Abstract:
Surface pattern has an important influence on the properties of nanomaterials. In this work, polypeptide-based curved nanorods with helical surface nanostructures were prepared. Poly(
γ-benzyl-
L-glutamate) (PBLG) polypeptide homopolymers and poly(
γ-benzyl-
L-glutamate)
-b-polyethylene glycol (PBLG
-b-PEG) polypeptide block copolymers were successfully synthesized by ring-opening polymerization of
γ-benzyl-
L-glutamate-
N-carboxyanhydride initiated by triethylamine and PEG-NH
2, respectively. For the PBLG
-b-PEG block copolymer, through partial deprotection of the benzyl group of the PBLG block and esterification reaction between the carboxyl group and cinnamyl alcohol, poly(
γ-benzyl-
L-glutamate-
co-cinnamonyl-
L-glutamate)
-b-polyethylene glycol (P(BLG/CLG)
-b-PEG) were obtained. The modified block copolymer P(BLG/CLG)
-b-PEG with cinnamyl oxy group is photo-cross-linkable. Under UV-irradiation at
λ = 254 nm, a cycloaddition reaction can occur on the C=C double bonds of the cinnamyl groups to cross-link polypeptide segments. PBLG nanorods were prepared by a selective precipitation method using tetrahydrofuran-
N,
N-dimethylformamide (THF-DMF) co-solvent as the initial solvent and water as the selective solvent. To the aqueous solution of the PBLG nanorods, THF was added to induce their bending. By changing the amount of THF introduced, the curving degree of the nanorods can be regulated. Using a similar method, PBLG/PBLG-
b-PEG and PBLG/P(BLG/CLG)-
b-PEG core-shell helical nanorods were prepared, in which the PBLG homopolymer formed the rod-like core and the PBLG-
b-PEG or P(BLG/CLG)-
b-PEG formed the surface helical nanopatterns. When THF was added to the aqueous solution of both the PBLG/PBLG-
b-PEG and PBLG/P(BLG/CLG)-
b-PEG helical nanorods, smooth curved nanorods were prepared and surface helices disappeared. Then for the PBLG/P(BLG/CLG)-
b-PEG helical nanorods, UV-irradiation was applied to crosslink the CLG segments of P(BLG/CLG)-
b-PEG, thus the helical surface patterns were fixed. Under THF treatment, these shell-crosslinked helical nanorods bent into curved helical nanorods. Therefore, crosslinking of the P(BLG/CLG)
-b-PEG segments can retain the helical surface patterns without hindering the curving of the PBLG nanorods under THF treatment. These PBLG curved nanorods and PBLG/P(BLG/CLG)-
b-PEG curved helical nanorods are structurally stable and able to maintain structural features in aqueous solutions. The arrangement manner of PBLG lateral phenyl groups is characterized by circular dichroism (CD). It was found that the shrinkage of phenyl groups on the PBLG lateral phenyl groups under THF induction drived the curving of the nanorods.