Calculations of the Gibbs Free Energy of Adsorption of Some Small Molecules and Amino Acid Decomposition Products on MCM-41 Mesoporous Silica

Mesoporous silica is a widespread adsorbent used, in particular, as a substrate in chemical and biochemical sensors. The prediction of its adsorption properties with respect to various small molecules is of key importance for the virtual design of sensing and other devices. In this work, the Gibbs free energies of adsorption of some small molecules (analytes) on the surface and in pores of MCM-41 mesoporous silica have been evaluated using an efficient original approach based on thermodynamic integration and classical molecular dynamics. Acetone, water, ammonia, methylamine, and some amino acid decomposition products important for food quality control (putrescine, cadaverine, indole, and skatole) are considered as analytes, while unmodified silica and silica modified with two different commonly used grafting groups, aminopropyl and phenyl, are considered as an adsorbent (substrate). The results obtained indicate that the sensitivity and selectivity of silica-based chemical sensors can be controlled by properly selecting specific grafting groups.