Peptide chirality sensing by a cyclodextrin-polythiophene conjugate.

A new cyclodextrin-polythiophene conjugate (CDPT) has been prepared by attaching permethyl-α-cyclodextrins to polythiophene (PT) through a hexamethylene tether. Circular dichroism spectral examination of CDPT revealed that only a weak positive Cotton effect (Δε=0.1 M(-1) cm(-1)) was induced at the main band of the PT in dimethyl sulfoxide and similarly weak bisignate signals in pure and aqueous methanol solutions, which indicates that the α-cyclodextrins appended to PT with a long tether are ineffective in inducing a homochiral structure in the PT backbone. Nevertheless, enantiomeric amino acids and dipeptides added to an aqueous methanolic solution of CDPT caused chirality-dependent hypochromic changes in the UV/Vis spectra, which enabled us to sense these species and quantitatively determine the enantioselectivity by observing the difference in absorbance upon interaction with pairs of enantiomers. Enantiomeric D,D/L,L-dipeptide pairs rather than D/L-amino acid pairs were better differentiated in general, the highest DD/LL selectivity of 13.7 being observed for Phe-Phe.