Multipeptide-metalloporphyrin assembly on a dendrimer template and photoinduced electron transfer based on the...

To construct an artificial photosynthetic system, peptide dendrimers [n-(X-HLY)PAMAMs: X = R, E; Y= L, F; n=4, 8, 16, 32 and 64 segments], in which amphiphilic alpha-helix peptides (X-HLY: R-HLL, E-HLL and R-HLF) were introduced at the end groups of polyamidoamine dendrimers (PAMAMs), were designed and synthesized. The peptide dendrimers 64-(X-HLY)PAMAMs are novel synthetic biopolymers with an enormous molecular weight, about 160 kDa, and with a regulated amino acid sequence and three-dimensional conformation. The peptide dendrimers bound Fe(III)- or Zn(II)-mesoporphyrin IX per two alpha-helices; this afforded a multimetalloporphyrin assembly similar to the natural light-harvesting antennae in photosynthetic bacteria. Circular dichroism studies and peroxidase activity measurements revealed that metalloporphyrins were coordinated to the peptide dendrimers in a regulated manner and packed more densely with the growth of the dendrimer generation. Fluorescence quenching and photoreduction studies with methylviologen demonstrated that the photoinduced electron-transfer function with the peptide dendrimer-multi-Zn-MP was accomplished more effectively as the dendrimer generation increased. Thus, the three-dimensional assembly of metalloporphyrins and peptides in the dendrimer was an effective module for light-harvesting antennae in an artificial photosynthetic system.