瓜环与喹啉及其衍生物的相互作用

利用荧光光谱分析方法考察六、七及八元瓜环与喹啉、异喹啉、7-甲基喹啉相互作用的结构特征以及光学特性。与核磁共振技术比较,荧光光谱分析方法具有高灵敏性的特点,不仅可观察到喹啉及其衍生物与七元瓜环相互作用而引起的荧光性质变化;还能观察到它们与六元瓜环或八元瓜环相互作用所产生的变化,这是通常的NMR方法所不能实现的。实验表明喹啉、异喹啉、7-甲基喹啉与六、七及八元瓜环有包结作用,形成多种不同包结比的稳定包结配合物。实验也证实,瓜环与客体之间相互作用受到3种效应的协同影响:(1)疏水性的笼体效应(瓜环以其特殊的疏水性笼状结构,可与多种有机物发生疏水性的笼体作用);(2)亲水性的端口效应(瓜环端口环绕的羰基氧通过离子-偶极相互作用来键合金属离子或有机分子的带电部分);(3)相互作用的客体分子或瓜环笼体空间大小,即尺寸效应。     

Fluorescence Enhancement of Carbendazim Fungicide in Cucurbit[6]uril

The potential increase in fluorescence of a benzimidazole-type fungicide (carbendazim) due to complexation with cucurbit[6]uril is reported. The fluorescence of the probe carbendazim in aqueous Na₂SO₄ solution (pH=7.61) at room temperature is found to increase by a maximum factor of ∼10.0 and blue-shifted up to ∼11±1 nm with the increase in cucurbit[6]uril concentration up to ∼5 mM. This fluorescence enhancement is the result of formation of a 1:1 guest-host inclusion complex, in which the guest carbendazim is incorporated inside the hydrophobic cavity of the host curbit[6]uril through the amido-ester part. Such mode of inclusion is supported by NMR spectral measurements, in which upon encapsulation, the resonance of the methyl-protons of the amido-ester moiety is shifted significantly to upfield in the ¹H NMR spectrum. Also, to assess the formation of inclusion complex, solid samples prepared by co-evaporation have been studied, using differential scanning calorimetry (DSC). Measurement of the enhancement as a function of cucurbit[6]uril concentrations yielded a value of the equilibrium constant (K _a ) of 271±10 M⁻¹ at 25°C. From the temperature dependence of the equilibrium constants, ΔH and ΔS values have been negative in sign, indicating the dipole-dipole interactions and the steric factors associated with the formation of this inclusion complex. It might be proposed that the spectral changes due to the inclusion of carbendazim are the result of decrease in the polarity of the surrounded media rather than the loss of carbendazim rotational mobility.     

Discotic liquid crystals of cucurbit[7]uril (CB[7])-functionalised Laponite clays

ABSTRACT

Here we demonstrate that in the presence of the small, barrel-shaped molecule cucurbit[7]uril (CB[7]) Laponite clay particles undergo a phase transition into a birefringent gel with lamellar structure and a fluid, Laponite-poor aqueous solution. We employ various characterisation methods and polarised light microscopy to study this transition and the system's structural and optical properties. Furthermore, when dried completely we obtain a layered, transparent composite film, still retaining some liquid-crystalline structure that can be rehydrated reversibly. We argue that this new system may be a model system for anisotropic patchy particles.     

光谱法研究羟基葫芦[6]脲与甲基橙的分子识别作用

采用紫外和荧光光谱法研究羟基葫芦[6]脲(HOCB6)与甲基橙(MO)之间的包结作用,考察了溶液的pH值、常见有机溶剂和表面活性剂等对该包结物的形成及荧光强度的影响。实验结果表明,随着主体分子的加入,MO荧光增强且蓝移,说明客体被纳入主体分子的疏水性穴腔,形成内包结物。主客体分子之间主要通过疏水作用形成1∶1型的HOCB6-MO包结物,其包结常数为1.41×102 L·mol-1。同时采用葫芦[6]脲(CB6)、对-二甲氨甲基杯[8]芳烃和β-环糊精与MO的作用进行比较。研究发现,MO也能与葫芦[6]脲形成1∶1型的内包结物,但包结常数较小(34.65 L·mol-1);与β-环糊精形成1∶2型的内包结物,其包结常数为6.14×106 L2·mol-2;与对-二甲氨甲基杯[8]芳烃形成1∶1型的外包结物,导致荧光强烈猝灭,包结常数为1.35×104 L·mol-1。     

