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The compound MOF-14 (Cu3(BTB)2, BTB = 4,4',4''-benzenetribenzoate) was synthesized by ball milling and characterized by powder X-ray diffraction (XRD). The raw material was activated using an efficient single washing step to ensure a free pore access. Nitrogen adsorption measurements were carried out to determine the specific areas of the samples before and after activation. To interpret the activation process in terms of blocking effects in the micropore channels, NLDFT evaluations (Nonlocal Density Functional Theory) of the MOF-14 nitrogen isotherms were carried out. In connection with the appearance of additional hysteresis loops in the nitrogen isotherms, calculations of the mesopore size distribution were performed using the method of Barret, Joyner, and Halenda (BJH). The results are compared to those of a structurally analogue MOF, namely HKUST-1 (Cu3(BTC)2, BTC = 1,3,5-benzenetricarboxylate). This comparison showed notable differences regarding the impact of the activation step on the formation of mesopores and their size distribution.
The formation and growth of hydroxylamine reduced silver nanoparticles were investigated by simultaneous Raman and UV/Vis spectroscopy coupled to an acoustic levitator as a sample holder. Based on the UV/Vis spectra, a two step particle formation mechanism with fast initial formation and adjacent coalescence can be proposed for the reduction of silver nitrate with hydroxylamine. The presence of the analyte adenine during particle formation resulted in differences in the adenine SERS signature compared to experiments, where adenine was added after particle synthesis. It was possible to monitor the adenine and sodium chloride induced aggregation of the nanoparticles and its dynamics based on both the extinction spectra and the SERS data. Correlating the information from the extinction spectra with the SERS intensity, the maximum SERS signals were observed at maximum extinction of the aggregated nanoparticle solution at the Raman excitation wavelength.
The formation of magnesium fluoride sols and xerogels according to the fluorolytic sol–gel synthesis based on the reaction of Mg(OMe)2 with non-aqueous HF has been thoroughly investigated by X-ray scattering (WAXS/XRD), TEM, SAXS, DLS and 19F MAS NMR spectroscopy. Mechanistic insights were gained by following the reaction progress and formation of intermediate phases of the fluorination of magnesium alkoxides. For F:Mg ratios of 0.3 and 0.4 the formation of two crystalline phases was observed containing the recently obtained compound [Mg6F2(OCH3)10(CH3OH)14] hexanuclear dicubane units. The stoichiometric reaction yields magnesium fluoride nanoparticles with crystallite sizes below 5 nm, which show broad reflections in the X-ray diffraction pattern. Metal fluoride sols prepared by this way undergo tremendous changes over the first several weeks after synthesis. Immediately after the fluorination, particles of about 120 nm—probably agglomerates—are formed, which break apart in the course of about one month of ageing and low-viscous, transparent sols with particles of about 12 nm are obtained. At the same time structural re-organisation processes within the magnesium fluoride particles are observed by an increase of the (110) reflection in WAXS.
Quinaldine (2-methyl quinoline) is a liquid at room temperature, which can be supercooled to reach finally the glassy state. By heating the glass above the glass transition temperature Tg = 180 K the sample performs two subsequent transitions into, likewise, dielectrically active phases. Thus, the reorientational relaxations of these phases as well as the kinetics of the phase transitions can be tracked in a highly resolved way by dielectric spectroscopy. X-ray diffraction analysis clearly shows two structurally different crystalline phases in addition to the supercooled liquid. Calorimetric measurements support the notion of first order phase transitions, occurring irreversibly in the supercooled regime, and suggest that the intermediate crystalline phase is metastable, too. Analyzing the quite distinct dielectric relaxation strengths, we discuss the possible nature of the two crystalline phases. Additionally, a very similar behavior to quinaldine is observed for 3-methyl quinoline, indicating a broad field of polymorphism among the quinoline derivatives.
Monodisperse, citrate-stabilized gold nanoparticles of sizes ranging from 15 to 40 nm were synthesized and characterized by small angle X-ray scattering and UV-vis experiments. Identical surface properties of nanoparticles of different sizes to avoid variation in the chemical surface-enhanced Raman scattering (SERS) enhancement, as well as selection of experimental conditions so that no aggregation took place, enabled the investigation of enhancement of individual nanospheres. Enhancement factors (EFs) for SERS were determined using the dye crystal violet (CV). EFs for individual gold nanospheres ranged from 102 to 103, in agreement with theoretical predictions. An increase of the EFs of individual spheres with size can be correlated to changes in the extinction spectra of nanoparticle solutions. This confirms that the increase in enhancement with increasing size results from an increase in electromagnetic enhancement. Beyond this dependence of EFs of isolated gold spheres on their size, EFs were shown to vary with analyte concentration as a result of analyte-induced aggregation. This has implications for the application of nanoparticle solutions as SERS substrates in quantitative analytical tasks.
Fractionation of a 70% ethanolic extract from twigs of Lindera obtusiloba BLUME (Japanese spicebush, Tohaku) yielded fi ve fractions of different polarity. The antifi brotic activity within the chloroform phase was best assessed by an in vitro bioassay using rat hepatic stellate cell (HSC) proliferation and their autocrine transforming growth factor beta (TGF-β) expression as sensitive fibrosis-associated read out. Chromatography of the chloroform extract on Sephadex LH-20 or liquid-liquid extractions yielded a crystalline compound as an active principle, which was identifi ed from NMR and ESI-MS analyses, its melting point, and its optical rotation as (7S,7'S,8S,8'S)-3,4:3',4'-bis(methylenedioxy) -7,9':7',9-diepoxy-lignane [(+)-episesamin]. X-Ray diffraction confirmed the structure and provided, for the fi rst time, directly its absolute confi guration. (+)-Episesamin blocked proliferation and the profi brotic autocrine TGF-β expression HSC without signifi cant cytotoxicity.