In
this work we studied the host–guest interactions between
confined molecules and zeolites and their relationship with the energies
involved in the reaction of methylation of benzene by methanol in
H-ZSM-5 and H-Beta zeolites employing density functional theory (DFT)
methods and the quantum theory of atoms in molecules. Results show
that the strength of the interactions related to adsorption and coadsorption
processes is higher in the catalyst with the larger cavity; however,
the confinement effects are higher in the smaller zeolite, explaining,
from an electronic viewpoint, the reason why the stabilization energy
is higher in H-ZSM-5 than in H-Beta. The confinement effects of the
catalyst on the confined species for methanol adsorption, benzene
coadsorption, and the formed intermediates dominate this stabilization.
For the transition state (TS), the stability of the TS is achieved
due to the stabilizing effect of the surrounding zeolite framework
on the formed carbocationic species (CH3
+) which
is higher in H-ZSM-5 than in H-Beta. In both TSs the methyl cation
is multicoordinated forming the following H2O···CH3
+···CB concerted bonds.
It is demonstrated that, through the electron density analysis, the
criteria can be defined to discriminate between interactions related
to the confinement effects and the reaction itself (adsorption, coadsorption,
and bond-breaking and bond-forming processes) and, thus, to discriminate
the relative contributions of the degree of confinement to the reaction
energies for two zeolite catalysts with different topologies.
The evolutionary processes that shape the unique biodiversity of the Neotropical Chaquean Domain are still poorly understood, and choosing an appropriate model to address evolutionary questions is essential for understanding the current patterns of Chaquean diversity. We used the Turnera sidoides autopolyploid complex as a model to assess current and past environmental factors and the processes that shaped and maintain its intraspecific variation in the Chaquean Domain. Based on current and past niche modelling, cytogeographical and genetic divergence analyses, we provide strong evidence that the T. sidoides complex has been in an active process of intraspecific allopatric diversification at the diploid level since the early Pleistocene. Further diversification of the complex involved the emergence of independent polyploid series in each morphologically divergent lineage. Cytotypes in each series do not differ in diagnostic morphological traits, but are reproductively isolated and have different ecological requirements. Currently, each subspecies/morphotype and cytotype are true species according to the biological, evolutionary and ecological concepts; however, they are still considered to be the same morphological species. Our study has clarified the effect of the complex processes of diversification occurring in the Chaquean Domain on T. sidoides and that much diversity is overlooked when only the morphological species concept is considered when estimating the diversity of Neotropical ecoregions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.