Energy Transfer in β-Turned Peptide-Bridged Porphyrin Dimers

Abstract

β-Turned peptide-bridged diporphyrinyl compounds were prepared. Each isomeric monozinc complexes were easily available; metal-free porphyrin–peptide–zinc porphyrin and zinc porphyrin–peptide–metal-free porphyrin. In the isomers, the intramolecular energy transfer efficiencies from zinc porphyrin moiety to metal-free porphyrin moiety were the same from analysis of the steady-state fluorescence spectra, indicating that the efficiencies should be independent upon the linked peptide spacer and dependent upon the distance between the porphyrin moieties in the molecule. Singlet energy might migrate intramolecularly from zinc porphyrin moiety to metal-free one mainly by through-space mechanism.

Synthetic molecular systems based on porphyrins as models for the study of energy transfer in photosynthesis

“…The porphyrin dimers with macrocycles covalently linked through cyclic dipeptides, viz., piperazine2,5-diones (compounds 41a,b and 42a,b), 62 b-folded oligopeptides (dimers 43a,b, 44a ± d, 45a,b) 63 and the oligo-L-proline spacers 46a ± i and 47a ± i, 64 were synthesised for studies of intramolecular interactions and energy transfer between the porphyrin components.…”

“…Thus rigid b-folded structures of the dipeptides in the molecules 43a,b, 44a ± d and 45a,b are determined by the formation of hydrogen bonds between the carbonyl groups of the porphyrins and amino groups of amino acid residues of the peptides. 63 Due to the cyclic side chain, the oligo-L-proline spacers in the dimers 46a ± i and 47a ± i acquire fairly stable helical conformations provided the number of amino acid residues is no less than four. 18,64 The general strategy of the preparation of these compounds is based on the use of standard protocols of the peptide synthesis.…”

“…The bisporphyrin 43a was easily converted into the dizinc complex 43b by treatment with an excess of zinc acetate. 63 The dimers in which both porphyrin residues are linked to aspartic acid were synthesised in the following way. First, the b-carboxy group of Boc-L-Asp(OH)-OH was selectively protected followed by protection of the a-carboxy group.…”

“…The selectively metallated dimers 44c,d were synthesised by the condensation of the zinc-containing porphyrin component with the porphyrin free base. 63 The synthesis of the dimer 45a included condensation of 5-(pcarboxyphenyl)-10,15,20-tri-p-tolylporphyrin (49) with piperidine-4-carboxylic acid, reaction of the product with D-proline to yield the amino acid derivative 55 and condensation of the latter with the zinc ± porphyrin complex 54b in the presence of DCC. 63 The bisporphyrin 45b was synthesised from the zinc complex of compound 55 and the porphyrin free base 54b in a similar way.…”

“…63 The synthesis of the dimer 45a included condensation of 5-(pcarboxyphenyl)-10,15,20-tri-p-tolylporphyrin (49) with piperidine-4-carboxylic acid, reaction of the product with D-proline to yield the amino acid derivative 55 and condensation of the latter with the zinc ± porphyrin complex 54b in the presence of DCC. 63 The bisporphyrin 45b was synthesised from the zinc complex of compound 55 and the porphyrin free base 54b in a similar way. 63 This strategy was also used in the synthesis of the bisporphyrin donor ± acceptor model systems 46a ± i and 47a ± i linked by oligoproline spacers.…”