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New Lennard-Jones parameters are presented for [Cd.sup.2+] and [Pb.sup.2+] ion-water interactions and a general methodology is described to obtain these parameters for any ion. [Cd.sup.2+] has shown a lesser diffusion coefficient when compared to [Pb.sup.2+], despite its smaller atomic radius, indicating a more persistent first coordination shell for the cadmium(II) ion.

A resorcarene derivative designed with pendant arms having sulfur donor atoms namely 5,11,17, -23-ethylthiomethylated calix[4] resorcarene is described. Electrical conductance provided key information regarding the composition of metal-ion complexes and their decomposition.

The tautomeric forms of benximidazole N-oxide derivatives in solution using nuclear magnetic resonance (NMR) techniques are studied. In the gas phase, the N-hydroxy tautomer is more stable than the N-oxide, whereas in solution the stabilization of one form or the other depended on hydrogen bond formation involving the N-hydroxy/N-oxide moiety.

The synthesis and structural characterization, determined by H1 and C13 NMR, for a new tetraester calix[4] arene derivative containing mixed pendant arm in its lower rim are reported. The medium effect on the binding process of tetraester calix[4]arene for metal cations are examined to establish the sites of interaction of the ligand with the metal cation, the composition of complex formed and the strength of ligand-cation interaction in different media.

The interaction of lower rim calix940arene derivatives containing ester and ketone functional groups and bivalent cations has been investigated in various solvents. The presence of actonitrile leads to ligand's preorganization and these ligands discriminate between the various bivalent cations to the extent that a selectivity peak is found in terms of Gibbs energies when complexation data are plotted against cation solvation.

The crystal and molecular structure of [Ru[(DMAP).sub.6]][Cl.sub.2].6[C.sub.3]C[H.sub.2]OH (DMAP = 4-dimethylaminopyridine) is studied by using X-ray diffraction method. The density functional theory (DFT) calculations have shown that in {[Ru.sup.II][(DMAP).sub.5]} the DMAP ligands have competed for the [pi] electron density of the ruthenium making the fragment a weaker [pi]-donor.

Reaction of trans-Ru(DMSO)4C12 with DMAP (DMAP = 4-dimethylaminopyridine) yields the yellow [Ru(DMAP)6]2~ cation in good yield. The crystal and molecular structure of [Ru(DMAP)6]Cl2.6CH3CH2OH was determined by X-ray diffraction methods. The complex crystallizes in the trigonal F~3 space group with a = b = 16.373(1), c = 20.311(1) A, y = 120°, and Z = 3 molecules per unit cell. The reaction of [Ru(DMAP)6]2~ in aerobic water gives the red [Ru'°(DMAP)5(OH)]2~ cation. This complex shows a chemical behavior similar to [Ru'°(NH3)5Cl]2~ and allows the preparation of a family of [Ru(DMAP)5L]'~ complexes. Their electronic properties indicate that the {Ru°(DMAP)5} fragment is a weaker 7r-donor than {Ru"(NH3)5}. Our density functional theory (DFT) calculations show that in {RuH(DMAP)5} the DMAP ligands can compete for the ~r electron density of the ruthenium making the fragment a weaker ir-donor. [ABSTRACT FROM AUTHOR]

Diverse models of intramolecular charge transfer (ICT) have been proposed for interpreting the origin of the charge-transfer (CT) state in donor-acceptor (D-A) dyes. However, a large variety of fused-heterocyclic dyes containing a pseudo-aromatic ring in the rigid structure have shown to be incompatible with them. To approximate a solution within the ICT concept, we reported a novel ICT model called partially aromatized intramolecular charge transfer (PAICT). PAICT involves the generation of a CT state from an ICT that occurred within a pre-excited D-A fused-heterocyclic structure possessing a pseudo-aromatic or unstable aromatic ring as the acceptor moiety. The model was proposed from the multiple-emissive mesomeric D-A N 1 - aryl-2-(trifluoromethyl)benzo[ b ][1,8]naphthyridin-4(1 H )-one, whose excited mesomeric states, which are defined by the aromatic and pseudo-aromatic forms of the pyrindin-4(1 H )-one ring, led to a common partial aromatized CT state upon excitation via PAICT. The latter was supported through theoretical calculations on the excited mesomeric states, one-dimensional (1D) and two-dimensional (2D) excitation-emission measurements in different solvents, and the detection of three excited states by lifetime measurements upon 370 nm excitation. The existence of mesomerism was supposed from: (i) two overlapping bands at 370-390 (or 400-420 nm) in UV-vis spectra, (ii) the direct interaction between the pyridinic nitrogen of one molecule and the carbonylic oxygen of the other found in the solid state and, (iii) the detection of three excited states by lifetime measurements. The PAICT opens new perspectives for interpreting the charge-transfer phenomenon in fused-heterocyclic dyes, in particular, those containing a pseudo-aromatic or unstable aromatic ring as an acceptor moiety.

