1,721,037 research outputs found
Chemical patterns in simple flow systems
No full textThe addition of flow to chemical reaction-diffusion systems provides robust pattern-forming mechanisms which are expected to occur in a wide variety of natural and artificial systems. Experiments demonstrating some of these mechanisms are presented here, including the differential-flow-induced chemical instability (DIFICI), which gives rise to traveling chemical waves, and flow-distributed oscillations (FDO), which produce stationary concentration patterns
From Clocks to Synchrony: The Design of Bioinspired Self‐Regulation in Chemical Systems
No full textFeedback plays a vital role in the self-regulation of processes that govern biological structure and function such as the switches, rhythms, and synchronized states that are observed in cells. This chapter discusses the mechanisms of feedback and nonequilibrium state selection in the bioinspired chemical systems. The language that has evolved through the study of self-organization in chemical systems extends across multiple disciplines, and scientists are becoming increasingly adept at engineering functional feedback in both chemical and biological systems for applications. In living systems, autocatalysis is used as a switch to initiate processes in response to chemical signals. The Belousov–Zhabotinsky reaction remains the only homogeneous system to display long-lived oscillations in closed batch reactor. One of the remarkable discoveries regarding single-celled organisms such as bacteria was their ability to display collective behavior and form multicellular communities. The simplest response of cells is synchronization of activity, driven by intercellular chemical communication and feedback in the signaling mechanism
Switches induced by quorum sensing in a model of enzyme-loaded microparticles
Get PDFQuorum sensing refers to the ability of bacteria and other single-celled organisms to respond to changes in cell density or number with population-wide changes in behaviour. Here, simulations were performed to investigate quorum sensing in groups of diffusively coupled enzyme microparticles using a well-characterized autocatalytic reaction which raises the pH of the medium: hydrolysis of urea by urease. The enzyme urease is found in both plants and microorganisms, and has been widely exploited in engineering processes. We demonstrate how increases in group size can be used to achieve a sigmoidal switch in pH at high enzyme loading, oscillations in pH at intermediate enzyme loading and a bistable, hysteretic switch at low enzyme loading. Thus, quorum sensing can be exploited to obtain different types of response in the same system, depending on the enzyme concentration. The implications for microorganisms in colonies are discussed, and the results could help in the design of synthetic quorum sensing for biotechnology applications such as drug delivery
Ester hydrolysis: Conditions for acid autocatalysis and a kinetic switch
Get PDFAutocatalysis can be used to obtain a sharp switch in state after a programmable time lag. Here, autocatalysis driven by acid concentration during the dissolution and hydrolysis of solid esters was investigated. In a generic model of the process, conditions were identified for observation of a kinetic switch with the introduction of an inhibitor species, bicarbonate, to delay the onset of autocatalysis. The kinetic profiles from the hydrolysis of two esters, d-gluconic acid δ-lactone and dl-lactide, were examined and evidence for dissolution-limited acid autocatalysis was obtained with lactide
Kinetics of the urea–urease clock reaction with urease immobilized in hydrogel beads
No full textFeedback driven by enzyme catalyzed reactions occurs widely in biology and has been well characterized in single celled organisms such as yeast. There are still few examples of robust enzyme oscillators in vitro that might be used to study nonlinear dynamical behavior. One of the simplest is the urea–urease reaction that displays autocatalysis driven by the increase in pH accompanying the production of ammonia. A clock reaction was obtained from low to high pH in batch reactor and bistability and oscillations were reported in a continuous flow rector. However, the oscillations were found to be irreproducible and one contributing factor may be the lack of stability of the enzyme in solution at room temperature. Here, we investigated the effect of immobilizing urease in thiol-poly(ethylene glycol) acrylate (PEGDA) hydrogel beads, prepared using emulsion polymerization, on the urea–urease reaction. The resultant mm-sized beads were found to reproduce the pH clock and, under the conditions employed here, the stability of the enzyme was increased from hours to days
Influence of oxygen on chemoconvective patterns in the iodine clock reaction
Get PDFThere is increasing interest in using chemical clock reactions to drive material formation; however, these reactions are often subject to chemoconvective effects, and control of such systems remains challenging. Here, we show how the transfer of oxygen at the air–water interface plays a crucial role in the spatiotemporal behavior of the iodine clock reaction with sulfite. A kinetic model was developed to demonstrate how the reaction of oxygen with sulfite can control a switch from a low-iodine to high-iodine state under well-stirred conditions and drive the formation of transient iodine gradients in unstirred solutions. In experiments in thin layers with optimal depths, the reaction couples with convective instability at the air–water interface forming an extended network-like structure of iodine at the surface that develops into a spotted pattern at the base of the layer. Thus, oxygen drives the spatial separation of iodine states essential for patterns in this system and may influence pattern selection in other clock reaction systems with sulfite
Exploitation of Feedback in Enzyme-catalysed Reactions
Get PDFSome cellular systems, such as yeast, bacteria and slime mould, display dynamic behavior including switches and rhythms driven by feedback in enzyme-catalysed reactions. The mechanisms of these processes have been well investigated and recent attention has turned to generating similar responses in synthetic biocatalytic systems, with a view to creating bioinspired analogues for applications. Here we discuss how feedback arises in the reaction mechanisms of some enzyme-catalyzed reactions invitro, the behaviour obtained and the emerging applications. These autocatalytic reactions may provide insights into behaviour in cellular systems as well as new methods for drug delivery, sensing and repair that can be exploited in living systems
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