Understanding the Coordination Modes of [Cu(acac)2(imidazole)n=1,2] Adducts by EPR, ENDOR, HYSCORE, and DFT Analysis

Ritterskamp, Nadine; Sharples, Katherine Mary; Richards, Emma; Folli, Andrea; Chiesa, Mario; Platts, James Alexis; Murphy, D. M.

doi:10.1021/acs.inorgchem.7b01874

Cited by 20 publications

(20 citation statements)

References 65 publications

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“…Structure solution and refinement in the monoclinic space group C2/c revealed the structure of a tetranuclear complex of the formula [Ni 4 (OCH 3 ) 4 (acac) 4 (CH 3 OH) 4 ] (Figure S12 and Tables S3-S4 in the Supplementary Materials). This heterocubane-type compound was already reported [81] Our values recorded for [Cu(acac)2] are very similar to those from previous reports [84][85][86][87][88][89]. The higher HFS is in line with a lower degree of spin delocalisation from Cu II over the ligand for opocompared with acac -.…”

Section: Epr Spectroscopy For [Cu(opo)2] and [Fe(opo)3]supporting

confidence: 89%

“…In solution [Cu(acac)2] adds coordinating solvent molecules in the two axial positions to form hexacoordinate species [Cu(acac)2(L)2] what has been studied in detail using EPR spectroscopy [84][85][86] and we assume the same behaviour for [Cu(opo)2]. Very similar spectra were obtained for the opo and acac complexes (Figure 3 The bond distances and angles are very similar to those reported previously for [Fe(opo) 3 ]•DMSO [57] and also to those of [Fe(acac) 3 ] [74], proving the high similarity of the two ligands.…”

Section: Epr Spectroscopy For [Cu(opo)2] and [Fe(opo)3]mentioning

confidence: 99%

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FeIII, CuII and ZnII Complexes of the Rigid 9-Oxido-phenalenone Ligand—Spectroscopy, Electrochemistry, and Cytotoxic Properties

Butsch

Haseloer

Schmitz

et al. 2021

IJMS

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The three complexes [Fe(opo)3], [Cu(opo)2], and [Zn(opo)2] containing the non-innocent anionic ligand opo− (opo− = 9-oxido-phenalenone, Hopo = 9-hydroxyphenalonone) were synthesised from the corresponding acetylacetonates. [Zn(opo)2] was characterised using 1H nuclear magnetic resonance (NMR) spectroscopy, the paramagnetic [Fe(opo)3] and [Cu(opo)2] by electron paramagnetic resonance (EPR) spectroscopy. While the EPR spectra of [Cu(opo)2] and [Cu(acac)2] in dimethylformamide (DMF) solution are very similar, a rather narrow spectrum was observed for [Fe(opo)3] in tetrahydrofuran (THF) solution in contrast to the very broad spectrum of [Fe(acac)3] in THF (Hacac = acetylacetone, 2,4-pentanedione; acac− = acetylacetonate). The narrow, completely isotropic signal of [Fe(opo)3] disagrees with a metal-centred S = 5/2 spin system that is observed in the solid state. We assume spin-delocalisation to the opo ligand in the sense of an opo− to FeIII electron transfer. All compounds show several electrochemical opo-centred reduction waves in the range of −1 to −3 V vs. the ferrocene/ferrocenium couple. However, for CuII and FeIII the very first one-electron reductions are metal-centred. Electronic absorption in the UV to vis range are due to π–π* transitions in the opo core, giving Hopo and [Zn(opo)2] a yellow to orange colour. The structured bands ranging from 400 to 500 for all compounds are assigned to the lowest energy π−π* transitions. They show markedly higher intensities and slight shifts for the CuII (brown) and FeIII (red) complexes and we assume admixing metal contributions (MLCT for CuII, LMCT for FeIII). For both complexes long-wavelength absorptions assignable to d–d transitions were detected. Detailed spectroelectrochemical experiments confirm both the electrochemical and the optical assignments. Hopo and the complexes [Cu(opo)2], [Zn(opo)2], and [Fe(opo)3] show antiproliferative activities against HT-29 (colon cancer) and MCF-7 (breast cancer) cell lines in the range of a few µM, comparable to cisplatin under the same conditions.

