Bifunctional 3-Hydroxy-4-Pyridinones as Potential Selective Iron(III) Chelators: Solution Studies and Comparison with Other Metals of Biological and Environmental Relevance

The binding ability of five bifunctional 3-hydroxy-4-pyridinones towards Cu2+ and Fe3+ was studied by means of potentiometric and UV–Vis spectrophotometric measurements carried out at I = 0.15 mol L−1 in NaCl(aq),T = 298.15 K and 310.15 K. The data treatments allowed us to determine speciation schemes featured by metal-ligand species with different stoichiometry and stability, owing to the various functional groups present in the 3-hydroxy-4-pyridinones structures, which could potentially participate in the metal complexation, and in the Cu2+ and Fe3+ behaviour in aqueous solution. Furthermore, the sequestering ability and metal chelating affinity of the ligands were investigated by the determination of pL0.5 and pM parameters at different pH conditions. Finally, a comparison between the Cu2+ and Fe3+/3-hydroxy-4-pyridinones data herein presented with those already reported in the literature on the interaction of Zn2+ and Al3+ with the same ligands showed that, from the thermodynamic point of view, the 3-hydroxy-4-pyridinones are particularly selective towards Fe3+ and could therefore be considered promising iron-chelating agents, also avoiding the possibility of competition, and eventually the depletion, of essential metal cations of biological and environmental relevance, such as Cu2+ and Zn2+.

Catalytic and co-ordination chemistry of enolate oxazoline K2-N,O-ligands to group 9 & 11 transition metals

The co-ordination chemistry and resulting catalytic potential of Group 9 and 11 transition metal centered complexes with the 2-acylmethyl-2-oxazoline skeleton are detailed. Each of the synthesized ligand species were treated with either a Copper (II) or Cobalt (II) salt to promote co-ordination, in all cases deprotonation of the ligand occurred. These complexes have, thereafter, been examined by infrared spectroscopy (IR), UV-Visible spectroscopy (UV-Vis), mass spectrometry (MS), cyclic voltammetry (CV), combustion analysis (EA) and x-ray diffraction and probed for their potential redox properties. In the case of Cu(II) chelated complexes, no desirable redox behaviour was observed. Although, with respect to Co(II) complexes, one complex displayed favourable redox potential. The redox active species have been shown to effectively catalyze the polymerization of methyl methacrylate with tosyl chloride as an initiator, through an ATRP-like mechanism. Work within also reflects preliminary co-ordination to Iridium and Rhodium metal centers. Successfully synthesized Iridium complexes have been tested with respect to their oxidative properties. Positive results have been observed in their ability to perform oxidative addition with both HSnPh3 and MeI. Both small molecule species have been effectively added to an Ir(I) complex, formally changing its oxidation state to Ir(III).

Catalytic and co-ordination chemistry of enolate oxazoline K2-N,O-ligands to group 9 & 11 transition metals

The co-ordination chemistry and resulting catalytic potential of Group 9 and 11 transition metal centered complexes with the 2-acylmethyl-2-oxazoline skeleton are detailed. Each of the synthesized ligand species were treated with either a Copper (II) or Cobalt (II) salt to promote co-ordination, in all cases deprotonation of the ligand occurred. These complexes have, thereafter, been examined by infrared spectroscopy (IR), UV-Visible spectroscopy (UV-Vis), mass spectrometry (MS), cyclic voltammetry (CV), combustion analysis (EA) and x-ray diffraction and probed for their potential redox properties. In the case of Cu(II) chelated complexes, no desirable redox behaviour was observed. Although, with respect to Co(II) complexes, one complex displayed favourable redox potential. The redox active species have been shown to effectively catalyze the polymerization of methyl methacrylate with tosyl chloride as an initiator, through an ATRP-like mechanism. Work within also reflects preliminary co-ordination to Iridium and Rhodium metal centers. Successfully synthesized Iridium complexes have been tested with respect to their oxidative properties. Positive results have been observed in their ability to perform oxidative addition with both HSnPh3 and MeI. Both small molecule species have been effectively added to an Ir(I) complex, formally changing its oxidation state to Ir(III).

