14:15 〜 14:30
[MIS14-09] Effects of pH on the ribose synthesis in the formose reaction: implication for abiotic synthesis on ancient Mars
キーワード：リボース、ホルモース反応、初期火星
DNA, RNA, and proteins work together to support the essential system of the present life. RNAs catalyze biological reactions as well as have nucleotide sequence transcribed from DNA. Therefore, abiotic RNA formation has been regarded as an essential step of the origin of life. Ribose is an essential constituent of RNA and is known to form in the formose reaction in which a series of condensation and polymerization of formaldehyde forms many sugar molecules. Ribose synthesis by the formose reaction is known to proceed under alkaline conditions, but the effects of pH on the ribose synthesis have not been clear. The effects of pH on the formose reaction is important to constrain the possibility of ribose synthesis on prebiotic Earth and on ancient Mars. Therefore, this study investigates the effects of pH on the formose reaction and evaluated potential ribose synthesis on ancient Mars. Ancient Mars is shown to have liquid water on the surface and/or subsurface and had CO2-rich atmosphere. Thus, photochemical formaldehyde formation would have been possible. Moreover, it is estimated that pH of surface water acidified from mildly alkaline to acidic from Noachian to Hesperian based on the mineral composition found by some of Mars surface explorations.
The formose reaction experiments were conducted with formaldehyde and glycolaldehyde in phosphate buffer solutions of different pH. Ribose was formed even in neutral solutions. The yields decreased one orders of magnitude by the decrease of pH by 1. Ribose formation was below our detection limit in acidic solution, pH < 4, although tetroses were formed.
These results suggest that ribose was spontaneously formed from formaldehyde and glycolaldehyde even in near neutral aquatic environments implying that environments existed on Noachian Mars could promote spontaneous ribose formation.
The formose reaction experiments were conducted with formaldehyde and glycolaldehyde in phosphate buffer solutions of different pH. Ribose was formed even in neutral solutions. The yields decreased one orders of magnitude by the decrease of pH by 1. Ribose formation was below our detection limit in acidic solution, pH < 4, although tetroses were formed.
These results suggest that ribose was spontaneously formed from formaldehyde and glycolaldehyde even in near neutral aquatic environments implying that environments existed on Noachian Mars could promote spontaneous ribose formation.