瓜环与咪唑[4,5,f]-1,10-菲咯啉衍生物相互作用模式的测试

以合成的三种的咪唑[4,5,f]-1,10-菲咯啉衍生物为客体,以瓜环(cucurbit[n]uriln=6～8)为主体,利用1H NMR技术,荧光光谱和紫外吸收光谱方法,测试了主客体相互作用形式、形成包结物的结构特征及其光学性质,三种方法得到的结果相同.研究表明,六元瓜环(Q[6])仅能与2-(4-甲基苯基)-咪唑-[4,5,f]菲咯啉(W1)盐酸盐相互作用(包结比为1:1);七元瓜环(Q[7])与三种客体2-(4-甲基苯基)-咪唑-[4,5,f]菲咯啉,2-(2-甲基苯基)-咪唑-[4,5,f]菲咯啉(W2)以及2-(3-甲氧基苯基)-咪唑-[4,5,f]菲咯啉(W3)的盐酸盐均以1:1的物质的量比发生相互作用;而八元瓜环(Q[8])除与W1形成的是1:2的包结物外,与另外两种客体W2,W3也是形成1:1的包结配合物.     

Tuning protonation states of tripelennamine antihistamines by cucurbit[7]uril

The formation of host–guest complexes of cucurbit[7]uril (CB7) with the antihistamine drug tripelennamine (TRP) was studied by optical and NMR spectroscopy. The experimental and computational results are consistent with inclusion of a single TRP molecule in CB7. Addition of CB7 has tuned drug protonation states associated with (de)protonation of the ethyldimethylammonium and exocyclic nitrogens with an increase in the associated pK_a values by 1.5 and 2.5 units, respectively. The incorporation of antihistamines drugs such as TRP in cucurbiturils could be utilized for switching their capability for selective binding to histamine H₁‐receptors, in the future. Copyright © 2015 John Wiley & Sons, Ltd.     

瓜环[n](n=7,8)与盐酸法舒地尔的相互作用研究

分别以NMR技术、电喷雾质谱、紫外光谱和红外光谱等分析方法考察了瓜环[n](n=7, 8)与盐酸法舒地尔的相互作用. 实验结果显示, 盐酸法舒地尔与两种瓜环都形成了1∶1的包结配合物, 但其主客体配合物的作用模式随着瓜环空腔大小的不同而各不相同. 通过紫外吸收光谱法计算出瓜环[n](n=7, 8)与盐酸法舒地尔的包结常数分别为2 524 L/mol, 1 216 L/mol, 其范围在200 L/mol~10 000 L/mol之内,这说明瓜环对盐酸法舒地尔具有潜在的药物缓释作用.     

<Emphasis Type="Italic">Cis</Emphasis>/<Emphasis Type="Italic">trans</Emphasis> Fluorescent Recognition by Naphthalimide Dyes ⊂ CB [7] Assembly

A novel method to recognize cis/trans isomers was studied here. The naphthalimide dye as guest could bind with host cucurbit [7]uril (CB [7]) and 1:1 naphthalimide dye ? CB [7] assembly was formed. Moreover, this assembly was used as a fluorescent probe to recognized Fumaric acid (FA) and maleic acid (MA) via fluorescence titration. Two carboxyls in MA are in the same side, they could form stable interaction with the assembly and the fluorescence intensity decreased obviously when naphthalimide dye ? CB [7] was titrated by MA (nearly quenched in 1.5 equiv). But two carboxyls in FA are in opposite sides, the interaction between FA and the assembly was weak and not stable, and the fluorescence intensity changed inconspicuously when the assembly was titrated by FA.     

