Photoresponsive peptide and polypeptide systems: Part 9. Synthesis and reversible photochromism of azo aromatic poly(L‐α,ω‐diaminobutyric acid)

Abstract

AbstractPoly(L‐α,ω‐diaminobutyric acid) having azo aromatic side chains was synthesized by the water‐soluble carbodiimide procedure. The photoresponsive properties of the polypeptide poly[N7‐p‐(phenylazo)benzoyl‐L‐α,ω‐diaminobutyric acid] (PPABLDBA) due to the trans (about 71%, under visible light) cis (under ultraviolet light) photoisomerization of the azo aromatic moieties in the side chains were investigated by absorption and circular dichroism spectroscopy in hexafluoro‐2‐propanol (HFIP). The starting slightly turbid solution of trans‐PPABLDBA becomes clear on irradiation at 360 nm, accompanied by photoconversion of the conformer of the azo moieties to cis. The backbone conformation of PPABLDBA in HFIP is right‐handed helical (helical content, about 60%) when the azo moieties are trans (71%), while the conformation is random coil when cis. The backbone conformational transition of PPABLDBA from helical to coil is mostly reversible under the influence of light.