Synthesis and Self-assembly Behavior of Porphyrin-based Polypeptides

Poly(gamma-benzyl-L-glutamate) (PBLG) with propargyl terminal group and porphyrin derivatives containing single azide group (TFPP-N-3) were used as reactants to synthesize porphyrin-based polypeptide (TFPP-PBLG) using a click reaction. The molecular structures of the polymers, including molecular weight, polydispersity index, and composition were characterized by nuclear magnetic resonance spectroscopy (H-1-NMR), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectrophotometer (UV-Vis), and gel permeation chromatography (GPC). The critical water content (CWC) for the aggregation of the TFPP-PBLG polymers was determined by turbidity measurement (OD). By a selective precipitation method with water as the selective solvent, bowl-like aggregates with obvious pits were obtained. The solution self-assembly behavior was studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), dynamic laser light scattering (DLS) and small-angle X-ray scattering (SAXS). The results show that the TFPP-PBLG polymers can self-assemble into bowl-like aggregations when the PBLG chain is relatively short. Upon the addition of water, solubility of the solvent for polymers decreases, and the polymers aggregate into micelles. The pi - pi stacking effect contributed by porphyrin derivatives results in a relatively stable structure of the micelles. During the dialysis process, the solvent within the micelle diffuses outward while water is difficult into the micelles, causing the micelle to collapse and form a pit structure. As the solvent further diffuses, the pit becomes larger, ultimately leading to a bowl-like aggregate structure. Increasing the length of the PBLG makes the initial micelles more stable, which inhibits the collapse of the micelles under the dialysis process, as a result, ellipsoid micelles are maintained. The stability of the initial formed micelle is crucial in determining whether it undergoes depression during the subsequent dialysis process, ultimately resulting in the formation of nanobowls.