Preparation and Characterization of N-4-Nitrophenyl-L-prolinol Nanocrystals in Sol-Gel Matrices

Organic nanocrystals of N-4-nitrophenyl-l-prolinol (NPP) have been grown in sol-gel matrices prepared from silicon alkoxide precursors. Our process is based on the control of the nucleation and growth kinetics of the dye in the pores of dense gels. Nanocomposites gel-glasses are obtained with a high optical quality due to the small size of the nanocrystals (10-20 nm). Differential scanning calorimetry experiments evidenced clearly the melting point of NPP nanocrystals, which is registered 51°C above that of NPP powder. Micro-Raman and solid state NMR spectroscopies allowed us to demonstrate that our nanocrystallization process does not chemically modify NPP molecules. We specified also the nature of interactions existing between the NPP nanocrystals and the xerogels. These strong interactions, which explain the important increase of the melting point of the nanocrystals in comparison to the NPP powder, are hydrogen bonds between nitro groups of NPP and uncondensed silanol functions of the silicate network.     

Validation of an analytical method to determine trace metal impurities in fluoride compounds by flame atomic absorption spectroscopy

 The development of an analytical method for the determination of some heavy metals (Fe, Cu, Co, Zn and Ni) in fluoride compounds [Cu(BF₄)₂, Sn(BF₄)₂, Pb(BF₄)₂ and HBF₄] by flame atomic absorption spectroscopy is described. This method is to be used as a routine analytical method in an industrial quality control laboratory. To this end the "performance characteristics" of an instrumental analytical method such as matrix effects, sensitivity, linearity, detection and quantitation limits, precision and accuracy were evaluated for every system under study. The results of these investigations showed that non-spectral interferences (due to the presence of large concentrations of major metals such as Cu, Sn and Pb) were observed. Nevertheless it was possible to define a matrix concentration interval where matrix effects were not statistically significant, and therefore a direct calibration approach could be used as the calibration tool whenever the major metal concentration was not higher than 40×10^–3 kg l^–1. A guide to the developement of an analytical method for trace metal determination is provided. General tools for quality control have been used in order to show how an analytical method can be tested daily and evaluated in a convenient manner. Received: 29 January 1997 Accepted: 11 March 1997     

The synthesis of a precursor of polybenzimidazole (PBI) and blends with polyamic acid (PAA)

The precursor of polybenzimidazole (PBI), poly(3,3′-diamino-4,4′-benzidine isophthalamide) (PDABI), was synthesized from poly(3,3′-dinitro-4,4′-benzidine isophthalamide) (PDNBI) by reduction. With increasing temperature, the NH₂ moiety which was protected by SnCl₅^?1 could cyclize and form PBI. Blends with polyamic acid (LaRC-TPI) were prepared. Clear blend films were prepared at up to 400°C. The IR spectra displayed shifts in the NH stretching band, thereby providing evidence for specific interactions related to the miscibility of their cured blends. © 1993 John Wiley & Sons, Inc.     

NMR spectroscopic study of the inclusion complex of desloratadine with β-cyclodextrin in solution

Desloratadine (DES) is an antihistamine used in the treatment of allergies and chronic urticaria. ¹H NMR spectroscopic study of varying ratios of DES and β-Cyclodextrin (β-CD) in D₂O suggests the formation of a 1:1 inclusion complex formed by the penetration of Cl-substituted aromatic ring into the β-CD cavity. The stoichiometry and binding constant of the complex were determined by Scott’s method.     

Na3Fe(C2O4)3·5H2O的热解过程和FAB-MS断裂规律

以红外光谱法为主要手段，原位“跟踪”测定铁（Ⅲ）与乙二酸形成的配合物Ｎａ３Ｆｅ（Ｃ２Ｏ４）３．５Ｈ２Ｏ的热解过程，分析了气、固相热解产物。并以色谱分析、差热－热重分析和Ｘ－射线粉末衍射法定性、定量地验证其结果。测定了该配合物快原子轰击质谱，提出了断裂规律。铁的二元羧酸配合物的质谱尚属首见。     

Copper(I) hexafluoroantimonate - an example of a compound with Cu in a solely fluorine environment

Yellow-orange single crystals of CuSbF₆, were prepared by reacting Cu wire (∼10 mmol) with SbF₅ (∼3 mmol) in liquid anhydrous hydrogen fluoride (aHF) and by reduction of Cu(SbF₆)₂ with Cu metal in aHF. CuSbF₆ crystallizes rhombohedral at 296 K with the LiSbF₆ structure type, with a = 530.4(4) pm, c = 1453(1) pm and Z = 3, space group R (no. 148). The structure is dominated by isolated layers of regular [SbF₆]⁻ octahedra and Cu⁺ cations.An attempt to prepare CuF by reaction between CuSbF₆ and CsF in aHF at ∼190 K failed. Instead of CuF, a mixture of Cu and CuF₂ was obtained.     

铝交联皂石的合成和表征及催化性能

用XRD、化学分析、IR、MASNMR、TPD等手段表征了合成皂石及其铝交联物的结构。结果表明:皂石的交联密度与四面体层电荷和交联条件(Al/土比)有关。在乙醇氨化反应中,交联皂石显示了较好的催化活性和选择性。皂石的交联密度与液相产物分布的关系表明层柱材料对此反应具有择形催化作用。醇氨化反应可能是在吸附态NH_3和气相醇分子间进行的。     

乙苯脱氢铁系催化剂的穆斯堡尔谱研究

用穆斯堡尔法对乙苯脱氢铁系催化剂在反应条件下进行了研究。结果表明,反应前催化剂中的铁主要以α-Fe_2O_3和α-FeOOH的形式存在,在反应中主要组分为Fe_3O_4。用K_2CO_3和α-Fe_2O_3在高温下加热可以生成KFeO_2,后者在室温下很不稳定,在同样条件下很容易转化为Fe_3O_4。但钾的存在可促进催化剂中Fe~(3+)还原为Fe~(2+),有利于电子的交换,对催化活性起着助催作用。     

Sodium-23 Nuclear Magnetic Resonance Spectroscopy

With the availability of Fourier transform spectrometers, ²³Na-NMR spectroscopy has become an important tool. It affords direct insight into solvation and ion pairing phenomena, both in organic and in bio-inorganic systems. Monitoring the chemical shifts and linewidths of ²³Na signals gives access to binding constants, reorientational correlation times and the microdynamics of the sodium coordination shell. The binding of other cations can also be studied by ²³Na-NMR spectroscopy, in competition experiments.     

Taking snapshots of photoexcited molecules in disordered media by using pulsed synchrotron X-rays

Photoexcited molecules are quintessential reactants in photochemistry. Structures of these photoexcited molecules in disordered media in which a majority of photochemical reactions take place remained elusive for decades owing to a lack of suitable X-ray sources, despite their importance in understanding fundamental aspects in photochemistry. As new pulsed X-ray sources become available, short-lived excited-state molecular structures in disordered media can now be captured by using laser-pulse pump, X-ray pulse-probe techniques of third-generation synchrotron sources with time resolutions of 30-100 ps, as demonstrated by examples in this review. These studies provide unprecedented information on structural origins of molecular properties in the excited states. By using other ultrafast X-ray facilities that will be completed in the near future, time-resolution for the excited-state structure measurements should reach the femtosecond time scales, which will make "molecular movies" of bond breaking or formation, and vibrational relaxation, a reality.