title: Glycine Polymerization on Oxide Minerals.
abstract: It has long been suggested that mineral surfaces played an important role in peptide bond formation on the primitive Earth. However, it remains unclear which mineral species was key to the prebiotic processes. This is because great discrepancies exist among the reported catalytic efficiencies of minerals for amino acid polymerizations, owing to mutually different experimental conditions. This study examined polymerization of glycine (Gly) on nine oxide minerals (amorphous silica, quartz, α-alumina and γ-alumina, anatase, rutile, hematite, magnetite, and forsterite) using identical preparation, heating, and analytical procedures. Results showed that a rutile surface is the most effective site for Gly polymerization in terms of both amounts and lengths of Gly polymers synthesized. The catalytic efficiency decreased as rutile > anatase > γ-alumina > forsterite > α- alumina > magnetite > hematite > quartz > amorphous silica. Based on reported molecular-level information for adsorption of Gly on these minerals, polymerization activation was inferred to have arisen from deprotonation of the NH3+group of adsorbed Gly to the nucleophilic NH2group, and from withdrawal of electron density from the carboxyl carbon to the surface metal ions. The orientation of adsorbed Gly on minerals is also a factor influencing the Gly reactivity. The examination of Gly-mineral interactions under identical experimental conditions has enabled the direct comparison of various minerals' catalytic efficiencies and has made discussion of polymerization mechanisms and their relative influences possible Further systematic investigations using the approach reported herein (which are expected to be fruitful) combined with future microscopic surface analyses will elucidate the role of minerals in the process of abiotic peptide bond formation.
authors.affiliation: Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo, 152-8550, Japan. nkitadai@elsi.jp.
authors.forename: Norio
authors.initials: N
authors.lastname: Kitadai
authors.affiliation: Institute of Nature and Environmental Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa, 920-1192, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Oonishi
authors.affiliation: Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo, 152-8550, Japan.
authors.forename: Koichiro
authors.initials: K
authors.lastname: Umemoto
authors.affiliation: Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo, 152-8550, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Usui
authors.affiliation: Institute of Nature and Environmental Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa, 920-1192, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Fukushi
authors.affiliation: Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka, 560-0043, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Nakashima
mesh_terms: D000327:Adsorption; D002384:Catalysis; D005998:Glycine / Q000737:chemistry*; D008903:Minerals; D058105:Polymerization
chemical_list: D008903:Minerals; D005998:Glycine
keywords: Amino acid; Astrobiology; Chemical evolution; Peptide; Protein