Abstract
The hemocyanin protein binds and transports molecular oxygen via two copper atoms at its core. The singlet state of the {{rm{Cu}}}_{2}{{rm{O}}}_{2} core is thought to be stabilised by a superexchange pathway, but detailed in situ computational analysis is complicated by the multi-reference character of the electronic ground state. Here, electronic correlation effects in the functional site of hemocyanin are investigated using a novel approach, treating the localised copper 3d electrons with cluster dynamical mean field theory. This enables us to account for dynamical and multi-reference quantum mechanics, capturing valence and spin fluctuations of the 3d electrons. Our approach explains the stabilisation of the experimentally observed di-Cu singlet for the butterflied {{rm{Cu}}}_{2}{{rm{O}}}_{2} core, with localised charge and incoherent scattering processes across the oxo-bridge that prevent long-lived charge excitations. This suggests that the magnetic structure of hemocyanin is largely influenced by the many-body corrections.
Highlights
The hemocyanin protein binds and transports molecular oxygen via two copper atoms at its core
Molecular O2 is in a spin triplet configuration, and the Cu ions in deoxyHc are known to be in the Cu(I) d10 singlet configuration
This mechanism is supported by superconducting quantum interference device (SQUID) measurements that report a large superexchange coupling[7] between the two Cu centres, and a diamagnetic ground state[8]
Summary
The hemocyanin protein binds and transports molecular oxygen via two copper atoms at its core. U % 8 À 8:5 eV in the case of both molecules[40] and solids[41], it appears that in nature many-body quantum effects stabilise the low-spin singlet in spite of the butterflied structure of the Cu2O2 core (Fig. 2c, d).
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