Exploding Chemical Gardens: A Phase‐Change Clock Reaction

Dynamics of the osmotic lysis of mineral protocells and its avoidance at the origins of life

The osmotic rupture of a cell, its osmotic lysis or cytolysis, is a phenomenon that active biological cell volume regulation mechanisms have evolved in the cell membrane to avoid. How then, at the origin of life, did the first protocells survive prior to such active processes? The pores of alkaline hydrothermal vents in the oceans form natural nanoreactors in which osmosis across a mineral membrane plays a fundamental role. Here, we discuss the dynamics of lysis and its avoidance in an abiotic system without any active mechanisms, reliant upon self-organized behaviour, similar to the first self-organized mineral membranes within which complex chemistry may have begun to evolve into metabolism. We show that such mineral nanoreactors could function as protocells without exploding because their self-organized dynamics have a large regime in parameter space where osmotic lysis does not occur and homeostasis is possible. The beginnings of Darwinian evolution in proto-biochemistry must have involved the survival of protocells that remained within such a safe regime.

Light-modulated colour transformation in highly intertwined vertically growing silver tungstate tubes

Achieving control over growth kinetics in chemical garden architectures is challenging due to the nonequilibrium conditions. In this study, we demonstrate the vertical growth of silver tungstate chemical garden tubes under both illuminated and dark conditions, a phenomenon not observed in a comparable silver-based system, specifically silver silicate, under light exposure. Physicochemical factors, viz. thermo chemical radius of the tungstate anion, its density-buoyancy relation, the osmotic pressure gradient, and the hydration enthalpy, contributed to the tube appearance in silver tungstate even in light. Tubes grown in light illumination were greyish black, while dark-grown tubes were creamy white, and both tubes appeared twisted and highly intertwined. The colour of the as obtained silver tungstate tubes could be transformed via exposure to light. In the presence of a strong oxidizing agent, the growing tubes retain the original creamy white colour even under illumination. Colour transformation in chemical garden tubes has not yet been observed, and this report could lead the way.

Comparative Evaluation of Chemical Garden Growth Techniques

Chemical gardens are an exciting area of self-organized precipitation structures that form nano- and micro-sized structures in different shapes. This field has attracted great interest from researchers due to the specific characteristics and potential applications of these structures. Today, research on chemical gardens has provided deeper information regarding the formation mechanisms of these structures, and several techniques have been developed for chemical garden growth. However, they all show different growth patterns and lead to the formation of structures with a variety of morphological, chemical, or physical properties. This study aimed to evaluate the effects of different production techniques on chemical garden growth, taking into consideration the growth patterns, morphology, microstructure, and chemical composition. The chemical garden structures obtained in seed and injection experiments, two common methods, showed highly similar surface structures, void formation, and chemical composition. The membrane growth method has a small number of applications; thus, it was comprehensively evaluated to add new insights to the existing limited data. It produced the most stable and standard structures in a flat sheet-like shape and showed different morphologies than those observed in other two methods. Overall, this study presented significant results about the effect of growth techniques on chemical garden structures and similar systems.

Periodic Nucleation of Calcium Phosphate in a Stirred Biocatalytic Reaction

Highly ordered superstructures composed of inorganic nanoparticles appear in natural and synthetic systems, however the mechanisms of non-equilibrium self-organization that may be involved are still poorly understood. Herein, we performed a kinetic investigation of the precipitation of calcium phosphate using a process widely found in microorganisms: the hydrolysis of urea by enzyme urease. With high initial ratio of calcium ion to phosphate, periodic precipitation was obtained accompanied by pH oscillations in a well-stirred, closed reactor. We propose that an internal pH-regulated change in the concentration of phosphate ion is the driving force for periodicity. A simple model involving the biocatalytic reaction network coupled with burst nucleation of nanoparticles above a critical supersaturation reproduced key features of the experiments. These findings may provide insight to the self-organization of nanoparticles in biomineralization and improve design strategies of biomaterials for medical applications.