| Protocell membrane provides compartmentalization for the origin of life,allowing protocells to exchange material,energy and information between themselves and their surroundings,and to develop a possible site for simple metabolic reaction,replication,or growth and division process.The current model of protocell compartments can be classified as:liposomes,fatty acid vesicles,inorganic colloidosomes,coacervate droplets,oil droplets and so on.Clays and minerals have the characteristic of charge,high specific surface area,selective adsorption ability and the ability to shielding ultraviolet light.And it can catalyze the synthesis and enrichment of key biomolecules such as amino acids,peptides and proteins.Therefore,the clay and mineral surfaces can serve well as plausible sites for prebiotic chemistry.In this study,we employ synthesized LDHs,an anionic clay,as model of clay particles.The interaction between LDHs and egg yolk lecithin are investigated,and the possible transmembrane mechanism of LDHs particles is also proposed.In contrast to the phospholipid-based membranes of all modern cells,early cell membranes are generally considered to be composed of simple-single chain amphiphiles.We synthesized dodecyl hydrogen sulfate(DHS)and employ it as a constituent of a protocell compartment model.It was systematically investigated that the phase behavior,physico-chemical properties and typical characteristics of primitive cell membranes in respect of selective permeability,fast exchange,self-reproduction and stability under primordial environments.We expect such kind of model of protocell compartments could shed some light on our understanding of the nature and characteristics of primitive membranes and could provide some information for the origin of life.Main contents and conclusions:(1)In this paper,we prepared and selected egg yolk lecithin liposome as protocell models.The permeability of Calcein and Nile red to the protocell membranes was studied.And then we explored the interaction between different size LDHs particles(100 nm and 500 nm)and liposome membranes,including the adsorption,migration process(trans membrane dynamics)and the morphological change of the bilayer.The possible transmembrane mechanism of LDHs particles was proposed.We expect this work could help us explore the role that LDHs and protocell membrane interaction played in the origin of life.(2)Dodecyl hydrogen sulfate(DHS),having some relevance on early earth,was synthesized and the basic properties of DHS solution were systematically studied.To study the phase behavior of DHS aqueous solution,different physico-chemical properties are measured,such as surface tension,transmittance,polarity of microenvironment and molar conductivity,combined with visual method,electronic microscopy and dynamic light scattering.Vesicles are formed when the concentrations are between-0.4 mM(critical aggregate concentration)and 10 mM.Oil droplets appear when the concentration of DHS is more than?10 mM.Alkyl sulfonic acids can self-assemble into vesicles alone without any additives when the solution pH is close to their apparent pKa(3.11).The DSC trace for DHS solutions and the release of fluorescent dyes(Nile red)encapsulated between the hydrophobic bilayers of vesicles with the addition of urea confirms the existence of hydrogen bonding.Furthermore,we employ DHS vesicles as model of protocells and the DHS membrane boundary displayed several typical characteristics of primitive bio-membranes as follows:(i)selective permeability(permeable to Calcein,Nile red,K+ and Cl-but impermeable to FITC-BSA),(ii)fast exchange and self-reproduction(When excess micelles were added into the vesicle solutions,the equilibrium of micelles??monomers??vesicles is established and shifted by the fast exchange of DHS molecules between the aggregates and the surrounding solution,allowing the growth,shape and division processes),and(iii)the stability under possible prebiotic environments(The DHS vesicles have been found to be stable over a year at 0.5 mM and at 5 mM,pH = 3.0). |
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