The Generation of an Organic Inverted Chemical Garden

Metal Catalysis Acting on Nitriles in Early Earth Hydrothermal Systems

Hydrothermal systems are areas in which heated fluids and organic molecules rush through basaltic material rich in metals and minerals. By studying malononitrile and acetonitrile, we examine the effects of metal and mineral nanoparticles on nitrile compounds in anoxic, hydrothermal conditions representing a prebiotic environment of early Earth. Polymerization, reduction, cyclization, and a phenomenon colloquially known as 'chemical gardening' (structure building via reprecipitation of metal compounds or complexing with organics) are all potential outcomes with the addition of metals and minerals. Reduction occurs with the addition of rhodium (Rh) or iron (II) sulfide (FeS), with positive identification of ethanol and ethylamine forming from acetonitrile reduction. We find that polymerization and insoluble product formation were associated with oxide minerals, metallic nickel (Ni), and metallic cobalt (Co) acting as catalysts. Oxide minerals strongly promoted polymerization into insoluble, tar-like products of nitriles. FeS, iron-nickel alloy (FeNi), and rhodium are unique cases that appear to act as reagents by actively participating in chemical gardening without returning to their initial state. Further, FeS tentatively had a phase change into the mineral parabutlerite. This research aims to identify metals and metal minerals that could best serve nitrile catalysis and reactions on early Earth.

Growth of chemical gardens in gaseous acidic atmospheres

The generation of chemobrionic architectures through slow injection of aqueous silicate solution in gaseous TiCl₄ is demonstrated. The tubes were characterized by XRD, SEM and wet chemistry control experiments, and their mechanism of formation was unraveled. These structures serve as laboratory models for calthemites or soda straws.

Dissimilar chemobrionic growth in copper silicate chemical gardens in the absence or presence of light

The effect of the absence of light on chemical garden growth has been neglected although the gardens resemble hydrothermal vents that grow in dark in the sea/ocean. Herein, we report the differential growth of chemobrionic structures in copper silicate when identical reactions to yield copper silicate chemical gardens were carried out in the presence or absence of light. Irradiating the copper silicate chemical garden during its growth with different wavelengths of light independently resulted in morphologically divergent tubes.

Flow-driven synthesis of calcium phosphate-calcium alginate hybrid chemical gardens

Systems far-from-equilibrium self-assemble into spatiotemporal structures. Here, we report on the formation of calcium alginate gardens along with their inorganic hybrids when a sodium alginate solution containing sodium phosphate in various compositions is injected into a calcium chloride reservoir. The viscoelastic properties of the membranes developed are controlled by the injection rate, while their thickness by the amount of sodium phosphate besides diffusion. Inorganic hybrid membranes with constant thickness are synthesized in the presence of a sufficient amount of sodium phosphate. The electrochemical characterization of the membranes suggests that the driving force is the pH-gradient developing along the two sides; hence, the cell potential can be controlled by the addition of alkaline sodium phosphate into the sodium alginate solution.

Pattern selection of directionally oriented chitosan tubes

The growth of viscoelastic curved materials, inspired by biological systems, may give rise to various complex structures. One of the simplest ways to control the pattern formation is to vary the orientation of the reaction vessel while keeping all other experimental conditions constant. Here, we report the self-organization of soft chitosan tubes by injecting acidic chitosan sol into a pool of sodium hydroxide solution, where the adhesive force between the gel and container keeps the tubules on the bottom of the reactor. The horizontal growth of the tubular structure undergoes spontaneous symmetry breaking, where instabilities develop on the surface of the chitosan tubules. Transformation of folds into wrinkles and finally to a smooth tube takes place by varying the orientation of the container. In addition to characterizing the evolving structures, we have also shown that the linear growth rate of the tube scales with the tilt angle of the container from the horizontal.

Plausible Emergence of Biochemistry in Enceladus Based on Chemobrionics

Saturn's satellite Enceladus is proposed to have a soda-type subsurface ocean with temperature able to support life and an iron ore-based core. Here, it was demonstrated that ocean chemistry related to Enceladus can support the development of Fe-based hydrothermal vents, one of the places suggested to be the cradle of life. The Fe-based chemical gardens were characterized with Fourier-transform (FT)IR spectroscopy and XRD. The developed chemobrionic structures catalyzed the condensation polymerization of simple organic prebiotic molecules to kerogens. Further, they could passively catalyze the condensation of the prebiotic molecule formamide to larger polymers, suggesting that elementary biochemical precursors could have emerged in Enceladus.

