Catalytic turnover purifications

The single crystal catalysts, -1 cm in diameter and 1 mm thick, are typically aligned within 0.5 of the desired orientation. Thermocouples are generally spot-welded to the edge of the crystal for temperature measurement. Details of sample mounting, cleaning procedures, reactant purification, and product detection techniques are given in the related references. The catalytic rate normalized to the number of exposed metal sites is the specific activity, which can be expressed as a turnover frequency (TOF), or number of molecules of product produced per metal atom site per second. 

Several comments [38] are appropriate regarding these guidelines. The first is obviously the most important, and is universally applicable to all synthetic strategies. Chromatographic or other purification techniques often provide a practical solution to low selectivity in unfavorable cases, however. Points 2 and 3 address auxiliary-based techniques, and are predicated on the higher cost of chiral reagents. Condition 3 is less important when a chiral catalyst has a high turnover number or when the chiral auxiliary is very inexpensive. Point 4 also becomes less important in catalytic processes as the turnover number increases. 

ATP-dependent adenylation domain in the loading module of the PKS, transferred to the ACP domain of this module, and then reduced in situ by an adjacent enoylreductase domain [248], Some years later, the heterologous overexpression and purification of RapL and validation of its ability to convert L-lysine to L-pipecolic acid by a cyclodeamination reaction that involves redox catalysis (NAD+ZNADH) were reported. Turnover is presumed to go through a reversible oxidation of the a-amine to imine, internal cyclization, and subsequent re-reduction of the cyclic A -piperideine-2-carboxylate intermediate. RapL also accepts L-ornithine as a substrate, although with a significantly reduced catalytic efficiency [249]. 

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