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1.
Chemistry ; 27(68): 17066-17077, 2021 Dec 06.
Article in English | MEDLINE | ID: mdl-34643965

ABSTRACT

Heuristic rules that allow identifying the preferred mixed-valence isomers and Jahn-Teller axis arrangements in the water oxidation catalyst [(Mn4 O4 )(V4 O13 )(OAc)3 ]n- and its activated form [(Mn4 O4 )(V4 O13 )(OAc)2 (H2 O)(OH)]n- are derived. These rules are based on computing all combinatorially possible mixed-valence isomers and Jahn-Teller axis arrangements of the MnIII atoms, and associate energetic costs with some structural features, like crossings of multiple Jahn-Teller axes, the location of these axes, or the involved ligands. It is found that the different oxidation states localize on different Mn centers, giving rise to clear Jahn-Teller distortions, unlike in previous crystallographic findings where an apparent valence delocalization was found. The low barriers that connect different Jahn-Teller axis arrangements suggest that the system quickly interconverts between them, leading to the observation of averaged bond lengths in the crystal structure. We conclude that the combination of cubane-vanadate bonds that are chemically inert, cubane-acetate/water bonds that can be activated through a Jahn-Teller axis, and low activation barriers for intramolecular rearrangement of the Jahn-Teller axes plays an essential role in the reactivity of this and probably related compounds.


Subject(s)
Manganese , Water , Catalysis , Oxidation-Reduction , Vanadates
2.
Chemistry ; 27(68): 17078-17086, 2021 Dec 06.
Article in English | MEDLINE | ID: mdl-34523763

ABSTRACT

We report IR and UV/Vis spectroscopic signatures that allow discriminating between the oxidation states of the manganese-based water oxidation catalyst [(Mn4 O4 )(V4 O13 )(OAc)3 ]3- . Simulated IR spectra show that V=O stretching vibrations in the 900-1000 cm-1 region shift consistently by about 20 cm-1 per oxidation equivalent. Multiple bands in the 1450-1550 cm-1 region also change systematically upon oxidation/reduction. The computed UV/Vis spectra predict that the spectral range above 350 nm is characteristic of the managanese-oxo cubane oxidation state, whereas transitions at higher energy are due to the vanadate ligand. The presence of absorption signals above 680 nm is indicative of the presence of MnIII atoms. Spectroelectrochemical measurements of the oxidation from [Mn 2 III Mn 2 IV ] to [Mn 4 IV ] showed that the change in oxidation state can indeed be tracked by both IR and UV/Vis spectroscopy.


Subject(s)
Manganese , Water , Catalysis , Oxidation-Reduction , Oxygen
3.
Chemistry ; 21(23): 8380-3, 2015 Jun 01.
Article in English | MEDLINE | ID: mdl-25906986

ABSTRACT

A novel octacobalt-containing polyoxoniobate, Na6 K12 [H2 Co8 O4 (Nb6 O19 )4 ]⋅39 H2 O, has been prepared by a combination of hydrothermal and diffusion methods. The polyanion [H2 Co8 O4 (Nb6 O19 )4 ](18-) incorporates a tetrameric assembly of Lindqvist-type [Nb6 O19 ](8-) fragments trapping a {Co(II) 4 Co(III) 4 } cluster which comprises a central {Co(III) 4 O4 } cubane core, surrounded by another four Co(II) ions linkers. Furthermore, magnetic measurements show that the compound exhibits antiferromagnetic interactions.

4.
Chem Biol Interact ; 222: 87-96, 2014 Oct 05.
Article in English | MEDLINE | ID: mdl-25451568

ABSTRACT

Polyoxometalates (POMs) are early transition metal oxygen anion clusters. They display interesting biological effects mainly related to their antiviral and antitumor properties. On the other hand, copper compounds also show different biological and pharmacological effects in cell culture and in animal models. We report herein for the first time, a detailed study of the mechanisms of action of a copper(II) compound of the group of HPOMs with the formula K7Na3[Cu4(H2O)2(PW9034)2]20H2O (PW9Cu), in a model of human osteosarcoma derived cell line, MG-63. The compound inhibited selectively the viability of the osteosarcoma cells in the range of 25-100µM (p<0.01). Besides, we have clearly shown a more deleterious action of PW9Cu on tumor osteoblasts than in normal cells. Cytotoxicity studies also showed deleterious effects for PW9Cu. The increment of reactive oxygen species (ROS) and the decrease of the GSH/GSSG ratio were involved in the antiproliferative effects of PW9Cu. Moreover, the compound caused cell cycle arrest in G2 phase, triggering apoptosis as determined by flow cytometry. As a whole, these results showed the main mechanisms of the deleterious effects of PW9Cu in the osteosarcoma cell line MG-63, demonstrating that this compound is a promissory agent for cancer treatments.


Subject(s)
Antineoplastic Agents/pharmacology , Bone Neoplasms/drug therapy , Coordination Complexes/pharmacology , Copper/pharmacology , Osteosarcoma/drug therapy , Oxides/pharmacology , Tungsten Compounds/pharmacology , Antineoplastic Agents/chemistry , Apoptosis/drug effects , Bone Neoplasms/metabolism , Bone Neoplasms/pathology , Cell Cycle Checkpoints/drug effects , Cell Line, Tumor , Cell Survival/drug effects , Coordination Complexes/chemistry , Copper/chemistry , DNA Fragmentation , Glutathione/metabolism , Humans , Lysosomes/drug effects , Lysosomes/metabolism , Membrane Potential, Mitochondrial/drug effects , Osteosarcoma/metabolism , Osteosarcoma/pathology , Oxidative Stress/drug effects , Oxides/chemistry , Phosphatidylserines/metabolism , Tungsten Compounds/chemistry
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