Husk-like microcapsule formation in material self-assembly

Abstract

Solid microspheres, that were phase-separated in aqueous suspensions of thermal heterocomplex molecules made by heating a mixture of amino adds, transformed into husk-like microcapsules as pH increased. The transformation from solid microspheres into microcapsules proceeded at two different time scales. Rapid dissolution of thermal heterocomplex molecules fi'om the outer surfaces only during a short period was followed by slow dissolution of those molecules from their inside. The difference of the rates of dissolution led to the formation ofmicrocapsules carrying smaller inner kernels as remnants. Thermal heterocomplex molecules from amino acids consisted of many different kinds of chemical species whose distinction could be identified by isoelectric electrofocussing When the aqueous environment in which those heterocomplex molecules were made had a sutficiently low pH value, most of those thermal products could participate in formation of solid microspheres. As the pH value of the environment increased, supramolecules as the members of the solid particles were gradually dissolved into the solution by disconnecting both intaand inter-molecular bonding. Those dissolved molecular species then suffered conformational changes depending upon the pH value of the solution. Some of the molecular species decreased their diffusion coefticient due to pH-dependent conformational changes, and could aggregate onto the parental particles again. Sfight differences in the diffusion coefficients of those molecular species that varied their conformations led to a wide variety of morphological structures. Various microstructures that could have served as matrices for prebiotic chemical syntheses could be diverse. Our present observation suggests that a wide variety of microstructures of prebiotic significance could be conceivable depending upon how the pH value of the aqueous environment developed historically on the primitive earth.