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A new ligand, namely, 2-(5-(pyren-1-yl)pentyl)-9-methyl-1,10-phenanthroline, as well as new bis(2,9-dialkyl-1,10-phenanthroline)copper(II) complexes were designed, which were immobilized on multiwalled carbon nanotube (MWCNT) electrodes. These complexes show a high tendency of autoreduction into their copper(I) form according to electrochemical and EPR experiments. These complexes exhibit strong interactions with MWCNT sidewalls either with or without anchor functions such as the pyrene moiety. The pyrene-modified derivative can be electropolymerized on glassy carbon and MWCNT electrodes to form a poly-[bis(2-(5-(pyren-1-yl)pentyl)-9-methyl-1,10-phenanthroline)copper(II)] metallopolymer film. Furthermore, these MWCNT-supported bis(2,9-dialkyl-1,10-phenanthroline)copper complexes demonstrate a low overpotential for a 4H

Iron centers featuring thiolates in their metal coordination sphere (as ligands or substrates) are well-known to activate dioxygen. Both heme and non-heme centers that contain iron-thiolate bonds are found in nature. Investigating the ability of iron-thiolate model complexes to activate O2 is expected to improve the understanding of the key factors that direct reactivity to either iron or sulfur. We report here the structural and redox properties of a thiolate-based dinuclear Fe complex, [FeII 2(LS)2] (LS2- = 2,2′-(2,2′-bipyridine-6,6′-iyl)bis(1,1-diphenylethanethiolate)), and its reactivity with dioxygen, in comparison with its previously reported protonated counterpart, [FeII 2(LS)(LSH)]+. When reaction with O2 occurs in the absence of protons or in the presence of 1 equiv of proton (i.e., from [FeII 2(LS)(LSH)]+), unsupported μ-oxo or μ-hydroxo FeIII dinuclear complexes ([FeIII 2(LS)2O] and [FeIII 2(LS)2(OH)]+, respectively) are generated. [FeIII 2(LS)2O], reported previously but isolated here for the first time from O2 activation, is characterized by single crystal X-ray diffraction and Mössbauer, resonance Raman, and NMR spectroscopies. The addition of protons leads to the release of water and the generation of a mixture of two Fe-based "oxygen-free" species. Density functional theory calculations provide insight into the formation of the μ-oxo or μ-hydroxo FeIII dimers, suggesting that a dinuclear μ-peroxo FeIII intermediate is key to reactivity, and the structure of which changes as a function of protonation state. Compared to previously reported Mn-thiolate analogues, the evolution of the peroxo intermediates to the final products is different and involves a comproportionation vs a dismutation process for the Mn and Fe derivate, respectively.

The ligands N,N'-bis(3-tert-butyl-5-methoxysalicylidene)-1,2-ethanediamine and N,N'-bis(3-tert-butyl-5-methoxysalicylidene)-1,3-propanediamine were chelated to V(IV)═O (1, 2), Cu(II) (3, 4), Co(II) (5), and Co(III) (6). The X-ray crystal structures of 1-6 were solved. The vanadium center in 1-2 resides in square pyramidal geometry, with an axially bound oxo ligand, whereas the metal ion displays a tetrahedrally distorted square planar geometry in 3-5. The extent of distortion is correlated to the length of the diamine spacer: The longer the linker, the larger the tetrahedral distortions. Complex 6 is octahedral with a bidentate acetate molecule that completes the coordination sphere. All the complexes were characterized by UV-vis and EPR spectroscopies, as well as DFT calculations and electrochemistry. Complexes 1-6 exhibit a reversible one-electron oxidation wave in the range -0.11-0.26 V vs Fc+/Fc. The cations 1+ and 2+ were structurally characterized, showing an octahedral V(V) ion with one oxo and one water molecule coordinated in axial positions. Their vis-NIR spectra are dominated by a band at 727 and 815 nm, respectively, which is assigned to a phenolate-to-vanadium(V) charge transfer (CT) transition. The crystal structures of 3+ and 4+ are congruent with Cu(II)-radical species, wherein the metal center remains four-coordinated. Both feature a Class II (Robin-Day classification scale) IVCT transition at around 1200 nm (e > 1 mM cm-1), indicative of partial localization of the radical. The structure of 5+ displays a square pyramidal cobalt ion, where the fifth (axial) coordination is occupied by a water molecule. It displays a NIR feature at 1244 nm and is described as intermediate between high spin Co(III) and Co(II) radical. In the presence of acetate the dimer [(5)2(μ-OAc)]+ forms, which was structurally characterized and shows a blue shift and lowering in intensity of the NIR absorption band in comparison to 5+. Complex 6+ is a genuine Co(III) radical complex, wherein the phenoxyl moiety is localized on one side of the molecule.

