Porphyrins with multiple crown ether voids: novel systems for cation complexation studies

Porphyrins appended with crown ether, benzo-15-crown-5, at the methine positions have been synthesized and characterized. The fully and partially substituted porphyrins and their metallo (Co, Cu, and Zn) derivatives describe one or more ether cavities in the periphery that are capable of recognizing spherical cations. The ability of these macrocycles to complex cations (Na+, K+, Mg2+, Ca2+, Ba2', and NH4+) is investigated by use of visible, 'H NMR, ESR, and emission spectral studies. The tetrasubstituted crown porphyrin (TCP) exhibits very high selectivity for K+. The cations (K', Ba2+, and NH4+) that require two crown ether cavities for complexation promote dimerization of the porphyrins. The ESR study of the cation-induced porphyrin dimers reveals axial symmetry with the porphyrin planes separated by -4.2 A. This distance increases from the fully substituted to partially substituted porphyrins. The cations (K', Ba2+, and NH4') quench efficiently the fluorescence of the free base porphyrins and their metallo derivatives. The quenching process is attributed to the steric geometry of the dimers.

Solvent extraction and lanthanide complexation studies with new terdentate ligands containing two 1,3,5-triazine moieties

The extracting agent 2,6-bis(4,6-di-pivaloylamino-1,3,5-triazin-2-yl)-pyridine (L-5) in n-octanol was found, in synergy with 2-bromodecanoic acid, to give D-Am/D-Eu separation factors (SFs) between 2.4 and 3.7 when used to extract the metal ions from 0.02-0.12 M HNO3. Slightly higher SFs (4-6) were obtained in the absence of the synergist when the ligand was used to extract Am(III) and Eu(III) from 0.98 M HNO3. In order to investigate the possible nature of the extracted species crystal structures of L-5 and the complex formed between Yb(III) with 2,6-bis(4,6-di-amino-1,3,5-triazin-2-yl)-pyridine (L-4) were also determined. The structure of L-5 shows 3 methanol solvent molecules all of which form 2 or 3 hydrogen bonds with triazine nitrogen atoms, amide nitrogen or oxygen atoms, or pyridine nitrogen atoms. However, L-5 is relatively unstable in metal complexation reactions and loses amide groups to form the parent tetramine L-4. The crystal structure of Yb(L-4)(NO3)(3) shows ytterbium in a 9-coordinate environment being bonded to three donor atoms of the ligand and three bidentate nitrate ions. The solvent extraction properties of L-4 and L-5 are far inferior to those found for the 2,6-bis-(1,2,4-triazin-3-yl)-pyridines (L-1) which have SF values of ca. 140 and theoretical calculations have been made to compare the electronic properties of the ligands. The electronic charge distribution in L-4 and L-5 is similar to that found in other terdentate ligands such as terpyridine which have equally poor extraction properties and suggests that the unique properties of L-1 evolve from the presence of two adjacent nitrogen atoms in the triazine rings.

Bis- and tris-(3-aminopropyl) derivatives of 14-membered tetraazamacrocycles containing pyridine: synthesis, protonation and complexation studies

New N-(3-aminopropyl) (L-1, L-2) and (2-cyanoethyl) (L-3, L-4) derivatives of a 14-membered tetraazamacrocycle containing pyridine have been synthesized. The protonation constants of L-1 and L-2 and the stability constants of their complexes with Ni2+, Cu2+, Zn2+ and Cd2+ metal ions were determined in aqueous solutions by potentiometry, at 298.2 K and ionic strength 0.10 mol dm(-3) in KNO3. Both compounds have high overall basicity due to the presence of the aminopropyl arms. Their copper(II) complexes exhibit very high stability constants, which sharply decrease for the complexes of the other studied metal ions, as usually happens with polyamine ligands. Mono- and dinuclear complexes are formed with L-2 as well as with L-1, but the latter exhibits mononuclear complexes with slightly higher K-ML values while the dinuclear complexes of L-2 are thermodynamically more stable. The presence of these species in solution was supported by UV-VIS-NIR and EPR spectroscopic data. The single crystal structures of [Cu(H2L2)(ClO4)](3+) and [(CoLCl)-Cl-3](+) revealed that the metal centres are surrounded by the four nitrogen atoms of the macrocycle and one monodentate ligand, adopting distorted square pyramidal geometries. In the [(CoLCl)-Cl-3](+) complex, the macrocycle adopts a folded arrangement with the nitrogen atom opposite to the pyridine at the axial position while in the [Cu(H2L2)(ClO4)](3+) complex, the macrocycle adopts a planar conformation with the three aminopropyl arms located at the same side of the macrocyclic plane.

