Metal Ion Chelating Research Articles

Crystallization vs Metal Chelation: Solution Self-Assembly of Dual Responsive Block Copolymers

We herein report the synthesis and characterization of dual stimuli-responsive poly(2-iso-propyl-2-oxazoline)-block-poly(2-acrylamido glycolic acid) (PiPrOx-b-PAGA) double hydrophilic block copolymers (BCPs) by an effective combination of ring-opening and reversible addition–fragmentation chain transfer (RAFT) polymerization. The resulting materials are responsive toward several external triggers: (1) the PiPrOx segment undergoes a coil-to-globule transition upon heating above the cloud point temperature (TCP), (2) the PAGA block chelates M2+ metal ions and provides straightforward access to nanostructured hybrid materials, and (3) prolonged heating above the TCP for PiPrOx enables crystallization-driven solution self-assembly (CDSA) toward anisotropic micelles and superstructures. We are further able to show that the cloud point temperature (TCP) of PiPrOx-b-PAGA micelles can be tuned from ∼30 to 68 °C by varying either the BCP composition (PiPrOx to PAGA ratio) or by the amount of metal ions being present. The different aggregates were characterized by transmission electron microscopy (TEM), wide-angle X-ray scattering (WAXS), and dynamic light scattering (DLS). Our results indicate that micellar size, shape, and TCP are closely connected to BCP composition and the nature of chelated metal ions. In our opinion, such inorganic–organic hybrid materials are of interest with regard to (photo)catalysis, as sensors, or as potential drug delivery systems.

Kaempferol-zinc(II) complex synthesis and evaluation of bone formation using zebrafish model

Flavonoids are known for their wide range of bioactive properties including beneficial effect on bone formation. Their intense metal ion chelating capacity endorsed their nomination as a new biomaterial for biomedical applications. The present study examined the functional role of Kaemferal-Zinc(II) (Kaem-Zn) complex in bone formation, in vitro and in vivo. The cyto-compatibility assay confirmed that upto 25 μM of Kaem and Kaem-Zn complex was non-toxic. In fact, it facilitates ALP activity and accumulation of calcium in osteoblast; it was confirmed by Alizarin red and von Kossa staining. In addition to this, osteoblast markers, Runx2, type 1 col., ALP mRNAs expression, and osteocalcin and osteonectin secretory proteins level were also induced by the Kaem-Zn complex. Furthermore, bone forming ability of Kaem and Kaem-Zn was assessed by zebrafish model. The optimal concentration of Kaem and Kaem-Zn was determined by the viability assay of Zebrafish larvae. Osteoblasts distribution in scale, vertebrae and caudal fin ossification was studied by alizarin red staining accompanied by confocal imaging were carried out in adult zebrafish exposed to Kaem and Kaem-Zn complex. To sum up, our findings showed that Kaem promotes bone growth, and Kaem-Zn complex has further strengthened it. Kaem-Zn complex could be an effectively explored and used use in bone tissue engineering.

Purification and structural characterization and antioxidant activity of levan from Bacillus megaterium PFY-147

An exopolysaccharide (EPS)-producing bacterial PFY-147 was separated from Hiqiher vineyard soil and determined as Bacillus megaterium by 16S rDNA analysis and morphological. The PFY-147-EPS was purified by gel-filtration chromatography. The average molecular weight (Mw) of purified EPS was 1.878 × 106 Da. The total carbohydrate contents, uronic acid and sulfated group content in PFY-147-EPS were found to be 90.37 ± 1.48%, 7.24 ± 0.36% and 2.39 ± 0.36%, respectively. The PFY-147-EPS was found to be a levan containing a backbone of 2,6-substituted β-fructoses by high performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopy. The atomic force microscopy (AFM) presented that the levan formed pointed or thorny structural in aqueous solution. Scanning electron microscopy (SEM) of the levan showed compact and nonuniform block sizes morphology. Moreover, the levan exhibited higher thermal stability with a degradation temperature of 265.63 °C in DSC analysis. The levan possessed strong 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, Superoxide anion (O2−) radical, hydroxyl (OH) radical and and2,20-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS+) scavenging activities and strong metal ion chelating activity. The WHC and WSI of levan were 231.29 ± 3.76% and 97.34 ± 1.72%, respectively. These might have implications in food and medicine, as well as in pharmaceutical industries.

