Engineering pH-responsive switching of donor-π-acceptor chromophore alignments along a peptide nanotube scaffold.

A cyclic tri-ß-peptide cyclo(ß-Ala-ß-Ala-ß-Lys) having diethylaminonaphthalimide at the ß-Lys side chain (CP3Npi) self-assembled into a peptide nanotube in a solution of HFIP and water. CD spectra of the CP3Npi nanotubes show a negative Cotton effect at 441 nm and a positive Cotton effect at 393 nm, indicating that D-π-A naphthalimide chromophores are aligned in a left-handed chiral way along the nanotube. The CP3Npi nanotubes bear positive charges under acidic conditions retaining the nanotube structure but pH-responsive switching of D-π-A naphthalimide alignments along the nanotube between a left-handed chiral and random arrangement was observed. The peptide nanotube is a stable scaffold for attaining pH-responsive alignment switching of side-chain chromophores.

Chiral and random arrangements of flavin chromophores along cyclic peptide nanotubes on gold influencing differently on surface potential and piezoelectricity.

Two kinds of peptide nanotubes are prepared from cyclo(ß-Asp(flavin)-ß-alanine-ß-alanine) (C3FAA) and cyclo(ß-Asp(flavin)-ethylenediamine-succinic acid) (C3FES). The flavin chromophores are protruding on the C3FAA and C3FES peptide nanotube surfaces in random and chiral ways, respectively. The surface potentials of the C3FAA nanotube bundles on a gold substrate become larger than the C3FES nanotube bundles of the corresponding thicknesses. The converse piezoelectric coefficients are as small as less than 1 pm V-1. The peptide nanotube bundles are subjected to a thermal anneal treatment which raises up all the surface potentials and also the converse piezoelectricity of the C3FES nanotube bundles of 3 pm V-1. The macrodipole of the C3FAA nanotube and the chiral arrangement of the flavin groups in the C3FES nanotube are considered to contribute influentially to the surface potential and the piezoelectricity, respectively.