Ascorbic Acid In Aqueous Solution Research Articles

Evidence of carrier mediated transport of ascorbic acid through mammalian cornea

The purpose of the present study was to evaluate the transport of ascorbic acid, a water soluble molecule, through a predominantly lipophilic cornea. Thus in-vitro permeation of ascorbic acid from aqueous drops through freshly excised mammalian cornea was studied. Aqueous isotonic ophthalmic solutions of ascorbic acid of different concentrations (0.125% w/v to 2% w/v) (pH 5.4) were made. Further 1.0% w/v or 0.5% w/v ascorbic acid solution containing NaCl or dextrose as tonicity modifiers or Na +K +-ATPase inhibitors were also made. Permeation characteristics of drug were evaluated by putting 1 ml formulation on freshly excised cornea fixed between donor and receptor compartments of an all-glass modified Franz diffusion cell and measuring the drug permeated in the receptor by spectrophotometry at 265 nm, after 120 min. Statistical analysis was done by one-way analysis of variance (ANOVA) followed by Dunnett’s test or paired t-test. Increase in drug concentration in the formulation resulted in an increase in the quantity permeated but after a certain level increase in permeation with increase in concentration was minimal. Aqueous drops made isotonic with dextrose showed decreased permeation through paired cornea compared with aqueous drops made isotonic with NaCl from 1% w/v ascorbic acid solution suggesting likely involvement of Na + co-transporter but there was decreased permeation through 0.5% w/v ascorbic acid solution made isotonic with NaCl as compared to solution made isotonic with dextrose. Further aqueous drops containing Na +K +-ATPase inhibitor {MAG-Mono Ammonium Glycyrrhizinate (25 μmol)} showed decreased corneal permeation from 0.5% w/v ascorbic acid solution but there was not significant decrease from 1% ascorbic acid solution since MAG is a competitive inhibitor of ascorbic acid. Aqueous drops containing Na +K +-ATPase inhibitor {MAG (50 μmol) or Ouabain (1 mmol)} showed decreased corneal permeation of ascorbic acid compared with control from 1% ascorbic acid solution confirming the involvement of Na + co-transporter.

Preparation of counterion stabilized concentrated silver sols

A strategy for obtaining stable concentrated silver dispersions without dedicated stabilizing agents is presented. This approach consists of rapidly mixing aqueous solutions of silver salicylate and ascorbic acid. By using salicylate as Ag+ counterion, it is possible to prepare stable sols with metal concentrations up to two orders of magnitude higher than with silver nitrate. The stabilizing effect of the counterion is the result of a decreased ionic strength due to salicylate protonation and its adsorption on the surface of silver. Both effects increase the range of the electrostatic repulsive forces by expanding the electrical double layer.

Experimental study on equilibrium solubility (at low partial pressures), density, viscosity and corrosion rate of carbon dioxide in aqueous solutions of ascorbic acid

In this paper, ascorbic acid as a new carbon dioxide (CO 2) absorbent was investigated. The equilibrium solubility of CO 2 into 0.5, 1 and 1.5 mol dm −3 (M) aqueous ascorbic acid solutions were measured experimentally with a stirred batch reactor at total atmospheric pressure over the CO 2 partial pressure ranging from 0 to 45 kPa and temperatures between 298 and 313 K. The results of the gas solubility are presented as loading capacity (mol CO 2/mol ascorbic acid) as function of partial pressure of CO 2 for all experimental runs. Experimental results showed that solubility of CO 2 increases with increase in molar concentration of ascorbic acid solution at a given temperature and decreases with increase in temperature at a given concentration. The densities and viscosities of the ascorbic acid solutions were measured at the same conditions of the solubility measurement. Some corrosion rate tests were also performed on carbon steel at temperature of 308 K. It was observed that viscosity and corrosion rate increase when the molar concentration of ascorbic acid solution increases.

