Copper Coordination Environment Research Articles

High pressure-derived nonsymmetrical [Cu2O]2+ core for room-temperature methane hydroxylation.

Nonsymmetrical oxygen-bridged binuclear copper centers have been proposed and modeled as intermediates and transition states in several C─H oxidation pathways, leading to the postulation that structural dissymmetry enhances the reactivity of the bridging oxygen. However, experimentally characterizing the structure and reactivity of these transient species is remarkably challenging. Here, we report the high-pressure synthesis of a metastable nonsymmetrical dicopper-μ-oxo compound with exceptional reactivity toward the mono-oxygenation of aliphatic C─H bonds. The nonequivalent coordination environment of copper stabilizes localized mixed valency and greatly enhances the hydrogen atom abstraction activity of the bridging oxygen, enabling room-temperature hydroxylation of methane under pressure. These findings highlight the role of dissymmetry in the reactivity of binuclear copper centers and demonstrate precise control of molecular structures by mechanical means.

Integrated Experimental and Theoretical Investigation of Copper Active Site Properties of a Lytic Polysaccharide Monooxygenase from Serratia marcescens.

In this paper, we employed a multidisciplinary approach, combining experimental techniques and density functional theory (DFT) calculations to elucidate key features of the copper coordination environment of the bacterial lytic polysaccharide monooxygenase (LPMO) from Serratia marcescens (SmAA10). The structure of the holo-enzyme was successfully obtained by X-ray crystallography. We then determined the copper(II) binding affinity using competing ligands and observed that the affinity of the histidine brace ligands for copper is significantly higher than previously described. UV-vis, advanced electron paramagnetic resonance (EPR), and X-ray absorption spectroscopy (XAS) techniques, including high-energy resolution fluorescence detected (HERFD) XAS, were further used to gain insight into the copper environment in both the Cu(II) and Cu(I) redox states. The experimental data were successfully rationalized by DFT models, offering valuable information on the electronic structure and coordination geometry of the copper center. Finally, the Cu(II)/Cu(I) redox potential was determined using two different methods at ca. 350 mV vs NHE and rationalized by DFT calculations. This integrated approach not only advances our knowledge of the active site properties of SmAA10 but also establishes a robust framework for future studies of similar enzymatic systems.

Boron and nitrogen doping modulating the coordination environment of copper in biochar for reformative electrocatalytic CO2 reduction

In the past decades, the widespread application of heavy metal phytoremediation technology in soil has led to an increase in the yield of hyperaccumulating plants year by year. Therefore, there was a pressing demand for exploring an efficient reprocessing method to utilize the plant tissue loaded with heavy metals. Elsholtzia Harchowensis is the hyperaccumulating plant that can enrich copper, and it has a common distribution in copper areas and has been applied in the field of soil remediation of copper tails. Carbon dioxide (CO2), as a major greenhouse gas, its emission reduction and resource utilization are of great significance for China to achieve the "carbon peaking and carbon neutrality strategy". Electrochemical methods have received widespread attention due to their advantages such as mild conditions and controllable products. Copper-based materials, which can convert CO2 into utilizable fuels or chemicals, are currently hot catalysts in this field. This study prepared two types of copper containing biochar, Cu/C-BN and Cu/C, using Elsholtzia Harchowensis as raw material. The rich types of elements in plant cells make the catalyst have special spatial structure and element composition, and both catalysts exhibited good pore structures. Meanwhile, the introduction of two non-metallic elements, B and N, suppressed the hydrogen evolution reaction (HER) in the system, and the Faraday efficiency (FE) of methane (CH4) was significantly improved. In a 1.0 M KHCO3, the Cu/C-BN material electrode had an instantaneous current density of 13.8 mA/cm2 at -0.82 V vs. RHE. The electrode potential was -0.32 V vs. RHE under the condition of electrolytic 8 h, the current reached a stable value of 0.33 mA/cm2, resulting in a FE of 31.3 % for CH4 and 26.9 % for carbon monoxide (CO). On contrary, the FE of CH4 and CO was only 1.5 % and 19.8 % for Cu/C material at -0.32 V vs. RHE, respectively. The doping of both boron and nitrogen significantly improved the electrochemical activity and CH4 selectivity towards CO2RR.

