First-principles theory of muon and muonium trapping in the protein chain of cytochrome c and associated hyperfine interactions

The microscopic details of the electron transfer in cytochrome c (cyt c) are being investigated by the Muon Spin Relaxation (μSR) technique. We are using the Hartree-Fock Cluster Procedure to determine the most likely trapping sites for μ⁺ and muonium (Mu) in the protein chain, and have performed extensive calculations in single amino acid molecules of the protein chain of cyt c. The double-bonded oxygen atom of the carboxyl group was identified as the trapping site for both μ⁺ and Mu. Utilizing the wave functions we obtained from the Hartree-Fock calculations, we have determined the hyperfine field that the μ⁺ in Mu experiences while the latter is trapped at the oxygen.