title: Wavy membranes and the growth rate of a planar chemical garden: Enhanced diffusion and bioenergetics.
abstract: 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.
authors.affiliation: Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge CB2 3RA, United Kingdom;
authors.forename: Yang
authors.initials: Y
authors.lastname: Ding
authors.affiliation: Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390;
authors.forename: Bruno
authors.initials: B
authors.lastname: Batista
authors.affiliation: Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390;
authors.forename: Oliver
authors.initials: O
authors.lastname: Steinbock
authors.affiliation: Instituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones Científicas-Universidad de Granada, E-18100 Armilla, Granada, Spain; Instituto Carlos I de Física Teórica y Computacional, Universidad de Granada, E-18071 Granada, Spain.
authors.forename: Julyan H E
authors.identifier: 0000-0001-7392-0957
authors.initials: JH
authors.lastname: Cartwright
authors.affiliation: Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge CB2 3RA, United Kingdom; sssc1@cam.ac.uk.
authors.forename: Silvana S S
authors.initials: SS
authors.lastname: Cardoso
mesh_terms: D004058:Diffusion; D004734:Energy Metabolism; D060086:Hydrothermal Vents; D056656:Lab-On-A-Chip Devices; D008567:Membranes, Artificial
chemical_list: D008567:Membranes, Artificial
keywords: chemical gardens; chemobrionics; hydrothermal vents; origin of life