Ring-size controlled dimerization of synthetic zinc chlorophyll derivatives possessing a 1-azacycloalkyl group through mutual coordination of amino moiety to central zinc atom

Synthesis and Self-Aggregation of Chlorophyll-a Derivatives Possessing a Hydroxymethyl Group in the C20-Substituent with Ethynylene and/or Phenylene Linkers

Chlorophyll(Chl)-a derivatives containing some rigid linkers in the C20 substituents, which were inserted between a hydroxymethyl group and the chlorin π-skeleton, were synthesized and their self-aggregation abilities were investigated. Measurements of electronic absorption, circular dichroism and infrared absorption spectra revealed that the zinc complex of a Chl-a derivative bearing a (p-ethynyl)benzyl alcoholic moiety at the C20-position gave its J-aggregates in an aqueous micellar solution through the hydrogen and coordination bonding. These results exhibited the potential of Chl-a derivatives bearing a hydroxyl group in the C20 substituents as the model compounds for chlorosomal light-harvesting antennas.

Sterically controlled and pH-dependent self-aggregation of synthetic zinc 3-(alkylamino)methylated chlorophyll-a derivatives in aqueous micellar solution

Zinc methyl 3-(methyl/ethylamino)methyl-pyropheophorbides-[Formula: see text] were prepared as models of photosynthetically active bacteriochlorophyll-[Formula: see text] possessing the 3[Formula: see text]-hydroxy group. The synthetic methylamino analog predominantly dimerized via two Zn[Formula: see text]N coordination bonds in aqueous Triton X-100 micelles, while the more sterically crowding and less coordinating ethylamino derivative self-aggregated to form large oligomers through single coordination and hydrogen bonds, Zn[Formula: see text]N–H[Formula: see text]O=C-13, similarly as in the natural self-aggregates of bacteriochlorophyll-[Formula: see text]. The artificial self-aggregates were dependent on the aqueous pH, but the dimer was less pH-sensitive and also more tolerant to the additional Triton X-100.