聚乙烯醇/酸化碳纳米管高亲水性三维孔电极膜的制备与电化学性能

在酸化碳纳米管的基础上, 采用电泳沉积和冷冻-解冻循环交联工艺制备了高亲水性聚乙烯醇/酸化碳纳米管(PVA/a-MWCNTs)水凝胶电极膜. 该电极膜具有三维连通纳米孔结构, 同时还具有高电活性面积、 低表面电荷传递电阻以及良好的扩散通透性等电化学特性. 该电极膜对多巴胺(DA)有很好的电化学响应特性, 并且对多巴胺的电化学还原电流不受抗坏血酸(AA)干扰, 在过量抗坏血酸存在下, PVA/a-MMWCNTs水凝胶电极膜对多巴胺还原电流的一阶导数与多巴胺的浓度在2×10^-6 ~2×10^-3 mol/L范围内呈线性关系, 检出限达到1×10^-6 mol/L, 灵敏度达到12.3 μA/(mmol·L^-1), 同时还表现出了较好的电极稳定性和重现性.     

Antiallergic Activity of 6-Deoxy-2-O-methyl-6-(N-hexadecanoyl)amino-l-ascorbic Acid

Allergy is an excessive immune response to a specific antigen. Type I allergies, such as hay fever and food allergies, have increased significantly in recent years and have become a worldwide problem. We previously reported that an ascorbic acid derivative having palmitoyl and glucosyl groups, 2-O-α-d-glucopyranosyl-6-O-hexadecanoyl-l-ascorbic acid (6-sPalm-AA-2G), showed inhibitory effects on degranulation in vitro and on the passive cutaneous anaphylaxis (PCA) reaction in mice. In this study, several palmitoyl derivatives of ascorbic acid were synthesized and a structure–activity relationship study was performed to discover more potent ascorbic acid derivatives with degranulation inhibitory activity. 6-Deoxy-2-O-methyl-6-(N-hexadecanoyl)amino-l-ascorbic acid (2-Me-6-N-Palm-AA), in which a methyl group was introduced into the hydroxyl group at the C-2 position of ascorbic acid and in which the hydroxyl group at the C-6 position was substituted with an N-palmitoyl group, exhibited much higher inhibitory activity for degranulation in vitro than did 6-sPalm-AA-2G. 2-Me-6-N-Palm-AA strongly inhibit the PCA reaction in mice at lower doses than those of 6-sPalm-AA-2G. These findings suggest that 2-Me-6-N-Palm-AA may be a promising therapeutic candidate for allergic diseases.     

Interaction of some antioxidants with Belousov-Zhabotinsky reaction based on catechol-BrO 3 − -Mn2+-H2SO4 system

Temporal evolution of a new Mn(II) catalyzed Belousov-Zhabotinsky (BZ) chemical oscillator with catechol (1.2-dihydroxybenzene) as organic substrate is reported within narrow range of concentrations of initial reagents at 30°C. After optimizing the oscillation parameters the system was perturbed with the antioxidants like ascorbic acid and inosine. It is found that ascorbic acid acts as co-substrate within certain concentration limit, whereas inosine acts as a quencher of oscillations. Addition of ascorbic acid to the BZ system decreases induction time thus acting synergistically to help the reaction to enter quickly into the oscillatory regime. A good linear dependence of induction time on the concentration of ascorbic acid (R ² = 0.9948) and inosine (R ² = 0.955) is reported. Inosine has been found to increase the induction time and quench the oscillations. It is mentioned that the magnitude of induction time decreases to a greater extent with ascorbic acid as compared to the magnitude of its increase with the same concentration of inosine. This is pointing to the fact that ascorbic acid is stronger antioxidant than inosine as depicted by their interaction with catechol-based BZ chemical oscillator. Temporal evolution of the BZ reaction with the injection of antioxidants at different stages of reaction is also reported.     

Effect of ascorbic acid and its derivatives on the radiation-chemical transformations of hydroxyl-containing organic compounds

The effect of ascorbic acid, 5,6-O-isopropylidyl-2,3-O-dimethylascorbic acid, and 2-O-glucopyranosylascorbic acid on the formation of main radiolysis products of ethanol and aqueous ethanol, ethylene glycol, α-methylglucopyranoside, and maltose solutions was studied by means of continuous radiolysis. The obtained results indicate that ascorbic acid effectively reacts with the carbon-centered hydroxyl-containing radicals derived from the substrates, thus decreasing the yield of their recombination and fragmentation products. It was found that the interaction of ascorbic acid and its derivatives with the carbon-centered radicals during the radiolysis of deaerated ethanol and its aqueous solutions may occur via both reducing and oxidizing mechanisms and that ascorbic acid in the aerated solutions acts as a hydrogen donor, reducing mainly the HO ₂ ^· radical to hydrogen peroxide.     

