Absence Of Ascorbic Acid Research Articles

Coupling reactions between reduced intermediates of insensitive munitions compound analog 4-nitroanisole

Explosives, pesticides, and pharmaceuticals contain toxic nitroaromatic compounds that may form even more toxic azo compounds if they encounter reducing conditions in the environment. We investigated the mechanism by which 4,4′-dimethoxyazobenzene forms in anaerobic sludge incubations of 4-nitroanisole, an analog for the insensitive munitions compound 2,4-dinitroanisole (DNAN). Because studies have reported the mechanism to involve the coupling of reduced nitroaromatic intermediates, specifically aromatic amines and nitrosoaromatics, by nucleophilic processes, we abiotically paired 10 mM 4-aminoanisole with 2 mM 4-nitrosoanisole in nitrogen-flushed microcosms. However, only 7 μM of 4,4′-dimethoxyazobenzene had formed after 24 h. We identified the major product to be 4-methoxy-4′-nitrosodiphenylamine. Repeating this experiment in phosphate buffer at pH 5.1, 7.1, and 8.6 demonstrated that the formation of this unexpected product is acid catalyzed. We found that 4-methoxy-4′-nitrosodiphenylamine is more toxic than 4,4′-dimethoxyazobenzene to the bioluminescent bacterium Aliivibrio fischeri, with IC50 values of 0.1 μM and 0.5 μM, respectively. Both products are several orders of magnitude more toxic than reduced 4-nitroanisole intermediates 4-aminoanisole and 4-nitrosoanisole, as well as DNAN and its aromatic amine metabolites. Six-fold more 4,4′-dimethoxyazobenzene formed when we incubated 4-nitrosoanisole with ascorbic acid, a reducing agent, than when we incubated 4-nitrosoanisole with 4-aminoanisole in the absence of ascorbic acid. We therefore suspect that 4-hydroxylaminoanisole, the first reduction product of 4-nitrosoanisole, is a better nucleophile than 4-aminoanisole and couples more readily with 4-nitrosoanisole. Slightly basic and reducing conditions can prevent the formation and persistence of toxic coupling products on sites contaminated with nitroaromatics, i.e. DNAN-contaminated firing ranges.

Multilayered fibroblasts constructed by accelerated cellular self-assembly and applications for regenerative medicine_suppl

Regenerative medicine research requires animal experiments to evaluate treatment effects. According to the 3Rs prin­ciples, alternative models have been developed and utilized to evaluate the efficacy and safety of new products. Three-dimensional (3D) cell cultures have been recognized for their relevant structures and biological functions that are akin to native tissues. They can better represent in vivo conditions than two-dimensional (2D) cell cultures. Herein, we present a fast and simple technique for the construction of 3D dermal fibroblasts (3D-DFs) without exogenous scaffolds. The 3D-DFs can be obtained within 3 days by seeding DFs at a level that exceeds their confluent density and culturing them in the presence of ascorbic acid. The 3D-DFs have a compact, multilayer structure as revealed by histology and their collagen content is drastically increased compared to the monolayer. The 3D-DF-derived extracellular matrix can serve for 3D culturing of other cells. A gap closure assay was performed with the 3D-DFs to represent a 3D-wounded dermal model. Interestingly, the multilayered structure of the 3D-DFs could be regenerated after wounding even when cultured in the absence of ascorbic acid. Moreover, skin grafting using the 3D-DFs was demonstrated in vitro using wounded in vitro human full-thickness skin models. The 3D-DFs will be potentially useful for regenerative medicine and as tissue models for in vitro studies.

Multilayered fibroblasts constructed by accelerated cellular self-assembly and applications for regenerative medicine.

