负载型Cu-Pd双金属纳米氧化物催化剂催化合成碳酸二乙酯：Cu（I）作为活性中心

催化反应活性与催化剂活性组分的存在价态密切相关,所以探讨催化剂在反应过程中的活性中心及其价态变化,对于催化反应机理和催化剂的研究都显得十分重要.目前对于氧化羰基合成碳酸二甲酯催化剂的机理的探讨很多,主要存在的争议是Cu+还是Cu2+作为活性中心,以及铜物种的配位状态.大多体系都是以分子筛为载体的铜基催化剂,其活性中心的研究存在铜离子在分子筛中的定位问题,而且催化活性也会受到分子筛结构的影响.采用这种方法研究活性中心的影响因素较多,存在一定的局限性.因此,直接制备纳米级的铜基氧化物用于本催化体系,有利于更直观简单地探索其活性中心.纳米级金属氧化物材料是一种新型的功能性材料,而纳米铜基氧化物(CuO和Cu2O)因其独特的物化性质和结构而引起广泛关注.我们采用水热法制备纳米CuO及其它氧化物,研究了NaOH浓度对催化剂的催化性能的影响;葡萄糖是一种还原性较强的还原剂,其用量必定会对所制备的氧化物的物种有所影响.为了探究Cu0和Cu+在本体系中的作用,采用不同葡萄糖用量制备了具有不同Cu2O含量的PdCl2/Cu-Cu2O催化剂.在上述研究基础上,我们采用X射线衍射、场发射扫描电子显微镜、热重分析、等离子体原子发射光谱等表征手段研究了负载型纳米铜基氧化物催化剂在合成碳酸二乙酯反应中催化性能差异的原因,旨在直接考察活性中心主要是Cu+还是Cu2+,避免分子筛等体系中载体结构的影响,研究结果更具参考性.结果发现, NaOH浓度为5 mol/L时制备的PdCl2/CuO和PdCl2/Cu-Cu2O催化剂的性能优于其他浓度下制备的催化剂,这可能是由于不同浓度的碱溶液会对铜离子的沉淀过程产生不同的影响;相同NaOH浓度下制备的催化剂中, PdCl2/Cu-Cu2O催化剂的催化性能明显优于PdCl2/CuO催化剂,这可能是由于PdCl2/Cu-Cu2O催化剂更有利于反应过程中电子的传递,从而表现出更好的催化性能,我们推测Cu0和Cu+可能更有利催化乙醇氧化羰基合成DEC;表征分析发现PdCl2/CuO和PdCl2/Cu-Cu2O均具有很好的热稳定性,两种催化剂中PdCl2负载量几乎相同,因此,主要影响催化性能的因素是载体CuO和Cu-Cu2O中铜的价态.采用不同葡萄糖用量制备了含有不同Cu2O含量的PdCl2/Cu-Cu2O催化剂,其中, PdCl2/Cu-Cu2O-2催化剂中含有更多的Cu2O,在反应中乙醇转化率达到了7.2%, DEC的选择性为97.9%, DEC的时空收率可达到151.9 mg·g–1·h–1.由此可见在乙醇气相氧化羰基合成DEC体系中, Cu+是主要的活性中心.     

Density functional theory study of the carbonyl-ene reaction of encapsulated formaldehyde in Cu(I), Ag(I), and Au(I) exchanged FAU zeolites

Carbonyl-ene reactions, which involve C-C bond formation, are essential in many chemical syntheses. The formaldehyde-propene reaction catalyzed by several of the group 11 metal cations, Cu(+), Ag(+), and Au(+) exchanged on the faujasite zeolite (metal-FAU) has been investigated by density functional theory at the M06-L/6-31G(d,p) level. The Au-FAU exhibits a higher activity than the others due to the high charge transfer between the Au and the reactant molecules, even though it is located at a negatively charged site of the zeolite. This site enables it to compensate for the charge of the Au(+) ion. The NBO analysis reveals that the 6s orbital of the Au atom plays an important role, inducing a charge on the probe molecules. Moreover, the effect of the zeolite framework makes the Au-FAU more active than the others by stabilizing the high charge induced transition structure. The activation energy of the reaction catalyzed by Au-FAU is 13.0 kcal/mol whereas that of Cu and Ag-FAU is found to be around 17 kcal/mol. The product desorption needs to be improved for Au-FAU; however, we suggest that catalysts with high charge transfer might provide a promising activity.     

