Category Archives: Inorg Chem

Conflicting Role of Water in the Activation of H2O2 and the Formation and Reactivity of Non-Heme Fe(III)-OOH and Fe(III)-O-Fe(III) Complexes at Room Temperature.

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Conflicting Role of Water in the Activation of H2O2 and the Formation and Reactivity of Non-Heme Fe(III)-OOH and Fe(III)-O-Fe(III) Complexes at Room Temperature.

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Spectroscopic Analyses on Reaction Intermediates Formed during Chlorination of Alkanes with NaOCl Catalyzed by a Nickel Complex.

Spectroscopic Analyses on Reaction Intermediates Formed during Chlorination of Alkanes with NaOCl Catalyzed by a Nickel Complex.

Inorg Chem. 2015 Nov 5;

Authors: …

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Correlation between the Stereochemistry and Bioactivity in Octahedral Rhodium Prolinato Complexes.

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Correlation between the Stereochemistry and Bioactivity in Octahedral Rhodium Prolinato Complexes.

Inorg Chem. 2015 Aug 7;

Authors: Rajaratnam R, Martin EK, Dörr M, Harms K, Casini A, Meggers E

Abstract
Controlling the relative and absolute configuration of octahedral metal complexes constitutes a key challenge that needs to be overcome in order to fully exploit the structural properties of octahedral metal complexes for applications in the fields of catalysis, materials sciences, and life sciences. Herein, we describe the application of a proline-based chiral tridentate ligand to decisively control the coordination mode of an octahedral rhodium(III) complex. We demonstrate the mirror-like relationship of synthesized enantiomers and differences between diastereomers. Further, we demonstrate, using the established pyridocarbazole pharmacophore ligand as part of the organometallic complexes, the importance of the relative and absolute stereochemistry at the metal toward chiral environments like protein kinases. Protein kinase profiling and inhibition data confirm that the proline-based enantiopure rhodium(III) complexes, despite having all of the same constitution, differ strongly in their selectivity properties despite their unmistakably mutual origin. Moreover, two exemplary compounds have been shown to induce different toxic effects in an ex vivo rat liver model.

PMID: 26251218 [PubMed – as supplied by publisher]

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Reduction of (Formazanate)boron Difluoride Provides Evidence for an N-Heterocyclic B(I) Carbenoid Intermediate.

Reduction of (Formazanate)boron Difluoride Provides Evidence for an N-Heterocyclic B(I) Carbenoid Intermediate.
Inorg Chem. 2015 Aug 7;
Authors: Chang MC, Otten E
Abstract
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Nonheme Fe(IV) Oxo Complexes of Two New Pentadentate Ligands and Their Hydrogen-Atom and Oxygen-Atom Transfer Reactions.

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Nonheme Fe(IV) Oxo Complexes of Two New Pentadentate Ligands and Their Hydrogen-Atom and Oxygen-Atom Transfer Reactions.

Inorg Chem. 2015 Jul 22;

Authors: Mitra M, Nimir H, Demeshko S, Bhat SS, Malinkin SO, Haukka M, Lloret-Fillol J, Lisensky GC, Meyer F, Shteinman AA, Browne WR, Hrovat DA, Richmond MG, Costas M, Nordlander E

Abstract
Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) framework have been synthesized, viz. [N-(1-methyl-2-benzimidazolyl)methyl-N-(2-pyridyl)methyl-N-(bis-2-pyridyl methyl)amine] (L(1)) and [N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L(2)), where one or two pyridyl arms of N4Py have been replaced by corresponding (N-methyl)benzimidazolyl-containing arms. The complexes [Fe(II)(CH3CN)(L)](2+) (L = L(1) (1); L(2) (2)) were synthesized, and reaction of these ferrous complexes with iodosylbenzene led to the formation of the ferryl complexes [Fe(IV)(O)(L)](2+) (L = L(1) (3); L(2) (4)), which were characterized by UV-vis spectroscopy, high resolution mass spectrometry, and Mössbauer spectroscopy. Complexes 3 and 4 are relatively stable with half-lives at room temperature of 40 h (L = L(1)) and 2.5 h (L = L(2)). The redox potentials of 1 and 2, as well as the visible spectra of 3 and 4, indicate that the ligand field weakens as ligand pyridyl substituents are progressively substituted by (N-methyl)benzimidazolyl moieties. The reactivities of 3 and 4 in hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions show that both complexes exhibit enhanced reactivities when compared to the analogous N4Py complex ([Fe(IV)(O)(N4Py)](2+)), and that the normalized HAT rates increase by approximately 1 order of magnitude for each replacement of a pyridyl moiety; i.e., [Fe(IV)(O)(L(2))](2+) exhibits the highest rates. The second-order HAT rate constants can be directly related to the substrate C-H bond dissociation energies. Computational modeling of the HAT reactions indicates that the reaction proceeds via a high spin transition state.

