Biphasic behavior

Biphasic behavior suggests the presence of two active sites. The magnitude of the difference in their activities suggests these may correspond to diperoxo and monoperoxometal sites. Under our experimental conditions, the monoperoxo site would be formed upon reaction of the diperoxo site with olefin in the absence of excess BuOOH. 

In Fig. 9.2 we present results of a first-of-a-kind study of the hydration of the first-transition-row metals within the quasichemical framework. The biphasic behavior of the actual hydration free energy is consistent with features inferred experimentally. Removing the ligand field effects reveals the linear decrease [12]. The results shown in Fig. 9.2 are largely outside the purview of extant simulation techniques, but are treated simply in the quasichemical framework developed below. 

The SCN anation of Co(NH3)5H20 has only recently been recognized to form (NH3)5CoSCN + in parallel with the stable N-bonded Co(NH3)5NCS +. The system has been fully analyzed and illustrates well the difficulties in detecting biphasic behavior. 

The solutions to the equations give the biphasic behavior with the two rates defined as... 

To eliminate the possibility that the biphasic behavior in chloride-containing solutions may be caused by changes in electrode and mediator properties, the temperature dependence of E° of the mediator 2,6-... 

Mean clearance (CL) values for cetuximab are displayed as a function of dose in Fig. 14.3. Mean CL values decreased from 0.079 to 0.018 L/h/m2 after single cetuximab doses of 20 to 500 mg/m2, respectively. In the dose range 20 to 200 mg/m2, CL values decreased with dose. At doses of 200 mg/m2 and greater, CL values leveled off at a value of approximately 0.02 L/h/m2. This biphasic behavior suggests the existence of two elimination pathways. The elimination of cetuximab apparently involves a specific, capacity-limited elimination process that is saturable at therapeutic concentrations, in parallel with a nonspecific first-order elimination process that is non-saturable at therapeutic concentrations. Increasing doses of cetuximab will therefore ultimately lead to the saturation of the elimination process that is capacity-limited and that follows Michaelis-Menten kinetics, whereas the first-order process will become the dominant mechanism of elimination beyond a particular dose range. 

These results could suggest that what has been traditionally been described as "biphasic" behavior may reflect a combination of chemical reaction and mass transfer effects, with each limiting xylan reaction and removal at different stages or modes of operation. This effect might be better described by a model that incorporates reaction of solids to form soluble species as a function of temperature and acid concentration coupled with a second mass transfer step that is affected by flow. On this basis, we plan to investigate whether the pore leaching model could be simplified and adapted in this way to better describe hemicellulose hydrolysis. 

Fig. 9.5 Biphasic behavior of the ionic liquid [Pyi,4] TFSA/ 2 M AICI3 at 25 and 80°C.

The ionic liquid [EMIMJTFSA shows, at room temperature, biphasic behavior on addition of AICI3. AICI3 dissolves well in [EMIM] TFSA up to a concentration of about 2.5 mol L-1, then a biphasic mixture is obtained on further addition of AICI3. The upper phase of the mixture AICI3/[EMIM] TFSA is clear and colorless while the lower one is pale and more viscous. On further addition of AICI3 the viscosity of the lower phase increases. It is worth noting that Al can only be electrodeposited from the upper phase, the clear one, at AICI3 concentrations > 5 mol L 1. Furthermore, after a few days a precipitate which contains A1(TFSA)3 forms as a third phase. 

Similar to the AlCl3/[EMIM]TFSA mixture, the mixture of AlCh/IPyip] TFSA shows biphasic behavior with increase in the concentration of AlCh up to 1.6 M. In contrast to the AlQj/tEMIMJTFSA mixture, the lower phase is colorless while the upper one is pale and more viscous. By adding more AICI3 the volume of the lower phase decreases till a concentration of 2.7 mol L-1 is reached, then only one solid phase can be formed at room temperature. The biphasic mixture of AlCb/ITyi TFS A becomes monophasic by heating to a temperature of about 80 0 C. The electrodeposition of aluminum occurs only from the upper phase at AICI3 concentrations > 1.6 mol L . 

We observed that only a small fraction of the adsorbed mass would desorb even after a number of successive desorption steps. The investigation on laboratory contaminated soil showed a biphasic behavior, namely an easily desorbed fraction and a desorption resistant fraction. Both field contaminated and aged soils also showed the same behavior. The first stage involved a loosely bound fraction and the second stage involved a tightly bound fraction. The desorption constants calculated or estimated for the two fractions were em-... 

