Speaker: Prof. Dr. Nejat Bulut
Title: Mechanism for high-spin to low-spin transition in hemoglobin HbA
Date/Time: April 18, 2018 / 13:40-14:30
Abstract: The hemoglobin molecule consists of four heme groups, each containing an iron atom as the active site. In the human adult hemoglobin (HbA), upon O2 binding, each heme group exhibits a transition from a high-spin (S=2) to a low-spin (S=0) state. We study the mechanism of this transition in HbA by using an extended Haldane-Anderson model of a transition-metal impurity placed in a semiconductor host. We determine the model parameters for HbA by the density functional theory (DFT). The quantum Monte Carlo (QMC) technique is then used to study this model. The combined DFT+QMC results show that new states, which we call as impurity bound states (IBS), form both in deoxy- and oxy-heme groups. The IBS are magnetically correlated electronic states arising from the impurity-host hybridization and the Coulomb interactions at the impurity orbitals. The IBS states are well known to exist in dilute magnetic semiconductors such as (Ga,Mn)As. The DFT+QMC results show that the spin state of the HbA molecule is determined by the electron occupancy of the IBS: the IBS are occupied in deoxy-HbA, while they are unoccupied in oxy-HbA. We suggest that the high-spin to low-spin transition is direct experimental evidence for the existence of impurity bound states in HbA, and that they are intimately related to the functioning of this molecule.
Contact: İnanç Adagideli