Bis- and tris-(methylphosphonic) acid derivatives of a 14-membered tetraazamacrocycle containing pyridine: synthesis, protonation and complexation studies

Two N-methylphosphonic acid derivatives of a 14-membered tetraazamacrocycle containing pyridine have been synthesized, H4L1 and H6L2. The protonation constants of these compounds and the stability constants of complexes of both ligands with Ni2+, Cu2+ and Zn2+ were determined by potentiometric methods at 298 K and ionic strength 0.10 mol dm(-3) in NMe4NO3. The high overall basicity of both compounds is ascribed to the presence of the phosphonate arms. H-1 and P-31 NMR spectroscopic titrations were performed to elucidate the sequence of protonation, which were complemented by conformational analysis studies. The complexes of these ligands have stability constants of the order of or higher than those formed with ligands having the same macrocyclic backbone but acetate arms. At pH = 7 the highest pM values were found for solutions containing the compound with three acetate groups, followed immediately by those of H6L2, however, as expected, the increasing pH favours the complexes of ligands containing phosphonate groups. The single-crystal structure of Na-2[Cu(HL1)]NO3.8H(2)O has shown that the coordination geometry around the copper atom is a distorted square pyramid. Three nitrogen atoms of the macrocyclic backbone and one oxygen atom from one methylphosphonate arm define the basal plane, and the apical coordination is accomplished via the nitrogen atom trans to the pyridine ring of the macrocycle. To achieve this geometric arrangement, the macrocycle adopts a folded conformation. This structure seems consistent with Uv-vis-NIR spectroscopy for the Ni2+ and the Cu2+ complexes and with the EPR for the latter.

Ditopic hexaazamacrocycles containing pyridine: synthesis, protonation and complexation studies

Structural studies of metal complexes of five ditopic hexaazamacrocycles containing two pyridine rings ([n] py(2)N(4) n = 18, 20, 22, 24 and 26) have been carried out. The synthesis of macrocycles [22]- to [26]- py(2)N(4) are also reported. The protonation constants of the last three compounds and the stability constants of their complexes with Ni2+, Cu2+, Zn2+, and Pb2+ were determined at 25 degreesC in 0.10 mol dm(-3) KNO3 in aqueous solution. Our results with [22] py(2)N(4) show significant differences from those described previously, while [24] py(2)N(4) has not been studied before and [ 26] py2N4 is a new compound. Mononuclear and dinuclear complexes of the divalent metal ions studied with [ 22]- to [26]- py(2)N(4) were found in solution. The stability constants for the ML complexes of the three ligands follow the Irving - Williams order: NiL2+ < CuL2+ >> ZnL2+ > PbL2+, however for the dinuclear complexes the values for Pb2+ complexes are higher than the corresponding values for the Ni2+ and the Zn2+ complexes. The X-ray single crystal structures of the supramolecular aggregates [Cu-2([20] py(2)N(4))(H2O)(4)][Cu(H2O)(6)](SO4)(3) . 3H(2)O ( 1) and [Cu-2([20] py(2)N(4))(CH3CN)(4)][Ni([20] py(2)N(4))](2)(ClO4)(8) . H2O (2), which are composed of homodinuclear [Cu-2([20] py(2)N(4)])(H2O)(4)](4+) ( 1a) and [Cu-2([20] py(2)N(4)])(CH3CN))(4)](4+) (2a), and mononuclear species, [Cu(H2O)(6)](2+) (1b) and [Ni([20] py(2)N(4))](2+) ( 2b), respectively, assembled by an extensive network of hydrogen bonds, are also reported. In both homodinuclear complexes the copper centres are located at the end of the macrocycle and display distorted square pyramidal coordination environments with the basal plane defined by three consecutive nitrogen donors and one solvent molecule, water in 1a and acetonitrile in 2a. The macrocycle adopts a concertina-type conformation leading to the formation of macrocyclic cavities with the two copper centres separated by intramolecular distances of 5.526(1) and 5.508(7) Angstrom in 1a and 2a, respectively. The mononuclear complex [Ni([20] py(2)N(4)])](2+) displays a distorted octahedral co-ordination environment with the macrocycle wrapping the metal centre in a helical shape. EPR spectroscopy of the copper complexes indicated the presence of mono- and dinuclear species.

