Modulation of Metal Recognition by a Novel Calix[4]arene Bearing Two Bipyridine Units as a Molecular Gate (original) (raw)
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Pure and Applied Chemistry, 2000
The conformational properties of calix[4]arene derivatives have been exploited to synthesize new receptors for the selective encapsulation of metal ions and neutral molecules. 1,3-Dialkoxycalix[4]arene-crown-5 conformers fixed in the 1,3-alternafe structure are the most selective potassium ionophores known sofar which have a K+/Na+ selectivity higher than valinomycin. The corresponding crown-6 derivatives show a very high Cs+/Na+ selectivity which allows their use in the removal of I3'Cs from highly salted radioactive waste. Highly preorganized and rigid cone calix[rl]arene derivatives, in which the C2v a Clv interconversion is inhibited after the introduction of bridges at the lower and upper rim, are able to complex small organic molecules having acidic CH groups, both in the gas phase and in CDCl3 solution.
Anion Effects on the Recognition of Ion Pairs by Calix[4]arene-Based Heteroditopic Receptors
The Journal of Organic Chemistry, 2002
A novel heteroditopic receptor (5) based on a rigid calix arene cavity bearing at the upper rim four arylsulfonamido binding sites has been synthesized. The binding abilities of this new host have been investigated in apolar solvents toward a series of tetramethylammonium salts (tosylate, chloride, acetate, trifluoroacetate, and picrate) and compared with those of monotopic and heteroditopic calix[4]arene-bis(crown-3)-based receptors 1 and 2 in order to evaluate the role of the anion on ion-pair recognition. While monotopic host 1 shows an efficiency order toward the different salts that increases when the anion is less interactive (Hofmeister trend), an opposite role of the counteranion on the recognition process was observed with host 5 (anti-Hofmeister trend). A more complex behavior is experienced by host 2, which shows a high and leveled efficiency for all the anions tested. The results obtained were explained on the basis of the different types of ion pairs present in the recognition process. Further information on the role of the anion were obtained by the "dual host" strategy utilizing the tri-n-butylthioureido derivative of tren 7, which forms a stable complex with chloride anion. The very high efficiency shown by these heteroditopic hosts opens new routes in supramolecular projects and is a very interesting tool in the molecular recognition of ion-pairs and its applications.
2021
Recent developments in the field of sensing and recognition revealed that artificial receptors based on calix[4]arenes with π-conjugated fluorophoric or chromophoric moieties are efficient in enhancing selectivity/sensitivity as well as the binding affinity for ionic or molecular recognition. Herein, via studying the reaction of dimethylformamide dimethyl acetal (DMF–DMA) with p-tert-butylthiacalix[4]arene tetrahydrazides in three different conformers (i.e., cone, partial-cone, and 1,3-alternate), the formation of novel lower rim p-tert-butylthiacalix[4]arene derivative (cone, partial-cone, and 1,3-alternate) conformers in high yields (80, 95, and 85%, respectively) was achieved. The structure of isolated products was confirmed using different spectroscopic and analytical techniques such as FT-IR, H NMR, C NMR, and elemental analysis. Importantly, the synthesized receptors showed preferential uptakes of alkali (Na, K and Cs), heavy (Pb, Cd, Hg, and Ag) and transition (Ni, Co, and Cu...
Journal of Luminescence, 2014
Design and evaluation of a single molecular receptor for multiple analytes reveal that calix[4]arene based molecular receptor 4 shows a highly selective response towards Cu 2 þ and F À ions with detection limits of 0.5 mM and 0.7 mM respectively when examined through UV-vis, fluorescence and 1 H NMR spectroscopy. Simultaneous binding studies on 4 towards metal ion and fluoride reveal that it exhibits a negative allosteric effect towards Cu 2 þ /F À .
Supramolecular Chemistry, 2017
A number of calix[4]arene-based molecules were designed incorporating amide moiety with variation in conformation, rigidity at the binding sites and steric crowding at the upper rim to investigate the anion sensing property of this series of ionophores. These compounds were synthesised and characterised, molecular structures of two of the compounds were established by single-crystal X-ray study. Anion binding property of these ionophores, investigated with the aid of 1 H NMR and UV-vis spectroscopy, revealed that three (1-3) out of four ionophores strongly interact with F − , in addition, ionophore 2 interacts with CN − and H 2 PO − 4 , ionophore 3 interacts with CH 3 COO − and H 2 PO − 4 and ionophore 4 does not interact with any anions. NMR titration was carried out to determine binding constant with strongly interacting anions. Crystal structure analysis revealed that strong intramolecular N − H • interaction in 4 prevented the anions to interact with the N-H protons of the amide moiety. Interestingly, 2 with F − and CN − exhibits sharp colour change in acetonitrile-chloroform. Apparently, conformation of the calix moiety, flexibility of the binding sites and intramolecular H-bonding played critical role towards determination of selectivity. Computational study was performed to investigate the interaction site(s) and also to corroborate some of the experimental results. Anion binding study of functionalised calix[4]arenes revealed that conformation, flexibility and intramolecular interaction in calix moiety play critical role to determine ion selectivity. One of the receptors performs as sensitive colorimetric sensor for F − and CN − , computational study also corroborates most of the experimental results.
Calix[4]arene-based ditopic receptors for simultaneous recognition of fluoride and cobalt(II) ions
Tetrahedron Letters, 2012
A series of calix[4]arene based ditopic receptors possessing bipyridyl and hydrazone units have been synthesized and evaluated for ionic recognition. It has been observed that the synthesized derivatives function as allosteric receptors for simultaneous recognition of Co 2+ and F À ions through non-covalent interactions. Significant bathochromic shifts in the UV-visible spectrum with a profound colour change promise their use to engineer novel applications.
Homotropic negative allostery in alkali metal ion recognition by biscalix[4]arene-based receptor
Tetrahedron Letters, 2004
A novel host which shows homotropic and negative allostery for alkali metal ion recognition is constructed by utilizing a biscalix[4]arene skeleton bearing biphenyls and ester moieties. As the ionic radius of the guest increases, recognition of the second guest is suppressed more effectively. A larger ion changes the structure of the first binding site more drastically to cause conformational change unfavorable for the guest binding of the second site.