Diphenol e

When a noncyclizable diphenol (e.g., 4-methylcatechol) is used, both the accumulation of the quinone product and the decrease in the oxygen concentration are linear with time, and there is no lag period. 

Additional hypotheses for their mechanism of action have more recently been proposed. It is well known that proanthocyanidins are able to complex metals through their ortho-diphenol groups. This property is often viewed as imparting negative traits (e.g., reduction of the bioavailability of essential mineral micronutrients, especially iron and zinc) [87]. Since iron depletion causes severe limitation to microbial growth, their ability to bind iron has been suggested as one of the possible mechanisms explaining the antimicrobial activity of proanthocyanidins [88] (Table 1). 

These heterobimetallic M1-M2-binol complexes constitute a new class of widely applicable chiral catalysts as shown in Scheme 3.16. The new catalysts consist of a central metal ion (e.g., La3+, Al3+, Sm3+, Ga3+), three alkali metal ions (e.g., Li+, Na+, K+), and three chiral diphenol... 

The thiolate species (182) and (183) do not require photo excitation in order to initiate polymerization (182) consumes 200 equivalents MMA in 18 h at 35 °C (Mn = 22,000, Mn(calc) = 20,000, Mw/ Mn= 1.12) 446 The propagating species is again believed to be an enolate.447 Propagation is accelerated upon addition of (185), with 100 equivalents of MMA requiring just 90 seconds for full conversion. The steric bulk of the Lewis acid prevents scrambling of the propagating enolate between the two aluminum centers.448 Hence, for aluminum diphenolates, ortho substitution is essential, whilst smaller Lewis acids such as Me3Al may only be used successfully at low temperatures, e.g., —40 °C. 

Surface complex formation with ligands that form bidentate, mononuclear surface complexes, e.g., oxalate, salicylate, citrate, diphenols, etc. 

Polysulfone supports are well suited for the fifth method listed in Table 1. In this approach. Method E, the support film is saturated with a water solution containing diamines, polyamines or diphenols, plus other additives such as acid acceptors and surfactants. The saturated film is contacted with a nonmlscible solvent containing di- or triacyl chloride reactants. A condensation polymer forms at the interface. The film is dried to bond the thin Interfacial film to the support surface. In some... 

Mason (30) and Pierpoint (31) have described the involvement of o-diphenols in plants and how they contribute to abnormal plant pigmentation. o-Diphenols are oxidized to o-quinones by enzymes of the phenolase complex (o-diphenol O2 oxidoreductase, E.C. 1.10.3.1) and by peroxidase (E.C. 1.11.1.7). o-Quinones react with amino acids, proteins, amines and thiol groups of proteins to polymerize and from reddish-brown pigments. Concentrations of caffeic acid are doubled in both bean (8) and peanut... 

So-called blue multinuclear copper oxidase enzymes, such as laccase and ascorbate oxidase, catalyze the stepwise oxidation of organic substrates (most likely in successive one-electron steps) in tandem with the four-electron reduction of O2 to water, i.e. no oxygen atom(s) from O2 are incorporated into the substrate (Eq. 4) [15]. Catechol oxidase, containing a type 3 center, mediates a two-electron substrate oxidation (o-diphenols to o-chinones), and turnover of two substrate molecules is coupled to the reduction of O2 to water [34,35]. The non-blue copper oxidases, e.g. galactose oxidase and amine oxidases [27,56-59], perform similar oxidation catalysis at a mononuclear type 2 Cu site, but H2O2 is produced from O2 instead of H2O, in a two-electron reduction. 

Catechol and Guaiacol Derivatives. The only diphenol in Table I behaved as two separate monophenols. Catechols also generally react as diphenols, i.e., they produce twice the 765 nm absorbing color with F-C reagent as does a typical monophenol. Table II shows molar extinc-... 

Nickerson, T. A., Moore, E. E. and Zimmer, A. A. 1964. Spectrophotometric determination of calcium in milk using 2,2 -(ethanediylidene-dinitrilo) diphenol (glyoxal bis (2-hydroxyanil). Anal. Chem. 36, 1676-1677. 

Nalidixic acid (l-ethyl-7-methyl-l.8-naphtlmdine-4-one-3-carboxylic add), many tradenames (e.g.. Nalidicron ), is an antibacterial. Bisacodyl [4,4 -(2-pyridylmethylene)diphenol diacetate], tradename Dulcolax, is a laxative. 

This class includes enzymes that use diphenols or related compounds as electron donors and oxygen as the acceptor, thereby forming the oxidized donor and water. Members include catechol oxidase (E.C. 1.10.3.1), laccase (E.C. 1.10.3.2), and o-aminophenol oxidase (E.C. 1.10.3.4). Laccase is also known as / -diphenoloxidase. whereas catechol oxidase is also known as diphenoloxidase, phenoloxidase, polyphenoloxidase, o-diphenolase, phenolase and tyrosinase. Many of these names are also used in reference to a different enzyme, monophenol monooxygenase (E.C. 1.14.18.1). This enzyme will be discussed further in Section 1.8.2.2. 

Busquets S, Ametller E, Fuster G, Olivan M, Raab Y, Argiles JM, Lopez-Soriano FJ. 2007. Resveratrol, a natural diphenol, reduces metastatic growth in an experimental cancer model. Cancer Lett 245 144-148. 

In the first case, the reaction produces a methylene-diphenol (MDPh), i.e molecules in which two phenolic rings are linked by a methylene group. In the second case, the reaction produces an aromatic ether, i.e., a molecule in which two aromatic rings are linked by a dimethyl-ether group. However, these compounds are relatively unstable and rapidly decay (producing a formaldehyde molecule) to the corresponding methylene-diphenols (MDPh). Thus, the first reaction step is the rate limiting step, whereas the second one determines the final product and the total stoichiometry of the reaction. 

Figure 5-1 Examples of Metal Chelates. Only the relevant portions of the molecules are shown. The chelate formers are (A) thiocarbamate, (B) phosphate, (C) thioacid, (D) diamine, (E) o-phenantrolin, (F) a-aminoacid, (G) o-diphenol, (H) oxalic acid. Source From K. Pfeilsticker, Food Components as Metal Chelates, Food Sci. Technol., Vol. 3, pp. 45-51, 1970.

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