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Radical Clock Substrates Measure Nonstatistical Dynamical Effects in Cytochrome P450-Mediated C-H Functionalization

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Dynamic effects, not just rearrangement rates, govern cytochrome P450 clock reactions. This study reveals nonstatistical dynamics and carbocation pathways explain product selectivity, resolving long-standing mysteries in radical chemistry.

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Area of Science:

  • Biochemistry
  • Chemical Dynamics
  • Computational Chemistry

Background:

  • Cytochrome P450 enzymes activate C-H bonds through radical intermediates.
  • Radical clock substrates probe intermediate lifetimes, but selectivity data lacks correlation with rearrangement rates.

Purpose of the Study:

  • To elucidate the factors controlling product selectivity in P450 radical clock reactions.
  • To resolve the discrepancy between experimental selectivity and theoretical predictions.

Main Methods:

  • Ab initio direct dynamics simulations.
  • Analysis of dynamic (momentum) nonstatistical effects.
  • Investigation of carbocation versus radical intermediate pathways.

Main Results:

  • Dynamic nonstatistical effects, not just rearrangement rates, dictate radical pair intermediate fate.
  • Explains the lack of correlation between U/R selectivity and radical rearrangement rates.
  • Identifies carbocation intermediates in some clock reactions, influenced by ionization energy and C-C bond elongation.

Conclusions:

  • P450 clock reaction outcomes depend on dynamic effects and nonstatistical pathway branching.
  • Transition state theory alone is insufficient for interpreting clock reaction results.
  • Integrating two-state reactivity with dynamic effects is crucial for understanding P450 clock experiments.