Chelate interaction

Enolates of phenylglycinol amides also exhibit good diastereoselectivity.97 A chelating interaction with the deprotonated hydroxy group is probably involved here as well. 

Complexes of bismuth chloride with 2 equiv of the AT,AT-substituted dithioxamide ligands of the general formulas [BiCl3 RNHC(S)C(S) NHR 2] (R = Me, Et, Pr, nBu, CH2Ph) likely involve five-membered chelate interactions (123) as demonstrated by the structurally characterized example [BiCl3 EtNHC(S)C(S)NHEt 2] Me2CO, which involves a seven-coordinate pentagonal bipyramidal environment for bismuth (124), with chlorine atoms in axial positions [Bi-Cl 2.635(10) and 2.717(1) A] and one equatorial [Bi-Cl 2.651(12) A] with four sulfur centers [Bi-S 2.818(13)-3.042(12) A],... 

A variety of derivatives of bis-[Bi(tr)2X, X = Cl or N03], tris-(Bitr3), and tetra-([Bi(tr)4X][Na]) tropolonate complexes of bismuth (178, 179) have been prepared and spectroscopically characterized (176, 177, 180). Solid-state structures for examples of bis-(tropolonate) derivatives confirm the chelate interaction (171) and in the case of the nitrate derivative, reveal intermolecular alkoxide-bismuth [Bi-0 2.688 and 2.666 A] dimer contacts 52, which are slightly longer than the chelate bonds [Bi-0 2.130-2.323 A],... 

Jackson, G. A. and Morgan, J. J. (1978). Trace metal-chelator interactions and phytoplankton growth in seawater media theoretical analysis and comparison with reported observations, Limnol. Oceanogr., 23, 268-282. 

A complete systematic description of protein-metal complexation has yet to be presented, but it is apparent that many mechanisms are involved. Some proteins may participate in classical chelation interactions via polycarboxy clusters on their surfaces.2 Others interact with metals via coordination with polyhis-tidyl or other aromatic domains.13 5 Still others may interact with metals via sulfhydryl residues.13 The literature on immobilized metal affinity reveals examples of unexplained retention that may involve yet other mechanisms.1... 

To enhance the removal of substances with high sorption properties, for example diclofenac (log = 2.7 and log A ow = 4.5. 8), ferric and aluminium salts may be added, increasing their removal rate to as much as 50-70% [66]. This strategy can also improve the removal of acidic compounds, for example naproxen, by ioiuc or chelating interactions [55]. 

Carboxypeptidase A was the first zinc enzyme to yield a three-dimensional structure to the X-ray crystallographic method, and the structure of an enzyme-pseudosubstrate complex provided a model for a precatalytic zinc-carbonyl interaction (Lipscomb etai, 1968). Comparative studies have been performed between carboxypeptidase A and thermolysin based on the results of X-ray crystallographic experiments (Argosetai, 1978 Kesterand Matthews, 1977 Monzingoand Matthews, 1984 Matthews, 1988 Christianson and Lipscomb, 1988b). Models of peptide-metal interaction have recently been utilized in studies of metal ion participation in hydrolysis (see e.g., Schepartz and Breslow, 1987). In these examples a dipole-ion interaction is achieved by virtue of a chelate interaction involving the labile carbonyl and some other Lewis base (e.g.. 

Figure 8.3 Procedure for MPC assembling at an Au electrode surface, similar to layer-by-layer deposition, by the chelating interactions between divalent (transition) metal ions and pyridine moieties.14 (Reprinted with permission from S. Chen et al., J. Phys. Chem. B 2002,106, 1903-1908. Copyright 2002 American Chemical Society.)...

Here, the specific and strong chelating interaction between 6 x Histidine and the tetradentate nitrilotriacetic acid (NTA) mediated by Ni2+ [43] was used for the immobilization of a reconstituted LHCII mutant, whose c-terminus was extended by 6 x Histidine residues via genetic engineering (cf. Fig. 13(A)). NTA terminated thiols and OEG (spacer) thiols were used to built up a mixed SAM (X = 0.4) on a substrate coated by 23 nm silver and 5 nm Au (the gold layer was used to protect the silver film from being oxidized). 

Fig. 13. (A) Schematic representation of the interaction between neighboring residues of the His-tag (6 consecutive Histidine residues) and an NTA-complexed Ni2+ ion. (B) The performance of LHCII immobilization via chelating interaction. SPR kinetic curve of LHCII immobilization and regeneration cycles, monitored with an Nd YAG DPSS laser (X = 473 nm). (C) Surface plasmon field-enhanced fluorescence emission spectrum of surface attached LHCII compared with the fluorescence emission from free LHCII in solution, excited by an Nd YAG DPSS laser (X — 473 nm).

Li-Chan, E., Kwan, L., and Nakai, S. (1990). Isolation of immunoglobulins by competitive displacement of cheese whey proteins during metal chelate interaction chromatography. J. Diary Sci. 73, 2075-2086. 

Plunkett and Arnold [3] reported imprinted supports based on metal-chelate interactions made in the pores of 10 pm Lichrosphere beads. These were highly stable, even after prolonged use for several hundred hours, and achieved reasonable separations of related Z w-imidazole model compounds. Unfortunately no direct comparison with the performance of bulk-imprinted material was presented. A photograph of part of a silica bead containing imprinted polymer is shown in Fig. 12.1. 

Arnold and co-workers have developed an approach that allows both the imprinting and the subsequent chiral separation of free amino acids to be carried out in aqueous solutions [39]. The recognition was based on metal coordination-chelation interactions using A-(4-vinylbenzyl)iminodiacetic acid as the functional monomer. (For a further discussion of this system see Chapters 6 and 9.) The method worked best for aromatic amino acids (Fig. 17.11). 

In general, bifunctional carbamoylmethylphosphonates (CMP) and carbamoylmethylphosphine oxides (CMPO) readily form complexes with actinide ions in aqueous and nonaqueous solutions. Complexes isolated in the solid state contain ligands chelated to the central metal ion, and the bidentate chelate interaction has been confirmed by single crystal X-ray structure determinations... 

Ytterbium triisopropoxide (10-20 mol%) catalyzes the ring-opening of epoxides with trimethylsilyl azide at ambient temperature to yield vicinal azide alcohols (eq. (25)) [191]. Complexation/chelation interactivity of functionalized substrates affects the regioselectivity in the product. 

There is an increase in the importance of electrophilic catalysis by zinc cation relative to acetic acid for deprotonation of the a-carbonyl carbons of hydroxyace-tone, a substrate which provides a second stabilizing chelate interaction between the hydroxy group at the substrate and the metal dication that is expressed at transition state for proton transfer [19]. For example, the third-order rate constants kx for the Zn +-assisted acetate-ion-promoted deprotonation of the a-CHs and a-CH20H groups of hydroxyacetone are 32-fold and 770-fold larger, respectively, than the corresponding second-order rate constants kAco for proton transfer to acetate anion assisted by solvent water that is present at 55 M (Scheme 1.12). This shows that Zn + stabilizes the transition state for proton transfer from the a-CHs... 

Prediction and analysis of diastereoselectivity is based on steric, stereoelectronic, and chelating interactions in the TS. ° For example, the facial selectivity of the reaction above is governed by a chloride ligand on titanium, which shields one face of the dienophile. 

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