Synthesis and Swelling Behaviors of P(AMPS-co-AAc) Superabsorbent Hydrogel Produced by Glow-Discharge Electrolysis Plasma

Highly swelling P(2-acrylamido-2-methyl-1-propanesulfonic acid- co-acrylic acid) (P(AMPS-co-AAc)) superabsorbent hydrogel was synthesized in aqueous solution by a simple one-step using glow-discharge electrolysis plasma technique, in which N,N’-methylenebisacrylamide was used as a crosslinking agent. The structure, thermal stability and morphology of P(AMPS-co-AAc) superabsorbent hydrogel were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. A mechanism for synthesis of P(AMPS-co-AAc) superabsorbent hydrogel was proposed. The reaction parameters affecting the equilibrium swelling (i.e., discharge voltage, discharge time, macroscopic temperature of the liquid phase, mass ratio of AMPS to AAc, and content of crosslinker) were systematically optimized to achieve a superabsorbent hydrogel with a maximum swelling capacity. The hydrogel formed which absorbed about 1,685 g H₂O/g dry hydrogel of the optimized product was used to study the influence of various pH values and salts solutions (NaCl, KCl, MgCl₂, and CaCl₂) on the equilibrium swelling. In addition, swelling kinetics in distilled water and on–off switching behavior were preliminarily investigated. The results showed that superabsorbent hydrogel was responsive to the pH and salts.     

Ascorbic acid determination in biological fluids using ascorbate oxidase immobilized on alkylamine glass beads in a flow injection potentiometric system

A flow injection method was developed aimed at the determination of ascorbic acid in biological fluids, particularly fruit juices. The enzyme ascorbic oxidoreductase (EC 1.10.3.3), extracted fromCucurbita maxima, was immobilized onto alkylamine glass beads using glutaral-dehyde as a bifunctional agent. The ascorbic acid concentration was related to oxygen saturation. Fall in oxygen concentration, as a result of ascorbic acid oxidation, was detected by a low cost, homemade oxygen electrode. The calibration graph was linear over the range 0.05 to 3.00 mM (RSD 1%), the maximum number of samples that could be analysed was 90/h. The immobilized enzyme retained its initial activity for 2 mo with more than 600 assays.     

Kinetic determination of ascorbic acid by the 2,6-dichlorophenolindophenol reaction with a stopped-flow technique.

The reaction of ascorbic acid with 2.6-dichlorophenolindophenol is applied for the kinetic determination of ascorbic acid in 0.05M oxalic acid. Stopped-flow techniques are used; the concentrations of the reactants of the second-order reaction can be adjusted so that the transmittance signal remains nearly invariant for a wide range of voltage. Theoretical and experimental results are in very good agreement. Analytical working curves are presented for the determination of ascorbic acid in the ranges 5.0·10^-4–1.0·10^-2M and 5.0·10^-5–1.0-·10^-3M with errors of 1.0% and 2.2%. respectively. The method is simple, fast and sensitive.     

Reactions of cyclopentanone, γ-butyrolactone,and their derivatives with α-hydroxyethyl radicals

The interaction of cyclopentanone, 2-cyclopentenone, 1,3-cyclopentanedione, 3-methyl-1,2-cyclopentanedione, γ-butyrolactone, 2(5H)-furanone, ascorbic acid, and 5,6-O-isopropylidenyl-2,3-O-dimethylascorbic acid with α-hydroxyethyl radicals (α-HER) generated during the radiolysis of deaerated ethanol has been studied in the continuous irradiation mode. The test compounds, except γ-butyrolactone, oxidize α-HER. 2(5H)-Furanone and 2-cyclopentenone give hydroxyethylation products via the free-radical chain mechanism. In contrast to 2(5H)-furanone and 2-cyclopentenone, ascorbic and 5,6-O-isopropylidenyl-2,3-O-dimethyl-L-ascorbic acids are weaker oxidants for α-HER and attach these radicals at the multiple carbon-carbon bonds.     

