PH oscillator

G. P. Misra and R. A. Siegel. Multipulse drug permeation across a membrane driven by a chemical pH-oscillator. J. Control. Release 79 293—297, 2002. 

The formaldehyde-sulfite reaction displays non-linear dynamics it is a clock reaction with a sudden pH excursion (from ca 7 up to ll).280 The induction period in batch processes is explained by the internal buffer systems, HS03 -S03. However, flow reactors also exhibit pH oscillations and bistability. 

Figure 4.16 Illustration of conversion of pH oscillations to oscillations in drug flux across a lipophilic membrane. Reprinted from [96] with permission from Wiley-Liss Inc., a subsidiary of John Wiley and Sons, Inc.

Giannos, S., Dinh, S., and Berner, B., Temporally controlled drug delivery systems Coupling of pH oscillators with membrane diffusion, Journal of Pharmaceutical Sciences, Vol. 84, No. 5, 1995, pp. 539-543. 

Hocker, C.G., I.R. Epstein, K. Kustin K. Tornheim. 1994. Glycolytic pH oscillations in a flow reactor. Biophys. Chem. 51 21-35. 

Suprathreshold pertiurbation pH oscillations in glycolysis, 32,34 in papain membreme, 9 Pharmacology, see Chronopharmacology Phase plane analysis, 6,492 of birhythmicity, 17,96-100 of Ca oscillations, 366 of cAMP relay and oscillations, 183-7, 216,217... 

Self-oscillations of sweUing and deswelling for the poly(N-isopropylacry-lamide-co-acryhc acid) hydrogels were realized by coupling pH and temperatme in the external solution media. The pH oscillations were also observed for the system consisting of iodate-sulfite-thiosulfate and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) when polymeric acid was substituted for sulfuric acid... 

The system used in the Landolt clock reaction, IOj/SOl , when treated with [Fe(CN)6] , shows oscillations in a CSTR. A modification of the mechanism proposed previously resolves a number of problems. A slightly different system, I03/HS03/S20i produces a small number of high-amplitude pH oscillations (up to 2 units of pH) over a narrow range of conditions in a closed system. ... 

An exciting application of coupling to another nonlinear system was demonstrated by Yoshida et al. who created a self-oscillating gel by coupling a pH oscillating reaction with a polymeric gel that expands and contracts with... 

Figure lb displays examples of pH oscillations observed in Cell II, with glucose level and pH fixed in Cell I. Oscillations persist for about one week, and period increases steadily with time. This drift, along with the ultimate cessation of oscillations, is believed to follow from the slow buildup of gluconate ion in Cell II (see below), which acts as a buffering species (77,72). In the present work, we shall ignore these aspects, which are not relevant to the capacity of the system to initiate oscillations. A more comprehensive analysis of the system is needed to account for these phenomena. 

Figure 1. a) Schematic of glucose-driven chemomechanical oscillator, b) pH oscillations observed in Cell II at varying mole fractions of MAA incorporated into the hydrogel membrane, and varying glucose concentrations in Cell I (Reproduced from reference 10. Copyright American Chemical Society.)... 

Measurement of Force Produced by a pH-Responsive Hydrogel in a pH Oscillator... 

A Landolt pH-oscillator based on a bromate/sulfite/ferrocyanide reaction has been developed with a room temperature period of 20 minutes and a range of 3.1periodic oscillations in volume in a pH responsive hydrogel. A continuously stirred, constant volume, tank reactor was set-up in conjuction with a modified JKR experiment and is used to show that the combination of a pH oscillator and a pH responsive hydrogel can be used to generate measurable force. 

The work outlined in this chapter makes use of pH as the stimuli for the system. This stimuli is delivered by a Bromate/Sulfite/Ferrocyanide pH oscillator developed by Edblom, Orban and Epstein (8), The benefits of the system are as follows ... 

Indeed, PAAc cryogels coupled with a bromate oscillator oscillated between swollen and collapsed states [31]. The reactions of bromate, sulfite, and ferrocyanide ions were conducted in an open continuously stirred tank reactor. Four feed solutions (potassium bromate, sodium sulfite, potassium ferrocyanide, and sulfuric acid) were supplied continuously to the reactor, during which the pH of the reaction solution was monitored as a function of time. The flow rate of the feed solutions is an important parameter in determining the extent of pH oscillations. In Fig. 21, pH versus time plots are shown for four different reduced flow rates k, defined as the flow rate of the feed solutions divided by the reaction volume. It is seen that the pH of the solution oscillates between 6.2-6.9 and 3.2-3.8. The dissociation degree a of a weak electrolyte relates to pH by ... 

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