Bottlebrush Block Copolymers at the Interface of Immiscible Liquids: Adsorption and Lateral Packing.

Amphiphilic bottlebrush block copolymers (BBCPs), having a hydrophilic bottlebrush polymer (BP) linked covalently to a hydrophobic BP, were found to segregate to liquid-liquid interfaces to minimize the free energy of the system. The key parameter influencing the outcome of the experiments is the ratio between the degree of polymerization of the backbone (NBB) and that of the side-chain brushes (NSC). Specifically, a spherical, star-like configuration results when NBB < NSC, while a cylindrical, bottlebrush-like shape is preferred when NBB > NSC. Dynamic interfacial tension (γ) and fluorescence recovery after photobleaching (FRAP) measurements show that the BBCP configuration influences the areal density and in-plane diffusion at the fluid interface. The characteristic relaxation times associated with BBCP adsorption (τA) and reorganization (τR) were determined by fitting time-dependent interfacial tension measurements to a sum of two exponential relaxation functions. Both τA and τR initially increased with NBB up to 92 repeat units, due to the larger hydrodynamic radius in solution and slower in-plane diffusivity, attributed to a shorter cross-sectional diameter of the side-chains near the block junction. This trend reversed at NBB = 190, with shorter τA and τR attributed to increased segregation strength and exposure of the bare water/toluene interface due to tilting and/or wiggling of the backbone chains, respectively. The adsorption energy barrier decreased with higher NBB, due to a reduced BBCP packing density at the fluid interface. This study provides fundamental insights into macromolecular assembly at fluid interfaces, as it pertains to unique bottlebrush block architectures.

3D Printing of Aqueous Two-Phase Systems with Linear and Bottlebrush Polyelectrolytes.

We formed core-shell-like polyelectrolyte complexes (PECs) from an anionic bottlebrush polymer with poly (acrylic acid) side chains with a cationic linear poly (allylamine hydrochloride). By varying the pH, the number of side chains of the polyanionic BB polymers (Nbb), the charge density of the polyelectrolytes, and the salt concentration, the phase separation behavior and salt resistance of the complexes could be tuned by the conformation of the BBs. By combining the linear/bottlebrush polyelectrolyte complexation with all-liquid 3D printing, flow-through tubular constructs were produced that showed selective transport across the PEC membrane comprising the walls of the tubules. These tubular constructs afford a new platform for flow-through delivery systems.

Structural and evolutionary characteristics of dynamin-related GTPase OPA1.

OPA1 is a dynamin-related GTPase that controls mitochondrial fusion, cristae remodeling, energetics and mtDNA maintenance. However, the molecular architecture of OPA1 is poorly understood. Here we modeled the structure of human OPA1 by the threading approach. We found that the C-terminal region of the OPA1 protein had multiple functional domains, while the N-terminal region was rich in alpha helices and did not include specific domains. For the short soluble forms of OPA1, we observed that there were obvious hydrophobic regions near the two cleavage sites and the N-terminal was positively charged after cleavage. The blue native analysis revealed that the protein could form stable homodimers. In addition, the evolutionary conservation of the C-terminal region, where most of the known mutated disease-related sites were located, was significantly higher than that of the N-terminal region. These findings provided new insights into the structure and biochemical function of OPA1.