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991.
Abstract— Kinetic studies of the hematoporphyrin–sensitized photooxidation of l -tryptophan and tryptamine at pH 10 in either homogeneous aqueous solutions or in aqueous dispersions of Triton X–100 and cetyltrimethylammonium bromide micelles indicate that the indole substrates are attacked via a mixed type I (electron transfer from triplet dye)/type II (1 O2 -involving) mechanism. Both reactive intermediates, generated by micelle-solubilized hematoporphyrin, can diffuse to attack substrate molecules located in either the bulk aqueous phase or a different micelle. In particular, incorporation of the substrate into a micelle has only minor effects on its reactivity toward1 O2 , although the 1 O2 —indole interaction appears to be more efficient in cationic micelles owing to a favourable orientation of the target with respect to the attacking species. On the other hand, the electron transfer from triplet porphyrin to a micellized substrate is virtually non-operative when the latter is located in an anionic micelle, whereas in neutral or cationic micelles, the efficiency of the process is again controlled by the substrate orientation. Studies of tryptamine photooxidation sensitized by meso-tetra-(4-sulfonato-phenyl) porphine in the presence of sodium dodecylsulphate micelles lend further support to the abovementioned conclusions. 相似文献
992.
Irma L. Botto Enrique J. Baran José C. Pedregosa Pedro J. Aymonino 《Monatshefte für Chemie / Chemical Monthly》1979,110(4):895-898
The infrared and laser-Raman spectra of crystalline Ba2V2O7 are reported and discussed by means of a Site Symmetry analysis.
28. Mitt. der Reihe Orthovanadate und verwandte Verbindungen. 27. Mitt.:E. J. Baran undM. E. Escobar, J. Phys. Chem. Solids, im Druck; 26. Mitt.:E. J. Baran, I. L. Botto, J. F. Ramos undP. J. Aymonino, Mh. Chem.109, 1139 (1978); 25. Mitt.:E. J. Baran, J. Mol. Struct.48, 441 (1978); 24. Mitt.:E. J. Baran undI. L. Botto, J. inorg. nucl. Chem.40, 1603, (1978); 23. Mitt.:M. E. Escobar undE. J. Baran, Z. Anorg. allg. Chem.,441, 273 (1978). 相似文献
993.
Experimental analysis of floc size distributions in a 1-L jar under different hydrodynamics and physicochemical conditions 总被引:1,自引:0,他引:1
This study focuses on the relation among hydrodynamics, physicochemical conditions, and floc size. During ortho-kinetic flocculation, the floc size is controlled by a balance between hydrodynamic stress and aggregate strength. Special attention was paid to the influence of a hydrodynamic sequencing on both the aggregate strength and the flocculation processes. Experimental research was conducted in a 1-L jar for two different pH values. The hydrodynamic sequencing was made up of successive slow and rapid mixing periods, and different slow mixing intensities were studied. First, the large floc size was shown to decrease with increasing velocity gradient (G), with an expected trend (d proportional variant epsilon(-1/4)). Then, the aggregate strength was shown to depend on two main factors: the flocculation history and the physicochemical conditions, which control the cohesion forces between primary particles. Finally, flocculation processes are discussed in terms of aggregation and breakup phenomena, with relation to local hydrodynamics and physicochemical conditions. 相似文献
994.
The use of composite biosensors for multianalyte detection strategies is discussed. Graphite–Teflon rigid composite biosensors offer the possibility of coimmobilization of several enzymes by simple physical inclusion in the bulk of the electrode matrix with no covalent linkages. A novel trienzyme graphite–Teflon–glucose oxidase (GOD)–alcohol oxidase (AOD)–peroxidase (HRP)–ferrocene bisosensor yielded amperometric steady-state currents similar to those obtained with graphite–Teflon–GOD–HRP–ferrocene and graphite–Teflon–AOD–HRP–ferrocene electrodes for the same concentration of glucose and ethanol, respectively. The performance of the trienzyme biosensor for multianalyte detection was evaluated with the simultaneous determination of glucose and ethanol after separation by HPLC, in samples of sweet wine. The simultaneous analysis of several analytes in the same sample should imply that, with an adequate dilution, the concentration levels of the analytes can be included within the ranges of linearity of the corresponding calibration plots. The use of two composite biosensors in a parallel configuration, so that different analytes can be simultaneously detected with no need of chromatographic separation, is also discussed. The usefulness of this approach was evaluated by the simultaneous analysis of glucose and ethanol in sweet wine, and of glucose and lactic acid in red wine. 相似文献
995.
A method based on selective pressurized liquid extraction (SPLE) followed by gas chromatography–negative ion chemical ionization-mass spectrometry (GC–NCI-MS) has been evaluated for analysis of decabromodiphenyl ether (PBDE-209) in sediment samples. Instrumental operating conditions such as source temperature and system pressure were optimized in the NCI-MS system, giving an instrumental detection limit of 2 pg. The limit of determination of the entire SPLE–GC–NCI-MS procedure was around 50 pg g–1 dry weight (dw), with repeatability of replicates between 4 and 21% relative standard deviation. Application of the method to 13 different river and marine sediment samples collected in Spain revealed that levels of decabromodiphenyl ether ranged between 2 and 132 ng g–1 dry weight. 相似文献
996.
