From supramolecular selectivity to nanocapsules.

摘要

A family of three 2-aminopyrazine derivatives were prepared and co-crystallized with thirty carboxylic acids. Our theoretical charge calculations and experimental results from 90 reactions demonstrated that decreasing the charge on the hydrogen-bond acceptor sites results in a decrease of the supramolecular yield (the frequency of occurrence of the desired outcome). However, synthon crossover (undesired connectivity) was observed 7/12 times and was unavoidable due to competitive binding sites present in the N-heterocyclic bases chosen.;To avoid synthon crossover, we used a strategy based on geometric bias. We utilized hydrogen-bonding two-point contacts and halogen-bonding single-point contacts for supramolecular reactions with the 2-aminopyrazine family of compounds. The desired two-point contact and single-point contact (N···I or N···Br) appeared in 9/9 times even in the presence of other potentially interfering intermolecular interactions. In addition, the role of charge in controlling the presence/absence of proton transfer was also highlighted.;To establish a hierarchy in halogen-bonding interactions we designed and synthesized a library of eight molecules equipped with two different halogen bond donors and combined with variety of halogen-bond acceptors. 11 Halogen-bonded co-crystals were obtained; however, positional disorder of I/Br atoms obscures a complete analysis. This problem was solved by introducing asymmetry in the halogen-bond donor molecules. Finally, successfully demonstrated an unprecedented hierarchy in halogen-bond interactions based on electrostatics.;We developed high-yielding Suzuki-Miyaura coupling reactions of tetraboronic pinacolyl ester cavitand to iodoarenes with a range of functional groups (electron withdrawing/donating group and a heterocycle) that show robustness and versatility, making it a 'launch pad' for the synthesis of many new cavitands in a facile manner. We have also successfully demonstrated cavitand functionalization from tetraaldehyde to tetraoximes using 'solvent assisted grinding', irrespective of the position of the aldehyde.;Finally, we prepared tetra-substituted pyridyl and carboxylic acid cavitands having an ellipsoidal cavity capable of encapsulating asymmetric guest molecules and was subsequently obtained the first of its kind, C2v symmetric molecular capsule with encapsulated asymmetric guest molecule.