Regenerative medicine research requires animal experiments to evaluate the treatment effects. According to the 3Rs principles, alternative models have been developed and utilized to evaluate the efficacy and safety of new products. Three-dimensional (3D) cell cultures have been recognized for their relevant structures and biological functions akin to native tissues. They can better represent in vivo conditions than two-dimensional (2D) cell cultures. Herein, we present a fast and simple technique for the construction of 3D dermal fibroblasts (3D-DFs) without exogenous scaffolds. The 3D-DFs can be obtained within 3 days by seeding DFs at a level that exceeds their confluent density and culturing in the presence of ascorbic acid. The 3D-DFs had a compact multilayer structure, as revealed from their histology. The collagen content of the resulting 3D-DFs drastically increased compared to in a monolayer. The 3D-DF-derived extracellular matrix can serve for the 3D culturing of other cells. A gap closure assay was performed with the 3D-DFs to represent a 3D-wounded dermal model. Interestingly, the multilayered structure of the 3D-DFs could be regenerated after wounding even when cultured in the absence of ascorbic acid. Moreover, skin grafting of the 3D-DFs was demonstrated in vitro using wounded full-thickness skin models as an alternative to animal experiments. The 3D-DFs will potentially be useful for regenerative medicine or as tissue models for in vitro studies.

Effect of lignin fractions isolated from different biomass sources on cellulose oxidation by fungal lytic polysaccharide monooxygenases

BackgroundLytic polysaccharide monooxygenases (LPMOs) are copper-dependent enzymes that oxidatively cleave recalcitrant lignocellulose in the presence of oxygen or hydrogen peroxide as co-substrate and a reducing agent as electron donor. One of the possible systems that provide electrons to the LPMOs active site and promote the polysaccharide degradation involves the mediation of phenolic agents, such as lignin, low-molecular-weight lignin-derived compounds and other plant phenols. In the present work, the interaction of the bulk insoluble lignin fraction extracted from pretreated biomass with LPMOs and the ability to provide electrons to the active site of the enzymes is studied.ResultsThe catalytic efficiency of three LPMOs, namely MtLPMO9 with C1/C4 regioselectivity, PcLPMO9D which is a C1 active LPMO and NcLPMO9C which is a C4 LPMO, was evaluated in the presence of different lignins. It was correlated with the physicochemical and structural properties of lignins, such as the molecular weight and the composition of aromatic and aliphatic hydroxyl groups. Moreover, the redox potential of lignins was determined with the use of large amplitude Fourier Transform alternating current cyclic voltammetry method and compared to the formal potential of the Cu (II) center in the active site of the LPMOs, providing more information about the lignin-LPMO interaction. The results demonstrated the existence of low-molecular weight lignin-derived compounds that are diffused in the reaction medium, which are able to reduce the enzyme active site and subsequently utilize additional electrons from the insoluble lignin fraction to promote the LPMO oxidative activity. Regarding the bulk lignin fractions, those isolated from the organosolv pretreated materials served as the best candidates in supplying electrons to the soluble compounds and, finally, to the enzymes. This difference, based on biomass pretreatment, was also demonstrated by the activity of LPMOs on natural substrates in the presence and absence of ascorbic acid as additional reducing agent.ConclusionsLignins can support the action of LPMOs and serve indirectly as electron donors through low-molecular-weight soluble compounds. This ability depends on their physicochemical and structural properties and is related to the biomass source and pretreatment method.

Chondrogenic differentiation of human chondrocytes cultured in the absence of ascorbic acid.

Bioreactor systems will likely play a key role in establishing regulatory compliant and cost-effective production systems for manufacturing engineered tissue grafts for clinical applications. However, the automation of bioreactor systems could become considerably more complex and costly due to the requirements for additional storage and liquid handling technologies if unstable supplements are added to the culture medium. Ascorbic acid (AA) is a bioactive supplement that is commonly presumed to be essential for the generation of engineered cartilage tissues. However, AA can be rapidly oxidized and degraded. In this work, we addressed whether human nasal chondrocytes can redifferentiate, undergo chondrogenesis, and generate a cartilaginous extracellular matrix when cultured in the absence of AA. We found that when chondrocytes were cultured in 3D micromass pellets either with or without AA, there were no significant differences in their chondrogenic capacity in terms of gene expression or the amount of glycosaminoglycans. Moreover, 3D pellets cultured without AA contained abundant collagen Types II and I extracellular matrix. Although the amounts of Collagens II and I were significantly lower (34% and 50% lower) than in pellets cultured with AA, collagen fibers had similar thicknesses and distributions for both groups, as shown by scanning electron microscopy imaging. Despite the reduced amounts of collagen, if engineered cartilage grafts can be generated with sufficient properties that meet defined quality criteria without the use of unstable supplements such as AA, bioreactor automation requirements can be greatly simplified, thereby facilitating the development of more compact, user-friendly, and cost-effective bioreactor-based manufacturing systems.