Iron centers featuring thiolates in their metal coordination sphere (as ligands or substrates) are well-known to activate dioxygen. Both heme and non-heme centers that contain iron-thiolate bonds are found in nature. Investigating the ability of iron-thiolate model complexes to activate O

The tetradentate ligand based on (1-imidazolium-3,5-ditert-butylphenol) units was prepared and chelated to group 10 metal ions (Ni(II), Pd(II), and Pt(II)), affording complexes 1, 2, and 3, respectively. The X-ray crystal structures of 1–3 show a square planar metal ion coordinated to two N-heterocyclic carbenes and two phenolate moieties. The cyclic voltammetry curves of complexes 1–3 show two reversible oxidation waves in the range 0.11–0.21 V (E1/21) and 0.55–0.65 V (E1/22) vs Fc+/Fc, which are assigned to the successive oxidations of the phenolate moieties. One-electron oxidation affords mononuclear (S = 1/2) systems. Complex 1+·SbF6– was remarkably stable, and its structure was characterized. The coordination sphere is slightly dissymmetric, while the typical patterns of phenoxyl radicals were observed within the ligand framework. Complex 1+ exhibits a rhombic signal at g = 2.087, 2.016, and 1.992, confirming its predominant phenoxyl radical character. The g-values are slightly smaller for 2+ (2.021,...

International audience; A new tridentate ligand based on acridine has been synthetized. The central acridine heterocycle bears two pyridine coordinating units at positions 4 and 5. The terdentate 2,7-di-tert-butyl-4,5-di(pyridin-2-yl)acridine (dtdpa) was then coordinated to a ruthenium(II) cation. The corresponding homoleptic complex could only be obtained where both ligands coordinate to the ruthenium in a fac fashion. Thus, a heteroleptic compound (2) was constructed in combination with a terpyridine ligand in order to constrain the ligand to adopt a mer geometry. Such a coordination imposes a dramatic twist on the acridine heterocycle, resulting in an unexpected photophysical behavior. The electrochemical and photophysical properties of both complexes were studied, and the molecular structure of 2 was determined by X-ray diffraction. The two compounds absorb at low energy wavelengths, and a very weak luminescence is detected only for complex 2 in the near-infrared region.

The synthesis of two new iron chelators built on the tris-l-serine trilactone scaffold of enterobactin and bearing a 8-hydroxyquinoline (oxinobactin) or 8-hydroxyquinoline-5-sulfonate (sulfoxinobactin) unit has been described. The X-ray structure of the ferric oxinobactin has been determined, exhibiting a slightly distorted octahedral environment for Fe(III) and a Δ configuration. The Fe(III) chelating properties have been examined by potentiometric and spectrophotometric titrations in methanol-water 80/20% w/w solvent for oxinobactin and in water for sulfoxinobactin. They reveal the extraordinarily complexing ability (pFe(III) values) of oxinobactin over the p[H] range 2-9, the pFe value at p[H] 7.4 being 32.8. This was supported by spectrophotometric competition showing that oxinobactin removes Fe(III) from ferric enterobactin at p[H] 7.4. In contrast, the Fe(III) affinity of sulfoxinobactin was largely lower as compared to oxinobactin but similar to that of the ligand O-TRENSOX having a TREN backbone. These results are discussed in relation to the predisposition by the trilactone scaffold of the chelating units. Some comparisons are also made with other quinoline-based ligands and hydroxypyridinonate ligand (hopobactin).