Díez-Barra E García-Martínez JC del Rey R Rodríguez-López J Giacalone F Segura JL Martín N 《The Journal of organic chemistry》2003,68(8):3178-3183
New chiral, soluble binaphthyl derivatives that incorporate stilbenoid dendrons at the 6,6'-positions have been prepared. The synthesis of the new enantiopure dendrimers was performed in a convergent manner by Horner-Wadsworth-Emmons (HWE) reaction of the appropriately functionalized 1,1'-binaphthyl derivative (R)-1 and the appropriate dendrons (R)(2n)G(n)-CHO. Different electroactive units were incorporated in the peripheral positions of the dendrons in order to tune both the optical and electrochemical behavior of these systems. Fluorescence measurements on the chiral dendrimers reveal a strong emission with maxima between 409 and 508 nm depending upon the substitution pattern. Finally, the redox properties of the dendrimers were determined by cyclic voltammetry, showing the influence of the functional groups at the peripheral positions of the dendrimer on the redox behavior of these systems. 相似文献
997.
We have studied theoretically the partition equilibrium of a cationic drug between an electrolyte solution and a membrane with pH-dependent fixed charges using an extended Donnan formalism. The aqueous solution within the fixed charge membrane is assumed to be in equilibrium with an external aqueous solution containing six ionic species: the cationic drug (DH(+)), the salt cations (Na(+) and Ca(2+)), the salt anion (Cl(-)), and the hydrogen and hydroxide ions. In addition to these mobile species, the membrane solution may also contain four fixed species attached to the membrane chains: strongly acid sulfonic groups (SO(3)(-)), weakly acid carboxylic groups in dissociated (COO(-)) and neutral (COOH) forms, and positively charged groups (COO...Ca(+)) resulting from Ca(2+) binding to dissociated weakly acid groups. The ionization state of the weak electrolyte groups attached to the membrane chains is analyzed as a function of the local pH, salt concentration, and drug concentration in the membrane solution, and particular attention is paid to the effects of the Ca(2+) binding to the negatively charged membrane fixed groups. The lipophilicity of the drug is simulated by the chemical partition coefficient between the membrane and external solutions giving the tendency of the drug to enter the membrane solution due to hydrophobic interactions. Comparison of the theoretical results with available experimental data allows us to explain qualitatively the effects that the pH, salt concentration, drug concentration, membrane fixed charge concentration, and Ca(2+) binding exert on the ionic drug equilibrium. The role of the interfacial (Donnan) electric potential difference between the membrane and the external solutions on this ionic drug equilibrium is emphasized throughout the paper. 相似文献
998.
Mercedes de Frutos Alejandro Cifuentes Jose Carlos Diez-Masa 《Journal of separation science》1997,20(1):29-33
The behavior of bovine whey proteins in Reversed-Phase High Performance Liquid Chromatography (RP-HPLC) systems has been investigated. The Linear Solvent Strength (LSS) model has been applied to the separation of these proteins studying how their retention time and band broadening change when different gradient parameters are modified. From our results it is deduced that the LSS model describes the behaviour of the whey proteins in RP-HPLC. Also, it seems that ts (the retention time for non-retained solutes) depends on the size of these proteins. The good fit observed between experimental data and the equations deduced from the LSS model allows the prediction of a gradient shape that permits a rapid analysis of the above mentioned proteins. 相似文献
999.
The reaction between copper (II) and azide has been studied spectrophotometrically at four wavelengths, at 25 degrees , and ionic strength 4.00M (sodium perchlorate). The formation constants beta(2) and beta(3) found are 2.90 +/- 0.08 x 10(4) and 3.02 +/- 0.07 x 10(6) respectively. The results obtained from potentiometric measurements with a solid-state electrode disagree with those calculated from the spectrophotometric data. Causes of the discrepancy are discussed. 相似文献
1000.
S. Moreira A. E. S. Vives O. L. A. D. Zucchi E. F. O. de Jesus V. F. Nascimento Filho S. M. B. Brienza 《Journal of Radioanalytical and Nuclear Chemistry》2006,270(1):167-171
Summary In this study the concentrations of P, S, Cl, K, Ca, Mn, Fe, Zn and Br in twenty-nine brands of national and international
beers were determined by synchrotron radiation total reflection X-ray fluorescence analysis (SR-TXRF). The results were compared
with the limits established by the Brazilian legislation and the nutritional values established by National Agricultural Library
(NAL, USA). The measurements were performed at the X-Ray Fluorescence Beamline at Brazilian National Synchrotron Light Laboratory,
in Campinas, S?o Paulo, Brazil, using a polychromatic beam for excitation. A small volume of 5 ml of beers containing an internal
standard used to correct geometry effects was analyzed without pretreatment. The measuring time was 100 seconds and the detection
limits obtained varied from 1 mg . l-1 for Mn and Fe to 15 mg . l-1 for P. 相似文献