Improving Metal Adsorption on Triethylenetetramine (TETA) Functionalized SBA‐15 Mesoporous Silica Using Potentiometry, EPR and ssNMR

AbstractNanomaterials have received growing attention in the treatment and diagnosis of neurological disorders because the low blood brain barrier permeability hinders the classical pharmacological approach. Metal ion chelators combined with nanoparticles prove effective in the treatment of neurodegeneration and are under extensive studies. Most chelating agents and metallodrugs compete with endogenous molecules for metal coordination, and do not reach the active site. Determining the competition between metallodrugs and endogenous molecules requires knowing the stability constants of formed metal complexes. In this study, for the first time, potentiometric titrations are used to determine metal complex formation constants, and to quantify ligand content in functionalized materials. This new potentiometric approach allows physico–chemical characterization of mesoporous functionalized materials and their metal adsorption capacity in water solution. The potentiometric results are compared with isotherm models obtained by spectroscopic measurements and yield rewarding data fitting. The potentiometric method described here can be extended to different types of nanostructured materials carrying surface ionizable groups.

Inhibition of urease activity by different compounds provides insight into the modulation and association of bacterial nickel import and ureolysis

The nickel-dependent urease enzyme is responsible for the hydrolysis of urea to ammonia and carbon dioxide. A number of bacteria produce urease (ureolytic bacteria) and are associated with various infectious diseases and ammonia emissions from agriculture. We report the first comprehensive comparison of the inhibition of urease activity by compounds analysed under the same conditions. Thus, 71 commercially available compounds were screened for their anti-ureolytic properties against both the ureolytic bacterium Klebsiella pneumoniae and purified jack bean urease. Of the tested compounds, 30 showed more than 25% inhibition of the ureolytic activity of Klebsiella pneumoniae or jack bean urease, and among these, carbon disulfide, N-phenylmaleimide, diethylenetriaminepentaacetic acid, sodium pyrrolidinedithiocarbamate, 1,2,4-butanetricarboxylic acid, tannic acid, and gallic acid have not previously been reported to possess anti-ureolytic properties. The diverse effects of metal ion chelators on ureolysis were investigated using a cellular nickel uptake assay. Ethylenediaminetetraacetic acid (EDTA) and dimethylglyoxime (DMG) clearly reduced the nickel import and ureolytic activity of cells, oxalic acid stimulated nickel import but reduced the ureolytic activity of cells, 1,2,4-butanetricarboxylic acid strongly stimulated nickel import and slightly increased the ureolytic activity of cells, while L-cysteine had no effect on nickel import but efficiently reduced the ureolytic activity of cells.

Facile synthesis of metal-polyphenol-formaldehyde coordination polymer colloidal nanoparticles with sub-50 nm for T1-weighted magnetic resonance imaging

Plant polyphenol-based coordination polymers (CPs) with ultra-small particle size and tailorable compositions are highly desired in biomedical applications, but their synthesis is still challenging due to the sophisticated coordination assembly process and unavoidable self-oxidation polymerization of polyphenol. Herein, a general ligand covalent-modification mediated coordination assembly strategy is proposed for the synthesis of water-dispersible CPs with tunable metal species (e.g., Gd, Cu, Ni, Zn, Fe) and ultra-small diameter (8.6–37.8 nm) using nontoxic plant polyphenol (e.g., tannic acid, gallic acid) as a polymerizable ligand. Polyphenol molecules react with formaldehyde firstly, which can effectively retard the oxidation induced self-polymerization of polyphenol and lead to the formation of metal ions containing CPs colloidal nanoparticles. These ultrafine nanoparticles with stably chelated metal ions are highly water dispersible and thus advantageous for bioimaging. As an example, ultra-small Gd contained CPs exhibit higher longitudinal relaxivity (r1 = 25.5 L mmol−1 s−1) value with low r2/r1 (1.19) than clinically used Magnevist (Gd-DTPA, r1 = 3.7 L mmol−1 s−1). Due to the enhanced permeability and retention effect, they can be further used as a positive contrast agent for T1-weighted MR imaging of tumour.

