Thiosubstituted Organophosphorus Acids as Selective Extractants for Ag(I) from Acidic Thiourea Solutions

Abstract

This paper deals with the solvent extraction of silver from thiourea leaching Ag ore liquors as an alternative to the traditional process involving cyanide. The investigation of the extraction mechanism of silver from acidic thiourea solution had not been clearly established to date.

The extraction behavior of silver using di(2‐ethylhexyl)dithiophosphoric acid (D2EHDTPA) and di(2,4,4‐trimethylpentyl) thiophosphinic acid (CYANEX 302) was studied. The effect of various parameters such as concentrations of metal, mineral acid, thiourea, and extractant has been investigated. The extracted complexes have been identified through a slope method analysis as AgX(HX)₅ for CYANEX 302 and AgX for D2EHDTPA, where HX denotes the extractant. Moreover, complete stripping was ensured with a mixture of NH₄SCN and H₂SO₄. In addition we showed that a first step of extraction with D2EHPA or CYANEX 272 results in the preferential separation of Fe(III) from the Ag(I) leach solution.     

Selective extraction,separation and recovery of Cu(II) in presence of Zn(II) and Ni(II) from leach liquor of waste printed circuit board using microcapsules coated with Cyanex 272

The study was conducted to optimize the selective extraction and recovery of Cu(II) in the presence of Zn(II) and Ni(II) from the leach liquor of waste printed circuit boards (PCBs). The extraction experiments were carried out according to 2⁴ factorial design of experiment to optimize the extraction factors. The design was analyzed using MINITAB to determine the main effects and interactions of the chosen extraction factors. The factors chosen were: extraction pH, amount of Cyanex 272 in dispersed phase during MC-Xs preparation, amount of MC-Xs and temperature. The pH, amount of MC-Xs and temperature were found to be statistically significant. The optimized experimental conditions for the Cu(II) extraction in presence of Zn(II) and Ni(II) were extraction pH 6.0, amount of Cyanex 272 in dispersed phase 3 g, amount of MC-Xs 2.5 g and Temperature 45 °C. Factorial design of experiment was also carried out to determine the Cu(II) stripping factors from the loaded MC-Xs using H₂SO₄ solution. The liquid-liquid extraction Cu(II) was conducted with the prime aim to evaluate the nature of Cu(II) complex extracted by Cyanex 272. Results showed that the extraction species is [Cu(HA₂)(Ac)·2HA]. Finally, a complete process for the separation and recovery of Cu(II), Zn(II) and Ni(II) from the leach liquor of waste PCBs was conducted based on the optimized experimental condition and effect of pH on extraction.     

Complexation Behavior of Iron(III) with Aloxime 800, D2EHPA,CYANEX 272, CYANEX 302, and CYANEX 301

Abstract

The extraction of iron(III) has been studied from chloride solutions with di(2‐ethylhexyl)phosphoric acid (D₂EHPA), bis(2,4,4‐trimethylpentyl)phosphinic acid (CYANEX 272) and its sulfur‐substituted analogs, called CYANEX 302, and CYANEX 301, and 5‐dodecylsalicylaldoxime (Aloxime 800).

Job's method was applied for the characterization of the iron(III) complexes dissolved in hexane. In the case of D₂EHPA and CYANEX 272, a 1:1 ligand‐to‐metal ratio was observed, thus inferring the coordination of additional compounds. No chloride transport occurred during extraction, therefore suggesting the formation of [Fe(OH)₂L] complexes. With CYANEX 302, a ratio of 2:1 was obtained, whereas for CYANEX 301, the results of Job's method indicated the presence of four extractant molecules around the metal ion. Less hydrolysis or the possible oxidation of the sulfur‐substituted organophosphinic acids and the corresponding reduction of Fe(III) towards Fe(II) may explain this behavior. In the case of Aloxime 800, the formation of the [FeL₃] species is suggested.

