NOVEL MODEL COMPOUNDS FOR PHOTOINDUCED ELECTRON-TRANSFER - STRUCTURESOF THE FOLDED CONFORMERS OF ZINC(II)-PYROPHEOPHYTIN-ANTHRAQUINONE DYADS

The solution structures of the P4-epimers of Zn(II)-pyropheophytin-ant hraquinone dyads (ZnPQ1 and ZnPQ2) were determined using two-dimension al NMR spectroscopy and molecular modeling, The mutual orientation of the anthraquinone and Zn-pyropheophytin rings was found to be differen t in the two P4-epimeric dyads on the basis of the ROESY correlations, observed between the quinone and phorbin protons. The anthraquinone r ing is situated below the phorbin macrocycle in both dyads, ZnPQ1 and ZnPQ2, In ZnPQ1, the ring planes show tilting, the anthraquinone ring being in a sloping position below subrings B, C and E of the phorbin m acrocycle, In ZnPQ2, the two pi-systems are almost parallel with the a nthraquinone ring being located approximately below the center of the phorbin macrocycle. (C) 1997 by John Wiley & Sons, Ltd.