Estudo das interações intercomponentes em rotaxanos contendo macrociclos baseados em éter de coroa

Abstract

Rotaxanes are mechanically interlocked molecules that have attracted interest due to their functional properties and the dynamics between their components. These compounds can act as molecular machines, capable of modulating coordinated movements in response to external stimuli. The interactions between the constituent parts, such as the molecular thread and the macrocycle, play a crucial role in these movements, influencing their nature and execution. However, detailed energetic analyses of the interactions between components particularly in crown ether rotaxanes with different charge states remain underexplored in the solid state. In this context, the present work aimed to understand intercomponent interactions, offering a comparative analysis of intercomponent stabilization energies in neutral and charged rotaxanes. Specifically, it sought to evaluate how the presence or absence of charge on the thread influences the nature and intensity of the interactions between the molecular thread and the macrocycle. To this end, thirteen crystalline structures of rotaxanes containing a crown ether-derived macrocycle were selected six neutral and seven charged determining their intercomponent contact areas and stabilization energies. To assess the intercomponent interactions, contact area data were collected from the Voronoi Dirichlet polyhedron using the ToposPro program, and the intercomponent stabilization energies were initially calculated using MOPAC software (PM6-D3H4X) to identify the most suitable counterion for evaluating the intercomponent stabilization energy. Subsequently, more accurate values were obtained through quantum mechanical calculations using Density Functional Theory (DFT) with the Gaussian 09 package. Finally, the Molecular Electrostatic Potential (MEP) was obtained. The results showed that charged rotaxanes exhibited higher stabilization energies (average of -81.5 kcal mol-1) compared to neutral rotaxanes (average of -35 kcal mol-1), attributed to NH···O and CH···O interactions. The total contact area varied among the compounds, and the introduction of a second anion slightly increased this area without a gain in stabilization energy. Furthermore, the molecular electrostatic potential surfaces demonstrated the influence of charge in favoring these interactions; however, when two charges are involved, this increase does not necessarily lead to greater intercomponent stabilization. These results highlight the importance of electrostatic complementarity in the design of functional supramolecular systems especially rotaxanes and provide structural and energetic insights that may assist in the development of new interlocked molecules with tailored properties.