PMID: 26198840 [PubMed – as supplied by publisher]

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Reactivity of Cys4 Zinc Finger Domains with Gold(III) Complexes: Insights into the Formation of “Gold Fingers”.

Reactivity of Cys4 Zinc Finger Domains with Gold(III) Complexes: Insights into the Formation of “Gold Fingers”.

Inorg Chem. 2015 Apr 3;

Authors: Jacques A, Lebrun C, Casini A, Kieffer I, Proux O, Latour JM, Sénèque O

Abstract
Gold(I) complexes such as auranofin or aurothiomalate have been used as therapeutic agents for the treatment of rheumatoid arthritis for several decades. Several gold(I) and gold(III) complexes have also shown in vitro anticancer properties against human cancer cell lines, including cell lines resistant to cisplatin. Because of the thiophilicity of gold, cysteine-containing proteins appear as likely targets for gold complexes. Among them, zinc finger proteins have attracted attention and, recently, gold(I) and gold(III) complexes have been shown to inhibit poly(adenosine diphosphate ribose)polymerase-1 (PARP-1), which is an essential protein involved in DNA repair and in cancer resistance to chemotherapies. In this Article, we characterize the reactivity of the gold(III) complex [Au(III)(terpy)Cl]Cl2 (Auterpy) with a model of Zn(Cys)4 “zinc ribbon” zinc finger by a combination of absorption spectroscopy, circular dichroism, mass spectrometry, high-performance liquid chromatography analysis, and X-ray absorption spectroscopy. We show that the Zn(Cys)4 site of Zn·LZR is rapidly oxidized by Auterpy to form a disulfide bond. The Zn(2+) ion is released, and the two remaining cysteines coordinate the Au(+) ion that is produced during the redox reaction. Subsequent oxidation of these cysteines can take place in conditions of excess gold(III) complex. In the presence of excess free thiols mimicking the presence of glutathione in cells, mixing of the zinc finger model and gold(III) complex yields a different product: complex (Au(I))2·LZR with two Au(+) ions bound to cysteines is formed. Thus, on the basis of detailed speciation and kinetic measurements, we demonstrate herein that the destruction of Zn(Cys)4 zinc fingers by gold(III) complexes to achieve the formation of “gold fingers” is worth consideration, either directly or mediated by reducing agents.

PMID: 25839236 [PubMed – as supplied by publisher]

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Formazanate Ligands as Structurally Versatile, Redox-Active Analogues of β-Diketiminates in Zinc Chemistry.

Formazanate Ligands as Structurally Versatile, Redox-Active Analogues of β-Diketiminates in Zinc Chemistry.

Inorg Chem. 2014 Dec 10;

Authors: Chang MC, Roewen P, Travieso-Puente R, Lutz M, Otten E

Abstract
A range of tetrahedral bis(formazanate)zinc complexes with different steric and electronic properties of the formazanate ligands were synthesized. The solid-state structures for several of these were determined by X-ray crystallography, which showed that complexes with symmetrical, unhindered ligands prefer coordination to the zinc center via the terminal N atoms of the NNCNN ligand backbone. Steric or electronic modifications can override this preference and give rise to solid-state structures in which the formazanate ligand forms a 5-membered chelate by binding to the metal center via an internal N atom. In solution, these compounds show dynamic equilibria that involve both 5- and 6-membered chelates. All compounds are intensely colored, and the effect of the ligand substitution pattern on the UV-vis absorption spectra was evaluated. In addition, their cyclic voltammetry is reported, which shows that all compounds may be electrochemically reduced to radical anionic (L2Zn(-)) and dianionic (L2Zn(2-)) forms. While unhindered NAr substituents lie in the plane of the ligand backbone (Ar = Ph), the introduction of sterically demanding substituents (Ar = Mes) favors a perpendicular orientation in which the NMes group is no longer in conjugation with the backbone, resulting in hypsochromic shifts in the absorption spectra. The redox potentials in the series of L2Zn compounds may be altered in a straightforward manner over a relatively wide range (∼700 mV) via the introduction of electron-donating or -withdrawing substituents on the formazanate framework.