An empirical model was used by Opdyke and Loehr [17] to describe the contaminant rate of release (ROR) similar to what we observed a relatively rapid release of the chemical followed by a much slower release of the remaining chemical. The non-linear equation used to describe this biphasic behavior during desorption was given by... 

When nucleation is highly unfavorable (i.e., a l) the polymer system exhibits a biphasic behavior depending on the total monomer concentration A0. In this case there is a sharp phase transition between the all-monomer state for A0 < 1 /K, where l/K is the critical monomer concentration. When A0 exceeds 1 /K the free monomer concentration stays fixed at [A eq = l/K. This type of nonsmooth behavior at x = lforcr = 1 is called a transcritical bifurcation in non-linear dynamics [191]. It is also widely known as phase transition in physics. Figure 10.5 shows that for a less than unity, the transition is smooth. Hence we see that the... 

The anaerobic reduction of the trinuclear copper center for ascorbate oxidase with different substrates presents a distinct picture. The reaction with reductate is monophasic with a unimolecular rate constant of 100 sec (18), independent of pH. Rapid freeze-quench EPR experiments indicate that the type-2 EPR signal vanishes more slowly 18). The pulse radiolysis studies of the radicals of lumiflavin, deazaflavin, CO2 ", and MV at pH 7.0 129,130) showed a biphasic behavior with an initial, faster reaction k = 97-127 sec " ) and a final, slower reaction k 2 sec" ) 129). Different results have been obtained by Farver and Pecht 130) with CO2 " as a substrate. They found a triphasic reaction with unimolecular rate constants k = 201 sec S 2 = 20 sec", and ks = 2.3 sec. The first constant is twice that in a study by Kyritsis et al. 129), whereas the third constant is identical. The second constant was not observed in the study. 

Trimmer, M., NichoUs, J. C., Morley, N., Cavies, C. A., and Aldridge, J. (2005). Biphasic behavior of anammox regulated by nitrite and nitrate in an estuarine sediment. Applied and Environmental... 

Figure 19 Dependence of the observed rate constant (ktp) for the cleavage of PNPP on the ligand concentration in different vesicular blends (25 °C, [copper(II)] = 1.8xlO- M), (20) and 2Ci6Br, A CTABr, O 2C,6GlyBr, A (21) and 2C (,Br, 2C]5GlyBr, . The inset shows the time course of the absorbance increase observed upon addition of Cu(NO3)2 to the two different vesicular blends (20), (21), O- Only vesicles made of (20) and 2CigBr show clearly biphasic behavior. The fast uptake of copper(II) by the ligand on the outer layer of the bilayer is followed by a much slower process, probably copper(II) permeation...

When one studies sorption processes, be they with metals, oxyanions, radionuclides, or organic chemicals, a biphasic behavior is almost always observed... 

The details of the evolution towards tetragonal symmetry as x approaches 0.5 are somewhat uncertain. The PXD data for the composition closest to x=0.5, x=0.506, were refined as a combination of both orthorhombic and tetragonal forms. The optimized scale factors for the two components were in the approximate ratio 4 (orthorhombic) 1 (tetragonal). Biphasic behavior for x close to 0.5 has been noted previously (25). 

The qualitative behavior is identical for all parameter settings The phosphorylated STAT-5 in the cytoplasm shows a biphasic behavior, the total amount of STAT-5 in the cytoplasm decreases monotonically. However, the quantitative behavior depends on the parameters. Thus, if simulated model predictions are compared to experimental data, it is difficult to decide whether discrepancies between simulated and measured data result from inadequate parameters or from an insufficient model. To resolve this simulation dilemma [29], we will estimate the parameters from the experimental data. Mathematically, the equations of the system under investigation can be summarized as ... 

Preliminary time-resolved fluorescence measurements give a somewhat better indication of what the cage lifetime might be. ° Both the rise in the fluorescence of the anion and the decay of neutral emission of 8-hydroxy-1,3,6-pyrene were measured. Careful examination of both the rise of the anion and the decay of the neutral indicate the presence of biphasic behavior. The biphasic kinetics can more readily be seen in DjO. It is quite possible that the faster rate constant is due to protons that immediately escape the cage, while the slower decay is due to the destruction of the cage. 

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