Non-autonomous zinc-methylimidazole oscillator and the formation of layered precipitation structures in a hydrogel.

Oscillations are one of the intrinsic features of many animate and inanimate systems. The oscillations manifest in the temporal periodic change of one or several physical quantities describing the systems. In chemistry and biology, this physical quantity is the concentration of the chemical species. In most chemical oscillatory systems operating in batch or open reactors, the oscillations persist because of the sophisticated chemical reaction networks incorporating autocatalysis and negative feedback. However, similar oscillations can be generated by periodically changing the environment providing non-autonomous oscillatory systems. Here we present a new strategy for designing a non-autonomous chemical oscillatory system for the zinc-methylimidazole. The oscillations manifested in the periodic change of the turbidity utilizing the precipitation reaction between the zinc ions and 2-methylimidazole (2-met) followed by a partial dissolution of the formed precipitate due to a synergetic effect governed by the ratio of the 2-met in the system. Extending our idea spatiotemporally, we also show that these precipitation and dissolution phenomena can be utilized to create layered precipitation structures in a solid agarose hydrogel.

Design of non-autonomous pH oscillators and the existence of chemical beat phenomenon in a neutralization reaction.

The beat in physical systems is a transparent and well-understood phenomenon. It may occur in forced oscillatory systems and as a result of the interference of two waves of slightly different frequencies. However, in chemical systems, the realization of the latter type of the beat phenomenon has been lacking. Here we show that a periodic titration of acid and alkaline solutions with each other using programmable syringe pumps in a continuous stirred-tank reactor exhibits the beat phenomenon in the temporal pH oscillation pattern if the time periods of sinusoidal inflow rates of the reagents are slightly different. Interestingly, the frequency of the chemical beat pattern follows the well-known relationship from physics, namely the frequency of the beat is equal to the absolute value of the difference of the two wave frequencies. Based on our strategy, we can design and engineer non-autonomous pH oscillatory systems, in which the characteristics of the temporal oscillations (amplitude, time period) can easily and precisely be controlled by the experimental conditions such as the inflow rates and feed concentrations. The demonstrated phenomena can be exploited in practical applications, we use the non-autonomous pH oscillators to drive the reversible assembly and disassembly of pH-sensitive building blocks (oleic acid and gold nanoparticles), both highly relevant in nanotechnology and biomedical applications.

Chemical Resonance, Beats, and Frequency Locking in Forced Chemical Oscillatory Systems.

Resonance, beats, and synchronization are general and fundamental phenomena in physics. Their existence and their in-depth understanding in physical systems have led to several applications and technological developments shaping our world today. Here we show the existence of chemical resonance, chemical beats, and frequency locking phenomena in periodically forced pH oscillatory systems (sulfite-hydrogen peroxide and sulfite-formaldehyde-gluconolactone pH oscillatory systems). Periodic forcing was realized by a superimposed sinusoidal modulation on the inflow rates of the reagents in the continuous-flow stirred tank reactor. The dependence of the time period of beats follows the relation known from classical physics for forced physical oscillators. Our developed numerical model describes qualitatively the resonance and beat phenomena experimentally revealed. Application of periodic forcing in autonomously oscillating systems can provide new types of oscillators with a controllable frequency and new insight into controlling irregular chemical oscillation regimes.