Characterization and cytoprotective properties of Sargassum natans fucoidan against urban aerosol-induced keratinocyte damage

The escalation of fine particulate matter (PM) air pollution has recently become a global concern. Evidence is fast accumulating on PM exposure-related skin damage. The present study explored the therapeutic potentials of fucoidan purified from Sargassum natans against damaging effects of PM exposure on human HaCaT keratinocytes. Fucoidan (SNF7) was purified from S. natans by an enzyme-assisted extraction and purified by anion exchange chromatography. SNF7 (≈50 kDa) was identified as a fucoidan containing 70.97% fucose and 36.41 ± 0.59% of sulfate. Treatment of fine dust from Beijing, China (CFD) increased intracellular ROS levels in HaCaT cells triggering DNA damage and apoptosis. Treatment of SNF7 dose-dependently attenuated CFD-induced surge of intracellular ROS levels in keratinocytes by increasing antioxidant defense enzymes. Moreover, SNF7 chelated metal ions Pb2+, Ba2+, Sr2+, Cu2+, Fe2+, and Ca2+ coming from CFD. The results substantiated the potential therapeutic effects of SNF7 against CFD-induced oxidative stress. Further studies could promote SNF7's use as an active ingredient in cosmetics.

Characterization of lactic acid bacteria derived exopolysaccharides for use as a defined neuroprotective agent against amyloid beta1\u201342-induced apoptosis in SH-SY5Y cells

Alzheimer’s disease (AD) is a disease characterized by cerebral neuronal degeneration and loss in a progressive manner. Amyloid beta (Aβ) in the brain is toxic to neurons, being a main risk factor for initiation and continuation of cognitive deterioration in AD. Neurotoxicity of Aβ origin is also linked to oxidative stress characterized by excessive lipid peroxidation, protein oxidation, changes in antioxidant systems, and cerebral DNA damage in AD. Furthermore, Aβ can induce oxidative neuronal cell death by a mitochondrial dysfunction. Cellular injury caused by oxidative stress can be possibly prevented by boosting or promoting bodily oxidative defense system by supplying antioxidants in diet or as medications. However, most synthetic antioxidants are found to have cytotoxicity, which prevents their safe use, and limits their administration. For this reason, more attention has been paid to the natural non-toxic antioxidants. One of the most promising groups of non-toxic antioxidative compounds is thought to be polysaccharides. This study investigated the characterization and protective action exerted by exopolysaccharides (EPSs) originated from Lactobacillus delbrueckii ssp. bulgaricus B3 and Lactobacillus plantarum GD2 to protect from apoptotic activity exerted by Aβ1-42 among SH-SY5Y cells. We characterized EPSs by elemental analysis, FTIR, AFM, SEM, and XRD. The antioxidant effects of EPSs were determined by the DPPH free radical scavenging activity, hydroxyl radical scavenging activity, metal ion chelating activity, lipid peroxidation inhibitory activity, and superoxide anion scavenging activity method. The protective effects of EPSs were determined by flow cytometry and RT-PCR. Mannose ratio, molecular weight, functional groups, surface morphology, and amorphous character structure of EPSs are thought to play a role in the protective effect of EPSs. EPSs reduced apoptotic activity of Aβ1-42 in addition to their depolarizing effect on mitochondrial membrane potential in concentration-dependent manner. These observations contribute the inclusion of EPSs among the therapeutic options used to manage various neurological disorders in the traditional medicine in a scientific manner, indicating that EPSs may be promising natural chemical constituents that need advanced research and development for pharmacological therapy of AD.

