Sequential two-step

In this study, anaerobic and aerobic processes using sequential two-step UASB/CSTR reactors were found to form a feasible process for treating the leachate from food solid waste. COD removal efficiencies for the first and second anaerobic, aerobic and total system processes were 79%, 42%, 89%, and 98%, respectively. The COD loading rate used ranged from 4.3 to 16kg/m3/d. 

In a semi-logarithmic plot of log Nt/N0 versus t, a single straight line is obtained in the case of the simple mechanism according to Eq. (5.73). In the case of sequential two-step deactivation, Eq. (5.75), two straight lines are obtained if the model is fitted well by the data. More complicated cases should not be treated by simple curve-fitting. 

The results demonstrate that under conditions of deactivation according to the first-order law a constant amount of enzyme per unit time has to be added, whereas under conditions of sequential two-step first-order deactivation the amount of enzyme added has to be increased steadily. 

Moreover, the cyclization of the keto-silylenolether 17 [10] diastereoselectively yields the all-c/s-annulation product 9a exclusively. The outcome of this experiment clearly supports a sequential two-step mechanism for the reactions in question. 

In order for the reaction to take place with the mechanism in the Grote-Hynes theory as well as in the Kramers theory, the reactant must surmount over the transition-state barrier only by diffusional Brownian motions regulated by solvent fluctuations. In the two-step mechanism of the Sumi-Marcus model, on the other hand, surmounting over the transition-state barrier is accomplished as a result of sequential two steps. That is, the barrier is climbed first by diffusional Brownian motions only up to intermediate heights, from which much faster intramolecular vibrational motions take the reactant to the transition state located at the top of the barrier. 

The rate constant with the form of eq.(S) can be obtained only when reaction tal place as a result of sequential two (or more) steps. It is easy to prove eq.(S) for a single intermediate state M, but in this case the a value in eq.(6) reduces to unity. It is when M is continuously distributed [described by a continuous variable X in eq.(4)] that a becomes smaller than unity.This form of eq.(S) has been used also by Troe for describing the pressure dependence of photoisomerization rates of stilbenes in solvents, without specifying sequential two steps underlying it. 

Results for the sodium salt were interpreted as indicating a sequential two step degradation. The trihydrate showed first order kinetics at 37 and 50 C but at the higher temperatures its degradation rate was consistent with formation of a solid plus a gas. Rate constants were derived which were extrapolated to 20°C and used to calculate the time for 10% degradation as 1.25 and 3.2 years for the sodium salt and trihydrate respectively. However, these authors made no mention of the possible effect of water content which is well known to be important for the solid state stability of all penicillins. 

Results consistent with sequential two step degradation were found for both amoxicillin trihydrate and sodium salt in open containers at 80 to 140°C... 

Immunoassays of various designs for estimating free thyroid hormones using antibody extraction techniques have been developed. These assays are subdivided as either sequential two-step assays or simultaneous one-step Canalogue ) assays. Each procedure involves the direct incubation of serum with a specific anti-T4 or anti-T3 antibody, during which thyroid hormones reach a new equilibrium with all of the binders present. A slight decrease in free hormone concentration occurs, but is insignificant if the antibody sequesters less than 5% of the total amount of hormone present in the specimen. Thus the amount of immunoex-tracted T4 or T3 closely approximates the undisturbed free hormone concentration that preexists in serum at equilibrium. 

A sequential two-step immunoassay for FT4 was first introduced commercially in 1979. Subsequently, a number of manual and automated procedures have become available for FT4 and FT3. The earliest kit methods used radioactive labels and antibody-coated tubes or microbeads, but automated systems are now available that use nonisotopic tracers and a variety of sofid-phase formats. One two-step FT4 method involves the application of serum to glass-fiber... 

Electronic conductivity of molecules including redox metalloproteins with accessible low-lying redox states in nanogap electrode configurations or in situ STM displays quite different patterns. These are dominated by sequential two-step (or multiple-step) hopping through the redox center, induced both by potential variation and environmental configurahonal fluctuations. Both redox molecules and... 

In situ STM tunneling spectroscopic data, i.e. tunneling current/oveipotential correlations are shown in Fig. 8-9. These data follow, notably, clearly the pattern of sequential two-step interfacial electrochemical electron transfer. Both Os-complexes show a clear maximum which follows closely the equilibrium potentials, cf eqns. (8-21)-(8-23). These are well separated, at 0.60 and 0.24 V (vs, SHE) for [Os(bpy)2(p2p)2] and [Os(bpy)2(pOp)Cl], respectively. The on-off current ratios are about 50 for the Os-complexes corresponding to about 1 nA current rise. Further, the peak potential follows a linear dependence on the bias voltage, Fig. 8-10, as expected from eqns. (8-21)-(8-23). The slope is -0.5 according with values of the potential distribution parameters close to unity and f close to zero. The Co-complex shows a much smaller peak current, i.e. 5-10 pA current rise instead of the 1 nA rise for the Os-complexes. This points to a significant role of the interfacial electrochemical electron transfer step between the substrate electrode and the redox centre as this step is three orders of magnitude faster for the Os-complexes than for the Co-complex, cf above. 

Mixed primary secondary diols are very often separated into their enantiomers in a sequential two-step acylation wherein the first step - acylation of the primary hydroxyl group - shows high regio- but very poor enantioselectivity. The useful enantiomer-differentiating step is realized in the second step by acylation of the already monoacylated diol (31—36, 46, 72,107—110,120, 125). On the other hand, as expected, mixed primary tertiary diols are not acylated at the tertiary hydroxyl group (47, 48, 51-54, 56-62,106). 

The photodissociation rate of the cyanobenzene cation at 568 nm is found to be significantly increased in the presence of CW CO2 laser radiation.Without the laser present, the dissociation is via a sequential two-step mechanism (19), and the... 

The interaction of solute molecules with the ion-exchange stationary phase can be regarded as a sequential two-step process. Initially the solute must diffuse from the mobile phase (usually aqueous) into the stationary phase (often organic). The distribution between the two phases is largely responsible for the retention of a particular solute. Secondly, the solute must interact with, and diffuse through, the stationary phase. 

Friis and coworkers [80] considered an intermediate mechanism, in which an electron first transfers to the molecule and the molecule begins to relax towards the reduced state. However, before it is fully relaxed to the reduced state, an electron transfer from the molecule to the second electrode occurs when the temporarily occupied level passes the Fermi level of the second electrode. They called this process coherent two-step electron transfer. More recently, Kuznetsov and Ulstrup [81] have developed a systematic theory for the sequential two-step process. The electron transfers from one electrode to the molecule and reduces the molecule, and then transfers to the second electrode and reoxidizes the molecule, so the process is reviewed as a cycle of consecutive molecular reduction and reoxidation. A particular interesting feature in the theory is that each reduction-reoxidation cycle is composed of a large number of individual electron transfer events between the molecule and both the tip and the substrate. This significantly enhances the tunneling current compared to a single electron transfer. 

Scheme 4.14 Sequential two-step cascade for the production of (2S,3S)-2-aminopentane-1,3-diol starting from propanal and P-hydroxypyruvate by coupling a transketolase (TK) and an co-transamlnase (co-TA).

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