Site-differentiated solid solution in (Na(1-x)Cu(x))2Ta4O11 and its electronic structure and optical properties

The (Na(1-x)Cu(x))(2)Ta(4)O(11) (0 ≤ x ≤ 0.78) solid-solution was synthesized within evacuated fused-silica vessels and characterized by powder X-ray diffraction techniques (space group: R3c (#167), Z = 6, a = 6.2061(2)-6.2131(2) ?, c = 36.712(1)-36.861(1) ?, for x = 0.37, 0.57, and 0.78). The structure consists of single layers of TaO(7) pentagonal bipyramids as well as layers of isolated TaO(6) octahedra surrounded by Na(+) and Cu(+) cations. Full-profile Rietveld refinements revealed a site-differentiated substitution of Na(+) cations located in the 12c (Wyckoff) crystallographic site for Cu(+) cations in the 18d crystallographic site. This site differentiation is driven by the linear coordination geometry afforded at the Cu(+) site compared to the distorted seven-coordinate geometry of the Na(+) site. Compositions more Cu-rich than x ~ 0.78, that is, closer to "Cu(2)Ta(4)O(11)", could not be synthesized owing to the destabilizing Na(+)/Cu(+) vacancies that increase with x up to the highest attainable value of ~26%. The UV-vis diffuse reflectance spectra show a significant red-shift of the bandgap size from ~4.0 eV to ~2.65 eV with increasing Cu(+) content across the series. Electronic structure calculations using the TB-LMTO-ASA approach show that the reduction in bandgap size arises from the introduction of Cu 3d(10) orbitals and the formation of a new higher-energy valence band. A direct bandgap transition emerges at k = Γ that is derived from the filled Cu 3d(10) and the empty Ta 5d(0) orbitals, including a small amount of mixing with the O 2p orbitals. The resulting conduction and valence band energies are determined to favorably bracket the redox potentials for water reduction and oxidation, meeting the thermodynamic requirement for photocatalytic water-splitting reactions.     

Pt@Pd(x)Cu(y)/C core-shell electrocatalysts for oxygen reduction reaction in fuel cells

A series of carbon-supported core-shell nanoparticles with Pd(x)Cu(y)-rich cores and Pt-rich shells (Pt@Pd(x)Cu(y)/C) has been synthesized by a polyol reduction of the precursors followed by heat treatment to obtain the Pd(x)Cu(y)/C (1 ≤ x ≤ 3 and 0 ≤ y ≤ 5) cores and the galvanic displacement of Pd(x)Cu(y) with [PtCl(4)](2-) to form the Pt shell. The nanoparticles have also been investigated with respect to the oxygen reduction reaction (ORR) in proton-exchange-membrane fuel cells (PEMFCs). X-ray diffraction (XRD) analysis suggests that the cores are highly alloyed and that the galvanic displacement results in a certain amount of alloying between Pt and the underlying Pd(x)Cu(y) alloy core. Transmission electron microscopy (TEM) images show that the Pt@Pd(x)Cu(y)/C catalysts (where y > 0) have mean particle sizes of <8 nm. Compositional analysis by energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) clearly shows Pt enrichment in the near-surface region of the nanoparticles. Cyclic voltammograms show a positive shift of as much as 40 mV for the onset of Pt-OH formation in the Pt@Pd(x)Cu(y)/C electrocatalysts compared to that in Pt/C. Rotating disk electrode (RDE) measurements of Pt@PdCu(5)/C show an increase in the Pt mass activity by 3.5-fold and noble metal activity by 2.5-fold compared to that of Pt/C. The activity enhancements in RDE and PEMFC measurements are believed to be a result of the delay in the onset of Pt-OH formation.     