A comparative study was carried out to identify the ligand‐to‐metal ratio of the iron(III) complexes in anhydrous circumstances. These studies showed that 1:1 ligand‐metal complexes are easily formed in the case of the organophosphoric‐ and organophosphinic‐acid extractants. A higher ligand‐metal ratio may be possible, but is not always a necessary condition for iron(III) extraction. Even the coexistence of [FeCl₂L], [FeClL₂] and to a smaller extent [FeL₃] is quite presumable in anhydrous media. Finally, FT‐IR spectra as well as UV‐VIS spectra of the hexane phases make it possible to gain a better insight into the complexation characteristics of iron(III).     

Extraction and Separation of Zr(IV) and Hf(IV) from Nitrate Medium by Some CYANEX Extractants

Abstract

A solvent extraction study has been carried out to extract and separate zirconium and hafnium from nitrate medium by using some phosphine oxide extractants (CYANEX 921, CYANEX 923, and CYANEX 925) in kerosene. The influence of the different factors affecting the extraction process was studied in detail. Apparently the rate of extraction of Zr(IV) and Hf(IV) in CYANEX 921, CYANEX 923, and CYANEX 925 is reasonably fast. The extraction increases with increasing temperature, suggesting that the reaction is endothermic. The stripping percent of Zr(IV) and Hf(IV) by 0.5 M HNO₃ from the loaded organic phase after two stages reached 97.5% and 10.2%, respectively, which lead to good separation of the two metals. Under the optimum conditions, the extraction of zirconium was about 90, 87.6, and 91.6% and separation factors equal to 17, 21.4, and 40.7 were obtained for CYANEX 921, CYANEX 923, and CYANEX 925, respectively. The results obtained reveal that 2.0 M nitric acid is the optimum acid concentration for the separation of Zr(IV) and Hf(IV) and 0.4 M CYANEX 925 performs more efficient separation compared with other organophosphorus extractants.     

Preparation of waste-based Cu–Cu2O/SiO2 photocatalyst from serpentine tailings and waste printed circuit boards and photoreduction of Cr(VI)

In China, a large amount of serpentine tailings and waste printed circuit boards (WPCBs) are produced every year. Serpentine tailings contain about 43% SiO₂ and WPCBs contain about 20% Cu. Reusing their resources can not only solve the problem of environmental pollution, but also produce certain economic benefits. In this study, waste-based SiO₂ support, waste-based Cu–Cu₂O and Cu–Cu₂O/SiO₂ photocatalyst were prepared using serpentine tailings and WPCBs as Si and Cu sources. The waste-based SiO₂ of 750 nm particle size was obtained by precipitation of 0.7 mol/L Na₂SiO₃ solution from the serpentine tailings and its specific surface area reached 57.72 m²/g after 600 °C calcination. Cu and the waste-based Cu–Cu₂O were loaded on the waste-based Cu₂O and SiO₂ support, respectively, and the phase structure of the catalysts has not changed by the characterization of SEM, XRD and XPS. The activity of the photocatalytic reduction of Cr (VI) with the waste-based catalysts showed in the following order: Cu₂O < Cu₂O/SiO₂<Cu–Cu₂O < Cu–Cu₂O/SiO₂, inferring by the investigation of photoelectric properties that Cu prevented the recombination of Cu₂O electron-hole pairs, the Cu–Cu₂O dispersed on SiO₂ support surface to obtain a higher specific surface area. The waste-based Cu–Cu₂O/SiO₂ photocatalyst showed no obvious deactivation after 5 cycles. The mechanism revealed that photogenerated electrons are the major reactive species for the photodegradation of Cr (VI). The study indicates that the waste-based Cu–Cu₂O/SiO₂ is potentially a developed, low-cost catalyst from sustainable resources. The production of Cu–Cu₂O/SiO₂ photocatalyst by using WPCBs and serpentine tailings represents the potential usage of waste into valuable material.     

