EPR spectral simulation for silk fibroin-Cu(II) complexes with multiple components

The simulation for electronic paramagnetic resonance (EPR) spectrum with hyperfine couplings as well as multiple coordination components is often difficult. Here we develop a simulation approach based on the second-order perturbation theory to address these issues. The EPR spectral simulations of the silk fibroin-Cu(II) complexes are taken as examples to illustrate this approach, efficiently revealing the function of Cu(II) in the spinning process of silkworm. In addition, this approach would be useful for the EPR simulations of complexes containing Fe(II), Mn(II), V(III) and other paramagnetic ions.