Speciation Studies of Bifunctional 3-Hydroxy-4-Pyridinone Ligands in the Presence of Zn2+ at Different Ionic Strengths and Temperatures

The acid–base properties of two bifunctional 3-hydroxy-4-pyridinone ligands and their chelating capacity towards Zn2+, an essential bio-metal cation, were investigated in NaCl aqueous solutions by potentiometric, UV-Vis spectrophotometric, and 1H NMR spectroscopic titrations, carried out at 0.15 ≤ I/mol −1 ≤ 1.00 and 288.15 ≤ T/K ≤ 310.15. A study at I = 0.15 mol L−1 and T = 298.15 K was also performed for other three Zn2+/Lz− systems, with ligands belonging to the same family of compounds. The processing of experimental data allowed the determination of protonation and stability constants, which showed accordance with the data obtained from the different analytical techniques used, and with those reported in the literature for the same class of compounds. ESI-MS spectrometric measurements provided support for the formation of the different Zn2+/ligand species, while computational molecular simulations allowed information to be gained on the metal–ligand coordination. The dependence on ionic strength and the temperature of equilibrium constants were investigated by means of the extended Debye–Hückel model, the classical specific ion interaction theory, and the van’t Hoff equations, respectively.

Novel phthalonitrile derivatives as potential compounds for extraction and complexation of metal cations

The synthesis and the binding properties of novel phthalonitrile derivatives 1-3 towards metal cations have been described in this paper. The complexation and extraction of some transition and heavy metal cations have been followed by UV-visible spectrophotometry absorption in methanol. The conductivity studies have been used in order to confirm complex’s stoichiometries. The treatment of UV spectra by digital program showed the formation of ML (with ML2 in some cases) (M=metal, L=ligand) species. Beyond the discussion of the stability profiles of complexes particular attention is paid to the selectivity towards Cu2+ in the 1st sequence of transition metal cations and towards Hg2+ in the sequence of heavy metal cations.

Voltammetry of the aqueous complexation–dissociation coupled to transfer (ACDT) mechanism with charged ligands

The voltammetry of the ACDT mechanism shows different responses depending on whether the ligand species is neutral or charged. Analytical solutions are deduced to calculate the current–potential signal and gain insight into the physicochemical processes behind it.

Chemical Speciation of Environmentally Significant Metals: An IUPAC contribution to reliable and rigorous computer modelling

The mobility and bioavailability of metal ions in natural waters depend on their chemical speciation, which involves a distribution of the metal ions between different complex (metal-ligand) species, colloid-adsorbed species and insoluble phases, each of which may be kinetically labile or inert. For example, in fresh water the metal ions are distributed among organic complexes (e.g., humates), colloids (e.g., as surface-adsorbed species on colloidal phases such as FeOOH), solid phases (e.g., hydroxide, oxide, carbonate mineral phases), and labile complexes with the simple inorganic anionic ligands commonly present in natural waters (e.g., for Zn

Asymmetry of chlorophylls in photosynthetic proteins: from the viewpoint of coordination chemistry

We conducted a meta-analysis of (bacterio)chlorophyll [(B)Chl] molecules in photosynthetic pigment-protein complexes from the viewpoint of coordination chemistry. We surveyed the ligand species and site in the axial coordination of 146 Chl and 21 BChl molecules in 42 reported crystal structures of 12-type proteins. The imidazolyl moiety of histidine (His) is the most abundant ligand, and the second is water, a much weaker ligand. We focused on the positions, the circumstances, and the macrocycle sides for the coordination of the 31 hydrated (B)Chl molecules found in these proteins. A ligand water molecule of a hydrated (B)Chl is not necessarily hydrogen-bonded to the surrounding protein residues. A hydrated (B)Chl seems to occupy the redundant space where more strongly coupled His-Chl complexes cannot be formed. It is noted that 28 of 31 hydrated (B)Chl molecules (90) were coordinated from the α-side of the (bacterio)chlorin macrocycle, the opposite side from which the C 17-propionic ester protrudes. Among them, all five hydrated Chl molecules at the edges of the proteins were coordinated from the α-side, suggesting that (B)Chl molecules prefer this side for the coordination bondings to the β-side. The analysis also revealed that each (B)Chl binding site was composed of both the protein residues and the neighboring pigment molecules contributing roughly equally. It can be safely said that the cofactor pigments aggregated even in the proteins. Penta-coordination is advantageous to flexible adjustment of intermolecular orientations of (B)Chl molecules in the aggregates.