Toward the origin of life over feldspar surfaces: Adsorption of amino acids and catalysis of conformational interconversions

摘要

Feldspars are a group of tectosilicate minerals terminated with a full layer of hydroxyl groups and have been regarded as "hotbed" for birth of life. In this study, periodic density functional theory calculations are conducted to address two associated issues, as adsorption of amino acids and conformational interconversions over feldspar surfaces. Distribution of glycine isomers depends strongly on the number of interacted surface silanols (n), and canonical isomers exist exclusively for n <= 2 while zwitterions predominate for n = 3. Adsorption of amino acids is significantly affected by sidechains, especially those forming H-bonds with surfaces; however, sidechain contacts with feldspar surfaces disfavor zwitterion stabilization, and zwitterions become preferred without sidechain contacts. For all amino acids, conformational interconversions undergo four elementary steps, and proton transfer between two carboxylic-O atoms (step 2) is always rate-decisive. Step 2 is greatly accelerated with catalysis of surface silanols and activation barriers depend significantly on sidechains. All amino acids have moderate activation barriers and conformational interconversions (in both forward and reverse directions) proceed favorably at ambient conditions. Sidechains of amino acids exhibit influences through sidechain contacts with surfaces rather than as substituent effect.