Extending classical molecular theory with polarization.

Area of Science:

• Chemical Physics
• Computational Chemistry
• Biophysics

Background:

• Understanding short-ranged atom-atom interactions is crucial for molecular modeling.
• The binding of carbon monoxide (CO) to heme proteins like myoglobin (Mb) is a key area of study.
• Existing theories may not fully capture the electrostatic contributions to these interactions.

Purpose of the Study:

• To present a classical, polarizable electrostatic theory for short-ranged atom-atom interactions.
• To model CO monomer and its interaction with iron, as a precursor to understanding heme proteins.
• To investigate the nature of the Fe-CO bond in heme compounds.

Main Methods:

• Developed a classical electrostatic theory incorporating smeared atomic partial charges.
• Constructed detailed models for CO monomer and CO-iron interactions.
• Fitted models using equilibrium distance data to represent bond-length-dependent dipole.
• Applied the theory to analyze CO binding in myoglobin and model heme compounds.

Main Results:

• Accurately represented the bond-length-dependent dipole of CO monomer.
• Successfully reproduced key features of CO binding to myoglobin and heme models.
• Identified a significant classical, noncovalent
• electrostatic bond
• in the Fe-CO interaction.
• Determined that binding energy is primarily polarization energy, comparable to hydrogen bond energies.

Conclusions:

• A classical electrostatic approach effectively describes short-ranged atom-atom interactions.
• The Fe-CO interaction in heme proteins has a substantial electrostatic component.
• This theory provides insights into noncovalent bonding and molecular interactions in biological systems.