Affinity For Cu Research Articles

Ascorbate Oxidation by Cu(Amyloid-β) Complexes: Determination of the Intrinsic Rate as a Function of Alterations in the Peptide Sequence Revealing Key Residues for Reactive Oxygen Species Production.

Along with aggregation of the amyloid-β (Aβ) peptide and subsequent deposit of amyloid plaques, oxidative stress is an important feature in Alzheimer's disease. Cu bound to Aβ is able to produce reactive oxygen species (ROS) by the successive reductions of molecular dioxygen, and the ROS produced contribute to oxidative stress. In vitro, ascorbate consumption parallels ROS production, where ascorbate is the reductant that fuels the reactions. Because the affinity of Cu for Aβ is moderate compared to other biomolecules, the rate of ascorbate consumption is a combination of two contributions. The first one is due to peptide-unbound Cu and the second one to peptide-bound Cu complexes. In the present Article, we aim to determine the amounts of the second contribution in the global ascorbate consumption process. It is defined as the intrinsic rate of ascorbate oxidation, which mathematically corresponds to the rate at an infinite peptide to Cu ratio, i.e., without any contribution from peptide-unbound Cu. We show that, for the wild-type Cu(Aβ) complex, this value equals 10% of the value obtained for peptide-unbound Cu and that this value is strongly dependent on peptide alterations. By examination of the dependence of the intrinsic rate of ascorbate oxidation, followed by UV-vis spectroscopy, for several altered peptides, we determine some of the key residues that influence ROS production.

The cytoplasmic Cu+‐chaperones of Pseudomonas aeruginosa

Copper is a micronutrient required by multiple enzymes as a redox co‐factor. However, free Cu is toxic, leading to Fe‐S cluster disassembly and reactive oxygen species. As such, immune cells use phagosomal Cu‐overload to clear pathogens. Thus, bacteria need to direct Cu to correct targets while maintaining non‐toxic levels. To limit toxicity, cells sequester and drive the efflux of Cu using various mechanisms. Among these, single cytoplasmic Cu‐chaperones mobilize the metal within the cell compartments. We recently used RNA‐seq to show that Pseudomonas has a network of proteins that mobilize Cu among cellular compartments. Importantly, our study uncovered the unusual presence of two putative Cu‐chaperones in these bacteria (CopZ1 and CopZ2). Both are under the control of the cytoplasmic Cu‐sensor CueR and consequently copZ1 and copZ2 expression is induced by exposure to Cu. Why is there two Cu‐chaperones in Pseudomonas? and why do both respond to Cu‐imbalances? We hypothesize that metabolically linked via Cu‐exchange, these two Cu‐chaperones deliver metal to different targets. We have observed that CopZ1 and CopZ2 share 37% identity (51% similarity), contain the invariant Cu‐binding motif (CxxC), and exhibit similar secondary structure in line with the βαββαβ‐fold, characteristic of Cu‐chaperones. Both proteins bind Cu with 1:1 stoichiometry and sub‐femtoMolar affinities. However, CopZ2 has 100‐times higher affinity for Cu compared to that of CopZ1. We determined the exchange of Cu between both proteins. As expected from the affinity constants, the Cu‐exchange equilibrium is displaced to the formation of the metallated‐CopZ2 form. Interestingly, both chaperones are able to transfer Cu to non‐cognate chaperones from other organisms, suggesting limited molecular recognition during metal‐exchange. Although both genes are equally induced by Cu‐stress, we observed that CopZ2 is 10‐times more abundant than CopZ1, under resting conditions and upon Cu stress. The differential response to Cu (affinities), protein levels, and their distinct electrostatic surface potential suggest that CopZ1 and CopZ2 deliver Cu to different targets and perhaps receive the metal from different molecules. Currently, we are testing which are these targets and Cu‐donors.Support or Funding InformationThis work was supported by NIH Grant R01 GM114949 to J.M.A..This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The transport of metal ions in hydrogels containing humic acids as active complexation agent

The complexation and transport/immobilization abilities of humic acids are the most important environmental qualities of these substances. Therefore, the study of these properties is important for understanding their role both in natural systems and in human-driven applications. This contribution is focused on the diffusion of metal ions (Co, Cu and Ni) studied by means of a diffusion couple, and their immobilization in humic hydrogels. It was found that the diffusion characteristics of metal ions are strongly affected by their reactivity and their initial concentrations. The concentration dependence of Cu diffusivity exhibited a different trend when compared to Co and Ni, which the result of the high affinity of Cu to humic acids. When a metal ion is first complexed by humic acids it is bound in an exchangeable mode, which can be transferred to a nonexchangeable one. Our results indicate that the dynamic equilibrium established in the diffusion process includes mainly Cu ions in an exchangeable mode as a result of their high affinity and the high amount of bound Cu. Their transformation of bound Cu ions in strong Cu-humic complexes is very slow. In contrast, Co and Ni have much lower affinities to humic acids, thus their diffusivities are less affected by their reaction with humic acids.

