Testing the potential of the ferrocene chromophore as a circular dichroism probe for the assignment of the screw-sense preference of tripeptides

Abstract

A combined strategy utilizing experimental (infrared, nuclear magnetic resonance, circular dichroism, X-ray) and computational (time-dependent density functional theory) techniques is illustrated on tripeptides to investigate their chiroptical properties. Eight stereoisomers of monosubstituted ferrocene, Boc-Pro-Pro-Ala-NHFc, have been prepared and conformationally characterized in depth to reach some guidelines for a future design of ferrocene-based chromophores. The origin of the sign change in circular dichroism spectra near the absorption maximum of a ferrocene chromophore (about 470 nm) is strongly correlated with the sign of the dihedral angle describing deviation of the directly attached amide plane from planarity of the cyclopentadienyl ring. These findings may provide some guidelines for the design of new chiroptical ferrocene-based probes for the assignment of the screw-sense preference of short peptides.