Abstract
We present a simulation study of supramolecular aggregates formed by three-arm azobenzene (Azo) stars with a benzene-1,3,5-tricarboxamide (BTA) core in water. Previous experimental works by other research groups demonstrate that such Azo stars assemble into needle-like structures with light-responsive properties. Disregarding the response to light, we intend to characterize the equilibrium state of this system on the molecular scale. In particular, we aim to develop a thorough understanding of the binding mechanism between the molecules and analyze the structural properties of columnar stacks of Azo stars. Our study employs fully atomistic molecular dynamics (MD) simulations to model pre-assembled aggregates with various sizes and arrangements in water. In our detailed approach, we decompose the binding energies of the aggregates into the contributions due to the different types of non-covalent interactions and the contributions of the functional groups in the Azo stars. Initially, we investigate the origin and strength of the non-covalent interactions within a stacked dimer. Based on these findings, three arrangements of longer columnar stacks are prepared and equilibrated. We confirm that the binding energies of the stacks are mainly composed of – interactions between the conjugated parts of the molecules and hydrogen bonds formed between the stacked BTA cores. Our study quantifies the strength of these interactions and shows that the – interactions, especially between the Azo moieties, dominate the binding energies. We clarify that hydrogen bonds, which are predominant in BTA stacks, have only secondary energetic contributions in stacks of Azo stars but remain necessary stabilizers. Both types of interactions, – stacking and H-bonds, are required to maintain the columnar arrangement of the aggregates.
Highlights
The formation of supramolecular aggregates is governed by the non-covalent interactions between their molecular constituents
We have previously studied columnar assemblies of three-arm Azo stars using density functional theory and fully atomistic molecular dynamics (MD) simulations [46,47]
Based on the hydrogen bonding potential included in DREIDING, we explicitly model the hydrogen bonds between the BTAs of opposing TrisAzo molecules
Summary
The formation of supramolecular aggregates is governed by the non-covalent interactions between their molecular constituents. The type of arrangement, affects the structure, shape, size as well as other chemical and physical properties of the resulting materials [1]. It is, not surprising that supramolecular aggregation phenomena are found in countless biological systems [2,3,4]. The applications of supramolecular structures are as multifaceted as the underlying molecules. Such structures are utilized, for instance, in gels [7] and sensing devices [8]. Little-exploited but very promising is the usage of supramolecular systems as adhesives [6,9], in medical and drug delivery applications [6,10], as synthetic biomaterials [11], and in devices to probe or manipulate biological systems [3,12]
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