A combined experimental and computational approach was used to distinguish between different polymorphs of the pharmaceutical drug aspirin. This method involves the use of abinitio random structure searching (AIRSS), a density functional theory (DFT)-based crystal structure prediction method for the high-accuracy prediction of polymorphic structures, with DFT calculations of nuclear magnetic resonance (NMR) parameters and solid-state NMR experiments at natural abundance. AIRSS was used to predict the crystal structures of form-I and form-II of aspirin. The root-mean-square deviation between experimental and calculated 1H chemical shifts was used to identify form-I as the polymorph present in the experimental sample, the selection being successful despite the large similarities between the molecular environments in the crystals of the two polymorphs. 相似文献
The fluoroquinolone antibacterial agents possess photo-sensitizing properties that lead to phototoxic responses in both human and animal subjects. The phototoxicity order reported in humans is: fleroxacin > lomefloxacin, pefloxacin > ciprofloxacin ? enoxacin, norfloxacin and ofloxacin. Studies both in vivo and in vitro have related this phototoxicity to the generation of reactive oxygen species including hydrogen peroxide and the hydroxyl radical. We determined the quantum yields of singlet oxygen generation (φΔ,) by detection of the singlet oxygen (1O2) luminescence at 1270 tun for several fluoroquinolones, naphthyridines and other structurally related compounds. All the fluoroquinolones examined have low φΔ values ranging from 0.06 to 0.09 in phosphate buffer at pD 7.5. We also determined the 1O2 quenching constants for these compounds and their values were on the order of 106M?1 s1, except for lomefloxacin whose rate constant was 1.8 × 107M?1 s?1. The φΔ values were significantly decreased in a solvent of lower polarity such as methanol (0.007 ≤φΔ≤ 0.02). The production of 1O2 by these antibiotics did not correlate with the order reported for their phototoxicity. We also measured the photogeneration (λ > 300 nm) of superoxide by these antibacterials in dimethylsulfoxide using electron paramagnetic resonance and the spin trap 5,5-dimethyl-l-pyrroiine N-oxide. Although there is not a one-to-one correspondence between the relative rates of superoxide generation and the phototoxicity ranking of the fluoroquinolones, the more phototoxic compounds tended to produce superoxide at a faster rate. Nevertheless, the magnitudes of the observed differences do not appear sufficient to explain the range of fluoroquinolone phototoxicity potencies in human and animal subjects in general and the high activity of fleroxacin and lomefloxacin in particular. For these latter drugs the photoinduced loss of the F8 atom as fluoride and the concomitant generation of a highly reactive carbene at C-8 provide a more plausible mechanism for their potent phototoxic and photocarcinogenic properties. 相似文献
Zusammenfassung Tabakmosaikvirus hoher spezifischer Aktivität, das am Phosphor und/oder Kohlenstoff markiert war, wurde biosynthetisch hergestellt. Damit wurde jeweils ein Blatt einer Pflanze von Nicotiana tabacum infiziert und der etwaige Transport von intaktem Virus durch das Leitungssystem der Pflanzen dadurch weitgehend unterbunden, daß die Leitgefäße des behandelten Blattes durchtrennt wurden.Das aus den unbehandelten Blättern der Pflanze nach 17 1/2, 48 und 72 Stdn. isolierte Virus wies im Vergleich zum eingesetzten TMV einen viel geringeren Anteil an Gesamtradiokohlenstoff im Protein auf. Dies deutet darauf hin, daß das Virus der unbehandelten Blätter höchstens zu einem sehr geringen Teil aus intakt transportiertem TMV bestehen könnte.Die nicht im TMV enthaltenen Polynukleotide der unbehandelten Blätter enthalten 7 Stdn. nach der Infektion verhältnismäßig viel32P, doch tritt derselbe innerhalb 70 Stdn. zum allergrößten Teil in niedermolekulare Verbindungen über.Die in Puffer unlöslichen Polynukleotide der unbehandelten Blätter (Blattnukleinsäure) weisen ein mit der Zeit abnehmendes Verhältnis von32P/14C auf. Auch innerhalb der Nukleinsäure (NS) des TMV dieser Blätter nimmt dieses Verhältnis zunächst ab, steigt aber später wieder an.Die angeführten Ergebnisse stehen mit der Vorstellung im Einklang, daß das Virus NS abspaltet und sowohl die systemische Infektion der Pflanze wie auch die Virusvermehrung mindestens zum Teil durch diese freie NS bewirkt wird. Die aus dem Virus stammende freie NS unterliegt zum großen Teil lebhaftem Abbau, wobei ihre Komponenten wahrscheinlich dem Aufbau normaler Blattbestandteile dienen.Mit 3 Abbildungen 相似文献