Synthesis and Characterization of the Perthiatriarylmethyl Radical and Its Dendritic Derivatives with High Sensitivity and Selectivity to Superoxide Radical.

EPR spectroscopy, coupled with the use of tetrathiatriarylmethyl (TAM) radicals, has been a reliable method to detect the superoxide radical (O2.- ). However, the specificity and biocompatibility of TAM radicals need to be further improved. Although derivatization may overcome the drawbacks of current TAM radicals, esterification or amidation through the carboxylic groups greatly changes their redox properties and makes them inert to O2.- . Herein, the synthesis of a perthiatriarylmethyl (PST) radical and its dendritic derivatives, PST-TA and PST-NA, in which PST is covalently linked with dendrons containing three (TA) and nine (NA) carboxylic acids, respectively. The results show that PST rapidly reacts with O2.- to yield a unique quinone methide product. Dendritic modification of PST slightly decreases the reactivities of PST-TA and PST-NA, but notably increases their biostability toward various oxidoreductants. The detection limit of PST-NA to O2.- was estimated to be 2.1 nm min-1 over 60 min of detection. Importantly, PST-NA shows threefold higher sensitivity to O2.- in the presence and absence of ascorbic acid than that of the classic spin-trapping technique. In addition, the application of PST-NA to detect extracellular O2.- generation in stimulated RAW 264.7 macrophages was also explored. This study demonstrates that PST-NA has great potential for specific detection and quantitation of O2.- in extracellular sites.

Ascorbic Acid can Reverse the Inhibition of Phytic Acid, Sodium Oxalate and Sodium Silicate on Iron Absorption in Caco-2 cells.

The objective of the present study is to determine the effect of phytic acid (PA), sodium oxalate (SO) and sodium silicate (SS) on non-heme iron bioavailability in both the presence and absence of ascorbic acid (AA) using an in vitro digestion/Caco-2 cell model, and the levels of AA needed to promote Fe absorption from Fe complexed with PA, SO or SS were also determined. The results indicated that adding PA at 1:1, 3:1, 5:1 and 10:1 molar as compared to Fe decreased ferrous iron uptake by 55.80 %(P < 0.05), 72.33 % (P < 0.05), 73.32 % (P < 0.05), and 73.26 % (P < 0.05), respectively. Adding SS at 1:1, 3:1, 5:1 and 10:1 molar as compared to Fe also decreased ferrous iron uptake by 51.40 % (P < 0.05), 66.12 %(P < 0.05), 60.19 % (P < 0.05) and 45.11 % (P < 0.05), respectively. Adding SO at 5:1 and 10:1 molar as compared to Fe decreased ferrous iron uptake by 40.81 % (P < 0.05) and 33.14 % (P < 0.05), respectively. When adding AA to iron plus organic acid medias reached molar ratios of 5:5:1 AA:PA:Fe, 3:5:1 AA:SO:Fe and 5:5:1 AA:SS:Fe, iron absorption from FeSO4 were significantly increased (P < 0.05). However, no significant effect was observed in iron absorption from FeCl3 when adding AA to the media. The results showed that PA, SS or SO decreases iron uptake from ferrous Fe, and AA can counteract their inhibiting effect on ferrous iron absorption and thus increase ferrous iron uptake. The results may be important for elucidating factors affecting iron bioavailability in the small intestine and for the development of foods with improved iron bioavailability.

