QUADRUPOLE PARAMETERS OF NITROGEN NUCLEI IN THE CATION-RADICAL P-700(CENTER-DOT-CRYSTALS OF PHOTOSYSTEM-I() DETERMINED BY ESEEM OF SINGLE)

The cation radical of the primary donor P-700 of photosystem I (PS I) is investigated by ESEEM on single crystals of PS I from the cyanobact erium Synechococcus elongatus. The nuclear quadrupole parameters K and eta of five different N-14 nuclei are determined and N-14 hyperfine c ouplings (hfc's) of P-700(.+) are evaluated. For comparison the cation of methyl-chlorophyllide a is studied in frozen solution. The N-14 hf c data agree with published results Ibr the N-15-labeled cation radica ls of P-700 and chlorophyll a and are discussed in terms of a chloroph yll a dimer model for the cation radical P-700(.+).