1,3-Diamido-calix[4]arene Conjugates of Amino Acids: Recognition of -COOH Side Chain Present in Amino Acids, Peptides, and Proteins by Experimental and Computational Studies

Lower rim 1,3-diamido conjugates of calix[4]arene have been synthesized and characterized, and the structures of some of these have been established by single crystal XRD. The amido-calix conjugates possessing a terminal −COOH moiety have been shown to exhibit recognition toward guest molecules possessing −COOH moiety, viz., Asp, Glu, and reduced and oxidized glutathione (GSH, GSSG), by switch-on fluorescence in aqueous acetonitrile and methanol solutions when compared to the control molecules via forming a 1:1 complex. The complex formed has been shown by mass spectrometry, and the structural features of the complexes were derived on the basis of DFT computations. The association constants observed for the recognition of Asp/Glu by Phe-calix conjugate, viz., 532/676 M−1, are higher than that reported for the recognition of Val, Leu, Phe, His, and Trp (16−63 M−1) by a water-soluble calixarene (Arena, G., et al. Tetrahedron Lett. 1999, 40, 1597). For this recognition, there should be a free −COOH moiety fr...