Fig. 5: Pulse EPR spectrum of rVCP.
From: Eustigmatophyte model of red-shifted chlorophyll a absorption in light-harvesting complexes
a Scheme of the energies of the triplet sublevels of a 3Car (D > 0 and E < 0) as a function of an external magnetic field, B0, aligned with the 3Car zfs axis Y. Whenever the energy of the microwave radiation matches the energy gap between T0 and either T+1 or T−1, a transition can be observed (XI or XII for B0 parallel to Y, respectively). The transitions can be either emissive (E) or absorptive (A) depending on the relative populations of the high-field triplet sublevels involved, indicated by the thickness of the level bars. b FS-ESE spectrum of rVCP (black) and Chl a dissolved in Triton X-100 micelles (green) at 50 K. The difference (orange curve) between the FS-ESE spectrum of rVCP and the FS-ESE spectrum of Chl a, which corresponds to the ‘pure’ 3Car spectrum, has been vertically translated for clarity. The simulation of the 3Car spectrum for Fx303/Fx305 (blue line) is calculated considering a population of the triplet state by means of TTET starting from the triplet state of the closest conserved Chl a (Chls a403 and a408, respectively). The polarizations of the simulated 3Car components were determined on the basis of atomic coordinates for the acceptor-donor pairs derived from the crystallographic structure10 and an initial donor 3Chl polarisation (Px:Py:Pz = 0.375:0.425:0.200)5, resulting in a 3Car polarization of (Px:Py:Pz = 0.41:0.20:0.39) for both Fx303 and Fx305 (a molecular scheme of the acceptor-donor pair with the zfs tensors of the two molecules is reported at the bottom of the panel). The simulated 3Car spectra were calculated using the following parameters: D = −41.0 mT; E = −4.1 mT; linewidths (lwx, lwy, lwz) = (2.0, 2.0, 2.5) mT. Canonical transitions discussed in the text have been highlighted in the low-field half of the spectra. A = absorption, E = emission.