The effect of composition, temperature and pressure on the oxidation state and coordination environment of copper in silicate melts

Copper is a redox variable element that may occur as Cu0, Cu+, and Cu2+ in the Earth’s crust. The oxidation state will affect its partitioning between coexisting minerals, melts and fluids and hence its behaviour in magmatic processes. Copper bearing silicate glasses were quenched from melts with 23 synthetic compositions (19 CaO-Na2O-MgO-Al2O3-SiO2 (CNMAS), two “granites” containing K2O ± H2O, and Fe-bearing “MORB” and “andesite”) equilibrated at oxygen fugacities (fO2), expressed in log units relative to the fayalite-magnetite-quartz (FMQ) buffer, ranging from −0.7 to 14, temperatures from 900 to 1500 °C and pressures from 0 to 2.5 GPa. Cu K-edge X-ray absorption near edge structure (XANES) spectra were recorded from the glasses and a pre-edge feature in the XANES spectra was found to scale with the proportion of Cu+. Cu+/ΣCu (where ΣCu = Cu+ + Cu2+) was quantified by fitting the intensity of the pre-edge feature as a function of fO2 to the thermodynamically expected relationship. Cu+/ΣCu was found to only weakly depend on melt composition, with more basic melts (e.g., basalts rather than granites) preferentially stabilising Cu2+. Increasing temperature stabilises Cu+, while increasing pressure had little effect on Cu+/ΣCu in CNMAS melts but preferentially stabilised Cu2+ in granite melts. Cu+/ΣCu can be predicted in silicate melts by the empirical equation:log(Cu2+/Cu+) = 0.25(ΔFMQ + 8.58 − 25050/T + 940P/T – 0.02P) − 4.73 + 5400/T + 1.99Λ + (280P – 90P2)where T is temperature in K, P is pressure in GPa and Λ is the optical basicity of the composition. The effects of fO2, melt composition, temperature and pressure on Cu+/ΣCu indicate that Cu+ will be the dominant oxidation state in terrestrial silicate melts (e.g., Cu+/ΣCu = 99% in an andesitic melt at 900 °C, 1 GPa and ΔFMQ = 1). The electron exchange reaction Cu2+ + Fe2+→ Cu+ + Fe3+ occurs on cooling and, given the abundance of Fe in natural melts, the oxidation state of Cu in natural glasses is unlikely to correspond to that in the original melt.

A DFT study on the copper-single-atom modified 2D electride Ca2N monolayer for ethanol dehydrogenation

Two-dimensional (2D) electrides, with electrons confined in interlayer spaces instead of at atomic proximities, have received considerable attention due to their exotic properties. However, the current exploration of electrides in the field of catalysis urgently needs to be expanded. Here, we report novel thermodynamically stable Cu single-atom-modified 2D electride Ca2N monolayer catalysts for ethanol dehydrogenation using density functional theory calculations. The interaction and synergistic catalytic mechanism of copper single atoms and Ca2N monolayers were thoroughly revealed. The coordination environment of copper greatly affects the reaction sites for ethanol dehydrogenation. Furthermore, it was found that the strong electron transfer ability of Ca2N monolayer promoted the adsorption and activation of ethanol molecules on the catalyst, resulting in a cleavage energy barrier of the O–H bond as low as 0.29 eV on Cu1/Ca2N. Furthermore, turnover frequency (TOF) analysis demonstrates that Cu1/Ca2N exhibits significantly higher activity compared to Ca2N with lower energetic span (δE) of 2.52 eV at 298.15 K for the cycle of ethanol dehydrogenation to acetaldehyde. Our work demonstrates a new avenue to the discovery of 2D electride-based catalysts and provides new insights into the mechanism of ethanol dehydrogenation.

