Site‐specific reversible immobilization and purification of His‐tagged protein on poly(2‐acetamidoacrylic acid) hydrogel beads

Ni²⁺‐complexed poly(2‐acetamidoacrylic acid) (PAAA) hydrogel beads were developed for the site‐specific reversible immobilization and purification of the histidine‐tagged green fluorescent protein (His‐tagged GFP). PAAA hydrogel beads were prepared by photopolymerization, and significantly improved mechanical properties of PAAA hydrogel beads were observed in comparison with PAAA hydrogel from our previous study. Confocal laser scanning microscopy was used to determine the binding of His‐tagged GFP to the hydrogel beads in three‐dimensional space. Photoluminescence spectroscopy revealed 89% of binding efficiency of His‐tagged GFP to the Ni²⁺‐PAAA hydrogel beads, 51% of yielding recovery. The maximum binding capacity of His‐tagged GFP was estimated to be 0.45 µg/mg of Ni²⁺‐PAAA hydrogel beads. The recombinant His‐tagged GFP from the soluble fraction of E. coli BL21(DE3) cell lysates was purified with Ni²⁺‐PAAA hydrogel beads. The major advantage of the Ni²⁺‐PAAA hydrogel beads system was simple preparation procedures of producing the matrix, because PAAA hydrogel beads had relatively enhanced mechanical strength than soft hydrogels. Copyright © 2012 John Wiley & Sons, Ltd.     

Cobalt(III)‐Mediated Permanent and Stable Immobilization of Histidine‐Tagged Proteins on NTA‐Functionalized Surfaces

We present the cobalt(III)‐mediated interaction between polyhistidine (His)‐tagged proteins and nitrilotriacetic acid (NTA)‐modified surfaces as a general approach for a permanent, oriented, and specific protein immobilization. In this approach, we first form the well‐established Co²⁺‐mediated interaction between NTA and His‐tagged proteins and subsequently oxidize the Co²⁺ center in the complex to Co³⁺. Unlike conventionally used Ni²⁺‐ or Co²⁺‐mediated immobilization, the resulting Co³⁺‐mediated immobilization is resistant toward strong ligands, such as imidazole and ethylenediaminetetraacetic acid (EDTA), and washing off over time because of the high thermodynamic and kinetic stability of the Co³⁺ complex. This immobilization method is compatible with a wide variety of surface coatings, including silane self‐assembled monolayers (SAMs) on glass, thiol SAMs on gold surfaces, and supported lipid bilayers. Furthermore, once the cobalt center has been oxidized, it becomes inert toward reducing agents, specific and unspecific interactions, so that it can be used to orthogonally functionalize surfaces with multiple proteins. Overall, the large number of available His‐tagged proteins and materials with NTA groups make the Co³⁺‐mediated interaction an attractive and widely applicable platform for protein immobilization.     

Metal‐ion complexes in the angiogenetic effect

The complex formation between two polysaccharides, hyaluronic acid (Hyal) and its sulphated derivative (HyalS), and two metal ions, Cu²⁺ and Zn²⁺ was investigated in aqueous solution by thermodynamic and spectroscopic techniques. A stoichiometry for the complex species in solution was obtained. The bioactivity of the metal‐polysaccharide complexes was then evaluated in terms of their influence on endothelial cell migration and adhesion. The biological response of the complex species was found to be dependent of both the polysaccharide (Hyal or HyalS) and the metal ion (Cu²⁺ or Zn²⁺).     

New Insight in Copper‐Ion Binding to Human Islet Amyloid: The Contribution of Metal‐Complex Speciation To Reveal the Polypeptide Toxicity