A sustainable reduction route of graphene oxide by industrial waste lignin for versatile applications in energy and environment

The high toxicity of chemical reducing agents for graphene oxide (GO) and the high-polluting emission of industrial waste lignin as black liquor are always the two troubling issues in clean production. Herein, we reported a sustainable win-win route to utilize waste lignin as a green reducing agent of GO through hydrothermal method. Various hydrothermal conditions were investigated to reveal the reduction capability and mechanism of lignin towards GO. Results indicated that lignin could repair the conjugated structure of GO, while the hydroxyl ions in water could cause the decarboxylation of GO. The lignin-reduced GO composites (LRGOs) prepared at acidic and neutral pHs tended to form hydrogels, while the alkaline LRGOs were monodispersed graphene nanosheets in water. The alkaline LRGO suspensions exhibited reversible sol-gel transition by adding acid/base, and irreversible gelation by metal ions chelation. Besides, they could self-assemble into a robust film with excellent mechanical properties (306.7 ± 47.9 MPa in tensile strength, 135.2 ± 45.3 GPa in modulus) and electrical conductivity (399.5 ± 58.3 S/cm) through vacuum filtration and annealing. The freeze-dried LRGO aerogels and their carbonized products showed excellent absorption capacities for various organic solvents. As electrode materials, the LRGO aerogels also displayed a high pseudo-capacitance of 213.8 F/g at 1 A/g. These findings of LRGOs showed a huge application potential in clean energy and environmental pollution treatment.

Evidence for the involvement of IL-1β and TNF-α in anti-inflammatory effect and antioxidative stress profile of the standardized dried extract from Miconia albicans Sw. (Triana) Leaves (Melastomataceae)

Ethnopharmacological relevanceMiconia albicans (Melastomataceae), commonly known in Brazil as “canela-de-velho”, is used in folk medicine for treating rheumatoid arthritis and reducing pain and inflammation. The aim of the current work wasto provide data on physicochemical characterization of the drug plant and dried extract from M. albicans leaves, as well as investigate the anti-inflammatory effect and antioxidant stress profile from the standardized dried extract of this species employing different model systems. Materials and methodsplant material (dried crushed leaves) was extracted by turboextraction using 50% ethanol (v/v). Different pharmacological techniques were performed to establish quality control parameters of the plant drug, and dried extract of M. albicans (DEMA) was chemically characterized by HPLC-PDA to selection of the chemical marker. Total phenolic and flavonoid contents were determined by the Folin-Ciocalteu and AlCl3 colorimetric methods, respectively. Antioxidant potential of the DEMA was investigated by employing different in vitro antioxidant assays, including DPPH and ABTS radical scavenging assays, ferric reducing antioxidant assay, NO scavenging assay, metal ion (Fe2+) chelating activity and antioxidant capacity by inhibition of lipid peroxidation (TBARS). Finally, anti-inflammatory activity of the DEMA was evaluated using two models of acute inflammation: carrageenan induced inflammation and mechanical hyperalgesia. Results and discussionM. albicans leaves, after drying in forced air circulation chamber at ±40 °C for 48 h and crushing in knife mill, presented a moisture content below the maximum allowed for plant drugs (6.4%). The powder of M. albicans was classified as moderately coarse and total ash content was found to be 6.27%. Preliminary phytochemical screening of DEMA revealed the presence of flavonoids, tannins, saponins, leucoanthocyanins and steroids. DEMA had significant higher total phenolic (551.3 mg gallic acid equivalent/g of dried extract) and flavonoid contents (367.19 mg catechin equivalent/g of dried extract). Two major compounds (λ = 340 nm) were identified in DEMA by HPLC-PDA: the flavonoids rutin and quercetin. Rutin content, selected as chemical marker, was determined and found to be 1.16 mg/g dried extract (r = 0.9941). Regarding to antioxidant activity, our results revealed the DEMA exhibited good antioxidant activity on different models. M. albicans treatment also reduced the levels of TNF-α e IL-1β and consequently inflammatory nociception and edema caused by carrageenan injection. Based on previous studies and our results, is possible to suggest a positive correlation between the flavonoids rutin and quercetin and the antioxidant and anti-inflammatory capacities. ConclusionTogether, these data suggest that M. albicans has the possibility of use in conditions such as arthritis or other joint pain, even needing other work to better consolidate this profile.