高活性铜催化剂无受体乙醇催化脱氢制乙醛研究

相较于Wacker工艺进行乙醛工业化生产,发展多相催化体系实现乙醇直接无氧催化脱氢制乙醛和副产氢气,从生产工艺和经济价值方面无疑是一条更加安全高效的路线.在此,我们发展了一种高效、稳固的Cu/SiO₂催化剂,用于乙醇的无受体催化脱氢.通过氨蒸发法制备得到高度分散的Cu颗粒,在没有任何平衡气体的纯乙醇进料条件下,显示出超强的热稳定性.活性组分Cu和载体SiO₂之间的强相互作用,使其具有优异的催化性能.通过反应条件优化,在250℃下实现了较高的乙醇转化率(>40%)和乙醛选择性(>95%),且催化剂在固定床连续反应过程中可稳定运行超过400 h.     

Cu3(BTC)2: CO oxidation over MOF based catalysts

Crystalline and amorphized MOFs (Cu(3)(BTC)(2)) have been demonstrated to be excellent catalysts for CO oxidation. The catalytic activity can be further improved by loading PdO(2) nanoparticles onto the amorphized Cu(3)(BTC)(2).     

Nanostructured Cu(x)Ce1-xO2-y mixed oxide catalysts: characterization and WGS activity tests

Cu(x)Ce(1-x)O(2-y) mixed oxide catalysts were prepared by different preparation procedures: co-precipitation, the sol-gel peroxide route, and the sol-gel citric acid-assisted route. The resulting solids were investigated by means of XRD, BET, H(2) and CO temperature-programmed reduction (TPR), oxidation (TPO) and desorption (TPD) analyses, and N(2)O pulse selective reaction. It was confirmed that H(2) (CO) consumed for complete reduction of well-dispersed and bulk-like CuO phases to Cu(0), reduction of surface ceria and H(2) (CO) adsorption on the catalyst surface contribute to the total H(2) (CO) consumption. Among catalysts examined, the Cu(0.15)Ce(0.85)O(2-y) mixed oxide sample prepared by means of co-precipitation method exhibits the highest activity and stability for water-gas shift (WGS) pulse reaction in the range of employed operating conditions. WGS activity of copper-ceria mixed oxide catalysts is determined by the extent of surface ceria reduction and dispersion of copper species.     

Cu/SiO2催化剂结构对乙酸甲酯加氢性能的影响

采用尿素水解法制备了Cu/SiO₂催化剂, 探究其用于乙酸甲酯(MA)加氢制取乙醇的催化性能, 并通过N₂物理吸附、X射线衍射(XRD)、程序升温还原(TPR)、透射电子显微镜(TEM)和X射线光电子能谱(XPS)等表征方法分析了催化剂的物理化学特性, 探究了铜负载量和还原温度等对催化剂结构的影响, 以及与催化活性之间的关系. 发现在铜负载量分别为10%、20%和30% (质量分数, w)的催化剂中, 铜负载量为20%的催化剂因具有较多且分散均匀的活性组分而表现出最佳的加氢效果. 接着在铜负载量为20%的催化剂上研究了还原温度(270, 350, 450 ℃)对催化性能的影响, 发现在350 ℃下还原的催化剂活性最高, 在最佳的反应条件下, 乙酸甲酯转化率达到97.8%, 乙醇选择性达到64.9% (理论最大值为66.6%), 主要归属于它具有较高的铜物种分散度, 最合适的Cu⁰/(Cu⁰+Cu⁺)摩尔比例, 同时实现了解离氢气和活化乙酸甲酯的功能.     