Electronic absorption spectra of ascorbic acid in water and water–dialkylsulfoxide mixtures

Gaussian analysis (LinkFit program) was used to deconvolute overlapping absorption bands due to neutral and anionic forms of ascorbic acid (AA). It has been shown that the neutral form of AA predominates in aqueous solutions of AA containing dialkylsulfoxides (DASO) because a hydrogen-bonded complex forms between DASO and AA molecules.

Control of silver–polymer aggregation mechanism by primary particle spatial correlations in dynamic fractal-like geometry

Silver nanocrystals have been prepared by reacting silver nitrate with ascorbic acid in aqueous solution containing a low concentration of a commercial polynaphthalene sulfonate polymer (Daxad 19). Various crystalline morphologies have been obtained simply by tuning the reaction temperature. We have investigated the nanoparticle formation mechanism at three different temperatures by in situ and time resolved small angle X-ray scattering measurements. By modeling the scattering intensity with interacting spherical particles in a fractal-like polymer-Ag matrix, we found signatures of nucleation, growth and assembly of primary particles of about 15-20 nm. We observed how the time evolution of both spatial correlations between primary particles and the dynamic fractal geometry of the polymer-Ag matrix could influence and determine both the aggregation mechanism and the morphology of forming nanostructures in solution.

An Amperometric Proton Selective Sensor with an Elliptic Microhole Liquid/Gel Interface for Vitamin-C Quantification

An amperometric ascorbic acid selective sensor utilizing the transfer reaction of proton liberated from the dissociation of ascorbic acid in aqueous solution across an elliptic micro-hole water/ organic gel interface is demonstrated. This redox inactive sensing platform offers an alternative way for the detection of ascorbic acid to avoid a fouling effect which is one of the major concerns in redox based sensing systems. The detection principle is simply measuring the current change with respect to the assisted transfer of protons by a proton selective ionophore (e.g., ETH 1778) across the micro-hole interface between the water and the polyvinylchloride-2-nitrophenyloctylether gel phase. The assisted transfer reaction of protons generated from ascorbic acid across the polarized micro-hole interface was first characterized using cyclic voltammetry. An improved sensitivity for the quantitative analysis of ascorbic acid was achieved using differential pulse stripping voltammetry with a linear response ranging from 1 to 100 µM concentrations of ascorbic acid. As a demonstration, the developed sensor was applied for analyzing the content of vitamin-C in different types of commercial pharmaceutical tablets and syrups, and a satisfactory recovery from these samples were also obtained.

2,2,6,6-Tetramethylpiperidine-1-oxyl-mediated living mini-emulsion polymerization of styrene under ambient pressure in a semi-batch process: effect of ascorbic acid

2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO)-mediated living mini-emulsion polymerization of styrene with feeding of an ascorbic acid aqueous solution throughout the polymerization was performed at 90 °C under ambient pressure. The concentrations of sodium dodecylbenzenesulfonate (SDBS) and ascorbic acid were varied to study the shell polymerization mechanism of latex particles and evolution of growing chains. Interactions between SDBS and ascorbic acid and incompatibility between ascorbic acid and styrene were evident from UV-visible analyses. High hydrophilicity of ascorbic acid in the aqueous phase was proved using a gravimetric method. Accordingly, the formation of a surface barrier on particles was proposed because of the interactions between SDBS and ascorbic acid. For higher SDBS concentration, the surface barrier on the particles was denser. Therefore, the polymerization rate decreased with increasing SDBS concentration. However, the polymerization rate increased with increasing ascorbic acid concentration. This was due to a higher consumption rate of TEMPO by ascorbic acid. Free TEMPO tended to reside in surface zones of the particles because of the surface activity between the aqueous and oil phases. The surface zones were thus the main loci where TEMPO was consumed by ascorbic acid. The estimated number-average molecular weight (Mn) of growing chains increased in a linear fashion with conversion. This indicated that the growing chains were produced via living mini-emulsion polymerization. For these growing chains, the estimated Mn and final polydispersity increased with increasing SDBS concentration. This was caused by a decrease in TEMPO concentration in the surface zones of particles with increasing SDBS concentration. The ‘livingness’ of polystyrene was identified by conducting bulk polymerization of chain extension. Based on the results obtained, a shell polymerization mechanism of latex particles was proposed, and living mini-emulsion polymerization was limited to the surface zones of particles. Copyright © 2010 Society of Chemical Industry

