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1.
2.
The action of ultra violet rays of 260 nm on aqueous solutions of bases, nucleosides and nucleotides of DNA at 77°K is studied by electron spin resonance. It is shown that the free radicals observed are similar, with a few noteworthy exceptions to those induced by X-rays, under the same conditions of temperature, in the solid state. Contrary to what might be excepted on the basis of the results obtained by X-rays, the variation in the yield in paramagnetic centres in each sequence studied does not seem to be important. 相似文献
3.
ALBERT VAN DE VORST 《Photochemistry and photobiology》1971,13(4):321-336
Abstract— –The photosensitization of amino acids by proflavine is studied using the technique of electron spin resonance spectroscopy. The analysis of the line shape as a function of the incident microwave power (both in the presence and absence of oxygen) and the dependence of the numbers of free radicals on the intensity of the incident light allow one to suggest that two types of radicals are formed. One is formed by a biphotonic process, the nature of the radicals being the same as in the case of ionising radiation, while the other is probably the RO2 radical formed as a result of photodynamic action. 相似文献
4.
The literature concerning the chemical and electrochemical reactions of nitric oxide, nitrous acid and nitrogen dioxide in aqueous solutions is reviewed briefly, with emphasis on electrochemical reductions at platinum electrodes in acidic solutions. The voltammetric behavior of NO and NO2 at a Pt electrode in perchloric acid is virtually identical to that for HNO2 and this is explained on the basis of a common electroactive precursor concluded to be NO+. Three cathodic waves are obtained for acidic solutions of NO, HNO2 and NO2. The first two waves correspond to reduction of NO+ to NO and N2O3 to NO, respectively. The presence of N2O3 results from decomposition of the parent compounds. The presence of Br- or Cl- in acidic solutions of the title compounds promotes the voltammetric reductions at lower H+ concentrations. This probably results from formation of electroactive nitrosyl halides. 相似文献
5.
Pierce KM Hope JL Johnson KJ Wright BW Synovec RE 《Journal of chromatography. A》2005,1096(1-2):101-110
A fast and objective chemometric classification method is developed and applied to the analysis of gas chromatography (GC) data from five commercial gasoline samples. The gasoline samples serve as model mixtures, whereas the focus is on the development and demonstration of the classification method. The method is based on objective retention time alignment (referred to as piecewise alignment) coupled with analysis of variance (ANOVA) feature selection prior to classification by principal component analysis (PCA) using optimal parameters. The degree-of-class-separation is used as a metric to objectively optimize the alignment and feature selection parameters using a suitable training set thereby reducing user subjectivity, as well as to indicate the success of the PCA clustering and classification. The degree-of-class-separation is calculated using Euclidean distances between the PCA scores of a subset of the replicate runs from two of the five fuel types, i.e., the training set. The unaligned training set that was directly submitted to PCA had a low degree-of-class-separation (0.4), and the PCA scores plot for the raw training set combined with the raw test set failed to correctly cluster the five sample types. After submitting the training set to piecewise alignment, the degree-of-class-separation increased (1.2), but when the same alignment parameters were applied to the training set combined with the test set, the scores plot clustering still did not yield five distinct groups. Applying feature selection to the unaligned training set increased the degree-of-class-separation (4.8), but chemical variations were still obscured by retention time variation and when the same feature selection conditions were used for the training set combined with the test set, only one of the five fuels was clustered correctly. However, piecewise alignment coupled with feature selection yielded a reasonably optimal degree-of-class-separation for the training set (9.2), and when the same alignment and ANOVA parameters were applied to the training set combined with the test set, the PCA scores plot correctly classified the gasoline fingerprints into five distinct clusters. 相似文献
6.
BARB FLORIN DAN; IONESCU VLAD; KONING WILLEM DE 《IMA Journal of Mathematical Control and Information》1994,11(4):277-309
In this paper, we deal with the digital output-measurement-feedbackH control problem for Pritchard-Salamon infinite-dimensionalsystems with unbounded input and output operators. A discretePopov-theory-based solution is given in terms of the solvabilityof Kalman-Szegö-Popov-Yakubovitch systems associated withthe equivalent discrete-time time-invariant system obtainedby lifting the T-periodic continuous-time system. 相似文献
7.
8.
Mineral and short-chain carboxylic acid vapours and NO(x) gases were reacted with cyclohexene oxide (1,2-epoxycyclohexane) to quantitatively produce specific, thermally stable cyclohexyl derivatives. Subsequent analysis of these derivatives by gas chromatography with mass spectroscopy and flame ionisation detection afforded a multi analyte method for the assay of these gaseous acidic atmospheric species. Derivatisation was found to be quantitative for the derivatives tested and the method highly sensitive (to 0.3 mg/m3 for a 30 l sample), accurate, precise and free from apparent interferences. The technique has been applied to "acid stack gases" and a number of other acid rich atmospheres and the results obtained show good agreement with the single analyte wet chemical determinations indicating that the approach has considerable potential as a routine analytical method for measuring such atmospheric pollutants. The high specificity of the reaction mechanism and its potential for the analysis of analyte mixtures is illustrated in the assay of nitric acid and its acid anhydride, dinitrogen pentoxide. 相似文献
9.
Carper WR Wahlbeck PG Antony JH Mertens D Dölle A Wasserscheid P 《Analytical and bioanalytical chemistry》2004,378(6):1548-1554
The molecular structure and rotational motion of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) were studied over a wide temperature range using the Bloembergen–Purcell–Pound 13C NMR spin–lattice relaxation method and NOE factors. Examination of the spin–lattice relaxation times (T
1) and the rates (R
1=1/T
1) of the 1-butyl-3-methylimidazolium cation reveals the relative motions of each carbon in the imidazolium cation. The rotational characteristics of the [BMIM] cation are supported by ab-initio molecular structures of [BMIM][PF6] using density functional theory (DFT) and Hartree–Fock (HF) methods. The ab-initio gas phase structures of [BMIM][PF6] indicate that the 1-butyl-3-methylimidazolium C2 hydrogen, the ring methyl group, and the butyl side-chain hydrogen atoms form hydrogen bonds with the hexafluorophosphate anion. 相似文献
10.
Volmer DA Brombacher S Whitehead B 《Rapid communications in mass spectrometry : RCM》2002,16(24):2298-2305
In this study, the performance of monolithic columns was evaluated for ultrafast liquid chromatography/mass spectrometry (LC/MS) analyses and for high-resolution separations of several azaspiracid biotoxin analogs. Because of their high permeability, monolithic columns offer a number of advantages over conventional packed columns; viz., very low backpressures and relatively flat van Deemter curves at high flow rates. That is, very high flow rates can be used for ultrafast analyses or, by using longer than normal columns, high-resolution separations are possible. In a series of experiments, we varied the mobile phase flow rates between 1 and 8 mL/min, and studied their impact on chromatographic parameters such as retention time, resolution, number of plates and pressure. The chromatographic run times could be reduced to ca. 30 s without a significant change in the separation efficiency. A signal intensity comparison revealed interesting differences between atmospheric-pressure chemical ionization (APCI) and electrospray ionization (ESI) in their flow-rate dependency. An explanation with respect to the behavior as of a mass-flow or a concentration-dependent device is given in the paper. Additionally, the column length was varied between 10 and 70 cm. As a result, the number of theoretical plates increased substantially. In the example shown in the report, an increase from 13 000 plates for a 10-cm column to 80 000 for a 70-cm column is demonstrated. In addition, the potential of the monolithic columns for high-resolution LC/MS separations is shown for a complex biotoxin mixture, which was separated on a 40-cm-long column. 相似文献