Selective and rapid uptake of Cu(II) by bis(benzimidazole) modified oxirane and thiirane resins

The benzimidazole containing ligand 1,3-bis(benzimidazol-2-yl)propylamine (bbpaH) was anchored onto poly(glycidyl methacrylate-co-trimethylolpropane trimethacrylate) (GMT) and onto the thiirane analogue of poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) (GME-S). Abbreviations of the modified polymers are GMT-bbpaH and GME-S-bbpaH. A multistep synthesis was applied in an attempt to increase the ligand concentration on the polymer GMT, This resulted in the resin GMT-bbpaH(ind) of which the solid state CP MAS ¹³C-NMR data showed that in this case only a monobenzimidazole was formed, i.e. only the 3-benzimidazole group was formed.Batch extraction capacities were determined for the chloride salts of Cu²⁺, Ni²⁺, Co²⁺, Cd²⁺, Zn²⁺ and Ca²⁺ in the pH range 0.9–6.0 in buffered solutions at room temperature. All three resins show a high selectivity for Cu²⁺ under competitive conditions, with maximum ligand occupations of 54%, 64% and 27% for GMT-bbpaH, GME-S-bbpaH and GMT-bbpaH(ind), respectively. The resin GMT-bbpaH also takes up some Zn²⁺ ions at pH > 4.5, the maximum ligand occupation being 17%. The resin GME-S-bbpaH shows some affinity for Zn²⁺ and Cd²⁺ ions in this pH range, with ligand occupations of 17% and 7%, respectively. Only GMT-bbpaH(ind) shows complete selectivity for Cu(II) at pH > 3, although the maximum Cu²⁺-uptake capacity is rather low.Kinetic experiments showed that the oxirane derivative exhibits a faster uptake kinetics compared with the thiirane analogue. Incomplete stripping of the Cu(II)-loaded ion-exchange resins and loss of Cu(II)-uptake capacity was observed during the regeneration experiments.     

One unexpected mixed-valence Cu(I,II)-cyanide coordination polymer in situ originating from the cleavage of acetonitrile

Solvothermal reaction of CuCl₂·2H₂O and 2-(4-pyridyl)benzimidazole (PyHBIm) in a acetonitrile-water mixed solvent afforded a mixture of [Cu^I₂Cu^II(CN)₂(PyHBIm)₂Cl₂]_n (1) and [Cu^II(PyH₂BIm)₂Cl₄] (2). Complex 1 is a mixed-valence 1D ribbon Cu(I,II)-cyanide coordination polymer. One Cu(II) center linearly links two Cu(I) ions via two μ₂-CN bridges. XPS spectrum and bond valence sum (BVS) analysis have confirmed the mixed-valence characteristics. Cu(II) ion adopts a centrosymmetric square-planar geometry surrounded by two cyanides and two pyridyl groups. Cu(I) ions adopt a trigonal geometry coordinated by cyanide, imidazole group and Cl⁻ anion. The cyanide ligand is in situ generated from the cleavage of acetonitrile solvent, which indicates that acetonitrile is an environmentally friend cyanating agent. The mechanism of acetonitrile in situ cleavage under solvothermal condition is explained. Complex 2 is a centrosymmetric mononuclear Cu(II) compound. Four equivalent Cl⁻ anions lie on the equatorial plane. The protonated PyH₂BIm⁺ cation as a monodentate ligand coordinates to Cu(II) center via pyridyl terminal.     

Preparation of Cu(II)-Imprinted Smart Microgels for Selective Separation of Copper Ions

In this study, we demonstrate a new kind of surface imprinted smart polymer by using methacrylic acid (MAA) as function monomer, attapulgite as the support material, ethylene glycol dimethacrylate (EGDMA) as a crosslinker, and 2, 2’-azobisisobutyronitrile (AIBN) as initiator to prepare Cu(II)-imprinted microgels. The results showed that the prepared imprinted microgels have a high affinity for Cu²⁺ over Ca²⁺ and Mg²⁺, and the adsorption equilibrium data fitted Freundlich isotherm model well. In addition, Cu(II)-imprinted smart microgels had pH sensitivity to control the selection recognition property. Besides, It is suggested that the Cu(II)-imprinted microgels was a material that was efficient, low-cost, and could be reused five times with about 15% regeneration loss.     

