Exciton coupled circular dichroism ECCD

Exciton coupled circular dichroism (ECCD) spectra. 139... 

Exciton-coupled circular dichroism (ECCD) spectroscopy was performed on the Aib-Stb-D peptide to fiirther substantiate the interaction between the methyl stilbene side-chains, which was observed via PL experiments. The interaction between the excited state of chromophores in a chiral environment causes split Cotton effects upon absorption of circularly polarized light by the chromophores (29, 30). It can be observed from Figure 7 that Aib-Stb-D exhibits a split CD Cotton effect presumably because of the chiral presentation of the methyl stilbene molecules on the same side of the a-helical peptide the asymmetric nature of the split observed may be due to some other electronic transitions or of additional background ellipticity, as has been observed in other systems (29, 31). The ECCD results confirm the close proximity of the methyl stilbene side chains mediated by the peptide backbone, which permits interaction between the side-chains in the excited state. 

Cm profiles from structural studies by circular dichroism or fluorescence spectroscopy can be readily validated by comparison with results from function. Several labeling methods exist to study self-assembly under meaningful high-dilution conditions (FRET [6] ECCD, exciton-coupled circular dichroism [67]). Validated Cm profiles from structural studies or from other functions such as catalysis can be used to dissect self-assembly in water with self-assembly in the bilayer membrane (Fig. 11.13B, a vs b) [21]. 

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