Two new mononuclear FeII complexes, [(L52aH)FeII](PF6)2 (1-(PF6)2) and [(L52a)FeII]BPh4 (2-(BPh4)) have been synthesized with the new aminopyridyl ligand bearing a pivaloylamido arm L52aH (2,2-dimethyl-N-[6-({[2-(methyl-pyridin-2-ylmethyl-amino)-ethyl]-pyridin-2-ylmethyl-amino}-methyl)-pyridin-2-yl]-propionamide), or its deprotonated form L52a-. The structures of the ferrous complexes have been determined by X-ray analysis. The mononuclear FeII is in a pseudo-octahedral environment in both complexes, the six positions around the metal center being occupied by five nitrogen atoms and one oxygen atom from the ligand. Whatever the protonation state of the amide function, the structures are very similar, the FeII being 6-fold coordinated by the two amines, three pyridines, and the oxygen atom from the ligand. These two complexes exhibit an acid/base equilibrium in solution that has been studied by UV-vis spectroscopy and cyclic voltammetry in acetonitrile. The reactivity of 1-(PF6)2 with H2O2 in methanol affords the formation of a new low-spin FeIII(OOH) intermediate in which the oxygen atom is retained in the coordination sphere of the metal.

Continuing our work toward a system mimicking the electron-transfer steps from manganese to P(680)(+) in photosystem II (PS II), we report a series of ruthenium(II)-manganese(II) complexes that display intramolecular electron transfer from manganese(II) to photooxidized ruthenium(III). The electron-transfer rate constant (k(ET)) values span a large range, 1 x 10(5)-2 x 10(7) s(-1), and we have investigated different factors that are responsible for the variation. The reorganization energies determined experimentally (lambda = 1.5-2.0 eV) are larger than expected for solvent reorganization in complexes of similar size in polar solvents (typically lambda approximately 1.0 eV). This result indicates that the inner reorganization energy is relatively large and, consequently, that at moderate driving force values manganese complexes are not fast donors. Both the type of manganese ligand and the link between the two metals are shown to be of great importance to the electron-transfer rate. In contrast, we show that the quenching of the excited state of the ruthenium(II) moiety by manganese(II) in this series of complexes mainly depends on the distance between the metals. However, by synthetically modifying the sensitizer so that the lowest metal-to-ligand charge transfer state was localized on the nonbridging ruthenium(II) ligands, we could reduce the quenching rate constant in one complex by a factor of 700 without changing the bridging ligand. Still, the manganese(II)-ruthenium(III) electron-transfer rate constant was not reduced. Consequently, the modification resulted in a complex with very favorable properties.

Tyrosinase (Ty) is a copper-containing enzyme widely present in plants, bacteria, and humans, where it is involved in biosynthesis of melanin-type pigments. Development of Ty inhibitors is an important approach to control the production and the accumulation of pigments in living systems. In this paper, we focused our interest in phenylthiourea (PTU) and phenylmethylene thiosemicarbazone (PTSC) recognized as inhibitors of tyrosinase by combining enzymatic studies and coordination chemistry methods. Both are efficient inhibitors of mushroom tyrosinase and they can be considered mainly as competitive inhibitors. Computational studies verify that PTSC and PTU inhibitors interact with the metal center of the active site. The KIC value of 0.93 μM confirms that PTSC is a much more efficient inhibitor than PTU, for which a KIC value of 58 μM was determined. The estimation of the binding free energies inhibitors/Ty confirms the high inhibitor efficiency of PTSC. Binding studies of PTSC along with PTU to a dinuclear copper(II) complex ([Cu2(μ-BPMP)(μ-OH)](ClO4)2 (1); H-BPMP = 2,6-bis-[bis(2-pyridylmethyl)aminomethyl]-4-methylphenol) known to be a structural and functional model for the tyrosinase catecholase activity, have been performed. Interactions of the compounds with the dicopper model complex 1 were followed by spectrophotometry and electrospray ionization (ESI). The molecular structure of 1-PTSC and 1-PTU adducts were determined by single-crystal X-ray diffraction analysis showing for both an unusual bridging binding mode on the dicopper center. These results reflect their adaptable binding mode in relation to the geometry and chelate size of the dicopper center.