A highly sensitive and selective detection of Cr(VI) and ascorbic acid based on nitrogen-doped carbon dots

A highly sensitive and selective detection of hexavalent chromium (Cr(VI)) and ascorbic acid (AA) was proposed using nitrogen-doped carbon dots (N-CDs). In the absence of AA, the quantitative detection of Cr(VI) was realized through Cr(VI) acting as a quencher to quench the fluorescence of N-CDs by inner filter effect (IFE) and static quenching effect. Under the optimal conditions, the linear range for Cr(VI) detection was from 0.01 to 250μM with a detection limit of 5nM (S/N = 3). In the presence of AA, the fluorescence intensity could be rapidly enhanced compared with the fluorescence of N-CDs/Cr(VI) system since Cr(VI) can be reduced into trivalent chromium (Cr(III)) by AA. And a wide linear range for AA detection was obtained from 1 to 750μM. The detection limit was 0.3μM (S/N = 3). More importantly, this method can be successfully applied to the detection of Cr(VI) in real water samples, and AA in vitamins C tablets and human serum sample.

Degradation of naphthalene by liquid-phase oxidation over ordered mesoporous V-m-TiO2 catalysts

The vanadium species doped mesoporous anatase TiO2 samples were successfully synthesized via a facile one-pot EISA method. The physical chemical properties were characterized by XRD, N2 sorption, UV–Vis, Py-IR, SEM, TEM and XPS techniques, and the catalytic performance were also investigated in the oxidation of naphthalene with hydrogen peroxide. The vanadium species with 4+ or 3+ valence can be homogeneously tetrahedrally incorporated into the mesoporous framework of anatase TiO2, and it would increase the Bronsted acidity resulting in the promotion of catalytic performance. Naphthalene conversion of 26.1% can be obtained over 10 V-m-TiO2 sample in the absence of ascorbic acid. The catalytic performance was much higher than other samples with the same loading of vanadium species prepared by impregnation or coprecipitation even though they were in the presence of ascorbic acid as reductant. Although the intrinsic reusability for 10 V-m-TiO2 sample was poor, the catalytic performance was promoted and the catalytic reusability can be kept well by introduction of ascorbic acid into the oxidation system even after repeated reaction for five times.

Study of lipid peroxidation and ascorbic acid protective role in large unilamellar vesicles from a new electrochemical performance

In this contribution an electrochemical study is described for the first time of lipid peroxidation and the role of antioxidant on lipid protection using large unilamellar vesicles (LUVs). In order to simulate the cell membrane, LUVs composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) were used. A vesicle-modified electrode was constructed by immobilizing DOPC LUVs onto carbon paste electrodes (CPEs). Lipid peroxidation was studied electrochemically by incubating the vesicle-modified electrodes with hydroxyl (HO) radicals generated via the Fenton reaction. Oxidative damage induced by HO was verified by using square wave voltammetry (SWV) and was indirectly measured by the increase of electrochemical peak current to [Fe(CN)6]4− which was used as the electrochemical label. Ascorbic acid (AA) was used as the antioxidant model in order to study its efficacy on free radical scavenging. The decrease of the electrochemical signal confirms the protective key role promoted by AA in the prevention of lipid peroxidation in vesicles. Through microscopy, it was possible to observe morphologic modification on vesicle structures after lipid peroxidation in the presence or absence of AA.

Hen egg yolk phosvitin stimulates osteoblast differentiation in the absence of ascorbic acid.

Egg yolk phosvitin, one of the most highly phosphorylated extracellular matrix proteins known in nature, has a strong calcium binding and reducing capacity. Here, we investigated the effects of phosvitin on osteoblast differentiation and osteogenic gene expression in cultured mouse osteoblastic MC3T3-E1 cells by using alkaline phosphatase activity analysis, alizarin red S staining and real-time PCR assay. Alkaline phosphatase activity and alizarin red S staining analyses demonstrated no significant difference between differentiating MC3T3-E1 cells cultured in the presence of phosvitin and those cultured in the presence of ascorbic acid after 21 days of differentiation. Our real-time PCR assay also indicated the two groups were similar in the expression of the osteogenic gene markers, collagen type I, osteocalcin, runt-related transcription factor 2, and bone morphogenetic protein-2. Our findings indicate that phosvitin plays a similar role to that of ascorbic acid in osteoblast differentiation and mineralisation. © 2017 Society of Chemical Industry.