Steam Reforming of Methanol Over Cu/CeO2 Catalysts Studied in Comparison with Cu/ZnO and Cu/Zn(Al)O Catalysts

A series of Ce_1-xCu_xO_2- mixed oxides were synthesized using a co-precipitation method and tested as catalysts for the steam reforming of methanol. XRD patterns of the Ce_1-xCu_xO_2- mixed oxides indicated that Cu²⁺ ions were dissolved in CeO₂ lattices to form a solid solution by calcination at 773K when x < 0.2. A TPR (temperature-programmed reduction) investigation showed that the CeO₂ promotes the reduction of the Cu²⁺ species. Two reduction peaks were observed in the TPR profiles, which suggested that there were two different Cu²⁺ species in the Ce_1-xCu_xO_2- mixed oxides. The TPR peak at low temperature is attributed to the bulk Cu²⁺ species which dissolved into the CeO₂ lattices, and the peak at high temperature is due to the CuO species dispersed on the surface of CeO₂. The Ce_1-xCu_xO_2- mixed oxides were reduced to form Cu/CeO₂ catalysts for steam reforming of methanol, and were compared with Cu/ZnO, Cu/Zn(Al)O and Cu/AL₂O₃ catalysts. All the Cu-containing catalysts tested in this study showed high selectivities to CO₂ (over 97%) and H₂. A 3.8wt% Cu/CeO₂ catalyst showed a conversion of 53.9% for the steam reforming of methanol at 513K (W/F = 4.9 g h mol^-1), which was higher than that over Cu/ZnO (37.9%), Cu/Zn(Al)O (32.3%) and Cu/AL₂O₃ (11.2%) with the same Cu loading under the same reaction conditions. It is likely that the high activity of the Cu/CeO₂ catalysts may be due to the highly dispersed Cu metal particles and the strong metalsupport interaction between the Cu metal and CeO₂ support. Slow deactivations were observed over the 3.8wt% Cu/CeO₂ catalyst at 493 and 513K. The activity of the deactivated catalysts can be regenerated by calcination in air at 773K followed by reduction in H₂ at 673K, which indicated that a carbonaceous deposit on the catalyst surface caused the catalyst deactivation. Using the TPO (temperature-programmed oxidation) method, the amounts of coke on the 3.8wt% Cu/CeO₂ catalyst were 0.8wt% at 493K and 1.7wt% at 513K after 24h on stream.     

Effect of Cu(II) ligands on electroless copper deposition rate in formaldehyde solutions: An EQCM study

The electroless copper deposition rate for 6 Cu^II complexes decreases in the ligand sequence: nitrilotriacetic acid (NTA) > N,N,N′,N′-tetrakis-(2-hydroxypropyl)-ethylenediamine (Quadrol) > glycerol > L(+)-tartrate ~ sucrose > -tartrate. Both Cu^II complex stability and specific ligand effects were found to influence the Cu deposition process. The specific ligand effects are most obvious in the case of Quadrol (high kinetic activity at a high Cu^II complex stability), glycerol and sucrose (additional reaction of Cu₂O formation by interaction of Cu^II with ligand). According to the EQCM data for 11 Cu^II complexes (including data from the former study) the higher kinetic activity is demonstrated by complexes with ligands containing amino groups; this factor is more important for Cu deposition rate than copper complex stability. A potential dependence of the Cu reduction partial current on the electrode potential has been extracted from the EQCM data in the complete electroless plating bath. An increase in Cu^II reduction rate was found to occur in electroless plating solution for Cu^II complexes with NTA and Quadrol compared with that in formaldehyde-free solutions. Possible reasons for the acceleration of the partial Cu^II reduction reaction and the overall process kinetics are discussed using a hypothetical reaction sequence involving intermediate copper oxy-species and active Cu* formation as well as development of the preferred Cu surface structure.     

