Optical Reporting by Conjugated Polymers via Conformational Changes - Advanced Fluorescence Reporters in Chemistry and Biology - page 405

Fig. 14 (a) Schematic drawing of the conformational changes of the synthetic peptides JR2E
(negatively charged), JR2K (positively charged) and the JR2K-JR2E heterodimer. (b) Fluores-
cence spectra of POWT being bound to JR2E, JR2K or the JR2K-JR2E heterodimer [ 27 ]
occurs where the protein goes from a compacted form to a more extended
shape. This change in conformation was reflected in the POWT fluorescence
spectra by a slight blue shift and an increase in fluorescence intensity, indicating
a decrease in polymer planarity and a separation between adjacent polymer chains.
As described, this system could also be employed for the detection of a specific
protein, calcineurin.
Their next step was to synthesize by chemical oxidation, a negatively charged
polythiophene acetic acid (PTAA)-Li for direct association with the previously
discussed positively charged peptide JR2K [ 28 ]. It was found that the negatively
charged carboxylic acid side chains of the polythiophene helped to induce the
formation of a helix in the JR2K peptide just as the negatively charged peptide
had previously. The change from polymer in solution to helical conformation
resulted in both a blue-shift and an increase in fluorescence intensity because of a
twisting in the backbone, shorter conjugation lengths, and a reduction in aggrega-
tion and quenching from the previously more planar form. In this example, it was