Modulation of the Coordination Environment of Copper for Stable CO2 Electroreduction with Tunable Selectivity

Manipulating the product selectivity of an electrochemical CO2 reduction reaction (CO2RR) is challenging due to the unclear and uncontrollable active sites. Here, we report stable CO2RR operation with tunable product selectivity over a family of molecule-modulated copper catalysts. The coordination environment of Cu in catalysts is modulated by an imidazole-based molecule via different synthetic routes. Various carbonaceous products ranging from carbon monoxide, methane, and ethylene were selectively produced via, respectively, tuning the coordination environment of copper atoms from Cu-N, Cu-C, and Cu-Cu. Density functional theory (DFT) calculations reveal that the Cu-N sites weaken the adsorption energy of the *CO intermediate, which is beneficial for CO desorption. The Cu-C and Cu-Cu sites, respectively, facilitate the formation of *OCOH and *(CO)2 intermediates, favoring the CH4 and C2H4 pathways. This work provides a stable and simple model system for studying the influence of coordination elements on the product selectivity of CO2RR.

Spectroscopic and QM/MM studies of the Cu(I) binding site of the plant ethylene receptor ETR1

Herein, we present, to our knowledge, the first spectroscopic characterization of the Cu(I) active site of the plant ethylene receptor ETR1. The x-ray absorption (XAS) and extended x-ray absorption fine structure (EXAFS) spectroscopies presented here establish that ETR1 has a low-coordinate Cu(I) site. The EXAFS resolves a mixed first coordination sphere of N/O and S scatterers at distances consistent with potential histidine and cysteine residues. This finding agrees with the coordination of residues C65 and H69 to the Cu(I) site, which are critical for ethylene activity and well conserved. Furthermore, the Cu K-edge XAS and EXAFS of ETR1 exhibit spectroscopic changes upon addition of ethylene that are attributed to modifications in the Cu(I) coordination environment, suggestive of ethylene binding. Results from umbrella sampling simulations of the proposed ethylene binding helix of ETR1 at a mixed quantum mechanics/molecular mechanics level agree with the EXAFS fit distance changes upon ethylene binding, particularly in the increase of the distance between H69 and Cu(I), and yield binding energetics comparable with experimental dissociation constants. The observed changes in the copper coordination environment might be the triggering signal for the transmission of the ethylene response.

A Coordination Network Featuring Two Distinct Copper(II) Coordination Environments for Highly Selective Acetylene Adsorption.

Single crystals of 2D coordination network {Cu2 L 2 ⋅ (DMF)3(H2O)3} n (1‐DMF) were prepared by reaction of commercial reagents 3‐formyl‐4‐hydroxybenzoic acid (H2 L) and Cu(NO3)2 in dimethylformamide (DMF). The single‐crystal structure shows two distinct Cu(II) coordination environments arising from the separate coordination of Cu(II) cations to the carboxylate and salicylaldehydato moieties on the linker, with 1D channels running through the structure. Flexibility is exhibited on solvent exchange with ethanol and tetrahydrofuran, while porosity and the unique overall connectivity of the structure are retained. The activated material exhibits type I gas sorption behaviour and a BET surface area of 950 m2 g−1 (N2, 77 K). Notably, the framework adsorbs negligible quantities of CH4 compared with CO2 and the C2H n hydrocarbons. It exhibits exceptional selectivity for C2H2/CH4 and C2H2/C2H n , which has applicability in separation technologies for the isolation of C2H2.

