The Glutathione/Metallothionein System Challenges the Design of Efficient O2‐Activating Copper Complexes

Copper complexes are of medicinal and biological interest, including as anticancer drugs designed to cleave intracellular biomolecules by O₂ activation. To exhibit such activity, the copper complex must be redox active and resistant to dissociation. Metallothioneins (MTs) and glutathione (GSH) are abundant in the cytosol and nucleus. Because they are thiol‐rich reducing molecules with high Cu^I affinity, they are potential competitors for a copper ion bound in a copper drug. Herein, we report the investigation of a panel of Cu^I/Cu^II complexes often used as drugs, with diverse coordination chemistries and redox potentials. We evaluated their catalytic activity in ascorbate oxidation based on redox cycling between Cu^I and Cu^II, as well as their resistance to dissociation or inactivation under cytosolically relevant concentrations of GSH and MT. O₂‐activating Cu^I/Cu^II complexes for cytosolic/nuclear targets are generally not stable against the GSH/MT system, which creates a challenge for their future design.     

The Cu(I)–glutathione complex: factors affecting its formation and capacity to generate reactive oxygen species

Cu²⁺ ions and reduced glutathione (GSH) swiftly interact to form the physiologically occurring Cu(I)–[GSH]₂ complex. Prompted by the recently reported ability of this complex to generate superoxide radicals from molecular oxygen, the present study addressed how the concentration of Cu²⁺ and GSH, the pH, and the temperature affect the formation of the Cu(I)–[GSH]₂ complex and its capacity to generate superoxide radicals and hydrogen peroxide. Increasing concentrations of Cu²⁺ and GSH, added at a fixed molar ratio of 1:3, led to a proportionally greater production of superoxide anions, hydrogen peroxide, and oxidized glutathione (GSSG). GSSG formation was found to closely reflect the formation of Cu(I)–[GSH]₂. Biologically relevant changes in pH (e.g., from 6.8 to 7.7) and temperature (from 22 to 37 °C) did not affect the formation of the Cu(I)–[GSH]₂, as assessed by GSSG production. However, production of superoxide radicals increased as the pH values were incremented. An opposite effect was observed regarding hydrogen peroxide production. The ability of a freshly prepared Cu(I)–[GSH]₂ complex (assayed within a minute from its formation) to generate superoxide radicals was incremented by as the temperature was increased. Such ability, however, correlated inversely with the temperature when, before assaying for superoxide, the earlier referred preparation was incubated during 30 min in the presence of oxygen. Under the latter condition, hydrogen peroxide linearly accumulated in time, suggesting that an increased autodismutation underlies the apparent time-dependent “aging” of the capacity of the complex to generate superoxide.     

Electrochemical Investigation of the Role of Reducing Agents in Copper‐Catalyzed Nitric Oxide Release from S‐Nitrosoglutathione

Studies of nitric oxide (NO) release from S‐nitrosoglutathione (GSNO) decomposition by Cu²⁺ in the presence of reducing agents were performed using a nickel porphyrin and Nafion‐coated microsensor in order to compare the efficiency of sodium hydrosulfite (Na₂S₂O₄) and sodium borohydride (NaBH₄) to that of the most abundant endogenous reducer, glutathione (GSH). When it was mixed to Cu(NO₃)₂ and added to equimolar concentration of GSNO, each reducing agent caused a NO release (measured in terms of oxidation current) but only NaBH₄ induced a proportional rise if its concentration doubled and that of Cu²⁺ remained constant. For Na₂S₂O₄, there was a mild increase and for GSH, no change. Furthermore, when Cu²⁺ concentrations ranging from 0.5 to 5 μM were mixed with 2 μM reducing agent and added to 2 μM GSNO_, the NO oxidation current linearly increased with NaBH₄ and was constant with Na₂S₂O₄. Concerning GSH, Cu²⁺ dose‐dependently increased the NO release from GSNO only if the Cu²⁺‐to‐reducer ratio was ≤1. However, GSH formed the catalytic species Cu⁺ even in excess of Cu²⁺ and GSNO as indicated by suppression of the Cu²⁺/GSH‐induced NO release when the Cu⁺ chelator neocuproine was added to GSNO. This work shows that, among the 3 reducing agents, only NaBH₄ allows Cu²⁺ to dose‐dependently increase the NO release from GSNO for Cu²⁺‐to‐reducer ratios ranging from 0.25 to 2.5. Despite this good effectiveness, excess of NaBH₄ compared to both Cu²⁺ and GSNO seems to be required for optimal NO release.     