FA(I):A(+) and FA(II):Cu(+) laser activity and photographic sensitization at the low coordinated surfaces of AgBr ab initio calculations

The twofold potentials of F(A)(I):Au(+) and F(A)(II)Cu(+) color centers at the low coordinated surfaces of AgBr thin films in providing tunable laser activity and photographic sensitization were investigated using ab initio methods of molecular electronic structure calculations. Clusters of variable size were embedded in simulated Coulomb fields that closely approximated the Madelung fields of the host surfaces, and the nearest neighbor ions to the F(A) defect site were allowed to relax to equilibrium in each case. Based on the calculated Stokes shifted optical transition bands and horizontal shifts along the configuration coordinate diagrams, both F(A)(I):Au(+) and F(A)(II):Cu(+) color centers were found to be laser active. The laser activity faded quickly as the bromide ion coordination decreased from 5 (flat) to 4 (edge) to 3 (corner) and as the size of the impurity cation increased from Cu(+) to Au(+). The latter relation was explainable in terms of the axial perturbation of the impurity cation. The smallest calculated Stokes-shift at the corner surface suggested that emission had the same oscillator strength as absorption. All relaxed excited states RESs of the defect containing surfaces were deep below the lower edges of the conduction bands of the defect free ground state surfaces, indicating that F(A)(I):Au(+) and F(A)(II):Cu(+) are suitable laser defects. The probability of orientational destruction of the two centers attributed to the assumed RES saddle point ion configurations along the <110> axis was found to be directly proportional to the size of the impurity cation, with activation energy barriers of about 0.655-3.294 eV for Cu(+), and about 1.887-3.404 eV for Au(+). The possibility of exciton (energy) transfer from the sites of higher coordination to those of lower coordination is demonstrated. The more laser active F(A)(II):Cu(+) center was more easily formed than the less laser active F(A)(I):Au(+) center. The Glasner-Tompkins empirical relation was generalized to include F(A) centers at the low coordinated surfaces of silver bromide thin film. As far as color photographic sensitization is concerned, the lowest unoccupied molecular orbitals of the selected dye molecules in the excited states were high enough for electron injection. F(A) defect formation and rotational diffusion of silver clusters reduced the energy gaps between the excited dye molecules and the lower edges of the conduction bands and allowed for hole injection. About 54-60% of the reduction of silver ions at the flat surface of AgBr was attributed to the host anions and F(A) defect formation, leaving about 40-46% for the reduction of photoelectrons as well as the electrons of the developer or dye molecules. The unrelaxed rotational diffusions of the central Ag(4) by 90 degrees decreased the latter percentage, but were severely hindered by activation energy barriers.     

Functional analogues of the dioxygen reduction site in cytochrome oxidase: mechanistic aspects and possible effects of Cu(B)

Catalytic reduction of O(2) and H(2)O(2) by new synthetic analogues of the heme/Cu site in cytochrome c and ubiquinol oxidases has been studied in aqueous buffers. Among the synthetic porphyrins yet reported, those employed in this study most faithfully mimic the immediate coordination environment of the Fe/Cu core. Under physiologically relevant conditions, these biomimetic catalysts reproduce key aspects of the O(2) and H(2)O(2) chemistry of the enzyme. When deposited on an electrode surface, they catalyze the selective reduction of O(2) to H(2)O at potentials comparable to the midpoint potential of cytochrome c. The pH dependence of the half-wave potentials and other data are consistent with O-O bond activation at these centers proceeding via a slow generation of a formally ferric-hydroperoxo intermediate, followed by its rapid reduction to the level of water. This kinetics is analogous to that proposed for the O-O reduction step at the heme/Cu site. It minimizes the steady-state concentration of the catalytic intermediate whose decomposition would release free H(2)O(2). The maximum catalytic rate constants of O(2) reduction by the ferrous catalyst and of H(2)O(2) reduction by both ferric and ferrous catalysts are comparable to those reported for cytochrome oxidase. The oxidized catalyst also displays catalase activity. Comparison of the catalytic properties of the biomimetic complexes in the FeCu and Cu-free forms indicates that, in the regime of rapid electron flux, Cu does not significantly affect the turnover frequency or the stability of the catalysts, but it suppresses superoxide-releasing autoxidation of an O(2)-catalyst adduct. The distal Cu also accelerates O(2) binding and minimizes O-O bond homolysis in the reduction of H(2)O(2).     

