No abstract

An efficient pseudo-spectral numerical method is introduced for calculating a self-consistent field (SCF) approximation for the linear susceptibility of ordered phases in block copolymer melts (sometimes referred to as the random phase approximation). Our method is significantly more efficient than that used in the first calculations of this quantity by Shi, Laradji and coworkers, allowing for the study of more strongly segregated structures. We have re-examined the stability of several phases of diblock copolymer melts, and find that some conclusions of Laradji et al. regarding the stability of the Gyroid phase were the result of insufficient spatial resolution. We find that an epitaxial (k = 0) instability of the Gyroid phase with respect to the hexagonal phase that was considered previously by Matsen competes extremely closely with an instability that occurs at a nonzero crystal wavevector k.

Numerical self-consistent-field theory calculations by Tyler and Morse [Phys. Rev. Lett. 94, 208302 (2005)] predict a stable orthorhombic network phase with space group in very weakly segregated diblock copolymer melts. Here, we examine the predicted stability of this phase within a simple Landau theory of weakly ordered crystals, and within a straightforward extension of Leibler's theory of weakly segregated diblock copolymer melts. An Fddd structure with a ratio of unit cell parameters (a:b:c)=(1:2:2 square root 3) is found to compete very closely with the hexagonal (H) and lamellar (L) phases along the predicted H-L phase boundary, and to be stable within a very narrow range of parameters around this metastable boundary.

Utilizing the dynamic amidation and aza-Michael addition chemistry, a set of high strength, recyclable, and self-healable covalent adaptable networks (CANs) are synthesized by reacting the precursor and commercial oligoamine cross-linkers under mild temperature (25–50 °C) and solvent-free conditions. The amide linkages present in these CANs are readily hydrolyzable under mild acidic (pH = 5.3) conditions, whereas the aza-Michael adducts with secondary amines are thermally reversible. Utilizing the above, these CANs are depolymerized under ambient conditions in mild acidic solution and recycled with retention of original mechanical properties. The crack on the material surface is self-healed at 50 °C. The precursor, a Knoevenagel condensation product of terephthalaldehyde and diethyl malonate, is easily synthesized in a large scale. Suitable model compounds are synthesized and studied to further understand the transformations involved in the polymerization–depolymerization of these networks. These networks exhibit adequate tensile properties (ultimate tensile strength ≤35 MPa and Young’s modulus ≤3 GPa), and the properties can be tuned further by suitably changing the oligoamine cross-linker. The simplicity of synthesis, cost effectiveness, adequate mechanical property, stability in aqueous and organic media, and recyclability along with self-healability render these CANs suitable for a range of applications.

G protein-coupled receptors (GPCRs) are typically characterized by their seven transmembrane (7TM) architecture, and interaction with two universal signal-transducers namely, the heterotrimeric G-proteins and β-arrestins (βarrs). Synthetic ligands and receptor mutants have been designed to elicit transducer-coupling preferences and distinct downstream signaling outcomes for many GPCRs. This raises the question if some naturally-occurring 7TMRs may selectively engage one of these two signal-transducers, even in response to their endogenous agonists. Although there are scattered hints in the literature that some 7TMRs lack G-protein coupling but interact with βarrs, an in-depth understanding of their transducer-coupling preference, GRK-engagement, downstream signaling and structural mechanism remains elusive. Here, we use an array of cellular, biochemical and structural approaches to comprehensively characterize two non-canonical 7TMRs namely, the human decoy D6 receptor (D6R) and the human complement C5a receptor (C5aR2), in parallel with their canonical GPCR counterparts, CCR2 and C5aR1, respectively. We discover that D6R and C5aR2 couple exclusively to βarrs, exhibit distinct GRK-preference, and activate non-canonical downstream signaling partners. We also observe that βarrs, in complex with these receptors, adopt distinct conformations compared to their canonical GPCR counterparts despite being activated by a common natural agonist. Our study therefore establishes D6R and C5aR2 as bona-fide arrestin-coupled receptors (ACRs), and provides important insights into their regulation by GRKs and downstream signaling with direct implications for biased agonism.