Type‐2 diabetes (T2D) is considered to be a potential threat on a global level. Recently, T2D has been listed as a misfolding disease, such as Alzheimer's and Parkinson's diseases. Human islet amyloid polypeptide (hIAPP) is a molecule cosecreted in pancreatic β cells and represents the main constituent of an aggregated amyloid found in individuals affected by T2D. The trace‐element serum level is significantly influenced during the development of diabetes. In particular, the dys‐homeostasis of Cu²⁺ ions may adversely affect the course of the disease. Conflicting results have been reported on the protective role played by complex species formed by Cu²⁺ ions with hIAPP or its peptide fragments in vitro. The histidine (His) residue at position 18 represents the main binding site for the metal ion, but contrasting results have been reported on other residues involved in metal‐ion coordination, in particular those toward the N or C terminus. Sequences that encompass regions 17–29 and 14–22 were used to discriminate between the two models of the hIAPP coordination mode. Due to poor solubility in water, poly(ethylene glycol) (PEG) derivatives were synthesized. A peptide fragment that encompasses the 17–29 region of rat amylin (rIAPP) in which the arginine residue at position 18 was substituted by a histidine residue was also obtained to assess that the PEG moiety does not alter the peptide secondary structure. The complex species formed by Cu²⁺ ions with Ac‐PEG‐hIAPP(17–29)‐NH₂, Ac‐rIAPP(17–29)R18H‐NH₂, and Ac‐PEG‐hIAPP(14–22)‐NH₂ were studied by using potentiometric titrations coupled with spectroscopic methods (UV/Vis, circular dichroism, and EPR). The combined thermodynamic and spectroscopic approach allowed us to demonstrate that hIAPP is able to bind Cu²⁺ ions starting from the His18 imidazole nitrogen atom toward the N‐terminus domain. The stability constants of copper(II) complexes with Ac‐PEG‐hIAPP(14–22)‐NH₂ were used to simulate the different experimental conditions under which aggregate formation and oxidative stress of hIAPP has been reported. Speciation unveils: 1) the protective role played by increased amounts of Cu²⁺ ions on the hIAPP fibrillary aggregation, 2) the effect of adventitious trace amounts of Cu²⁺ ions present in phosphate‐buffered saline (PBS), and 3) a reducing fluorogenic probe on H₂O₂ production attributed to the polypeptide alone.     

Reversible and Selective Fluorescence Detection of Histidine Using a Naphthalimide‐Based Chemosensing Ensemble

We described a new ensemble‐approach‐based chemosensor, NCH‐Cu²⁺, for highly selective and reversible detection of histidine (His) in aqueous solution and live cells. The ligand NCH exhibited specific binding with Cu²⁺ ions over other metal ions, accompanied with a 92.2 % fluorescence quenching. The decomplexation of NCH‐Cu²⁺ ensemble by His led to the liberation of the fluorophore, NCH, and thus the fluorescence was recovered. The specific fluorescence enhancement of NCH‐Cu²⁺ towards His showed a good linearity with a detection of limit at 70 nm . Quantification of intracellular His at the single cell level was achieved by microscopy and flow cytometry. Besides the UV/Vis and emission titration, reversibility of the NCH‐Cu²⁺ towards His was further confirmed by imaging and cytometry analysis. In addition, microscopy studies revealed that NCH‐Cu²⁺ was distributed in the lysosome of live cells, where it could be employed as a fluorescent biosensor for imaging of His at subcellular level.     

A Bis‐Oxime Derivative of Diaza‐18‐Crown‐6 as an Ionophore for Silver Ion

A new pendant‐arm derivative of diaza‐18‐crown‐6, containing two oxime donor groups, has been synthesized and incorporated into a polyvinyl chloride (PVC) membrane ion‐selective electrode. The electrode shows selectivity for Ag⁺ ion, with a near Nernstian response. Pb²⁺, Cu²⁺, Hg²⁺, and Tl⁺ are major interfering ions, with Cd²⁺ having minor interference. The electrode shows no potentiometric response for the ions Mg²⁺, Al³⁺, K⁺, Ca²⁺, Ni²⁺, Fe³⁺, and La³⁺, and is responsive to H⁺ at pH<6.     

Click‐Conjugation of Nanogold‐Functionalized PAMAM Dendrimer: Toward a Novel Electrochemical Detection Platform

This work reports a new electrochemical monitoring platform for sensitive detection of Cu²⁺ coupling click chemistry with nanogold‐functionalized PAMAM dendrimer (AuNP‐PAMAM). The system involved an alkyne‐modified carbon electrode and an azide‐functionalized AuNP‐PAMAM. Initially, the added Cu²⁺ was reduced to Cu⁺ by the ascorbate, and then the azide‐modified AuNP‐PAMAM was covalently conjugated to the electrode via Cu⁺‐catalyzed azide‐alkyne click reaction. The carried AuNPs accompanying PAMAM dendrimer could be directly monitored by stripping voltammetry after acidic pretreatment. By introduction of high‐loading PAMAM dendrimer with gold nanoparticles, as low as 2.8 pM Cu²⁺ (ppt) could be detected, which was 125‐fold lower than that of gold nanoparticle‐based labeling strategy. The method exhibited high specificity toward target Cu²⁺ against other potentially interfering ions, and was applicable for monitoring Cu²⁺ in drinking water with satisfactory results.     

