were also confirmed by ESEEM measurements conducted for the primary electron donors P870 from Rhodobacter sphaeroides and P960 from Rhodopseudomonas viridis . A somewhat different spin-density ratio of 60%/40% was reported later in Ref. based on theoretical KS-DFT computations. Photo-CIDNP MAS NMR measurements carried out for the selectively 13 C-isotope labeled Rhodobacter sphaeroides WT predicted the spin density to be strongly delocalized over the two BChl a molecules of the SP .