J . A m . Chem. Soc. 1989, 1 1 1 , 6339-6350
6339
Host-Guest Complexation. 50. Potassium and Sodium Ion-Selective Chromogenic Ionophores Roger C. Helgeson,t Bronislaw P. Czech,$ Eddy Chapoteau,' Carl R. Gebauer,' Anand Kumar,' and Donald J. Cram*,t Contribution f r o m the Department of Chemistry and Biochemistry, University of California at Los Angeles. Los Angeles, California 90024, and Technicon Instruments Corporation, Tarrytown, New York 10591. Received February 17, 1989
Abstract: Making use of the principles of complementarity and preorganization, we have designed two potassium and one sodium ion-selective chromogenic ionophores useful for colorimetric assays of body and other fluids. Practical syntheses of 1-4 are described, and the UV-visible spectral changes in the presence and absence of Na' and K+ ions are reported at pH's that optimize the spectral differences. Compounds 3 and 4 exhibit high sensitivity (detection limits of -4 X M for K+ and 2 X IO-' M for Na') and selectivities estimated to be greater than 1000 for both [K+]/[Na+] and [Na+]/[K+], respectively, in essentially aqueous solution. Compounds 1 and 2 show highly sensitivity (IO-' M for K') and high selectivity for K+ over Na' in 80% dioxane-20% water.
Takagi et al.' were the first to bond a corand (benzo-15crown-5) to a chromogenic indicator system (picrylamine) to compose a n analytical reagent (5) useful for measuring colorimetrically the amount of K+ in the presence of Na+.' The method
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ft involved a K+-selective extraction (factor, K + / N a + > 100) from water into chloroform of K+5--5 vs (Na+5Na+5-.5). T h e importance of Na' and K+ assays coupled with the growing sophistication in host design for alkali-metal ion selectivity has led to many studies of potentially useful chromogenic ligand systems, most of which are based on easily synthesized corands or cryptands. T h e extensive literature has been thoroughly reviewed.*~~ Spherand 6 binds N a + and K+ picrates a t 25 "C in CDCI, saturated with D20with -AGO values of 19.3 and