Colorimetric determination of the activity of alkaline phosphatase based on the use of Cu(II)-modulated G-quadruplex-based DNAzymes.

A colorimetric detection scheme is introduced for the determination of alkaline phosphatase (ALP) activity based on Cu(II)-modulated G-quadruplex-based DNAzymes. It is exploiting the strong affinity of Cu(II) for pyrophosphate (PPi) upon which the cofactor PPi is trapped by Cu(II). Hence, the activity of the DNAzyme is inhibited. ALP catalyzes the hydrolysis of PPi, causing the release of Cu(II). DNAzyme, in turn, is activated and catalyzes the cleavage of the DNA probe substrate. The released G-rich sequence folds into the G-quadruplex, which can bind hemin and catalyze the oxidation of 2,2'-azinobis (3-ethylbenzothiozoline)-6-sulfonate (ABTS), and this leads to an increase in absorbance at 420nm. Absorbance increases linearly with increasing ALP activity in 0.07 to 300U.L-1 range, with a 70mU.L-1 detection limit. The method was applied in ALP inhibition tests and to the determination of ALP activity in spiked serum samples where it gave satisfactory results. Graphical abstract A colorimetric method has been developed for the detection of alkaline phosphatase based on the use of Cu(II)-modulated G-quadruplex-based DNAzymes.

Thermo-responsive ion imprinted polymer on the surface of magnetic carbon microspheres for identification and removal of low-concentrations of Cu2+

Environmental contextBecause of the multiple industrial applications of metals, contamination by metal ions is widespread and can at times endanger the environment and the health of human beings. We prepared ion-imprinted adsorbents to achieve selective recognition and smart separation of low-concentrations of copper ions from water. These smart imprinted materials have high potential for selective adsorption and removal of contaminant copper ions, particularly at very low concentrations. AbstractA temperature-responsive magnetic adsorbent (poly(N-propyl acrylamide) grafted magnetic carbon microspheres, Cu2+-IIP) was synthesised by ion imprinting technology for low concentration Cu2+ removal. Cu2+-IIP was prepared by using N-propyl acrylamide as a thermo-sensitive functional monomer, N,N-methylene-bis-acrylamide as a cross-linker and ammonium persulfate as an initiator. The morphologies and microstructures of samples were characterised by transmission electron microscopy, Fourier transform infrared spectrometry, thermogravimetry and vibrating sample magnetometry. Adsorption experiments were conducted in terms of kinetics, isotherms and selective recognition adsorption at low feed concentrations. Results indicate that Cu2+-IIP possesses good recognition selectivity and affinity for Cu2+, and can be separated from the treated solution quickly by applying an external magnetic field. The adsorption capacity towards Cu2+ depends on temperature and reaches a maximum value of 45.46 mg g−1 at 35 °C, higher than that of the non-imprinted polymer. The adsorption behaviour of Cu2+ on Cu2+-IIP can be well defined with both the pseudo-second-order kinetic model and Langmuir isotherm model. Cu2+-IIP performs good adsorption selectivity towards Cu2+ because the relative selectivity factors of Cu2+ with respect to Ni2+, Zn2+ and Cd2+ are 7.14, 7.60 and 6.77, respectively. The adsorption capacity of Cu2+-IIP remained 88.41 % after five cycles.

Antiviral activity and metal ion-binding properties of some 2-hydroxy-3-methoxyphenyl acylhydrazones.