DNA-based biosensor for the electrocatalytic determination of antioxidant capacity in beverages

Reactive oxygen species (ROS) are produced as a consequence of normal aerobic metabolism and are able to induce DNA oxidative damage. At the cellular level, the evaluation of the protective effect of antioxidants can be achieved by examining the integrity of the DNA nucleobases using electrochemical techniques. Herein, the use of an adenine-rich oligonucleotide (dA 21) adsorbed on carbon paste electrodes for the assessment of the antioxidant capacity is proposed. The method was based on the partial damage of a DNA layer adsorbed on the electrode surface by OH radicals generated by Fenton reaction and the subsequent electrochemical oxidation of the intact adenine bases to generate an oxidation product that was able to catalyze the oxidation of NADH. The presence of antioxidant compounds scavenged hydroxyl radicals leaving more adenines unoxidized, and thus, increasing the electrocatalytic current of NADH measured by differential pulse voltammetry (DPV). Using ascorbic acid (AA) as a model antioxidant species, the detection of as low as 50 nM of AA in aqueous solution was possible. The protection efficiency was evaluated for several antioxidant compounds. The biosensor was applied to the determination of the total antioxidant capacity (TAC) in beverages.

Apparent molar volume, viscosity B-coefficient, and adiabatic compressibility of tetrabutylammonium bromide in aqueous ascorbic acid solutions at T = 298.15, 308.15, and 318.15 K

Apparent molar volumes ϕν and viscosity B-coefficients for tetrabutyl ammonium bromide (TBAB) in (0.00, 0.05, 0.10, and 0.15) mol dm−3 aqueous ascorbic acid solutions have been determined from solution density and viscosity measurements at temperatures over the range 298.15 to 318.15 K as function of concentration of ascorbic acid solutions. In the investigated temperature range, the relation: ϕν0 = a0 + a1T + a2T2, have been used to describe the partial molar volume ϕν0. These results, in conjunction with the results obtained in pure water, have been used to calculate the standard volumes of transfer Δϕν0 and viscosity B-coefficients of transfer for TBAB from water to aqueous ascorbic acid solutions for rationalizing various interactions in the ternary solutions. The structure making or breaking ability of TBAB has been discussed in terms of the sign of (δ2ϕν0/δT2)P. An increase in the transfer volume of TBAB with increasing ascorbic acid concentration has been explained by Friedman-Krishnan co-sphere model. The activation parameters of viscous flow for the ternary solutions studied have also been calculated and explained by the application of transition state theory.

Highly Surface‐roughened “Flower‐like” Silver Nanoparticles for Extremely Sensitive Substrates of Surface‐enhanced Raman Scattering

AbstractSurface‐enhanced Raman scattering (SERS) is a new optical spectroscopic analysis technique with potential for highly sensitive detection of molecules. Recently, many efforts have been made to find SERS substrates with high sensitivity and reproducibility. In this Research News article, we provide a focused review on the synthesis of monodispersed silver particles with a novel, highly roughened, “flower‐like” morphology by reducing silver nitrate with ascorbic acid in aqueous solutions. The nanometer‐scale surface roughness of the particles can provide several hot spots on a single particle, which significantly increases SERS enhancement. The incident polarization‐dependent SERS of individual particles is also studied. Although the different “hot spots” on a single particle can have a strong polarization dependency, the total Raman signals from an individual particle usually have no obvious polarization dependency. Moreover, these flower‐like silver particles can be measured by SERS with high enhancement several times, which indicates the high stability of the hot spots. Hence, the flower‐like silver particles here can serve as highly sensitive and reproducible SERS substrates.

