Catecholate anion

Iron transporters known as siderophores occur in various bacteria. They coordinate iron in a complex that involves three catechol residues. A natural host molecule called entero-bactin is shown along with a cryptand-like molecule (9) that is one of several that were devised to mimic this complexation behavior (reviewed in Roosen-berg, 2000 Raymond, 2003). The catechols deprotonate to the catecholate anions, which provide six oxygen donors for ferric ion The host thus completely envelops the cation permitting transport as the complex. 

The redox potentials for several quionones (Q 3,5-di-tert-butyl-o-quinone, o-benzoquinone, p-benzoquinone, and tetrafluoro-o-benzoquinone), their semi-quinone anion radicals (SQ- -) and their fully reduced forms [catechols (H2Cat) and catechol anions (HCat-)] in four aprotic solvents [acetronitrile (AN), di-methylformamide (DMF), dimethylacetaminde (DMA), and dimethyl sulfoxide (Me O)] are summarized in Table 12.2.12... 

We decided that it would be more effective to use vicinal dihydroxy-organic reagents. The ammonium salt of tricatechol ether of monosilicic acid (formed from biogenic silica from diatomite) was obtained. This salt contains the cation of ammonium, catechol anion and a hexacoordinated atom of silicon as 2 3 1. This salt is a dimer and is formed from the reaction (Eq. 1) ... 

Fig. 3. Enzyme converts planar catecholate anion to tetrahedral form (//). Oxygen complexes (III) to finally give peroxide (IV)...

Silicon is also more electropositive (Pauling eleetronegativity index 1.8) than carbon (2.4), and the silicon-carbon bond is polarized Si -C . Tetravalent silicon, a weak Lewis acid, is thus essentially attacked by anions (F, etc.) to form hyper-valent silicon derivatives. This phenomenon is used for the sterie control of reactions that proceed in the coordination sphere of silicon. For instance, fluorides and catecholate anions, among others, catalyze the stereoselective reaction between an allylsilane and an aldehyde leading to the corresponding homoallylic alcohols via an anionic intermediate of pentavalent silicon ... 

Formation of superoxide ion attached to iron is probable when iron is in the ferrous state or has a ferrous character. Thus, reactivity of superoxide ion has attracted attention in the mechanistic studies of the enzymatic reactions. Reaction of superoxide ion was studied in some details by Moro-oka and Foote in 1976 [13]. Both types of intra- and extra-diol oxygenation products are formed from 1 as shown in Scheme 3. Products 5 and 13-15 are also formed. Since the same products are formed also from the quinone 6, the common intermediate is assumed for both the reactions of catechol and quinone. The product formation is explained by the O2 attack to the activated catecholate anion radical forming a peroxide ion. The initial step forming a radical species is similar to that in... 

Conversion of Aromatic Rings to Nonaromatic Cyclic Structures. On treatment with oxidants such as chlorine, hypochlorite anion, chlorine dioxide, oxygen, hydrogen peroxide, and peroxy acids, the aromatic nuclei in lignin typically ate converted to o- and -quinoid stmctures and oxinane derivatives of quinols. Because of thein relatively high reactivity, these stmctures often appear as transient intermediates rather than as end products. Further reactions of the intermediates lead to the formation of catechol, hydroquinone, and mono- and dicarboxyhc acids. 

B-C bonds, 3, 97 B-N bonds, 3, 97 B-O bonds, 3,94 B-P bonds, 3, 97 B-Si bonds, 3, 97 oxo acid anion complexes, 3, 96 Borates, alkoxo-, 3, 94 Borates, amidotrihydro-, 3,92 Borates, aryloxo-, 3, 94 Borates, carboxylato-, 3,96 Borates, catechol, 3,95 Borates, chlorosulfato-, 3,97 Borates, dicarboxylato-, 3,96 Borates, dipyrazol-l-yl-, 3, 92 Borates, halogeno-, 3,92 Borates, halogenohydro-, 3,90 Borates, hydro-, 3,90 Borates, hydrohydroxo-, 3,90 Borates, hydropyrazol-l-yl-, 3, 92 Borates, hydroxo-, 3,94 Borates, hydroxycarboxylato-, 3,96 Borates, inositol, 3, 95 Borates, monoalkyl-, 3, 92 Borates, monophosphido-, 3, 92 Borates, peroxohydroxo-, 3, 94 Borates, polyol, 3, 95 Borates, pyrrol-l-yl-, 3, 92 Borates, sulfato-, 3, 97 Borates, tetrabromo-, 3, 92 Borates, tetrachloro-, 3, 92 Borates, tetrafluoro-, 3, 92 minerals, 6, 847 Borates, tetrahalogeno-mixed, 3, 93 nB NMR, 3, 92 Borates, tetraiodo-, 3, 92 Borates, tetranitrato-, 3, 96 Borates, tetraperchlorato-, 3, 97 Borates, tripyrazol-l-yl-, 3, 92 Borax, 3,101 Borazines... 

