Journal article
How to Conceptualize Catalytic Cycles? The Energetic Span Model
Accounts of Chemical Research, Vol.44(2), pp.101-110
Feb/2011
Abstract
A computational study of a catalytic cycle generates state energies (the E-representation), whereas experiments lead to rate constants (the k-representation). Based on transition state theory (TST), these are equivalent representations. Nevertheless, until recently, there has been no simple way to calculate the efficiency of a catalytic cycle, that is, its turnover frequency (TOF), from a theoretically obtained energy profile. In this Account, we introduce the energetic span model that enables one to evaluate TOFs in a straightforward manner and in affinity with the Curtin-Hammett principle. As shown herein, the model implies a change in our kinetic concepts. Analogous to Ohm's law, the catalytic chemical current (the TOF) can be defined by a chemical potential (independent of the mechanism) divided by a chemical resistance (dependent on the mechanism and the nature of the catalyst). This formulation is based on Eyring's TST and corresponds to a steady-state regime. In many catalytic cycles, only one transition state and one intermediate determine the TOF. We call them the TOF-determining transition state (TOTS) and the TOF-determining Intermediate (IDI). These key states can be located, from among the many states available to a catalytic cycle, by assessing the degree of TOF control (X-TOF; this last term resembles the structure reactivity coefficient in classical physical organic chemistry. The TDTS-TDI energy difference and the reaction driving force define the energetic span (delta E) of the cycle. Whenever the TDTS appears after the TDI, delta E is the energy difference between these two states; when the opposite is true, we must also add the driving force to this difference. Having SE, the TOE is expressed simply in the Arrhenius-Eyring fashion, wherein delta E serves as the apparent activation energy of the cycle. An Important lesson from this model Is that neither one transition state nor one reaction step possess all the kinetic information that determin
Details
- Title
- How to Conceptualize Catalytic Cycles? The Energetic Span Model
- Creators
- Sebastian Kozuch (null) - The Weizmann Institute of ScienceSason Shaik (null)
- Resource Type
- Journal article; Review
- Publication Details
- Accounts of Chemical Research, Vol.44(2), pp.101-110; Feb/2011
- Number of pages
- 10
- Language
- English
- DOI
- https://doi.org/10.1021/ar1000956
- Grant note
- S.K. acknowledges the support of Koshland Fellowship, awarded by the Weizmann Institute of Science. S.S. is supported by an ISF grant (53/09)._ALMAME_DELIMITER_
- Record Identifier
- 993265930703596
Metrics
38 Record Views