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Section: Epr Spectroscopy For [Cu(opo)2] and [Fe(opo)3]supporting

confidence: 89%

Section: Epr Spectroscopy For [Cu(opo)2] and [Fe(opo)3]mentioning

confidence: 99%

FeIII, CuII and ZnII Complexes of the Rigid 9-Oxido-phenalenone Ligand—Spectroscopy, Electrochemistry, and Cytotoxic Properties

Butsch

Haseloer

Schmitz

et al. 2021

IJMS

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“…Imidazoles are an important class of very stable aromatic N-heterocycles frequently found in natural products, metalloenzymes, pharmaceuticals and other functional synthetics (Fox, 1943;Sezen & Sames, 2003;Ritterskamp et al, 2017;Vargas-Oviedo et al, 2017). Today, the wide variety of studies on imidazole synthesis have become a 'master key' of research due to the wide range of applications of imidazole derivatives in diverse biological and industrial processes (Vichier-Guerre et al, 2016;Arepally et al, 2017;Rajendiran et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Studies via X-ray analysis on intermolecular interactions and energy frameworks based on the effects of substituents of three 4-aryl-2-methyl-1H-imidazoles of different electronic nature and their in vitro antifungal evaluation

et al. 2018

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The crystal structures of 2‐methyl‐4‐phenyl‐1H‐imidazole, C10H10N2, (3a), 4‐(4‐chlorophenyl)‐2‐methyl‐1H‐imidazole hemihydrate, C10H9ClN2·0.5H2O, (3b), and 4‐(4‐methoxyphenyl)‐2‐methyl‐1H‐imidazole, C11H12N2O, (3c), have been analyzed. It was found that the electron‐donating/withdrawing tendency of the substituent groups in the aryl ring influence the acid–base properties of the 2‐methylimidazole nucleus, changing the strength of the intermolecular N—H…N interactions. This behaviour not only influences the crystal structure but also seems to have an important effect on the antifungal activity. Considering the substituent groups, that is, H in (3a), Cl in (3b) and OMe in (3c), the formation of strong N—H…N connections has the probability (3a) > (3b) > (3c), while compound (3c) proves to be more active than (3a) and (3b) at all concentrations against C. neoformans.

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“…As reference groups we have somewhat arbitrarily chosen those of Marina Bennati (Göttingen) [209][210][211], Robert Bittl (Berlin) [212][213][214], Dave Britt (UC Davis) [215][216][217], Jack Freed (Cornell) [218][219][220], Daniella Goldfarb (Weizmann) [221][222][223], Brian Hoffman (Northwestern) [224][225][226], Gunnar Jeschke (Zurich) [227][228][229], Chris Kay (London) [230,231], Yasuhiro Kobori (Kobe) [232][233][234], Wolfgang Lubitz (Mülheim/Ruhr) [235][236][237], Damian Murphy (Cardiff) [238][239][240], Thomas Prisner (Frankfurt/Main) [241][242][243], Christiane Timmel (Oxford) [244][245][246], Sabine van Doorslaer (Antwerp) [247][248][249], and Stefan Weber (Freiburg) [250][251][252].…”