Construction,analytical study and application of a new chloramine-t selective electrode

A chloramine-T (CAT) selective electrode with a liquid membrane of nickel batho-phenanthroline—chloramine-T dissolved in 2-nitro-p-cymene is described. The liquid membrane electrode exhibits rapid and near Nernstian response to chloramine-T activity from 10^-1 to 10^-4 M. The response is unaffected by pH in the range 5–9. Major interferences are penodate and perchlorate. In analytical applications, direct potentiometnc methods for the determination of chloramme-T, ascorbic acid, and arsenic(III), and a titnmetric method for ascorbic acid are described. Ascorbic acid and arsenic(IU) in the ranges 0.4–40 and 0.5–2 mg, respectively, can be determined with relative errors of 1–2%. The method has been applied to the determination of ascorbic acid in pharmaceutical preparations.     

Amperometric microcells for alkaline phosphatase assay

To develop simple electrochemical immunoassays, a screen printed amperometric microcell with graphite working and Ag/AgCl reference electrodes was tested for the determination of alkaline phosphatase enzyme (ALP) and anti-humanIgG conjugated ALP (alpha-hIgG-ALP) activity in 5-10 microl samples. To ensure reproducible, steady state conditions, the working electrode surface was coated with mass-transport controlling hydrogel layer. The kinetic response curves of the hydrogel coated electrodes were linear. In addition, the hydrogel layer reduced the nonspecific adsorption of the alpha-hIgG-ALP conjugate on the working electrode surface. The measurements were made in the range of 2 divided by 4000 mU ml(-1) enzyme activities using ascorbic acid 2-phosphate (AAP) as the enzyme substrate. AAP is commercially available, non-toxic and has excellent stability. The sensitivity of the determinations was about 71% of the sensitivity which could be achieved using p-aminophenylphosphate (PAPP), a not easily accessible and unstable enzyme substrate. The experimentally determined kinetic parameters of the ALP enzyme catalyzed reactions were the same with the bare and hydrogel layer coated electrodes.     

Ascorbic acid biosensor using ascorbate oxidase immobilized on alkylamine glass beads

A biosensor for ascorbic acid based on enzyme kinetics of ascorbate oxidase (E.C.1.10.3.3.) was developed. The enzyme was extracted fromCucurbita maxima, or jerimun and immobilized by covalent bounding, using glutaradehyde as a bifunctional agent, on alkylamine glass beads, with and without enzyme active site protection. A low-cost, home-made oxygen electrode was applied as a transducer. The system has sensitivity from 62.5 up to 500 μM of ascorbic acid with satisfactory operation for more than 2 mo.     

Application of differential pulse polarography to the assay of ascorbic acid

A polarographic method for the determination of ascorbic acid in pharmaceutical preparations and fruit juices is described. The method is based on the oxidation of ascorbic acid by iodine, and the resulting iodide, after removal of excess iodine, is oxidized with bromine to iodate which is measured polarographically. The method enables analysis of solutions as dilute as 1.7 × 10^?6M ascorbic acid.     

Preparation of enzymatically cross-linked sulfated chitosan hydrogel and its potential application in thick tissue engineering

For the requirement of preliminary vascularization, the scaffolds for thick tissue engineering should possess not only good cell affinity, but also anticoagulant ability. In this paper, an enzymatically crosslinked hydrogel scaffold based on sulfated chitosan (SCTS) was prepared. Firstly, sulfated chitosan-hydroxyphenylpionic acid (SCTS-HPA) conjugate was synthesized, and its structure was identified by FITR and ¹H NMR. And then an enzymatically crosslinked hydrogel was prepared in the presence of horseradish peroxidase (HRP) and hydrogen peroxide (H₂O₂). The gelation time, mechanical property, morphology and cytotoxicity to human umbilical vein endothelial cells (HUVECs) of the hydrogel was evaluated in vitro, the tissue compatibility of SCTS scaffold was studied in vivo. The results showed that the gelation time, mechanical property, morphology of the dehydrated hydrogel could be controlled by the HRP and H₂O₂ concentration. The cytotoxicity test showed that the hydrogel extracts had no cytotoxicity to HUVECs. The in vivo assay indicated that SCTS-HPA scaffold showed good tissue compatibility, and no thrombus formation. All these results indicated that the SCTS-HPA scaffold could be used as thick tissue engineering scaffold.     