In an early method Kodama and Tsubota [567] determined tin in seawater by anion exchange chromatography and spectrophotometry with catechol violet. 

The CL enhancement of the lucigenin reaction with catecholamines in the presence of HTAH micelles was used for determination of dopamine, norepinephrine, and epinephrine [42], However, the presence of an anionic surfactant, SDS, inhibits the CL of the system. The aforementioned CL enhancement in the presence of HTAH can be explained in the following way the deprotonated forms of the catecholamines are expected to be the principal species present in aqueous alkaline solution due to the dissociation of the catechol hydroxyl groups, and to react with lucigenin to produce CL. The anionic form of the catecholamines and the hydroxide ion interact electrostatically with and bond to the cationic micelle, to which the lucigenin also bonds. Therefore, the effective concentration of the... 

Aminophthalate anion Atmospheric pressure active nitrogen Analyte pulse perturbation-chemiluminescence spectroscopy Arthromyces rasomus peroxidase Ascorbic acid Adenosine triphosphate Avalanche photodiode 5-Bromo-4-chloro-3-indolyl 2,6-Di-t< r/-bu(yl-4-mclhyl phenol Bioluminescence Polyoxyethylene (23) dodecanol Bovine serum albumin Critical micelle concentration Calf alkaline phosphatase Continuous-addition-of-reagent Continuous-addition-of-reagent chemiluminescence spectroscopy Catecholamines Catechol... 

Fe(III) displacement of Al(III), Ga(III), or In(III) from their respective complexes with these tripodal ligands, have been determined. The M(III)-by-Fe(III) displacement processes are controlled by the ease of dissociation of Al(III), Ga(III), or In(III) Fe(III) may in turn be displaced from these complexes by edta (removal from the two non-equivalent sites gives rise to an appropriate kinetic pattern) (343). Kinetics and mechanism of a catalytic chloride ion effect on the dissociation of model siderophore-hydroxamate iron(III) complexes chloride and, to lesser extents, bromide and nitrate, catalyze ligand dissociation through transient coordination of the added anion to the iron (344). A catechol derivative of desferrioxamine has been found to remove iron from transferrin about 100 times faster than desferrioxamine itself it forms a significantly more stable product with Fe3+ (345). 

Rates of ligand exchange depend quite strongly on the coordina-tive environment of the metal center. The water exchange rate of Fe(H2O)5(OH)is almost three orders of magnitude higher than that of Fe(H20)g+, and follows a dissociative, rather than an associative exchange mechanism (20). Fe(1120)5(OH)has also been shown to form inner-sphere complexes with phenols (27), catechols (28), and a-hydroxycarboxylic acids (29) much more quickly than Fe(H20) +. The mechanism for complex formation with phenolate anion (A-) is shown below (27) ... 

The major absorption in the 31P n.m.r. spectrum of an equimolar solution of penta-phenoxyphosphorane and sodium phenoxide in DMF-acetonitrile is due to the hexaphenoxyphosphate anion, as predicted from the low equilibrium constant estimated for equation (2) (page 35).27 Catechol and phosphorus oxychloride in refluxing benzene gave the spirophosphorane(108), which with triethylamine gave the salt (109).45 On the basis of its 31P chemical shift in DMF solution, (108) was formulated86 as the free six-co-ordinate acid (110), but it seems probable that DMF is... 

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