Synthesis of capped nanosized Mn1−xZnxFe2O4 (0⩽x⩽0.8) by microwave refluxing for bio-medical applications

Substituted ferrites [Mn_1−xZn_xFe₂O₄ (0⩽x⩽0.8)] of nanoscale dimensions have been prepared by a novel microwave refluxing method. The effect of different parameters [such as pH, reflux time, presence of PEG (MW-3350) molecules] on particle morphology and size has been studied. Characterization of the above capped particles was done by XRD, FTIR, TEM and SQUID magnetometry. The as-prepared particles were further used for magnetoliposome preparation.     

Cucurbit[n]urils/CdS-MoS2的表征及可见光催化性能

为了降低CdS光生电子-空穴的复合对其光催化性能的影响,利用窄带隙半导体MoS₂和有机大分子瓜环(cucurbit[n]uril,Q[n])对CdS进行改性研究. 本文采用水热法合成了Q[n]/CdS-MoS₂\\(n=6,7,8)复合光催化剂. 利用FT-IR、XRD、XPS、SEM、UV-Vis和PL等手段对产物结构、形貌和光学等性质进行表征,并考察Q[n]/CdS-MoS₂复合催化剂对次甲基蓝、罗丹明B和结晶紫溶液的催化降解性能. 结果表明,瓜环对CdS-MoS₂颗粒生长结晶起到了调控作用,Q[n]/CdS-MoS₂(n=6,7,8)形成了具有花瓣状叶片的花团,催化剂表面积增大,活性位点增加,禁帯宽度减小,电子-空穴对得到了更好的分离和迁移. Q[6]/CdS-MoS₂和Q[7]/CdS-MoS₂对亚甲基蓝具有良好的光催化活性,催化过程为羟基自由基原理.     

Evolution of structures,stabilities, and electronic properties of anionic [AunRb]− (n = 1–10) clusters: comparison with pure gold clusters

The geometric structures, stabilities, and electronic properties of small size anionic [Au_nRb]^? and Au_n+1^? (n = 1–10) clusters have been systematically investigated by using density functional theory. The optimised geometries show that the structures of [Au_nRb]^? clusters favour the three-dimensional structure at n ≥ 8. The Rb atoms tend to occupy the most highly coordinated position and form the largest probable number of bonds with gold atoms. One Au atom capped on [Au_n-1Rb]^? structures is the dominant growth pattern for n = 2–8 and Rb atom capped on Au_n^? structures for n = 9–10. The averaged atomic bonding energies, fragmentation energies, second-order difference of energies, and highest occupied molecular orbital–lowest unoccupied molecular orbital gaps exhibit a pronounced even–odd alternations phenomenon. The charges in [Au_nRb]^? clusters transfer from the Rb atoms to Au_n host. In addition, it is found that the most favourable dissociation channel of the [Au_nRb]^? clusters is to eject a Rb atom and the highest energy dissociation path is Rb^? anion ejection.     

Theoretical study on complexation of the perchlorate,permanganate, pertechnate and perrhenate anions with dodecabenzylbambus[6]uril

By using quantum chemical calculations, the most probable structures of the anionic complex species dodecabenzylbambus[6]uril–ClO₄^?, dodecabenzylbambus[6]uril–MnO₄^?, dodecabenzylbambus[6]uril–TcO₄^? and dodecabenzylbambus[6]uril–ReO₄^? were derived. In these four complexes, each of the considered anions, included in the macrocyclic cavity, is bound by 12 weak hydrogen bonds between methine hydrogen atoms on the convex face of glycoluril units and the respective anion. Further, the corresponding interaction energies of the investigated four anionic complexes were calculated; the absolute values of these calculated energies increase in the series of ReO₄^? < TcO₄^? < MnO₄^? < ClO₄^?.     

