Electron spin echo of spin-polarised radical pairs in intact and quinone-reconstituted plant photosystem I reaction centers

Light-induced spin-polarised P700+A1− pairs in intact and quinone-reconstituted photosystem I reaction centres were studied by electron spin echo (ESE) spectroscopy. The observed strong ESE envelope modulation was attributed to magnetic dipolar and exchange interactions in the pairs. The values of these interactions were derived from Fourier-transformed time traces and appeared to be D = −1.71 ± 0.05 G and J = 0.010 ± 0.015 G, respectively. A magnetic field effect on the radical pair lifetime induced by microwave pumping was observed. The reconstituted 2,3-dibromo-1,4-naphthoquinone was shown to be located in the same (A1) site as the native phylloquinone.