The functional replacement of the primary ubiquinone (QA) in the photosynthetic reaction center (RC) from Rhodo-bacter sphaeroideswith synthetic vitamin K derivatives has provided a powerful tool to investigate the electron transfer mechanism. To investigate the binding mode of these qui-nones to theQAbinding sitewe have determined the binding free energy and charge recombination rate from QA ± to D + (kAD) of 29 different 1,4-naphthoquinone derivatives with systematically altered structures.