Here we report on the results obtained from an antiviral screening, including herpes simplex virus, vaccinia virus, vesicular stomatitis virus, Coxsackie B4 virus or respiratory syncytial virus, parainfluenza-3 virus, reovirus-1 and Punta Toro virus, of three 2-hydroxy-3-methoxyphenyl acylhydrazone compounds in three cell lines (i.e. human embryonic lung fibroblast cells, human cervix carcinoma cells, and African Green monkey kidney cells). Interesting antiviral EC50 values are obtained against herpes simplex virus-1 and vaccinia virus. The biological activity of acylhydrazones is often attributed to their metal coordinating abilities, so potentiometric and microcalorimetric studies are here discussed to unravel the behavior of the three 2-hydroxy-3-methoxyphenyl compounds in solution. It is worth of note that the acylhydrazone with the higher affinity for Cu(II) ions shows the best antiviral activity against herpes simplex and vaccinia virus (EC50~1.5µM, minimal cytotoxic concentration=60µM, selectivity index=40).

Complexation of copper in acetate-rich low-temperature hydrothermal fluids: Evidence from ab initio molecular dynamics simulations

Acetate ions are widely distributed in various geo-fluids and can be enriched in metamorphic brines under saturated vapor pressure in the temperature range of 80 to 200°C. To examine the potential role of acetate in transporting metals, we conducted a series of ab initio molecular dynamics (MD) simulations to investigate the complexation of Cu+ with Cl−, HS− and acetate ions. All the ab initio MD simulations were conducted at the temperature of 150°C and pressures of 10bar or 1000bar. The ionic compositions of aqueous solutions for the simulations include four groups: (1) Cu+ and CH3COO−; (2) Cu+, CH3COO− and Cl−; (3) Cu+, CH3COO−, Cl− and HS−; and (4) Cu+, CH3COO− and HS−. The simulation results demonstrated some important regularities for complexation of copper with acetate. The static computation results suggest that Cu+ forms linear complexes with one or two acetate ions, rather than with one acetate ion in a nearly symmetric bidentate structure. The stoichiometry of the complexes, which can be represented by [Cu(CH3COO)(H2O)], [(CH3COO)2Cu]− and [Cu(CH3COO)Cl]−, depends on the fluid composition, environmental pressure and solvated structures of the acetate ligands in these complexes. Compared with Cl−, the acetate ion is a ligand of higher affinity for Cu+, and the solvated structure of acetate ligands can prevent Cl− from approaching Cu+. The presence of HS− also inhibits the formation of a Cu-Cl bond, thereby enhancing the stability of the Cu-OH2 bond in [Cu(CH3COO)(H2O)]. We also investigated the free energy surfaces of the ligand exchange reactions, CuCH3COO2-+2Cl-=CuCl2-+2CH3COO-andCuCH3COO2-+2HS-=CuHS2-+2CH3COO-. Combined with the results from ab initio MD simulations, we conclude that the order of affinity of Cu+ to form complexes in these conditions is HS−>CH3COO−>Cl−>H2O. These conclusions provide important evidence for evaluating the role of acetate ligands in transporting Cu during low temperature mineralization.

The Stoichiometry of Isoquercitrin Complex with Iron or Copper Is Highly Dependent on Experimental Conditions.

Interaction of flavonoids with transition metals can be partially responsible for their impact on humans. Stoichiometry of the iron/copper complex with a flavonoid glycoside isoquercitrin, a frequent component of food supplements, was assessed using competitive and non-competitive methods in four (patho)physiologically-relevant pH values (4.5. 5.5, 6.8, and 7.5). Isoquercitrin chelated all tested ions (Fe2+, Fe3+, Cu2+, and Cu+) but its affinity for Cu+ ions proved to be very low. In general, the chelation potency dropped with pH lowering. Metal complexes of 1:1 stoichiometry were mostly formed, however, they were not stable and the stoichiometry changed depending on conditions. Isoquercitrin was able to reduce both Cu2+ and Fe3+ ions at low ratios, but its reducing potential was diminished at higher ratios (isoquercitrin to metal) due to the metal chelation. In conclusion, this study emphasizes the need of using multiple different methods for the assessment of chelation potential in moderately-active metal chelators, like flavonoids.

