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Rate Constants K (rate + constant_k)
Selected AbstractsInvestigation of the anti-fungal activity of coptisine on Candida albicans growth by microcalorimetry combined with principal component analysisJOURNAL OF APPLIED MICROBIOLOGY, Issue 4 2009W.-J. Kong Abstract Aims:, This study investigated the anti-fungal activity of coptisine on Candida albicans growth. Methods and Results:, The metabolic power-time curves of Candida albicans growth at 37°C affected by coptisine were measured by microcalorimetry using an LKB-2277 Bioactivity Monitor with stop-flow mode. Then, the diameter of inhibitory zones in the agar layer was observed using agar cup method, and the minimal inhibitory concentration (MIC) of coptisine on Candida albicans growth was determined by serial dilution method. From the principal component analysis on nine quantitative parameters obtained from the power-time curves, we could easily evaluate the anti-fungal activity of coptisine by analysing the change of values of the main two parameters, growth rate constant k and maximum power output in the log phase Pm, log. The results showed that coptisine had strong anti-fungal activity: at a low concentration (45 ,g ml,1) began to inhibit the growth of Candida albicans and at a high concentration (500 ,g ml,1) completely inhibited Candida albicans growth. Coptisine gave big inhibitory zones with diameters between 11 and 43 mm within test range, and the MIC of it was 1000 ,g ml,1. Conclusions:, Coptisine had strong anti-fungal activity on Candida albicans growth. The method of microcalorimetry applied for the assay of anti-fungal activity of coptisine was quantitative, sensitive and simple. Significance and Impact of the Study:, This work will provide useful information for the development of chemical biology policy in the use of anti-microbials in food and drug production. [source] Tunable transport of glucose through ionically-crosslinked alginate gels: Effect of alginate and calcium concentrationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Mari-Kate E. McEntee Abstract Alginate beads have numerous biomedical applications, ranging from cell encapsulation to drug release. The present study focuses on the controlled release of glucose from calcium-alginate beads. The effects of alginate concentrations (1,6 wt %) and calcium chloride concentrations (0.1,1.0M) on glucose release from beads were examined. It was found that the time required for complete glucose release from beads could be tuned from 15 min to over 2 h, simply by varying alginate and calcium chloride concentrations in beads. For calcium-alginate beads with sodium alginate concentrations of 1,4 wt %, higher sodium alginate concentrations lead to more prolonged release of glucose and thus a smaller value of a rate constant k, a parameter shown to be proportional to the diffusion coefficient of glucose in the alginate gel. For beads with sodium alginate concentrations of 4,6 wt %, there was no statistically significant difference in k values, indicating a lower limit for glucose release from calcium-alginate beads. Similarly, higher calcium chloride concentrations appear to extend glucose release, however, no conclusive trend can be drawn from the data. In a 50 : 50 mixture of calcium-alginate beads of two different alginate concentrations (1 and 4 wt %), glucose release showed a two-step profile over the time range of 20,50 min, indicating that the pattern and time of glucose release from beads can be tuned by making combinations of beads with varying alginate and/or calcium chloride concentrations. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Kinetics and mechanism of oxidation of the drug mephenesin by bis(hydrogenperiodato)argentate(III) complex anionINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2007Shigang Shen Mephenesin is being used as a central-acting skeletal muscle relaxant. Oxidation of mephenesin by bis(hydrogenperiodato)argentate(III) complex anion, [Ag(HIO6)2]5,, has been studied in aqueous alkaline medium. The major oxidation product of mephenesin has been identified as 3-(2-methylphenoxy)-2-ketone-1-propanol by mass spectrometry. An overall second-order kinetics has been observed with first order in [Ag(III)] and [mephenesin]. The effects of [OH,] and periodate concentration on the observed second-order rate constants k, have been analyzed, and accordingly an empirical expression has been deduced: k, = (ka + kb[OH,])K1/{f([OH,])[IO,4]tot + K1}, where [IO,4]tot denotes the total concentration of periodate, ka = (1.35 ± 0.14) × 10,2M,1s,1 and kb = 1.06 ± 0.01 M,2s,1 at 25.0°C, and ionic strength 0.30 M. Activation parameters associated with ka and kb have been calculated. A mechanism has been proposed to involve two pre-equilibria, leading to formation of a periodato-Ag(III)-mephenesin complex. In the subsequent rate-determining steps, this complex undergoes inner-sphere electron transfer from the coordinated drug to the metal center by two paths: one path is independent of OH, whereas the other is facilitated by a hydroxide ion. In the appendix, detailed discussion on the structure of the Ag(III) complex, reactive species, as well as pre-equilibrium regarding the oxidant is provided. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 440,446, 2007 [source] Supramolecular catalysis induced by polysaccharides.JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2003Homogeneous hydrolysis of p -nitrobenzyl amylose xanthate Abstract p -Nitrobenzyl amylose xanthate (AmXNB) was synthesized and characterized by 13C NMR spectroscopy in solution and the solid state. The degree of substitution (DS), calculated from the sulfur content, was 7.0, and this value was similar to that obtained from solid-state 13C NMR using the signal of C-1 as internal standard. The hydrolysis of AmXNB was studied in 10% (v/v) DMSO with,µ,=,0.5 (KCl) at 25,°C. The basic hydrolysis was pseudo-first order, but the water-catalyzed hydrolysis in the pH range 7,9 showed a biphasic plot of ln (,Absorbance) vs time, as has been observed for cellulose xanthate esters, occurring through two parallel reactions with rate constants k,H2O (fast),=,5.3,×,10,5 s,1 and k,H2O (slow),=,3.3,×,10,6 s,1. The fast hydrolysis was more than three orders of magnitude faster than that of the O -ethyl analog. The activation parameters were ,H,,=,20.5,kcal,mol,1 and ,S,,=,+10 cal K,1,mol,1. They showed that the acceleration of the fast hydrolysis of AmXNB and cellulose analogs is due to an entropy of activation effect. There is a linear increase of logk,H2O (fast) with increase in the concentration of the small Li+ ion that produces an increase of the 3-D hydrogen-bond network of water while the large singly charged iodide ion has a considerable inverse effect. These results are strongly consistent with the theory that the supramolecular catalysis induced by modified polysaccharide esters is due to the 3-D hydrogen-bond network of the water in the solvation shell. Copyright © 2003 John Wiley & Sons, Ltd. [source] Microcalorimetric studies on influence of Sm3+, Dy3+ on growth and sporulation of Bacillus thuringiensisCHINESE JOURNAL OF CHEMISTRY, Issue 12 2004Ru-Ming Zhao Abstract By using an LKB-2277 Bioactivity Monitor and cycle-flow method, the thermogenic curves of aerobic growth for Bacillus thuringiensis cry II strain at 28 °C have been obtained. The metabolic thermogenic curves of Bt cry II contain two distinct parts: the first part reflects the changes of bacterial growth phase and the second part corresponds to sporulation phase. From these thermogenic curves in the absence or presence of Sm3+, Dy3+ ions, the thermokinetic parameters such as the growth rate constants k, the interval time ,I, the maximum power PMAX1 and heat-output QLOG for log phase, the maximum power PMAX2 and heat-output QSTAT for stationary phase, the heat-output QSPOR for sporulation phase and total heat effects QT were calculated. Sm3+ and Dy3+ ions have promoting action on the growth of Bt cry II in their lower concentration range, on the other hand, they have inhibitory action on the sporulation of Bt in their higher concentration range. It has also been found that the effects of Sm3+ and Dy3+ ions on Br firing the sporulation phase were far greater than those during the bacterial growth phase. It was concluded that the application of Bt for controlling insecticide could not be affected by the presence of the rare-earth elements in the environmental ecosystem. [source] | ||||||||||