Binding metal

The dependence of chiral recognition on the formation of the diastereomeric complex imposes constraints on the proximity of the metal binding sites, usually either an hydroxy or an amine a to a carboxyHc acid, in the analyte. Principal advantages of this technique include the abiHty to assign configuration in the absence of standards, enantioresolve non aromatic analytes, use aqueous mobile phases, acquire a stationary phase with the opposite enantioselectivity, and predict the likelihood of successful chiral resolution for a given analyte based on a weU-understood chiral recognition mechanism. 

In addition to being a remarkable demonstration of the power of computer-based combinatorial design of a protein fold, this designed peptide is the shortest known peptide consisting entirely of naturally occurring amino acids that folds into a well-ordered structure without metal binding, oligomerization or disulfide bond formation. 

The incorporation of S-N chains between metal centres by the use of heteroaryl substituents in complexes of the type 14.7 has been proposed as a way to generate new materials that may function as molecular wires. However, the synthesis of thiazyl chains bearing metal-binding sites has yet to be achieved. 

Apometallothioneins metal binding models, 6, 673 Apoplastocyanin structure, 6, 650 Aquadioxo cations, 2, 296 Aquapentaammine complexes structure, 1, 8... 

Fig. 5. Structure-based alignment of the sequences of the water-soluble Rieske fragment from bovine heart bci complex (ISF), the water-soluble Rieske fragment from spinach b f complex (RFS), and of the Rieske domain of naphthalene dioxygenase (NDO) and of the metal binding loops of rubredoxin (RXN) and transcriptional factor TFIIS (TFI). The numbering of the j3 strands is the same for the ISF and RFS. The metal binding ligands are highlighted the asterisks indicate those residues that are fully conserved between the three Rieske proteins.

Fig. 7. Comparison of the cluster binding fold of the water-soluble Rieske fragment from bovine heart 6ci complex (ISF, left PDB file IRIE) with the structure of ru-bredoxin (middle PDB file 7RXN) and with the zinc-ribbon motif (right PDB file ITFl). The metal binding loops are shown as ball-and-stick models of the backbone atoms.

In view of the structural homology, it is likely that the cluster binding subdomadn of Rieske proteins accommodating two metal ions has evolved from an archadc mononuclear metal binding domain. A simi-... 

Grill, E., Winnacker, E.-L. Zenk, M.H. (1987). Phytochelatins, a class of heavy-metal-binding peptides from plants, are functionally analogous to metallo-thioneins. Proceedings of the National Academy of Sciences, USA, 84, 439-43. 

The fact that f.a.b.-m.s. can be used to observe cluster ions has been exploited in a study of metal binding to cyclodextrins, and in an investigation of the complexes formed between a 3-O-methylmannose dodecasac-charide and alkyltrimethylammonium ions having decyl and hexadecyl as alkyl chains. In the latter study, the larger organic cation was shown to form the stronger complex. 

Blue copper proteins. A typical blue copper redox protein contains a single copper atom in a distorted tetrahedral environment. Copper performs the redox function of the protein by cycling between Cu and Cu. Usually the metal binds to two N atoms and two S atoms through a methionine, a cysteine, and two histidines. An example is plastocyanin, shown in Figure 20-29Z>. As their name implies, these molecules have a beautiful deep blue color that is attributed to photon-induced charge transfer from the sulfur atom of cysteine to the copper cation center. 

---