Effects of Lipid Bilayers and Polarity of the Organic Substrate on the Belousov–Zhabotinsky Reaction

Abstract

The Belousov–Zhabotinsky (BZ) reaction is characterized by oscillations in the concentration of some intermediates that resembles oscillations from biological systems 1, 2). One of the applications the BZ reaction has is on polymerization reactions, where radicals produced in the BZ reaction are used to trigger the polymerization process 3, 4). In these systems, the availability of radicals to participate in the BZ reaction is reduced and it increases the induction period (IP). In some conditions, the BZ reaction might also show an IP, which is a period in the beginning of the reaction, before the oscillations start 2). During the IP, the system accumulates intermediates until it is able to periodically produce enough bromide to inhibit the autocatalytic oxidation of Ce3+ to Ce4+ 2). The IP is an important part of the BZ reaction behavior. By better understanding it, we might get clues to improve current reaction mechanisms as well as be able to control the overall reaction behavior. The IP can differ according to the organic substrate of the reaction. The traditional organic substrate used in BZ reactions is malonic acid (MA). Switching it to one of its structural analogs, such as methylmalonic acid (MetMA), ethylmalonic acid (EtMA), or buthylmalonic acid (ButMA), the IP increases 5~ 9). This was suggested to be explained by a decrease on the substrate’s reactivity 5~ 9). Besides the reactivity, each of these substrates have a different hydrophobicity as represented by the octanol/water partition coefficient, logP. If a hydrophobic environment is added to the BZ reaction system, some of these substrates might partition into it and their availability in the aqueous phase will be compromised. Hence, by switching the organic substrate, there are at least two parameters that could be used to control the reaction behavior. One approach to assess the effects of a hydrophobic compartment into the BZ reaction, is to add lipid membranes into it. Lipid bilayers are known to interfere with the BZ reaction, likely by capturing some hydrophobic intermediates such as Br2 into the hydrophobic microenvironment of lipid membranes 10~ 15). The effects of lipid membranes in the BZ reaction depend on the membrane properties, particularly membrane fluidity 15). Here, we investigate how the BZ reaction in a stirred batch reactor responds to MA, MetMA, EtMA, or Effects of Lipid Bilayers and Polarity of the Organic Substrate on the Belousov–Zhabotinsky Reaction