Carboxymethylated polyethylenimine modified magnetic nanoparticles specifically for purification of His‐tagged protein

Employing immobilized metal‐ion affinity chromatography and magnetic separation could ideally provide a useful analytical strategy for purifying His‐tagged protein. In the current study, a facile route was designed to prepare CMPEI‐Ni²⁺@SiO₂@Fe₃O₄ (CMPEI=carboxymethylated polyethyleneimine) magnetic nanoparticles composed of a strong magnetic core of Fe₃O₄ and a Ni²⁺‐immobilized carboxymethylated polyethyleneimine coated outside shell, which was formed by electrostatic interactions between polyanionic electrolyte of carboxymethylated polyethyleneimine and positively charged surface of 3‐(trimethoxysilyl)propylamin modified SiO₂@Fe₃O₄. The resulting CMPEI‐Ni²⁺@SiO₂@Fe₃O₄ composite nanoparticles displayed well‐uniform structure and high magnetic responsiveness. Hexa His‐tagged peptides and purified His‐tagged recombinant retinoid X receptor alpha were chosen as the model samples to evaluate the adsorption, capacity, and reusability of the composite nanoparticles. The results demonstrated the CMPEI‐Ni²⁺@SiO₂@Fe₃O₄ nanoparticles possessed rapid adsorption, large capacity, and good recyclability. The obtained nanoparticles were further used to purify His‐tagged protein in practical environment. It was found that the nanoparticles could selectively capture His‐tagged recombinant retinoid X receptor protein from complex cell lysate. Owing to its easy synthesis, large binding capacity, and good reusability, the prepared CMPEI‐Ni²⁺@SiO₂@Fe₃O₄ magnetic nanoparticles have great potential for application in biotechnological fields.     

Ferrocene‐tagged ionic liquid stabilized on silica‐coated magnetic nanoparticles: Efficient catalyst for the synthesis of 2‐amino‐3‐cyano‐4H‐pyran derivatives under solvent‐free conditions

An advanced novel magnetic ionic liquid based on imidazolium tagged with ferrocene, a supported ionic liquid, is introduced as a recyclable heterogeneous catalyst. Catalytic activity of the novel nanocatalyst was investigated in one‐pot three‐component reactions of various aldehydes, malononitrile and 2‐naphthol for the facile synthesis of 2‐amino‐3‐cyano‐4H‐pyran derivatives under solvent‐free conditions without additional co‐catalyst or additive in air. For this purpose, we firstly synthesized and investigated 1‐(4‐ferrocenylbutyl)‐3‐methylimidazolium acetate, [FcBuMeIm][OAc], as a novel basic ferrocene‐tagged ionic liquid. This ferrocene‐tagged ionic liquid was then linked to silica‐coated nano‐Fe₃O₄ to afford a novel heterogeneous magnetic nanocatalyst, namely [Fe₃O₄@SiO₂@Im‐Fc][OAc]. The synthesized novel catalyst was characterized using ¹H NMR, ¹³C NMR, Fourier transform infrared and energy‐dispersive X‐ray spectroscopies, X‐ray diffraction, and transmission and field emission scanning electron microscopies. Combination of some unique characteristics of ferrocene and the supported ionic liquid developed the catalytic activity in a simple, efficient, green and eco‐friendly protocol. The catalyst could be reused several times without loss of activity.     

Improved Voltammetric Response of L‐Tyrosine on Multiwalled Carbon Nanotubes‐Ionic Liquid Composite Coated Glassy Electrodes in the Presence of Cupric Ion

L ‐Tyrosine can exhibit a small anodic peak on multiwalled carbon nanotubes (MWCNTs) coated glassy carbon electrodes (GCE). At pH 5.5 its peak potential is 0.70 V (vs. SCE). When an ionic liquid (i.e., 1‐octyl‐3‐methylimidazolium hexafluorophosphate, [omim][PF₆]) is introduced on the MWCNT coat, the peak becomes bigger. Furthermore, in the presence of Cu²⁺ ion the anodic peak of L ‐tyrosine increases further due to the formation of Cu²⁺‐L ‐tyrosine complex, while the peak potential keeps unchanged. Therefore, a sensitive voltammetry based on the oxidation of Cu²⁺‐L ‐tyrosine complex on MWCNTs‐[omim][PF₆] composite coated electrode is developed for L ‐tyrosine. Under the optimized conditions, the anodic peak current is linear to L ‐tyrosine concentration in the range of 1×10^?8–5×10^?6 M, and the detection limit is 8×10^?9 M. The modified electrode shows good reproducibility and stability. In addition, the voltammetric behavior of other amino acids is explored. It is found that among them tryptophan (Trp) and histidine (His) can also produce sensitive anodic peak under same experimental conditions, and their detection limits are 4×10^?9 M and 4×10^?6 M, respectively.     

