Online

Sharafi, Mona

Chemistry

2020

Ph. D.

Finding sustainable ways to create complex, sequence-defined polymers is essential for future advances in the fields of medicine, electronics, and energy. Thus, inspired by how nature builds functional macromolecules, this account aims to discover catalysts, which will facilitate the accurate replication of synthetic nanoscale structures. In this regard, the comprehensive sight of the work described within this dissertation is to resolve the following fundamental questions: i) How to generate large, preorganized macromolecules which can behave as supramolecular hosts to tune the properties of molecules present in the vicinity of them? ii) What shapes do sequence-defined oligomers/polymers adopt in solution under various conditions? In what ways can local polymer conformations be manipulated by binding to supramolecular hosts? iii) Can we exploit the folding behavior of these polymers as a powerful tool to provide selective reactivity at the nanoscale and enhance the replication accuracy? Various synthetic approaches leading to the successful precise manufacturing of synthetic macromolecules including molecular strips, large macrocycles and porous cages are described. A significant portion of my PhD research was also focused on the framework of selective catalysis for polymers functionalization and replication; a unique concept which hasn't been reported previously. Selective catalysis at the molecular scale represents a cornerstone of chemical synthesis. However, it still remains an open question how to elevate tunable catalysis to larger length-scales, where nanoscale structures (e.g. whole polymer chains) act as the substrates and get functionalized in a selective manner. The efficient synthesis of a hydrazone-linked tetrahedron with large opening, which acts as a catalyst to sizeselectively functionalize polydisperse polymer-mixtures is described in details. Experimental and computational evidence are provided to support a dual catalytic effect exerted by the molecular tetrahedron, which (i) helps to unfold the polymer substrates and (ii) exposes the amino groups on the polymeric side chains to the 12 triglyme units of the tetrahedron to accelerate aminolysis. I was able to demonstrate complete reversal of the intrinsic size-selectivity for polymer functionalization with our tetrahedral cage as the catalyst. This finding enable the possibility to engineer hydrolytically stable molecular polyhedra as organocatalysts for size- and future site-selective, post-synthetic polymer modification (inspired by post-translational protein modification).