Ion and Molecular Recognition by Lower Rim 1,3-Di-conjugates of Calix[4]arene as Receptors

The background of possible selectivity–affinity correlations and their limitations is reviewed, with typical crown ether and cryptand complexes, ionic associations, hydrogen bonded complexes and complexes driven by van der Waals, stacking or hydrophobic interactions, with some additional topics including associations based on metal coordination as supplementary material. This tutorial review is addressed to students and researchers interested in molecular recognition, and relates to the design of sensors, of discriminators for separation processes, of supramolecular devices and of drug compounds. A theoretical analysis of selectivity in supramolecular host–guest complexes, defined as a difference in binding free energies for structurally related guests, as a function of total binding free energy shows that for certain types of intermolecular interactions one may observe a correlation between selectivity and affinity. Such correlation fails however if the selectivity is due to additional interactions at a secondary binding sites, which is expected in complexes with anisotropic guest molecules. Several clear examples of theoretically expected selectivity–affinity correlations are found. The influence of reaction conditions on the experimentally observed selectivity, defined as a difference in complexation degrees with different guests in the presence of added receptor, is illustrated. The importance of often neglected solvent effects on selectivity is exemplified with ionophore and hydrogen bonded complexes.

Selectivity in supramolecular host-guest complexes.

The nature of the cation−π interaction has been examined by carrying out high level ab initio calculations of both metallic (Li+,Na+,K+, and Ag+) and organic (NH4+, C(NH2)3+, and N(CH3)4+) cations with different classes of π systems, viz. alkenes (ethene), arenes (benzene), and heteroarenes (pyrrole). The calculations, which include a rigorous decomposition of the interaction energies, indicate that the interaction of these π systems with the metal cations is characterized by contributions from both electrostatic and induction energies, with the contribution of the latter being dominant. Though the contributions of dispersion energies are negligible in the cation−π complexes involving Li+ and Na+, they assume significant proportions in the complexes involving K+ and Ag+. In the π complexes of the organic cations, the repulsive exchange contributions are much larger than the attractive electrostatic contributions in the π complexes of organic cations, and thus, the contributions of both induction and dispe...

Cation-π Interactions: A Theoretical Investigation of the Interaction of Metallic and Organic Cations with Alkenes, Arenes, and Heteroarenes

Coordination chemistry of calix[4]arene derivatives with lower rim functionalisation and their applications

Turning the volume down on heavy metals using tuned diatomite. A review of diatomite and modified diatomite for the extraction of heavy metals from water.

The solvent control on the ability of a partially substituted lower rim calix(4)arene derivative 5,11,17,23,tetra-tert-butyl[25,27-bis(hydroxy)-26,28-bis(ethylthioethoxy)]-calix(4)arene, 1 to host soft metal cations (Hg(II) and Ag(I)) is demonstrated through 1H NMR, electrochemical (conductance measurements), and thermodynamic characterization of the complexation process in a wide variety of solvents. Solvent−ligand interactions were assessed from 1H NMR measurements involving 1 and various solvents in CDCl3. Thus, the formation of a 1:1 1−CH3CN adduct is reported. As far as metal cations are concerned, depending on the medium their complexation with 1 was only observed for Hg(II) and Ag(I). Thus, in acetonitrile, 1 is more selective for Hg(II) relative to Ag(I) by a factor of 2.2 × 103. In methanol the selectivity is reversed to an extent that the affinity of 1 for Ag(I) is 1.4 × 103 higher than that for Hg(II). However, 1 is unable to recognize selectively these cations in N,N-dimethylformamide while in...

Solvent control on the selective, nonselective, and absent response of a partially substituted lower rim calix(4)arene derivative for soft metal cations (mercury(II) and silver(I)). Structural and thermodynamic studies.