Preparation of a Cu(II)-PVA/PA6 Composite Nanofibrous Membrane for Enzyme Immobilization

PVA/PA6 composite nanofibers were formed by electrospinning. Cu(II)-PVA/PA6 metal chelated nanofibers, prepared by the reaction between PVA/PA6 composite nanofibers and Cu²⁺ solution, were used as the support for catalase immobilization. The result of the experiments showed that PVA/PA6 composite nanofibers had an excellent chelation capacity for Cu²⁺ ions, and the structures of nanofibers were stable during the reaction with Cu²⁺ solution. The adsorption of Cu(II) onto PVA/PA6 composite nanofibers was studied by the Langmuir isothermal adsorption model. The maximum amount of coordinated Cu(II) (q_m) was 3.731 mmol/g (dry fiber), and the binding constant (K_l) was 0.0593 L/mmol. Kinetic parameters were analyzed for both immobilized and free catalases. The value of V_max (3774 μmol/mg·min) for the immobilized catalases was smaller than that of the free catalases (4878 μmol/mg·min), while the K_m for the immobilized catalases was larger. The immobilized catalases showed better resistance to pH and temperature than that of free form, and the storage stabilities, reusability of immobilized catalases were significantly improved. The half-lives of free and immobilized catalases were 8 days and 24 days, respectively.     

The integral capacitance,kinetics and mechanisms of the Cu/Cu(II) system in sulphuric acid media

Galvanostatic investigation has been carried out on the Cu/Cu(II) system 2 M H₂SO₄ + 0.7 M CuSO₄, at 298 K. The pseudo-capacitance (integral capacitance) has been extracted as a function of overvoltage from the portion of the charging curve prior to plateaux. It has been found that the pseudo-capacitance, for both anodic and cathodic processes depended upon the current density and time. On the basis of the above findings the reaction mechanism has been suggested to be Cu?Cu(I)_ad^v + ve^?, Cu(I)_ad^v?Cu(I) + (1 ? v)e^?, Cu(I)?Cu(II)e^?.     

Reaction of N-Acetylcysteine with Cu2+: Appearance of Intermediates with High Free Radical Scavenging Activity: Implications for Anti-/Pro-Oxidant Properties of Thiols

We studied the kinetics of the reaction of N-acetyl-l-cysteine (NAC or RSH) with cupric ions at an equimolar ratio of the reactants in aqueous acid solution (pH 1.4–2) using UV/Vis absorption and circular dichroism (CD) spectroscopies. Cu²⁺ showed a strong catalytic effect on the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) radical (ABTSr) consumption and autoxidation of NAC. Difference spectra revealed the formation of intermediates with absorption maxima at 233 and 302 nm (ε₃₀₂/Cu > 8 × 10³ M⁻¹ cm⁻¹) and two positive Cotton effects centered at 284 and 302 nm. These intermediates accumulate during the first, O₂-independent, phase of the NAC autoxidation. The autocatalytic production of another chiral intermediate, characterized by two positive Cotton effects at 280 and 333 nm and an intense negative one at 305 nm, was observed in the second reaction phase. The intermediates are rapidly oxidized by added ABTSr; otherwise, they are stable for hours in the reaction solution, undergoing a slow pH- and O₂-dependent photosensitive decay. The kinetic and spectral data are consistent with proposed structures of the intermediates as disulfide-bridged dicopper(I) complexes of types cis-/trans-Cu^I₂(RS)₂(RSSR) and Cu^I₂(RSSR)₂. The electronic transitions observed in the UV/Vis and CD spectra are tentatively attributed to Cu(I) → disulfide charge transfer with an interaction of the transition dipole moments (exciton coupling). The catalytic activity of the intermediates as potential O₂ activators via Cu(II) peroxo-complexes is discussed. A mechanism for autocatalytic oxidation of Cu(I)–thiolates promoted by a growing electronically coupled –[Cu^I₂(RSSR)]_n– polymer is suggested. The obtained results are in line with other reported observations regarding copper-catalyzed autoxidation of thiols and provide new insight into these complicated, not yet fully understood systems. The proposed hypotheses point to the importance of the Cu(I)–disulfide interaction, which may have a profound impact on biological systems.     

