The epitaxial sexiphenyl (0 0 1) monolayer on TiO2(1 1 0): A grazing incidence X-ray diffraction study

A para-sexiphenyl monolayer of near up-right standing molecules (nominal thickness of 30 Å) is investigated in-situ by X-ray diffraction using synchrotron radiation and ex-situ by atomic force microscopy. A terrace like morphology is observed, the step height between the terraces is approximately one molecular length. The monolayer terraces, larger than 20 μm in size, are extended along the [0 0 1] direction of the TiO₂(1 1 0) substrate i.e. along the Ti-O rows of the reconstructed substrate surface. The structure of the monolayer and its epitaxial relationship to the substrate is determined by grazing incidence X-ray diffraction. Extremely sharp diffraction peaks reveal high crystalline order within the monolayer, which was found to have the bulk structure of sexiphenyl. The monolayer terraces are epitaxially oriented with the (0 0 1) plane parallel to the substrate surface (out-of-plane order). Four epitaxial relationships are observed. This in-plane alignment is determined by the arrangement of the terminal phenyl rings of the sexiphenyl molecules parallel to the oxygen rows of the substrate.     

Isolierung und struktur des dreikernigen hexamethylbenzolzirkonium-komplexes [(Me6C6)3Zr3Cl6]2+ [(Al2Cl7)−]2

Crystals of the trinuclear complex [(Me₆C₆)₃Zr₃Cl₆][Al₂Cl₇]₂ have been obtained from the reaction of ZrCl₄, hexamethylbenzene, AlCl₃, and Al in benzene. They are monoclinic, space group C2/2, with Z  4 and lattice parameters a 14.167(3), b 27.779(7), c 15.721(3) Å and β 94.27(4)°. The Zr atoms form a regular triangle. Each pair of Zr atoms is bridged by two Cl atoms. The fifth coordination site of each Zr atom is occupied by a h⁶-Me₆C₆ group. The cation is almost isostructural with the known trinuclear cation [(Me₆C₆)₃Nb₃Cl₆]²⁺. Important distances are: ZrZr 3.35, ZrCl 2.56, and Zrcenter of C₆ ring 2.17 Å. One of the two independent [Al₂Cl₇]^? anions occurs in a staggered conformation and one occurs in an eclipsed conformation.     

Temperature-dependent behavior of a symmetric long-chain bolaamphiphile with phosphocholine headgroups in water: from hydrogel to nanoparticles

The temperature-dependent self-assembly of the single-chain bolaamphiphile dotriacontan-1,1'-diyl-bis[2-(trimethylammonio)ethyl phosphate] (PC-C32-PC) was investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), X-ray scattering, rheological measurements, and dynamic light scattering (DLS). At room temperature this compound, in which two phosphocholine headgroups are connected by a C(32) alkyl chain, proved to be capable of gelling water very efficiently by forming a dense network of nanofibers (Kohler et al. Angew. Chem., Int. Ed. 2004, 43, 245). A specific feature of this self-assembly process is that it is not driven by hydrogen bonds but solely by hydrophobic interactions of the long alkyl chains. The nanofibers have a thickness of roughly the molecular length and show a helical superstructure. A model for the molecular structure of the fibrils which considers the extreme constitution of the bolaamphiphile is proposed. Upon heating the suspensions three different phase transitions can be detected. Above 49 degrees C, the temperature of the main transition where the alkyl chains become "fluid", a clear low-viscosity solution is obtained due to a breakdown of the fibrils into smaller aggregates. Through mechanical stress the gel structure can be destroyed as well, indicating a low stability of these fibers. The gel formation is reversible, but as a drastic rearrangement of the molecules takes place, metastable states occur.     

Stereoselective methadone disposition after administration of racemic methadone to anesthetized Shetland ponies assessed by capillary electrophoresis

The enantioselectivity of the pharmacokinetics of methadone was investigated in anesthetized Shetland ponies after a single intravenous (0.5 mg/kg methadone hydrochloride; n = 6) or constant rate infusion (0.25 mg/kg bolus followed by 0.25 mg/kg/h methadone hydrochloride; n = 3) administration of racemic methadone. Plasma concentrations of l -methadone and d -methadone and their major metabolites, l - and d -2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), respectively, were analyzed by CE with highly sulfated γ-cyclodextrin as chiral selector and electrokinetic analyte injection from liquid/liquid extracts prepared at alkaline pH. In both trials, the d -methadone concentrations were lower than those of l -methadone and the d -EDDP levels were lower than those of L-EDDP. For the case of a single intravenous bolus injection, the plasma concentration versus time profile of methadone enantiomers was analyzed with a two-compartment pharmacokinetic model. l -methadone showed a slower elimination rate constant, a lower body clearance, and a smaller steady-state volume of distribution than d -methadone. d -methadone and d -EDDP were eliminated faster than their respective l -enantiomers. This is the first study that outlines that the disposition of racemic methadone administered to anesthetized equines is enantioselective.     

甘油氧化的光谱电化学傅里叶变换衰减全反射谱红外光谱薄膜流动池中硼酸镍层厚度的优化

在碱性甘油电氧化反应中,利用电化学傅里叶变换衰减全反射谱红外光谱法,研究了薄膜流动池中滴注硼酸镍催化剂负载量对玻碳电极性能的影响.连续操作的径向流动池包括一个位于内反射元件上方50μm的钻孔电极,可实现红外光谱分析.这是在确定条件下对电催化剂进行简便和可重复筛选的一个适合的方法,同时还提供了对复杂反应(如甘油氧化)产物选择性的检测.通过对泵送电解液进行更耗时的定量高效液相色谱分析,结果表明,衰减全反射红外光谱法可快速鉴定产物.在层流条件下,水中使用0.1 M甘油和1 M KOH,流速为5μL min-1时,甘油转化率较高.转化率和选择性取决于催化剂的负载量,负载量又决定了催化剂层的厚度和粗糙度.由于在更粗糙的膜中停留时间更长有利于再吸附和C-C键断裂,因此当负载量最高达210μg cm-2时,甘油转化率为73％且甲酸选择性接近80％.当最低负载量为13μg cm-2时,甘油转化率达到63％,甲酸选择性降至60％,相应地,C2物种(如乙醇酸盐)选择性较高,为8％.因此,只有催化剂负载量较低时才能形成几微米厚度范围内的薄膜,此时才适合进行优质催化剂的筛选.