Crystallization-Driven Self-Assembly of Coil−Comb-Shaped Polypeptoid Block Copolymers

Naisheng Jiang -  Louisiana State University

"Polymers that can self-assembly into a variety of nanostructures in solution are useful in many biomedical applications such as drug delivery."

cryo-TEM images

Representative cryo-TEM images for (a) PNMG121-b- PNDG46 and (b) PNMG124-b-PNDG63 in diluted methanol solutions (1 mg/mL).

What did the Scientists Discover?

Polymers that can self-assembly into a variety of nanostructures in solution are useful in many biomedical applications such as drug delivery. Here, researchers show that polypeptoids, a class of peptidomimetic polymers, can self-assembly into a series of nanostructures including long fibers, short rods, and two-dimensional sheets due to the so-called crystallization-driven self-assembly (CDSA) mechanism. Solution SAXS/WAXS at CHESS allowed the researchers to monitor the structural evolution of diblock copolypeptoids within a wide range of length scales during CDSA. It was found that the final shape and morphology of nanostructures rely on the chemical composition, preferred crystalline orientation and self-assembly pathway of the polypeptoids in solution. For example, with relatively short crystalline block, the PNMG105-b-PNDG20 molecules slowly assemble themselves unidirectionally into long nanofibrils or filaments as that solution is cooled below its crystallization point.

 

SAXS/WAXS profiles
Top: SAXS profiles of the 5 mg/mL PNMG105-b-PNDG20 methanol solution at a different waiting time (t). The solid line corresponds to the best-fit to the final equilibrium SAXS result based on the cylindrical micelle model described in the text. The corresponding MAXS/WAXS profiles in the high q regime were plotted at the bottom. The intensity data at different times have been shifted vertically by multiplying the MAXS/WAXS intensity by a factor of 5 for clarity.

What are the broader impacts of this work?

The morphology of nanocarriers can greatly affect their transportation, blood circulation time and cell uptake during a drug delivery process. It is known that CDSA is capable to create wide variety of nanostructures or potential nanocarriers in solution from polypeptoids. However, there are many aspects of this process remain poorly understood. The SAXS/WAXS studies here provide a better understanding of the fundamental relationships between chemical composition, micellar morphology, and CDSA pathway.

Why did this research need CHESS?

X-ray scattering measurements with the in-vacuum flow cell at the CHESS BioSAXS station provided crucial SAXS/WAXS data with very good statistics and easy solvent background subtraction.

Collaborators:

  • Naisheng Jiang, Department of Chemistry, Louisiana State University
  • Tianyi Yu, Department of Chemistry, Louisiana State University
  • Omead A. Darvish, Department of Chemistry, Louisiana State University
  • Shuo Qian, Neautron Scattering Division, Oak Ridge National Laboratory
  • Igor Kevin Mkham Tsengam, Department of Chemical and Biomolecular Engineering, Tulane University
  • Vijay John, Department of Chemical and Biomolecular Engineering, Tulane University
  • Donghui Zhang, Department of Chemistry, Louisiana State University

Publication Citation:

Naisheng Jiang, Tianyi Yu, Omead A. Darvish, Shuo Qian, Igor Kevin Mkam Tsengam, Vijay John, and Donghui Zhang "Crystallization-Driven Self-Assembly of Coil−Comb-Shaped Polypeptoid Block Copolymers: Solution Morphology and Self- Assembly Pathway," Macromolecules 2019 52 (22), 8867-8877 DOI: 10.1021/acs.macromol.9b01546

How was the work funded?

The X-ray study performed at CHESS was supported by the National Science Foundation under NSF award DMR-1829070 for CHEXS and the National Institutes of Health/National Institute of General Medical Sciences. This research was also supported by NSF award CHE-1609447.