Molecular association complex of urea with polyethylene: 2. The new preparation methods and morphological study

New systems for preparing urea-polyethylene complex have been discovered: (a) solid urea-polyethylene solution in xylene with a small amount of aniline; (b) solid urea with seeds-polyethylene solution in xylene. Scanning electron microscopy showed that the complex consisted of lamellae of the order of 1000 Å in size. Polyethylene molecules perpendicular to the lamellae exist as extended chains in the hexagonal urea tunnels, much as paraffin molecules in the urea-paraffin complex. Extended chain crystals similar to those crystallized under high pressure were obtained by elimination of the skeletal urea lattices of the complex by methanol. This morphology reflects the conformation of the guest polyethylene molecules.     

A hexagonal C3-symmetric (H2O)7 guest fits well into a C3-symmetric terbium complex cavity

A C₃-symmetric terbium complex {[Tb₂(pztc)₃]?6.5H₂O}_n (1) (pztc = pyrazine-2,3,5,6-tetracarboxylate), with hexagonal cavities, has been synthesized under hydrothermal conditions and characterized by X-ray single-crystal diffraction, elemental analysis, IR, TGA, PXRD and fluorescence measurements. The layer structure of the 2D complex is just like the structure of graphite. The most appealing structure is that a hexagonal C₃-symmetric (H₂O)₇ guest fits into the hexagonal C₃-symmetric terbium complex cavity very fitly. Furthermore, when the water clusters are driven off, the framework does not collapse and the luminescence intensity increases.     

Structural investigations of the poly(ε-caprolactam)-urea inclusion compound

An interesting inclusion compound (IC) between guest poly(ε-caprolactam) (PεCL) and host urea was successfully obtained, for the first time, by co-crystallization from their common solution. X-ray diffraction, infrared spectroscopy and differential scanning calorimetry have been utilized for a detailed structural investigation of PεCL-urea IC (U IC) crystals. The results were compared with those obtained for well-known structures of the hexagonal polyethylene-U IC, the trigonal polyethylene oxide-U IC and the ‘large tetragonal’ poly(propylene)-U IC. The structure of PεCL-U IC reconfirms that the urea host molecules may crystallize, even in the presence of a rather slim polymer guest, into an IC with a lattice channel diameter of more than 5.25 Å.     

Diffusional and orientational dynamics of various single terylene diimide conjugates in mesoporous materials

Mesoporous silica materials are ideally suited as host–guest systems in nanoscience with applications ranging from molecular sieves, catalysts, nanosensors to drug-delivery-systems. For all these applications a thorough understanding of the interactions between the mesoporous host system and the guest molecules is vital. Here, we investigate these interactions using single molecule spectroscopy (SMS) to study the dynamics of three different terylene diimide (TDI) dyes acting as molecular probes in hexagonal and lamellar mesoporous silica films. The diffusion behaviour in the hexagonal phase is represented by the trajectories of the single molecules. These trajectories are highly structured and thus provide information about the underlying host structure, such as domain size or the presence of defects inside the host structure. The three structurally different TDI derivatives allowed studying the influence of the molecular structure of the guest on the translational diffusion behaviour in the hexagonal phase and the lamellar phase. In the lamellar phase, the differences between the three guests are quite dramatic. First, two populations of diffusing molecules – one with parallel orientation of the molecules to the lamellae and the other with perpendicular orientation – could be observed for two of the TDI derivatives. These populations differ drastically in their translational diffusion behaviour. Depending on the TDI derivative, the ratio between the two populations is different. Additionally, switching between the two populations was observed. These data provide new insights into host–guest interactions like the influence of the molecular structure of the guest molecules on their diffusional as well as on their orientational behaviour in structurally confined guest systems.     

Structural information of long-chain fatty material obtained rapidly and conveniently by the use of X-ray diffraction studies of single crystals of urea and thiourea adducts

X-ray diffraction patterns of single crystals of urea or thiourea adducts of long chain fatty material (channel type of inclusion compounds) yield diffuse, continuous layer lines instead of the usual spots obtained with ordinary crystals. These lines result because adduct crystals have order in one dimension only, (the channel direction) whereas in ordinary crystals there is order in three dimensions which yields spots. These continuous layer lines offer possibilities for structure determination of the included molecule (guest). From their spacing, i.e., their distance from the equator, the length of the guest can be quickly calculated. This in turn can give information on 1) degree of branching, 2)cis-trans isomerism if the substance is unsaturated, and 3) molecular weight of the guest. From an evaluation of the intensities of the various orders of the layer lines, the position of a substituent group (such as a methyl, hydroxyl or keto group) on the hydrocarbon chain of the guest can be determined.     