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

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

Harnessing the Flexibility of Peptidic Scaffolds to Control their Copper(II)‐Coordination Properties: A Potentiometric and Spectroscopic Study

Designing small peptides that are capable of binding Cu²⁺ ions mainly through the side‐chain functionalities is a hard task because the amide nitrogen atoms strongly compete for Cu²⁺ ion coordination. However, the design of such peptides is important for obtaining biomimetic small systems of metalloenyzmes as well as for the development of artificial systems. With this in mind, a cyclic decapeptide, C‐Asp, which contained three His residues and one Asp residue, and its linear derivative, O‐Asp, were synthesized. The C‐Asp peptide has two Pro? Gly β‐turn‐inducer units and, as a result of cyclization, and as shown by CD spectroscopy, its backbone is constrained into a more defined conformation than O‐Asp, which is linear and contains a single Pro? Gly unit. A detailed potentiometric, mass spectrometric, and spectroscopic study (UV/Vis, CD, and EPR spectroscopy) showed that at a 1:1 Cu²⁺/peptide ratio, both peptides formed a major [CuHL]²⁺ species in the pH range 5.0–7.5 (C‐Asp) and 5.5–7.0 (O‐Asp). The corrected stability constants of the protonated species (log K*_CuH(O?Asp)=9.28 and log K*_CuH(C?Asp)=10.79) indicate that the cyclic peptide binds Cu²⁺ ions with higher affinity. In addition, the calculated value of K_eff shows that this higher affinity for Cu²⁺ ions prevails at all pH values, not only for a 1:1 ratio but even for a 2:1 ratio. The spectroscopic data of both [CuHL]²⁺ species are consistent with the exclusive coordination of Cu²⁺ ions by the side‐chain functionalities of the three His residues and the Asp residue in a square‐planar or square‐pyramidal geometry. Nonetheless, although these data show that, upon metal coordination, both peptides adopt a similar fold, the larger conformational constraints that are present in the cyclic scaffold results in different behaviour for both [CuHL]²⁺ species. CD and NMR analysis revealed the formation of a more rigid structure and a slower Cu²⁺‐exchange rate for [CuH(C‐Asp)]²⁺ compared to [CuH(O‐Asp]²⁺. This detailed comparative study shows that cyclization has a remarkable effect on the Cu²⁺‐coordination properties of the C‐Asp peptide, which binds Cu²⁺ ions with higher affinity at all pH values, stabilizes the [CuHL]²⁺ species in a wider pH range, and has a slower Cu²⁺‐exchange rate compared to O‐Asp.     

Electrochemical Behaviour of the Anticancer Dacarbazine‐Cu2+ Complex and Its Analytical Applications

Electrochemical reduction of the dacarbazine‐Cu²⁺ complex was investigated using cyclic voltammetry and square wave voltammetry at a hanging mercury drop electrode. The reduction of the dacarbazine‐Cu²⁺ complex is irreversible. A reduction mechanism is proposed comprising a one‐electron reduction of the Cu²⁺ directly within the complex. The sharp peak of the adsorbed dacarbazine‐Cu²⁺ complex associated with an effective interfacial accumulation facilitates the determination of the anticancer drug dacarbazine in pharmaceutical formulations and biological fluids. Detection limits for dacarbazine of 6.12×10^?10 M, 1.57×10^?10 M and 1.97×10^?9 M were achieved for the determination of the drug in vial, human urine and serum, respectively.     

Dioxygen Activation of a Trinuclear CuICuICuI Cluster Capable of Mediating Facile Oxidation of Organic Substrates: Competition between O‐Atom Transfer and Abortive Intercomplex Reduction

