Chemical waves trigger wave

The versatility of this behavior witnesses about a large potential for such dynamic information processing. By using one parameter (time delay), one is able to ignite very different cells in the reactor. The chemical wave coming to a cell may trigger a cascade of other processes. 

Figure 13.5 Spatiotemporal effects of a bioautocatalytic chemical wave revealed by time-resolved mass spectrometry, (a) Investigation of a chemical wave due to "passive" transduction and a bienzymatic amplification system. (A) Experimental setup incorporating a horizontal drift cell and mass spectrometer. (B) Schematic representation of chemical wave propagation in the drift cell due to the passive and the enzyme-accelerated transduction. (b) Transduction of labeled and unlabeled ATP along the drift cell. Concentration of the C. g-ATP trigger 0 M (A) and 5 x 10 M (B). Exponential smoothing with a time constant of 4.1 s has been applied, and followed by normalization (scaling to the maximal value). The dashed line denotes the time lapse between half-maxima of the normalized curves (0.5 level) corresponding to the passive and accelerated chemical transduction 93 and 740 s in the case of the 10 and 5 x 10 iW trigger solutions, respectively [6], Adapted from Ting, H., Urban, P.L (2014) Spatiotemporal Effects of a Bioautocatalytic Chemical Wave revealed by Time-resolved Mass Spectrometry. RSCAdv. 4 2103-2108 with permission from the Royal Society of Chemistry...

TYSON and FIFE [4] have presented a theory of target pattern formation in the BZ reaction, based on the assumption that at the center of each pattern there is a heterogeneity which periodically triggers waves of excitation (either oxidation or reduction) which then propagate away from the center at speeds determined by the chemical composition of the medium at the wave front. They describe the chemistry of the reaction in terms of the highly successful Oregonator model [5,6]. In suitably scaled and reduced form the Oregonator equations are... 

From the results of the calculations, we can determine approximate thresholds in initial perturbations in radius and concentration necessary for trigger wave propagation. We find the expected trend that as the excitation concentration increases, the critical radius which must be excited for trigger wave propagation decreases. In the following section, we will calculate how likely such a threshold perturbation is to occur by means of an internal fluctuation in the chemical concentrations. 

Fig. 7. Chemical front propagation in the period-1 domain ( 2 = 1.4). (Top panel) Deterministic reaction-diffusion equation simulation of a circulating trigger wave. The diffusion coefficient in reduced units is AtD/ Ax) = 1 /8. The times reported in the figure are in units of 10 At with At = 1.783 x 10 . The concentration of species X is plotted as a function of space and time. (Middle panel) Automaton simulation for the same parameter values as in the top panel. (Bottom panel) Automaton simulation with D = /2.

As shown in Section 2.2.7, chemical reactions may be triggered by electrons or holes from an electrode as illustrated by SrnI substitutions (Section 2.5.6). Instead of involving the electrode directly, the reaction may be induced indirectly by means of redox catalysis, as illustrated in Scheme 2.15 for an SrnI reaction. An example is given in Figure 2.30, in which cyclic voltammetry allows one to follow the succession of events involved in this redox catalysis of an electrocatalytic process. In the absence of substrate (RX) and of nucleophile (Nu-), the redox catalysis, P, gives rise to a reversible response. A typical catalytic transformation of this wave is observed upon addition of RX, as discussed in Sections 2.2.6 and 2.3.1. The direct reduction wave of RX appears at more negative potentials, followed by the reversible wave of RH, which is the reduction product of RX (see Scheme 2.21). Upon addition of the nucleophile, the radical R is transformed into the anion radical of the substituted product, RNu -. RNu -... 

Catalysis by various low-valent metalloporphyrins of the type already depicted in Section 3.7.2 (see reference lb for a precise list) is represented in Figures 4.3 and 4.4 for several cyclic and acyclic 1,2-dibromides. A striking example of the contrast between redox and chemical catalyses is shown in Figure 4.3a, with fluorenone anion radical on the one hand and iron(I) octaethylporphyrin on the other. Starting with the oxidized, inactive form of the catalyst, in each case—the active form is produced at a reversible wave. Addition of the same amount of 1,2-dibromocyclohexane triggers a catalytic increase in the current that is considerably less in the first... 

The alterations in neurotransmitter activity which trigger or accompany the onset of natural sleep and distinguish slow wave or non-REM from REM sleep, provide one of the most compelling arguments in favour of chemical neurotransmission being specifically involved in mechanisms of conscious awareness. For an extensive review on neurochemistry and sleep, see Gottes-man (1999). 

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