A general strategy for metal compound encapsulated into network-structured carbon as fast-charging alkali-metal ion battery anode

Evolution of fast-charging alkali-metal ion battery (AIB) is of great importance, but severely limited by the high ion/electron transport resistance in the electrode structure. Carbon-based composites have demonstrated competitive results for accelerating the related technology development. However, their efficient design, versatile synthesis and diverse structural variability remain the major challenges. Herein, we propose a general and versatile protocol for synthesizing a hierarchical network structure composed of metal compound (e.g., metal oxide, metal selenide and metal sulfide) encapsulated in carbon nanoparticle unit, and demonstrate its superiority for fast-charging anode of AIB. Key to this strategy is utilization of a rational hybrid assembly comprising of chelating resin and metal ions as building blocks. The strong coordinate-covalent bond between chelating resin and metal ions not only realizes a highly homogeneous organic/inorganic interface at the molecular level, but also confines metal ions to in-situ generate metal compound nanoparticles uniformly distributed into the carbon framework after a carbonization treatment, endowing a strong binding at the carbon/non-carbon interface structure. Benefitting from the well-organized structure, the resultant network-structured metal compound@carbon composites exhibit extraordinary fast-charging alkali-metal ion storage performance. For example, the typical network-structured Fe2O3@carbon composite anode can be fully charged within 2.2 ​min and discharge continuously for more than 120 ​min with a large charge/discharge capacity of 730 ​mAh g−1 in lithium ion batteries, and is able to be fully charged within 5.6 ​min accompanying with a long discharge time of about 110 ​min and a high charge/discharge capacity of 92 ​mAh g−1 in potassium ion batteries.

Molecular Insights Into Di(2-Picolyl) Amine-Induced Cytotoxicity and Apoptosis in Human Kidney (HEK293) Cells.

Di(2-picolyl) amine (DPA) is a pyridine derivative known to chelate metal ions and thus has potential anticancer properties; however, its effect on normal cells remains unchartered necessitating further research. This study, therefore, investigated the mechanistic effects of DPA-induced cytotoxicity and apoptosis in the HEK293 cell line. Methods required that an half the maximum inhibition concentration (IC50) was derived using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. Analyses aimed to assess oxidative stress, membrane damage, and DNA fragmentation by means of biochemical assays were performed. Luminometry analysis was carried out to understand the mechanism of apoptosis induction by determining the levels of adenosine triphosphate (ATP) and the activities of caspase-8, -9, and -3/7. Western blotting was used to ascertain the expression of apoptotic and stress-related proteins. An IC50 of 1,079 µM DPA was obtained. Antioxidant effect correlated with a minimum increase in reactive oxygen species induced lipid peroxidation. The increase in initiator caspase-8 and -9 and executioner caspase-3/7 activities by DPA-induced apoptosis albeit prompting a decline in the levels of ATP. Furthermore, DPA brought about the following consequences on HEK293 cells: markedly elevated tail lengths of the comets, poly (ADP-ribose) polymerase 1 cleavage, and apoptotic body formation observed in the late stages. The cytotoxic effects of DPA in HEK293 cells may be mediated by induction of apoptosis via the caspase-dependent mechanism.

The formation of di-copper (II) complexes with a hetero-site cyclopeptide–spectroscopic and potentiometric studies

The interest in cyclic peptide research has increased in the last decade. These compounds are resistant to enzymatic degradation and possess a more rigid scaffold than their linear analogues. This paper presents the results of combined potentiometric and spectroscopic studies on the coordination properties of hetero-site cyclopeptide (CDP) with the c(HHKHHPHDHKHP) sequence. Thermodynamic stability constants for ligands and complex forms have been determined in a system with a double excess of copper ions, i.e. with a molar ratio to ligand L:Cu(II) of 1:2. The interaction was characterised by UV–Vis, CD, EPR and ESI-MS methods over a wide pH range. CDP is a good chelator for divalent metal ions, it creates mono-, di- and trinuclear complexes with copper(II) ions over a wide range of pH. It was found that promotion of di-copper(II) complexes is connected with a higher flexibility of the cyclopeptide chain.

Systemic lupus erythematosus: Possible localization of trypsin-like and metalloprotease active centers in the protein sequence of the monoclonal light chain (NGTA2-Me-pro-Tr).