A series of nine Ni(II) salophen complexes involving one, two, or three alkyl-imidazolium side-chains was prepared. The lengths of the side-chains were varied from one to three carbons. The crystal structure of one complex revealed a square planar geometry of the nickel ion. Fluorescence resonance energy transfer melting of G-quadruplex structures in the presence of salophen complex were performed. The G-quadruplex DNA structures were stabilized in the presence of the complexes, but a duplex DNA was not. The binding constants of the complexes for parallel and antiparallel G-quadruplex DNA, as well as hairpin DNA, were measured by surface plasmon resonance. The compounds were selective for G-quadruplex DNA, as reflected by equilibrium dissociation constant KD values in the region 0.1-1 μM for G-quadruplexes and greater than 2 μM for duplex DNA. Complexes with more and shorter side-chains had the highest binding constants. The structural basis for the interaction of the complexes with the human telomeric G-quadruplex DNA was investigated by computational studies: the aromatic core of the complex stacked over the last tetrad of the G-quadruplex with peripherical cationic side chains inserted into opposite grooves. Biochemical studies (telomeric repeat amplification protocol assays) indicated that the complexes significantly inhibited telomerase activity with IC50 values as low as 700 nM; the complexes did not significantly inhibit polymerase activity.

MnIII(bpy)Cl3H2O (Goodwin, H. A.; Sylva, R. N. Aust. J. Chem. 1965, 18, 1743) crystallizes in the triclinic space group P1, with a = 6.627(1) A, b = 9.991(7) A, c = 10.116(4) A, α = 84.38(4)°, β = 73.47(3)°, γ = 78.48(3)°, V = 629 A,3 and Z = 4. The MnIII ion has an octahedral surrounding distorted by a strong Jahn−Teller effect. Two chloride ions and the water molecule are involved into a network of hydrogen bonds. A careful study of aqueous solutions of MnIIILCl3H2O (L = bipyridine or phenanthroline) at different pH demonstrated the formation by condensation and disproportionation of [L2MnIIIO2MnIVL2](ClO4)3 (Cooper, S. R.; Calvin, M. J. Am. Chem. Soc. 1977, 99, 6623), [MnIV3O4L4(H2O)2](ClO4)4 (Sarneski, J. E.; et al. J. Am. Chem. Soc. 1990, 112, 7255) and [Mn4O6(bpy)6](ClO4)4 (Philouze, C.; et al. J. Am. Chem. Soc. 1994, 116, 8557). Condensation of MnLCl3H2O has been studied theoretically using partial charge models. It was possible to identify the mononuclear MnIII and MnIV species which are able to ...

A Co(II) anilinosalen catalyst containing proton relays in the first coordination sphere has been synthesized that catalyzes the electrochemical production of hydrogen from acid in dichloromethane and acetonitrile solutions. The complex has been spectroscopically and theoretically characterized in different protonation and redox states. We show that both coordinated anilido groups of the neutral Co(II) complex can be protonated into aniline form. Protonation induces an anodic shift of more than 1 V of the reduction wave, which concomitantly becomes irreversible. Hydrogen evolution that originates from the aniline protons located in the first coordination sphere is observed upon bulk electrolysis at −1.5 V of the protonated complex in absence of external acid. Structures for intermediates in the catalytic reaction have been identified based on this data.

Two new iron complexes, [L(5)(3)Fe(II)Cl]PF(6) (1.PF(6)) and [(L(5)(3)H(+))Fe(III)Cl(3)]PF(6) (2.PF(6)), were synthesized (L(5)(3) = N-methyl-N,N',N'-tris(2-pyridylmethyl)propane-1,3-diamine), and their molecular structures were determined by X-ray crystallography. Their behavior in solution was studied by UV-vis spectroscopy and electrochemistry. Upon addition of a base to an acetonitrile solution of 2, the new unsymmetrical dinuclear complex [L(5)(3)Fe(III)OFe(III)Cl(3)](+) was detected. Treating 1 with hydrogen peroxide has allowed us to detect the low spin [L(5)(3)Fe(III)OOH](2+). Its spectroscopic properties (UV-vis, EPR and resonance Raman) are similar to those reported for related FeOOH complexes obtained with amine/pyridine ligands. Using stopped-flow absorption spectroscopy, the formation and degradation of [L(5)(3)Fe(III)OOH](2+) has been monitored, and a mechanism is proposed to reproduce the kinetic data.