Methionine 109 plays a key role in Cu(II) binding to His111 in the 92–115 fragment of the human prion protein

The cellular prion protein (PrPC) is a monomeric glycoprotein expressed mainly in the central nervous system. Although its function is not understood, it has been proposed to be involved in Cu transport. Human PrP (hPrP) can bind up to six Cu(II) ions at its unstructured N-terminal region; two of them at the non-octarepeat region, encompassing His96 and His111. The Cu(II) coordination features of these two sites are practically identical, yet Cu ions have a preference for binding at the His111 site, which is unique in that it contains two Met residues in a MKHM motif. Here, the hPrP(92–115) peptide fragment, containing both His binding sites, and its variants with Met to Ile substitutions have been studied, to evaluate the role of Met109 and Met112 in the relative Cu(II) loading into the His111 and His96 sites. The fact that Cu(II) bound to His96 and His111 display distinct circular dichroism spectra allowed to discern Cu binding to each site under different experimental conditions. Through a combination of spectroscopic and calorimetric studies, we demonstrate that His111 has a slightly higher affinity for Cu(II) than His96, and that Met109 plays an important role in the binding preference of Cu(II) for the His111 site. Met109 profiles as a highly important residue that, not only assures a preferential loading of Cu(II) ions into the His111 site, but it also serves as a Cu(I) anchoring residue and it might be a key player for Cu transport by hPrP.

Adsorption isotherm, kinetics and thermodynamic analysis of Cu(II) ions onto the dried algal biomass ( Spirulina platensis )

In the present study, the removal of Cu(II) ions from aqueous solution have been studied by using a newly prepared biosorbents from Spirulina platensis (SP). SEM-EDX, FTIR and XRD analyses of the biosorbents have been reported. Langmuir monolayer adsorption capacity of ultrasonic assisted SP (UASP) for Cu(II) ions (817.7 mg/g) was found to be higher as compared with raw SP (RSP) and sulphuric acid modified SP (SMSP). Adsorption kinetics and isotherms of Cu(II) ions onto UASP followed the pseudo-first order and Freundlich models. Adsorption process was measured as exothermic and spontaneous in nature. UASP showed higher affinity for Cu(II) ions.

Oligopeptide models of the metal binding loop of the bacterial copper efflux regulator protein CueR as potential Cu(I) chelators

Copper(I) binding features of oligopeptides, mimicking the metal binding loops (MBL) of the bacterial copper efflux regulator protein CueR, were investigated with an aim of exploring potential candidates for Cu(I)-sequestration. Two of the studied ligands comprise the MBL of E. coli CueR (Ac-ACPGDDSADCPI-NH2; EC) and V. cholerae CueR (Ac-SCPGDQGSDCPI-NH2; VC) while the third peptide is a His-containing variant of VC (Ac-SCHGDQGSDCSI-NH2; HS). UV-titrations of the ligands by Cu(I) at pH = 7.4 and monitoring the characteristic SCys− → Cu(I) charge transfer bands, together with CD-experiments, indicated the exclusive formation of monomeric Cu(I)-complexes (CuL) up to a 1:1 Cu(I):L ratio and the presence of oligometallic/cluster type complexes at Cu(I)-excess. Such a change in speciation and the domination of the latter species was also supported by comparing the ESI-MS spectra obtained at 0.9:1 and 2:1 Cu(I):peptide ratios. pH-dependence of the UV spectra of the Cu(I):peptide 1:1 complexes reflected the formation of the two thiolate-Cu(I) bonds well below neutral pH, as two successive deprotonation processes could be fitted by apparent pKa values falling in the pH range of 1.8–3.0 and 4.3–5.5. Cu(I)-binding affinity of the ligands was determined by competition experiments applying the bicinchoninate ion for the displacement of the Cu(I)-ligated peptides. The obtained conditional stability constants (logβ11pH7.4 = 15.3, 15.8 and 16.3 for Cu(EC), Cu(VC) and Cu(HS), respectively) indicate a strong affinity of Cu(I) to each ligand and suggest a slight destabilizing effect of charge repulsion between sidechain groups in EC while a possible Cu(I)-coordination of the histidine residue in HS.