Study of the Interaction of Some Potential Anticancer Gold(III) Complexes with Biologically Important Thiols Using NMR,UV–Vis,and Electrochemistry

The interaction of gold(III) complexes [Au(en)Cl₂]Cl, [Au(en)₂]Cl₃, [Au(cis‐DACH)Cl₂]Cl, and [Au(cis‐DACH)₂]Cl₃ (en = ethylenediamine, DACH = cis‐1,2‐diaminocyclohexane) with biologically important thiols, such as glutathione (GSH), dl ‐penicillamine (PSH), mercaptoacetic acid (MAA), and N‐(2‐mercaptopropionyl)glycine (MPG), has been studied using ¹H, ¹³C NMR, UV–vis spectroscopy and electrochemistry in aqueous solution. Kinetic data revealed that the reactivity of their substitution reaction followed the order: [Au(en)Cl₂]⁺ > [Au(en)₂]³⁺ > [Au(cis‐DACH)Cl₂]⁺ > [Au(cis‐DACH)₂]³⁺. The thiol reactivity increased with decreasing its size, viz. MAA ≫ MPG > PSH > GSH. Square wave stripping voltammetry displayed peaks for Au(III) and Au(I) at +0.875 V and +1.4 V respectively. The interaction of the complexes with thiols resulted in reduction of gold(III) to gold(I) and thiol ligands (RSH) were oxidized to disulfide (RSSR).     

catena‐Poly[disodium [[diformato­tricopper(II)]‐di‐μ3‐formato‐tetra‐μ2‐formato]]: a new mode of bridging between binuclear and mononuclear formate–copper(II) units

The novel title polymeric copper(II) complex, {Na₂[Cu₃‐(CHO₂)₈]}_n, consists of sodium cations and infinite anionic chains, in which neutral dinuclear [Cu₂(O₂CH)₄] moieties alternate with dianionic [Cu(O₂CH)₄]²⁻ units. Both metal‐containing moieties are located on crystallographic inversion centers. The syn–syn bridging configuration between the mononuclear and dinuclear components yields a structure that is significantly more dense than the structures previously reported for mononuclear–dinuclear copper(II) carboxyl­ates with syn–anti or anti–anti bridging modes.     

Di‐μ‐hydroxido‐bis{[bis(6‐methyl‐2‐pyridylmethyl)(2‐phenylethyl)amine‐κ3N′,N′′,N′′′]copper(II)} bis(perchlorate)

The title compund, [Cu₂(OH)₂(C₂₂H₂₅N₃)₂](ClO₄)₂, is a copper(II) dimer, with two [CuL]²⁺ units [L is bis(6‐methyl‐2‐pyridylmethyl)(2‐phenylethyl)amine] bridged by hydroxide groups to define the {[CuL](μ‐OH)₂[CuL]}²⁺ cation. Charge balance is provided by perchlorate counter‐anions. The cation has a crystallographic inversion centre halfway between the Cu^II ions, which are separated by 3.0161 (8) Å. The central core of the cation is an almost regular Cu₂O₂ parallelogram of sides 1.931 (2) and 1.935 (2) Å, with a Cu—O—Cu angle of 102.55 (11)°. The coordination geometry around each Cu^II centre can be best described as a square‐based pyramid, with three N atoms from L ligands and two hydroxide O atoms completing the coordination environment. Each cationic unit is hydrogen bonded to two perchlorate anions by means of hydroxide–perchlorate O—H...O interactions.     

