Rita Hernandez-Molina

Cucurbituril as a New Macrocyclic Ligand for Complexation of Lanthanide Cations in Aqueous Solutions

(Aqua)lanthanide complexes with cucurbituril {[Gd(NO3)(H2O)4](C36H36N24O12)}(NO3)2·7H2O (1), {[Gd(NO3)(C2H5OH)(H2O)3](C36H36N24O12)}(NO3)2·5.5H2O (2), {[Ho(NO3)(H2O)4](C36H36N24O12)}(NO3)2·7H2O (3), {[Yb(NO3)(H2O)4](C36H36N24O12)}(NO3)2·6H2O (4), {[La(H2O)6(SO4)](C36H36N24O12)}(NO3)·12H2O (5), {[Gd(H2O)4]2(C36H36N24O12)3}Br6·45H2O (6), and {[Ce(H2O)5]2(C36H36N24O12)2}Br6·26H2O (7) were obtained in high yield by reaction of cucurbituril with aqueous solutions of lanthanide(III) species. The crystal structures of the compounds show a packing of 1:1, 2:2, and 2:3 in the (cucurbituril)lanthanide complexes in which cucurbituril plays a bidentate ligand role, and water molecules of the (aqua)lanthanide complexes form hydrogen bonds with carbonyl groups of the cucurbituril molecule. The guest water molecule is situated in the cucurbituril molecule cavity of 2 and 5. The crystal structure of 6 is a packing of three-deck sandwiches, built from alternating cucurbituril molecules and Gd(H2O)43+ ions. The largest distance between outermost oxygen atoms in the sandwiches is 30.04 A. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Coordinating ability of phenylenediamines

Abstract The coordinating ability of aromatic diamines is conditioned both by the low basicity of the nitrogen atoms and their situation in ortho, meta or para positions on the aromatic ring. Important aspects of the aromatic diamines taking into account their possible applications are: processes based on electron transfer forming Wurster type radical colored cations; trace analysis of metal ions and other species based on catalysis of the oxidative coloration system; the development of biosensors coated with poly(o-phenylenediamine) and their mutagenic and toxic character. o-Phenylenediamine ligands coordinate in a monodentate, chelating bidentate and bridging bidentate fashion in dinuclear complexes; p-phenylenediamine is mainly a bridging bidentate ligand as expected.

Emf(H) data analysis of weak metallic complexes using reduced formation functions

A general method for the study of weak metal complexes by emf(H) measurements has been developed using reduced formation functions instead of classical formation functions. This approach consists of subtracting the contribution of the products of the hydrolysis (protolysis) of the metallic cation (anion), as well as the possible protonated species of the ligand from the total number of associated H+, and from the total concentrations of metal or ligand, observing only the contribution of the reaction of interest. This was carried out using the FONDO version of the generalized least-squares computer program LETAGROP, written to analyze these reduced formation functions. The aim of this communication was to show in greater detail than in previous publications the data analysis of reactions in solution using these reduced formation functions. The method is illustrated using emf(H) data for the three-component systems H+–Be(II)–serine, H+–Mo(VI)–NTA and H+–V(IV)–V(V) investigated recently.

Reactions of the heterometallic cuboidal clusters Mo3MS4 (M = Co, Ni, Pd, Cu) and Mo3NiSe4 with CO: electron counts and kinetic/thermodynamic studies with M = Ni, Pd

Abstract The aqueous solution reactions of heterometallic cube derivatives of [Mo3S4(H2O)9]4+, written here as [Mo3MS4(H2O)10]4+ (tetrahedral M = Fe, Co, Ni, Pd, Cu) with carbon monoxide are considered. Thermodynamically favourable reactions complete in 330 min are detected with M = Co (Group 9), and Ni and Pd (Group 10) containing cubes having 15 and 16 metal electrons, respectively, but no corresponding reactions are observed with M = Fe, Cu cubes having 14 and 17 metal electrons, respectively. A similar reaction is observed with the Se-containing cube [Mo3NiSe4(H2O)10]4+, and with the higher oxidation state cube [Mo3CuS4(H2O)10]5+ (16 electrons) [Mo3S4(H2O)9]4+ and Cu(CO)+ are obtained as final products. On bubbling N, through the latter CO is removed, and approaching quantitative reformation of [Mo3CuS4(H2O)10]5+ is observed. Greater difficulty is experienced in removing carbon monoxide from the other carbonyl adducts (M = Co, Ni, Pd) using N2.

