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

Date of Award

1994

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

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

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