Die kristallisation eines geschmolzenen molekülkomplexes aus hochmolekularem polyoxyethylen und harnstoff

The structural transformation of a molecular complex (MC) of polyoxyethylene and urea on cooling from the molten state has been investigated by DSC and X-ray analysis. A high-temperature polymorphic from of the MC was found to be formed, which transforms into the known crystal form of the MC with a hexagonal crystal modification on cooling.     

Nature and Size of Included Guest Molecule Determines Architecture of Crystalline Cyclodextrin Host Matrix

Owing to its annular shape, the cyclic hexasaccharide α-cyclodextrin (α-CD) can form inclusion complexes in aqueous solution. If these are crystallized, the guest molecules are invariably accommodated in the cavities of the host. Depending on size and molecular or ionic character of the guest, different crystal modifications are formed belonging to the herringbone or brick-type cage structures or to the channel structures. Small molecular guests lead to herringbone cages, small aromatic guests crystallize in brick-type cages whereas ionic and long molecular guests are enclosed in infinite channels. Thus, there is a clear dependence of crystal packing on the physical properties of the guest molecule. Polyiodide cocrystallizes with α-CD in different channel forms with iodine atoms arranged linearly in the channels. The packing of the channels is in tetragonal, hexagonal or sheet-like arrays, depending on counterions which are located in voids between the channels. If a α-CD is replaced by the larger β-CD (channel diameters 5 and 6.2 Å resp.), polyiodide now adopts a zigzag structure — a clear case of an influence of host matrix geometry on guest configuration.     

Crystalline complex between poly(γ-methyl l-glutamate) and dimethyl phthalate

The crystalline complex between poly(γ-methyl l-glutamate) (PMLG) and dimethyl phthalate (DMP) has been formed in films cast from a solution in dichloroethane. It has the stoichiometry of 1 mol of DMP to three or four residues of PMLG and shows two definite characteristics in X-ray diffraction patterns; one is the large hexagonal unit cell with the edge of around 28 Å and another the ‘extra’ 5.07 Å meridional reflection which can not be interpreted by a PMLG α-helical conformation. The structural examination for the films with various DMP contents is carried out by X-ray, viscoelastic, and d.s.c. measurements and the following structure is proposed for the crystalline complex. Four PMLG are associated to form a group which is hexagonally packed and DMP molecules, located in the gaps between groups, form a specific favourable helical structure along PMLG chains in which the van der Waals stacking of benzene rings of DMP is significant.     

Crystal structure and complexation and fluorescence behaviors of 1,4-bis (9-anthracenylmethyl) piperazine

The crystal structure of the photoinduced electron transfer (PET) fluoroionophore (3) was clarified by X-ray crystallographic analysis. A molecule 3 sits on a center of symmetry such that two anthracene ring systems are in an anti conformation with respect to one another across the piperazine ring. Intermolecular C-H···π and π···π interactions are observed. It was found that 3 was displayed unique photophysical properties in the presence of guest cations. Complexation of 3 with Zn2+ and NH?+ increased the fluorescence intensities of the host by a factor of 20.     

The effect of water and guest hydrophobicity on the complexation of oligomers with solid α-cyclodextrin

α-Cyclodextrin (α-CD), a cyclic oligosaccharide, can form inclusion complexes (ICs) with polymer molecules in which α-CD molecules stack in the columnar crystal to form a molecular tube. Physical mixtures of α-CD powder and oligomeric liquids such as poly(ethylene glycol) (PEG) have been shown to spontaneously form an IC, which is accompanied by a solid-state α-CD phase transformation from the cage to the columnar crystal structure. In this paper, the phase transformation is tracked with wide-angle X-ray diffraction as a function of temperature, atmospheric water vapor content and the type of guest molecule. A first-order kinetic model is used to describe the kinetics of complexation. The time required to completely complex PEG200 (200 g/mol) at low water activities is greater than 300 h, whereas only a few hours are necessary at high water activities. Solid-state complexation of α-CD with a hydrophobic guest molecule (hexatriacontane, HTC), is also reported here for the first time. Slower complexation kinetics are observed for α-CD with HTC compared to PEG600 (600 g/mol).     

