Role of Fast and Slow Inhibitors in Oscillatory Rhythm Design.

In biological or abiotic systems, rhythms occur, owing to the coupling between positive and negative feedback loops in a reaction network. Using the Semenov-Whitesides oscillatory network for thioester hydrolysis as a prototype, we experimentally and theoretically analyzed the role of fast and slow inhibitors in oscillatory reaction networks. In the presence of positive feedback, a single fast inhibitor generates a time delay, resulting in two saddle-node bifurcations and bistability in a continuously stirred tank reactor. A slow inhibitor produces a node-focus bifurcation, resulting in damped oscillations. With both fast and slow inhibitors present, the node-focus bifurcation repeatedly modulates the saddle-node bifurcations, producing stable periodic oscillations. These fast and slow inhibitions result in a pair of time delays between steeply ascending and descending dynamics, which originate from the positive and negative feedbacks, respectively. This pattern can be identified in many chemical relaxation oscillators and oscillatory models, e.g., the bromate-sulfite pH oscillatory system, the Belousov-Zhabotinsky reaction, the trypsin oscillatory system, and the Boissonade-De Kepper model. This study provides a novel understanding of chemical and biochemical rhythms and suggests an approach to designing such behavior.

Multiple iodide autocatalysis paths of chemo-hydrodynamical patterns in the Briggs-Rauscher reaction.

Autocatalytic feedback is often regarded as the core step for the chemo-hydrodynamical patterns in the nonlinear reaction system. The Briggs-Rauscher (BR) reaction shows sequential chemo-hydrodynamical patterns with three states, i.e. labyrinth, high iodine state, and rotating dendritic patterns. The short-lived labyrinth patterns, depending on [Mn2+]0, the ratio of [CH2(COOH)2]0 and [KIO3]0 and light intensities, result from iodide autocatalytic loop, which has three paths (involving Mn2+-induced radical reactions, the oxidation of iodomalonic compounds, and light-induced radical reactions, respectively). The high iodine state appears in a high ratio of [CH2(COOH)2]0 and [KIO3]0, relating to the autocatalytic path involving the oxidation of iodomalonic compounds. The light-induced radical autocatalytic path can act as a convenient control parameter to modulate the patterns in the first stage by increasing the iodine radicals. The dendritic patterns in the third stage result from the Marangoni effect caused by the evaporation of the solutions and reactions between H2O2 and iodine-containing species, which is independent of [CH2(COOH)2]0 and [Mn2+]0. This work contributes to a better understanding of the complex spatiotemporal patterns in the chemo-hydrodynamical system.

Peptide-Modulated pH Rhythms.

Many drugs adjust and/or control the spatiotemporal dynamics of periodic processes such as heartbeat, neuronal signaling and metabolism, often by interacting with proteins or oligopeptides. Here we use a quasi-biocompatible, non-equilibrium pH oscillatory system as a biomimetic biological clock to study the effect of pH-responsive peptides on rhythm dynamics. The added peptides generate feedback that can lengthen or shorten the oscillatory period during which the peptides alternate between random coil and coiled-coil conformations. This modulation of a chemical clock supports the notion that short peptide reagents may have utility as drugs to regulate human body clocks.

Development of sulfur doped carbon quantum dots for highly selective and sensitive fluorescent detection of Fe2+ and Fe3+ ions in oral ferrous gluconate samples.

Sulfur-doped carbon quantum dots (S-CQDs) with stable blue fluorescence were synthesized through a facile one-step hydrothermal method by using ascorbic acid and thioglycolic acid as carbon and sulfur sources. The prepared S-CQDs exhibited a sensitive and selective response to Fe3+ ions in comparison with Fe2+ and other metal ions, In the presence of adequate H2O2, Fe2+ was completely transformed to Fe3+ that is the determinable form of iron ions, and the difference in the change of the fluorescence intensity of S-CQDs before and after adding H2O2 was used for detection of Fe2+ and Fe3+ ions, respectively. Under the optimum experimental conditions, the fluorescence intensity of S-CQDs gradually decreased with increasing of Fe3+ concentration ranging from 0 to 200 µM. Good linearity was achieved over the range of 0-200 µM. The detection limit of the developed method was 0.050 µM for Fe3+. The recoveries of Fe2+ and Fe3+ spiked in real samples ranged from 98.2% to 112.4%. Finally, the proposed S-CQDs integrated with Fenton system was applied to the detection of Fe2+ and Fe3+ ions in oral ferrous gluconate samples, which presents potential applications in the speciation and determination of Fe2+ and Fe3+ ions in complex samples.

Graphene oxide composites for magnetic solid-phase extraction of trace cytokinins in plant samples followed by liquid chromatography-tandem mass spectrometry.

In this work, an easy, effective, and sensitive method based on graphene oxide@silica@magnetite composites as adsorbent of magnetic solid-phase extraction combined with liquid chromatography and tandem mass spectrometry, was established and validated for the trace analysis of cytokinins in different plants. The prepared magnetic composite was characterized by infrared spectroscopy, transmission electron microscopy, Brunauer-Emmett-Teller analysis, and magnetic hysteresis. Under the optimized conditions, good linearities in the range of 0.5-100 ng/mL were obtained with the corresponding linear correlation coefficient >0.9989 for the investigated four cytokinins, and good sensitivity levels were achieved with low detection limits ranging from 93 to 120 pg/mL. The established magnetic solid-phase extraction with liquid chromatography and tandem mass spectrometry method has been validated in the separation and analysis of four cytokinins in plant samples with good recoveries between 78.9 and 97.3% for four cytokinins with the relative standard deviations lower than 13.5%.