Investigating the adsorption mechanism of glycine in comparison with catechol on cristobalite surface using density functional theory for bio-adhesive materials

Abstract

Using periodic Density Functional Theory (DFT) calculations and DFT-based molecular dynamics simulations, we studied the adhesion mechanism of glycine amino acid and the catechol part of L-dopa on the cristobalite surface. The optimized glycine and catechol molecules are initially placed vertically 3 Å above the cristobalite surface with a vacuum thickness of approximately 40 Å. The catechol adhesion on the cristobalite surface previously studied showed strong binding energy both in dry and wet adsorption. Glycine is the second most abundant amino acid in the mussel adhesive protein, which would have a significant contribution in mussel adhesion. This study of glycine will further enlighten the understanding of marine mussel adhesion. We believe that all the proteins exist in the Mytilus edulis foot protein (mefp) are contributing in this unique and versatile adhesion of marine mussel. We observed that glycine molecules formed four hydrogen bonds with the surface silanols and acted as donors and acceptors. Four hydrogen bond formation is also observed during catechol adhesion on the cristobalite surface. The average binding energy of both molecules on the cristobalite surface lies in the range of hydrogen binding energy. Surface binding energy values of 20.23 and 14.45 kcal mol⁻¹ were obtained for glycine and catechol adsorption, respectively. Including the dispersion energy term further raised the binding energy to 31.29 kcal mol⁻¹ for glycine and 28.58 kcal mol⁻¹ for catechol. The binding energy values suggest that glycine adsorption on the dry cristobalite surface is much stronger as compared to that of catechol.