Investigation of the structure of poly(vinyl alcohol)-iodine complex hydrogels prepared from the concentrated polymer solutions

The structure and dynamics of poly(vinyl alcohol) (PVA)-iodine complex hydrogels that were prepared from concentrated PVA solutions have been characterized by high-resolution solid-state ¹³C NMR spectroscopy. The fully relaxed dipolar decoupling (DD)/MAS ¹³C NMR spectrum indicates that the hydrogels contain at least two components, a highly mobile and broader components. The former is assigned to the soluble or well water-swollen PVA chains that are not closely associated with the PVA-iodine complexes, whereas the latter may be mainly ascribed to the aggregated PVA chains that are produced by the formation of the PVA-iodine complexes because no diffraction peaks due to the conventional PVA crystallites are observed by wide-angle X-ray diffractometry. Furthermore, ¹³C spin-lattice relaxation time (T_1C) analyses reveal that the broader component is composed of the highly restricted component probably assignable to PVA molecular chain aggregates containing the PVA-iodine complexes and the less mobile component. As for the former component, their CH resonance line measured by the T_1C-filtering method is successfully resolved into 7 constituent lines by the least-squares curve fitting. The statistical analysis of the integrated intensities of the constituent lines thus obtained also reveals that the probability f_a for the formation of intramolecular hydrogen bonding in the successive two OH groups along each chain and another probability f_t of the trans conformation are, respectively, as high as 0.86 and 0.88. This fact indicates that the PVA molecular chain aggregates containing the PVA-iodine complexes should be composed of PVA segments with the trans-rich conformation and the PVA-iodine complexes therein may also be formed with these several trans-rich segments surrounding the rod-like polyiodine cores in agreement with the so-called aggregation model. Moreover, several new diffraction peaks that should be interpreted in terms of the hexagonal structure are observed for the PVA-iodine complex hydrogels in the low 2θ region in the wide-angle X-ray diffraction (WAXD) profile measured by a strong X-ray source at SPring-8. This suggests the necessity of more detailed WAXD characterization to propose a new structure model, which should be referred to as the hexagonal aggregation model, for the PVA-iodine complexes.     

Synthesis and characterization of monetite and hydroxyapatite whiskers obtained by a hydrothermal method

High temperature hydrothermal syntheses, using calcium nitrate tetrahydrate, sodium dihydrogen phosphate and urea as precursors, and characterization of hydroxyapatite (HAp) whiskers are reported herein. The morphology and chemical composition of the crystals from a monetite to a hydroxyapatite phase were controlled by varying the starting concentrations of the precursors and the solution pH through the amount of urea that is decomposed during heating. X-ray diffraction (XRD) analysis, infrared spectroscopy (IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) were used to investigate the products of the syntheses in order to find the optimum reaction conditions for obtaining the desired morphology and phase composition. Different morphologies ranging from single crystals of monetite through rods and plates of hydroxyapatite with different size distribution to whisker-like single hydroxyapatite crystal were achieved by simply varying the starting concentration of urea. Structural refinement of the hydroxyapatite whiskers confirmed a strong preferential orientation along the c-axis direction of the hexagonal crystal structure, which was significantly different from the usually observed random crystal orientation. TEM and SEM analysis of the apatite whiskers confirmed single crystal structure with the a c-axis orientation parallel to the long axis of the whiskers, with sizes up to 150 μm in length, 10 μm in width and with a thickness of about 300 nm, that grew from the same centre of nucleation, forming flaky-like particles.     

Role of Guest Molecules on the Hydrate Growth at Vapor‐Liquid Interfaces

Systematic molecular dynamics simulations have been performed to illustrate the roles of guest molecules played in the process of hydrate growth at vapor‐liquid interfaces. In our simulations, guest molecules are represented by a commonly used single‐site Lennard–Jones model, and the roles of guest molecules on hydrate growth have been investigated separately from the effect of water–guest molecule attractive interaction ε and that of molecular size σ, respectively. Our simulation results demonstrate that the water‐guest molecule attraction regulates the pathway and rate of nucleus growth, whereas the size of guest molecules determines the dynamically preferable structure. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2621–2629, 2013     

Host–guest interactions in tetramethyl-cucurbit[6]uril with anti-tuberculosis drug isoniazid

A novel supramolecular host–guest complex of anti-tuberculosis drug isoniazid (INH) with symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril (TMeQ[6]) has been investigated using ¹H NMR spectroscopy methods, mass spectrometer and single-crystal X-ray diffraction analysis. The result revealed that the INH guest is located the portal of the TMeQ[6] host in both the solutions and the solid state. The driving forces for the association between the guest INH and the host TMeQ[6] are made by a balance between hydrogen bonding interactions and ion-dipole interactions.     

