Chelate type

Keto ester in H bonding enol form ca 1650 Keto from normal chelate-type H bond... 

Ketoaldehyde in enol form 1670-1645 Lowering caused by chelate-type H bonding... 

The general coordination modes of amidinate and guanidinate (R = NR 2) ligands are shown in Scheme 4. Both ligands display a rich coordination chemistry in which both chelating and bridging coordination modes can be achieved. By far the most common coordination mode is the chelating type A. 

Partially hydrolyzed polyacrylamides, carboxymethylcellulose, polysaccharides, and acrylamido methylpropane sulfonate have been screened to investigate the performance of aluminum citrate as a chelate-type crosslinker. An overview of the performance of 18 different polymers has been presented in the literature [1646]. The performance of the colloidal dispersion gels depends strongly on the type and the quality of the polymer used. The gels were mixed with the polymers at two polymer concentrations, at three polymer-to-aluminum ratios, and in different concentrations of potassium chloride. The gels were quantitatively tested 1,7, 14, and 28 days after preparation. 

Optical activity in metal complexes may also arise either if one of the ligands bound to the metal in the first co-ordination sphere is itself optically active or if the complex as a whole lacks a centre of inversion and a plane of symmetry. Thus all octahedral cts-complexes of the tris-or bis-chelate type have two isomeric forms related by a mirror plane, the d- and /-forms. These species have circular dichroism spectra of identical intensities but opposite in sign. The bands in the circular dichroism spectrum are, of course, modified if ligand exchange occurs but they are also exceedingly sensitive to the environment beyond the first co-ordination sphere. This effect has been used to obtain association constants for ion-pair formation. There also exists the possibility that, if such compounds display anti-tumour activity, only one of the mirror isomers will be effective. 

Such high maintenance of cytotoxic activity in the in vitro serum medium and long in vivo circulation of Pt in the blood for DCM-Dex/CDDP conjugate were due to the strength of six-membered chelate-type coordination of the platinum atom with carrier polymer and steric hindrance of carrier polymer. Summarized in Table 2 are the results of the compartment model analysis. The show excretion rate of the Pt complex into urine by the DCM-Dex/CDDP conjugate compared with rapid excretion by the free CDDP in rats supported the longer circulation time for the Pt polymer complex in the blood (Figure 3). 

EXTRACTION OF COORDINATIVELY SATURATED METAL CHELATE TYPE COMPLEXES (TYPE lll-B)... 

The most important chelate types are illustrated in Figure 2.7. Compounds in column A display a metal ion with coordination number four. The coordination number six is represented by the chelates of column B and C. Rows a, b, and c cover bi-, tri- and tetraftmctional or -dentate ligands, respectively. The types Ab and the types of column B contain additional monofunctional ligands to complete the coordination numbers of four and six, respectively. 

The factors which cause an increase in melt viscosity of molten, unplasticized PVC are also responsible for the gelation of solutions of homo- and/or copolymer (I). For that matter, an analogous explanation is envoked, and it has been shown that displacement of simple ligands on the metal soaps by chelating types of ligands—i.e., those which possess pi-electron rich substituents adjacent to the principal point of attachment, will reverse gelation. 

In order to develop an artificial restriction enzyme that can cleave a desired sequence, an oligonucleotide tag needs to be attached to the catalysis site. The artificial enzyme shown in Fig. 6.15 has an oligonucleotide tag (the rectangle) connected to a metal-chelate-type catalysis site (the circle). The catalytic site was fixed to a particular site on the substrate upon base pairing between the artificial enzyme and the substrate. When the Lu-chelate site was connected to single-stranded DNA, and the DNA moiety was hybridized to RNA with the complementary sequence, the RNA was hydrolyzed at the desired site. If the DNA sequence in the artificial enzyme is designed appropriately, RNA can be cleaved at any site desired. 

Palladium-chelated azomethine ylides 135 react exclusively as ( , )-dipoles with N-phenylmaleimide to furnish stereoselective cycloadducts of chelated types 136(86CC631). 

Additionally, Lewis acid complexes of carbonyl compounds bearing heteroatom-containing functionality (X) in appropriate proximity are an interesting subject to be addressed. Such chelate-type carbonyl-Lewis acid complex formation is generally a favorable process, and can bring an enhancement of reactivity and selectivity by the effective activation of the carbonyl moiety compared to the nonchelation case, implying considerable utility in organic synthesis [7]. 

The H-bond complexes formed between phenol derivatives and bis-l,8-(dimethylamino)-naphthalene (175) in 1,2-dichloroethane and tetrachloroethylene solution were characterized by FTIR spectroscopy. Compound 175 acts as an effective proton sponge for its ability to form a six-membered chelate-type structure including aN H N moiety. The stability constants of the 1 1 and 2 1 complexes are strongly dependent on the pXa value of the phenols and increase also with the polarity of the solvent. No complex formation was detected in tetrachloroethylene when H was replaced by... 

Based on the consideration that suitable ligand should be able to coordinate to the divalent tin metal center of the intermediate enolate, which has a vacant d orbital, the achiral, chelate-type asymmetric reaction was examined employing the diamines 1 s-z as chiral auxiliaries. 

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