A New Polynuclear Copper‐Complex‐Substituted Tungstoarsenate(V)

A new polynuclear copper‐complex‐substituted dimeric tungstoarsenate(V), H₂[{Cu(2,2′‐bpy)}₈(H₂O)₂(AsW₉O₃₄)₂] · 12H₂O ( 1 ) (2,2′‐bpy = 2,2′‐bipydine), was synthesized hydrothermally and its structure was determined by single‐crystal X‐ray diffraction. The title compound has Ci symmetry and consists of two trilacunary Keggin anions [α‐AsW₉O₃₄]^9– supported by eight copper complex cations. The compound was also characterized by IR and fluorescence spectroscopy, TG analysis, and magnetic measurements. The emission spectrum of the compound in solid‐state exhibits a redshift relative to those of Na₈[A‐HAsW₉O₃₄] · 11H₂O and the free ligand 2,2′‐bpy. Magnetic measurements of the compound indicate competing ferro‐ and antiferromagnetic intramolecular coupling among the Cu^II atoms in the cluster anion.     

A Minimalist Approach to C?H Activation by Copper

The complex [Cu₂( 1 )₂]²⁺ ( 1 = 1,3‐bis(1‐methyl‐1H‐benzimidazol‐2‐yl)benzene) undergoes slow oxidation by dioxygen in DMF solution to give the hydroxylated product [Cu₂( 2 ‐H)₂]²⁺ ( 2 = 2,6‐bis(1‐methyl‐1H‐benzimidazol‐2‐yl)phenol) characterized by an X‐ray crystal‐structure analysis. The oxidation occurs much faster when Cu^II is mixed with 1 in the presence of H₂O₂, with 80% hydroxylation observed within a few minutes. The mononuclear complex formed with 1‐methyl‐2‐phenyl‐1H‐benzimidazole ( 3 ) shows no hydroxylation under these conditions. It is concluded that the hydroxylation requires the presence of a ligand capable of stabilizing a binuclear species, but no special coordinative activation of the copper is required.     

Facially Dispersed Polyhydride Cu9 and Cu16 Clusters Comprising Apex‐Truncated Supertetrahedral and Square‐Face‐Capped Cuboctahedral Copper Frameworks

By using a linear tetraphosphine, meso‐bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm), nona‐ and hexadecanuclear copper hydride clusters, [Cu₉H₇(μ‐dpmppm)₃]X₂ (X=Cl ( 1 a ), Br ( 1 b ), I ( 1 c ), PF₆ ( 1 d )) and [Cu₁₆H₁₄(μ‐dpmppm)₄]X₂ (X₂=I₂ ( 2 c ), (4/3) PF₆?(2/3) OH ( 2 d )) were synthesized and characterized. They form copper‐hydride cages of apex‐truncated supertetrahedral {Cu₉H₇}²⁺ and square‐face‐capped cuboctahedral {Cu₁₆H₁₄}²⁺ structures. The hydride positions were estimated by DFT calculations to be facially dispersed around the copper frameworks. A kinetically controlled synthesis gave an unsymmetrical Cu₈H₆ cluster, [Cu₈H₆(μ‐dpmppm)₃]²⁺ ( 3 ), which readily reacted with CO₂ to afford linear Cu₄ complexes with formate bridges, leading to an unprecedented hydrogenation of CO₂ into formate catalyzed by {Cu₄(μ‐dpmppm)₂} platform. The results demonstrate that new motifs of copper hydride clusters could be established by the tetraphosphine ligands, and the structures influence their reactivity.     

