Orientation stability activation energy

In enzymic reactions the central ES<= EP transformation is very fast, and the value of kcat is very high. In addition to correctly oriented binding of the substrate at the active center of the enzyme, an effective decrease in activation energy of this reaction step might also be provided by stabilization of the transition state of the substrate molecule in the ES complex. 

The orientation and reactivity effects of each group are explained on the basis of resonance and field effects on the stability of the intermediate arenium ion. To understand why we can use this approach, it is necessary to know that in these reactions the product is usually kinetically and not thermodynamically controlled (see p. 214). Some of the reactions are irreversible and the others are usually stopped well before equilibrium is reached. Therefore, which of the three possible intermediates is formed is dependent not on the thermodynamic stability of the products but on the activation energy necessary to form each of the three... 

The Ir film, after the BEN treatment at 920 °C for 30 min, followed by a 4-h diamond growth at 770 °C, was not covered with diamond, and there were domains of both Ir(OOl) and Ir(lll) adjacent to each other [12]. The reason for this was not clear, but both the higher stability of Ir(lll) surface over Ir(OOl), and the low activation energy of Ir atom transport seemed to contribute to this result. The formation of Ir(lll) domains after BEN and diamond growth seems to indicate that a deposition of Ir(lll) film on StTiO fOOl) will be possible not simply by electron-beam evaporation but by a post-treatment. If this is actually the case, a growth of (lll)-oriented diamond will occur on Ir(l 11). 

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