ascorbic-acid and ferric-hydroxide

Carbon nanotube (CNT) modification of microelectrodes can result in increased sensitivity without compromising time response. However, dip coating CNTs is not very reproducible and the CNTs tend to lay flat on the electrode surface which limits access to the electroactive sites on the ends. In this study, aligned CNT forests were formed using a chemical self-assembly method, which resulted in more exposed CNT ends to the analyte. Shortened, carboxylic acid functionalized single-walled CNTs were assembled from a dimethylformamide (DMF) suspension onto a carbon-fiber disk microelectrode modified with a thin iron hydroxide-decorated Nafion film. The modified electrodes were highly sensitive, with 36-fold higher oxidation currents for dopamine using fast-scan cyclic voltammetry than bare electrodes and 34-fold more current than electrodes dipped in CNTs. The limit of detection (LOD) for dopamine was 17 ± 3 nM at a 10 Hz repetition rate and 65 ± 7 nM at 90 Hz. The LOD at 90 Hz was the same as a bare electrode at 10 Hz, allowing a 9-fold increase in temporal resolution without a decrease in sensitivity. Similar increases were observed for other cationic catecholamine neurotransmitters, and the increases in current were greater than for anionic interferents such as ascorbic acid and 3,4-dihydroxyphenylacetic acid (DOPAC). The CNT forest electrodes had high sensitivity at 90 Hz repetition rate when stimulated dopamine release was measured in Drosophila . The sensitivity, temporal resolution, and spatial resolution of these CNT forest modified disk electrodes facilitate enhanced electrochemical measurements of neurotransmitter release in vivo.

Topics: 3,4-Dihydroxyphenylacetic Acid; Animals; Ascorbic Acid; Dimethylformamide; Dopamine; Drosophila; Electrochemical Techniques; Ferric Compounds; Fluorocarbon Polymers; Microelectrodes; Nanotubes, Carbon; Neurotransmitter Agents; Oxidation-Reduction

Acellular hemoglobins developed as oxygen bridging agents with volume expanding properties ("blood substitutes") are prone to autoxidation and oxidant-mediated structural changes in circulation. In the presence of hydrogen peroxide and either ascorbate or urate we show that ferric hemoglobin functions as a true enzymatic peroxidase. The activity saturates with both substrates and is linearly dependent on protein concentration. The activity is enhanced at low pH with a pKa of 4.7, consistent with protonation of the ferryl species (Fe(IV)-OH) as the active intermediate. To test whether these redox reactions define its behaviour in vivo we exchanged transfused guinea pigs with 50% polymerized bovine Hb (PolyHbBv) and monitored plasma levels of endogenous ascorbate and urate. Immediately after transfusion, met PolyHbBv levels increased up to 30% of total Hb and remained at this level during the first 24 h post transfusion. Plasma ascorbate decreased by 50% whereas urate levels remained unchanged after transfusion. A simple kinetic model, assuming that ascorbate was a more active ferric heme reductase and peroxidase substrate than urate, was consistent with the in vivo data. The present finding confirms the primary and secondary roles of ascorbate and urate respectively in maintaining the oxidative stability of infused Hb.

Topics: Animals; Ascorbic Acid; Blood Substitutes; Buffers; Drug Carriers; Ferric Compounds; Guinea Pigs; Hemoglobins; Humans; Kinetics; Oxygen; Oxyhemoglobins; Peroxidases; Uric Acid

Ferritin and ferric hydroxide represent two forms of iron which are less available for absorption than that present in the 'common pool' of non-haem dietary iron. In the present study the absorption of iron from these two compounds was compared in 35 multiparous women when fed in water, in maize porridge and in maize porridge containing 100 mg ascorbic acid. The geometric mean absorption for 3 mg ferritin iron was 0.7% and for ferric hydroxide, 2.4%. Comparable figures when fed with maize porridge were 0.4% and 0.4% respectively. When 100 mg ascorbic acid was present in the porridge, absorption was enhanced from both sources, being 12.1% for ferritin and 10.5% for ferric hydroxide. These results indicate that the fraction of iron in ferritin and ferric hydroxide that enters the 'common pool' of non-haem dietary iron is profoundly influenced by the nature of the diet. The greater the concentration of enhancing ligands, the closer does the absorption of iron from these compounds approximate that of the non-haem dietary iron pool.

Topics: Adult; Anemia, Hypochromic; Animals; Ascorbic Acid; Dialysis; Female; Ferric Compounds; Ferritins; Humans; Hydrogen-Ion Concentration; Intestinal Absorption; Iron; Male; Rats; Rats, Inbred Strains