Removal of Ag(l), Cu(II) and Zn(ll) ions with a supported liquid membrane containing cryptands as carriers

The interface behaviour in the facilitated co-transport of Ag(I), Cu(II) and Zn(II) ions through supported liquid membranes (SLMs) made of a flat-sheet polypropylene membrane support containing cryptands (2.2.2 or 2.2.1) as carriers was studied. The liquid-liquid extraction tests showed a maximum distribution coefficient when the carrier concentration was greaterthan 10⁻⁴M. In transport experiments the transmembrane flux increased with increasing carrier concentration reaching a limiting value at greater than 10⁻³M concentration. The calculation ofthe diffusion coefficients in membranes showed ahigherdiffusivityof2.2.2-metal complexes with respect to 2.2.1-metal complexes for silver ions. A sequence of diffusivity D(Ag+)>D(Cu²⁺)>D(Zn²⁺) was obtained, but carrier 2.2.1 showed a higher selectivity through copper ions. A sequence of diffusivity D(Cu²⁺)>D(Zn²⁺)>D(Ag⁺) was obtained. The diffusivity was significantly higher when using Celgard 2500 support compared to Celgard 2400 or 2402. Variable metal ion concentrations in the feed phase fluxes almost zero, at less than 10⁻² M concentration, were obtained. In the transient state of the transport through the SLM, different molar flow rates at the feed-membrane and membrane-strip interfaces were observed. The selectivity of the interfaces containing 2.2.2 in the separation binary mixtures of ions showed the following separation factors: SF_AgZn = 2.50, SF_AgCu = 1.64, SF_cuZn = 1.42.     

Interactions of polyelectrolytes bearing carboxylate and/or sulfonate groups with Cu(II) and Ni(II)

The interactions between the water-soluble polyelectrolytes poly(acrylic acid) (PAA) and poly(vinyl sulfonic acid) (PVS), and Cu(II) and Ni(II) are studied by the liquid-phase polymer-based retention (LPR) technique. Assuming a Ni(II)-PVS interaction of electrostatic nature, the nature of the Ni(II)-PAA interaction is found to be electrostatic, while Cu(II)-PAA interactions imply the formation of coordinative bonds. The charge related formation constants for the systems Ni(II)-PAA, Ni(II)-PVS, and Cu(II)-PVS are found to be 57.57×10², 43.4×10², and 60.5×102 M⁻¹, respectively in a 0.010 M NaNO₃ aqueous solution at pH 5, and 1.4×10² for both systems containing Ni(II) and 1.3×10² M⁻¹ for the system Cu(II)-PVS in a 0.10 M NaNO₃ aqueous solution at pH 5.     

Unique entangled Cu(II)-MOF featuring self-penetrating and polyhelix motifs generated from rigid azobenzenetetracarboxylic acid and N-donor coligands

A unique 3D entangling Cu(II)-metal organic framework, namely, {[Cu₄(abtc)₂(btab)₆·3H₂O]·2H₂O}_n (1), has been successfully constructed from Cu^II and 3,3′,5,5′-azo benzene tetracarboxylate building units with the aid of N-donor bridging spacers [1,4-bis(triazol)butane], and directs a rare self-penetrating structure with polyhelix motifs and presents a new (4,4,8)-connected (4.6⁵)₂(6⁴.7.8)₂(4².6²⁰.7².8⁴) topology. The magnetic investigations demonstrate that complex 1 exhibits antiferromagnetic coupling interaction between the adjacent Cu(II) ions.     

