Amino acids as ligands

Amino acid is one of the most important biological ligands. Researches on the coordination of metal-amino acid complexes will help us better understand the complicated behavior of the active site in a metal enzyme. Up to now many Ln-amino acid complexes [50] and 1 1 or 1 2 transition metal-amino acid complexes [51] with the structural motifs of mononuclear entity or chain have been synthesized. Recently, a series of polynuclear lanthanide clusters with amino acid as a ligand were reported (most of them display a Ln404-cubane structural motif) [52]. It is also well known that amino acids are useful ligands for the construction of polynuclear copper clusters [53-56], Several studies on polynuclear transition metal clusters with amino acids as ligands, such as [C03] [57,58], [Co2Pt2] [59], [Zn6] [60], and [Fe ] [61] were also reported. 

Fig. 18 Heptanuclear trigonal prismatic clusters with amino acids as ligands...

In nomenclature for amino acids as ligands, the atoms in the R group are labeled with Greek letters starting with (5 for the first atom attached to the a carbon followed by y and 8 and e. The common bioinorganic ligands histidine, cysteine, and aspartic acid have their atoms labeled in the manner shown in Figure 2.5. The... 

Engberts and co-workers (216,217) investigated the use of commercially available amino acids as ligands for Cu(II) in the Diels-Alder reaction. For the cycload-... 

Figure 7.9 Mechanistic interpretation for catalysis by Lewis acids containing aromatic a-amino acids as ligands.

In a typical dimeric 1 2 complex, the two RE(III) ions are linked through a quadruple bridge (P2-iiN )4- Each of the metal ions is further coordinated by four water molecules, CN = 8. A representative structure, [Eu2(Ala)4(H20)8] " ", is shown in Figure 3.31a. While most dimeric RE(III)-carboxylic acid complexes are centrosymmetric, with amino acids as ligands, similarly structured complexes are only obtainable when the racemic form of the ligands are used for the synthesis [127]. 

Wapnir RA, Stiel L. 1986. Zinc intestinal absorption in rats Specificity of amino acids as ligands. J Nutr 116 2171-2179. 

Significant progress was achieved using amino acids as ligands in the Cu-catalyzed reaction not only aryl iodides, but also aryl bromides (without electron-donating substituents) were used as starting materials and led to product formation in 90-98% and 72-85% yields, respectively (Scheme 3.34) [67]. The catalytic system was found to be very sensitive to the nature of the solvent and base. A plausible mechanism was reported and the involvement of Cu(I)/Cu(III) species was proposed (Scheme 3.35). 

Compound 119 involves a cyclic amide of an ca-amino acid as ligand. Related to this are complexes containing cyclic amides like uracil (121), barbituric acid, 5,5-dimethylbarbituric acid [116], 2,5-piperazinedione (85) [226], and 2-chloro-6-hydroxypyridine (86) [221], respectively, to accomplish pentacoordination at silicon. 

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