2,035 research outputs found
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100th Anniversary of Macromolecular Science Viewpoint: Opportunities in the Physics of Sequence-Defined Polymers
Polymer science has been driven by ever-increasing molecular complexity, as polymer synthesis expands an already-vast palette of chemical and architectural parameter space. Copolymers represent a key example, where simple homopolymers have given rise to random, alternating, gradient, and block copolymers. Polymer physics has provided the insight needed to explore this monomer sequence parameter space. The future of polymer science, however, must contend with further increases in monomer precision, as this class of macromolecules moves ever closer to the sequence-monodisperse polymers that are the workhorses of biology. The advent of sequence-defined polymers gives rise to opportunities for material design, with increasing levels of chemical information being incorporated into long-chain molecules; however, this also raises questions that polymer physics must address. What properties uniquely emerge from sequence-definition? Is this circumstance-dependent? How do we define and think about sequence dispersity? How do we think about a hierarchy of sequence effects? Are more sophisticated characterization methods, as well as theoretical and computational tools, needed to understand this class of macromolecules? The answers to these questions touch on many difficult scientific challenges, setting the stage for a rich future for sequence-defined polymers in polymer physics
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Phase Separation: Bridging Polymer Physics and Biology
Significant parallels exist between the phase separation behavior of polymers in solution and the types of biomolecular condensates, or ‘membraneless organelles,’ that are of increasing interest in living systems. Liquid-liquid phase separation allows for compartmentalization and the sequestration of materials, and can be harnessed as a sensitive strategy for responding to small changes in the environment. Here, I review many of the parallels and synergies between ongoing efforts to study and take advantage of phase separation in living vs. synthetic materials
The Effect of GnRH at Time of Insemination on Initiation of LH Pulses and Subsequent Progesterone
Research has indicated that luteinizing hormone (LH) pulses play a vital role in corpus luteum (CL) formation and subsequent progesterone concentrations. Therefore, our objectives were to determine: 1) when LH pulses begin following onset of estrus, 2) the effect an injection of gonadotropin releasing hormone (GnRH) would have on initiation of LH pulses, and 3) the effect LH pulse initiation had on subsequent plasma progesterone concentrations. Cows were synchronized with the Select Synch + Controlled Internal Drug Releasing device (CIDR) protocol (d -7 100 μg GnRH and CIDR; d 0 25 mg prostaglandin (PG) and removal of CIDR; estrus detected with HeatWatch). Following detection in estrus, a jugular catheter was inserted in each cow (n = 10). Based on initiation of estrus, cows were allotted into two treatments: 1) GnRH given 12 h (12.5 ± 1.2 h) after the initiation of estrus (n = 5; 100 μg) and 2) Control (n = 5). Blood samples were collected at 15-min intervals for 6 h at 12 h (bleed 1), 26 h (bleed 2), 40 h (bleed 3), 54 h (bleed 4), and 68 h (bleed 5) after the onset of estrus. The interval from onset of estrus to bleed 1 and ovulation was similar between treatments. The GnRH cows tended to have a greater area under the LH curve for bleed 1 compared to control cows. No differences were detected in bleeds 2, 3, 4, or 5. Average concentration of LH for GnRH cows in bleed 1 tended to be greater than control. No differences were detected in bleeds 2, 3, 4, or 5. No differences were detected in pulse frequency between treatments in bleeds 1, 3, 4, or 5, but in bleed 2, control tended to have more pulses than GnRH (2.5 ± 0.5 vs 1.4 ± 0.4). The GnRH-treated cows tended to have greater subsequent progesterone concentrations; however, GnRH-treated cows that had no LH pulses during bleed 2 had lower progesterone concentrations than cows with pulses (control or GnRH). In summary, injecting cows with GnRH approximately 12 h after the onset of estrus tended to reduce LH pulses 26-32 h following initiation of estrus, and elimination of LH pulses between 26-32 h resulted in decreased concentrations of progesterone during the subsequent cycle
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Design Rules for Encapsulating Proteins into Complex Coacervates
