title: Tunneling in ligand binding to heme proteins.
abstract: Rebinding of carbon monoxide to the beta chain of hemoglobin after photodissociation by a laser flash is intramolecular below about 200 K. Above 25 K, rebinding occurs via classical over-the-barrier motion; below, quantum-mechanical tunneling dominates. Both are described by an energy spectrum peaked at Epeak=4.0 kilojoules per mole. The barrier width d(E), determined from the energy dependence of the tunneling rate, depends on barrier height, d(E) approximately 0.05 nanometer X (E/Epeak) 1.5.
mesh_terms: D002248:Carbon Monoxide; D002263:Carboxyhemoglobin; D006454:Hemoglobins; D008024:Ligands; D010782:Photolysis; D013696:Temperature; D013816:Thermodynamics
chemical_list: D006454:Hemoglobins; D008024:Ligands; D002248:Carbon Monoxide; D002263:Carboxyhemoglobin