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The synthesis and characterization of a dinuclear bis(thiosemicarbazone) cobalt complex [Co L (NCS) ] is reported. This complex exhibits significant catalytic activity for hydrogen production in DMF by using triethylammonium (Et NHBF ) as the proton source. Cyclic voltammetry data allowed a maximum turnover frequency of 130 s for 1 m proton concentration to be determined. The catalytic nature of the process and the production of dihydrogen were confirmed by gas analysis during controlled potential electrolysis experiments. Quantum chemical calculations show that the complex displays a ligand-assisted metal-centered reactivity and supports a catalytic mechanism involving ligand-based reduction and protonation steps followed by metal-centered processes.

Mononuclear manganese(II) and iron(III) flavonolates were synthesized as synthetic enzyme-substrate complexes, and their oxygenation reactions as biomimetic functional models with relevance to flavonol 2,4-dioxygenases are briefly described.

1-Aminocyclopropane-1-carboxylic acid oxidase (ACCO) is a nonheme Fe(II)-containing enzyme that is related to the 2-oxoglutarate-dependent dioxygenase family. The binding of substrates/cofactors to tomato ACCO was investigated through kinetics, tryptophan fluorescence quenching, and modeling studies. α-Aminophosphonate analogs of the substrate (1-aminocyclopropane-1-carboxylic acid, ACC), 1-aminocyclopropane-1-phosphonic acid (ACP) and (1-amino-1-methyl)ethylphosphonic acid (AMEP), were found to be competitive inhibitors versus both ACC and bicarbonate (HCO(3)(-)) ions. The measured dissociation constants for Fe(II) and ACC clearly indicate that bicarbonate ions improve both Fe(II) and ACC binding, strongly suggesting a stabilization role for this cofactor. A structural model of tomato ACCO was constructed and used for docking experiments, providing a model of possible interactions of ACC, HCO(3)(-), and ascorbate at the active site. In this model, the ACC and bicarbonate binding sites are located close together in the active pocket. HCO(3)(-) is found at hydrogen-bond distance from ACC and interacts (hydrogen bonds or electrostatic interactions) with residues K158, R244, Y162, S246, and R300 of the enzyme. The position of ascorbate is also predicted away from ACC. Individually docked at the active site, the inhibitors ACP and AMEP were found coordinating the metal ion in place of ACC with the phosphonate groups interacting with K158 and R300, thus interlocking with both ACC and bicarbonate binding sites. In conclusion, HCO(3)(-) and ACC together occupy positions similar to the position of 2-oxoglutarate in related enzymes, and through a hydrogen bond HCO(3)(-) likely plays a major role in the stabilization of the substrate in the active pocket.

Two-photon excitation of curcuminoid borondifluoride nanoparticles in water results in rather efficient luminescence in the near infrared region due to a high two-photon cross-section.

This article describes a series of nine complexes of boron difluoride with 2'-hydroxychacone derivatives. These dyes were synthesized very simply and exhibited intense NIR emission in the solid state. Complexation with boron was shown to impart very strong donor-acceptor character into the excited state of these dyes, which further shifted their emission towards the NIR region (up to 855 nm for dye 5 b, which contained the strongly donating triphenylamine group). Strikingly, these optical features were obtained for crystalline solids, which are characterized by high molecular order and tight packing, two features that are conventionally believed to be detrimental to luminescence in organic crystals. Remarkably, the emission of light from the π-stacked molecules did not occur at the expense of the emission quantum yield. Indeed, in the case of pyrene-containing dye 4, for example, a fluorescence quantum yield of about 15 % with a fluorescence emission maximum at 755 nm were obtained in the solid state. Moreover, dye 3 a and acetonaphthone-based compounds 1 b, 2 b, and 3 b showed no evidence of degradation as solutions in CH(2) Cl(2) that contained EtOH. In particular, solutions of brightly fluorescent compound 3 a (brightness: ε×Φ(f) =45,000 M(-1) cm(-1)) could be stored for long periods without any detectable changes in its optical properties. All together, these new dyes possess a set of very interesting properties that make them promising solid-state NIR fluorophores for applications in materials science.

In our quest for the elaboration of supramolecular models of metallo-enzyme active sites, we became interested in developing new methodologies for the selective functionalization of the large rim of calix[6]arenes. Here, we describe a novel reaction, i.e. the ipso-chlorosulfonylation of calixarene derivatives. The process has been found to be highly efficient, selective and versatile. The regioselectivity is controlled by the nature of the O-substituents at the small rim. Indeed, when O-alkylated by a protonable imidazole group, the aromatic rings are deactivated toward an electrophilic attack and the anisol units can be selectively ipso-chlorosulfonylated under mild conditions (rt). Performing the reaction at a higher temperature allowed the per-chlorosulfonylation to take place. Hence, the synthesis of various sulfonate and sulfonamide derivatives is reported. Finally, a combination of ipso-nitration and chlorosulfonylation allows the per-functionalization of the aromatic units at the large rim in selective alternate positions. Overall, this novel methodology opens new routes to a variety of calixarenes, allowing the tuning of their physical properties without drastically altering their hydrophobic conic cavities.

The complex [Fe(indH)(solvent)3](ClO4)2 (1) has been isolated from the reaction of equimolar amounts of 1,3-bis(2′-pyridylimino)isoindoline (indH) and Fe(ClO4)2 in acetonitrile and characterized by X-ray crystallography and several spectroscopic techniques. It is a suitable catalyst for the oxidation of thioanisoles and benzyl alcohols with H2O2 as the oxidant. Hammett correlations and kinetic isotope effect experiments support the involvement of an electrophilic metal-based oxidant. A metastable green species (2) is observed when 1 is reacted with H2O2 at −40 °C, which has been characterized to have a FeIII(μ-O)(μ-O2)FeIII core on the basis of UV-Vis, electron paramagnetic resonance, resonance Raman, and X-ray absorption spectroscopic data.