Substrate s

P = the concentration of predators S = substrate concentration (food for prey)... 

Coating element(s) Substrates Properties obtained or improved Stage of development References... 

Unlike many of the catalysts that chemists use in the laboratory, enzymes are usually specific in their action. Often, in tact, an enzyme will catalyze only a single reaction of a single compound, called the enzyme s substrate. For example, the enzyme amylase, found in the human digestive tract, catalyzes only the hydrolysis of starch to yield glucose cellulose and other polysaccharides are untouched by amylase. 

Table 14-2. Performance of pcnlacene based OFETs. Mobility in cm2 V 1 s substrate temperature in °C. RT room temperature.

FIGURES. Voltammograms at a microelectrode of mercury of 2,2-diphenylvinyl phenyl sulphone in DMF, sweep rate 600 mV s , substrate concentration 10 3 m broken line curve (a) without proton donor present, full line curves (b) and (c) with phenol at concentration 0.5 and 4 x 10 3m, respectively, reference electrode Ag/Agl/I" 0.1m in DMF (after Reference 37). 

A kinetic resolution depends on the fact that the two enantiomers of a racemic substrate react at different rates with the enzyme. The process is outlined in Figure 6.1, assuming that the (S) substrate is the fast-reacting enantiomer (ks > ka) and Kic = 0-In ideal cases, only one enantiomer is consumed and the reaction ceases at 50% conversion. In most cases, both enantiomers are transformed and the enantiomeric composition ofthe product and the remaining starting material varies with the extent... 

S] + K )] for the hexokinase-catalyzed phosphorylation reactions of 2DG and D-glucose, respectively [S (substrate) + E (enzyme) — ES— -I- P (product)]. This constant (LC) accounts for the ratio of the arteriovenous extraction fraction (by transport and phosphorylation) of 2DG to that of D-glucose (LC= 1) under steady-state conditions. This concept can be directly applied to the case of 2DFG by employing the LC (-0.5) for 2DFG. 

Only the R(+) enantiomer of the herbicide 2-(2-methyl-4-chlorophenoxy)propionic acid was degraded (Tett et al. 1994), although cell extracts of Sphingomonas herbicidovorans grown with the R(-) or S -) enantiomer, respectively, transformed selectively the R -) or S(-) substrates to 2-methyl-4-chlorophenol (Nickel et al. 1997). 

FIG. 2 Localization of the biocatalyst with different phase distributions of substrate and product in two-phase medium. S substrate P product B biocatalyst. 

S substrate CD cinchonidine 3,4-HD 3,4-hexanedione 2,3-BD 2.3-butane-dione CD injection... 

CD cinchonidine S substrate 3,4-HD 3,4-hexanedione premixing technique Tr 20 °C pm 50 bar amount of catalysts used was calculated to have equal amount of surface platinum (Pts) in each reaction. 

S = substrate = p-nitrophenyl trimethylacetate P = product = p-nitrophenol A = trimethylacetic acid kx = 150 m3/mole-ksec k2 = 2.60 ksec-1... 

A Aqueous phase B Buffer solution C Organic solvent E Enzyme H HCN S Substrate P Product. 

Fig. 7. Scheme for a two-stage continuous cultivation technique. A = acid, 5 = base, M=medium, P = pump, S = substrate, Cl and C2 = base or acid flow, FI = culture flow, F2 = substrate flow, F3 = outflow, Z1 = medium flow... 

Several other color tests useful in the kinetic resolution of chiral compounds have been developed, most of them being based on the concept of testing R- and S-substrates separately as described above.77-80... 

Key (Gal/)A), = D-galactopyranosiduronic acid unit E = enzyme S = substrate U = binding subsite = catalytic site. 

The general theory of enzyme kinetics is based on the work of L. Michaelis and M. L. Menten, later extended by G. E. Briggs and J. B. S. Haldane.la The basic reactions (E = enzyme, S = substrate, P = product) are shown in equation 2.1 ... 

Scheme 10.1 Reaction sequence of the simplest case of Mi-chaelis-Menten kinetics. E = catalyst S = substrate ES = cata-lyst-substrate complex P= product = rate constants.

Catalysts/Reductant(s) Substrate Solvent Temperature [K] Dechlorination [%]b) TOFc) [h-1] Reference... 

---