Anomalous electron transport in metal/carbon multijunction devices by engineering of the carbon thickness and selecting metal layer

A longstanding concern in the research of amorphous carbon films is their poor electrical conductivity at room temperature which constitutes a major barrier for the development of cost effective electronic and optoelectronic devices. Here, we propose metal/carbon hybrid multijunction devices as a promising facile way to overcome room temperature electron transport issues in amorphous carbon films. By the tuning of carbon thickness and swapping metal layers, we observe giant (upto ∼7 orders) reduction of electrical resistance in metal/carbon multijunction devices with respect to monolithic amorphous carbon device. We engineer the maximum current (electrical resistance) from about 10−7 to 10−3 A (∼107 to 103 Ω) in metal (Cu or Ti)/carbon hybrid multijunction devices with a total number of 10 junctions. The introduction of thin metal layers breaks the continuity of relatively higher resistance carbon layer as well as promotes the nanostructuring of carbon. These contribute to low electrical resistance of metal/carbon hybrid multijunction devices, with respect to monolithic carbon device, which is further reduced by decreasing the thickness of carbon layers. We also propose and discuss equivalent circuit model to explain electrical resistance in monolithic carbon and metal/carbon multijunction devices. Cu/carbon multijunction devices display relatively better electrical transport than Ti/carbon devices owing to low affinity of Cu with carbon that restricts carbide formation. We also observe that in metal/carbon multijunction devices, the transport mechanism changes from Poole-Frenkel/Schottky model to the hopping model with a decrease in carbon thickness. Our approach opens a new route to develop carbon-based inexpensive electronic and optoelectronic devices.

Copper adsorption on composites of goethite, cells of Pseudomonas putida and humic acid

In the soil environment, iron oxides co‐occur commonly with different types of organic constituents to produce iron oxide–organic composites that play an important role in the biogeochemical cycling of trace metals. We investigated copper (Cu) adsorption on synthetic goethite, Pseudomonas putida (CCTCC M209319) bacterial cells, humic acid (HA) and their binary and ternary composites with batch adsorption experiments coupled with isothermal titration calorimetry (ITC). Morphological characterizations show that the three components can form closely combined and heterogeneous aggregates with one another. The kinetics of sorption of Cu to these composite materials conforms to the pseudo‐second‐order model, whereas the Cu sorptivities deviate from linear additivity. Specifically, Cu sorptivities on the binary goethite–P. putida and P. putida–HA and ternary goethite–P. putida–HA composites are less than expected assuming additivity, whereas the opposite is seen for the binary goethite–HA composite. There is considerable masking of adsorption sites in the ternary goethite–P. putida–HA system, but the binding sites on bacteria are not completely covered, as shown by the adsorption enthalpy and entropy (19.60 kJ mol−1 and 120.9 J mol−1 K−1, respectively) for the ternary composite. We conclude that the binding affinity of Cu for the binary goethite–humic acid composite is larger than that for the bacterial composites with goethite or humic acid, or both. This research indicates that bacteria, iron oxide and humic substances exhibit different behaviour in the sequestration of heavy metals when they form various binary and ternary complexes in natural environments.HighlightsHow does mineral–organic interaction affect the binding behaviour of trace elements? First investigation of Cu sorption to goethite–bacteria–humic acid composites. Goethite–HA shows enhanced Cu adsorption, whereas the opposite is true for bacterial complexes. Various bacteria–iron oxide–humic substance composites behave differently in metal sequestration.

Separation of Lead with a Novel Ion Separating Agent Prepared by Clothing a Chitin Whisker on a Potassium Tetratitanate Whisker.

Separation of Pb2+ from Cu2+-Pb2+ mixed solution by a newly-developed ion separating agent was examined, which was obtained by clothing chitin whiskers (ChW) on the surface of potassium tetratitanate whiskers (PTW). The separation capability and mechanism of the ion separating agent (ChW-PTW) was determined, based on the difference of the adsorption isotherm pattern and the adsorption kinetics model between ChW and PTW on Cu2+ and Pb2+, respectively. The results showed that the adsorption process of ChW could be described by Freundlish isotherm. The adsorption affinity of Cu2+ (kF = 0.085·g−1) on ChW was greater than Pb2+ (kF = 0.077 g−1). The adsorption pattern of PTW was inclined to the Langmuir isotherm, and Pb2+ (kL = 310.59 L·mmol−1) could be obviously more easily adsorbed on PTW than Cu2+ (kL = 25.85 L·mmol−1). The experimental data both fitted well with the pseudo-second order kinetics. The reaction rate of Pb2+ (k2 = 4.442 for ChW and k2 = 0.846 for PTW) was greater than that of Cu2+ on both ChW and PTW, while the diffusion rate of intra-particles of PTW was much higher than ChW. The adsorption model of ChW and PTW could illustrate well the separation mechanism of ChW-PTW and allowed for relevant results.

