2-[(R-phenyl)amine]-1,4-naphthalendiones as photosystem I electron acceptors. Structure-activity relationship of m- and p-PAN compounds with QSAR analysis

Nineteen 2-[(R-phenyl)amine]-1,4-naphthalendione derivatives (PAN) were tested on spinach thylakoids for their activity as electron acceptors. These molecules act as photosystem I electron acceptors in the micromolar range. AC50 values varied from 5 nM to 24 μM. QSAR analysis revealed a linear correlation of the m-PAN derivative log [1/AC50] with the energy difference of the LUMO and HOMO orbitals. The biological activity of p-PAN derivatives correlates linearly with structural parameters. Electron affinity is being the most important. The half wave I potential values (E1/2) of PAN compounds (from −213 to −569 mV vs. NHE) match with the mid-point potentials of the A0 to FX niche of PSI electron transport carriers. The log P values of PAN derivatives were 3.35 and 3.88, indicating that they are hydrophobic compounds. Therefore PAN compounds accept electrons at the hydrophobic A0 to FX niche of PSI.