Design and Synthesis of Microporous Dipeptide Structures and Guanidinium-carboxylate-based Organic Supramolecular Materials

Abstract

The basis of supramolecular chemistry is a detailed knowledge of fundamental molecular properties and non-covalent interactions, which is dedicated to the preparation of novel structures as functional materials. Here we discuss the design and synthesis of such new molecular self-assemblies. Based on the structures and properties of these molecules, this dissertation describes the two types of supramolecular structures in two different chapters.<br> Chapter 1 deals with the design, preparation, characterization and applications of chiral, bio-degradable, guest-specific and environment-friendly nanoporous crystalline dipeptides. In the hydrogen-bonded networks, dipeptides with hydrophobic L-amino acid residues are known to form pores of different diameters, ranging from 3-10 Å. The hydrophobic bulk and orientations of the side chains of these dipeptides provide further scope for structure-based modifications to fine-tune their pore dimensions. Thus, towards the liberation of space occupied by bulky hydrophobic terminals of the amino acid side chains from the periphery of channels, a series of dipeptides from non-proteinogenic and proteinogenic amino acids have been synthesized, crystallized and analyzed by single crystal X-ray diffraction methods. The majority of these dipeptides were obtained as porous structures. As nanoporous materials, a few of these dipeptides were studied for CO₂ and methane gas absorption and selectivity.<br> Chapter 2 demonstrates the supramolecular synthesis of charge-assisted complexes from binary acid-base components. The well-directed hydrogen bond formation between acids and bases is a very useful tool in designing new supramolecular assemblies. Here we pursued an approach to use 1,5,7 triazabicyclo[4.4.0]-dec-5-ene, a guanidine derivative, with di- or monocarboxylic acids to generate guanidinium-carboxylate complexes. These molecular structures were designed to explore the effects of limited hydrogen-bond forming ability of guanidinium moiety and carboxylate group, and to check the propensity of guanidinuimcarboxylate complexes for the inclusion of guest molecules, for instance the water molecules. In fact, these complexes in crystals have interacted with the water molecules or carboxyl groups in the absence of any other potential donors and formed different water networks and 1D molecular pattern, which as organic materials may find various future applications as proton conductors, selective ion channels and gelators etc.