Responsive organogels formed by supramolecular self assembly of PEG- block-allyl-functionalized racemic polypeptides into β-sheet-driven polymeric ribbons

Abstract

A chemically reactive hybrid diblock polypeptide gelator poly(ethylene glycol)-block-poly(dl-allylglycine) (PEG-b-PDLAG) is an exceptional material, due to the characteristics of thermo-reversible organogel formation driven by the combination of a hydrophilic polymer chain linked to a racemic oligomeric homopeptide segment in a range of organic solvents. One-dimensional stacking of the block copolymers is demonstrated by ATR-FTIR spectroscopy, wide-angle X-ray scattering to be driven by the supramolecular assembly of β-sheets in peptide blocks to afford well-defined fiber-like structures, resulting in gelation. These supramolecular interactions are sufficiently strong to achieve ultra low critical gelation concentrations (ca. 0.1 wt%) in N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and methanol. The critical gel transition temperature was directly proportional to the polymer concentration, so that at low concentrations, thermoreversibility of gelation was observed. Dynamic mechanical analysis studies were employed to determine the organogel mechanical properties, having storage moduli of ca. 15.1 kPa at room temperature.

Fig. 1

(a) Picture of reaction flasks of entry 1 of Table 1 after 12 h at rt (left) and entry 2 of Table 1 after 12 h at rt (right). (b) TEM image of the DMF gel of entry 1 of Table 1, negatively stained with 1 wt% uranyl acetate aqueous solution. (c) AFM height image of DMF gel of entry 1 of Table 1.

Fig. 2

(a) ¹H NMR spectrum of mPEG₁₁₂-b-PDLAG₁₂. (b) MALDI-TOF spectrum of mPEG₁₁₂-b-PDLAG₁₂.

Fig. 3

GPC (DMF eluent) traces of (a) of mPEG₁₁₂-b-PDLAG₁₂, and (b) mPEG₄₅-b-PDLAG₁₂.

Fig. 4

The ATR-FTIR spectrum of dried DMF gel made from mPEG₁₁₂-b-PDLAG₁₂.

Fig. 5

WAXS patterns of mPEG₁₁₂-b-PDLAG₁₂.

Fig. 6

Dynamic mechanical responses from 0.1 to 10 Hz over 3 h.

Scheme 1

Synthesis of mPEG-b-PDLAG.

Scheme 2

A schematic illustration of the nanofiber formed in the network structure of the DMF gel of mPEG-b-PDLAG₁₂.