Applications of a simultaneous assay of ascorbic acid, dehydroascorbic acid and ascorbic sulphate in biological materials

A modified spectrophotometric assay for ascorbic acid and its derivatives based on their reaction with 2,4-dinitrophenylhydrazine (DNPH) is described. Using standard ascorbic acid or ascorbic sulphate solutions, together with animal tissue or compound diet extracts, the conditions for ascorbic acid degradation were determined. For the differential measurement of reduced ascorbic acid (AA), dehydroascorbic acid (dAA) and ascorbic sulphate (AS), five series of simultaneous determinations were performed. These included the use of (1) KBrO3 for the hydrolysis of AS, (2) 2,6-dichlorophenolindophenol as an oxidant, (3) DNPH to form a hydrazone derivative with dAA and (4 and 5) two blanks (where ascorbate was degraded) to correct for interfering substances. A variety of vertebrate and invertebrate tissues were examined for their ascorbate content, and the advantages of the modified procedure over currently available assays are discussed. The results suggest that the Artemia cyst is a unique material in which ascorbic sulphate is present in large amounts whereas fish tissues do not contain this form of vitamin C.     

Colorimetric determination of ascorbic acid in pharmaceutical preparations and biological samples

A simple and rapid method is described for the determination of L-ascorbic acid, based on its reduction of iron (III). The iron(II) thus formed is complexed with quinaldic acid and pyridine. The absorbance is measured at 380 nm after extracting the complex into chloroform. Beer's law is obeyed over the concentration range 2.5–25 g ml^–1 ascorbic acid. The results obtained are accurate and reproducible with the standard deviation of 0.0076. The method has been applied to the analysis of pharmaceuticals and biological samples with satisfactory results.     

Structure and properties of chitosan salt complexes with ascorbic acid diastereomers

Russian Chemical Bulletin - The study attests the effect of l- and d-diastereomers of ascorbic acid, which were used to prepare a salt form of chitosan, on the conformational features, structure,...     

A thermal analysis study of ascorbic acid and its pharmaceutical formulations

In a previous publication, the thermogravimetric (TG) analysis of ascorbic acid was considered. Simultaneously with the production of the TG data, time-temperature plots were also generated on the work station which allowed the process to be classified as exothermic or endothermic and identified the energy change with the reaction sequence. This aspect is investigated in the present study. To maximize the energy change, the model mixtures were assessed at a mass ratio of 11. The analytical implications of this approach are explored. To avoid complications in this kind of analysis, the present study is restricted to the behavior of binary systems heat treated in nitrogen.     

Fluorescent reaction between ascorbic acid and DAN and its analytical application

Fluorescent reaction between ascorbic acid (AA) and 2,3-diamino-naphthalene (DAN) was studied. The experimental results showed that AA could react with DAN at pH = 10.2-10.5, and form the fluorescent heterocyclic condensation products which emitted strong fluorescence. The fluorescence intensity was measured in a 1 cm quartz cell with excitation and emission wavelengths of 400 and 520 nm, respectively. The relationship was obtained between the fluorescence intensity and AA concentration in the range of 2-300 mug ml(-1), the regression coefficient is 0.9993. The detection limit (signal-to-noise = 2) is 0.4 mug ml(-1).     

Structure, function and biological relevance of prolyl oligopeptidase

A group of serine peptidases, the prolyl oligopeptidase family, cannot hydrolyze proteins and peptides containing more than 30 residues. The crystal structure of prolyl oligopeptidase (POP) has shown that the enzyme is composed of a peptidase domain with an alpha/beta hydrolase fold and a seven-bladed beta-propeller domain. This domain covers the catalytic triad and excludes large, structured peptides from the active site. The mechanism of substrate selection has been reviewed, along with the binding mode of the substrate and the catalytic mechanism, which differ from that of the classical serine peptidases in several features. POP is essentially a cytosolic enzyme and has been shown to be involved in a number of biological processes, but its precise function is still unknown. Many reports addressed experimentally the possible role of POP in cognitive and psychiatric processes, its involvement in the inositol phosphate signaling pathway, and its ability to metabolize bioactive peptides. Inhibitors were designed to reveal the cellular functions of POP and to treat neurological disorders. Other studies concerned the cellular localization of POP, its presumed interaction with the cytoskeletal elements, and its involvement in peptide/protein transport/secretion processes. The possible role of POP in Alzheimer disease is an intriguing issue, which is still debated. Recently, recombinant bacterial POPs have been investigated as potential therapeutics for celiac sprue, an autoimmune disease of small intestine caused by the intake of gluten proteins.     

