Beyond Standard Quantum Chemical Semi-Classic Approaches: Towards a Quantum Theory of Enzyme Catalysis
The role transition structures (TSs) and vectors have played in discussing issues associated to enzyme catalysis is examined with focus on RubisCO; computations belong to standard semi-classic Born-Oppenheimer model with one-electron orbitals located at nuclear position coordinates. Here, theory is brought a step beyond starting from exact quantum schemes to get types of semi-classic Hamiltonians allowing for clear definitions of electronuclear separable models. Electronuclear quantum states (QSs) are given by linear superpositions over eigenfunctions of semi-classic Hamiltonians; base state functions are products of space and spin components. For frozen nuclei models amplitudes depend on nuclear configuration multiplying electronic diabatic base functions characterized by nodal pattern distributions. QS’ time evolution requires couplings to external fields and does not necessarily conserve total spin. RubisCO’s dioxygen and ethene-fragment quantum reactivity are examined and generalized. Conservation of nodal patterns permits links to exact semi-classic schemes ensuring correct presentation of bond forming processes; possible failures of LCAO-based computations without nodal control are discussed. These issues are examined in relation to catalysis representation. Pauling’s idea that TS signals bent out of equilibrium shape of reactant and product is framed in terms of transition QSs. A full quantum catalysis model is introduced.
KeywordsAbstract quantum mechanics Electromagnetic fields Quantum catalysts H + H system RubisCO Quantum transition states Photorespiration Angular momentum Diabatic states Quantum base states: dioxygen Ethylene Carbene
I dedicate this work to the memory of Prof. Carl-Ivar Brändén a great scientist who introduced us to the quest of enzyme catalytic sources by assigning the task of studying RubisCO’s mechanism.
The author is most grateful to all coworkers participating in these enterprises: J Andrés, M. Oliva,V S Safont, V Moliner, H. Fidder for beautiful insights on RubisCO catalytic mechanisms; Prof. G A Arteca for working in developments of the diabatic theory and model applications. Figure 10-1 was adapted from Monica Oliva’s thesis work, the present author is most grateful to her.
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