Metal catecholates

Several factors were found to affect dioxygen uptake by the metal catecholates. Of particular importance were (i) the coordination number of the metal, (ii) the relative basicity of both the catecholate ligand and the metal, (iii) the temperature, and (iv) the pressure of dioxygen. Under some circumstances, both the product containing reacted dioxygen and the unreacted starting catecholate complex existed in equilib-... 

Geometry of Metal Catechol Complexes. The coordination geometries of [Fe(cat)3]3" and [Cr(cat)3]3" have been determined by single crystal studies of the salts K3[M(cat)3] 1.5 H20 (M = Cr, Fe) in order to explore the crystal field effect of chromic ion on the coordination geometry and, indirectly, to determine the coordination geometry of enterobactin itself (26). 

While the absolute configuration of transition metal catecholates has not been determined by x-ray diffraction, the assignments are based on several lines of reasoning. In particular, for both the rhodium(III) and chromium(III) complexes, that isomer precipitated by A-tris(ethylenediamine)cobalt(III) is assigned the A configuration. 

Interception of a metal catecholate-dioxygen adduct,/. Am. Chem. Soc. 113 3181 (1991). 

G. Speier and Z. Tyekldr, The reaction of alkali metal catecholates with dioxygen in aprotic solvent,... 

BET = Brunauer-Emmett-Teller CMON = covalent metal-organic networks CTF = covalent triazine-based framework DCQNI = A,A -dicyanoquinodiimine DEF = A,A-diethylformamide DMA = A,A-dimethyl-acetamide FP-TRMC = flash-photolysis time-resolved microwave conductivity HHT = 2,3,6,7,10,11-hexa-hydroxytriphenylene M-CAT = metal-catecholate PSM = postsynthesis modifications PXRD = powder X-ray diffraction TCNQ = tetracyanoquinodimethane TOF = time-of-flight TTF = tetrathiafulvalene. 

Martell and Smith 1977), however, at the model pH of 6, is the dominant cation competitor, and almost 100% of the catechol ligand is in the form of the doubly protonated species. Because of the low activity of ionized catechol, only small amounts of metal-catechol complexes are formed. 

Various chemical species influence the rates of hydrolysis of penicillins, e.g. metal ions (Cu >Zn >Ni Co ) (80JCS(P2)1725), carbohydrates (78MI51101), certain amine-containing catechol derivatives (69JPS1102) and /3-cyclodextrin (71JA767). Some of these even show some of the characteristics of enzyme-catalyzed hydrolyses. 

The cyclohexylidene ketal, prepared from a catechol and cyclohexanone (AI2O3/ TsOH, CH2CI2, reflux, 36 h), is stable to metalation conditions (RX/BuLi) that cleave aiyl methyl ethers. The ketal is cleaved by acidic hydrolysis (coned. HCl/ EtOH, reflux, 1.5 h, 20°, 12 h) it is stable to milder acidic hydrolysis that cleaves tetrahydropyranyl ethers (1 AHCl/EtOH, reflux, 5 h, 91% yield). ... 

Transition metal complexes of o-benzoquinone, o-semiquinone and catecholate ligands. C. G. Pier-pontand R. M. Buchanan, Coord. Chem. Rev., 1981, 38, 45-87 (72). 

As strong metal ion chelators due to their catechol structure, tea flavonoids are able to bind and thus decrease the level of free cellular ferric and ferrous ions, which are required for the generation of reactive oxygen radicals via the Fenton reaction (Yang and Wang, 1993). 

Heavy-metal cations and oxyanions are generally toxic to bacteria although resistance may be induced by various mechanisms after exposure. Attention is drawn to an unusual example in which AF+ may be significant, since the catechol 1,2-dioxygenase and 3,4-dihydroxybenzoate (protocat-echuate) 3,4-dioxygenase that are involved in the metabolism of benzoate by strains of Rhizobium trifolii are highly sensitive to inhibition by AP (Chen et al. 1985). 

A common way to benefit from the ability to combine different molecular orbital methods in ONIOM is to combine a DFT or ab-initio description of the reactive region with a semi-empirical treatment of the immediate protein environment, including up to 1000 atoms. Due to the requirement for reliable semi-empirical parameters, as discussed in Section 2.2.1, this approach has primarily been used for non-metal or Zn-enzymes. Examples include human stromelysin-1 [83], carboxypeptidase [84], ribonucleotide reductase (substrate reaction) [85], farnesyl transferase [86] and cytosine deaminase [87], Combining two ab-initio methods of different accuracy is not common in biocatalysis applications, and one example from is an ONIOM (MP2 HF) study of catechol O-methyltransferase [88],... 

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