Ascorbic acid does not modulate potassium currents in cultured human lymphocytes.

Ascorbic acid (AA) is known to modulate lymphocyte function, but the mechanism of action is not clearly understood. As voltage-gated potassium currents play an important role in lymphocyte function, the effect of AA on voltage-gated potassium currents was studied. Peripheral blood mononuclear cells were cultured in the presence of increasing concentrations of AA (0, 0.125, 0.25, 0.5, and 1 mM). Potassium currents in resting lymphocytes were studied by whole cell patch clamp technique using a depolarizing protocol. Lymphocyte function was assessed by measuring interleukin-2 (IL-2) secretion after mitogenic stimulation by ELISA. The mean current density of potassium currents recorded from cells cultured for 48 h in the presence of 0.125 mM AA was not significantly different from that of cells cultured in the absence of AA. There was about 50% inhibition of IL-2 secretion in cell cultures with 0.125 mM AA when compared to controls without AA. At higher concentrations of AA, the IL-2 secretion decreased further. The results of the study indicate that the inhibition of lymphocyte function by AA in vitro may not be due to inhibition of potassium currents in the concentration tested.

Ascorbic acid increases demethylation in somatic cell nuclear transfer embryos of the pig (Sus scrofa).

ObjectiveInvestigated the effect and mechanism of ascorbic acid on the development of porcine embryos produced by somatic cell nuclear transfer (SCNT).MethodsPorcine embryos were produced by SCNT and cultured in the presence or absence of ascorbic acid. Ten-eleven translocation 3 (TET3) in oocytes was knocked down by siRNA injection. After ascorbic acid treatment, reprogramming genes were analyzed by realtime reverse transcription-polymerase chain reaction (RT-PCR). Furthermore, relative 5-methylcytosine and 5-hydroxymethylcytosine content in pronucleus were detected by realtime PCR.ResultsAscorbic acid significantly increased the development of porcine embryos produced by SCNT. After SCNT, transcript levels of reprogramming genes, Pou5f1, Sox2, and Klf were significantly increased in blastocysts. Furthermore, ascorbic acid reduced 5-methylcytosine content in pronuclear embryos compared with the control group. Knock down of TET3 in porcine oocytes significantly prevents the demethylation of somatic cell nucleus after SCNT, even if in the presence of ascorbic acid.ConclusionAscorbic acid enhanced the development of porcine SCNT embryos via the increased TET3 mediated demethylation of somatic nucleus.

Electrochemical Detection of Neurotransmitters Using Modified PEDOT Electrodes

This paper presents recent results from authors’ labs on the electrochemical detection of ascorbic acid (AA), serotonin (5-HT) and dopamine (DA) at poly[3,4-ethylenedioxythiophene], PEDOT, and PEDOT-Au electrodes. We could show that the technique used for preparing the PEDOT and the PEDOT-Au electrodes strongly affects the quality of the sensors. Pulse plating gave the best films with regard to their morphology and charge storage. Parameters of the pulse sequence, such as anodic and cathodic potentials, as well as pulse duration, were optimized. Acoustic impedance data (obtained by an Electrochemical Quartz Crystal Microbalance in dispersive mode) show that such films prepared by pulse plating display also maximal elastic storage and loss moduli. The detection limits for the above mentioned neurotransmitters were studied by differential pulse voltammetry in phosphate buffer solution, PBS (Fig. 1), in the presence and absence of AA. Compared to pristine PEDOT, the Au modified electrodes showed a considerable increase of sensitivity and selectivity for neurotransmitters detection. Fig. 1. The DPV curves measured in PBS with different concentrations of (a) 5-HT and (b) DA, on PEDOT layers in the presence of 300μM AA Figure 1

