Oxidation-Reduction Potential of Ascorbic Acid (Vitamin C)

Borsook, Henry; Keighley, Geoffrey

doi:10.1073/pnas.19.9.875

Cited by 105 publications

(74 citation statements)

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“…Exhaustive electroreduction of Co III TMPyP in an OTTLE cell has confirmed the product to be Co II TMPyP, with an associated reduction potential at pH 7.4 of +0.33 V vs NHE. 16 Ascorbate is found in circulating plasma at a concentration of ~60 μ M, 19 and because it has a reduction potential of −0.06 V, 20 it should easily be able to reduce Co III TMPyP(OH − )(H 2 O) to Co II TMPyP in vivo . We measured the rate of ascorbate reduction of the complex under pseudo-first-order conditions by stopped-flow spectrophotometry, following the disappearance of the 427 nm band of Co III TMPyP(OH − )(H 2 O).…”

Section: Resultsmentioning

confidence: 99%

Effect of Ascorbate on the Cyanide-Scavenging Capability of Cobalt(III) meso-Tetra(4-N-methylpyridyl)porphine Pentaiodide: Deactivation by Reduction?

Benz

Yuan

Cronican

et al. 2016

Chem. Res. Toxicol.

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The Co(III)-containing water-soluble metalloporphyrin cobalt(III) meso-tetra(4-N-methylpyridyl)porphine pentaiodide (CoIIITMPyP) is a potential cyanide-scavenging agent. The rate of reduction of CoIIITMPyP by ascorbate is facile enough that conversion to the Co(II)-containing CoIITMPyP should occur within minutes at prevailing in vivo levels of the reductant. It follows that any cyanide-decorporating capability of the metalloporphyrin should depend more on the cyanide-binding characteristics of CoIITMPyP than those of the administered form, CoIIITMPyP. Addition of cyanide to buffered aqueous solutions of CoIITMPyP (pH 7.4, 25–37 °C) results in quite rapid (k2 = ~103 M−1 s−1) binding/substitution of cyanide anion in the two available axial positions with high affinity (K′β = 1010 to 1011). Electron paramagnetic resonance spectroscopic measurements and cyclic voltammetry indicate that cyanide induces oxidation to the Co(III)-containing dicyano species. The constraints that these observations put on plausible mechanisms for the reaction of CoIITMPyP with cyanide are discussed. Experiments in which CoIIITMPyP and cyanide were added to freshly drawn mouse blood showed the same sequence of reactions (metalloporphyrin reduction → cyanide binding/substitution → reoxidation) to occur. Therefore, in cyanide-scavenging applications with this metalloporphyrin, we should be taking advantage of both the improved rate of ligand substitution at Co(II) compared to that at Co(III) and the increased affinity of Co(III) for anionic ligands compared to that of Co(II). Finally, using an established sublethal mouse model for cyanide intoxication, CoIIITMPyP, administered either 5 min before (prophylaxis) or 1 min after the toxicant, is shown to have very significant antidotal capability. Possible explanations for the results of a previous contradictory study, which failed to find any prophylactic effect of CoIIITMPyP toward cyanide intoxication, are considered.

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Section: Resultsmentioning

confidence: 99%

Effect of Ascorbate on the Cyanide-Scavenging Capability of Cobalt(III) meso-Tetra(4-N-methylpyridyl)porphine Pentaiodide: Deactivation by Reduction?

Benz

Yuan

Cronican

et al. 2016

Chem. Res. Toxicol.

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“…The formed hole remaining in the MPA-CdTe species after electron transfer, on the other hand, is subsequently regenerated by electron transfer from the sacrificial electron donor. It is known that the redox potential of H 2 A ( À 0.14 V at pH 4.5) 59 is sufficiently negative to reduce the holes photogenerated in MPA-CdTe species 25,45 , but it is too positive to directly reduce the [FeFe]-H 2 ase catalyst ( Supplementary Fig. S14).…”

