Dynamic and reactivity of guests within a water-soluble hosts and synthesis of cationic water-soluble cavitands.

摘要

The research presented in this thesis is a consolidated account of NMR and photochemical reactions carried in a water-soluble cavitand, called octa acid. In buffered aqueous solutions, octa acid forms stable complexes with different guest molecules. Product selectivity as a result of modification of the substituent forms the primary concept in each chapter.;Chapter 1 introduces the concept of supramolecular chemistry and supramolecular photochemistry with some examples from various research groups. The role of self-assembled cavitands as hosts for reactions is discussed specifically. Structure and properties of the cavitand used in this work termed octa acid (OA) and octa diethyl amine are presented along with some published results. A brief outline of the NMR techniques (COSY, DQF-COSY, NOESY, PGSE and DOSY) used to study the self-assembled complexes formed between hosts and guests analyzed is presented.;Synthesis and characterization of newly synthesized water soluble cavitands (octa diethyl amine, OAM and octa triethyl ammonium iodide, OTEAM) are explained in chapter 2. Complexation behavior of various guest molecules, the excited state behavior of these guests within the capsular assembly of OAM and OTEAM are studied in detail. Natures of complexes formed were analyzed by NMR spectroscopy. The complexes formed by the OAM as host and any guest molecules are shown to be stable in the gas phase, confirmed by ESI-MS studies. An attempt to synthesize the gold nanoparticles stabilized with OAM cavity is also explained.;Dynamic behavior of guest molecules within the host OA probed by various NMR techniques are discussed in chapter 3. The guest molecule that is imprisoned within a host is not stationary. The extent of freedom is dependent on weak interactions that hold the guest within the container. The mobility of the guest within the host is dictated by the free volume in host and the structure of the guest by itself.;Chapter 4 is comprised of the results from studies Norrish Type I and Type II photochemistry of optically pure &agr;-alkyl deoxybenzoins within the OA capsular assembly. The product distribution is different from that in an organic solvent was also dependent on the nature of the &agr;-alkyl chain. The communication between incarcerated optically pure &agr;-alkyl deoxybenzoins and molecules in the bulk solvent controlled by supramolecular factors such as coloumbic attraction and repulsion between a charged guest host complex and charged molecules in the bulk aqueous phase is explained.;Chapter 5 compares the photochemistry of alkyl aryl ketones bound to octa acid to their reaction and in homogeneous solutions. 1D and 2D NMR analysis of the complexes formed between the ketones and octa acid are provided. Nature of host-guest assembly is revealed by the NMR analysis. Photochemical results shows enhanced selectivity, particularly in the case of cyclic alkyl aryl ketones which is due to its preferred orientation that is confirmed by molecular dynamics study.