It was previously shown that several monoclonal light chains corresponding to the phagemid library of recombinant peripheral blood lymphocyte immunoglobulin light chains of patients with systemic lupus erythematosus specifically hydrolyze only myelin basic protein (MBP). Canonical enzymes usually have only one active site catalyzing some kind of chemical reaction. It was shown previously that in contrast to classical enzymes, preparations of one of the light chains (NGTA2-Me-pro-Tr) showed two optimal pH values, two optimal concentrations of metal ions, and two Km values for MBP. One protease active site of NGTA2-Me-pro-Tr was trypsin like, whereas second one was metal dependent. In this article, a search for protein sequences of NGTA2-Me-pro-Tr responsible for catalytic functions was carried out. We performed, for the first time, analysis of the homology of the protein sequence of NGTA2-Me-pro-Tr with those of several classical Zn2+ - and Ca2+ -dependent, as well as human serine, proteases. The analysis allowed us to identify the protein sequences of NGTA2-Me-pro-Tr responsible for serine-like activity, the binding of MBP, and chelation of metal ions and catalysis directly. The data obtained are summarized using hypothetical models of the structure of the two active centers of a very unusual light chain of antibodies (Abs). The findings obtained may be very important for understanding possible structure of active centers of very unusual light chain of Abs possessing several enzymatic activities.

Carnosine and Lung Disease.

Carnosine (β-alanyl-L-histidine) is a small dipeptide with numerous activities, including antioxidant effects, metal ion chelation, proton buffering capacity, and inhibitory effects on protein carbonylation and glycation. Carnosine has been mostly studied in organs where it is abundant, including skeletal muscle, cerebral cortex, kidney, spleen, and plasma. Recently, the effect of supplementation with carnosine has been studied in organs with low levels of carnosine, such as the lung, in animal models of influenza virus or lipopolysaccharide-induced acute lung injury and pulmonary fibrosis. Among the known protective effects of carnosine, its antioxidant effect has attracted increasing attention for potential use in treating lung disease. In this review, we describe the in vitro and in vivo biological and physiological actions of carnosine. We also report our recent study and discuss the roles of carnosine or its related compounds in organs where carnosine is present in only small amounts (especially the lung) and its protective mechanisms.

An EDTA-resistant pyrazinamidase from non-pathogen Pseudonocardia carboxydivorans.

To characterize a pyrazinamidase from non-pathogen Pseudonocardia carboxydivorans. A pyrazinamidase gene pncA encoding a 23-kDa protein PncA-Pse from P. carboxydivorans was over-expressed in Escherichia coli and characterized. This PncA-Pse can convert both pyrazinamide and nicotinamide efficiently with the optimal pH and temperature of pH 8.5 and 45°C, respectively. Although ferrous iron and manganese were detected in PncA-Pse, the enzymatic activity is not affected by EDTA with the final concentration of 10mM. Moreover, the enzymatic activity was not significantly affected with the addition of several metal ions, respectively. Based on the structure modeling, the 61st histidine which is associated with the metal binding, was mutated into alanine to get mutant H61A. No activity, iron and manganese were detected for H61A, which implies that PncA-Pse is a metal enzyme with resistance of the metal ion chelator EDTA, which is different from the previous reports. This is the first characterized pyrazinamidase from the genus Pseudonocardia, a non-pathogen.

Bio-properties of Saba banana (Musa \u2018saba\u2019, ABB Group): Influence of maturity and changes during simulated in vitro gastrointestinal digestion

Saba banana, a popular fruit crop grown in Southeast Asia, is an economical source of a variety of beneficial agents. This study examined the variations in total phenolic, flavonoid, and antioxidant activities of five maturity stages of Saba banana, and their changes during simulated in vitro gastrointestinal digestion as affected by varying structural compositions. Antioxidant activities were evaluated using ferric reducing antioxidant power (FRAP), metal ion chelating (MIC) activity, and 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays. Results of DPPH and ABTS were compared in terms of TEAC (Trolox Equivalent Antioxidant Capacity) and VCEAC (Vitamin C Equivalent Antioxidant Capacity) values. Bio-properties were found to be highest in mature green stage with values slightly decreased as ripening proceeded. Simulated digestion showed a continuous increase in total phenolic with comparatively faster release in structure-less state (slurry) than samples with intact structure (cut). The trend of antioxidant activities was increased in the gastric phase and then decreased at the onset of intestinal phase, except for MIC which showed a reverse effect. Our study indicated that the bio-properties of Saba banana were affected by maturity and modifications in its physical structure and composition could influence the release behaviors of food components during simulated digestion.