Collision-induced dissociation of MCl(+) adducts (M = Mg, Mn, Zn, Co, Ni and Cu) and Cu(+) and Ag(+) adducts of dithioalkyl ketene acetals

Electrospray ionization mass spectra of equimolar solutions of dithioalkyl ketene acetals 1 and 2 and metal chlorides (MgCl(2), MnCl(2), ZnCl(2), CoCl(2), NiCl(2) and CuCl(2)) produced abundant ligated metal ion adducts [1 + MCl](+) and [2 + MCl](+). In addition, CuCl(2) also gave rise to Cu(+) adducts. The ligated metal ion adducts upon collision-induced dissociation (CID) showed characteristic fragmentation pathways reflecting the favoured site of coordination. The results show that MgCl(+) prefers oxygen over sulfur, whereas the reverse is true for ZnCl(+) adducts, exemplified by the preferred fragmentation of [1 + MgCl](+) as elimination of MgCl(OH), while that of [1 + ZnCl](+) is expulsion of ZnCl(SCH(3)). Co and Ni chloride adducts tend to give stable metal coordinated species. Cleavage of the dithiolane ring followed by elimination of C(2)H(4)S is the preferred pathway during the CID of [2 + MCl](+) adducts. The CuCl(+) adducts of 1 and 2 showed reduction of Cu((I)) to Cu((0)) resulting in the M(+)(*)ions of 1 and 2. Abstraction of *CH(3) resulting in elimination of CuCH(3) was observed during CID of Cu(+) adducts of 1 and 2. A comparative study of the corresponding Ag(+) adducts revealed a similar behaviour.     

Bond dissociation energies and structures of CuNO(+) and Cu(NO)(2)(+)

The bond dissociation energies of CuNO(+), Cu(NO)(2)(+), and CuAr(+) are determined by means of guided ion beam mass spectrometry and quantum chemical calculations. From the experiment, the values D(0)(Cu(+)-NO) = 1.13 +/- 0.05, D(0)(ONCu(+)-NO) = 1.12 +/- 0.06, D(0)(Cu(+)-Ar) = 0.50 +/- 0.07, and D(0)(Cu(+)-Xe) = 1.02 +/- 0.06 eV are obtained. The computational approaches corroborate these results and provide additional structural data. The relative values of D(0)(Cu(+)-NO) and D(0)(Cu(+)-Xe) are consistent with the approximately thermoneutral formation of CuXe(+) upon interacting CuNO(+) with xenon. The sequential bond dissociation energies of Cu(NO)(2)(+) exhibit a trend similar to those of other Cu(I) complexes described in the literature. Although metathesis of nitric oxide to N(2) and O(2) is of considerable interest, no evidence for N-N- or O-O-bond formations in Cu(NO)(n)(+) ions (with n up to 3) is obtained within the energy range studied experimentally.     

EPR spectra of Cu(2+) in KH(2)PO(4) single crystals

Cu(2+) doped single crystals of KH(2)PO(4) were investigated using EPR technique at room temperature. The spectra of the complex contains large number of overlapping lines. Five sites are resolved and four of them are compatible with the tetragonal symmetry, and the fifth one belongs to an interstitial site. The results are discussed and compared with previous studies. Detailed investigation of the EPR spectra indicate that Cu(2+) substitute with K(+) ions. The principal values of the g and hyperfine tensors and the ground state wave function of Cu(2+) ions are obtained.     

