Aggregation of synthetic metallochlorins in hexane. A model of chlorosomal bacteriochlorophyll self-assemblies in green bacteria.

Metal 3(1)-hydroxy-13(1)-oxo-chlorins were systematically prepared and their visible and circular dichroism spectra were measured in a solution. All the synthetic complexes were monomeric in tetrahydrofuran. The Ni/Cu/Pd/Ag(II) complexes were still monomeric after dilution with 99-fold hexane. In contrast, the Co(II) complex, as well as the Mg/Zn/Cd(II) complexes, self-aggregated in 1% (v/v) tetrahydrofuran-hexane to form oligomers. In the less polar organic solvent, the Mn(III) complex fully dimerized and the Fe(III) complex partially dimerized. Infrared spectra of the synthetic metal chlorins in solid thin films revealed that the Ni/Cu/Pd/Ag(II) and ClFe(III) chlorins were 4- and 5-coordinated monomers, respectively, the AcOMn(III) chlorin formed a 6-coordinated dimer by mutual coordination of 3(1)-OetaetaetaMn, and the Co(II) chlorin as well as the Mg/Zn/Cd(II) chlorins self-aggregated by 13-C=OetaetaetaO-Hetaetaetametal to form large oligomers.