Supramolecular Chemistry Of Nitrogen Dioxide

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Title: Supramolecular Chemistry Of Nitrogen Dioxide
Author: Kang, Yanlong
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 .
URI: http : / /hdl .handle .net /10106 /41
Date: 2007-08-23

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Supramolecular Chemistry Of Nitrogen Dioxide. Available electronically from http : / /hdl .handle .net /10106 /41 .

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