Conformational properties of helical foldamers under force

The aim of this study is to investigate the mechanochemical behavior of foldamers able to change their conformation is a stimuli-responsive way. Peptidic secondary structures were studied in detail by atomic force microscopy (AFM) at the single-molecule level. Synthetic copolymers containing a polypeptide block were prepared by N-carboxyanhydride amino acid ring-opening polymerization. The polymer chains were grafted onto gold surfaces and their mechanochemical behavior was then studied by AFM single-molecule force spectroscopy (SMFS). The investigated polypeptide blocks were based on polyglutamate, which undergoes transitions from alpha-helix to random coil. This can be induced by external stimuli (pH, ionic strength, temperature) or simply by applying a force. The mechanically driven unfolding of the helical foldamer was characterized in detail. Stretching the folded peptide resulted in original features in the force-distance traces. Plateaus that are specific for the helical conformation were detected, quantified and discussed. Pulling-relaxing SMFS experiments were performed and led to a better understanding of the mechanically induced unfolding of an alpha-helix as a reversible phenomenon