Synthesis of new photosensitive H2BBQ2+[ZnCl4]2-/[(ZnCl)2(µ-BBH)] complexes, through selective oxidation of H2O to H2O2.

A new two-electron photosensitizer, H2BBQ2+[ZnCl4]2-/[(ZnCl)2(µ-BBH)] (BBQ stands for 2,5-bis[bis(pyridin-2-ylmethyl)amino]-1,4-quinone and BBH stands for 2,5-bis[bis(pyridin-2-ylmethyl)amino]-1,4-hydroquinone), has been synthesized and the oxidation state of the ligand was determined by X-ray crystallography and NMR spectroscopy. Under light illumination the H2BBQ2+[ZnCl4]2- + ZnCl2 is reduced quantitatively to [(ZnCl)2(µ-BBH)] (pH ∼ 5) oxidizing H2O to H2O2 as is evident by trap experiments. Electrochemistry gave a reversible two-electron ligand-centered redox wave for [(ZnCl)2(µ-BBH)]. UV-Vis, luminescence and EPR spectroscopies reveal the slow formation of a stable quinone diradical, intermediate of the reaction. DFT calculations are in agreement with the proposed mechanism. Based on this property an aqueous {[(ZnCl)2(µ-BBH)]||H2O2} solar rechargeable galvanic cell has been constructed.

pH-Dependent syntheses, structural and spectroscopic characterization, and chemical transformations of aqueous Co(II)-quinate complexes: an effort to delve into the structural speciation of the binary Co(II)-quinic acid system.

Cobalt(II) is an essential metal ion, which can react with biologically relevant substrates in aqueous media, affording discrete soluble forms. D-(-)-quinic acid is a representative metal ion binder, capable of promoting reactions with Co(II) under pH-specific conditions, leading to the isolation of the new species K[Co(C(7)H(11)O(6))(3)] x 3 CH(3)CH(2)OH (1), Na[Co(C(7)H(11)O(6))(3)] x 3 CH(3)CH(2)OH x 2.25 H(2)O (2), and [Co(C(7)H(11)O(6))(2)(H(2)O)(2)] x 3 H(2)O (3). Compounds 1-3 were characterized by elemental analysis, spectroscopic techniques (Fourier-transform infrared, UV-visible, electron paramagnetic resonance (EPR), electrospray ionization mass spectrometry), magnetic studies, and X-ray crystallography. Compound 1 crystallizes in the cubic space group P2(1)3, with a = 15.3148(19) A, V = 3592.0(8) A(3), and Z = 4. Compound 2 crystallizes in the orthorhombic space group P2(1)2(1)2(1), with a = 14.9414(8) A, b = 15.9918(9) A, c = 16.0381(9) A, V = 3832.1(4) A(3), and Z = 4. Compound 3 crystallizes in the monoclinic space group P2(1)/m, with a = 13.2198(10) A, b = 5.8004(6) A, c = 15.3470(12) A, beta = 108.430(7), V = 1116.45(17) A(3), and Z = 4. The lattices in 1-3 reveal the presence of mononuclear Co(II) units bound exclusively to quinate (1 and 2) or quinate and water ligands (3), thus projecting the unique chemical reactivity in each investigated system and suggesting that 3 is an intermediate in the synthetic pathway leading to 1 and 2. The octahedral sites of Co(II) are occupied by oxygens, thereby reflecting the nature of interactions between the divalent metal ion and quinic acid. The magnetic and EPR data on 1 and 3 support the presence of a high-spin octahedral Co(II) in an oxygen environment, having a ground state with an effective spin of S = 1/2. The significance of 3 is further reflected into the aqueous speciation of the binary Co(II)-quinic acid system, in which 3 appears as a competent participant linked to the solid state species 1. The physicochemical profiles of 1-3, in the solid state and in solution, earmark the importance of aqueous structural speciation, which projects chemical reactivity pathways in the binary Co(II)-quinate system, involving soluble Co(II) forms emerging through interactions with low molecular mass O-containing physiological substrates, such as quinic acid.

Probing for missing links in the binary and ternary V(V)-citrate-(H2O2) systems: synthetic efforts and in vitro insulin mimetic activity studies.

In a pH-specific fashion, V(2)O(5) and citric acid in the absence and presence of H(2)O(2) reacted and afforded, in the presence of NaOH and (CH(6)N(3))(2)CO(3), two new dinuclear V(V) binary non-peroxo (CH(6)N(3))(6)[V(2)O(4)(C(6)H(4)O(7))(2)].2H(2)O (1) and ternary peroxo (CH(6)N(3))(4)[V(2)O(2)(Omicron(2))(2)(C(6)H(5)O(7))(2)].6Eta(2)Omicron (2) species, respectively. Complexes 1 and 2 were further characterized by elemental analysis, UV/Vis, FT-IR, NMR (solution and solid state Cross Polarization-Magic Angle Spinning (CP-MAS)) and Raman spectroscopies, cyclic voltammetry, and X-ray crystallography. Both 1 and 2 are members of the family of dinuclear V(V)-citrate species bearing citrate with a distinct coordination mode and degree of deprotonation, with 2 being the missing link in the family of pH-structural variants of the ternary V(V)-peroxo-citrate system. Given that 1 and 2 possess distinct structural features, relevant binary V(III), V(IV) and V(V), and ternary V(V) species bearing O- and N-containing ligands were tested in in vitro cell cultures to assess their cellular toxicity and insulin mimetic capacity. The results project a clear profile for all species tested, earmarking the importance of vanadium oxidation state and its ligand environment in influencing further binary and ternary interactions of vanadium arising with variable mass cellular targets, ultimately leading to a specific (non)toxic phenotype and glucose uptake ability.

Synthesis and aqueous solution properties of multinuclear oxo-bridged vanadium(IV/V) complexes.

Reaction of the multifunctional phenolic ligands 2,5-bis[N,N-bis(carboxymethyl)aminomethyl]hydroquinone (H6cahq), 2,2'-bis[N,N-bis(carboxymethyl)aminomethyl]-4,4'-isopropylidenediphen ol(H6capd),2,2',2''-tris[N,N-bis(carboxymethyl)aminomethyl]-1,1 ,1-tris(4-hydroxyphenyl)ethane (H9catp) and the monofunctional 2-[N,N-bis(carboxymethyl)aminomethyl]-4-carboxyphenol (H3cacp), with VOSO4 and NaVO3 affords the oxo-bridged mixed-valence vanadium(IV/V) Na6[(VO)4(mu-O)2(mu-cahq)2] x Na2SO4 x 20H2O (1), HnNa(3-n)[(VO)2(mu-O)(mu-cacp)2] (2), HnNa(3-n)[(VO)4(mu-O)2(mu-capd)2] (3), HnNa(9-n)[(VO)6(mu-O)3(mu3-catp)2] (4). In addition to the synthesis, we report the infrared, magnetic, optical and electrochemical properties of these complexes. The hydrolytic stability at different pH values was also investigated using visible spectroscopy.