All structure optimizations and energy calculations employed a substractive QM/MM approach with electrostatic embedding as implemented in the modular program ComQum. ComQum interfaces the QM software Turbomole 51 and the MM software AMBER. For all the structure optimizations the dispersion-corrected TPSS-D3 functional with Becke-Johnson damping and a def2-SV(P) basis set were employed. For all calculations with TPSS the resolution of identity (RI) approximation with standard auxiliary basis sets was applied. All atoms in the MM region were kept fixed during the geometry optimizations.