Catalyst algorithm

Figure 13.36. Simplified 3D pharmacophoric model of CYP2B6 substrates as obtained with the Catalyst algorithm (186).The main features characteristic of substrates are three hydrophobic moieties (HI, H2, and H3) and a H-bond acceptor group (HB-A).

Molecular Field Analysis (CoMFA) and Catalyst. An early metabolic study using CoMFA involved the monoamine oxidase-catalyzed oxidation of MPTP analogs (185). A more recent study using the Catalyst algorithm described the pharmacophoric features characteristic of CYP2B6 substrates (186), a simplified representation ofwhich is given in Fig. 13.36. Pharmacophoric features of inhibitors have also been obtained for a number of CYP enzymes using 3D-QSAR methods (187-189). 

Normally, the reactor temperature and the stripper level controllers regulate he movement of the regenerated and spent catalyst slide valves, le algorithm of these controllers can drive the valves either fully Of [ or fully closed if the controller set-point is unobtainable. It is ext nely important that a positive and stable pressure differential be mail ined across both the regenerated and spent catalyst slide valves. r safety, a low differential pressure controller overrides the tempera re/level controllers should these valves open too much. The shutdov is usually set at 2 psi (14 Kp). 

Equations 1 and 2 can be solved numerically using an algorithm which handles stiff differential equations (28). Two sets of boundary conditions are required. For 0reduced catalyst is exposed to NO, the inlet gas composition is given by... 

FCC catalyst, 11 728-729 thermoelectric, 21 555, 556 Cooley-Tukey fast Fourier transform (fft) algorithm, 23 137 Cool flames, 7 442—443 Cooling... 

A full discussion of all the issues related to this concept is out of the scope of this preliminary communication. Instead, we present here the basics of the general approach, as well as a specific example illustrating one iteration in the optimization of Pd-catalyzed Heck reactions using bidentate ligands, which demonstrate higher catalytic activities and lifetimes than monodentates (6). The full technical details of the algorithms and the theoretical treatment of the catalyst library diversity will be published elsewhere (7). 

Another important feature of GAs is that they are tunable. This means that we can define the algorithm s fitness function to reflect the actual requirements from the catalyst. An optimal catalyst exhibits high activity, high stability, and high selectivity. These three figures of merit are directly related to the product yield, the turnover number (TON) and the turnover frequency (TOF), respectively. Often, however, an increase in one comes at the expense of another. Using GAs you can... 

The methods used for catalyst library design are quite divers. Industrial companies, like Symix, Avantium, hte GmbH, Bayer AG are using their own proprietary methods. In academic research the Genetic Algorithm (GA) is widely applied [11,12]. Recently Artificial Neural Networks (ANNs) and its combination with GA has been reported [13,14]. In these studies ANNs have been used for the establishment of composition-activity relationships. 

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