Sensitivity of Positive Ion Mode Electrospray Ionization Mass Spectrometry in the Analysis of Thiol Metabolites

High signal intensities of glutathione (GSH), [GSH+H]⁺ (m/z 308), cysteine (CySH), [CySH+H]⁺ (m/z 122), and homocysteine (hCySH), [hCySH+H]⁺ (m/z 136), are observed in ESI MS with on‐line electrochemistry (EC). Dimers formed by H‐bonding, which are not electrochemical products, are detected as [2GSH+H]⁺ (m/z 615), [2CySH+H]⁺ (m/z 243) and [2hCySH+H]⁺ (m/z 271) together with disulfide dimers GSSG, CySSCy and hCySSCyh, [GSSG+H]⁺ (m/z 613), [CySSCy+H]⁺ (m/z 241) and [hCySSCyh+H]⁺ (m/z 269). When dopamine is present a thiol/dopamine quinone (DAQ) adduct is observed. Formation of this adduct is proposed to occur by an electrochemical mechanism during ESI. Catalysis of thiol oxidation and analysis of thiol mixtures is addressed.     

Unified reciprocity of dithiophosphate by dichalcogenophosph(in)ate ligands on copper hydride nanoclusters via ligand exchange reaction

A structural study of ligand exchange on chalcogen‐passivated copper nanoclusters is far less developed. Herein, we report the synthesis of polyhydrido copper nanoclusters [Cu₂₀H₁₁{Se₂P(O ⁱBu)₂}₉] ( 2 ) passivated by Se‐donor ligands via ligand replacement reaction on [Cu₂₀H₁₁{S₂P(O ⁱPr)₂}₉] ( 1 ) with NH₄[Se₂P(O ⁱBu)₂]. In parallel to the synthesis of 2 , cluster [Cu₂₀H₁₁{S₂P(CH₂CH₂Ph)₂}₉] ( 4 ) was produced by the ligand exchange reaction on a new derivative of 1 , that is [Cu₂₀H₁₁{S₂P(O ⁿPr)₂}₉] ( 3 ). Solid state structures of both clusters 2 and 4 were unequivocally established by single‐crystal X‐ray diffraction studies and cluster 4 epitomizes exceptional case to preserve both the shape and size of the nanocluster during the course of ligand exchange. Structurally precise cluster 2 is the second example where the copper hydride nanocluster is stabilized by Se‐donor ligands. The anatomy of 2 can be visualized as a twisted cuboctahedral Cu₁₃ core, two triangular faces of which are capped by a Cu₆ cupola and a single Cu atom along the C₃ rotational axis.     

Syntheses and crystal structures of two heterometallic iodoplumbates containing mixed‐valence copper(I/II)

Mixed‐valence copper(I/II) atoms have been introduced successfully into a Pb/I skeleton to obtain two heterometallic iodoplumbates, namely poly[bis(tetra‐n‐butylammonium) [bis(μ₃‐dimethyldithiocarbamato)dodeca‐μ₃‐iodido‐hexa‐μ₂‐iodido‐tetracopper(I)copper(II)hexalead(II)]], {(C₁₆H₃₆N)₂[Cu₄^ICu^IIPb₆(C₃H₆NS₂)₂I₁₈]}_n , (I), and poly[[μ₃‐iodido‐tri‐μ₂‐iodido‐iodido[bis(1,10‐phenanthroline)copper(I)]copper(I)copper(II)lead(II)] hemiiodine], {[Cu^ICu^IIPbI₅(C₁₂H₈N₂)₂]·0.5I₂}_n , (II), under solution and solvothermal conditions, respectively. Compound (I) contains two‐dimensional anionic layers, which are built upon the linkages of Cu^II(S₂CNMe₂)₂ units and one‐dimensional anionic Pb/I/Cu^I chains. Tetra‐n‐butylammonium cations are located between the anionic layers and connected to them via C—H…I hydrogen‐bonding interactions. Compound (II) exhibits a one‐dimensional neutral structure, which is composed of [PbI₅] square pyramids, [Cu^II₄] tetrahedra and [Cu^IIN₄I] trigonal bipyramids. Face‐to‐face aromatic π–π stacking interactions between adjacent 1,10‐phenanthroline ligands stabilize the structure and assemble compound (II) into a three‐dimensional supramolecular structure. I₂ molecules lie in the voids of the structure.     

