The catalytic reaction of catalase was investigated, by means of a Clark oxygen sensor, in the presence of various concentrations of acetylsalicylic acid. Michaelis-Menten kinetic parameters were determined from Lineweaver-Burk plots, obtained in the absence and in the presence of the inhibitor. The inhibition pattern, suggested by the Lineweave-Burk plots, corresponds to a fully mixed inhibition mechanism. A kinetic method, based on the indicator reaction:
, was developed for the quantitative determination of acetylsalicylic acid. Calibration graphs of the reciprocal value of first-order rate constant versus acetylsalicylic concentration covered the concentration range (2.99–19.98)×10–4 mol/L, while the detection limit was 4.12×10–4 mol/L acetylsalicylic acid with a standard deviation of 2.1×10–5 mol/L. 相似文献
Electrokinetic tests, based on the streaming potential method, were used to elucidate interactions between cationic polyelectrolytes
and cellulosic fibers and to reveal aspects of fibers’ nanoporosity. The fibrillated and nanoporous nature of bleached kraft
fibers gave rise to time-dependent changes in streaming potential, following treatment of the wetted fibers with poly-diallyldimethylammonium
chloride. Electrokinetic test results were consistent with an expected longer time required for higher-mass polyelectrolytes
to diffuse into pore spaces, compared to lower-mass polyelectrolytes. Further evidence of the relative inability of polyelectrolyte
molecules to diffuse into the pores of cellulose was obtained by switching back and forth between high and low ionic strength
conditions during repeated measurement of streaming potential, after the fibers had been treated with a moderate amount of
cationic polymer. By changing the concentration of sodium sulfate it was possible to switch the sign of streaming potential
repeatedly from positive to negative and back again. Such results imply that a continuous path for liquid flow exists either
in a fibrillar layer or within the cell walls. The same concepts also helped to explain the dosages of high-charge cationic
polymer needed to achieve maximum dewatering rates, as well as the results of retention experiments using positively and negatively
charged microcrystalline cellulose particles. 相似文献
Novel mesoionic phenolates were synthesized via 4-hydroxyaryl-1,3-dithiolium salts and characterized spectroscopically by UV-Vis. The bathochromic effect induced by iodine
substituents was investigated for several solvents. A negative solvatochromism was recorded for the intramolecular charge
transfer absorption band.
Correspondence: Lucian M. Birsa, Department of Organic Chemistry, Al.I. Cuza University of Iasi, 700506 Iasi, Romania. 相似文献
The synthesis of phase change materials based on NaCl–CaCl2 molten salt mixture and mesoporous silica was investigated. The influence of mesoporous silica porosity and salt concentration on the thermal energy storage properties of the resulting materials is discussed. The nanocomposite samples were characterized by X-ray diffraction, differential scanning calorimetry, infrared spectroscopy, thermogravimetry, scanning electron microscopy and X-ray photoelectron spectroscopy. The mesoporous silica was found to act as a reactive matrix for the molten salts. Composite samples with up 95% wt. salt can be obtained and used as shape-stabilized phase change materials. The materials have heat of fusion values of up to 60.8 J g?1 and specific heat capacity between 1.0 and 1.1 J g?1 K?1. The samples exhibit thermal stability up to 700 °C and can be used for high-temperature thermal energy storage through both latent and sensible heat storage mechanisms.
A kinetic method for the determination of aromatic amines is reported. The method involves the formation of an azo dye between 1-(4-hydroxy-6-methylpyrimidin-2-yl)-3-methylpyrazolin-5-one and a diazonium salt formed from the amine in the presence of nitrite in weakly acidic media. The reaction is monitored via the initial rate of change of the absorbance of the azo dye at 420 nm, because this is proportional to the aniline concentration.The optimum acidity and concentration of reagents were established. The concentration ranges for which the calibration lines are linear are quite large. Detection limits were estimated. The effect of several metal ions usually present in real samples, e.g. waste water, was examined to assess interference. 相似文献
An ordered compact space is a compact topological space X, endowed with a partially ordered relation, whose graph is a closed set of X × X (cf. [4]). An important subclass of these spaces is that of Priestley spaces, characterized by the following property: for every x, y ? X with x ? y there is an increasing clopen set A (i.e. A is closed and open and such that a ? A, a ? z implies that z?A) which separates x from y, i.e., x ? A and y ? A. It is known (cf. [5, 6]) that there is a dual equivalence between the category Ld01 of distributive lattices with least and greatest element and the category P of Priestley spaces.In this paper we shall prove that a lattice L ? Ld01 is complete if and only if the associated Priestley space X verifies the condition: (E0) D ? X, D is increasing and open implies is increasing clopen (where A1 denotes the least increasing set which includes A).This result generalizes a well-known characterization of complete Boolean algebras in terms of associated Stone spaces (see [2, Ch. III, Section 4, Lemma 1], for instance).We shall also prove that an ordered compact space that fulfils (E0) is necessarily a Priestley space. 相似文献
A single-machine scheduling problem with precedence delays is analyzed. A set of n tasks is to be scheduled on the machine in such a way that the makespan is minimized. The executions of the tasks are constrained by precedence delays, i.e., a task can start its execution only after any of its predecessors has completed and the delay between the two tasks has elapsed. In the case of unit execution times and integer lengths of delays, the problem is shown to be NP-hard in the strong sense. In the case of integer execution times and unit length of delays, the problem is polynomial, and an O(n2) optimal algorithm is provided. Both preemptive and non-preemptive cases are considered. 相似文献
The paper presents a study regarding the possibility of obtaining zinc and magnesium ferrites starting from poly(vinyl alcohol)–metal nitrates solutions. By controlled heating of these solutions, a redox interaction takes place leading to the formation of some coordination compounds of the involved metal cations with the oxidation products of poly(vinyl alcohol) (PVA). FT-IR spectroscopy has evidenced the disappearance of the NO3? anions at 140 °C due to the redox interaction with PVA. Thermal analysis evidenced the difference in the interaction of the individual metal nitrates and PVA and thus the particularity of the preparation of each ferrite. The thermal decomposition of the synthesized precursors was finished below 400 °C as resulting from both thermal analysis and FT-IR spectroscopy. The obtained ferrites powders consist of fine nanoparticle with diameters ranging from 10 to 30 nm for the powders annealed at 500 °C, as resulting from the SEM images. The specific surface area of the powders obtained at 500 °C was 32.2 m2 g?1 for ZnFe2O4 and 21.7 m2 g?1 for MgFe2O4, characteristic of nanoscaled powders. The increasing of the annealing temperature at 1,000 °C leads to sintering of both ferrites, more advanced in the case of zinc ferrite. 相似文献