New dioxadiaza- and trioxadiaza-macrocycles containing one dibenzofuran unit with two amino pendant arms: synthesis, protonation and complexation studies

New dioxadiaza- and trioxadiaza-macrocycles containing one rigid dibenzofuran unit (DBF) and N-(2-aminoethyl) pendant arms were synthesized, N,N'-bis(2-aminoethyl)-[17]( DBF) N2O2 (L-1) and N,N'-bis(2-aminoethyl)-[22](DBF)N2O3 (L-2), respectively. The binding properties of both macrocycles to metal ions and structural studies of their metal complexes were carried out. The protonation constants of both compounds and the stability constants of their complexes with Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+ were determined at 298.2 K, in aqueous solutions, and at ionic strength 0.10 mol dm(-3) in KNO3. Mononuclear complexes with both ligands were formed, and dinuclear complexes were only found for L-2. The thermodynamic binding affinities of the metal complexes of L-2 are lower than those of L-1 as expected, but the Pb2+ complexes of both macrocycles exhibit close stability constant values. On the other hand, the binding affinities of Cd2+ and Pb2+ for L-1 are very high, when compared to those of Co2+, Ni2+ and Zn2+. These interesting properties were explained by the presence of the rigid DBF moiety in the backbone of the macrocycle and to the special match between the macrocyclic cavity size and the studied larger metal ions. To elucidate the adopted structures of complexes in solution, the nickel(II) and copper( II) complexes with both ligands were further studied by UV-vis-MR spectroscopy in DMSO-H2O 1 : 1 (v/v) solution. The copper(II) complexes were also studied by EPR spectroscopy in the same mixture of solvents. The crystal structure of the copper complex of L-1 was also determined. The copper(II) displays an octahedral geometry, the four nitrogen atoms forming the equatorial plane and two oxygen atoms, one from the DBF unit and the other one from the ether oxygen, in axial positions. One of the ether oxygens of the macrocycle is out of the coordination sphere. Our results led us to suggest that this geometry is also adopted by the Co2+ to Zn2+ complexes, and only the larger Cd2+ and Pb2+ manage to form complexes with the involvement of all the oxygen atoms of the macrocyclic backbone.

Studies on metal complex formation of environmentally friendly aminopolycarboxylate chelating agents

Aminopolykarboksyylaatteja, kuten etyleenidiamiinitetraetikkahappoa (EDTA), on käytetty useiden vuosikymmenien ajan erinomaisen metalli-ionien sitomiskyvyn vuoksi kelatointiaineena lukuisissa sovelluksissa sekä analytiikassa että monilla teollisisuuden aloilla. Näiden yhdisteiden biohajoamattomuus on kuitenkin herättänyt huolta viime aikoina, sillä niiden on havaittu olevan hyvin pysyviä luonnossa. Tämä työ on osa laajempaa tutkimushanketta, jossa on tavoitteena löytää korvaavia kelatointiaineita EDTA:lle. Tutkimuksen aiheena on kuuden kelatointiaineen metalli-ionien sitomiskyvyn kartoitus. EDTA:a paremmin luonnossa hajoavina nämä ovat ympäristöystävällisiä ehdokkaita korvaaviksi kelatointiaineiksi useisiin sovelluksiin. Työssä tutkittiin niiden kompleksinmuodostusta useiden metalli-ionien kanssa potentiometrisella titrauksella. Metalli-ionivalikoima vaihteli hieman kelatointiaineesta riippuen sisältäen magnesium-, kalsium-, mangaani-, rauta-, kupari-, sinkki-, kadmium-, elohopea-, lyijy- ja lantaani-ionit. Tutkittavat metallit oli valittu tähtäimessä olevien sovellusten, synteesissä ilmenneiden ongelmien tai ympäristönäkökohtien perusteella. Tulokset osoittavat näiden yhdisteiden metallinsitomiskyvyn olevan jonkin verran heikompi kuin EDTA:lla, mutta kuitenkin riittävän useisiin sovelluksiin kuten sellunvalkaisuprosessiin. Myrkyllisten raskasmetallien, kadmiumin, elohopen ja lyijyn kohdalla EDTA:a heikompi sitoutuminen on eduksikin, koska se yhdistettynä parempaan biohajoavuuteen saattaa alentaa tutkittujen yhdisteiden kykyä mobilisoida kyseisiä metalleja sedimenteistä. Useimmilla tutkituista yhdisteistä on ympäristönäkökulmasta etuna myös EDTA:a pienempi typpipitoisuus.