Molar volume, viscosity and conductance studies of some alkali metal chlorides in aqueous ascorbic acid

Molar volume, viscosity and conductance of lithium chloride (LiCl), sodium chloride (NaCl) and potassium chloride (KCl) in 0.01 m aqueous ascorbic acid have been calculated from density, viscosity and conductance data at temperatures 303.15, 308.15, 313.15 and 318.15 K. The solute–solvent interactions for LiCl, NaCl and KCl have been inferred from ϕ v o, B-coefficient of Jones–Dole equation and Λ m o values. The structure making/breaking behavior of LiCl, NaCl and KCl is inferred from the sign of [∂ 2 ϕ v o/∂T 2] p, d B/dT and temperature coefficient of Walden product i.e. d( Λ m o η o)/dT values. It has been found from molar volume, viscosity and conductance studies that LiCl, NaCl and KCl behaves as structure-breaker in 0.01 m aqueous ascorbic acid solution. The energy of activation for LiCl, NaCl and KCl is calculated from conductance and viscosity data and it has found that E Λ is less than E η .

Kinetics and Mechanism of the Oxidation of Ascorbic Acid in Aqueous Solutions by a trans-Dioxoruthenium(VI) Complex

The oxidation of ascorbic acid (H(2)A) by a trans-dioxoruthenium(VI) species, trans-[Ru(VI)(tmc)(O)(2)](2+) (tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), has been studied in aqueous solutions under argon. The reaction occurs in two phases: trans-[Ru(VI)(tmc)(O)(2)](2+) + H(2)A --> trans-[Ru(IV)(tmc)(O)(OH(2))](2+) + A, trans-[Ru(IV)(tmc)(O)(OH(2))](2+) + H(2)A --> trans-[Ru(II)(tmc)(OH(2))(2)](2+) + A. Further reaction involving anation by H(2)A occurs, and the species [Ru(III)(tmc)(A(2-))(MeOH)](+) can be isolated upon aerial oxidation of the solution at the end of phase two. The rate laws for both phases are first-order in both Ru(VI) and H(2)A, with the second-order rate constants k(2) = (2.58 +/- 0.04) x 10(3) M(-1) s(-1) at pH = 1.19 and k(2)' = (1.90 +/- 0.03) M(-1) s(-1) at pH = 1.24, T = 298 K and I = 0.1 M for the first and second phase, respectively. Studies on the effects of acidity on k(2) and k(2)(') suggest that HA(-) is the kinetically active species. Kinetic studies have also been carried out in D(2)O, and the deuterium isotope effects for oxidation of HA(-) by Ru(VI) and Ru(IV) are 5.0 +/- 0.3 and 19.3 +/- 2.9, respectively, consistent with a hydrogen atom transfer (HAT) mechanism for both phases. A linear correlation between log(rate constants) for oxidation by Ru(VI) and the O-H bond dissociation energies of HA(-) and hydroquinones is obtained, which also supports a HAT mechanism.

Biocompatible Water-in-Oil Emulsion as a Model to Study Ascorbic Acid Effect on Lipid Oxidation

A biocompatible water-in-oil (W/O) emulsion has been used as a model to study the effect of ascorbic acid (AA) on the oxidation of the oil (glycerol trioleate, GTO) continuous phase. The model system consisted of 3 wt % water dispersed in GTO containing 0.5 wt % sodium oleate (NaO)/oleic acid (OA) mixture (NaO/OA = 20/80 mol/mol %) as a stabilizer. To study the ascorbic acid effect on GTO light-promoted oxidation, we added aqueous solutions of ascorbic acid to GTO in place of distilled water. Results obtained as peroxide values show that ascorbic acid activity depends on its concentration and it is affected by the characteristics of the W/O interface. In the presence of ascorbyl palmitate (AP) or sorbitan trioleate (Span 85) in the continuous phase, ascorbic acid activity increases in the first few hours of oxidation. The effect of ascorbic acid has been related to emulsion structure by calculating characteristic parameters of the droplet size distributions by means of optical microscopy.