β-环糊精与罗丹明B及番红花红T包合作用的研究

合成了以β-环糊精为主体,罗丹明B及番红花红T为客体的包合物.用红外光谱、荧光光谱、共振瑞利散射光谱和差示扫描量热谱研究了β-环糊精与染料的包合机理.实验结果表明:β-环糊精与客体分子分别形成了1:1的包合物,客体分子进入β-环糊精分子的疏水性空腔内,当β-环糊精加入到一定浓度的客体溶液中时,罗丹明B体系的荧光强度和共振瑞利散射强度减弱,而番红花红T体系的荧光强度和共振瑞利散射强度增强.还通过荧光光谱法及共振瑞利散射光谱法分别测定了15、25和35 ℃ 3个不同温度时染料与β-环糊精包合体系的稳定常数.结果表明:包合物的形成主要取决于β-环糊精与客体分子的分子结构及两者作用力的大小,β-环糊精空腔大小与客体分子或其某些基团的大小越接近,越容易包合,包合物的稳定常数就越大.包合物的表观热力学常数显示,在上述包合体系反应的推动力是疏水作用力.     

Synthesis and properties of ZnS nanoparticles by solvothermal and pyrolysis routes using the Zn dithiocarbamate complex as novel single source precursor

In this work, the synthesis and characterization of ZnS nanoparticles prepared via two approaches, involving the thermal decomposition of the precursor complex in a furnace (pyrolysis) and by solvothermal process in the presence of hexadecylamine (HDA-ZnS), are reported. The precursor complex, Zinc (II) bis (N,N-diallyl dithiocarbamate), was synthesized and characterized by spectroscopic and single-crystal X-ray techniques. The spectroscopic analyses of the complex indicated a symmetrical bidentate coordination of the dithio ligand through the S-atoms. The single-crystal X-ray structure revealed a distorted square pyramidal coordinate geometry with S atoms around the Zn ion. The optical properties and the morphology of the as-prepared nanoparticles were studied by UV-Vis and photoluminescense spectroscopy, and transmission electron microscopy (TEM), respectively. HDA-ZnS are spherical and monodispersed with an average size of 4.5?nm, as estimated from the optical absorption spectrum and the TEM image. The ZnS nanoparticles obtained via pyrolysis in a furnace yielded the hexagonal wurtzite phase, whereas the HDA-ZnS nanoparticles showed a mixture of wurtzite and cubic phase with the cubic phase being dominant.     

Structure of a cyclopropane sorption complex of dehydrated fully Mn-exchanged zeolite X

The structure of a cyclopropane sorption complex of dehydrated fully Mn²⁺-exchanged zeolite X, Mn₄₆Si₁₀₀Al₉₂O₃₈₄ · 30C₃H₆ (a=24.690(4) Å), has been determined by single-crystal X-ray diffraction techniques in the cubic space group at 21(1)°C. The crystal was prepared by ion exchange in a flowing stream of 0.05 M aqueous Mn(NO₃)₂ for three days, followed by dehydration at 460°C and 2×10⁻⁶ Torr for two days, and exposure to 100 Torr of cyclopropane gas at 21(1)°C. The structure was determined in this atmosphere and was refined to the final error indices R₁=0.065 and R₂=0.071 with 509 reflections for which I>3σ (I). In this structure, Mn²⁺ ions are located at two crystallographic sites. Sixteen Mn²⁺ ions fill the octahedral site I at the centers of the hexagonal prisms (Mn–O=2.290(9) Å). The remaining 30 Mn²⁺ ions are at site II; each extends 0.41 Å into the supercage (an increase of 0.27 Å upon C₃H₆ sorption as compared to fully dehydrated Mn₄₆Si₁₀₀Al₉₂O₃₈₄) where it coordinates to three trigonally arranged framework oxygens at 2.148(8) Å and complexes weakly and facially to a cyclopropane molecule by a primarily quadrupolar interaction. The carbon atoms of each cyclopropane molecule are equivalent and equidistant from its Mn²⁺ ion (Mn–C=2.95(9) Å). Because of high thermal motion, the C–C bond length is inaccurately determined; the value found, 1.21(8) Å, is too small.     