Growth of copper–benzene-1,3,5-tricarboxylate on boron nitride nanotubes and application of the composite in methane sensing

A new composite material based on copper–benzene-1,3,5-tricarboxylate (Cu–BTC) deposited on boron nitride nanotubes (BNNTs) in a hydrothermal process were investigated for methane (CH4) sensing. The composite was characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The Cu–BTC deposited on the BNNTs had an average grain size of 80nm. The sensing performance of the as-grown product was studied for different concentrations of CH4 (20–200ppm) at 150°C. The results revealed that the Cu–BTC/BNNT composite exhibited high sensitivity and selectivity toward CH4. The good sensing performance of the composite was attributed to the high surface area and high affinity of Cu–BTC for CH4, which would allow the composite to act like a preconcentrator for CH4 gas sensing.

Synthesis, characterization and xanthine oxidase inhibition of Cu(II)–chrysin complex

Xanthine oxidase (XO) is a key enzyme catalyzing hypoxanthine to xanthine and then uric acid causing hyperuricemia. A Cu(II) complex of chrysin was synthesized and characterized by UV–vis absorption, Fourier transform infrared, nuclear magnetic resonance (1H NMR) and mass spectroscopy studies. The interaction of Cu(II)-complex with XO was investigated by spectroscopic methods and molecular simulation. The Cu(II)-chrysin complex exhibited a better inhibitory ability (IC50=0.82±0.034μM) against XO than its corresponding ligands chrysin and Cu2+ in a mix-competitive manner. The binding affinity of Cu(II)-chrysin complex with XO was much higher than that of chrysin. The hydrogen bonds and van der Waals forces played main roles in the binding. Analysis of circular dichroism spectra indicated that the complex induced the conformational change of XO. The molecular simulation found that the Cu(II)-chrysin complex inserted into the active cavity of XO with Cu acting as a bridge, occupying the catalytic center of the enzyme to avoid entry of the substrate xanthine, leading to the inhibition of XO. This study may provide new insights into the inhibition mechanism of the Cu(II)-chrysin complex as a promising XO inhibitor and its potential application for the treatment of hyperuricemia.

What Is the Preferred Conformation of Phosphatidylserine-Copper(II) Complexes? A Combined Theoretical and Experimental Investigation.

Phosphatidylserine (PS) has previously been found to bind Cu2+ in a ratio of 1 Cu2+ ion per 2 PS lipids to form a complex with an apparent dissociation constant that can be as low as picomolar. While the affinity of Cu2+ for lipid membranes containing PS lipids has been well characterized, the structural details of the Cu-PS2 complex have not yet been reported. Coordinating to one amine and one carboxylate moiety on two separate PS lipids, the Cu-PS2 complex is unique among ion-lipid complexes in its ability to adopt both cis and trans conformations. Herein, we determine which stereoisomer of the Cu-PS2 complex is favored in lipid bilayers using density functional theory calculations and electron paramagnetic resonance experiments. It was determined that a conformation in which the nitrogen centers are cis to each other is the preferred binding geometry. This is in contrast to the complex formed when two glycine molecules bind to Cu2+ in bulk solution, where the cis and trans isomers exist in equilibrium, indicating that the lipid environment has a significant steric effect on the Cu2+ binding conformation. These findings are relevant for understanding lipid oxidation caused by Cu2+ binding to lipid membrane surfaces and will help us understand how ion binding to lipid membranes can affect their physical properties.

Electrospray ionization in the study of the interactions between cytotoxic phosphino Cu(I) complexes and selected amino acids and GlyGlyHis peptide model.

