Isotopic Effects on Covalent Bond Confined in a Penetrable Sphere

Area of Science:

• Quantum chemistry
• Computational chemistry
• Biophysical chemistry

Background:

• The Born-Oppenheimer approximation is a cornerstone of molecular quantum mechanics.
• Understanding molecular behavior under confinement is crucial for catalysis and chemical reactivity.
• The role of electron-pair confinement in chemical processes remains an area of exploration.

Purpose of the Study:

• To develop a model for covalent bond confinement using a finite potential.
• To investigate the effects of confinement on molecular properties like bond energy and vibrational frequency.
• To explore the implications of electron-pair confinement in enzyme catalysis and isotopic effects.

Main Methods:

• Solving the Schrödinger equation for a confined two-electron molecule using the diffusion Monte Carlo method.
• Calculating total energies, internuclear distances, and vibrational frequencies of the confined system.
• Applying the model to illustrate hydrogen transfer in a C-H bond cleavage catalyzed by bovine serum amine oxidase.

Main Results:

• Confinement significantly increases bond energy and nuclear vibrational frequency, while decreasing internuclear distance.
• The energy gap between molecular isotopes increases with confinement.
• Confinement/deconfinement processes within an enzyme's active site can drastically reduce activation energy for chemical transformations.

Conclusions:

• Electron-pair confinement by finite potentials offers a new perspective on chemical reactivity and the tunnel effect.
• The model provides a semiquantitative explanation for enzyme catalysis, linking active site confinement to activation energy reduction.
• Confinement/deconfinement of electron-pair bonds by electrostatic forces within enzyme pockets may be a fundamental catalytic mechanism.