Section: Pulse Endormentioning

confidence: 99%

Biomolecular EPR Meets NMR at High Magnetic Fields

et al. 2018

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In this review on advanced biomolecular EPR spectroscopy, which addresses both the EPR and NMR communities, considerable emphasis is put on delineating the complementarity of NMR and EPR regarding the measurement of interactions and dynamics of large molecules embedded in fluid-solution or solid-state environments. Our focus is on the characterization of protein structure, dynamics and interactions, using sophisticated EPR spectroscopy methods. New developments in pulsed microwave and sweepable cryomagnet technology as well as ultrafast electronics for signal data handling and processing have pushed the limits of EPR spectroscopy to new horizons reaching millimeter and sub-millimeter wavelengths and 15 T Zeeman fields. Expanding traditional applications to paramagnetic systems, spin-labeling of biomolecules has become a mainstream multifrequency approach in EPR spectroscopy. In the high-frequency/high-field EPR region, sub-micromolar concentrations of nitroxide spin-labeled molecules are now sufficient to characterize reaction intermediates of complex biomolecular processes. This offers promising analytical applications in biochemistry and molecular biology where sample material is often difficult to prepare in sufficient concentration for NMR characterization. For multifrequency EPR experiments on frozen solutions typical sample volumes are of the order of 250 μL (S-band), 150 μL (X-band), 10 μL (Q-band) and 1 μL (W-band). These are orders of magnitude smaller than the sample volumes required for modern liquid- or solid-state NMR spectroscopy. An important additional advantage of EPR over NMR is the ability to detect and characterize even short-lived paramagnetic reaction intermediates (down to a lifetime of a few ns). Electron–nuclear and electron–electron double-resonance techniques such as electron–nuclear double resonance (ENDOR), ELDOR-detected NMR, PELDOR (DEER) further improve the spectroscopic selectivity for the various magnetic interactions and their evolution in the frequency and time domains. PELDOR techniques applied to frozen-solution samples of doubly spin-labeled proteins allow for molecular distance measurements ranging up to about 100 Å. For disordered frozen-solution samples high-field EPR spectroscopy allows greatly improved orientational selection of the molecules within the laboratory axes reference system by means of the anisotropic electron Zeeman interaction. Single-crystal resolution is approached at the canonical g-tensor orientations—even for molecules with very small g-anisotropies. Unique structural, functional, and dynamic information about molecular systems is thus revealed that can hardly be obtained by other analytical techniques. On the other hand, the limitation to systems with unpaired electrons means that EPR is less widely used than NMR. However, this limitation also means that EPR offers greater specificity, since ordinary chemical solvents and matrices do not give rise to EPR in contrast to NMR spectra. Thus, multifrequency EPR spectroscopy plays an important role in better understanding paramagnetic species such as organic and inorganic radicals, transition metal complexes as found in many catalysts or metalloenzymes, transient species such as light-generated spin-correlated radical pairs and triplets occurring in protein complexes of photosynthetic reaction centers, electron-transfer relays, etc. Special attention is drawn to high-field EPR experiments on photosynthetic reaction centers embedded in specific sugar matrices that enable organisms to survive extreme dryness and heat stress by adopting an anhydrobiotic state. After a more general overview on methods and applications of advanced multifrequency EPR spectroscopy, a few representative examples are reviewed to some detail in two Case Studies: (I) High-field ELDOR-detected NMR (EDNMR) as a general method for electron–nuclear hyperfine spectroscopy of nitroxide radical and transition metal containing systems; (II) High-field ENDOR and EDNMR studies of the Oxygen Evolving Complex (OEC) in Photosystem II, which performs water oxidation in photosynthesis, i.e., the light-driven splitting of water into its elemental constituents, which is one of the most important chemical reactions on Earth.

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Understanding the Coordination Modes of [Cu(acac)₂(imidazole)_n=1,2] Adducts by EPR, ENDOR, HYSCORE, and DFT Analysis

Cited by 20 publications

References 65 publications

FeIII, CuII and ZnII Complexes of the Rigid 9-Oxido-phenalenone Ligand—Spectroscopy, Electrochemistry, and Cytotoxic Properties

FeIII, CuII and ZnII Complexes of the Rigid 9-Oxido-phenalenone Ligand—Spectroscopy, Electrochemistry, and Cytotoxic Properties

Studies via X-ray analysis on intermolecular interactions and energy frameworks based on the effects of substituents of three 4-aryl-2-methyl-1H-imidazoles of different electronic nature and their in vitro antifungal evaluation

Biomolecular EPR Meets NMR at High Magnetic Fields

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