Tetrahedral [Cu(P)4][BF4]-type complexes (P = tertiary phosphine) are a class of monopositively charged compounds that have shown notable antitumor activity in both in vitro and in vivo tests. This biological property appears to be related to the peculiar physicochemical characteristics of these compounds. Although thermodynamically stable, they are labile at micromolar concentrations. Such a behavior allows the Cu(I) ion in [Cu(P)n]+ assemblies (n < 4) to interact with surrounding molecules, including the rich peptide/protein environment that metal complexes have to face in the physiological milieu on the way to tumor cells. The scope of this investigation was to study the interaction products that originate from the treatment in water/methanol mixtures of representative phosphino Cu(I) compounds with an excess of individual amino acids (AAs) selected on the basis of the donor atom likely involved in metal coordination (i.e. O-glycine, S-methionine and N-histidine). These interactions have been investigated in electrospray ionization mass spectrometry (ESI-MS), mainly in the positive ion mode [ESI(+)MS], and the interaction products have been characterized by sequential collisional experiments, performed by an ion trap instrument. Histidine and methionine, but not glycine, were able to mine Cu(I) from [Cu(P)n]+ assemblies through the formation of mixed [CuI(P)(AA)]+ and eventually [CuI(AA)2]+ adducts. The ability to substitute phosphine(s) by AAs and the strongest affinity for Cu(I) was proved by the study of the energetics of collisional-induced decomposition (CID) reactions [CuI(P)(AA)]+ → CuI(AA) + P]+. Among the investigated AAs, histidine displayed the strongest affinity for Cu(I). Transchelation of Cu(I) was similarly observed when [Cu(P)n]+ species were treated with the model tripeptide GlyGlyHis (GGH), the most investigated member of the amino terminal Cu(II) and Ni(II) (ATCUN) peptide family. GGH was able to form robust metal adducts not only with Cu(II) and the related divalent Zn(II) and Ni(II) ions, but also with monovalent ions, including Cu(I) and Ag(I). CID pathways of [CuI(GGH)]+ and [AgI(GGH)]+ were qualitatively superimposable and proceeded through losses of neutral fragments. Similar losses of neutral fragments were observed from [ZnII(GGH)] and [NiII(GGH)]. CID pathways of [CuII(GGH)]-/+ adducts instead took place mainly through intramolecular electron-transfer reactions comprising the reduction of Cu(II) to Cu(I) and the formation of fragment radical cations.

Synthesis of Highly Porous Coordination Polymers with Open Metal Sites for Enhanced Gas Uptake and Separation.

Metal-containing amorphous microporous polymers are an emerging class of functional porous materials in which the surface properties and functions of polymers are dictated by the nature of the metal ions incorporated into the framework. In an effort to introduce coordinatively unsaturated metal sites into the porous polymers, we demonstrate herein an aqueous-phase synthesis of porous coordination polymers (PCPs) incorporating bis(o-diiminobenzosemiquinonato)-Cu(II) or -Ni(II) bridges by simply reacting hexaminotriptycene with CuSO4·5H2O [Cu(II)-PCP] or NiCl2·6H2O [Ni(II)-PCP] in H2O. The resulting polymers showed surface areas of up to 489 m2 g-1 along with a narrow pore size distribution. The presence of open metal sites significantly improved the gas affinity of these frameworks, leading to an exceptional isosteric heat of adsorption of 10.3 kJ·mol-1 for H2 at zero coverage. The high affinities of Cu(II)- and Ni(II)-PCPs toward CO2 prompted us to investigate the removal of CO2 from natural and landfill gas conditions. We found that the higher affinity of Cu(II)-PCP compared to that of Ni(II)-PCP not only allowed for the tuning of the affinity of CO2 molecules toward the sorbent, but also led to an exceptional CO2/CH4 selectivity of 35.1 for landfill gas and 20.7 for natural gas at 298 K. These high selectivities were further verified by breakthrough measurements under the simulated natural and landfill gas conditions, in which both Cu(II)- and Ni(II)-PCPs showed complete removal of CO2. These results clearly demonstrate the promising attributes of metal-containing porous polymers for gas storage and separation applications.

Porphyrinic Metal–Organic Framework Catalyzed Heck-Reaction: Fluorescence “Turn-On” Sensing of Cu(II) Ion

It is of great importance for the highly selective, rapid, and sensitive detection of Cu(II) ion, as copper is an essential element in the environment and the human body, and exposure to high concentrations of Cu(II) will potentially cause health issues. In this work, we have developed a novel catalytic Heck reaction system based on Pd(II)-porphyrinic metal–organic framework (MOF), PCN-222-Pd(II), to generate highly fluorescent product in the presence of Cu(II). In this system, the achieved signal enlargement toward Cu(II) with high sensitivity not only takes advantage of a stronger binding affinity of Cu(II) over Pd(II) to the nitrogen atoms in the porphyrin, but also a rapid Pd(0)-catalyzed Heck-reaction triggered by the addition of Cu(II) ion. Compared with the previous detection methods, the current fluorescence “turn-on” approach not only realizes highly selective and sensitive detection of Cu(II) in aqueous solution, but also is able to separate the Cu(II) from the system. This work would open up a ...