Triangular Nanotoroids Self-Assembled from Polypeptide Homopolymers: The Formation Route and Mechanisms

Polymer nanotoroids have attracted increasing attentions recently. The topology of the nanotoroids is mainly limited to circular form, while noncircular forms are rarely observed. The preparation method and formation mechanism for noncircular nanotoroids are not well governed. Reported here is a finding of triangular nanotoroids self-assembled from hydrophobic polypeptides in solution. With the addition of water, the polypeptides become less soluble in the solution, they self-assemble into nanofibers. When more water is introduced, the polypeptides tend to shrink to decrease their interfacial area, which generates internal twist stress driving the nanofibers convolve into circular nanotoroids. Under further water additions, the polypeptides further shrink to decrease their interfacial area. As a result, the circular nanotoroids bend and fold into triangular nanotoroids, with saddle-like and V-shaped nanotoroids as the intermediates. This work presents a first example regarding triangular nanotoroids formed by polymers, and demonstrates an effective way by generating internal stress to regulating the topology of the polymer nanotoroids.