Eumelanin electrodes in buffered aqueous media at different pH values

Eumelanin, a quinone-based biomacromolecule, is the most common form of the biopigment melanin in the human body. Eumelanin has attracted great interest due to its physicochemical properties, such as metal-ion chelation, free radical scavenging, hydration-dependent (photo) electrical response and redox activity. Investigating the electron transfer properties of eumelanin is key to exploiting the electrochemical energy storage properties of the pigment. In this work, we investigated the redox behavior of chemically controlled eumelanin in NaCH3COO buffer solutions, at different pH values. For our study we used cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge and discharge. Eumelanin, in combination with aqueous electrolytes, provides an attractive case study for eco-designed storage devices based on abundant and environmentally benign materials and interfaces.

Electrochemical properties of aluminum tripolyphosphate modified chemically bonded phosphate ceramic anticorrosion coating

An inorganic coating, combining chemically bonded phosphate ceramic (CBPC) binder and aluminum tripolyphosphate (ATP) pigment, was designed and prepared for anti-corrosion treatment of steel. An electrochemical method was proposed to characterize and evaluate the corrosive behavior of the coating, and the influence of ATP contents associated with XRD and SEM/EDS techniques. The experimental results showed that the addition of the ATP pigment increased the corrosion potential and reduced the corrosion current density, porosity, and water absorption of a coating. Moreover, the polarization resistance (Rp) values were more than twice those of CBPC binder when the ATP was added. The best anti-corrosion profile of the coating was observed when the content of ATP pigment was 15%, which exhibited the least negative corrosion potential (Ecorr) and Rp and smallest corrosion current (Icorr). SEM-EDS results indicate that ATP exhibited more metal ion chelating power than the CBPC binder itself, which shows the better interfacial binding ability. The said coating cannot only provide excellent physical protection but form passivation layer on the surface of a steel substrate to protect it and prevent further corrosion.

Metal-Conductive Polymer Core-Shell Nanowires: Electroless Reduction of Pd and Cu On Polypyrrole/DNA Templates Bearing 2-2'-Bipyridyl Groups

A method for the preparation of conductive polymer nanowires bearing metal ion chelating 2,2’-bipyridyl groups is described. N-(3-pyrrol-1-yl-propyl)-2,2'-bipyridinium hexafluorophosphate (NP2PBH) was templated on λ-DNA in aqueous solution using FeCl3 as oxidant to initiate polymerization. The polyNP2PBH/DNA nanowires were then decorated with metals (Cu or Pd) by electroless deposition [Cu(NO3)2/ascorbate or PdCl42-/NaBH4]. UV-vis absorption spectra of the hybrid materials show the absorption peak due to the plasmon resonance of Cu at about 550 nm and a broad continuous band consistent with metallic Pd in the range 300−700 nm. The morphology, size and electrical properties of the hybrid nanostructures have been characterized using scanning probe techniques (atomic force microscopy (AFM), scanning conductance microscopy (SCM) and conductive atomic force microscopy (cAFM)). The polyNP2PBH/DNA nanowires show a continuous, smooth and uniform appearance (mean diameter 5.0 nm). Cu deposits on polyNP2PBH/DNA nanowires by a nucleation and growth process that leads eventually to smooth, conductive Cu nanowires. In contrast, Pd deposits in a non-uniform manner on polyNP2PBH/DNA and has inconsistent electrical conductivity. The electrical conductivity of single Cu/polyNP2PBH/DNA nanowires was estimated to be 1.6 ± 0.27 S cm-1 which we suggest is limited by electron transfer between Cu grains.