Transformation of Ethanol to Ethyl Acetate over Cu/SiO2 Catalysts Modified by ZrO2

Direct transformation of ethanol to ethyl acetate was investigated on a series of Cu(ZrO₂)/SiO₂ catalysts. Inductively coupled plasma(ICP), surface area analysis, X-ray diffraction(XRD), H₂-temperature programmed reduction(H₂-TPR), X-ray photoelectron spectroscopy(XPS), NH₃-temperature programmed desorption(NH₃-TPD) and Fourier transform-infrared spectroscopy(FTIR) techniques were used to characterize the catalysts. The results reveal that ZrO₂ can improve the dispersion of copper species and increase the acidity of the Cu(ZrO₂)/SiO₂ catalysts. The Cu⁰ is responsible for ethanol dehydrogenation to acetaldehyde, and both the Lewis acid and Brønsted acid sites were in favor of the selectivity to ethyl acetate. The synergistic effect of Cu⁰ and an appropriate amount of acidic sites played an important role in the production of ethyl acetate.     

Comparative study of Cu(II) catalytic sites immobilized onto different polymeric supports

The catalysts with copper(II) ions stabilized onto different polymeric matrixes are prepared on either bulk (Cu/chitosan, Cu/polyethyleneimine-polyacrylic acid (PPA), and Cu-diiminate-impregnated polystyrene, polyarylate, or polymethylmethacrylate) or composite supports (egg-shell type Cu/chitosan/SiO₂ and Cu/PPA/SiO₂). The morphology of the samples and peculiarities of Cu(II) cationic sites are studied by SEM and ESR methods, and the catalyst activities are compared in oxidation of o- and p-dihydroxybenzenes by air in water. The catalytic activity of Cu(II) centers is governed by the coordination of isolated copper ions: for the most active catalysts, i.e., Cu/chitosan and Cu/PPA, the symmetry of isolated Cu²⁺-sites approximates a coordinatively unsaturated square-planar structure. At the same time, accessibility of active sites to water differs for different polymers, so the contribution of hydrophilicity to the reaction pattern cannot be excluded. Redox transformations of the active sites in the course of catalytic tests do not cause copper leaching from the polymer matrix. The binary composite systems with a film of low-loaded hydrofilic Cu-polymer supported on macroporous SiO₂ demonstrate substantially higher activity in oxidation of hydroquinone and 3,4-dihydroxyphenylalanine, as compared with the bulk Cu/polymer samples. In turn, the specific activity of Cu/chitosan/SiO₂ exceeds significantly that of Cu/PPA/SiO₂ due to stabilization of a thinner and more uniform film of chitosan at the surface of silica.     

La—Cu—Mn系钙钛矿型（ABO3）催化剂性能

采用共沉淀法制得了Ｃｕ２＋部分取代Ｌａ３＋的Ｌａ１－ｘＣｕｘＭｎＯ３钙钛矿型催化剂，通过ＸＲＤ、ＴＰＲ、电镜分析及活性评价，研究了Ｃｕ２＋的部分取代对Ｌａ１－ｘＣｕｘＭｎＯ３系催化剂性能的影响．结果表明，Ｃｕ２＋部分取代Ｌａ３＋后，使催化剂易被还原，活化能降低，对ＣＨ４、ＣＯ氧化反应，均有最佳取代量使催化剂的活性最佳，其值分别为０．２和０．４，这是由于随ｘ值的增大，催化剂晶格缺陷增多，晶格氧的化学势增大的缘故     

Ce-doped ZnO (Ce(x)Zn(1-x)O) becomes an efficient visible-light-sensitive photocatalyst by co-catalyst (Cu2+) grafting