Cucurbit[7]uril Disrupts Aggregate Formation Between Rhodamine B Dyes Covalently Attached to Glass Substrates

Dye aggregation is detrimental to the performance of high optical density dye-doped photonic materials. To overcome this challenge, the ability of cucurbit[7]uril (CB7) as a molecular host to disrupt aggregate formation on glass substrates was examined. Rhodamine B was covalently attached to glass slides by initially coating the surface with azidohexylsiloxane followed by copper-catalyzed “click” triazole formation with rhodamine B propargyl ester. The absorption and emission spectra of rhodamine B coated slides in water indicated diverse heterogeneous properties as surface dye density varied. Fluorescence quenching due to dye aggregation was evident at high surface dye density. Addition of aqueous cucurbit[7]uril (CB7) to the surface-tethered dyes perturbed the spectra to reveal a considerable reduction in heterogeneity, which suggested that the presence of a surface in close proximity does not significantly impair CB7’s ability to complex with tethered rhodamine B.     

Epitaxial growth of cobalt clusters on the bare and the oxide film grown on NiAl(1 0 0) surfaces

The structure of the nano-sized cobalt clusters on bare NiAl(1 0 0) and an oxidized NiAl(1 0 0) surfaces have been investigated by AES, LEED and RHEED. The deposition of Co onto bare NiAl(1 0 0) at room temperature led to small crystalline Co grains and surface asperities of substrate. The latter is likely induced by replacement of surface Al, Ni atoms by Co deposit. At 800 K Co particles aggregate to form clusters, but incorporation of Co into bulk NiAl(1 0 0) could occur upon annealing at 900 K. On the other hand, pure face-centered cubic (fcc) phase of Co crystallites of ≈1 nm in diameter with inclusion of smaller-sized particles (D < 1 nm) are observed on Θ-Al₂O₃ after Co deposition at room temperature. After annealing the Co nano-clusters grow larger at expense of small particles (D ≈ 3 nm), where the [1 1 0] and [−1 1 0] axis of the Co(0 0 1) facets are parallel to the [1 0 0] and [0 1 0] directions of (0 0 1)oxide, respectively. The in-plane lattice constant of Co clusters is ca. 4% larger than that of bulk Co, yielding less strain at the Co/oxide interface. A 15° ± 10% random orientation of the normal to (0 0 1) facet of Co clusters with respect to (0 0 1)oxide surface was deduced from the “arc”-shape reflection spots in RHEED. These results suggest that both orientation and phase of Co clusters are strongly affected by the nature and structure of oxide surface.     

Polyol synthesis and magnetic study of Mn3O4 nanocrystals of tunable size

Nanosized manganese oxide particles were prepared by the so-called polyol process. The average diameter of the particles was controlled by the growth time. X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photon spectroscopy (XPS) show that the particles are well crystallized, pure, stoichiometric Mn₃O₄ single crystals of uniform size ranging from about 5 to 12 nm. The variation of their dc-magnetization, M, as a function of the magnetic field, H, and temperature, T, clearly corresponds to ferromagnetic ordering at low temperature, with a Curie temperature slightly higher than 40 K. The evidence for superparamagnetism in these particles, due to their very small size, has been discussed in the light of their M(H) and M(T) for zero-field-cooled (ZFC) and field-cooled (FC) plots.     

Determination of time dependence of domain growth by direct observation of small metal clusters

The in situ growth of small gold clusters on amorphous carbon substrates has been measured by direct observation, utilizing high (single-atom) resolution scanning transmission electron microscopy. The time dependence of the width of the distribution of characteristic microscopic spatial frequencies in the samples was seen to obey a power-law behavior, HWHM = (t − t₀)^−a. The exponent measured, a = 0.15 ± 0.06, was in good agreement with scaling theories for domain growth. An excess of single atoms and small clusters was observed at all times, over that predicted by a uniform growth model of clusters. It is suggested that these support single-atom and few-atom cluster migration and activated accretion as important components of cluster growth at all times.     

