Photoresponsive peptide and polypeptide systems: part II. Photochromism of poly(l‐ornithine) containing various azo‐contents in side chains

Abstract

Poly(L‐ornithine)s having various azo‐contents in the side chains were synthesized by the water‐soluble carbodiimide procedure. The photochemical properties of the polypeptides poly[Nδ‐p‐(phenylazo)benzoyl‐L‐ornithine] (PPABLO) containing 3–77 mol% azobenzene were investigated by absorption and circular dichroism spectroscopy in hexafluoro‐2‐propanol (HFIP) or water, and in HFIP‐water or methanol‐water solvent mixtures. The photochromism of the dichroic bands of the PPABLOs containing 20–77 mol% azobenzene in the visible and ultraviolet wavelength regions was found to be mostly reversible as a function of irradiation time at different wavelengths due to the photostationary state (above 80% trans‐cis photoisomerization) of the azo aromatic moieties. The PPABLO containing 3.2 mol% azobenzene in water exhibited conformational changes from random coil to helix by the addition of methanol or sodium dodecyl sulphate (SDS). The photo‐induced conformational change was observed in HFIP‐water‐SDS solvent mixtures, while no conformational change was seen in water and HFIP‐water solvent mixtures.

Photoresponsive Polypeptides. Photomodulation of the Macromolecular Structure in Poly(Nε((phenylazophenyl)sulfonyl)-l-lysine)

“…Several photochromic polypeptides have been described in the literature. Most of them have been obtained by introducing azobenzene units into the side chains of various poly(R-amino acid)s such as poly(Lphenylalanine), 13 poly(L-aspartate)s, [14][15][16] poly(L-glutamate)s, [17][18][19][20][21][22][23][24][25][26][27][28][29] poly(L-lysine), 30,31 poly(L-ornithine), 32,33 and other poly(L-lysine) analogs. 34,35 A photoresponsive azomodified elastin-like polypeptide, 36 a cyclic peptide including an azobenzene moiety able to switch the peptide conformation, 37 and an azobenzene-containing amphiphilic sequential polypeptide 38 have also been recently described.…”

Photoresponsive polypeptides: Photochromism and conformation of poly (L‐glutamic acid) containing spiropyran units

“…In fact, the photoisomerization of the side chains can produce reversible variations of the macromolecular conformation which, in turn, can be accompanied by reBiopolymers, Vol. 33, 1505-1517 (1993) Most work has been carried out with polypeptides containing azobenzene units in the side chains, [5][6][7][8][9][10][11][12][13][14] in which the generation of cis-and trans-azo photoisomers requires artificial sources of uv light. In recent preliminary reports we have described spiropyran-modified poly ( L-glutamic acid) l5 and poly (L-lysine) ) l6 in which the photomodulation of conformation was obtained by exposure to sunlight.…”

Photoswitchable Polypeptides

“…[32] 13.2.1.4 Azo-Modified Polypeptide Analogues of Poly(l-lysine) Yamamoto et al have investigated a series of photochromic polypeptides obtained by introducing azobenzene units into the side chains of poly(a-amino acid) homologues of poly(l-lysine), such as poly(l-ornithine), [39,40] poly(l-a,c-diaminobutanoic acid) [41] and poly(l-a,b-diaminopropanoic acid) [42] (Scheme 5, Structures VIII, n = 1, 2, 3, and 4). At appropriate and critical solvent compositions, the formation of the electrostatic complexes described above might be favored or inhibited by the electronic situation of the azo moieties, which differs depending on whether they are in the apolar, conjugated trans form, or in the more polar, unconjugated cis form.…”

“…[39,40] A sample of poly(l-ornithine) containing 48 mol% azo units was found to adopt the a-helix structure in HFP/water = 1/1. The CD spectra also exhibited a couplet of bands centered at about 320 nm, attributed to electronic interactions between the azo side chains in the trans configuration.…”