shape memory and are biocompatible. In this study, a shape memory polyurethane with both biocompatibility and a T_trans close to the body temperature was synthesized by using natural derivatives of isosorbide and castor oil in place of petroleum-based materials. Isosorbide and castor oil were used to form net points, and polycaprolactone diol (PCL diol) acted as the switching segment. The synthesized four polyurethane (PCL diol/isosorbide/castor oil, PICU-1, 2, 3, 4) with different isosorbide contents exhibited desired thermal and mechanical properties. In the thermo-cyclic shape memory testing experiment, the PICU series demonstrated good shape memory property, with more than 95% shape recovery ratio (R_r) and more than 90% shape fixity ratio (R_f), and PICU-3 recovered its shape within 20 s in a 37 °C water bath. In addition, the PICU series proved to be safe materials with excellent biocompatibility, as indicated by the observed C2C12 cells viability and proliferation. The stent made with the PICU-3 film showed near complete magnetization at 37 °C within 18 s and proved to be a suitable self-expanding stent.     

硫化铜纳米粒子的多种制备方法

纳米粒子制备方法的研究在整个纳米技术领域占有十分重要的地位。目前,虽然纳米粒子的制备方法很多［1~7］,但合成工艺简单、成本低廉、易于工业化的合成技术还不多,限制了纳米材料奇特而广泛的应用前景。 纳米材料的功能不但取决于其化学组成,而且取决于纳米粒子的形态和物理组成。例如二氧化钛粒子粒径为2000nm时,对可见光的散射率最大,遮盖力最强,广泛用于高档油漆、油墨颜料,而粒径减小至 10~60nm时,则具有透明性、强紫外线吸收能力,可用于高档化妆品、透明涂料等[8] 。此外,形状不同亦将影响纳米粒子的性能,如磁记录粒子a-…     

Low-Energy Electron Attachment to Serine Conformers: Shape Resonances and Dissociation Dynamics

Shape resonances of electron-molecule system formed in the low-energy electron attachment to four low-lying conformers of serine (serine 1, serine 2, serine 3, and serine 4) in gas phase are investigated using the quantum scattering method with the non-empirical model potentials in single-center expansion. In the attachment energy range of 0-10 eV, three shape resonances for serine 1, serine 2, and serine 4 and four shape resonances for serine 3 are predicted. The one-dimensional potential energy curves of the temporary negative ions of electron-serine are calculated to explore the correlations between the shape resonance and the bond cleavage. The bond-cleavage selectivity of the different resonant states for a certain conformer is demonstrated, and the recent experimental results about the dissociative electron attachment to serine are interpreted on the basis of present calculations.     

熔盐快速合成Pb1-xLaxTiO3粉体

采用全氧化物为原料，利用熔盐法合成了Pb_1-xLa_xTiO₃(0.0≤x≤0.40)，当x=0.45时，烧绿石相La₂Ti₂O₇出现。计算了合成反应活化能，并在700 ℃下在NaCl-KCl体系中仅用5 min就合成了Pb_0.9La_0.1TiO₃。Pb_1-xLa_xTiO₃陶瓷在0.00≤x<0.25时，晶体结构为四方相，在0.25≤x≤0.40时为立方相。采用700 ℃ NaCl-KCl和900 ℃的Na₂SO₄-K₂SO₄两种熔盐体系获得了尺寸分布集中的球形颗粒，这些表明熔盐法晶体生长为扩散控制生长机理。