Abstract
Non-covalent interactions (NCI) between molecules are important for all chemical and biochemical processes, especially in the fields of supramolecular chemistry and crystal engineering. A quantitative understanding of NCI therefore serves as a basis for the understanding of these complex fields. In this study, the role of NCI in two classes of systems was investigated using density functional theory, density functional tight binding, and Møller-Plesset second order perturbation theory. Natural bond orbital and energy decomposition analyses were also employed. Tyrosine-based dipeptide (TBD) nanotubes have many potential applications in the biomedical and nanotechnology fields because of their unique set of chemical and physical properties but their self-assembly mechanism is not fully understood. A bottom-up approach was used to identify the ground state monomers, dimers, and hexamers of the linear and cyclic forms of dityrosine and tryptophan-tyrosine. This work demonstrates that TDB assembly is primarily driven by hydrogen bonding and electrostatic interactions and supported by π-π stacking and dispersion forces. This work also proves that TDB assembly is energetically driven, and that cyclization has a stabilizing effect. Halogenated isatins, on the other hand, are bicyclic compounds commonly used in chemical and pharmaceutical synthesis. Several variants of bromoisatin, chloroisatin, fluoroisatin, and iodoisatin were compared, through monomeric and dimeric quantum chemical calculation as well as Hirshfeld surface and fingerprint plot analyses. These results show that halogenated isatin crystallization is primarily driven by oxygen-hydrogen and halogen-hydrogen electrostatic interactions and dispersion interactions involving oxygen and the six-membered isatin ring. Additionally, it demonstrates that larger halogens and C4 or C7 substitution favor halogen-oxygen interaction. The similarities between these two systems reveal that an alignment which maximizes hydrogen bonding and electrostatic interactions between two cyclic monomers is favored and will drive their structural organization.