Zu den Kristallstrukturen der Übergangsmetall(II)‐Dodekahydro‐closo‐Dodekaborat‐Hydrate Cu(H2O)5,5[B12H12]·2,5 H2O und Zn(H2O)6[B12H12]·6 H2O

On the Crystal Structures of the Transition‐Metal(II) Dodecahydro‐closo‐Dodecaborate Hydrates Cu(H₂O)_5.5[B₁₂H₁₂]·2.5 H₂O and Zn(H₂O)₆[B₁₂H₁₂]·6 H₂O By neutralization of an aqueous solution of the free acid (H₃O)₂[B₁₂H₁₂] with basic copper(II) carbonate or zinc carbonate, blue lath‐shaped single crystals of the octahydrate Cu[B₁₂H₁₂]·8 H₂O (≡ Cu(H₂O)_5.5[B₁₂H₁₂]·2.5 H₂O) and colourless face‐rich single crystals of the dodecahydrate Zn[B₁₂H₁₂]·12 H₂O (≡ Zn(H₂O)₆[B₁₂H₁₂]·6 H₂O) could be isolated after isothermic evaporation. Copper(II) dodecahydro‐closo‐dodecaborate octahydrate crystallizes at room temperature in the monoclinic system with the non‐centrosymmetric space group Pm (Cu(H₂O)_5.5[B₁₂H₁₂]·2.5 H₂O: a = 768.23(5), b = 1434.48(9), c = 777.31(5) pm, β = 90.894(6)°; Z = 2), whereas zinc dodecahydro‐closo‐dodecaborate dodecahydrate crystallizes cubic in the likewise non‐centrosymmetric space group F23 (Zn(H₂O)₆[B₁₂H₁₂]·6 H₂O: a = 1637.43(9) pm; Z = 8). The crystal structure of Cu(H₂O)_5.5[B₁₂H₁₂]·2.5 H₂O can be described as a monoclinic distortion variant of the CsCl‐type arrangement. As characteristic feature the formation of isolated [Cu₂(H₂O)₁₁]⁴⁺ units as a condensate of two corner‐linked Jahn‐Teller distorted [Cu(H₂O)₆]²⁺ octahedra via an oxygen atom of crystal water can be considered. Since “zeolitic” water of hydratation is also present, obviously both classical H–O^δ?···^+δH–O and non‐classical B–H^δ?···^+δH–O hydrogen bonds play a significant role for the stabilization of the structure. A direct coordinative influence of the quasi‐icosahedral [B₁₂H₁₂]^2? anions on the Cu²⁺ cations has not been determined. The zinc compound Zn(H₂O)₆[B₁₂H₁₂]·6 H₂O crystallizes in a NaTl‐type related structure. Two crystallographically different [Zn(H₂O)₆]²⁺ octahedra are present, which only differ in their relative orientation within the packing of the [B₁₂H₁₂]^2? anions. The stabilization of the crystal structure takes place mainly via H–O^δ?···^+δH–O hydrogen bonds, since again the hydrogen atoms of the [B₁₂H₁₂]^2? anions have no direct coordinative influence on the Zn²⁺ cations.     

Voltammetric Investigation of Zinc Release from Metallothioneins Modulated by the Glutathione Redox Couple and Separated with a Porous Membrane

Glutathione (GSH), in addition to serving as a redox buffer in cellular environment, has been suggested as a modulator in metal regulation and homeostasis by metallothioneins (MTs). The interactions of MTs with both GSH and its oxidized form GSSG have been shown to govern the direction of metal transfer. Common methods for the determination of zinc release from MTs modulated by GSH/GSSG either involve radioactive species or enzymes or are labor‐intensive. In this study, upon separation of Zn²⁺ from the reaction mixture of MTs and GSH with a centrifugal filter membrane, differential pulse voltammetry (DPV) was used for the Zn²⁺ quantification. The same approach is extended to the studies of metal transfer between Zn₇MT with a GSH/GSSG mixture and that between Zn₇MT with GSSG. The concomitant conversion between the free thiol and disulfide bonds was confirmed with UV‐vis spectrophotometry. The results demonstrate that GSSG, GSH, and the GSH/GSSG mixture all modulate zinc release from Zn₇MT. The percentage of zinc release increases in the order of GSH, GSSG, and the GSH/GSSG mixture. The new approach is demonstrated to be well suited for investigation of redox regulation of MT and its reaction with zinc‐containing enzymes.     