Cu-Ni bimetallic single atoms supported on TiO2@NG core-shell material for the removal of dibenzothiophene under visible light

Cu-Ni bimetallic single atoms supported on core–shell materials of TiO2@N-doped porous graphene were prepared using a precursor dilution strategy. HAADF-STEM and XRD results showed Cu and Ni atoms were uniformly dispersed on the surface of the N-doped porous graphene. XPS revealed the coordination environment of copper and nickel atoms, forming Cu-N4 and Ni-N4, which were conductive to the desulfurization. The photocatalytic performance of the catalysts was evaluated by the removal of dibenzothiophene from the model oil. The effect of the metal loading, temperature, reaction time, and reaction time on the desulfurization ratios was investigated. Experimental results showed the desulfurization activities of 1 wt% TiO2@Cu/Ni-NG was the best. The desulfurization ratios of DBT achieved 100% for 120 min under 30 °C, and the desulfurization ratios could still achieved 98.5% after 10 cycles. With the increase in the metal loading and reaction temperature, desulfurization ratios increased first and then decreased. The kinetics of the desulfurization reaction was established, which showed TiO2@Cu/Ni-NG could reduce the activation energy and accelerate the reaction rate because of the synergistic effect between the Cu and Ni single-atom loaded on the surface of nitrogen-doped graphene. The simple and universal preparation process of TiO2@Cu/Ni-NG makes it have a good application prospect.

Cover Feature: Structural Elucidation, Aggregation, and Dynamic Behaviour of N,N,N,N‐Copper(I) Schiff Base Complexes in Solid and in Solution: A Combined NMR, X‐ray Spectroscopic and Crystallographic Investigation (Eur. J. Inorg. Chem. 46/2021)

The Cover Feature shows Cu(I) complexes illustrated as extra-terrestrial beings in space. The celestial bodies are the heterocyclic motifs of the ligands and the spectroscopic techniques that shed light on the coordination environment of copper. In analogy to the tale of two kids hiding under one trench coat in order to pass as a taller adult, two complexes are stapled, forming a dimer. Next to them sits a monomeric structure. The aggregation behavior of Cu(I) complexes was studied. The cover art was designed by Knut T. Hylland and Vincent Meier. More information can be found in the Full Paper by S. DeBeer, M. Amedjkouh and co-workers.

Synthesis, crystal structure and Hirshfeld surface analysis of copper(I) nitrate -complex based on 1-(2,6-dimethylphenyl)-5-allylsulfanyl-1H-tetrazole

By means of the alternating current electrochemical technique and starting from copper wire electrodes in propanol solution of corresponding ligand and copper(II) nitrate, novel copper(I) -complex [Cu2(C12H14SN4)2(NO3)2] (1) has been obtained and X-ray structurally investigated: sp. gr. , a=7.352(3) Å, b=8.269(3) Å, c=12.723(4) Å, =82.08(3)0, =82.74(3)0, =88.37(3)0, V=759.9(5) Å3, Z=2, dcalc=1.625 g cm–3, (CuK)=3.502 mm–1, max=67.960, 4119 measured reflections, 1248 used reflections, 201 refined parameters, R(F2)=0.0915, S=0.95. The trigonal-pyramidal copper(I) coordination environment consists of nitrogen atom and allylic group of ligand, and of two oxygen atoms from crystallographically distinct nitrate anions. Due to a bridging function of oxygen atoms of nitrate anions, two metal-containing polyhedra are connected into {Cu2L2(NO3)2} topological units which are additionally stabilized by noncovalent interaction CuO(2). Comparatively weak hydrogen bonds C–HO exist in the crystal structure of [Cu2(C12H14SN4)2(NO3)2] (1).

Chemical gradients in automotive Cu-SSZ-13 catalysts for NOx removal revealed by operando X-ray spectrotomography

Nitrogen oxide (NOx) emissions are a major source of pollution, demanding ever-improving performance from catalytic after-treatment systems. However, catalyst development is often hindered by limited understanding of the catalyst at work, exacerbated by widespread use of model catalysts rather than technical catalysts, and by global rather than spatially resolved characterization tools. Here we combine operando X-ray absorption spectroscopy with microtomography to perform three-dimensional chemical imaging of the chemical state of copper species in a Cu-SSZ-13 washcoated monolith catalyst during NOx reduction. Gradients in copper oxidation state and coordination environment, resulting from an interplay of NOx reduction with adsorption–desorption of NH3 and mass transport phenomena, were revealed at micrometre spatial resolution while simultaneously determining catalytic performance. Crucially, direct three-dimensional visualization of complex reactions on non-model catalysts is feasible only by the use of operando X-ray spectrotomography, which can improve our understanding of structure–activity relationships, including the observation of mass and heat transport effects. Obtaining spatially resolved spectroscopic information for catalysts under working conditions remains challenging. Here, an approach that combines X-ray absorption spectroscopy with microtomography is introduced and showcased for the selective catalytic reduction of NOx with ammonia over a Cu-SSZ-13 washcoated monolith catalyst.

