Agropine,a new amino acid derivative from crown gall tumours

Agropine, an unusual compound produced in plant tumours was shown by mass spectrometry and proton and carbon-13 nmr spectroscopy to be a bicyclic derivative of glutamic acid and a hexitol sugar.     

Cerium oxide nanoparticles scavenge nitric oxide radical (˙NO)

In this study we have obtained evidence that cerium oxide nanoparticles (CeO(2) NPs) are able to scavenge nitric oxide radical. Surprisingly, this activity is present in CeO(2) NPs with a lower level of cerium in the 3+ state (CeO(2) NPs with low 3+/4+ ratio and therefore a reduced number of oxygen vacancies), in contrast to the superoxide scavenging properties which are correlated with an increased level of cerium in the 3+ state (CeO(2) NPs with high 3+/4+ ratio and therefore an increased number of oxygen vacancies).     

A scanning tunneling microscopy study of water on Si(111)-(7 × 7): adsorption and oxide desorption

Scanning tunneling microscopy and temperature-programmed desorption have been used to investigate the chemistry of water on Si(111)-(7 × 7) substrates which were misoriented 2° toward the [ 10] direction. Upon room temperature exposure to water, the adatoms of the (7 × 7) unit cell are still evident even after high exposures, implying that major modifications of the substrate do not occur. At high coverages, the distribution of reacted adatoms shifts from one controlled by dissociative adsorption across the adatom-rest atom pair to a statistical distribution based on the availability of dangling bonds. Desorption of the oxide layer which remains after water adsorption and the desorption of hydrogen have also been characterized. The oxide desorption occurs along well-defined wavefronts which originate at step edges and advance in directions consistent with the underlying substrate symmetry, primarily the [ 2] direction (i.e. the wave vector points in the [ 2] direction). In regions of the surface where the oxide has desorbed, the (7 × 7) unit cell can be seen clearly. Vacancies resulting from the loss of surface silicon atoms (via the etching) coalesce into islands in the clean regions of the terraces, but unlike desorption of oxide layers from Si(100), the desorption does not occur from the boundaries of these vacancy islands.     

Kinetics of adsorption of high molecular weight anionic polyacrylamide onto kaolinite: the flocculation process

The adsorption kinetics of anionic polyacrylamide flocculant onto kaolinite clay are examined as a function of flocculant dosage and pH. Special attention has been given to the flocculation effect during the adsorption process and the resulting inhibition of further adsorption. At pH 8.5 the adsorption capacity of anionic polyacrylamide on kaolinite is low while at pH 4.5, the adsorption capacity increases. Flocculant adsorption has been shown to be related to the amount of available surface area, pH, flocculant dosage, and the resulting floc strength, which controls the rate of new surface area exposure and hence the continuation of further adsorption. At both pH 4.5 and pH 8.5, complete adsorption is achieved at low flocculant dosages and adsorption equilibrium is achieved at high flocculant dosages after 1 day. In contrast, at intermediate flocculant dosages adsorption equilibrium is not reached over a 7-day period, due to a continuously increasing surface area.     

The fast atom bombardment mass spectra of glucosinolates and glucosinolate mixtures

The behaviour of glucosinolates and desulphoglucosinolates under fast atom bombardment conditions has been investigated. Relatively little fragmentation was noted in the mass spectra of these compounds. The positive ion fast atom bombardment mass spectra of glucosinolates exhibited abundant cationized and protonated molecula ions, thus complementing the previously reported electron impact and chemical ionization mass spectra of these compounds. Desulphoglucosinolates yield only the protonated molecular ion. Under negative ion conditions the spectra of glucosinolates were dominated by the molecular anion and this has been used as a means of analysing a crude plant extract containing a complex mixture of glucosinolates.     

Kinetic study of the reactions of the sodium dimer (Na2) with a range of atmospheric species

The reactions of Na(2) with a series of atmospheric constituents were studied using a fast flow tube with detection of Na(2) by laser induced fluorescence at 656.2 nm [Na(2)(A(1)Sigma(+)(u) - X(1)Sigma(+)(g))]. The resulting rate coefficients at 298 K for the reactions of Na(2) with OH, O(2), NO(2), NO, O(3), H, H(2) and H(2)O are: (1.01(+0.35)(-0.25)) x 10(-10), (2.95 +/- 0.46) x 10(-11), (1.79(+0.51)(-0.31)) x 10(-10), (1.33 +/- 0.16) x 10(-11), (8.0(+24)(-3.0)) x 10(-11), < or =6 x 10(-12), 相似文献   

Comparison of Novel Sampling Methods for the Analysis of Capillary Electrophoresis Fractions by Matrix-assisted Laser Desorption/Ionization Time-of-flight Mass Spectrometry

Two methods for the collection of capillary electrophoresis fractions for analysis by matrix-assisted laser desorption/ionization have been investigated; the first using a novel ion-porous joint design for dropwise fraction collection and the second, a process of electrospray deposition. Sensitivity, shot-to-shot reproducibility, effect of matrix preparation and influence of buffer additives encountered in micellar electrokinetic capillary chromatography (MECC) have been examined using a standard peptide, methionine enkephalin. The direct collection of droplets from the capillary outlet was found to give a superior signal intensity, whereas the electrospray method, in its first stage of development, suffered through dilution effects and excessively wide sample distribution. The target compound was successfully collected by electrospray deposition and results indicated that signal intensity and sample homogeneity would be enhanced if the sprayed output could be collected into the sample wells in its entirety. The advantage of using electrospray deposition for the preparation of matrix layers followed by direct droplet collection onto the electrosprayed matrix was clearly demonstrated by improvements in both sensitivity and shot-to-shot variance in signal intensity across the sample well compared with collection onto spotted matrix. In addition, compatibility of the droplet collection method with MECC was illustrated by the recovery of the compound of interest from a buffer containing 30 mm sodium dodecyl sulphate. © 1997 John Wiley & Sons, Ltd.     

Slurry sampling for the determination of arsenic, cadmium, and lead in mainstream cigarette smoke condensate by graphite furnace–atomic absorption spectrometry and inductively coupled plasma–mass spectrometry

The slurry sampling technique has been applied for the determination of As, Cd, and Pb in mainstream cigarette smoke condensate (MS CSC) by graphite furnace-atomic absorption spectrometry (GF-AAS) and inductively coupled plasma-mass spectrometry (ICP-MS). The MS CSC of the 1R4F Reference Cigarette was collected by electrostatic precipitation and was subsequently prepared as two slurry samples with and without the dispersing agent Triton X-100. Comparison of results determined by ICP-MS analyses of the 1R4F MS CSC slurry samples with those from the conventional microwave digestion method revealed good agreement. The precision of Triton X-100 slurry sampling and of microwave-assisted digestion was better than 10% RSD, and both were superior to slurry sampling without use of Triton X-100. The accuracy of the analytical results for the Triton X-100 slurry sample was further verified by graphite furnace-atomic absorption spectrometry (GF-AAS). For GF-AAS, the method limits of detection are 1.6, 0.04, and 0.5 microg x L(-1) for As, Cd, and Pb, respectively. For ICP-MS, the method limits of detection are 0.06, 0.01, and 0.38 microg x L(-1) for As, Cd, and Pb, respectively. The MS CSC of the 1R4F Reference Cigarette was collected in accordance with the Federal Trade Commission (FTC) smoking regime (35 mL puff volume of 2-s puff duration at an interval of 60 s) and the concentrations of As, Cd and Pb were 6.0+/-0.5, 69.3+/-2.8, and 42.0+/-2.1 ng/cigarette, respectively.