The crystal structure of the complex [U(tpa)(2)]I(3), 1 (tpa = tris[(2-pyridyl)methyl]amine), has been elucidated. The complex exists as only one enantiomer in the crystal leading to the chiral space group P2(1)2(1)2(1). The coordination geometry of the metal can be described as a distorted cube. Accidental oxidation of [U(tpa)(2)]I(3) led to the isolation of the unusual mononuclear bishydroxo complex of uranium(IV) [U(tpa)(2)(OH)(2)]I(2).3CH(3)CN, 2, which was structurally characterized. The controlled reaction of [U(tpa)(2)]I(3) with water resulted in the oxidation of the metal center and led to the formation of protonated tpa and of the trinuclear U(IV) oxo complex ([U(tpa)(mu-O)I](3)(mu(3)-I))I(2), 3. The solid state and solution structures of this trimer are reported. The pathway suggested for the formation of this complex is the oxidation of the [U(tpa)(2)]I(3) complex by H(2)O to form a U(IV) hydroxo complex which then decomposes, eliminating mono-protonated tpa. The comparison with the reported reaction with water of cyclopentadienyl derivatives points to a higher reactivity toward water reduction of the bis(tpa) complex with respect to the cyclopentadienyl derivatives. The reaction of U(III) with methanol in the presence of the supporting ligand tpa leads to formation of alkoxo complexes similarly to what is found for amide or cyclopentadienyl derivatives. The monomethoxide complex [U(tpa)I(3)(OMe)], 4, has been prepared in good yield by alcoholysis of the U(III) mono(tpa) complex. The crystal structure of this complex has been determined. The reaction of [U(tpa)(2)]I(3) with 2 equiv of methanol in acetonitrile allows the isolation of the bismethoxo complex of U(IV) [U(tpa)I(2)(OMe)(2)], 5, in 35-47% yield, which has been fully characterized. To account for the oxidation of U(III) to U(IV) the suggested mechanism assumes that hydrogen is evolved in both reactions. 相似文献
Laser ablation coupled to inductively coupled plasma mass spectrometry has been developed for the elemental imaging of Mg, Fe and Cu distribution in histological tissue sections of fixed eyes, embedded in paraffin, from human donors (cadavers). This work presents the development of a novel internal standard correction methodology based on the deposition of a homogeneous thin gold film on the tissue surface and the use of the 197Au+ signal as internal standard. Sample preparation (tissue section thickness) and laser conditions were carefully optimized, and internal normalisation using 197Au+ was compared with 13C+ correction for imaging applications. 24Mg+, 56Fe+ and 63Cu+ distributions were investigated in histological sections of the anterior segment of the eye (including the iris, ciliary body, cornea and trabecular meshwork) and were shown to be heterogeneously distributed along those tissue structures. Reproducibility was assessed by imaging different human eye sections from the same donor and from ten different eyes from adult normal donors, which showed that similar spatial maps were obtained and therefore demonstrate the analytical potential of using 197Au+ as internal standard. The proposed analytical approach could offer a robust tool with great practical interest for clinical studies, e.g. to investigate trace element distribution of metals and their alterations in ocular diseases.
Figure
Development of a new internal standard correction methodology for qualitative elemental imaging by LA-ICP-MS 相似文献
The Thorpe-Ziegler reaction has been used in the preparation of enaminonitriles and cyclic ketones for many years. A wide variety of bases1 have been employed to acomplish this reaction, the most effective being the alkali metal salts of aralkyl amines. The reaction conditions vary from room temperature to toluene reflux temperature for long periods of time1. 相似文献
A facile procedure, involving one-pot synthesis of CeVO4/BiVO4 and in-situ reduction of graphene oxide (GO), has been used to prepare CeVO4/BiVO4/rGO nanocomposites. Different ratios of the CeVO4–BiVO4 were prepared to afford composites represented as CBVG3, CBVG5, and CBVG7. The ternary nanocomposite materials were characterized by using powder X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), photoluminescence and UV–vis spectroscopic techniques. Photocatalytic efficiency of the as-prepared ternary nanocomposites was investigated through the photo degradation of methyl orange under a visible light irradiation at 470 nm. The photocatalytic performance was enhanced by loading the CeVO4/BiVO4 nanoparticles on reduced graphene oxide (rGO), given MO degradation rate of 57, 65, 80, and 90% for BVG, CBVG3, CBVG5, and CBVG7, respectively after exposure to visible light for 120 min. Effects of experimental process parameters including initial dye concentration, catalysts loading and effect of different modification regimes were studied using CBVG7, which exhibited the highest efficiency. The improvement in the photocatalytic efficiency may be attributed to increased surface area of the nanocomposites, enhanced light absorption capacity and improved charge separation. The study showed a one-pot synthesis route to prepare promising CeVO4/BiVO4/GO nanocomposites for the photo-enhanced degradation of dye contaminants.
We observed for the first time a strong angle-independent modification of spontaneous emission spectra from laser dyes in photonic crystals, made of inverse opals in titania. Comparison with spectra from such crystals with much smaller lattice spacing, for which emission is in the long wavelength limit, reveals inhibition of emission up to a factor approximately 5 over a large bandwidth of 13% of the first order Bragg resonance frequency. The center frequency and bandwidth of the inhibition agree with calculated total density of states, while the measured inhibition of vacuum fluctuations is much larger. Because of the specific location of the dye molecules, we likely probe the strongly modulated local photonic density of states. 相似文献