title: Effects of water molecules on rearrangements of formamide on the kaolinite basal (001) surface.
abstract: The effects of kaolinite mineral surfaces on the unimolecular rearrangements of formamide (FM) were investigated using periodic density functional theory in conjunction with pseudopotential plane-wave approach. Surface hydroxyl groups covering the octahedral surface of kaolinite were found to play the role of catalysts in the transformations of FM. They induce a reduction of 31 kcal/mol on the energy barrier for formation of its isomer aminohydroxymethylene (AHM), which is close to the reduction amount calculated for water-catalyzed reactions. This suggests that the kaolinite octahedral surface exerts a catalytic effect similar to that of the water molecule. As the tetrahedral surface does not contain catalytic surface hydroxyl groups, only water-assisted FM transformation was therefore studied on this surface whose energy barrier amounts to ∼17 kcal/mol. The combined effect of both water and kaolinite on FM rearrangements via triple hydrogen transfer reactions does not significantly lower the energy barriers, as compared to those of double hydrogen transfer reactions. The triple hydrogen transfer energy barriers amount to ∼20 and ∼36 kcal/mol, and the double ones are ∼21 and ∼40 kcal/mol for formation of formimic acid and AHM isomers, respectively. However, the energies of the systems in water-catalyzed channels lie below the available energies of the original reactants, and thus these channels are more favored than the water-free ones. With its multiple functions as both a supporting plate-form and a catalyst for FM reactions, kaolinite can thus be regarded as an important natural catalyst for prebiotic synthesis.
authors: Department of Chemistry, University of Leuven , B-3001 Leuven, Belgium.
authors: Huyen Thi
authors: HT
authors: Nguyen
authors: Minh Tho
authors: MT
authors: Nguyen
mesh_terms: D002384:Catalysis; D005559:Formamides / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry; D007536:Isomerism; D007616:Kaolin / Q000737:chemistry*; D008956:Models, Chemical; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
chemical_list: D005559:Formamides; D014867:Water; D007616:Kaolin; C031066:formamide; D006859:Hydrogen