Section: Resultsmentioning

confidence: 99%

Chitosan confinement enhances hydrogen photogeneration from a mimic of the diiron subsite of [FeFe]-hydrogenase

et al. 2013

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Nature has created [FeFe]-hydrogenase enzyme as a hydrogen-forming catalyst with a high turnover rate. However, it does not meet the demands of economically usable catalytic agents because of its limited stability and the cost of its production and purification. Synthetic chemistry has allowed the preparation of remarkably close mimics of [FeFe]-hydrogenase but so far failed to reproduce its catalytic activity. Most models of the active site represent mimics of the inorganic cofactor only, and the enzyme-like reaction that proceeds within restricted environments is less well understood. Here we report that chitosan, a natural polysaccharide, improves the efficiency and durability of a typical mimic of the diiron subsite of [FeFe]-hydrogenase for photocatalytic hydrogen evolution. The turnover number of the self-assembling system increases B4,000-fold compared with the same system in the absence of chitosan. Such significant improvements to the activity and stability of artificial [FeFe]-hydrogenase-like systems have, to our knowledge, not been reported to date.

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“…While the increment of swelling (%) of Gel 1 according to pH is due to the external solution, the amide groups of cross-linked PAAm chains undergo hydrolysis and get converted into carboxylic groups which begin to ionize as long as pH increases. This obviously produces anionically charged polymer chains which because of the mutual repulsion among carboxylate ions (-COO − ) results in an expansion of the network chains leading to an increase in swelling [56]. The relative slight increment of swelling (%) at pH ≤ 1-4 is due to the disappearance of electrostatic repulsion and the generation of hydrophobic interactions due to hydrogen bond formation between -COOH and -CONH 2 groups in Gel 1 .…”

Section: Effects Of Ionic Strength Dose Ph and Temperature On Swelmentioning

confidence: 99%

Synergistic effect of poly(acrylamide)-incorporated poly(L-ascorbic acid) hydrogels in controlled release and wound dressings

Awadallah‐F

2013

Designed Monomers and Polymers

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In this study, hydrogel specimens were synthesized by acrylamide (AAm) implying different quantities of L-ascorbic acid (LAA) vis-à-vis γ-rays radiation technique. The prepared gels were characterized by various techniques. Fix's theory was applied to poly(acrylamide) (P(AAm)/LAA) hydrogels and diffusion coefficients were evaluated. Hardness, water vapor transmission rate, tensile strength, and degree of adhesiveness were preformed on gel systems. The outcome results indicate that the hydrogel specimens are conveniently utilized in wound dressings as the first application. The second application of this gel system is drug release of anti-fungal terbinafine hydrochloride (TER-HCl), which was used in skin wound healings. Adsorption and release of TER-HCl to and fro from P(AAm/LAA) hydrogel specimens were examined. The impact of PLAA quantities into the gelling specimens on the adsorption capacities and the impact of pH on the releasing behavior of TER-HCl were investigated. The results showed the TER-HCl adsorption capacities of hydrogels are found to rise up from 9.5 ± 0.22 to 99 ± 0.18 mg TER-HCl per g dry gel, dependent on the gradient increment in quantity of PLAA in the gel structures. The results of in vitro TER-HCl release in different buffer solutions revealed that the paramount parameters affecting the drug release behavior of gel systems are pH of surrounding media and quantity of PLAA inside. In sum up, the prepared hydrogels have synergistic effect and they may be utilized in wound dressing and TER-HCl drug release of skin wound healings applications as well.

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Oxidation-Reduction Potential of Ascorbic Acid (Vitamin C)

Cited by 105 publications

References 0 publications

Effect of Ascorbate on the Cyanide-Scavenging Capability of Cobalt(III) meso-Tetra(4-N-methylpyridyl)porphine Pentaiodide: Deactivation by Reduction?

Effect of Ascorbate on the Cyanide-Scavenging Capability of Cobalt(III) meso-Tetra(4-N-methylpyridyl)porphine Pentaiodide: Deactivation by Reduction?

Chitosan confinement enhances hydrogen photogeneration from a mimic of the diiron subsite of [FeFe]-hydrogenase

Synergistic effect of poly(acrylamide)-incorporated poly(L-ascorbic acid) hydrogels in controlled release and wound dressings

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