Saturation rates

The first successful chiral resolutions through enantioselective membranes have been published recently, but few cases are applicable to the preparative scale, mainly due to mechanical and technical limitations. Low flow rates, saturation of the chiral selectors and loss of enantioselectivity with time are some of the common problems encountered and that should be solved in the near future. 

Another features of the ligand lipophilicity and the- stability of the complex on the rates are shown in Fig. 6 Rate saturation corresponds to the formation of a 1 1 or 2 1 ligand-metal ion complex. Non-micellar reactions of curves b and c indicate that the N-butyl ligand 38b forms a more active complex than N-methyl ligand 38a does. It may be interesting to note that in the micellar reaction of 38b, a flat... 

Green alga Scenedesmus subspicatus) DBTL 72-h EC50 (growth rate) >saturated solution ( 3 mg/l) >saturated solution ( 1.4 mg/l) Schering AG (1999a)... 

Figure 6-8 shows how the partial pressure of carbon dioxide in equilibrium with surface water oscillates in phase with the fluctuations in precipitation rate, saturation state, and temperature. The oscillations in alkalinity and bicarbonate concentrations have shifted in phase by about 90° because these quantities decrease when precipitation and evaporation are removing carbon from the system at above-average rates. 

As the light intensity was increased above 100 mW cm-2, the value of (Rp)max was hardly changed, as shown in Figure 5. A similar behavior was observed with the vinyl ether-based formulation, (Rp)max levelling off at about the same value (20 mol l"1 s"1) as for the acrylate formulation (18 moll-1 s-1). Such a rate saturation effect, which has been found in nearly all of the formulations studied, is difficult to explain. It is not due to a time resolution limitation of the RTIR technique, as shown... 

This rate expression has a common feature of catalysis-that of rate saturation. The (nonseparable) rate is proportional to the amount of catalyst. If reaction step (2) is slow ( 2 is small and the first term in the denominator of 8.2-12 is dominant), the rate... 

In this case, most of the catalyst is in the form of M A and the reaction is zero order with respect to A. Thus, the kinetics move from first order at low cA toward zero order as cA increases. This feature of the rate saturating or reaching a plateau is common to many catalytic reactions, including surface catalysis (Section 8.4) and enzyme catalysis (Chapter 10). 

A number of reductions of VOJ show acid catalysis with no rate saturation at high [H+]. This is consistent with a protonation equilibrium,... 

The Re monomer was completely inactive for the mixture of benzene and O2. NH3 treatment of the Re monomers at 553 K generated the catalyhc achvity. After around 30 min of the NH3 treatment, phenol synthesis activity appeared and the phenol formahon rate dramatically increased between 40 and 60 min of the NH3 treatment, followed by a gentle rate rise upon further treatment The reaction rate saturated at 3.75 x 10 s after 120min. Further NH3 treatment longer than 120 min did not improve the catalyhc activity. Notably, the phenol selechvity kept almost constant (90.1-93.9%) during the NH3 treatment at 553 K. 

This method is widely used because it provides hnear transformation of the hyperbolic function describing the rate saturation process. Double-reciprocal plots can be reasonably accurate if rate data can be obtained over a reasonable range of saturation, say from 0.3 E ax to 0.8 E ax. 

An alkylating agent (ICH2COO ) that acts as a potent irreversible inhibitor of enzymes containing reactive thiol, e-amino, and/or imidazole side-chain groups within their active sites. The carboxymethylation reaction with enzymes is typically a bimolecular process that takes place without rate-saturation behavior ... 

The contribution of diffusion to the rate does not follow rate saturation. Therefore, as one proceeds toward carrier saturation with substrate S, the rate will not simply reach a plateau, as is most often the case for one-substrate enzymes operating on extremely slow uncatalyzed reactions. Instead, a plot of v versus [S] will continue to rise with a constant slope, equal to /cd. It is usually a simple matter to extrapolate this noncarrier-mediated contribution back to each time-point for which a measurement was obtained and to obtain the corrected carrier-mediated rate by subtraction of the diffusional contribution. 

Net carrier transport can be examined whenever a transportable substrate is present on both sides of a membrane. Again for the case of a single class of carriers, the inward transport rate and outward transport rates show rate-saturation behavior ... 

An enzyme is said to obey Michaelis-Menten kinetics, if a plot of the initial reaction rate (in which the substrate concentration is in great excess over the total enzyme concentration) versus substrate concentration(s) produces a hyperbolic curve. There should be no cooperativity apparent in the rate-saturation process, and the initial rate behavior should comply with the Michaelis-Menten equation, v = Emax[A]/(7 a + [A]), where v is the initial velocity, [A] is the initial substrate concentration, Umax is the maximum velocity, and is the dissociation constant for the substrate. A, binding to the free enzyme. The original formulation of the Michaelis-Menten treatment assumed a rapid pre-equilibrium of E and S with the central complex EX. However, the steady-state or Briggs-Haldane derivation yields an equation that is iso-... 

A term used to refer to any chemical process whose rate depends upon saturation of a binding site. Rate saturation is observed in enzyme kinetics, metabolic... 

Referring to reactions in which the reaction velocity is independent of the reactant under consideration. For example, for the reaction A + B C, if the empirical rate expression is v = A [B], the reaction is first order with respect to B but zero order with respect to A. See Chemical Kinetics Rate Saturation Michaelis-Menten Equation... 

PULSE-CHASE EXPERIMENTS RATE OF REACTION CHEMICAL KINETICS Rate processes in aqueous solutions, CHEMICAL KINETICS RATE SATURATION BEHAVIOR RAY-ROSCELLI TREATMENT ISOMERIZATION ISO MECHANISMS RE-... 

CHEMICAL KINETICS RATE SATURATION MICHAELIS-MENTEN EQUATION ZERO-ORDER REACTIONS ORDER OF REACTION MOLECULARITY... 

Figure 17.15 Carbon dioxide exchange rate (net photosynthetic rate) of a 20 potato stand at different CO2 concentrations. The photosynthetic rates saturated above 1200 ppm while the CO2 compensation point occurred at 97 ppm (source Wheeler et al., 2008a).

Meanwhile, PPS liberated phenol in a Tris buffer solution (16). Ethanolamine works similarly and the reaction proceeded first with the expulsion of sulfate by nucleophilic attack of amine followed by liberation of phenol, presumably through the formation of a five-membered cyclic intermediate (Figure 8). Both steps of S042- and phenolate liberation were found to be catalyzed by Mg2+ ion. In Figures 9 and 10 the data are shown for the liberation of phenol. Figure 9 indicates clear rate saturation attributable to complexation in acetonit-... 

---