Ablation of aldehyde reductase aggravates carbon tetrachloride-induced acute hepatic injury involving oxidative stress and endoplasmic reticulum stress

Aldehyde reductase (Akr1a) has been reported to be involved in the biosynthesis of ascorbic acid (AsA) in the mouse liver. Because Akr1a is expressed at high levels in the liver, we aimed to investigate the role of Akr1a in liver homeostasis by employing a carbon tetrachloride (CCl4)-induced hepatotoxicity model. Akr1a-deficient (Akr1a−/−) and wild-type (WT) mice were injected intraperitoneally with CCl4 and the extent of hepatic injury in the acute phase was assessed. Liver damage was heavier in the Akr1a−/− mice than in the WT mice. Furthermore, severe hepatic steatosis was observed in the livers of Akr1a−/− mice compared to WT mice and was restored to the levels in WT mice by AsA supplementation. Since the presence or absence of AsA had no effect on the decrease in CYP2E1 activity after the CCl4 treatment, it appears that AsA plays a role in the process after the bioactivation of CCl4. Biomarkers for oxidative stress and ER stress were markedly increased in the livers of Akr1a−/− mice and were effectively suppressed by AsA supplementation. Based on these collective results, we conclude that Akr1a exerts a protective effect against CCl4-induced hepatic steatosis by replenishing AsA via its antioxidative properties.

Citrate-Induced Nanocubes: A Re-Examination of the Role of Citrate as a Shape-Directing Capping Agent for Ag-Based Nanostructures.

Seed-mediated syntheses utilizing facet-selective surface passivation provide the necessary chemical controls to direct noble metal nanostructure formation to a predetermined geometry. The foremost protocol for the synthesis of (111)-faceted Ag octahedra involves the reduction of metal ions onto pre-existing seeds in the presence of citrate and ascorbic acid. It is generally accepted that the capping of (111) facets with citrate dictates the shape while ascorbic acid acts solely as the reducing agent. Herein, a citrate-based synthesis is demonstrated in which the presence or absence of ascorbic acid is the shape-determining factor. Reactions are carried out in which Ag(+) ions are reduced onto substrate-immobilized Ag, Au, Pd, and Pt seeds. Syntheses lacking ascorbic acid, in which citrate acts as both the capping and the reducing agent, result in a robust nanocube growth mode able to withstand wide variations in the concentration of reactants, reaction rates, seed material, seed orientation and faceting, pH, and substrate material. If, however, ascorbic acid is included in these syntheses, then the growth mode reverts to one that advances the octahedral geometry. The implication of these results is that citrate, or one of its oxidation products, selectively caps (100) facets, but where this capability is compromised by ascorbic acid.

Trichloroethylene Degradation by Various Forms of Iron Activated Persulfate Oxidation with or without the Assistance of Ascorbic Acid

The oxidation of trichloroethylene (TCE), by Fe2+ activated persulfate (PS) to generate the sulfate radical (SO4–•) is limited due to the scavenging of SO4–• by excess Fe2+. This study focused on evaluating the potential for TCE oxidative degradation by iron activated persulfate (IAP) (including soluble iron and solid iron minerals), with the assistance of ascorbic acid (AsA). AsA, a water-soluble two-proton donor, may act as a reductant and a chelator, which may reduce iron oxides or complex soluble iron for PS activation. The results indicated that PS oxidation and various types of iron (Fe2+, Fe3+, FeOOH, Fe2O3) activated PS are able to degrade TCE in the presence or absence of AsA and are dependent upon the PS concentrations applied. Furthermore, the TCE degradation could be accelerated in the iron minerals activated PS system with the assistance of AsA. In addition, synthesized iron minerals with higher specific surface area resulted in a higher PS activation efficiency (i.e., lower PS consumption) a...