Simultaneous determination of aminothiols, ascorbic acid and uric acid in biological samples by capillary electrophoresis with electrochemical detection

A method based on capillary electrophoresis with electrochemical detection has been employed for the separation and determination of homocysteine, cysteine, reduced glutathione, ascorbic acid and uric acid. Effects of several important factors such as the acidity and concentration of the running buffer, separation voltage, injection time and detection potential were investigated to acquire the optimum conditions. The detection electrode was a 500 microm diameter platinum disk electrode at a working potential of +1.05 V (vs saturated calomel electrode). The five analytes were well separated within 10 min in a 50 cm long fused silica capillary at a separation voltage of 18 kV in a 100 mm phosphate buffer (pH 7.8). The relation between peak current and analyte concentration was linear over about 3 orders of magnitude with the detection limits (S/N = 3) ranging from 0.83 to 2.58 microm. The proposed method was successfully applied to determine cysteine, reduced glutathione, ascorbic acid and uric acid in human whole blood and rat brain tissues with satisfactory assay results and should find a wide range of bioanalytical applications.     

A highly selective and instantaneous upconversion fluorescent nanoprobe for ascorbic acid detection in biological samples

A novel turn-on fluorescent nanoprobe using lanthanide-doped up-conversion nanoparticles (UCNPs) and hexagonal cobalt oxyhydroxide (CoOOH) nanofl akes were prepared for monitoring ascorbic acid in fruit samples.     

Optical and electrochemical-mediated detection of ascorbic acid using manganese porphyrin and its gold hybrids

The developments concerning new hybrids based on porphyrin derivatives and colloids destined for the detection of ascorbic acid (AA) in the relevant range for medical investigations are presented. Mn(III) tetratolylporphyrin chloride (MnTTPCl), spherical gold colloid (n-Au), and their hybrid (MnTTPCl/n-Au) were chosen to be comparatively investigated by ultraviolet–visible spectroscopy in the presence of AA. The hybrid material (MnTTPCl/n-Au) has the best capacity to detect concentrations of AA in the range of 2.6 × 10^?6–4.38 × 10^?5 M. Modified glassy carbon (GC) electrodes were obtained by thin film deposition of MnTTPCl, n-Au alone, and in successive mixed thin films, comparing their response during the electrochemical oxidation of AA. The electrocatalytic effect of the MnTTPCl on the AA oxidation is justified both by the increase in the peak current density and by the shift toward more negative potentials (0.024 V). The GC/MnTTPCl electrode has the best electrocatalytic effect for the AA oxidation and is promising for sensor applications.     

Synthesis and biological activity of RS-abscisic acid and its analogs

Summary RS-Abscisic acid and some of its analogs have been obtained. The biological activity of these compounds has been studied in dependence on their structure.It was found that precursors of RS-abscisic acid suppress the growth of segments of coleoptiles to a considerably smaller extent than the acid itself.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. Timiryazev Institute of Plant Physiology. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 731–735, November–December, 1970.     

Synthesis and biological activity of RS-abscisic acid and its analogs

Chemistry of Natural Compounds - RS-Abscisic acid and some of its analogs have been obtained. The biological activity of these compounds has been studied in dependence on their structure. It was...     

Structural determination of ascorbic acid 2-o-phosphate formed via acid hydrolysis of an ascorbic acid 3-O-phosphinate

The synthesis and X-ray structural determination of 3-O-[(bis-morpholino)phosphinyl]-5,6-O-isopropylidene-l-ascorbate (9) are described. Acid-catalyzed hydrolysis of 9 afforded the 2-O-phosphate 6. Definitive structural proof of 6 is based on a study of the pH profile of its UV spectra as compared with those of ascorbic esters, 2 and 9 (Figs. 1–3).     

Electrochemical synthesis of self-doped polyaniline and its use to the electrooxidation of ascorbic acid

Self-doped polyaniline (PAN) film on platinum electrode surface has been synthesized via electrochemical copolymerization of aniline with orthanilic acid (OAA). Fourier transform infrared, UV–Vis, and elemental analysis indicate the formation of the copolymer and that the copolymer has the structure of a head-to-tail coupling of aniline and OAA units. It was found that the internal doping of PAN with OAA can extend the electroactivity of PAN in neutral and even in alkaline media. The obtained self-doped PAN (PAN-OAA)-coated platinum electrode is shown to be a good surface for the electrooxidation of ascorbic acid (AA) in phosphate buffer solution of pH 7. The anode peak potential of AA shifts from 0.63 V at bare platinum electrode to 0.34 V at the PAN-OAA-modified platinum electrode with greatly enhanced current response. A linear calibration graph is obtained over the AA concentration range of 5–60 mM using cyclic voltammetry. Rotating disk electrode voltammetry and chronoamperometry have been employed to investigate the electrooxidation of AA. The PAN-OAA-modified platinum electrode shows good stability and reproducibility.