Distance dependency of exciton coupled circular dichroism using turn and helical peptide spacers

Porphyrins are promising chromophores for the investigation of the still unexplored area of 3-dimensional structural studies of proteins by using the exciton coupled circular dichroism (CD) method. The synthesis, conformational characterization by FTIR absorption and (1)H-NMR, and CD properties are described for a model bis-porphyrin system based on homooligo-[L-(alphaMe)Val](n) peptides as rigid spacers. In particular, the coupled CD phenomenon is experimentally detected, the intensity of which is modulated by the interchromophoric distance. These results extend and integrate those already reported with steroid, dimeric steroid, and brevetoxin bridges.