The dioxygen activation of a series of Cu^ICu^ICu^I complexes based on the ligands ( L ) 3,3′‐(1,4‐diazepane‐ 1,4‐diyl)bis(1‐{[2‐(dimethylamino)ethyl](methyl)amino}propan‐2‐ol) ( 7‐Me ) or 3,3′‐(1,4‐diazepane‐1,4‐diyl)bis(1‐{[2‐(diethylamino)ethyl](ethyl)amino}propan‐2‐ol) ( 7‐Et ) forms an intermediate capable of mediating facile O‐atom transfer to simple organic substrates at room temperature. To elucidate the dioxygen chemistry, we have examined the reactions of 7‐Me , 7‐Et , and 3,3′‐(1,4‐diazepane‐1,4‐diyl)bis[1‐(4‐methylpiperazin‐1‐yl)propan‐2‐ol] ( 7‐N‐Meppz ) with dioxygen at ?80, ?55, and ?35 °C in propionitrile (EtCN) by UV‐visible, 77 K EPR, and X‐ray absorption spectroscopy, and 7‐N‐Meppz and 7‐Me with dioxygen at room temperature in acetonitrile (MeCN) by diode array spectrophotometry. At both ?80 and ?55 °C, the mixing of the starting [Cu^ICu^ICu^I( L )]¹⁺ complex ( 1 ) with O₂‐saturated propionitrile (EtCN) led to a bright green solution consisting of two paramagnetic species: the green dioxygen adduct [Cu^IICu^II(μ‐η²:η²‐peroxo)Cu^II( L )]²⁺ ( 2 ) and the blue [Cu^IICu^II(μ‐O)Cu^II( L )]²⁺ species ( 3 ). These observations are consistent with the initial formation of [Cu^IICu^II(μ‐O)₂Cu^III( L )]¹⁺ ( 4 ), followed by rapid abortion of this highly reactive species by intercluster electron transfer from a second molecule of complex 1 to give the blue species 3 and subsequent oxygenation of the partially oxidized [Cu^IICu^ICu^I( L )]²⁺ ( 5 ) to form the green dioxygen adduct 2 . Assignment of 2 to [Cu^IICu^II(μ‐η²:η²‐peroxo)Cu^II( L )]²⁺ is consistent with its reactivity with water to give H₂O₂ and the blue species 3 , as well as its propensity to be photoreduced in the X‐ray beam during X‐ray absorption experiments at room temperature. In light of these observations, the development of an oxidation catalyst based on the tricopper system requires consideration of the following design criteria: 1) rapid dioxygen chemistry; 2) facile O‐atom transfer from the activated cluster to substrate; and 3) a suitable reductant to rapidly regenerate complex 1 to accomplish efficient catalytic turnover.     

Application of 2‐(benzyliminomethyl)‐6‐methoxy‐4‐(4‐methoxyphenyl‐azo)phenol in construction of ion‐selective PVC membrane electrode for determination of copper (II) in mineral water sample

The potentiometric characteristics of a new Cu²⁺‐selective electrode based on 2‐(benzyliminomethyl)‐6‐methoxy‐4‐(4‐methoxyphenyl‐azo) phenol as an efficient ionophore has been evaluated. The effects of influential parameters on the potentiometric responses such as the amount of plasticizer, the amount of ionophore, pH of the sample solution, and the effect of coexisting ions on the electrode signal were subsequently investigated . The selectivity of the electrode was assessed by calculating the selectivity coefficients using the matched potential method. The optimum ratio of the amount of materials required for the preparation of the electrode was found to be 1.7: 32.1: 64.2: 2.0 corresponding to carboxylated PVC, dimethyl sebacate as solvent mediators, potassium tetrakis (p‐chlorophenyl) borate as the anion localizing agent, and ionophore, respectively. The electrode had a fast response (7s) as well as a satisfactory Nernstian slope (29.26±0.91 mV/decade) to Cu²⁺ over a wide concentration range of 2.0×10^?6‐ 5.0×10^?2 M with a low detection limit of 5.9×10^?7 M. The developed sensor was successfully used for the potentiometric titration of Cu²⁺ ion with EDTA and subsequently, efficient determination of this metal ion in a mineral water sample was performed.     

Bulk solvent‐free melt ring‐opening polymerization of L‐lactide catalyzed by Cu(II) and Cu(II)–Nd(III) complexes of the Salen‐type Schiff‐base ligand

A monometallic (Cu²⁺, 1) and a bimetallic (Cu²⁺ Nd³⁺, 2) Salen‐type Schiff‐base complexes with different reactive species, could efficiently catalyze the bulk solvent‐free melt ring‐opening polymerization (ROP) of L ‐lactide. Especially for the bimetallic complex 2, the involvement of rare earth ion was important and influential to the catalytic behaviors. Copyright © 2011 John Wiley & Sons, Ltd.     

