Shape and Diffusion of Circular Polyelectrolytes in Salt-Free Dilute Solutions and Comparison with Linear Polyelectrolytes

Secondary Structure-Dominated Layer-by-Layer Growth Mode of Protein Coatings

Benefiting from the luxury functions of proteins, protein coatings have been extended to various applications, including tissue engineering scaffolds, drug delivery, antimicrobials, sensing and diagnostic equipment, food packaging, etc. Fast construction of protein coatings is always interesting to materials science and significant to industrialization. Here, we report a layer-by-layer (LbL) multilayer-constructed coating of tannic acid (TA) and lysozyme (Lyz), in which the secondary conformations of Lyz dominate the growth rate of the TA/Lyz coating. As well characterized by various techniques (quartz crystal microbalance with dissipation (QCM-D), circular dichroism (CD) spectra, Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), contact angle, etc.), TA-induced conformational transition of Lyz to α-helices occurs at pH 8 from other secondary structures (β-sheets, β-turns, and random coils), which leads to the very fast growth of TA/Lyz with a number of deposited bilayers, with thicknesses of more than 90 nm for six bilayers. In contrast to the leading conformation of α-helices at pH 8, Lyz displayed multiple conformations (α-helices, β-sheets, β-turns, and random coils) at pH 6, which resulted in coating thicknesses of less than 30 nm for six bilayers. By the addition of NaCl, Tween 20, and urea, we further confirmed that the secondary conformations of Lyz relied greatly on the interactions between TA and Lyz and dominated the growth rate of the multilayers. We believe that these findings will help to understand the transformation of secondary conformations by TA or other polyphenols and inspire a new route to quickly build protein coatings.

One-step synthesis of poly(methacrylate)-b-polyester via “one organocatalyst, two polymerizations”

In a “one organocatalyst, two polymerizations” system, triarylsulfonium hexafluorophosphate salt could spontaneously catalyze photo-ATRP and ROP. A well-defined PTMC-b-PMMA block copolymer was successfully synthesized in one-step.

Understanding conformational and dynamical evolution of semiflexible polymers in shear flow

A clear description of the conformational and dynamical evolution of polymer chains in shear flow is the fundamental basis of microfluidic separations and macroscopic rheological behaviors. We employ graph theory analysis to analyze the local deformation and dynamics of linear polymer chains with different rigidities in shear flow based on the simulation trajectories that record the instantaneous conformations and dynamics. Our results show that all semiflexible chains experience quasi-periodic tumbling motions when the shear strain overwhelms the U-shape (or S-shape) deformation energy barrier. More interestingly, the contact map provides solid evidence for the asymmetric deformation in the whole tumbling motion. In the stretching process: at small and intermediate shear strength, flexible polymers show a quasi-affine deformation while semiflexible ones are initially unfolded from the center of the chains, then both of them follow the extension with half dumbbell- or dumbbell-like ends; at high shear strength, all polymer chains present only a dumbbell-like extension. In the collapse process, all chains prefer to initiate the folding from chain ends. This finding can facilitate our understanding on how semiflexible polymer chains relax and dissipate the stress in shear flow.

Individual circular polyelectrolytes under shear flow

Individual circular polyelectrolytes in simple shear flow are studied by means of mesoscale hydrodynamic simulations, revealing the complex coupling effects of shear rate, electrostatic interaction, and circular architecture on their conformational and dynamical properties. Shear flow deforms the polyelectrolyte and strips condensed counterions from its backbone. A decrease in condensed counterions alters electrostatic interactions among charged particles, affecting shear-induced polymer deformation and orientation. Circular architecture determines the features of deformation and orientation. At weak electrostatic interaction strengths, the polyelectrolyte changes its shape from an oblate ring at small shear rates to a prolate ring at large shear rates, whereas strong electrostatic interaction strengths are associated with a transition from a prolate coil to a prolate ring. Circular polyelectrolytes exhibit tumbling and tank-treading motions in the range of large shear rates. Further study reveals a similarity between the roles of intramolecular electrostatic repulsion and chain rigidity in shear-induced dynamics.