Electrochemical investigation of the interaction between lysozyme-shelled microbubbles and vitamin C

We report loading of vitamin C (ascorbic acid) on to lysozyme-shelled microbubbles. The interaction between lysozyme-shelled microbubbles and vitamin C was studied by use of cyclic and differential pulse voltammetry, zeta potential measurements, and scanning electron microscopy. The effect of microbubbles on electrochemical measurement of ascorbic acid was evaluated. The linear range for ascorbic acid obtained for differential pulse measurement in the presence of 1 mg mL^?1 microbubbles was 1–50 μmol L^?1 (y?=?0.067x?+?0.130, r ²?=?0.995), with a detection limit of 0.5 μmol L^?1. The experimental conditions, i.e., pH and ionic strength, were optimized to improve the interaction between ascorbic acid and lysozyme-shelled microbubbles. The results were satisfactory when the interaction was performed for 1 h in aqueous solution at pH 6. The amount of vitamin C loaded on the microbubbles (90 % of the analyte added, RSD _inter-expt. = 3 %, n?=?6) and the stability of microbubbles–ascorbic acid complex (until 72 h at 25 °C) were also evaluated by use of differential pulse voltammetry and zeta potential measurements.

Gallic Acid-Loaded Sodium Alginate-Based (Polyvinyl Alcohol-Co-Acrylic Acid) Hydrogel Membranes for Cutaneous Wound Healing: Synthesis and Characterization

Traditional wound dressings often cannot treat wounds caused by bacterial infections or other wound types that are insensitive to these wound treatments. Therefore, a biodegradable, bioactive hydrogel wound dressing could be an effective alternative option. The purpose of this study was to develop a hydrogel membrane comprised of sodium alginate, polyvinyl alcohol, acrylic acid, and gallic acid for treating skin wounds. The newly developed membranes were analyzed using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), sol-gel fraction, porosity, mechanical strength, swelling, drug release and data modelling, polymeric network parameters, biodegradation, and antioxidation (DPPH and ABTS) and antimicrobial activity against Gram-positive and negative bacteria. The results revealed that hydrogel membranes were crosslinked successfully and had excellent thermal stability, high drug loading, greater mechanical strength, and exhibited excellent biodegradation. Additionally, the swelling ability and the porosity of the surface facilitated a controlled release of the encapsulated drug (gallic acid), with 70.34% release observed at pH 1.2, 70.10% at pH 5.5 (normal skin pH), and 86.24% at pH 7.4 (wounds pH) in 48 h. The gallic acid-loaded hydrogel membranes showed a greater area of inhibition against Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli bacteria as well as demonstrated excellent antioxidant properties. Based on Franz cell analyses, the permeation flux of the drug from optimized formulations through mice skin was 92 (pH 5.5) and 110 (pH 7.4) μg/cm²·h⁻¹. Moreover, hydrogel membranes retained significant amounts of drug in the skin for 24 h, such as 2371 (pH 5.5) and 3300 µg/cm² (pH 7.4). Acute dermal irritation tests in rats showed that hydrogel membranes were nonirritating. Hydrogel membranes containing gallic acid could be an effective option for improving wound healing and could result in faster wound healing.     

Robust Hydrogel Adhesive with Dual Hydrogen Bond Networks

Hydrogel adhesives are attractive for applications in intelligent soft materials and tissue engineering, but conventional hydrogels usually have poor adhesion. In this study, we designed a strategy to synthesize a novel adhesive with a thin hydrogel adhesive layer integrated on a tough substrate hydrogel. The adhesive layer with positive charges of ammonium groups on the polymer backbones strongly bonds to a wide range of nonporous materials’ surfaces. The substrate layer with a dual hydrogen bond system consists of (i) weak hydrogen bonds between N,N-dimethyl acrylamide (DMAA) and acrylic acid (AAc) units and (ii) strong multiple hydrogen bonds between 2-ureido-4[1H]-pyrimidinone (UPy) units. The dual hydrogen-bond network endowed the hydrogel adhesives with unique mechanical properties, e.g., toughness, highly stretchability, and insensitivity to notches. The hydrogel adhesion to four types of materials like glass, 316L stainless steel, aluminum, Al₂O₃ ceramic, and two biological tissues including pig skin and pig kidney was investigated. The hydrogel bonds strongly to dry solid surfaces and wet tissue, which is promising for biomedical applications.     