A density functional theory study on the H2S molecule adsorption onto small gold clusters

An all-electron scalar relativistic calculation on Au_nH₂S (n = 1-13) clusters has been performed by using density functional theory with the generalized gradient approximation at PW91 level. The small gold cluster would like to bond with sulfur in the same plane and the H₂S molecule prefers to occupy the on-top and single fold coordination site in the cluster. The Au_n structures and H₂S molecule in all Au_nH₂S clusters are only slightly perturbed and still maintain their structural integrity. After adsorption, the S-H, H-H bond-lengths and most Au-Au bond-lengths are elongated, only a few Au-Au bond-lengths far from H₂S molecule are shortened. The reactivity enhancement of H₂S molecule is obvious and the strong gold-sulfur bond is observed expectedly. The most favorable adsorption takes place in the case that the H₂S molecule is adsorbed by an even-numbered Au_n cluster and becomes Au_nH₂S cluster with even number of valence electrons. It is believed that the strong scalar relativistic effect is favorable to H₂S molecule adsorption onto small gold clusters and is also one of the important reasons for the strong gold-sulfur bond.     

Effect of the geometric shape of Lu 2 O 3 : Eu spherical nanocrystals on their spontaneous luminescence

Monodisperse red phosphor particles 100 nm in diameter with the Lu_1.90Eu_0.10O₃ composition have been prepared using the developed technique for synthesizing spherical colloidal lutetium oxide particles with a size dispersion in the range 10–15%. The structure of spherical nanoparticles has been investigated, their excitation and photoluminescence spectra have been analyzed, and the lifetime of the ⁵ D ₀ excited state of Eu³⁺ ions has been considered. It has been found that the luminescence decay time for spherical particles increases by a factor of 1.39 compared to that for a powdered phosphor Lu₂O₃: Eu (5 at %) prepared and treated under the same temperature conditions as the Lu₂O₃: Eu (5 at %) spherical particles. This effect has been associated with the change in the photonic local density of states in spherical optical cavities consisting of particles of the phosphor.     

Chirality, defects, and disorder in gold clusters

Theoretical and experimental information on the shape and morphology of bare and passivated gold clusters is fundamental to predict and understand their electronic, optical, and other physical and chemical properties. An effective theoretical approach to determine the lowest-energy configuration (global minimum) and the structures of low energy isomers (local minima) of clusters is to combine genetic algorithms and many-body potentials (to perform global structural optimizations), and first-principles density functional theory (to confirm the stability and energy ordering of the local minima). The main trend emerging from structural optimizations of bare Au clusters in the size range of 12-212 atoms indicates that many topologically interesting low-symmetry, disordered structures exist with energy near or below the lowest-energy ordered isomer. For example, chiral structures have been obtained as the lowest-energy isomers of bare Au₂₈ and Au₅₅ clusters, whereas in the size-range of 75-212 atoms, defective Marks decahedral structures are nearly degenerate in energy with the ordered symmetrical isomers. For methylthiol-passivated gold nanoclusters [Au₂₈(SCH₃)₁₆ and Au₃₈(SCH₃)₂₄], density functional structural relaxations have shown that the ligands are not only playing the role of passivating molecules, but their effect is strong enough to distort the metal cluster structure. In this work, a theoretical approach to characterize and quantify chirality in clusters, based on the Hausdorff chirality measure, is described. After calculating the index of chirality in bare and passivated gold clusters, it is found that the thiol monolayer induces or increases the degree of chirality of the metallic core. We also report simulated high-resolution transmission electron microscopy (HRTEM) images which show that defects in decahedral gold nanoclusters, with size between 1-2 nm, can be detected using currently available experimental HRTEM techniques.     

Estimating the adsorption energy of element 113 on a gold surface

We report first-principle based studies of element 113 (E113) interactions with gold aimed primarily at estimating the adsorption energy in thermochromatographic experiments. The electronic structure of E113-Au _n systems was treated within the accurate shape-consistent small core relativistic pseudopotential framework at the level of non-collinear relativistic density functional theory (RDFT) with specially optimised Gaussian basis sets. We used gold clusters with up to 58 atoms to simulate the adsorption site on the stable Au(111) surface. Stabilization of the E113-Au _n binding energy and the net Bader charge of E113 and the neighboring Au atoms with respect to n indicated the cluster size used was appropriate. The resulting adsorption energy estimates lie within the 1.0–1.2 eV range, substantially lower than previously reported values.