A new calix[4]arene derivative containing mixed pendant arms in its lower rim, 5,11,17,23-tetra-tert-butyl-[25,27-bis(ethylethanoate)oxy-26,28-bis(ethylthioethoxy)]-calix[4]arene, 1, has been synthesized and characterizedby 1 H and 1 3 C NMR. 1 H NMR data carried out in CDCl 3 , CD 3 CN, CD 3 OD, and C 3 D 7 NO suggest that as far as acetonitrile is concerned, the hydrophobic cavity is likely to embrace a solvent molecule. It is shown that the hosting capacity of 1 toward metal cations is greater in acetonitrile than in N,N-dimethylformamide and in methanol. Thus, in the former solvent, complexation with various cations (Li + , Na + , Ag + , Ca 2 + , Cu 2 + , Hg 2 + , and Pb 2 + ) occurs while in the latter media, 1 interacts only with Ag + and Hg 2 + . This statement is corroborated by 'H NMR, conductance, calorimetric and potentiometric measurements. It is concluded that through molecular inclusion of acetonitrile in the hydrophobic cavity of 1, the hydrophilic cavity of the resulting adduct becomes more receptive to host metal cations than that of the free ligand. In propylene carbonate, the results show that the ligand loses its ability to interact with metal cations. Thus in acetonitrile, selective recognition of 1 for Hg 2 + is demonstrated to an extent that the selectivity for this cation is greater by factors of 1.8 x 10 3 , 1.9 x 10 3 , 6.9 x 10 3 , 1.8 x 10 4 , 4.1 x 10 4 and 4.5 x 10 4 , relative to Pb 2 + , Na + , Li + , Cu 2 + , Ag + , and Ca 2 + , respectively. This statement is supported by the thermodynamic characterization of the complexation process involving these systems in acetonitrile, N,N-dimethylformamide and in methanol. Thus, the medium effect on the binding process is carefully assessed. The results show that replacement of two ester groups in two alternate pendant arms of the tetraester calix[4]arene derivative by thioethyl moieties has altered significantly the binding capacity and the selective behavior of the latter relative to the former. Final conclusions are given.

Thermodynamics of host-guest interactions in lower rim functionalized calix[4]arenes and metal cations: The medium effect

Standard solution Gibbs energies, DeltasG degrees, of the resorcarene-based receptor 5,11,17,23-ethylthiomethylated calix[4]resorcarene, (characterized by 1H NMR and X-ray diffraction studies) in its monomeric state (established through partition experiments) in various solvents are for the first time reported in the area of resorcarene chemistry Transfer Gibbs energies of from hexane (reference solvent) to other medium are calculated Agreement between DeltatG degrees (referred to the pure solvents) and standard partition Gibbs energies, DeltapG degrees (solvent mutually saturated) is found Cation-ligand interactions were investigated through 1H NMR (CD3CN and CD3OD) and conductometric titrations in acetonitrile and methanol 1H NMR data revealed the sites of interaction of with the metal cation The composition of the metal-ion complexes (Ag+ and Pb2+ in acetonitrile and Ag+ and Cu2+ in methanol) was established through conductometric titrations Thus, complexes of 1:1 stoichiometry were formed between and Ag+ and Pb2+ in acetonitrile and Cu2+ in methanol However, in moving from acetonitrile to methanol, the composition of the silver complex was altered Thus, two metal cations are hosted by a unit of the ligand As far as Cu2+ and in acetonitrile is concerned, conductance data suggest that metalates are formed in which up to four units of Cu2+ are taken up per unit of resorcarene The contrasting behavior of with Cu2+ in acetonitrile relative to methanol is discussed As far as mercury (II) is concerned, the unusual jump in conductance observed in the titration of Hg2+ with in acetonitrile and methanol after the formation of a multicharged complex (undefined composition) is attributed to the presence of highly charged smaller units (higher mobility) resulting from the departure of pendant arms from the resorcarene backbone Isolation of these species followed by X-ray diffraction studies corroborated this statement The thermodynamic characterization of metal-ion complexes of Ag+ and Pb2+ in acetonitrile and Cu2+ and Ag+ in methanol is reported Final conclusions are given

Resorcarene-based receptor: versatile behavior in its interaction with heavy and soft metal cations

The synthesis and characterization (1H NMR) of two new lower rim calix(4)arene derivatives containing mixed pendent arms, namely, 5,11,17,23-tetrakis(1,1-dimethylethyl)-25,27-bis[2-(methylthio)etho...

New lower rim calix(4)arene derivatives with mixed pendent arms and their complexation properties for alkali-metal cations. Structural, electrochemical, and thermodynamic characterization

Angela F. Danil De Namor

Papers

Solvent control on the selective, nonselective, and absent response of a partially substituted lower rim calix(4)arene derivative for soft metal cations (mercury(II) and silver(I)). Structural and thermodynamic studies.

Thermodynamics of host-guest interactions in lower rim functionalized calix[4]arenes and metal cations: The medium effect

Resorcarene-based receptor: versatile behavior in its interaction with heavy and soft metal cations

New lower rim calix(4)arene derivatives with mixed pendent arms and their complexation properties for alkali-metal cations. Structural, electrochemical, and thermodynamic characterization