Precipitated droplets in-situ cross-linking polymerization and its applications

A novel, green and effective approach to fabricate uniform functional spherical polymer particles remains a huge challenge. Herein, we present a novel one-pot approach superior to traditional precipitation polymerization, called precipitated droplets in-situ cross-linking (PDIC) polymerization, by which uniform particles are fabricated on large scale without any toxic organic solvents or stabilizers. With this approach, functional spherical polymer particles can be fabricated continuously only relying on gravity, and the preparation process is thus super-fast. For example, polyacrylic acid (PAA) hydrogel particles with ultra-high adsorption capacity are fabricated within only 60 s. Moreover, we have successfully fabricated different functional hydrogel particles, including anticoagulant, reinforced and bactericidal particles, based on the monomers of 2-acrylamide-2-methylpropanesulfonic acid (AMPS), acrylamide (AM) and [2-(methacryloyloxy)ethyl]trimethylammonium chloride (DMC), respectively. This approach has several advantages: (i) the technology is green; (ii) the size and porosity of the particles can be well-controlled; (iii) various functional spherical hydrogel particles can be fabricated by using corresponding monomers. More importantly, this approach fits the commercialization of functional hydrogel particles on demand.     

Chitosan surface modified hydrogel as a therapeutic contact lens

Therapeutic contact lenses have attracted significant attention during the last decades. In this study, we used chitosan‐conjugated poly(2‐hydroxyethyl methacrylate) (PHEMA) for contact lens application. We aimed to increase affinity of anionic drugs, which are used in treatment of eye diseases. In this regard, we evaluated delivery of the small molecule anionic drug, ascorbic acid from the chitosan‐conjugated PHEMA. Chitosan immobilization improves drug loading efficiency and induces sustained release of ascorbic acid. The chitosan modified hydrogel also reduces the biofouling of tear fluid components. Our results showed that surface modification by chitosan inhibits protein and bacterial deposition on the contact lens. Protein absorption analysis revealed that neat PHEMA adsorbed tear proteins at a density of 28.4 ± 4.4 μg/cm², whereas the chitosan‐conjugated hydrogel adsorbed tear proteins at a density of 18.5 ± 1.8 μg/cm². Moreover, the neat PHEMA bacterial adhesion had a mean CFU value of 273 ± 27. However, a significant decrease in the number of bacterial colonies was observed in the chitosan group with a CFU value of 9 ± 6.     

Superabsorbent poly(acrylamide-co-itaconic acid) hydrogel microspheres: Preparation,characterization and absorbency

Poly(acrylamide-co-itaconic acid) (P(AM-co-IA)) hydrogel microspheres were prepared via inverse suspension polymerization method. DLS results showed the formation of the monodispersed hydrogel microspheres. The size of the hydrogel microspheres could be controlled by polymerization parameters. Absorbencies of P(AM-co-IA) microspheres in water and saline were investigated and calculated by size changes of each particle before and after swelling. The results showed that P(AM-co-IA) had high absorbencies, the weight of swollen particles was above 4000 times to that of the original dried microspheres. The superabsorbent hydrogel microspheres might find the potential applications in the fields of soil amendments, water shutoff agents, and drug delivery carriers.     

Inverse opal pH sensors with various protic monomers copolymerized with polyhydroxyethylmethacrylate hydrogel

pH sensitive inverse opal sensors were synthesized using various vinyl monomers containing acidic or basic substituents. Acrylic acid (AA), vinylphosphonic acid (VPA), vinylimidazole (VI), and dimethylaminoethylmethacrylic acid (DMAEMA) were respectively copolymerized with hydroxyethylmethacrylate (HEMA), the building block monomer of the hydrogel via UV-initiated photopolymerization. Opal templating and subsequent template removal enabled the fabrication of four inverse opal (IO) hydrogel colorimetric sensors, which responded to pH in different fashions. pH-dependent swelling of the IO hydrogel induced the red-shift of the diffracted color. The sensors containing AA or VPA, the proton donating monomers showed the color shifts from green to red with pH increase due to the increased concentration of carboxylate anions bound to the hydrogel. Diprotic VPA sensor exhibited two-step increases of diffracted wavelengths at its pK_a1 and pK_a2 respectively. The sensors containing proton acceptors, VI and DMAEMA showed the pH-dependent color changes in an opposite way to the AA sensor and the VPA sensor since their ionizations take place by lowering pH due to the protonation at the amino groups. The shapes of pH response curves of VI and DMAEMA sensors were similar but pK_bs were different from each other. Optical diffraction responses of four sensors were compared with the calculated concentration ratios of the ionized species to the total monomer with pH variation, and a deswelling effect in the vicinities of pK_as of phosphate buffer on the swelling response could be explained by shrinkage of PHEMA hydrogel under high ionic environment. In addition, copolymerization of AA, VPA and HEMA was carried out which resulted in a pH sensor exhibiting a wider range of pH for color change.