P-Sulfonatocalix[4]arene binding of monovalent, divalent and trivalent metal ions

Structural studies on p-sulfonatocalix[4]arene coordination compounds involving diverse metal ions with respect to their size and charge, caesium(I), copper(II) and neodymium(III) are reported. The metal coordination-driven self-assembly forms metallosupramolecules, either as a two-dimensional (2 D) or a three-dimensional (3D) network while retaining the commonly established bilayer array for p-sulfonatocalix[4]arene. The complex (Cs5-p-sulfonatocalix[4]arene-H+)·6H2O has five crystallographically independent caesium(I) ions with high coordination numbers. In the divalent complex {[Cu3(H2O)12-2(p-sulfonatocalix[4]arene)]2-}·2([Cu(H2O)5])2+·2NO3 -·7H2O, two different copper(II) coordination environments are present, one with octahedral stereochemistry while bridging two opposing calixarenes with the other having a square pyramidal geometry involving one sulfonate group. Eight-coordinate neodymium(III) metal ions prevail in Nd0.25(H2O)1.25(p-sulfonatocalix[4]arene + H+)0.25, involving four sulfonate groups from four different calixarenes.

Positional Isomerism in the N^N Ligand: How Much Difference Does a Methyl Group Make in [Cu(P^P)(N^N)]+ Complexes?

The synthesis and structural characterization of 5,6′-dimethyl-2,2′-bipyridine (5,6′-Me2bpy) are reported, along with the preparations and characterizations of [Cu(POP)(5,6′-Me2bpy)][PF6] and [Cu(xantphos)(5,6′-Me2bpy)][PF6] (POP = bis(2-(diphenylphosphanyl)phenyl)ether, xantphos = 4,5-bis(diphenylphosphanyl)-9,9-dimethyl-9H-xanthene). Single-crystal X-ray structure determinations of [Cu(POP)(5,6′-Me2bpy)][PF6] and [Cu(xantphos)(5,6′-Me2bpy)][PF6] confirmed distorted tetrahedral copper(I) coordination environments with the 5-methylpyridine ring of 5,6′-Me2bpy directed towards the (C6H4)2O unit of POP or the xanthene unit of xantphos. In the xantphos case, this preference may be attributed to C–H…π interactions involving both the 6-CH unit and the 5-methyl substituent in the 5-methylpyridine ring and the arene rings of the xanthene unit. 1H NMR spectroscopic data indicate that this ligand orientation is also preferred in solution. In solution and the solid state, [Cu(POP)(5,6′-Me2bpy)][PF6] and [Cu(xantphos)(5,6′-Me2bpy)][PF6] are yellow emitters, and, for powdered samples, photoluminescence quantum yields (PLQYs) are 12 and 11%, respectively, and excited-state lifetimes are 5 and 6 μs, respectively. These values are lower than PLQY and τ values for [Cu(POP)(6,6′-Me2bpy)][PF6] and [Cu(xantphos)(6,6′-Me2bpy)][PF6], and the investigation points to the 6,6′-dimethyl substitution pattern in the bpy ligand being critical for enhancement of the PLQY.

