Silanol-Assisted Carbinolamine Formation in an Amine-Functionalized Mesoporous Silica Surface: Theoretical Investigation by Fragmentation Methods

Abstract

The aldol reaction catalyzed by an amine-substituted mesoporous silica nanoparticle (amine-MSN) surface was investigated using a large molecular cluster model (Si392O958C6NH361) combined with the surface integrated molecular orbital/molecular mechanics (SIMOMM) and fragment molecular orbital (FMO) methods. Three distinct pathways for the carbinolamine formation, the first step of the amine-catalyzed aldol reaction, are proposed and investigated in order to elucidate the role of the silanol environment on the catalytic capability of the amine-MSN material. The computational study reveals that the most likely mechanism involves the silanol groups actively participating in the reaction, forming and breaking covalent bonds in the carbinolamine step. Therefore, the active participation of MSN silanol groups in the reaction mechanism leads to a significant reduction in the overall energy barrier for the carbinolamine formation. In addition, a comparison between the findings using a minimal cluster model and the Si392O958C6NH361 cluster suggests that the use of larger models is important when heterogeneous catalysis problems are the target. ABSTRACT: The aldol reaction catalyzed by an amine-substituted mesoporous silica nanoparticle (amine-MSN) surface was investigated using a large molecular cluster model (Si 392 O 958 C 6 NH 361 ) combined with the surface integrated molecular orbital/molecular mechanics (SIMOMM) and fragment molecular orbital (FMO) methods. Three distinct pathways for the carbinolamine formation, the first step of the amine-catalyzed aldol reaction, are proposed and investigated in order to elucidate the role of the silanol environment on the catalytic capability of the amine-MSN material. The computational study reveals that the most likely mechanism involves the silanol groups actively participating in the reaction, forming and breaking covalent bonds in the carbinolamine step. Therefore, the active participation of MSN silanol groups in the reaction mechanism leads to a significant reduction in the overall energy barrier for the carbinolamine formation. In addition, a comparison between the findings using a minimal cluster model and the Si 392 O 958 C 6 NH 361 cluster suggests that the use of larger models is important when heterogeneous catalysis problems are the target.

Electronic Structure Theory Calculations Using Modern Architectures: KNL vs Haswell

“…Finally, consider an application of the Haswell and KNL architectures to a transition state problem: a model catalytic system studied by de Lima Batista et al As illustrated in Figure , the model reaction begins with two reactants (acetone, propylamine) plus the model catalyst silanol, moves to a transition state, and ends with the product carbinolamine and the catalyst silanol. All geometries were optimized using MP2/6-31G+(d,p); the transition state was verified by an MP2 Hessian.…”

Surface-Radical Mobility Test by Self-Sorted Recombination: Symmetrical Product upon Recombination (SPR)

“…Particle designs could include the following. (i) Use of a particle system with variable tumbling rates to enhance surface radical diffusion and facilitate transiting off of volatile radicals, in particular given the importance of volatile alkoxy radicals as reactive intermediates in atmospheric chemistry. − (ii) An alkoxy radical surface migration system can be studied experimentally based on surface silanols with increasing water content to assess the effects on the radical migration distance. − Simulations of alkoxy radical surface migration can also be studied by silica cluster models with quantum mechanics/molecular mechanics methods . (iii) A complementary SPR/EPR method can be developed for product distribution by radical recombination and assist in distinguishing between stationary and migratory surface radicals.…”

New Aspects Towards a Molecular Understanding of the Allicin Immunostimulatory Mechanism via Colec12, MARCO, and SCARB1 Receptors

“…Molecular docking demonstrated that GSSA binds to SCARB1 receptors with −5.7 kcal/mol and very high geometric matching. In comparison, carbinoil stabilizes SCARB1 at −3.2 kcal/mol [48] and the LDL-derived pyrene-sphingomyelin binding energy was 7.1 ± 0.9 Kcal/mol [49]. SCARB1 receptors have been well described as a high-density lipoprotein receptor which mediates both the selective uptake of cholesterol esters and the efflux of cholesterol.…”