Dissertations from ProQuest

Title

Sodium-23 Nmr Studies Of Sodium Ion Transport Mediated By Synthetic Carriers Across Vesicle Membranes, And, Fullerides Of Fullerenes And Fulleroids: An Esr And Electrochemical Study

1994

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Chemistry

First Committee Member

Luis Echegoyen, Committee Chair

Abstract

Chapter 1. Cation transport across vesicle membranes mediated by different synthetic carriers have been studied systematically by using $\sp{23}$Na-NMR techniques. The transport abilities of a series of novel compounds, amide-crown-ethers, ester-crown-ethers, etc., were examined by the passive-transport method and the steady-state transport method. The data extracted from the steady-state transport system demonstrate that the tertiary amide-crown-ethers display the best Na$\sp+$ transport ability. It was found for the first time that some tertiary amide-crown-ethers, 18am-C10 and 18am-C18 have high Na$\sp+$ transport efficiencies, which are comparable to that of a naturally-occurring ionophore, monensin. Surprisingly, the Na$\sp+$ transport ability of 18am-C10 is even slightly better than that of monensin, which is the result of its optimal Na$\sp+$ binding ability and proper lipophilicity. It was discovered that for the amide-crown-ethers, the ring-sizes, the sidearm functional groups and the length of the lipophilic tails play important roles in facilitating cation transport across vesicle membranes. For the first time, the Na$\sp+$ transport mechanism has been studied using synthetic carriers in a vesicle system. Based on analysis of our experimental results, the diffusion-limited process was proposed for our synthetic carriers. The k$\sb{\rm diff}$ and K$\sb{\rm s}$ values of Na$\sp+$-15am-C10 were determined to be $\rm 3.2\times 10\sp3\ s\sp{-1}$ and 6.5 M$\sp{-1}$ respectively.Chapter 2. The reductive and oxidative electrochemistry of fullerenes has been studied. In a high vacuum system with a MeCN/toluene mixture solvent, and TBAPF$\sb6$ as supporting electrolyte, six electrochemically reversible reductions of C$\sb{60}$ and C$\sb{70}$ have been observed at $-$10$\sp\circ$C. The half-wave potentials are $-$0.99, $-$1.37, $-$1.87, $-$2.65, $-$2.95, and $-$3.26 V for C$\sb{60}$, and $-$0.97, $-$1.34, $-$1.78, $-$2.21, $-$2.60, and $-$3.07 V for C$\sb{70}$ (relative to Fc/Fc$\sp+$). In a high vacuum system and using TCE (1,1,2,2-tetrachloroethane) as solvent, with TBAPF$\sb6$ as supporting electrolyte, single-electron, chemically reversible electrochemical oxidations of C$\sb{60}$, and C$\sb{70}$ were also observed electrochemically for the first time. The potentials for the oxidation of C$\sb{60}$ and C$\sb{70}$ were +1.26 and +1.20 relative to Fc/Fc$\sp+$ respectively. More interestingly, a second single-electron oxidation of C$\sb{70},$ C$\sb{70}\sp+\ \to$ C$\sb{70}\sp{2+},$ was also observed by Osteryoung Square Wave Voltammetry (OSWV). The potential for this process is +1.75 relative to Fc/Fc$\sp+.$ESR spectra of C$\sb{60}\sp-$ and C$\sb{60}\sp{2-}$ observed in this thesis are very different from those in the literature. Two sharp lines for C$\sb{60}\sp-$ at g$\sb1$ = 1.999 and g$\sb2$ = 2.000 were first reported, which is probably caused by the co-existence of two possible Jahn-Teller distortions, prolate and oblate states. The ESR spectrum of C$\sb{60}\sp{2-}$ is also very unusual. Two sets of signals were observed. The low field one exhibits a well resolved pattern consisting of seven lines. A possible explanation based on $\sp$C splitting coupled with C$\sb{60}\sp{2-}$ aggregation is proposed.

Keywords

Chemistry, Analytical; Chemistry, Physical