Chelate rings Subject

Most mordant dyes are monoazo stmctures. The most important feature of this class of dyes is excellent fastness to light and washing. Mordant dyes are available ia aU shades of the spectmm with the exceptioa of bright violets, blues, and greens. To be useful, the metal complexes must be stable, ie, must not demetallize when subjected to dyebath conditions and aU aftertreatment processes, especially repeated washings. Chromium forms stable chelate rings with mordant dyes which are not affected by treatment with either weak acid or alkaU (see Coordination compounds). 

Rate constants for reaction of cis-[Pt(NH3)2(H20)Cl]+ with phosphate and with S - and 5/ -nucleotide bases are 4.6xl0-3, 0.48, and 0.16 M-1s-1, respectively, with ring closure rate constants of 0.17 x 10 5 and 2.55x10-5s-1 for subsequent reaction in the latter two cases 220). Kinetic aspects of interactions between DNA and platinum(II) complexes such as [Pt(NH3)3(H20)]2+, ds-[Pt(NH3)2(H20)2]2+, and cis-[Pt(NH3)2(H20)Cl]+, of loss of chloride from Pt-DNA-Cl adducts, and of chelate ring formation of cis-[Pt(NH3)2(H20)(oligonucleotide)]"+ intermediates implicate cis-[Pt(NH3)2(H20)2]2+ rather than cis-[Pt(NH3)2 (H20)C1]+, as usually proposed, as the most important Pt-binder 222). The role of aquation in the overall scheme of platinum(II)/DNA interactions has been reviewed 223), and platinum(II)-nucleotide-DNA interactions have been the subject of molecular modeling investigations 178). 

The results suggest that the five-membered peptide chelate ring, in which the atoms are nearly coplanar, may be more subject to steric effects than is the case for the gauche conformation of chelate rings of ethylenediamine and its C-methyl derivatives. However, the corresponding nucleophilic displacement reactions have not been studied and it is too early to draw... 

A wide range of multidentate amine ligands coordinate to platinum. The conformational analysis of chelate ring systems by NMR has been reviewed by Hawkins, and platinum complexes are included in this work.959 Amine ligands with sulfur groups can also act as chelates, and this subject has also been reviewed.960... 

Conformation of Ethylenediamine. Whether the ethylenediamine chelate ring is completely planar or puckered has also been a subject of controversy. The conformation of ethylenediamine may be cis if planar and gauche if puckered. Infrared studies have proved to be very useful in distinguishing cis, trans, and gauche conformation of 1,2-substituted... 

Most CD spectral studies of cobalt(III) complexes have been undertaken to investigate various sources of optical activity such as distribution of chelate rings, conformation of chelate rings, vicinal effect due to asymmetric carbon in an optically active ligand, and vicinal effect due to an asymmetric donor atom. Extensive reviews on these subjects have been written by Fujita and Shimura (1), Hawkins (2), and Mason (3). 

Alternatively, one of the metal-oxygen bonds in the acetylacetonate can cleave before or after electrophilic attack on the chelate ring that is undergoing cleavage, forming a five-coordinate intermediate. With the subsequent loss of a proton, a chelate ring with a 3-halo substituent is obtained. The trisacetylacetonates of Cr(III), Co(III), and Rh(III) were partially resolved on a 16-foot column of D-lactose hydrate. The optical activity of each of these chelates was measured before and after being subjected to a number of electrophilic substitution reactions. It was found that the substitution reactions did not cause total racemization, and therefore it was concluded that this alternative mechanism is unlikely (49). 

The chelate ring closing of glycine has been the subject of extensive isotope and kinetic studies, and the results are summarized in Scheme 3.5 (k, s" at 25°C). The reactions proceed with retention of the Co—O bond, and it is noteworthy that coordinated water is an active nucleophile in this intramolecular process. The acidic pathways, given by and k2 in Scheme 3.S, show general acid catalysis, which the authors interpret as due to rate-controlling elimination of water from the tetrahedral carbon in a cyclic intermediate. 

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