PREPARATION OF ZINC OXIDE NANOPARTICLE VIA UNIFORM PRECIPITATION METHOD AND ITS SURFACE MODIFICATION BY METHACRYLOXYPROPYLTRIMETHOXYSILANE

Zinc oxide nanoparticles were prepared by uniform precipitation using urea hydrolysis. The ZnO precursor was slowly deposited from aqueous solution. Anionic surfactant was added into solution to block ZnO crystal growth and its agglomeration. Then ZnO nanoparticles were synthesized by the calcination of the precursor at high temperature. Transmission electron microscope (TEM) observation and particle size analyzer demonstrated that the ZnO nanoparticle exhibited nearly spheric shape with 10-40 nm particle size. The surface of the ZnO nanoparticle was modified by methacryloxypropyltrimethoxysilane (MPS). FT-IR (Fourier transform-infrared spectrophotometry) and XPS (X-ray photoelectron spectrophotometry) revealed that MPS was grafted onto the zinc oxide nanoparticle. XRD (X-ray diffraction) showed that the ZnO nanoparticle was a hexagonal crystal with a perfect crystalline structure, and its crystalline morphology was not altered through surface modification. The activation index (AI) of the modified ZnO nanoparticle was measured. It was found that the surface of the ZnO nanoparticle was changed from hydrophilicity into hydrophobicity via surface modification, implying the enhancement of its compatibility with organic polymers. FE-SEM (field scanning electron microscopy) showed that the modified ZnO nanoparticles were homogeneously dispersed in PVC matrices. Consequently, ZnO nanoparticles were integrated with PVC matrices by the grafting organic molecule.     

PREPARATION OF ZINC OXIDE NANOPARTICLE VIA UNIFORM PRECIPITATION METHOD AND ITS SURFACE MODIFICATION BY METHACRYLOXYPROPYLTRIMETHOXYSILANE

Zinc oxide nanoparticles were prepared by uniform precipitation using urea hydrolysis. The ZnO precursor was slowly deposited from aqueous solution. Anionic surfactant was added into solution to block ZnO crystal growth and its agglomeration. Then ZnO nanoparticles were synthesized by the calcination of the precursor at high temperature. Transmission electron microscope (TEM) observation and particle size analyzer demonstrated that the ZnO nanoparticle exhibited nearly spheric shape with 10–40 nm particle size. The surface of the ZnO nanoparticle was modified by methacryloxypropyltrimethoxysilane (MPS). FT-IR (Fourier transform-infrared spectrophotometry) and XPS (X-ray photoelectron spectrophotometry) revealed that MPS was grafted onto the zinc oxide nanoparticle. XRD (X-ray diffraction) showed that the ZnO nanoparticle was a hexagonal crystal with a perfect crystalline structure, and its crystalline morphology was not altered through surface modification. The activation index (AI) of the modified ZnO nanoparticle was measured. It was found that the surface of the ZnO nanoparticle was changed from hydrophilicity into hydrophobicity via surface modification, implying the enhancement of its compatibility with organic polymers. FE-SEM (field scanning electron microscopy) showed that the modified ZnO nanoparticles were homogeneously dispersed in PVC matrices. Consequently, ZnO nanoparticles were integrated with PVC matrices by the grafting organic molecule.     

Unprecedented 4/5-methylimidazole linkage isomerism within a binuclear copper(II) complex molecule

A new dinuclear copper(II) complex namely [Cu₂(μ₂-1,4-CDTA)(H4Meim)(H5Meim)(H₂O)₂]·2H₂O (1,4-CDTA = Trans-14-cyclohexanediaminotetraacetate(4-) ion, H4Meim/H5Meim = 4/5-methylimidazole) has been synthesized and characterized by elemental analysis, thermo-gravimetry (TG), FT-IR and electronic (diffuse reflectance) spectroscopy. Single-crystal X-ray diffraction analysis reveals that in the dinuclear copper(II) complex molecule each tautomer (4-methylimidazole or 5-methylimidazole) is linked to a different metallic center within the same molecule. The results are briefly discussed on the basis of the previous literature. Attention is paid to the driving forces of this unusual reported structure in order to deepen on the factors that influence the linkage isomerism.