Coordinating ability of ligands derived from phenylenediamines

Abstract The preparation of coordinating agents derived from aromatic diamines is of special interest since the use of nitrogen atoms for coordination to a single cation is directly related to their situation in ortho, meta or para positions. In the case of diaminetetramethylenecarboxylic acids or Schiff bases derived from o-phenylenediamines, the proximity of the nitrogen atoms permits their simultaneous coordination to the same metal cation, leading mainly to monomer species. Combined with the lesser basicity of the nitrogen atoms of the aromatic diamines, the o-phenylenediaminetetramethylene-carboxylic acids are good sequestering agents for some metal ions. Complexes derived from o-phenylenediamine Schiff bases provide new and interesting environment for M–C funcionalities. Iron(III) complexes with o-phenylenediamine Schiff bases may present spin-crossover. On the other hand, the ligands derived from m- or p-phenylenediamines can only coordinate one nitrogen atom to any one metal cation. The formation of species with excess of ligand (2:1 ligand:metal ratio), with excess of metal (1:2 ratio), and monomers (1:1 ratio) is now possible. Moreover, the special conformation of the ligands with nitrogen atoms in meta or para positions on the aromatic ring facilitates the formation of dimer complexes since the ligands act as a bridge. The dinuclear complexes of those ligands with paramagnetic ions may present magnetic coupling. With the nitrogen atoms in para position, polymer complexes are also possible since the ligand acts as a bridge.

Preparation and characterization of triangular clusters [M3Q4(acac)3(py)3]+ (M=Mo, W; Q=S, Se)

Abstract Reactions of [M3Q4(H2O)9]4+ with acetylacetone (Hacac) and pyridine (py) in weakly alkaline solutions (pH 8–9) give mixed-ligand complexes [M3Q4(acac)3(py)3]+ (M=Mo, W; Q=S, Se), isolated as hexafluorophosphate salts. For M=Mo, Q=S and for M=W, Q=both S and Se, X-ray structural analysis has been carried out. The three compounds are isostructural and crystallize as [M3Q4(acac)3(py)3]PF6·CHCl3. Each M is attached to one capping (μ3) and two bridging (μ2) chalcogen atoms, one pyridine ligand and one chelating acetylacetonate ligand. The latter are coordinated symmetrically in positions trans to the μ2-Q bridges to give cluster cations with crystallographic threefold rotation symmetry (point group 3m or C3v). The structure is preserved in solution. CV experiments show two almost reversible waves due to consecutive one electron reductions with the ease of reduction decreasing in the order, Mo3S4>Mo3Se4>W3Se4>W3S4. FAB MS data are also discussed.

Synthesis, Reactivity, and Kinetics of Substitution in W3PdSe4 Cuboidal Clusters. A Reexamination of the Kinetics of Substitution of the Related W3S4 Cluster with Thiocyanate

The reaction of Pd(dba)(2) (dba = dibenzylideneacetone) with [W(3)Se(4)(H(2)O)(9)](4+) in 2 M HCl gives the cuboidal cluster [W(3)(PdCl)Se(4)(H(2)O)(9)](3+), which undergoes edge-to-edge condensation and crystallizes from Hpts solutions as edge-linked double-cubane cluster [{W(3)PdSe(4)(H(2)O)(9)}(2)](pts)(8) x 18 H(2)O (pts(-) = p-toluenesulfonate). The substitution of Cl(-) by different ligands, including phenylsulfinate PhSO(2)(-), was explored. The phenylsulfinate complex was crystallized as a 2:1 adduct with cucurbit[6]uril (C(36)H(36)N(24)O(12)), [W(3)(Pd(PhSO(2))Se(4)(H(2)O)(8.58)Cl(0.42)](2)(C(36)H(36)N(24)O(12))Cl(5.16) x 16.83 H(2)O, and its structure was determined by X-ray diffraction. Solution studies indicate that the Pd atom is able to stabilize the pyramidal tautomer of hypophosphorous and phosphorous acid: HP(OH)(2) and P(OH)(3). Kinetic studies were carried out on the reactions with H(3)PO(2) and thiocyanate, which were found to proceed in two and three kinetically resolvable steps, respectively. The kinetic results are discussed in terms of the mechanistic proposals put forward in the literature for related complexes. To gain insight into the details of the substitution kinetics in these kinds of clusters, the reaction of the related [W(3)S(4)(H(2)O)(9)](4+) complex with NCS(-) has been reexamined, and the results obtained provide for the first time information about the rates of substitution of the whole set of nine-coordinated water molecules.

