Catechol crystal structure

Klabunde T, Eicken C, Sacchettini JC and Krebs B. 1998. Crystal structure of a plant catechol oxidase containing a dicopper center. Nat Struct Biol 5 1084-1090. 

The more stable boron chelates can be isolated even from aqueous solution, whereas those of lower stabilities are only accessible from non-aqueous media. Catechol- and inositol-borates (3, 5 and 6) possesses a well-defined monomeric structure,75 whereas those obtained from monosaccharides and alditols are polymeric.121 A crystal structure determination122 has been carried out for sodium scyUo-inositol diborate (6). 

Os(bpy)2LL]2+/1+/0 (L-L are quinone, semiquinone, or catecholato ligands derived from catechol, 3,5-di-ter<-butylcatechol, or tetrachlo-rocatechol) have been characterized by UV/Vis/NIR and EPR spectroscopies. These spectroscopic properties and the crystal structure of [0s(bpy)2(dbcat)]C104 confirm an Os( III (-catecholate ground state for the +1 ion. This contrasts with the ground state of the +1 ions of Ru analogs, which are best described as Ru(II)-semiquinone complexes... 

Evans and coworkers62 described the synthesis and structural study of a series of pentacoordinate bis(catecholate) complexes of silicon(IV). The crystal structure of the anion of [Et3NH][SiMe(3,5-dncat)2] [H2(3, 5-dncat) = 3, 5-dinitrocatechol] is reported (Figure 7). 

A series of catecholate derivatives 189 and 190 were prepared from the parent dichloro complexes by reaction with o-catechol or tetrachloro-o-catechol and Me3N in hot methanol.83 The corresponding reaction with an unsymmetrical catechol, 3,5-di-ferf-butylcatechol produced a mixture of isomers 191a and 191b. The related dioxolene complexes 192 and the amidophenolate complexes 193 were also prepared by the same method. An X-ray crystal structure on the latter complex shows that the phenolate oxygen is trans to the aryl carbon atom. 

Like the PCD ES complex, the BphC ES complex also has an unsymmetri-cally chelated catecholate [155], A similar bond length asymmetry was also deduced from EXAFS studies on the 2,3-CTD-catechol complex, which showed four O/N scatterers at 2.10 A and one scatterer at 1.93 A [158]. This short bond is comparable in length to one Fe—OcatechoMe bond in the crystal structure of a synthetic Fe(II)-catecholate complex, [Fe(6-Me3-tmpa) (H-dbc)]+ [164], The significant asymmetry in catechol binding in the synthetic complex stems from the presence of a didentate but monoanionic catecholate. The much weaker affinity of Fe(II) for catecholate explains why the monoanionic ionization state is favored in the Fe(II) complex, a situation that is also likely to apply in the ES complexes. 

In 1998, Krebs and co-authors reported the crystal structures of the catechol oxidase isolated from sweet potatoes (Ipomoea batatas) in three catalytic states the native met (CunCun) state (Figure 5.2a), the reduced deoxy (Cu Cu1) form, and the complex with the inhibitor phenylthiourea (Figure 5.2b) [19]. Typically for the type 3 active site, each copper ion is coordinated by three histidine residues from the protein backbone. In the native met state, the two copper ions are 2.9 A apart and, in addition to six histidine residues, a bridging solvent molecule, most likely a hydroxide anion, has been refined in close proximity to the two metal centers... 

Figure 5.2 (a) Coordination sphere of the dinudear copper(ll) center in the met state, (b) Crystal structure of the inhibitor complex of catechol oxidase with phenylthiourea. Redrawn after Krebs and co-workers [60]. 

Figure 5.7 X-ray crystal structure projections of copper-catecholate adducts obtained by Comba and co-workers [41] (a, c and d), and x-ray crystal structure of one of the dicopper(ll)-catecholate adducts crystallized by Meyer and coworkers (b) [42],...

Impressive coordination ability of divalent phenolic ligands (Fig. 22, Table 11) was demonstrated in homoleptic catecholato derivatives [152]. Surprisingly, Ce(IV) was not reduced by the catechol dianion. In addition, the low solubility of the complex Na4[Ce(C6H402)4] 21H20 even permits its direct synthesis and crystallization from aqueous solutions (Eq. 14a, Table 11) [153]. The crystal structure consists of discrete 8-coordinate [Ce(cat)4)]4 dodecahedra. Each sodium is coordinated to two nonequivalent oxygens from two catecholato... 

VIDGREN, J., SVENSSON, L.A., LILJAS, A., Crystal structure of catechol O-methyltransferase, Nature, 1994,368, 354-357. 

The class of mononuclear dioxygenases [30] can e.g. perform hydroperoxidation of lipids, the cleavage of catechol and dihydroxylation of aromatics. A prominent example is naphthalene dioxygenase, which was the first identified by its crystal structure. It contains iron and a Rieske (2Fe-2S) cluster and is commonly referred to as a Rieske-type dioxygenase [33]. The iron in this case is flanked by two histidines and one aspartic acid residue. Among the mononuclear iron enzymes, the 2-His-l-carboxylate is a common motif, which flanks one-side of the iron in a triangle and plays an important role in dioxygen activation [34] (Fig. 4.17). 

Reaction of 0s04 with catechol or substituted catechols Rcat in chloroform yields the deep blue diamagnetic Os(Rcat)3 species (Rcat = catechol, 4-rerf-octyl-, 4-terr-butyl-, 3,5-di-ferf-butyl-catech-ol).486 X-Ray crystal structures of Os(cat)3 and of the tris complex with 3,5-di-terf-butylcatechol show these to have D3 symmetry the Os—O distances fall within the range 1.947 to 1.985 A (mean 1.960 A) and the C—O distances are between 1.30 and 1.35 A the catecholato (02C6H4 or 02C6H2) rings are essentially planar.666 For Os(cat)3, IR, Raman, HNMR and electrochemical data were obtained the latter showed two one-electron reversible reductions, presumably to [Os(cat)3] and [Os(cat)3]2-. The diamagnetism of these formally osmium(VI) species probably arises from the distortion from octahedral to Z>3 symmetry.486... 

The structures of several [M(catechol)3] complexes are known, including [Fe(cat)3], and all have been found to be pseudo-octahedral. There exists oifly one crystal structure of an iron(ni) tris(catechoylamide), namely of a synthetic compound trivially named bicappedTRENCAM (Figure 7). The... 

The involvement of metal ions in the color of anthocyanins and flavonoids was discovered almost a century ago, whereby the different colors of flowers originated from the same molecules under different conditions . The crystal structure of the pigment complex affords better understanding of the color and the role of metal ions , where Fe(III) and Mg(II) bind anthocyanins via the catechol moiety and Ca(II) binds flavone glycosides through a vicinal diol on the glycone. 

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