Stability of ascorbic acid in aqueous and aqueous-organic solutions for quantitative determination

The stability of ascorbic acid is studied in dependence on the pH of its aqueous solution. It is shown that itenhances in acidic and weakly alkaline media and upon the addition of acetonitrile. The stabilizing effect of ethanol is considerably lower. Processes occurring in aqueous and aqueous-organic solutions of ascorbic acid are considered and the results obtained are explained. These data are important for the development of analytical procedures and can be used in the chemical and pharmaceutical industries for improving the stability of preparations containing ascorbic acid.

Irradiation of human insulin in aqueous solution, first step towards radiosterilization

The degradation of irradiated human insulin in aqueous solutions was investigated in order to protect the protein against ionizing radiation. The influence of the drug concentration, excipients and irradiation temperature were studied. Aqueous solutions at pH 2 were irradiated by gamma rays or by accelerated electrons. Two different high-performance liquid chromatography (HPLC) methods were used: reverse-phase high-performance liquid chromatography (RP-HPLC)/UV and size exclusion liquid chromatography (SEC/UV) to investigate both the fragmentation and the formation of higher molecular weight proteins. In solution without excipients irradiated at ambient temperature at 10 kGy, the loss of human insulin is almost complete. Addition of radio-protecting excipients (free radicals scavengers) and cryo-irradiation allowed to decrease insulin degradation. The best radio-protector used was ascorbic acid in aqueous solution and oxidized glutathione in the frozen solutions. Only the combination of these two approaches (addition of scavenger and freezing) enables the irradiated human insulin in aqueous solution to meet the European Pharmacopoeia requirements for chemical potency (≥90%).

Sterility testing of insulin preparations

The appearance of precipitates and opalescent components hinders testing for the sterility of insulin suspensions by seeding in cultural media. The sampling procedure is improved by dissolving preparations in 0.2% aqueous ascorbic acid solution, which eliminates opalescence and precipitation and facilitates the reading and interpretation of the test results as the test solutions become transparent. This method is suitable with both direct inoculation and membrane filtration. The insulin solution in 0.2% ascorbic acid does not exhibit antimicrobial activity, which makes expedient testing with the more economical direct inoculation.

CV and NMR study on the reaction of Mo(VI) with 3,4-dihydroxybenzoic acid and ascorbic acid in aqueous solution

The gradual release of the ligand 3,4-dihydroxybenzoic acid (3,4-DHBA) from its molybdenum complex in the presence of ascorbic acid (AscA) in a weakly acidic aqueous solution (pH ∼ 3.5) is described. We observed that the formation of the 3,4-DHBA-semiquinone oxidation state and the semidehydroascorbate is a pre-requisite for the release of the 3,4-DHBA ligand. The interaction of these radicals leads at the same time to the further degradation of AscA resulting in, among other compounds, threonic acid which participates in the reaction with molybdenum. The comparison of the complexing ability indicated that threonic acid competes with protocatechuate, while ascorbic acid is a less good ligand for the Mo(VI). Solution studies on the reaction mechanism were performed by cyclic voltammetry, NMR spectroscopy and UV–Vis spectroscopy. Isolated precipitates were investigated by NMR spectroscopy. The antioxidant properties of 3,4-DHBA and AscA were also compared using the stable radical 2,2-diphenyl-1-picrylhydrazyl (DPPH).