Chagas disease, caused by Trypanosoma cruzi parasite, was described thousands of years ago. Currently, it affects millions of people, mostly in Latin America, and there are not suitable drugs for treating it. As an attempt to find appropriate drugs to deal with this problem, we report here on the design, synthesis, and characterization of 82 new compounds. Trypanosomicidal behavior in vitro showed more than 20 outstanding derivatives with anti-Trypanosoma cruzi activity. Furthermore, we studied the nonspecific toxicity against mammalian cells determining their selectivity and also performed mutagenicity studies. Proof of concept, in vivo studies, was conducted with two of the most promising derivatives (77 and 80). They were identified as candidates because they have (i) very simple and cost-effective syntheses; (ii) activity against different stages and strains of the parasite showing excellent in vivo behavior during the acute phase of Chagas disease; and (iii) neither nonspecific toxicity nor mutagenic activity.

The molecular and crystal structure of two dithiolactones (formally dimers of ε-caprothiolactone and ω-hexadecathiolactone) have been determined by X-ray diffraction at low temperature, revealing that the thioester group is planar with a synperiplanar orientation of the C═O double bond with respect to the S-C single bond. This conformational behavior is in contrast to that found for the smaller cyclic members of this family, where the antiperiplanar conformation is enforced. It is hypothesized that strain effects play a major role for the energy balance in the conformational preference. In this context, the molecular, vibrational (infrared and Raman), and electronic properties of ε-caprothiolactone have also been analyzed by using a combined experimental, including gas-phase helium I photoelectron spectroscopy, and computational approach.

Materials used in current technological approaches for the removal of mercury lack selectivity. Given that this is one of the main features of supramolecular chemistry, receptors based on calix[4]arene and calix[4]resorcarene containing functional groups able to interact selectively with polluting ions while discriminating against biologically essential ones were designed. Thus two receptors, a partially functionalized calix[4]arene derivative, namely, 5,11,17,23-tetra-tert-butyl [25-27-bis(diethyl thiophosphate amino)dihydroxy] calix[4]arene (1) and a fully functionalized calix[4]resorcarene, 4,6,10,12,16,18,22,24-diethyl thiophosphate calix[4]resorcarene (2) are introduced. Mercury(II) was the identified target due to the environmental and health problems associated with its presence in water Thus following the synthesis and characterization of 1 and 2 in solution ((1)HNMR) and in the solid state (X-ray crystallography) the sequence of experimental events leading to cation complexation studies in acetonitrile and methanol ((1)H NMR, conductance, potentiometric, and calorimetric measurements) with the aim of assessing their behavior as mercury selective receptors are described. The cation selectivity pattern observed in acetonitrile follows the sequence Hg(II) > Cu(II) > Ag(I). In methanol 1 is also selective for Hg(II) relative to Ag(I) but no interaction takes place between this receptor and Cu(II) in this solvent. Based on previous results and experimental facts shown in this paper, it is concluded that the complexation observed with Cu(II) in acetonitrile occurs through the acetonitrile-receptor adduct rather than through the free ligand. Receptor 2 has an enhanced capacity for uptaking Hg(II) but forms metalate complexes with Cu(II). These studies in solution guided the inmobilization of receptor 1 into a silica support to produce a new and recyclable material for the removal of Hg(II) from water. An assessment on its capacity to extract this cation from water relative to Cu(II) and Ag (I) shows that the cation selectivity pattern of the inmobilized receptor is the same as that observed for the free receptor in methanol. These findings demonstrate that fundamental studies play a critical role in the selection of the receptor to be attached to silicates as well as in the reaction medium used for the synthesis of the new decontaminating agent.

A thermodynamic study involving 7-nitro-1,3,5-triaza adamantane, 1, and its interaction with metal cations in nonaqueous media is first reported. Solubility data of 1 in various solvents were used to derive the standard Gibbs energies of solution, DeltaG(s)o in these solvents. The effect of solvation in the different media was assessed from the Gibbs energy of transfer taking acetonitrile as a reference solvent. 1H NMR studies of the interaction of 1 and metal cations were carried out in CD3CN and CD3OD and the data are reported. Conductance measurements revealed that this ligand forms lead(II) or zinc complexes of 1:1 stoichiometry in acetonitrile. It also revealed a stoichiometry of two molecules of 1 per mercury(II) and two cadmium (II) ions per molecule of 1. The addition of silver salt to 1 led to the precipitation of the silver-1 complex which was isolated and characterized by X-ray crystallography. At variance with conductance measurements in solution, in the solid state the X-ray structure shows a 1:1 stoichiometry in the Hg(II) complex. The thermodynamics of complexation of 1 and these cations provide a quantitative assessment of the selective behavior of this ligand for ions of environmental relevance.

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.

In the search for new therapeutic tools against American Trypanosomiasis palladium complexes with bioactive nitrofuran-containing thiosemicarbazones as ligands were obtained. Sixteen novel palladium (II) complexes with the formulas [PdCl2(HL)] and [Pd(L)2] were synthesized, and the crystal structure of [Pd(5-nitrofuryl-3-acroleine thiosemicarbazone)2] x 3DMSO was solved by X-ray diffraction methods. Most complexes showed higher in vitro growth inhibition activity against Trypanosoma cruzi than the standard drug Nifurtimox. In most cases, the activity of the ligand was maintained or even increased as a result of palladium complexation. In addition, the complexes' mode of antitrypanosomal action was investigated. Although the complexes showed strong DNA binding, all data strongly suggest that the main trypanocidal mechanism of action is the production of oxidative stress as a result of their bioreduction and extensive redox cycling. Moreover, the complexes were found to be irreversible inhibitors of trypanothione reductase.

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.