Synthesis and cytotoxic activity of metallic complexes of lawsone

In the present study, a series of metallic complexes of the 1,4-naphthoquinone lawsone (2-6) were synthesized and evaluated for potential cytotoxicity in a mouse leukemic macrophagic RAW 264.7 cell line. Cell viability was determined by the MTT assay. Significant growth inhibition was observed for the copper complex (4) with an IC(50) value of 2.5 μM. This compound was selected for further evaluation of cytotoxic activity on several human cancer cells including HT-29 (human colorectal adenocarcinoma), HepG2 (human hepatocellular carcinoma) and HeLa, (human cervical adenocarcinoma cells). Significant cell viability decrease was also observed in HepG2 cells. The apoptotic potential of this complex was evaluated in these cells. Compound 4 induced apoptosis by a mechanism that involves the activation of caspases 3, 8 and 9 and modulation of apoptotic-related proteins such as Bax, Bad, and p53. These results indicate that metal complexes of lawsone derivatives, in particular compound 4, might be used for the design of new antitumoral agents.

Acanthamoeba castellanii Neff: In vitro activity against the trophozoite stage of a natural sesquiterpene and a synthetic cobalt(II)-lapachol complex.

In this study, the in vitro activities of a natural sesquiterpene, alpha-cyperotundone, isolated from the root bark of Maytenus retusa and a cobalt(II)-complex of a natural occurring prenyl hydroxynaphthoquinone (lapachol) were evaluated against the trophozoite stage of Acanthamoeba castellanii Neff using a previously developed colorimetric 96-well microtiter plate assay, based on the oxido-reduction of Alamar Blue(R). The obtained activities showed that these two compounds were able to inhibit the in vitro growth of the amoebae at relatively low concentrations. Further identification of the molecular targets of these products and their effects on acanthamoebae should be determined to evaluate their possible therapeutic use.

Coordination of Phenylsulfinate PhSO2— to Mo3MS44+ Clusters (M = Ni, Pd)

Reaction of heterometal cuboidal clusters [Mo3(MCl)S4(H2O)9]3+ (M = Ni, Pd) with PhSO2Na in aqueous HCl leads to the substitution at Ni or Pd to give the [Mo3(M(PhSO2))(H2O)9—xClx](3—x)+species, isolated as supramolecular adducts with cucurbituril (Cuc) [Mo3(Ni(PhSO2))S4Cl1.17(H2O)7.83][Mo3(Ni(PhSO2))S4Cl2.22(H2O)6.78]Cl2.61 · Cuc · 15H2O (1) and [Mo3(Pd(PhSO2))S4Cl1.12(H2O)7.88][Mo3(Pd(PhSO2))S4Cl2.29(H2O)6.71]Cl2.59 · Cuc · 11H2O (2), respectively. Crystal structure of 1 and 2 was determined, revealing that the PhSO2 is coordinated via its sulfur atom (Ni — S 2.182 A, Pd — S 2.305 A). The structure of these isostructural compounds is built from triple aggregates {(cluster)(Cuc)(cluster)} united into zigzag chains via hydrogen bonds between coordinated PhSO2 and H2O ligands. Die Koordination von Phenylsulfinat PhSO2— an Mo3MS44+ Cluster (M = Ni, Pd). Die Reaktion von kubanartigen Clustern [Mo3(MCl)S4(H2O)9]3+ (M = Ni, Pd) mit PhSO2Na in Salzsaure fuhrt zum Ligandenaustausch an Ni oder Pd. Dabei entstehen die Komplexe [Mo3(M(PhSO2))(H2O)9—xClx](3—x)+, die sich als Supramolekularaddukte mit Kukurbituril (Cuc), [Mo3S4Ni(PhSO2)Cl1.17(H2O)7.83][Mo3S4Ni(PhSO2)Cl2.22(H2O)6.78]Cl2.61 · Cuc · 15H2O (1), [Mo3(Pd(PhSO2))S4Cl1.12(H2O)7.88][Mo3(Pd(PhSO2))Cl2.29(H2O)6.71]Cl2.59 · Cuc · 11H2O (2) isolieren lassen. Die Kristallstrukturen der isostrukturellen Komplexe 1 und 2 wurden bestimmt. Der Ligand PhSO2— ist durch das Schwefelatom koordiniert (Ni — S 2.175 A, Pd — S 2.305 A). Die Struktur zeigt, dass zwei Cluster- und ein Kukurbirurilmolekul Addukte vom Typ {(Cluster)(Kukurbituril)(Cluster)} bilden, die sich weiter durch Wasserstoffbrucken zwischen PhSO2 und koordiniertem H2O zu Zickzackketten verknupfen.