Direct Synthesis of Branched Gold Nanocrystals and Their Transformation into Spherical Nanoparticles

We report a facile synthesis of branched gold nanocrystals by the addition of a suitable amount of NaOH to an aqueous solution of cetyltrimethylammonium bromide (CTAB), HAuCl(4), and ascorbic acid. The branched nanocrystals were formed within minutes of reaction and showed monopod, bipod, tripod, and tetrapod structures. They are crystalline and have smooth surfaces. These gold multipods are kinetically controlled products and are thermodynamically unstable. The branched nanocrystals quickly transformed into spherical nanoparticles within 1 h of reaction, and the process was essentially complete after 2 days. The morphological transformation has been monitored by both UV-vis absorption spectroscopy and electron microscopy. The appearance of two major absorption bands for the branched gold nanocrystals eventually became only a single band at 529 nm for the spherical nanoparticles. The resulting nanoparticles are single crystals with diameters of 20-50 nm and do not show a faceted structure. When the freshly prepared branched nanocrystals are kept in a refrigerator at 4 degrees C, their multipod structure can be preserved for over a month without significant spectral shifts.

Enhancing survival and subsequent infectivity of conidia of potential mycoherbistats using UV protectants

Ultraviolet radiation (UV) can reduce the effectiveness of fungi used for biological control; therefore, this study examined the photostabilising effect of water- and oil-soluble UV protectants on conidium germination of Plectosporium alismatis and Colletotrichum orbiculare, pathogens with potential as biocontrol agents, and the ability of conidia of C. orbiculare to cause disease. Formulation in riboflavin (1%), proline (1%), propyl gallate (1%), melanin (0.1%) and ascorbic acid (5%) increased the germination of UVB-exposed conidia of P. alismatis to levels found in the dark control without causing a delay in germination. Formulation in (a) pyridoxin (5%), (b) an nC24 mineral oil (5%), and (c) ECCO 1422 (5% in the mineral oil) also resulted in germination similar to the control but germination was delayed. Protection was provided to conidia of C. orbiculare treated with 1% aqueous solutions of proline and folic acid in vitro. Formulation of conidia of C. orbiculare in a 5% aqueous emulsion of the mineral oil and aqueous solutions of melanin (0.01%), proline and tyrosine (both at 1%) significantly increased anthracnose development above control levels on leaf discs of Xanthium spinosum exposed to UVB dose of 16.7 kJ m−2. After exposure to natural sunlight at a UVB dose of 2.2 kJ m−2, anthracnose development was greater on leaf discs inoculated with conidia of C. orbiculare formulated in 1% aqueous solutions of ascorbic acid (1%), proline (1%), tyrosine (1%) and melanin (0.01%), or in 5% aqueous emulsions of a canola-derived oil and the mineral oil than by conidia formulated in water alone. Therefore, a range of compounds can provide conidia with protection from UVB. Of these, propyl gallate and oils similar to the mineral oil are likely to be cost effective. Such formulations can be combined with suitable application times to increase mycoherbisitat efficiency.

Electrocatalytic Determination of Ascorbic Acid at the Surface of 2,7‐Bis(ferrocenyl ethyl)fluoren‐9‐one Modified Carbon Paste Electrode

AbstractA chemically modified carbon paste electrode with 2,7‐bis(ferrocenyl ethyl)fluoren‐9‐one (2,7‐BFEFMCPE) was employed to study the electrocatalytic oxidation of ascorbic acid in aqueous solution using cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The diffusion coefficient (D=1.89×10−5 cm2 s−1), and the kinetic parameter such as the electron transfer coefficient, α (=0.42) of ascorbic acid oxidation at the surface of 2,7‐BFEFMCPE was determined using electrochemical approaches. It has been found that under an optimum condition (pH 7.00), the oxidation of ascorbic acid at the surface of such an electrode occurs at a potential about 300 mV less positive than that of an unmodified carbon paste electrode. The catalytic oxidation peak currents show a linear dependence on the ascorbic acid concentration and linear analytical curves were obtained in the ranges of 8.0×10−5 M–2.0×10−3 M and 3.1×10−5 M–3.3×10−3 M of ascorbic acid with correlation coefficients of 0.9980 and 0.9976 in cyclic voltammetry and differential pulse voltammetry, respectively. The detection limits (2δ) were determined to be 2.9×10−5 M and 9.0×10−6 M with cyclic voltammetry and differential pulse voltammetry, respectively. This method was also examined for determination of ascorbic acid in pharmaceutical preparations.