Cysteine related ligands

Ligand Effect. In Mo complexes containing cysteine-related ligands as potential catalysts, structural variations in the ligand have... 

Ru(VI) and Os(VI) nitrido complexes of cysteine (2 -) and related ligands have recently been prepared by the reactions of [Ru(N)(CH2. SiMe3)4], [Ru(N)(OSiMe3)4], and [Os(N)C14] with A-acetyl-L-cys-teine, 3-mercaptoproprionic acid, and 3-mercaptopropionamide (269). 

Table II shows the effect of structural variations in the cysteamine-related ligands (7). In contrast with the case in cysteine...

Replacing the cysteinate axial ligand with either imidazole or phenolate models the related enzymes HRP and catalase, respectively. In contrast to cysteinate, an imidazole ligand hardly interacts with the porphyrin a2 orbital. As a result, the spin densities of the singly occupied 32 orbital in Cpd I(HRP) are primarily located on the porphyrin ring, while in Cpd I(P450), the spin... 

Comparison of the stability of cadmium(ll) complexes of cysteine and related ligands with those of the corresponding nickel(ll) and zinc(ll) clearly shows that the stability order follows just opposite trends with respect to that of other amino acids log jS (Cd(ll)-complexes) > log jS (Ni(ll)-complexes) > log jS (Zn(ll)-complexes). 

Resonance Raman studies of Fe- and Cu-contalnlng proteins have led to the Identification of tyrosine, histidine, cysteine, and hydroxide ligands as well as Fe-0 and Fe-S clusters. For the Fe-0 clusters, the frequency and oxygen Isotope dependence of the Fe-O-Fe symmetric stretch relates to Fe-O-Fe bond angle, while the peak Intensity relates to the disposition of the other ligands In the cluster. 

The structure of PaFd was the first to be crystallographically determined (Adman et ai, 1973). The basic fold of the protein may be described as a pair of two stranded antiparallel )3 sheets. The two 4Fe 4S clusters are sandwiched between these /3 strands on one side and several helical segments on the other side. The clusters are packed in a predominantly hydrophobic environment. The internal sequence homology is clearly reflected in the structure the two clusters and much of the polypeptide chain are related by an approximate internal twofold rotation axis. The two clusters are ligated by the two sets of four cysteines in the two halves of the molecule. Surprisingly, each cluster is liganded by cysteines from both halves of the sequence, rather than cysteines from only one half (which are adjacent in the sequence). Cluster 1 is coordinated by Cys-8, -11, and -14 in the amino-terminal half and Cys-45 of the carboxy-terminal half, while cluster 2 is coordinated by Cys-35, -38, and -41 of the carboxy-terminal half and Cys-18 of the amino-terminal half. 

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