Yanlong Kang

Graduation Semester and Year

2005

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry

Department

Chemistry and Biochemistry

First Advisor

Dmitry Rudkevich

Abstract

Supramolecular chemistry has been defined as "chemistry beyond molecules", and involves investigating molecular systems held together reversibly by inter-molecular forces, not by covalent bonds. This dissertation discusses a supramolecular approach towards sensing, entrapment and utilization of NO2/N2O4 gases. Chapter 1 briefly discusses supramolecular chemistry and supramolecular chemistry of gases. In chapter 2, the interaction of NOx with metalloporphyrins is described. Specifically, ruthenium nitrosyl derivatives hold a special place in mimicking bio-relevant NO-metal interactions. A previously unnoticed reaction between NO2/N2O4 and a Ru(II) porphyrin is described. It causes disproportionation of N2O4 and leads to a stable nitrosyl nitrato complex. Our findings offer a new insight into the mechanism of sensing and fixation of NO2/N2O4 by metalloporphyrins. In chapter 3, the reaction between calixarenes and NO2/N2O4 gases was investigated. Exposure of tetra-O-alkylated cone or 1,3-alternate calix[4]arenes to NO2/N2O4, both in chloroform solution and in the solid state, resulted in deeply colored calixarene-nitrosonium (NO+) complexes. In the presence of a Lewis acid, such as SnCl4, stable calixarene-NO+ complexes were isolated in a quantitative yield and fully characterized. NO+ is found encapsulated within the calixarene cavity, and forms a stable charge-transfer complex. The NO+ encapsulation was also demonstrated in titration experiments with calixarenes and NO+SbF6- salt in chloroform. The complexation process is reversible, and the complexes dissociate upon addition of water and alcohol, recovering the parent calixarenes. Chapter 4 describes the polymer supported calixarenes. Functionalized calix[4]arenes were synthesized and attached to silica gels and polyethyleneglycol (PEG), which afforded solid materials capable of visual detection and entrapment of NO2/N2O4 both in the solid state and solution. The concept of encapsulated nitrosating reagent was introduced in chapter 5. Stable calixarene-NO+ complexes act as encapsulated nitrosating reagents; cavity effects control their reactivity and selectivity. They were effectively used for nitrosation of secondary amides. Unique size-shape selectivity was observed, allowing for favorable nitrosation of only less crowded N-Me amides. For robust, silica gel and PEG based calixarene materials, similar size-shape selectivity was observed. Enantiomerically pure encapsulating reagents were tested for nitrosation of racemic amide, showing modest but reproducible stereoselectivity.

Disciplines

Chemistry | Physical Sciences and Mathematics

Comments

Degree granted by The University of Texas at Arlington

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