Calixarene and Resorcarene Based Receptors: From Structural and Thermodynamic Studies to the Synthesis of a New Mercury(II) Selective Material

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.

Studies of the interaction of Potassium(I), Calcium(II), Magnesium(II), and Copper(II) with Cyclosporin A

Metal ion binding properties of the immunosuppressant drug cyclosporin A have been investigated. Complexation studies in acetonitrile solution using H-1 NMR and CD spectroscopy yielded 1:1 metal-peptide binding constants (log(10)K) for potassium(l), < 1, magnesium(II), 4.8 +/- 0.2. and calcium(II), 5.0 +/- 1.0. The interaction of copper(II) with cyclosporin A in methanol was investigated with UV/visible and electron paramagnetic resonance (EPR) spectroscopy. No complexation of copper(II) was observed in neutral solution. In the presence of base, monomeric copper(II) complexes were detected. These results support the possibility that cyclosporin A has ionophoric properties for biologically important essential metal ions. (C) 2003 Elsevier Inc. All rights reserved.

Solution cation-binding properties of segmented polyethylene oxide-A C-13 NMR spectroscopic study

Two segmented polyethylene oxides, SPEO-3 and SPEO-4, were prepared using a novel transetherification methodology. Their structures were confirmed by H-1 and C-13 NMR spectroscopy. The complexation of these SPEO's with alkali-metal ions in solution was investigated by C-13 NMR spectroscopy. The mole-fraction method was used to determine the complexation ratio of SPEO with LIClO4 at 25 degrees C, which showed that these formed 1:1 (polymer repeat unit/salt) complexes. The association constant, K, for the complex formation was calculated from the variation of the chemical shift values with salt concentration, using a standard nonlinear least-square fitting procedure. The maximum change in chemical shift (Delta delta) and the K values suggest that both SPEO-3 and SPEO-4 formed stronger complexes with lithium salts than with sodium salts. Unexpectedly, the K values were found to be different, when the variation of delta of different carbons was used in the fitting procedure. This suggests that several possible complexed species may be in equilibrium with the uncomplexed one. Structurally similar model compounds were also prepared and their complexation studies indicated that all of them also formed 1:1 complexes with Li salts. Interestingly, it was observed that the polymers gave higher K values suggesting the formation of more stable complexes in polymers when compared to the model analogues. (C) 2000 John Wiley & Sons, Inc.

Polyoxométallates hybrides : vers des systèmes covalents photoactifs dans le visible

Réalisé en cotutelle, sous la direction du Pr. Bernold Hasenknopf, à l'Institut Parisien de Chimie Moléculaire, Université Pierre et Marie Curie (Paris VI, France) et dans le cadre de l'Ecole Doctorale "Physique et Chimie des Matériaux" - Spécialité Chimie Inorganique (ED397).

Circular dichroism and nuclear magnetic resonance studies on the complexation of valinomycin with calcium

Complexation of valinomycin (VM) with the divalent cation Ca2+ in a lipophilic solvent, acetonitrile (CH3-CN), has been studied by using circular dichroism and proton and carbon- 13 nuclear magnetic resonance (‘H NMR and I3C NMR). From analyses of the spectral data, it is concluded that VM forms a 2:l (peptideion-peptide) sandwich complex with Ca2+, at low concentration of VM. At moderate conocentrations of the salt, in addition to the sandwich complex, an equimolar (1:l) complex different from those observed for potassium and sodium is also observed. At very large concentrations of the calcium salt, the data suggested a complex with a conformation similar to that of the free VM in polar solvents. Possible conformations for the sandwich and the equimolar VM-calcium complexes are proposed.

LANTHANIDE-INDUCED SHIFT AND RELAXATION RATE STUDIES OF THE AQUEOUS COMPLEXATION OF CITRATE

The aqueous complexation of lanthanide ions with citrate in pH 7.4 solution has been investigated with use of the lanthanide-induced shift and paramagnetic relaxation rate enhancement methods. The results show that citrate coordinates via hydroxyl and central carboxylate groups with lanthanide ions and forms 1:2 (Ln/cit) isostructural complexes through the lanthanide series. A new possible coordination geometry deduced from our experimental data is suggested and discussed.