- Rates and Equilibria of Alkali Metal and Silver Ion Complex Formation with Monensin in Ethanol
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Measurements are reported on the stability constants and the rates of formation and dissociation of alkali metal and silver complexes of monensin in ethanol.Among the alkali metal complexes the order of stability is Li++>K+>Rb+>Cs+ (with Cs+ ca.Li+).Compared with the neutral antibiotic ionophores, the stability constants of monensin complexes are in general higher and show a much sharper peak selectivity.Dissociation rate constants are very sensitive to cation size and reflect a similar (inverse) variation with cation size of the stability constants; the formation rate constants increase monotonically with increasing cation size from Li+ (9.0E7 M-1s-1) to Cs+(2.5E9 M-1S-1.The silver complex, AgMon, has a stability constant slightly higher than that of the most stable alkali metal complex, NaMon, and a remarkably high formation rate constant, kf=3.5E10 M-1s-1, approaching that of a diffusion-controlled reaction, despite the high solvation energy of Ag+.The kinetic and thermodynamic properties of monensin complexes are compared with those of other naturally occuring and synthetic macrocyclic ionophores.
- Cox, B. G.,Truong, Ng van,Rzeszotarska, J.,Schneider, H.
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p. 5965 - 5969
(2007/10/02)
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