Ligand effects mechanisms

Changing the amino acid sequence of the cloned receptors by mutating nucleotides within the receptor cDNAs has proven to be an effective mechanism by which to identify structural features of the receptors responsible for their unique functional properties. In particular, site-directed mutagenesis has been employed to determine the ligand binding domains of each opiate receptor. 

H. E. Bryndza, P. J. Domaille, R. A. Paciello, J. E. Bercaw. Kinetics and Mechanism of Phosphine Exchange for Rutheniumill) Complexes in the Series (r 5-CsMes)(PMeo,)2RuX. Ancillary Ligand Effects on Dative Ligand Dissociation. Organometallics 1989, 8, 379-385. 

The excellent catalytic activity is rationalized by a nonclassical metal-ligand bifunctional mechanism using an NH effect. As shown in Figure 1.18, frani-RuH(ri -BH4)(tolbinap)(dpen) (18A) (TolBINAP see Figure 1.2), a precata-... 

It is of interest to note the ligand effect on the mechanisms of decomposition of several copper complexes of the type LCuin-CH3 ... 

A corresponding reaction of acetate ion with AJP is also catalyzed by a bivalent metal ion. The reaction probably results in the formation of an acyl phosphate, which has not been identified as such but has been identified by trapping of the product with hydroxylamine. The best catalyst is beryllium ion, which catalyzes optimally at molar ratios of 1 to 1 or less. Acetate ion is presumably the reactive species, since the pH optimum of the reaction is 5. It is concluded from the pH effects in this study and in the transphosphorylation reaction that a complex of the metal ion and nucleophile must occur. Since acetate ion is a monodentate ligand, the mechanism postulated for the phosphorylation reaction above cannot be completely applicable to this case (36). 

The bis(l,2-enedithiolate) complexes discussed closely resemble the metal centers found in the dmso reductase family of Mo enzymes and in the tungsten enzymes. The reactivity of mono(l,2-enedithiolate) complexes remains a continuing challenge as synthetic chemists pursue accurate models for the xanthine oxidase and sulfite oxidase families of metal sites. New 1,2-dithiolate ligands [70,71] and complexes are needed to demonstrate ligand effects to help elucidation reaction mechanism. 

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