Mixtures of amino acids with hydroxy acids allow for the formation of peptide bonds in a plausible prebiotic scenario via ester bond formation followed by ester–amide exchange. Here, we investigate the ability of the ester-mediated reaction pathway to form even longer polymers with peptide backbones based on the specific details of the reaction protocol. Fresh monomers were fed to the polymer/monomer mixture periodically by an automated "day–night machine" that was designed to simulate wet–dry cycles that would have been common on the prebiotic Earth. Quantitative analysis of peptide bond formation in the complex oligomer mixture was enabled by a simple hydrolysis treatment. In the ester-mediated peptide elongation process, new monomers add to one end of the chain step-by-step without termination. The feed composition (hydroxy acids and/or amino acids) was found to determine the final oligomer distribution. Production of longer oligomers enriched in peptide bonds was more efficient when only amino acids were fed because of a smaller number of active oligomer chains. These results reveal a process for synthesizing longer depsipeptides and/or peptides that could form secondary structures, and possibly functional polymers.
Abstract It is shown that n th-order reactions (n ≥ 0) are globally stabilized by employing a reference model controller. KEYWORDS: Reference model controller CSTRGlobal stabilization
The shear stability of mini- and macroemulsion latexes is compared and quantitatively evaluated with respect to their particle-size distributions. The effect of a few externally added large particles on the shear stability of these two types of latexes was also investigated. All the latexes selected were in the colloidal size range (less than 1 micron). The original particle sizes for the macroemulsion latexes ranged from 141 to 241 nm, and those for the miniemulsion latexes ranged from 96 to 209 nm. The miniemulsion latexes were found to be more shear stable than were their macroemulsion latex counterparts over the particle-size range investigated. This trend was repeated even in the presence of a few large particles. Additionally, seeding experiments suggest that mini- and macroemulsion latexes incur different levels of shear aggregation due to inherent differences in their particle-size distributions. The shear rate used along with the particle size and number were quantitatively shown to significantly influence the aggregation process. Finally, a quantitative method for evaluating relative shear stability in emulsion polymerization was demonstrated, which, although not very rigorous, could serve as a starting point for further quantitative isolation and investigation of the various parameters that affect the shear aggregation process.
The paper focusses on reference model control of a continuous stirred tank reactor for solution polymerization of methylmethacrylate. The reactor is a nonsquare plant with more outputs than inputs. Two schemes are employed both of which under certain conditions, ensure global stabilization of the reactor.
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