The methylene blue-sulfide (HS-)-oxygen oscillator: mechanistic proposal and periodic perturbation

Abstract

Oscillations are observed in a CSTR during the methylene blue catalyzed oxidation of HS" by 02 at natural pH (=12). Oscillations in the concentration of the oxidized form of methylene blue can be observed spectrophotometrically, and oscillations in [02] can be observed amperometrically. Oscillations appear in a relatively narrow but significant range of flow rates and are inhibited by H202, presumably a product of the reduction of 02 by HS". A mechanism is proposed based on radical-chain processes and using inhibition as well as autocatalysis as the nonlinearities leading to oscillation. Removal of 02 by HS' is catalyzed by methylene blue, which is not itself reduced by HS" until almost all 02 is removed. The reduction of 02 leads 1 to H202 whose concentration may be high when the methylene blue is finally reduced. The oxidation of the reduced form of methylene blue by 02 is inhibited by H202 or some other product of the reduction of HS" by 02 or MB"1". Thus methylene blue remains in its reduced state until this inhibiting species is removed either by the flow or by reaction, probably with HS", or until the flow increases [02] to the point where a possibly autocatalytic radical-chain oxidation of the reduced form of methylene blue may begin. When methylene blue is reoxidized, 02 has been replenished, and the cycle repeats. Experiments also were carried out in which the oscillator was perturbed by varying the CSTR pumping rate sinusoidally. In all cases the response of the oscillator to perturbation was periodic or quasi-periodic. Regions of entrainment separated by regions of quasi-periodicity were found. AH peaks in the Fourier spectra of sinusoidally perturbed oscillators showing quasi-periodicity could be identified as linear combinations of the perturbing frequency and the natural frequency of the oscillator.

Chemical foundations of hydrogen sulfide biology

“…65122) is found to remain pure for several months in a vacuum desiccator [29,45]. Methylene blue also catalyzes H 2 S autoxidation and the mechanism involves H 2 O 2 as an intermediate (see 4.3 ) [150,151]. This might at least in part explain the unreliability of the methylene blue method for the measurement of H 2 S concentration [29,45,152].…”

Catalytic activity of CuS nanoparticles in hydrosulfide ions air oxidation

“…It is known that hydrosulfide ions oxidation in aqueous solutions at room temperatures in the absence of catalysts is a chain-radical process [1][2][3][23][24][25]. HS • and O 2…”

“…In the foregoing scheme, the stages (1) and (2) describe the initiation of chain-radical HS − oxidation on the surface of copper(II) sulfide nanoparticles, reactions (3) and (4) correspond to the propagation of chain HS − oxidation in the bulk of a solution, reaction (6) is the principal chain termination route [23,25]. Oxidation products (S x 2− , S 2 O 3 2− and SO 4 2− ) accumulate in the following reactions:…”

The methylene blue-D-glucose-O2 system. Oxidation of D-glucose by methylene blue in the presence and the absence of oxygen

“…The kinetic law derived is in agreement with the experimental equation. Comparison of equations (6) and (7) gives a ϭ k K 1 K 2 and b ϭ K 1 K 2 . The rate constant for reaction (c) can be calculated as 8.6 ϫ 10 Ϫ2 s Ϫ1 at 20ЊC.…”

“…Oscillations of the concentration of the oxidized form of methylene blue and in [O 2 ] appeared in a relatively narrow but significant range of flow rates and were inhibited by H 2 O 2 [6]. An attractive mechanism for this oscillator was proposed by Resch et al [7].…”