Anti-Galvanic Reduction of Silver Ion on Gold and Its Role in Anisotropic Growth of Gold Nanomaterials

The role of silver ions in the seed-mediated growth of gold nanostructures has been investigated. Silver submonolayer or monolayer on specific facet of gold is assumed in previously suggested mechanism owing to underpotential deposition (UPD) of silver by ascorbic acid having weak reducing power. Silver overpotential deposition by ascorbic acid, however, is confirmed by electrochemical stripping voltammetry, whereas submonolayer of silver on gold is spontaneously formed by anti-galvanic reduction in the absence of ascorbic acid. In the presence of cetyltrimethylammonium bromide (CTAB), silver overpotential deposition by ascorbic acid does not occur, but submonolayer of silver is formed on gold surface. Adsorption of silver and CTAB on gold dramatically hindered the electron transfer by the oxidation of ascorbic acid on gold, which reduces gold ions to metallic gold in seed-mediated growth. These results provide the evidence to the in-depth observation of mechanism in seed-mediated growth where the blockin...

Cobalt carbonate dumbbells for high-capacity lithium storage: A slight doping of ascorbic acid and an enhancement in electrochemical performances

Synthesis of materials with desirable nanostructures is a hot research topic owing to their enhanced performances in contrast to the bulk counterparts. Herein, dumbbell-shaped cobalt carbonate (CoCO3) nano architectures and the bulk counterpart of CoCO3 rhombohedra are prepared via a facile hydrothermal route in the presence and absence of ascorbic acid (AA), respectively. By comparison, it has been found that: the addition of AA in the hydrothermal crystallization system changes the shape of the building blocks from Co2CO3(OH)2 nanosheets to CoCO3 nanoparticles, and then further influences the final configuration of the products. When applied as anodes of lithium ion batteries, CoCO3 dumbbells deliver a 100th capacity of 1042 mAh g−1 at 200 mA g−1 and even exhibit a long-term value of 824 mAh g−1 over 500 cycles at 1000 mA g−1, which are much higher than the rhombohedral counterparts with corresponding 540 and 481 mAh g−1 respectively. The much higher capacity, better cycling stability and enhanced rate performance of CoCO3 dumbbells can be attributed to the higher specific surface area, smaller charge transport resistance and better structure stability resulting from the slight doping (∼4.6 wt%) of AA, and also relate with a novel lithium storage mechanism in CoCO3.

Dopamine and ascorbic acid electro-oxidation on Au, AuPt and Pt nanoparticles prepared by pulse laser ablation in water

ABSTRACT In this study, we have investigated the use of PtAu alloy nanoparticles (NPs) with four different compositions (from x = 0 to 100) as electrodes for the detection of dopamine (DA) in the presence of ascorbic acid (AA). The Au 100-x Pt x NPs were prepared by pulsed laser ablation in an alkaline solution without using any surfactants or capping agents. The diameter of the particle ranges from 2.5 nm for pure Pt to 5.2 nm for pure Au NPs. Cyclic voltammetry showed that the number of DA molecules being oxidized on the NPs surface decreases with the Au content (from 9.0 × 10 −11 mol on Au to 4.8 × 10 −11 mol on Pt NPs), which emphasizes the preponderant role of Au surface sites on the electrochemical oxidation of DA. On the other hand, the oxidation current of AA is greatly enhanced by alloying Au with Pt, and the peak current of the alloyed NPs is about two (Au 50 Pt 50 ) and four times (Au 70 Pt 30 ) higher than that of Au NPs. It is suggested that the oxidation of the lateral chain of AA on the Pt sites occurs simultaneously to the oxidation of the ascorbate anion to dehydro ascorbic acid on the Au sites. Finally, it was shown by differential pulse voltammetry that Au and Au 100-x Pt x NPs can detect DA in solutions containing AA with a concentration 1000× higher. For example, for Au 70 Pt 30 the sensitivity and detection limit for the detection of DA in presence of 2 mM AA were 3.34 μA μM −1 and 0.06 μM (at S/N = 3) respectively, essentially the same values (3.50 μA μM −1 cm −2 and 0.05 μM) as in the absence of AA.