Investigation of Cd(II), Pb(II) and Cu(I) complexation by glutathione and its component amino acids by ESI-MS and size exclusion chromatography coupled to ICP-MS and ESI-MS

The elucidation of structures of glutathione (GSH) complexes play an important role in the fundamental understanding of biochemical pathways of metal ion deactivation in plants. This article attempts to feature key studies for stoichiometry of metal complexes with glutathione and its constituent amino acids to obtain a better understanding of the different metal affinities of the complexation sites of glutathione. The SEC-ICP-MS experiments have indicated that oxidation process of glutathione was accelerated by metal ion presence in following order Cu⁺, Pb²⁺ and Cd²⁺. The redox activity of metal ions was confirmed by ESI-MS experiments, which allowed to observe formation of glutathione disulphide (GSSG) in time. The stoichiometry of Cd²⁺, Cu⁺ and Pb²⁺ complexes with GSH was defined by observing the isotope pattern of investigated metals and hydrogen loss or transfer during binding. The complexes with metal bound to sulphur of 1:1 and 1:2 stoichiometry were found in case of cadmium and lead. The number of hydrogen atoms lost during metal binding and the SEC-ESI-MS results allowed to elucidate that copper is bound by GSSG in ratio 1:1 and 1:2. Additionally, size exclusion chromatography coupled to electrospray MS allowed to differentiate more stable complexes from weak ones that could be created in the gas phase.     

Kinetics of the Catalytic Oxidation Reactions of Thiol Compounds in Aqueous Solutions in the Presence of Copper Ions

The kinetics of the catalytic oxidation reactions of thiol compounds with molecular oxygen in aqueous solutions in the presence of copper ions was studied in relation to the structures of oxidized thiols and the pH of the solution. A modified procedure used for the determination of [O₂] allowed us to obtain the kinetic characteristics of more than 30 thiols over a wide pH range. We found that weakly chelating thiols exhibited a first order of reaction with respect to [Cu⁺] and [O₂] under conditions when the [(Cu⁺)(RS^–)₂] complex occurred. In the oxidation of strongly chelating thiols in an alkaline medium, the order of reaction with respect to [Cu⁺] was equal to 2, and the rate of reaction was independent of [O₂]. We found that the introduction of small amounts of strongly chelating thiols into Cu⁺ solutions containing difficult-to-oxidize mercaptans resulted in a dramatic acceleration of mercaptan oxidation. We hypothesized that O₂ was effectively bound to the [(Cu⁺)(RS^–)₂] complexes in an alkaline medium in the case of strongly chelating thiols, and this was not the case with the complexes of weakly chelating thiols.     

[Cu(C8H16N4O2)0.5{N(CN)2}]n,a novel ladder‐like coordination polymer

A new polymeric copper complex, viz.catena‐poly[[[μ‐N,N′‐bis(3‐amino­propyl)oxa­mid­ato‐κ⁶N,N′,O:N′′,N′′′,O′]­dicopper(II)]‐di‐μ‐dicyan­amido‐1:1′κ²N¹:N⁵;2:2′κ²N¹:N⁵], [Cu₂(C₈H₁₆N₄O₂)(C₂N₃)₂]_n or [Cu(oxpn)_0.5{N(CN)₂}]_n [where H₂oxpn is N,N′‐bis(3‐amino­propyl)­ox­amide], has been ­synthesized by the reaction of Cu(oxpn), [Cu(ClO₄)₂]·6H₂O and NaN₃. In the crystal structure, the Cu atom is five‐coordinate and has a square‐pyrimidal (SP) configuration. In the polymer, dicyan­amide (dca⁻) groups link Cu^II cations in a μ‐1,5‐bridging mode, generating novel ladders in which each step is composed of dimeric [Cu₂(oxpn)]²⁺ cations. Abundant hydrogen bonds connect the polymer ladders into a two‐dimensional network structure.     

