Synthesis and cation binding properties of fluorescent calix[4]arene derivatives bearing tryptophan units at the lower rim |
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Authors: | Nives Galić Nataša Burić Renato Tomaš Leo Frkanec Vladislav Tomišić |
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Affiliation: | 1. Department of Chemistry , Faculty of Science, University of Zagreb , Horvatovac 102a, 10000 , Zagreb , Croatia ngalic@chem.pmf.hr;3. Department of Chemistry , Faculty of Science, University of Zagreb , Horvatovac 102a, 10000 , Zagreb , Croatia;4. Department of Organic Chemistry and Biochemistry , Ru?er Bo?kovi? Institute , Bijeni?ka 54, 10000 , Zagreb , Croatia |
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Abstract: | The fluorescent peptidocalixarenes, 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(O-methyl-l-tryptophanylcarbonylmethoxy)calix[4]arene (1) and 5,11,17,23-tetra-tert-butyl-25,27-di(O-methyl)-26,28-bis(O-methyl-l-tryptophanylcarbonylmethoxy)calix[4]arene (2), were prepared by introducing tryptophan subunits at a lower calixarene rim. Coordination abilities of 1 and 2 towards Eu(III) and alkali metal cations were studied by spectrophotometric, spectrofluorimetric, conductometric and potentiometric titrations in acetonitrile at 25°C. Rather strong complexation was observed for smaller alkali metal cations Li+ and Na+ (log K Li1 >6, log K Li2 >6, log K Na1 = 8.25, log K Na2 = 6.94), and moderate for K+ (log K K1 = 5.09, log K K2 = 4.09). Larger Rb+ and Cs+ cations did not fit in the ion binding site of 1 so no complexation was detected, whereas the more flexible ligand 2 accommodated Rb+ cation (log K Rb2 = 3.44). The fluorescence of 1 (λex = 280 nm, λem = 340 nm) was remarkably quenched by Eu(III). Stability constant of 1:1 (Eu3+:1) complex determined spectrofluorimetrically amounted to log K Eu1 = 6.16. |
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Keywords: | calixarenes alkali metal cations Eu(III) stability constants fluorescence |
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