Interplay of Electronic and Steric Effects to Yield Low‐Temperature CO Oxidation at Metal Single Sites in Defect‐Engineered HKUST‐1

In contrast to catalytically active metal single atoms deposited on oxide nanoparticles, the crystalline nature of metal‐organic frameworks (MOFs) allows for a thorough characterization of reaction mechanisms. Using defect‐free HKUST‐1 MOF thin films, we demonstrate that Cu⁺/Cu²⁺ dimer defects, created in a controlled fashion by reducing the pristine Cu²⁺/Cu²⁺ pairs of the intact framework, account for the high catalytic activity in low‐temperature CO oxidation. Combining advanced IR spectroscopy and density functional theory we propose a new reaction mechanism where the key intermediate is an uncharged O₂ species, weakly bound to Cu⁺/Cu²⁺. Our results reveal a complex interplay between electronic and steric effects at defect sites in MOFs and provide important guidelines for tailoring and exploiting the catalytic activity of single metal atom sites.     

A Self‐assembled L‐Cysteine and Electrodeposited Gold Nanoparticles‐reduced Graphene Oxide Modified Electrode for Adsorptive Stripping Determination of Copper

Glassy carbon electrode (GCE) modified with L‐cysteine and gold nanoparticles‐reduced graphene oxide (AuNPs‐RGO) composite was fabricated as a novel electrochemical sensor for the determination of Cu²⁺. The AuNPs‐RGO composite was formed on GCE surface by electrodeposition. The L‐cysteine was decorated on AuNPs by self‐assembly. Physicochemical and electrochemical properties of L‐cysteine/AuNPs‐RGO/GCE were characterized by scanning electron microscopy, atomic force microscopy, energy dispersive spectroscopy, Raman spectroscopy, X‐ray diffraction, cyclic voltammetry and adsorptive stripping voltammetry. The results validated that the prepared electrode had many attractive features, such as large electroactive area, good electrical conductivity and high sensitivity. Experimental conditions, including electrodeposition cycle, self‐assembly time, electrolyte pH and preconcentration time were studied and optimized. Stripping signals obtained from L‐cysteine/AuNPs‐RGO/GCE exhibited good linear relationship with Cu²⁺ concentrations in the range from 2 to 60 μg L⁻¹, with a detection limit of 0.037 μg L⁻¹. Finally, the prepared electrode was applied for the determination of Cu²⁺ in soil samples, and the results were in agreement with those obtained by inductively coupled plasma mass spectrometry.     

Synthesis and electrochemical sensing behaviour of a new ferrocene functionalized tet ‘a’ macrocyclic receptor towards transition metal ions

A new ferrocene functionalized macrocyclic receptor 1,8‐bis(ferrocenylmethyl)‐5,5,7,12,12,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradecane (R) has been designed and synthesized to study its potential application as chemosensor. The receptor has been characterized by spectral techniques and X‐ray diffraction. The compound crystallizes in the orthorhombic space group Pcab with four molecules in a unit cell (half‐a‐molecule in the asymmetric unit). The electrochemical studies of the receptor in dioxane–water (7:3 v/v, 25 °C) indicate that the receptor is pH‐dependent with a displacement of E_1/2 to more anodic potentials with a decrease in the pH from 12 to 5. The electrochemical behaviour of R was also studied in the presence of Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ in dioxane–water (7:3 v/v, 25 °C, [Buⁿ₄N][ClO₄]), showing that upon complexation the ferrocene–ferrocenium half‐wave potential shifts anodically in relation to that of the free receptor. The maximum electrochemical shift (ΔE_1/2) of 46 mV was found in the presence of Cu²⁺, followed by Co²⁺ (20 mV), Mn²⁺ (15 mV), Ni²⁺ (13 mV) and Zn²⁺ (9 mV). Moreover, the receptor R is able to electrochemically and selectively sense Cu²⁺ in the presence of the other transition metal cations studied. Copyright © 2007 John Wiley & Sons, Ltd.     

Ion‐Selective Electrodes Based on Hydrophilic Ionophore‐Modified Nanopores

We report the synthesis and analytical application of the first Cu²⁺‐selective synthetic ion channel based on peptide‐modified gold nanopores. A Cu²⁺‐binding peptide motif (Gly‐Gly‐His) along with two additional functional thiol derivatives inferring cation‐permselectivity and hydrophobicity was self‐assembled on the surface of gold nanoporous membranes comprising of about 5 nm diameter pores. These membranes were used to construct ion‐selective electrodes (ISEs) with extraordinary Cu²⁺ selectivities, approaching six orders of magnitude over certain ions. Since all constituents are immobilized to a supporting nanoporous membrane, their leaching, that is a ubiquitous problem of conventional ionophore‐based ISEs was effectively suppressed.