We have fabricated an efficient visible-light-sensitive Cu(2+)-grafted Ce-doped ZnO photocatalyst (Cu(2+)-Ce(x)Zn(1-x)O) by adopting a metal ion doping and co-catalyst modification. Impurity states were formed below the conduction band (CB) edge in Ce(x)Zn(1-x)O, and these impurity states induce the visible-light absorption. Ce(x)Zn(1-x)O without a Cu(2+)-co-catalyst showed negligible visible-light activity due to the low reduction power of electrons in impurity levels. Surprisingly, Cu(2+)-modification over Ce(x)Zn(1-x)O drastically increased its visible-light activity. Excited electrons in impurity states can transfer to the Cu(2+)-ions on the surface and form Cu(2+)/Cu(+) redox couples, which cause the efficient oxygen reduction through a multi-electron reduction process. One of the striking features of the present study is that the metal doped semiconductors which were inactive due to their impurity states become efficient visible-light photocatalysts upon co-catalyst modification. The successful strategy used here for designing a highly active visible-light photocatalyst would provide numerous opportunities to develop an efficient metal-ion based visible-light photocatalyst.     

Effect of Ti3+ on TiO2-supported Cu catalysts used for CO oxidation

In this paper, we have shown that Cu/TiO(2) catalysts are highly active in CO oxidation. For instance, a 3.4% Cu/TiO(2) catalyst exhibits a higher turnover rate for the effective removal of CO in air than 3-5% Pt/TiO(2) and 20% Cu/ZnO/Al(2)O(3) catalysts. A small amount of Cu(+) species is formed during the calcination treatment at 225 °C, which is the main active phase for the CO oxidation. However, it is proposed that some highly dispersed CuO can also form in the TiO(2) lattice during the calcination treatment. Furthermore, a strong electron interaction between Cu(2+) in highly dispersed CuO and Ti(3+) on rutile TiO(2) (Cu(2+)+Ti(3+)→Cu(+)+Ti(4+)) has been shown to occur. Overall, the reduction of Cu(+) is a major factor that contributes to the reaction rate of the CO oxidation.     

Intermolecular transfer of copper ions from the CopC protein of Pseudomonas syringae. Crystal structures of fully loaded Cu(I)Cu(II) forms

CopC is a small soluble protein expressed in the periplasm of Pseudomonas syringae pathovar tomato as part of its copper resistance response (cop operon). Equilibrium competition reactions confirmed two separated binding sites with high affinities for Cu(I) (10(-7) > or = K(D) > or = 10(-13) M) and Cu(II) (K(D) = 10(-13(1)) M), respectively. While Cu(I)-CopC was converted cleanly by O2 to Cu(II)-CopC, the fully loaded form Cu(I)Cu(II)-CopC was stable in air. Variant forms H1F and H91F exhibited a lower affinity for Cu(II) than does the wild-type protein while variant E27G exhibited a higher affinity. Cation exchange chromatography detected each of the four different types of intermolecular copper transfer reactions possible between wild type and variant forms: Cu(I) site to Cu(II) site; Cu(II) site to Cu(I) site; Cu(I) site to Cu(I) site; Cu(II) site to Cu(II) site. The availability of an unoccupied site of higher affinity induced intermolecular transfer of either Cu(I) or Cu(II) in the presence of O2 while buffering concentrations of cupric ion at sub-picomolar levels. Crystal structures of two crystal forms of wild-type Cu(I)Cu(II)-CopC and of the apo-H91F variant demonstrate that the core structures of the molecules in the three crystal forms are conserved. However, the conformations of the amino terminus (a Cu(II) ligand) and the two copper-binding loops (at each end of the molecule) differ significantly, providing the structural lability needed to allow transfer of copper between partners, with or without change of oxidation state. CopC has the potential to interact directly with each of the four cop proteins coexpressed to the periplasm.     

Well-studied Cu-BTC still serves surprises: evidence for facile Cu2+/Cu+ interchange

Cu-BTC (also known as HKUST-1) is a well-characterized metal-organic framework material produced in an industrial scale and widely studied for a number of potential applications by the scientific community. The co-existence of Cu(+) and Cu(2+) entities has already been observed in this material, but the presence of Cu(+) ions was attributed to oxide impurities. The results presented here clearly demonstrate that Cu(+) ions can be present in high concentrations inside the hybrid structure. Furthermore, switching between the two copper oxidation states can be induced by redox treatments, using vacuum and/or reducing gases at different sample temperatures.