Document Type dissertation Author Name Benco, John S URN etd-0410103-125803 Title The Rational Design and Synthesis of Ionophores and Fluoroionophores for the Selective Detection of Monovalent Cations Degree PhD Department Chemistry & Biochemistry Advisors W. Grant McGimpsey, Advisor James W. Pavlik, Committee Member Robert E. Connors, Committee Member Joseph S. Foos, Committee Member James P. Dittami, Department Head Keywords ionophore fluoroionophore Date of Presentation/Defense 2003-04-07 Availability unrestricted
The rational design, synthesis and complexation characteristics of several monovalent cation-selective ligands are described. Molecular modeling employing a combination of dynamics, mechanics (AMBER94) and electrostatics was used to design ligands for the complexation of ammonium, potassium, sodium and lithium ions. A modular technique was used to synthesize an ammonium selective ionophore based on a cyclic depsipeptide structure (8). The ionophore was incorporated into a planar ion selective electrode (ISE) sensor format and the selectivity tested versus a range of metal cations. It was found that the membrane containing the polar plasticizer NPOE (nitrophenyloctylether) in the absence of ionic additive exhibited near-Nernstian behavior (slope = 60.1 mV/dec @ 37¢ªC) and possessed high selectivity for ammonium ion over lithium and the divalent cations, calcium and magnesium (logK = -7.3, -4.4, -7.1 for lithium, calcium and magnesium ions, respectively). The same membrane also exhibited sodium and potassium selectivity that was comparable to that reported for nonactin (logK = -2.1, -0.6 for sodium and potassium, respectively, compared to -2.4, -0.9 in the case of nonactin).
N-(9-methylanthracene)-25,27-bis(1-propyloxy)calixarene-azacrown-5 (10) was synthesized and tested as a fluoroionophore for the selective detection of potassium ions. Compound 10 acts as an ¡°off-on¡± fluorescent indicator for ion complexation as a result of photoinduced intramolecular electron transfer (PET). Studies demonstrate that 10 is selective for potassium over other alkali metal cations, with excellent selectivity over sodium and lithium (log K ¡Â -3.5) and moderate selectivity over rubidium and cesium (log K ~ -1).
N-(9-methylanthracene)-25,27-bis(1-propyloxy)-4-tert-butylcalixarene-azacrown-3 (11) was synthesized and tested as a fluoroionophore for the selective detection of lithium cations. When exposed to lithium ions in a 75:25 dichloromethane/THF solvent mixture, the molecule, which operates on PET, exhibited a >106-fold enhancement in fluorescence emission intensity. Selectivity studies demonstrated that 11 effectively discriminates against sodium and potassium ions log K ¡Â -3.8 and log K ¡Â -2.3.
A fluorescent sodium optode based on a fluoroionophore consisting of aminorhodamine B covalently-linked through an amide bond to a calixarene has also been developed (12). The optode, fashioned by incorporation of the fluoroionophore into a single component polymer matrix, operates on the basis of PET. The fluorescence intensity increased linearly with increasing sodium ion concentration in the range 0.01 M to 2.0 M, exhibiting a three-fold enhancement over this range. The optode provides selectivity for sodium ions compared to potassium ions that is sufficient for clinical determinations of sodium ion concentration.
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