Molecular-dynamics simulation of chiral selectors immobilized onto an amorphous silica surface

Diamide-type chiral stationary phases (CSPs) based on N-3,5-dimethylbenzoyl -L-valine alkylamide covalently bonded to silica gel at different coverage densities whether or not end-capped silanol groups were prepared. The autho rs had developed a new preparation method for end-capped CSPs in which sily lation of the silanol groups is carried out first, and then a chiral select or is introduced into it by a hydrosilylation reaction. It was shown that t he silanol groups are effectively covered by the new preparation method. Th e optical resolution of DL-amino acids on the end-capped CSPs gave excellen t optical resolutions, especially when the coverage density was very low. I n this study, molecular-dynamics simulations were applied to investigate th e conformations of the non-end-capped CSPs and end-capped CSPs. It was foun d that with non-end-capped CSPs, the chiral selectors were lying almost par allel to the silica surface. In this case, several hydrogen bonds between t he surface silanol groups and the chiral selector were observed. This was n ot the case if end-capped CSPs were simulated. The degree of ligand flexibi lity increased with reducing the number of residual silanol groups.