Bio-inspired flow-driven chitosan chemical gardens

Organic chemical gardens of chitosan hydrogel develop upon injecting an acidic chitosan solution into an alkaline solution. Besides complex and budding structures, tubular hydrogel formations develop that exhibit periodic surface patterns. The underlying wrinkling instability is identified by its characteristic wavelength dependence on the diameter of the elastic material formed. The flow-driven conditions allow precise control over the structure that can help the design of soft bio-inspired materials. Our findings can also suggest a new direction in the field of chemobrionics.

Chasing Synthetic Life: A Tale of Forms, Chemical Fossils, and Biomorphs

This Essay focuses briefly on early studies elaborated by natural and chemical philosophers, and the once-called synthetic biologists, who postulated the transition from inanimate to animate matter and even foresaw the possibility of creating artificial life on the basis of physical and chemical principles only. Such ideas and speculations, ranging from soundness to weirdness, paved however the way to current developments in areas like abiotic pattern formation, cell compartmentalization, biomineralization, or the origin of life itself. In particular, the generation of biomorphs and their relationship to microfossils represents an active research domain and seems to be the logical way to bring the historical work up to the future, as some scientists are trying to make artificial cells. The last sections of this essay will also highlight modern science aimed at understanding what life is and, whether or not, it can be redefined in chemical terms.

Chemobrionics: From Self-Assembled Material Architectures to the Origin of Life

Self-organizing precipitation processes, such as chemical gardens forming biomimetic micro- and nanotubular forms, have the potential to show us new fundamental science to explore, quantify, and understand nonequilibrium physicochemical systems, and shed light on the conditions for life's emergence. The physics and chemistry of these phenomena, due to the assembly of material architectures under a flux of ions, and their exploitation in applications, have recently been termed chemobrionics. Advances in understanding in this area require a combination of expertise in physics, chemistry, mathematical modeling, biology, and nanoengineering, as well as in complex systems and nonlinear and materials sciences, giving rise to this new synergistic discipline of chemobrionics.

Wavy membranes and the growth rate of a planar chemical garden: Enhanced diffusion and bioenergetics

To model ion transport across protocell membranes in Hadean hydrothermal vents, we consider both theoretically and experimentally the planar growth of a precipitate membrane formed at the interface between two parallel fluid streams in a 2D microfluidic reactor. The growth rate of the precipitate is found to be proportional to the square root of time, which is characteristic of diffusive transport. However, the dependence of the growth rate on the concentrations of hydroxide and metal ions is approximately linear and quadratic, respectively. We show that such a difference in ionic transport dynamics arises from the enhanced transport of metal ions across a thin gel layer present at the surface of the precipitate. The fluctuations in transverse velocity in this wavy porous gel layer allow an enhanced transport of the cation, so that the effective diffusivity is about one order of magnitude higher than that expected from molecular diffusion alone. Our theoretical predictions are in excellent agreement with our laboratory measurements of the growth of a manganese hydroxide membrane in a microfluidic channel, and this enhanced transport is thought to have been needed to account for the bioenergetics of the first single-celled organisms.

Self-organization in precipitation reactions far from the equilibrium

Far from the thermodynamic equilibrium, many precipitation reactions create complex product structures with fascinating features caused by their unusual origins. Unlike the dissipative patterns in other self-organizing reactions, these features can be permanent, suggesting potential applications in materials science and engineering. We review four distinct classes of precipitation reactions, describe similarities and differences, and discuss related challenges for theoretical studies. These classes are hollow micro- and macrotubes in chemical gardens, polycrystalline silica carbonate aggregates (biomorphs), Liesegang bands, and propagating precipitation-dissolution fronts. In many cases, these systems show intricate structural hierarchies that span from the nanometer scale into the macroscopic world. We summarize recent experimental progress that often involves growth under tightly regulated conditions by means of wet stamping, holographic heating, and controlled electric, magnetic, or pH perturbations. In this research field, progress requires mechanistic insights that cannot be derived from experiments alone. We discuss how mesoscopic aspects of the product structures can be modeled by reaction-transport equations and suggest important targets for future studies that should also include materials features at the nanoscale.