Amide and Peptide Bond Formation: Interplay between Strained Ring Defects and Silanol Groups at Amorphous Silica Surfaces

作者：Rimola Albert^*; Sodupe Mariona; Ugliengo Piero

来源：Journal of Physical Chemistry C, 2016, 120(43): 24817-24826.

DOI：10.1021/acs.jpcc.6b07945

The formation of amide and peptide bonds on plain amorphous silica surfaces was studied by DFT-D3 methods on cluster silica surface models involving strained SiO rings as sources of reactivity. The amide/peptide bond-formation reaction was found to be thermodynamically and kinetically favored compared to the gas-phase processes because of the copresence of surface (SiO)(2)/(SiO)(3) strained ring defects, resulting from the high-temperature treatment of silica, and spatially close SiOH silanol groups. Preliminary extended calculations involving ammonia and formic acid provided insights into the most promising reaction paths for amide bond formation on defective silica surfaces. These paths were also employed to study glycine dipeptide formation. The reactions proceed through two steps: (i) silica ring opening by reaction with carboxylic acids to form a SiOC(= O) surface mixed anhydride (SMA) and (ii) reaction of the SMA with amines to form the amide product. The key point of the overall reaction is the synergy between the strained SiO rings and the spatially close silanol groups: SMA formation forces carboxylic acids to be immobilized on the surface, whereas SiOH groups act as effective mild Bronsted catalytic acidic sites through a silanol-assisted proton-relay mechanism in the second step. These results provide some atomistic insights into recent experimental findings on the formation of amides catalyzed by bare silica surfaces.

• 出版日期2016-11-3