Extended π-Systems in Diimine Ligands in [Cu(P^P)(N^N)][PF6] Complexes: From 2,2′-Bipyridine to 2-(Pyridin-2-yl)Quinoline

We describe the synthesis and characterization of [Cu(POP)(1)][PF6], [Cu(POP)(2)][PF6], [Cu(xantphos)(1)][PF6], and [Cu(xantphos)(2)][PF6] in which ligands 1 and 2 are 2-(pyridin-2-yl)quinoline and 2-(6-methylpyridin-2-yl)quinoline, respectively. With 2,2'-bipyridine (bpy) as a benchmark, we assess the impact of the extended π-system on structural and solid-state photophysical properties. The single crystal structures of [Cu(POP)(2)][PF6], [Cu(xantphos)(1)][PF6], and [Cu(xantphos)(2)][PF6] were determined and confirmed a distorted tetrahedral copper(I) coordination environment in each [Cu(P^P)(N^N)]+ cation. The xanthene unit in [Cu(xantphos)(1)][PF6] and [Cu(xantphos)(2)][PF6] hosts the quinoline unit of 1, and the 6-methylpyridine group of 2. 1H NMR spectroscopic data indicate that these different ligand orientations are also observed in acetone solution. In their crystal structures, the [Cu(POP)(2)]+, [Cu(xantphos)(1)]+, and [Cu(xantphos)(2)]+ cations exhibit different edge-to-face and face-to-face π-interactions, but in all cases, the copper(I) centre is effectively protected by a ligand sheath. In [Cu(POP)(2)][PF6], pairs of cations engage in an efficient face-to-face π-stacking embrace, and we suggest that this may contribute to this compound having the highest photoluminescence quantum yield (PLQY = 21%) of the series. With reference to data from the Cambridge Structural Database, we compare packing effects and PLQY data for the complexes incorporating 2-(pyridin-2-yl)quinoline and 2-(6-methylpyridin-2-yl)quinoline, with those of the benchmark bpy-containing compounds. We also assess the effect that Cu⋯O distances in the {Cu(POP)} and {Cu(xantphos)} domains of [Cu(P^P)(N^N)][X] compounds have on solid-state PLQY values.

Cu(ii)-induced twisting of the biphenyl core: exploring the effect of structure and coordination environment of biphenyl-based chiral copper(ii) complexes on interaction with calf-thymus DNA

Biphenyl core-based clip-like receptors get twisted after complexation with Cu2+. The extent of interaction of the optically active complexes with ct-DNA varies depending on the structure and coordination environment.

Using N-Terminal Coordination of Cu(II) and Ni(II) to Isolate the Coordination Environment of Cu(I) and Cu(II) Bound to His13 and His14 in Amyloid-β(4-16).

The amyloid-β (Aβ) peptide is a cleavage product of the amyloid precursor protein and has been implicated as a central player in Alzheimer's disease. The N-terminal end of Aβ is variable, and different proportions of these variable-length Aβ peptides are present in healthy individuals and those with the disease. The N-terminally truncated form of Aβ starting at position 4 (Aβ4-x) has a His residue as the third amino acid (His6 using the formal Aβ numbering). The N-terminal sequence Xaa-Xaa-His is known as an amino terminal copper and nickel binding motif (ATCUN), which avidly binds Cu(II). This motif is not present in the commonly studied Aβ1-x peptides. In addition to the ATCUN site, Aβ4-x contains an additional metal binding site located at the tandem His residues (bis-His at His13 and 14) which is also found in other isoforms of Aβ. Using the ATCUN and bis-His motifs, the Aβ4-x peptide is capable of binding multiple metal ions simultaneously. We confirm that Cu(II) bound to this particular ATCUN site is redox silent, but the second Cu(II) site is redox active and can be readily reduced with ascorbate. We have employed surrogate metal ions to block copper coordination at the ATCUN or the tandem His site in order to isolate spectral features of the copper coordination environment for structural characterization using extended X-ray absorption fine structure (EXAFS) spectroscopy. This approach reveals that each copper coordination environment is independent in the Cu2Aβ4-x state. The identification of two functionally different copper binding environments within the Aβ4-x sequence may have important implications for this peptide in vivo.

