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.

The complexation ability of a partially substituted lower rim calix[4]arene hydroxyamide derivative, 25,27-bis[N-(2-hydroxy-1,1-bishydroxymethylethyl)amino- carbonylmethoxy]calix[4]arene-26,28-diol, 1, for cations and anions was investigated through (1)H NMR, conductometry, spectrophotometry, and calorimetry in dipolar aprotic media. (1)H NMR studies of 1 in the deuterated solvents (acetonitrile, methanol, and dimethylsulfoxide) reflect ligand-solvent interactions in methanol and dimethylsulfoxide. As far as the cations are concerned, a selectivity peak is found when standard Gibbs energies of complexation of 1 with cations (alkaline-earth, zinc, and lead) are plotted against corresponding data for cation hydration. This finding reflects the key role played by the desolvation and binding processes in the overall complexation of this receptor and these cations in acetonitrile. This is also interpreted in terms of enthalpy and entropy data. Factors such as, the nature and the arrangement of donor atoms in the hydrophilic cavity of the ligand on cation complexation process, are discussed. This paper also addresses anion complexation processes. It is found that 1 interacts through hydrogen bond formation with fluoride, dihydrogen phosphate, and pyrophosphate in acetonitrile and N,N-dimethylformamide. The thermodynamics associated with these processes is fully discussed taking into account literature data involving calix[4]pyrroles and these anions in these solvents. Previous work regarding the water solubility of these ligands is discussed. It is concluded that 1 behaves as a ditopic ligand in dipolar aprotic media.

A partially substituted calix[4]resorcarene receptor, namely, 5,17-ethylthiomethylated calix[4]resorcarene, 1, has been synthesized and characterized by 1H NMR in CD3OD, CDCl3, and CD3CN and 13C NMR in CD3OD, as well as by 2D NMR. Partition data in the methanol-hexane and acetonitrile-hexane solvent systems show that the monomeric species are predominant in these solvents. The solubility of 1 in various solvents was determined at 298.15 K. These data were used to calculate the standard solution Gibbs energy of 1 in these solvents. Taking hexane as the reference solvent, the standard transfer Gibbs energy of 1 to various solvents was calculated. Good agreement is found between the DeltatG(o) values in the hexane-methanol and hexane-acetonitrile and the DeltapG(o) values of this ligand in these solvent systems. The higher partition constant of 1 in the hexane-methanol relative to the hexane-acetonitrile solvent system contrasts with corresponding data for the fully functionalized receptor, 2. This is explained in terms of the solvation differences of these receptors in these solvents as reflected in the DeltatG(o) values. The cation complexing properties of this receptor were investigated through 1H NMR, conductance, calorimetric, and potentiometric methods. Among the metal cations (alkali, alkaline earth, heavy, and transition), 1 interacts only with Ag+ in methanol and Hg2+ in propylene carbonate, acetonitrile, methanol, and N,N-dimethylformamide. While 1 forms a 1:1 complex with Ag+ in methanol, the hosting ability of the receptor for the mercury cation is enhanced in methanol, acetonitrile, and N,N-diethylformamide. Thus, Hg2+ complexes of 1:2 (ligand:metal cation) stoichiometry are found in these solvents. In moving to propylene carbonate, the composition of the mercury complex is altered from 1:2 to 1:1. The results are compared with corresponding data for 2 and these metal cations in the appropriate solvents. The lack of stability observed for 2 and Hg2+ in acetonitrile resulting from the departure of pendant arms from the resorcarene backbone greatly contrasts with the high stability observed for 1 and this metal cation in the various solvents. Preliminary results on the extraction of silver picrate by this ligand in the water-dichloromethane solvent system are reported. Final conclusions are given.

Novel pyridine-substituted calix[4]pyrrole (CP), has been synthesised and characterised by different analytical techniques ( 1 H NMR, microanalysis and mass spectroscopy). The cation-binding behaviour of this receptor was investigated by proton NMR spectroscopy, conductometric and UV titrations. 1 H NMR measurements reveal the sites of interaction of the ligand with metal cations in deuterated acetonitrile (CD 3 CN). The results show that introduction of one pyridine group to the pendent arm of the modified CP enables the produced hybrid to bind with metal cations [Cd(II), Pb(II), Hg(II)] in acetonitrile. No interaction was observed between this ligand and other metal cations in acetonitrile. The composition of the anion complexes was established through conductance measurements. In all cases, 1:1 complexes are formed. The thermodynamics of metal cations complexation in acetonitrile is discussed.

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Saw dust modified with chloroethylacetate was prepared. The product was used as an extracting agent for the solid-phase extraction of lead cations from aqueous media. The uptake performance of modified saw dust (MSD) for removal of Pb(II) cations was investigated using batch method. The influences of some experimental parameters like initial concentration of the cation, extraction time, concentration of the saw dust, pH and temperature were studied. Three adsorption isotherms [Langmuir, Freundlich and Dubinin-Redushkevish (D-R)] were used to analyze the equilibrium data. The sorption capacity of modified saw dust was found to be 78.1 mg/g at 298 K from 164 mg/l aqueous solution of lead cation. The mean free energy calculated from D-R model was found to be 15.81 KJ/mol, indicating that chemisorption is involved in the extraction process. The removal of lead cation does not change with increasing temperature. The present method has been compared with the previous methods.

Samples from sheets of the polymeric material Bayfol have been exposed to electron beam in the dose range 10-100 kGy. The resultant effect of electron beam irradiation on the thermal properties of Bayfol has been investigated using thermogravimetric analysis. The onset temperature of decomposition T 0 and activation energy of thermal decomposition E a were calculated, results indicating that the Bayfol polymer decomposes in one main weight loss stage. Also, the electron irradiation in the dose range 40-100 kGy led to a more compact structure of Bayfol polymer, which resulted in an improvement in its thermal stability with an increase in activation energy of thermal decomposition. The variation of transition temperatures with electron dose has been determined using differential thermal analysis. The results indicate that the electron irradiation in the dose range 40-100 kGy causes crosslinking that destroys the crystalline structure depressing the melting temperature and this is most suitable for applications requiring the molding of this polymer at lower temperatures. In addition, the mechanical and structural properties of Bayfol samples were measured and the results revealed that the tensile strength, elongation at break, yield strength, and intrinsic viscosity were affected by the electron doses.

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