On the Spectral Similarities between 1,2,6,7-Tetracyano-3,5-dihydro-3,5-diiminopyrrolizinato Complexes and Phthalocyanines – X-ray Crystal and Molecular Structure of Two Mixed Monopyrrolizinato Nickel(II) Complexes with the 2,4-tert-Butylacetylacetonide Ligand

Flamini, Alberto; Fares, Vincenzo; Pifferi, Augusto

doi:10.1002/(sici)1099-0682(200003)2000:3<537::aid-ejic537>3.0.co;2-z

Cited by 8 publications

(6 citation statements)

References 21 publications

(41 reference statements)

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“…When observed in amounts sufficient to characterize their spectroscopic properties, they were found to be high-spin, low-spin, or a mixture of these two cases. In general, the spin state of a Ni(II) complex depends on the relationship between the ligand field strength of the equatorial vs potential axial ligands (e.g., thermochromism and solvatochromism). − The gradual substitutions of water oxygens with peptide nitrogens bring the initially octahedral complexes closer to the spin crossover limit. In complexes involving main chain peptide nitrogen coordination equatorial 1N and 2N complexes are always high-spin and 4N complexes are always low-spin.…”

Section: Discussionmentioning

confidence: 99%

Human Annexins A1, A2, and A8 as Potential Molecular Targets for Ni(II) Ions

Wezynfeld

Bossak

Goch

et al. 2014

Chem. Res. Toxicol.

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Nickel is harmful for humans, but molecular mechanisms of its toxicity are far from being fully elucidated. One of such mechanisms may be associated with the Ni(II)-dependent peptide bond hydrolysis, which occurs before Ser/Thr in Ser/Thr-Xaa-His sequences. Human annexins A1, A2, and A8, proteins modulating the immune system, contain several such sequences. To test if these proteins are potential molecular targets for nickel toxicity we characterized the binding of Ni(II) ions and hydrolysis of peptides Ac-KALTGHLEE-am (A1-1), Ac-TKYSKHDMN-am (A1-2), and Ac-GVGTRHKAL-am (A1-3), from annexin A1, Ac-KMSTVHEIL-am (A2-1) and Ac-SALSGHLET-am (A2-2), from annexin A2, and Ac-VKSSSHFNP-am (A8-1), from annexin A8, using UV-vis and circular dichroism (CD) spectroscopies, potentiometry, isothermal titration calorimetry, high-performance liquid chromatography (HPLC), and electrospray ionization mass spectrometry (ESI-MS). We found that at physiological conditions (pH 7.4 and 37 °C) peptides A1-2, A1-3, A8-1, and to some extent A2-2 bind Ni(II) ions sufficiently strongly in 4N complexes and are hydrolyzed at sufficiently high rates to justify the notion that these annexins can undergo nickel hydrolysis in vivo. These results are discussed in the context of specific biochemical interactions of respective proteins. Our results also expand the knowledge about Ni(II) binding to histidine peptides by determination of thermodynamic parameters of this process and spectroscopic characterization of 3N complexes. Altogether, our results indicate that human annexins A1, A2, and A8 are potential molecular targets for nickel toxicity and help design appropriate cellular studies.

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Section: Discussionmentioning

confidence: 99%

Human Annexins A1, A2, and A8 as Potential Molecular Targets for Ni(II) Ions

Wezynfeld

Bossak

Goch

et al. 2014

Chem. Res. Toxicol.

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“…The formation of 1 accordingly implies oxidation of Co II to Co III by the oxygen dissolved in the solvent. The instability of the oxidation state Co II in solution is well recognized [42,44,55]. For reactions performed in O 2 atmosphere it is found that virtually complete oxidation of Co II to Co III had occurred.…”

Section: Oxidation Of Co II To Co Iiimentioning

confidence: 99%

Syntheses, Structures, and Polymorphism of β‐Diketonato Complexes – Co(thd)₃

Ahmed

Fjellvåg

Kjekshus

et al. 2007

Zeitschrift anorg allge chemie

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Oxidation of Co(thd) 2 dissolved in different solvents has been investigated in air and oxygen atmosphere. In oxygen atmosphere and at the boiling point of the solvents this treatment leads to oxidation of Co II to Co III , but also to degradation of some of the thd ligands and formation of a new mixed-ligand complex. Three pure-cultivated crystalline Co(thd) 3 phases are reported: 1 (room-temperature phase), 2 (low-temperature phase), and 3 (metastable phase) and in addition there exists an amorphous Co(thd) 3 phase (4) with approximate composition Co(thd) 3 · xH(thd); x ϭ 0.06. Reaction of metal(II) oxides (MO, M ϭ Mn, Fe, and Co) with H(thd) under air or O 2 atmosphere is an easy direct route to M(thd) 3 complexes. Structure determinations are reported for Co(thd) 3 (1Ϫ3) based on single-crystal X-ray diffraction data. Modification 1 crystallizes in space group P3c1 with a ϭ b ϭ 18.8100(10), c ϭ 18.815(2) Å at 295 K; R(wR2) ϭ 0.180, modification 2 in space group C2/c with a ϭ 28.007(12), b ϭ 18.482(8), 247 c ϭ 21.356(9) Å , β ϭ 97.999(5)°at 100 K; R(wR2) ϭ0.211, and modification 3 in space group Pnma with a ϭ 19.2394(15), b ϭ 18.8795(15), c ϭ 10.7808(8) Å at 100 K; R(wR2) ϭ 0.193. The molecular structures of 1Ϫ3 all comprise a central Co atom octahedrally co-ordinated by the ketonato O atoms of three thd ligands.The transformation between modifications 1 and 2 is of a fully reversible second-order character. Modifications 1 and 3 are, on the other hand, related by a quasi-reversible cycle. Heat treatment (specifically sublimation) of 1 leads to 3 whereas re-crystallization or prolonged storage at room temperature is required to regenerate 1. Co(thd) 3 has sufficient thermal stability to permit sublimation without degradation. The various forms of Co(thd) 3 are all diamagnetic, viz. a confirmation of the Co III valence state.

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“…A pivotal property of nickel( II ) complexes11–16 is that they exhibit the unique solvatochromism and thermochromism induced by the transformation of the nickel( II ) spin state between a low‐spin ( S =0) state with a tetracoordinate square‐planar structure and a high‐spin ( S =1) state with a hexacoordinate octahedral geometry,17, 18 triggered by the coordination of two solvent molecules to the nickel ion. The importance of control over nickel( II ) spin states has recognized not only in inorganic chemistry,17–20 but also in biological chemistry,21, 22 since it promotes the development of molecular memories and switches9, 17–20 as well as leading to further understanding of biological systems 21.…”

Section: Introductionmentioning

confidence: 99%