An Undergraduate Experiment To Explore Cu(II) Coordination Environment in Multihistidine Compounds through Electron Spin Resonance Spectroscopy

Electron spin resonance (ESR) or electron paramagnetic resonance (EPR) spectroscopy is an incisive technique for the characterization of paramagnetic centers in inorganic, bioinorganic, and organic molecules and materials. These measurements are enabled with the help of paramagnetic species, such as organic free radicals and ions, electronically excited states, and metal–ligand compounds, some of which with biological importance. In this experiment, analogues of histidine–copper coordination compounds are investigated to show students how ESR line shapes depend on the complexed copper ion electronic structure as well as how the spectral features elucidate the coordination environment of copper. These coordinated compounds play an important role in metal ion coordination in proteins and peptides. The experiment has two parts. First, three copper–imidazole complexes that mimic copper–histidine compounds in the human body are synthesized. Second, the ESR spectrum of each complex is obtained at 77 K from frozen chloroform/methanol and acetonitrile/methanol matrixes and used to elucidate the ligand arrangement of the Cu2+ ion and the effect on the unpaired electron density.

Metal organic frameworks-assisted fabrication of CuO/Cu2O for enhanced selective catalytic reduction of NOx by NH3 at low temperatures.

Porous CuO/Cu2O heterostructure was successfully synthesized through a metal organic frameworks (MOFs)-assisted template method. Tunable production of pure phase CuO and Cu2O could be achieved by regulating the coordination environment of copper. The copper oxides inherited the polyhedral morphology from the Cu MOFs and possessed higher surface area and larger pore volume. Compared with pure CuO and Cu2O, heterostructured CuO/Cu2O displayed remarkably enhanced NH3-SCR de-NOx activity and N2 selectivity in a low temperature range of 170-220 °C. Systematical in situ DRIFT characterization revealed that the NH3-SCR of NOx over CuO/Cu2O heterostructure followed Eley-Rideal (E-R) mechanism, which was greatly improved by the abundant Lewis acid sites, improved O2 adsorption and the synergistic effect between Cu+ and Cu2+. In addition, CuO/Cu2O heterostructure exhibited excellent H2O, SO2, alkali metals, and hydrocarbon durability, indicating its potential use in industrial NH3-SCR of NOx.

Clarifying the Copper Coordination Environment in a de Novo Designed Red Copper Protein.

Cupredoxins are copper-dependent electron-transfer proteins that can be categorized as blue, purple, green, and red depending on the spectroscopic properties of the Cu(II) bound forms. Interestingly, despite significantly different first coordination spheres and nuclearity, all cupredoxins share a common Greek Key β-sheet fold. We have previously reported the design of a red copper protein within a completely distinct three-helical bundle protein, α3DChC2. (1) While this design demonstrated that a β-barrel fold was not requisite to recapitulate the properties of a native cupredoxin center, the parent peptide α3D was not sufficiently stable to allow further study through additional mutations. Here we present the design of an elongated protein GRANDα3D (GRα3D) with Δ Gu = -11.4 kcal/mol compared to the original design's -5.1 kcal/mol. Diffraction quality crystals were grown of GRα3D (a first for an α3D peptide) and solved to a resolution of 1.34 Å. Examination of this structure suggested that Glu41 might interact with the Cu in our previously reported red copper protein. The previous bis(histidine)(cysteine) site (GRα3DChC2) was designed into this new scaffold and a series of variant constructs were made to explore this hypothesis. Mutation studies around Glu41 not only prove the proposed interaction, but also enabled tuning of the constructs' hyperfine coupling constant from 160 to 127 × 10-4 cm-1. X-ray absorption spectroscopy analysis is consistent with these hyperfine coupling differences being the result of variant 4p mixing related to coordination geometry changes. These studies not only prove that an Glu41-Cu interaction leads to the α3DChC2 construct's red copper protein like spectral properties, but also exemplify the exact control one can have in a de novo construct to tune the properties of an electron-transfer Cu site.