Manganese extraction with mixtures of bis(2,4,4-trimethylpentyl)dithiophosphinic acid and trioctyl phosphine oxide

It was shown that a strong synergistic effect (S ≈ 4000) takes place when extracting manganese (II) from sulfate solutions with mixtures of bis(2,4,4-trimethylpentyl)dithiophosphinic acid (CYANEX 301) and trioctyl phosphine oxide (TOPO. The synergistic effect is caused by the formation of the mixed complex Mn-HR-TOPO. Analysis of the manganese partition between organic and aqueous phase as well as of the IR and electron paramagnetic resonance spectra of the extracts showed that manganese forms a hexacoordinated complex with the dithiophosphinate ions and TOPO with an octahedral geometry. The composition of the complex can be presented as MnR₂?2TOPO.

Examples of the possible use of the CYANEX 301 and trialkyl phosphine oxide (TAPO, CYANEX 923) mixtures when processing manganese-containing liquors are given.     

Comprehensive Equilibrium Analysis of the Complexation of Cu(II) by Tetrathia-14-crown-4 in a Synergistic Extraction System Employing Didodecylnaphthalene Sulfonic Acid

Abstract

Liquid-liquid extraction experiments, UV/vis spectra, and equilibrium modeling by use of the program SXLSQA have been employed to reveal the origin of synergism in the extraction of Cu(II) from sulfuric acid by the tetradentate macrocycle tetrathia-14-crown-4 (TT14C4) combined with the cation exchanger didodecylnaphthalene sulfonic acid (HDDNS) in toluene. The key feature of the system is the 1:1 complexation of Cu(II) by TT14C4. HDDNS functions both as a source of exchangeable protons and as a solvating agent that promotes the formation of small, hydrated aggregates. In the absence of the cation-exchange vehicle provided by HDDNS, the macrocycle does not extract Cu(II) detectably. Combined with HDDNS, however, TT14C4 significantly enhances the extraction of the metal by HDDNS. Comparative UV/vis spectrophotometry indicates the formation of the deep-blue chromophore attributed to the complex ion Cu(TT14C4)²⁺, wherein the planar set of four endo sulfur donor atoms of TT14C4 circumscribes the metal cation. Modeling of the extraction and spectral absorbance data by use of the program SXLSQA supports the conclusion that this 1:1 complex accounts for essentially all of the extracted Cu(II) in excess of that extracted by HDDNS alone. The best model includes HDDNS aggregates incorporating Cu(TT14C4)²⁺ or Cu²⁺ ions. In the analysis, activity effects in both aqueous and organic phases have been taken into account by the Pitzer and Hildebrand-Scott treatments, respectively, with explicit inclusion of the formation of aqueous hydrogen sulfate ion. The model accounts for the effect of variation of the solute components CuSO⁴, H²SO⁴, HDDNS, and TT14C4.     

A Novel Cu(II)-Binding Peptide Identified by Phage Display Inhibits Cu2+-Mediated Aβ Aggregation

Copper (Cu) has been implicated in the progression of Alzheimer’s disease (AD), and aggregation of Cu and amyloid β peptide (Aβ) are considered key pathological features of AD. Metal chelators are considered to be potential therapeutic agents for AD because of their capacity to reduce metal ion-induced Aβ aggregation through the regulation of metal ion distribution. Here, we used phage display technology to screen, synthesize, and evaluate a novel Cu(II)-binding peptide that specifically blocked Cu-triggered Aβ aggregation. The Cu(II)-binding peptide (S-A-Q-I-A-P-H, PCu) identified from the phage display heptapeptide library was used to explore the mechanism of PCu inhibition of Cu²⁺-mediated Aβ aggregation and Aβ production. In vitro experiments revealed that PCu directly inhibited Cu²⁺-mediated Aβ aggregation and regulated copper levels to reduce biological toxicity. Furthermore, PCu reduced the production of Aβ by inhibiting Cu²⁺-induced BACE1 expression and improving Cu(II)-mediated cell oxidative damage. Cell culture experiments further demonstrated that PCu had relatively low toxicity. This Cu(II)-binding peptide that we have identified using phage display technology provides a potential therapeutic approach to prevent or treat AD.