We investigated the encapsulation of the model proteins bovine serum albumin (BSA), human hemoglobin (Hb), and hen egg white lysozyme (HEWL) into two-polymer complex coacervates as a function of polymer and solution conditions. Electrostatic parameters such as pH, protein net charge, salt concentration, and polymer charge density can be used to modulate protein uptake. While the use of a two-polymer coacervation system enables the encapsulation of weakly charged proteins that would otherwise require chemical modification to facilitate electrostatic complexation, we observed significantly higher uptake for proteins whose structure includes a cluster of like-charged residues on the protein surface. In addition to enhancing uptake, the presence of a charge patch also increased the sensitivity of the system to modulation by other parameters, including the length of the complexing polymers. Lastly, our results suggest that the distribution of charge on a protein surface may lead to different scaling behaviour for both the encapsulation efficiency and partition coefficient as a function of the absolute difference between the protein isoelectric point and the solution pH. These results provide insight into possible biophysical mechanisms whereby cells can control the uptake of proteins into coacervate-like granules, and suggest future utility in applications ranging from medicine and sensing to remediation and biocatalysis
Linear Viscoelasticity of Complex Coacervates
Rheology is a powerful method for materials characterization that can provide detailed information about the self-assembly, structure, and intermolecular interactions present in a material. Here, we review the use of linear viscoelastic measurements for the rheological characterization of complex coacervate-based materials. Complex coacervation is an electrostatically and entropically-driven associative liquid-liquid phase separation phenomenon that can result in the formation of bulk liquid phases, or the self-assembly of hierarchical, microphase separated materials. We discuss the need to link thermodynamic studies of coacervation phase behavior with characterization of material dynamics, and provide parallel examples of how parameters such as charge stoichiometry, ionic strength, and polymer chain length impact self-assembly and material dynamics. We conclude by highlighting key areas of need in the field, and specifically call for the development of a mechanistic understanding of how molecular-level interactions in complex coacervate-based materials affect both self-assembly and material dynamics
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Complex Coacervation of Polymerized Ionic Liquids in Non-acqueous Solvents
Oppositely charged polymerized ionic liquids (PILs) were used to form complex coacervates in two different organic solvents, 2,2,2-trifluoroethanol (TFE) and hexafluoro-2-propanol (HFIP), and the corresponding phase diagrams were constructed using UV–vis, NMR, and turbidity experiments. While previous studies on complex coacervates have focused almost exclusively on aqueous environments, the use of PILs in the current work enabled studies in solvents with substantially lower dielectric constants (27.0 for TFE, 16.7 for HFIP). The critical salt concentration required to induce complete miscibility was roughly 2-fold larger in HFIP compared with TFE, and two different PIL complexes, solidlike precipitates and liquidlike coacervates, were found in both systems. This study provides insight into the effects of low-dielectric-constant solvents on complex coacervation, which has not been widely studied because of the limited solubility of conventional polyelectrolytes in these media
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Linear Viscoelasticity and Time—Alcohol Superposition of Chitosan/Hyaluronic Acid Complex Coacervates
Complex coacervation is an associative liquid−liquid phase separation phenomenon resulting from the complexation of oppositely charged macroions. While it is well-known that the phase behavior and rheological character of the resulting coacervates can vary as a function of the identity of the various species present (i.e., macroions, salt, and solution conditions), the effect of solvent quality has been rarely studied. Here, the effect of adding small amounts of either methanol or ethanol to complex coacervates of the natural polymers chitosan and hyaluronic acid is described. The effect of cosolvent addition on the phase behavior and linear viscoelasticity of the resulting coacervates is characterized. Lastly, we explore the potential for using not only time−salt superposition but also time−alcohol and time−salt−alcohol superposition to provide insight into coacervate rheology
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