Interactions of iron(II) and iron(III) with gallic acid and its homologues: a potentiometric and spectrophotometric study

Powell, H. K. J.; Taylor, M.

doi:10.1071/ch9820739

Cited by 156 publications

(125 citation statements)

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“…Fe 3+ is reduced to Fe 2+ by phenols during oxidation, but oxidised back to Fe 3+ in the presence of O 2 , until all the phenolic substrates have been consumed (Powell and Taylor, 1982). The addition of ferrous sulphate increases the oxidation rate of (+)-catechin, as found by Oszmianski et al (1996).…”

Section: Oxygen In Must and Winementioning

confidence: 85%

Oxygen in Must and Wine: A review

Toit

Marais

Pretorius

et al. 2017

SAJEV

107

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The atmosphere consists of approximately 21% oxygen (O2). It plays a crucial role in many metabolic and chemical reactions on earth, thus it is of little surprise that it plays a very important role in the winemaking process. Wine can never be completely protected from it. The general use of sulphur dioxide as an anti-oxidant dates back to the early 18th century and the protection of wine from unwanted oxidative spoilage has been recognised . Oxygen can influence the composition and quality of wine drastically, either positively or negatively, and this will be the focus of this review. This review will also focus on the basic steps involved in oxidation, substrates for oxidation in wine and the evolution of wine constituents during the wine production process when in contact with different concentrations of O2. Basic reactions of oxygen in wineOxidation is the process where electron transfer takes place between reductive and oxidative partners. In wine, O 2 is predominantly responsible for this, with it being reduced to certain intermediates and eventually to hydrogen peroxide and then water. Molecular O2 exists as a diradical and is thus in a triplet ground state. This limits the reactivity of O2 and it cannot form bonds by accepting electron pairs. However, the addition of a single electron, originating from reduced transitional metal ions, can overcome this limitation. This leads to an unpaired electron in the resulting negatively-charged superoxide radical, with a second electron transfer resulting in a peroxide anion (Miller et al., 1990;Danilewicz, 2003). This phenomenon results in O2 being involved in various reactions in wine. Substrates for oxidation in winePhenolic molecules originating from grapes can basically be divided into the non-flavonoids and the flavonoids. The nonflavonoids, which are hydroxybenzoic and hydroxycinnamic derivatives, originate from the grape juice, and are normally the principal phenolic molecules in white wines at concentrations ranging from 50-250 mg/L, depending on the cultivar, winemaking techniques, etc. Examples of non-flavonoids are the tartaric esters of caffeic acid, p-coutaric acid and furanic acids. These molecules have been shown to be the main phenolic molecules in white wine that did not receive prolonged periods of skin contact, because they occur at higher concentrations in the grape juice (Margalit, 1997;Monagas et al., 2005).The second main group of grape-derived phenolics is the flavonoids. This group of molecules basically consists of two phenolic rings attached to a pyran ring. The flavanoids have a more complex structure than the non-flavonoids. In a young wine they are normally in a more unpolymerised state, but as wine matures they undergo different polymerisation reactions in which O 2 plays an important role. The most important flavonoids in wine are the anthocyanins, flavanols and flavonols. Anthocyanins occur mainly in the skins of red grape cultivars and are responsible for the colour of red wine. In young red wines their concentrations can range fr...

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Section: Oxygen In Must and Winementioning

confidence: 85%

Oxygen in Must and Wine: A review

Toit

Marais

Pretorius

et al. 2017

SAJEV

107

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“…Observed peptide oxidation by oxygen and iron from an [Fe(DOPA) 3 ] complex, as opposed to the bis or mono analogues, is consistent with a greater degree of Fe III -and less Fe II -ion character in the tris coordination environment. [16] Radical generation in the aerobic [Fe(AdopaTP) 3 ] complex coincided with an Fe III -ion signal (g = 4.209, 1537 G) of decreased intensity relative to the anaerobic sample (Figure 2 e). These data suggest the occurrence of a redox reaction in which ligand oxidation is accompanied by a Fe III !…”

Section: Marine Chemistrymentioning

confidence: 89%

Metal‐Mediated Cross‐Linking in the Generation of a Marine‐Mussel Adhesive

et al. 2004

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“…As the catechol moiety of esculetin is unhindered, two adjacent oxygen atoms become competent in the formation of coordinative bondings with Fe(III), thereby fulfilling the requirements for successful chelation. In general, Fe(III) catechol complex formation occurs over a wide pH range up to 9 (Powell and Taylor, 1982) and is thus capable of Fe(III) chelation in alkaline soils.…”

Section: Esculetin As a Prototype For Fe(iii)-mobilizing Catechols Sementioning

confidence: 99%