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

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.

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

Combined crystallographic and solution molecular dynamics study of allosteric effects in ester and ketone p-tert-butylcalix[4]arene derivatives and their complexes with acetonitrile, Cd(II), and Pb(II).

We describe here a procedure to bridge the gap in the field of calixarene physicochemistry between solid-state atomic-resolution structural information and the liquid-state low-resolution thermodynamics and spectroscopic data. We use MD simulations to study the kinetics and energetics involved in the complexation of lower rim calix[4]arene derivatives (L), containing bidentate ester (1) and ketone (2) pendant groups, with acetonitrile molecule (MeCN) and Cd(2+) and Pb(2+) ions (M(2+)) in acetonitrile solution. On one hand, we found that the prior inclusion of MeCN into the calix to form a L(MeCN) adduct has only a weak effect in preorganizing the hydrophilic cavity toward metal ion binding. On the other hand, the strong ion-hydrophilic cavity interaction produces a wide open calix which enhances the binding of one MeCN molecule (allosteric effect) to stabilize the whole (M(2+)) L(MeCN) bifunctional complex. We reach two major conclusions: (i) the MD results for the (M(2+)) 1(MeCN) binding are in close agreement with the "endo", fully encapsulated, metal complex found by X-ray diffraction and in vacuo MD calculations, and (ii) the MD structure for the more flexible 2 ligand, however, differs from the also endo solid-state molecule. In fact, it shows strong solvation effects at the calixarene lower bore by competing MeCN molecules that share the metal coordination sphere with the four CO oxygens of an "exo" (M(2+)) 2(MeCN) complex

Combined crystallographic and solution molecular dynamics study of allosteric effects in ester and ketone p-tert-butylcalix[4]arene derivatives and their complexes with acetonitrile, Cd(II), and Pb(II).

We describe here a procedure to bridge the gap in the field of calixarene physicochemistry between solid-state atomic-resolution structural information and the liquid-state low-resolution thermodynamics and spectroscopic data. We use MD simulations to study the kinetics and energetics involved in the complexation of lower rim calix[4]arene derivatives (L), containing bidentate ester (1) and ketone (2) pendant groups, with acetonitrile molecule (MeCN) and Cd(2+) and Pb(2+) ions (M(2+)) in acetonitrile solution. On one hand, we found that the prior inclusion of MeCN into the calix to form a L(MeCN) adduct has only a weak effect in preorganizing the hydrophilic cavity toward metal ion binding. On the other hand, the strong ion-hydrophilic cavity interaction produces a wide open calix which enhances the binding of one MeCN molecule (allosteric effect) to stabilize the whole (M(2+)) L(MeCN) bifunctional complex. We reach two major conclusions: (i) the MD results for the (M(2+)) 1(MeCN) binding are in close agreement with the "endo", fully encapsulated, metal complex found by X-ray diffraction and in vacuo MD calculations, and (ii) the MD structure for the more flexible 2 ligand, however, differs from the also endo solid-state molecule. In fact, it shows strong solvation effects at the calixarene lower bore by competing MeCN molecules that share the metal coordination sphere with the four CO oxygens of an "exo" (M(2+)) 2(MeCN) complex