Ribbon and Self‐Penetrated Hybrid Copper Molybdates with Ancillary Bis(4‐pyridylmethyl)piperazine Ligands

Hybrid copper molybdates containing the long‐spanning bis(4‐pyridylmethyl) piperazine (bpmp) ligand were prepared via hydrothermal synthesis and structurally characterized by single‐crystal X‐ray diffraction. The reduced copper phase and major product [Cu₄(MoO₄)₂(bpmp)₄]_n ( 1 ) shows 1D ribbon motifs with embedded {Cu^I₂O₂} dimeric units, built from the bpmp pillaring of [Cu₄(MoO₄)₂] linear clusters. The oxidized copper phase and minor product {[Cu₂(MoO₄)₂(bpmp)₄] · 24H₂O}_n ( 2 ) displays [Cu(bpmp)₂]_n²ⁿ⁺ mutually inclined interpenetrated cationic layers cross‐pillared by molybdate tetrahedra into an unprecedented 6‐connected self‐penetrated network with 4⁸5²6⁵ topology.     

Reversible Ca2+ Switch of An Engineered Allosteric Antioxidant Selenoenzyme

A Ca²⁺‐responsive artificial selenoenzyme was constructed by computational design and engineering of recoverin with the active center of glutathione peroxidase (GPx). By combining the recognition capacity for the glutathione (GSH) substrate and the steric orientation of the catalytic selenium moiety, the engineered selenium‐containing recoverin exhibits high GPx activity for the catalyzed reduction of H₂O₂ by glutathione (GSH). Moreover, the engineered selenoenzyme can be switched on/off by Ca²⁺‐induced allosterism of the protein recoverin. This artificial selenoenzyme also displays excellent antioxidant ability when it was evaluated using a mitochondrial oxidative damage model, showing great potential for controlled catalysis in biomedical applications.     

Darstellung,Kristallstruktur und Eigenschaften des Kupfer(II)‐Indium(III)‐Orthophosphats Cu3In2[PO4]4

Contributions on Crystal Chemistry and Thermal Behaviour of Anhydrous Phosphates. XXIV. Preparation, Crystal Structure, and Properties of Copper(II) Indium(III) Orthophosphate Cu₃In₂[PO₄]₄ Crystals of Cu₃In₂[PO₄]₄ were grown by chemical vapour transport (temperature gradient 1273 K → 1173 K) using chlorine as transport agent. The mixed metal phosphate forms a new structure type (P2₁/c, Z = 2, a = 8.9067(6), b = 8.8271(5), c = 7.8815(5) Å, β = 108.393(5)°, 13 atoms in asymmetric unit, 2549 unique reflections with F_o > 4σ, 116 variables, R(F²) = 0.065). The crystal structure shows a hexagonal closest packing of [PO₄]^3– tetrahedra. Close‐packed layers parallel (1 0 –1) are stacked according to the sequence A, B, A′, B′, A. The octahedral interstices in this packing are completely occupied by two In³⁺, one (Cu1)²⁺ and a “dumb bell” (Cu2)₂⁴⁺. In the latter case four of the six phosphate groups that belong to this octahedral void act as bi‐dentate ligands, thus forming dimers [(Cu2)₂O₁₀] with d_Cu–Cu = 3.032 Å. Cu₃In₂[PO₄]₄ is paramagnetic (μ_eff = 1.89 μ_B, θ_P = –16.9 K). The infrared and UV/Vis reflectance spectra are reported. The observed d‐electron levels of the Cu²⁺ cations agree well with those obtained from angular overlap calculations.