PMID: 25493709 [PubMed – as supplied by publisher]

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Caffeine-Based Gold(I) N-Heterocyclic Carbenes as Possible Anticancer Agents: Synthesis and Biological Properties.

Caffeine-Based Gold(I) N-Heterocyclic Carbenes as Possible Anticancer Agents: Synthesis and Biological Properties.
Inorg Chem. 2014 Feb 5;
Authors: Bertrand B, Stefan L, Pirrotta M, Monchaud D, Bodio E, Richard P, Le Gendre P,… Continue reading

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Anionogenic Mixed Valency in KxBa1-xO2-δ

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Anionogenic Mixed Valency in KxBa1-xO2-δ

Inorg Chem. 2013 Dec 11;

Authors: Giriyapura S, Zhang B, de Groot RA, de Wijs GA, Caretta A, van Loosdrecht PH, Kockelmann W, Palstra TT, Blake GR

Abstract
We have synthesized members of an isostructural solid solution series KxBa1-xO2-δ (x < 0.41, δ < 0.11) containing mixed-valent dioxygen anions. Synthesis in liquid ammonia solution allows a continuous range of compounds to be prepared. X-ray and neutron diffraction show that KxBa1-xO2-δ adopts the tetragonal rocksalt-derived structure of the end members KO2 and BaO2, without any structural phase transition down to 5 K, the lowest temperature studied here. We identify four oxygen-oxygen stretching modes above 750 cm(-1) in the measured Raman spectra, unlike the spectra of KO2 and BaO2 which both contain just a single mode. We use density functional theory calculations to show that the stretching modes in KxBa1-xO2-δ arise from in-phase and anti-phase coupling of the stretching of nearest-neighbor oxygen dimers when the valence state of the dimers lies between -1 and -2 because of mixed cation coordination. This coupling is a direct signature of a novel type of anionogenic mixed valency.

PMID: 24328297 [PubMed – as supplied by publisher]

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Cobalt Corrole Catalyst for Efficient Hydrogen Evolution Reaction from H2O under Ambient Conditions: Reactivity, Spectroscopy, and Density Functional Theory Calculations.

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Cobalt Corrole Catalyst for Efficient Hydrogen Evolution Reaction from H2O under Ambient Conditions: Reactivity, Spectroscopy, and Density Functional Theory Calculations.

Inorg Chem. 2013 Mar 18;52(6):3381-7

Authors: Mondal B, Sengupta K, Rana A, Mahammed A, Botoshansky M, Dey SG, Gross Z, Dey A

Abstract
The feasibility of a hydrogen-based economy relies very much on the availability of catalysts for the hydrogen evolution reaction (HER) that are not based on Pt or other noble elements. Significant breakthroughs have been achieved with certain first row transition metal complexes in terms of low overpotentials and large turnover rates, but the majority of reported work utilized purified and deoxygenated solvents (most commonly mixtures of organic solvents/acids). Realizing that the design of earth abundant metal catalysts that operate under truly ambient conditions remains an unresolved challenge, we have now developed an electronically tuned Co(III) corrole that can catalyze the HER from aqueous sulfuric acid at as low as -0.3 V vs NHE, with a turnover frequency of 600 s(-1) and ≫10(7) catalytic turnovers. Under aerobic conditions, using H2O from naturally available sources without any pretreatment, the same complex catalyzes the reduction of H(+) with a Faradaic Yield (FY) of 52%. Density functional theory (DFT) calculations indicate that the electron density on a putative hydride species is delocalized off from the H atom into the macrocycle. This makes the protonation of a [Co(III)-H](-) species the rate determining step (rds) for the HER consistent with the experimental data.

PMID: 23445187 [PubMed – in process]

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Ligand exchange and spin state equilibria of Fe(II)(N4Py) and related complexes in aqueous media.

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Ligand exchange and spin state equilibria of Fe(II)(N4Py) and related complexes in aqueous media.
Inorg Chem. 2012 Jan 16;51(2):900-13
Authors: Draksharapu A, Li Q, Logtenberg H, van den Berg TA, Meetsma A, Ki… Continue reading

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DNA cleavage activity of Fe(II)N4Py under photo irradiation in the presence of 1,8-naphthalimide and 9-aminoacridine: unexpected effects of reactive oxygen species scavengers.

DNA cleavage activity of Fe(II)N4Py under photo irradiation in the presence of 1,8-naphthalimide and 9-aminoacridine: unexpected effects of reactive oxygen species scavengers.

Inorg Chem….

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