Disulfide, coordination modes

The coordination modes of disulfide S22- in some representative compounds are listed in Table 16.5.1. Their molecular structures are shown in Fig. 16.5.2. 

The complex [Mn4(S2)2(CO)i5l contains two disulfide ligands and has been obtained by oxidation of [Mn2(SSnMe3)2(CO)8] " Similar to [Mn3(S2)2(CO)9(SH)] (see Chapter 1.10.5), the disulfide groups are coordinated in different coordination modes. Each manganese atom is coordinated pseudo-ociahedx Wy by six ligands, but the coordination spheres of the individual atoms differ with respect to the total number of sulfur ligands. Two of them are coordinated to three sulfur atoms, the other ones to two and one, respectively. The family of tetranuclear complexes... 

Many transition metal complexes bearing dithiocarboxylato ligands have been studied from various points of view. Their coordination modes depend on the metals and the other ligands on the metals. The complexes sometimes show interesting properties, such as electron conductivity. Synthetic methods are usually as same as those of the main-group-element complexes bearing dithiocarboxylato ligands. The insertion of carbon disulfide into the metal-carbon bond is especially used in the synthesis of transition metal complexes. 

The second mode of toxicity is postulated to involve the direct interaction of the epidithiodiketopiperazine motif with target proteins, forming mixed disulfides with cysteine residues in various proteins. Gliotoxin, for example, has been demonstrated to form a 1 1 covalent complex with alcohol dehydrogenase [13b, 17]. Epidithiodi-ketopiperazines can also catalyze the formation of disulfide bonds between proxi-mally located cysteine residues in proteins such as in creatine kinase [18]. Recently, epidithiodiketopiperazines have also been implicated in a zinc ejection mechanism, whereby the epidisulfide can shuffle disulfide bonds in the CHI domain of proteins, coordinate to the zinc atoms that are essential to the tertiary structure of that domain, and remove the metal cation [12d, 19],... 

Although diphosphine disulfides of formula R2P(S)P(S)R2 take up a trans conformation in the solid state (see Section 5.2.3), upon coordination to a metal centre they can rearrange to adopt a cis conformation, hence facilitating bidentate chelation of the metal (e.g., Equation 78).117 In addition, a cis-bridging mode has also been proposed for these ligands in bi-metallic complexes.117... 

Carbon disulfide reacted with 33 in the presence of free RNC affording [Cu dmpz-CS2 (RNC)2], 36, The KC=S) in 36 appeared at 1330 cm1, suggesting an NS coordination of the dithiocarboxylate anion. This mode of coordination was suggested in 1968 by Trofimenko (54) in the case of metal(II)... 

In addition, urease is inhibited by a variety of agents including fluoride and disulfides, as observed recently in the acetohydroxamate-inhibited C319A variants of K. aero-genes urease. It is proposed that this mode of inhibition involves coordination of the inhibitor to only one nickel center, while another involves the inhibitor bridging the dinickel center. Urease is slowly inhibited by fluoride in both the presence and absence of substrate, and fluoride binding rates are directly proportional to inhibitor concentration. Fluoride inhibition is pH-dependent due to a protonation... 

Kidera et al. have applied the normal mode refinement technique to the determination of the dynamic structures of wild-type and mutant C77A/C95A lysozyme, the mutant structure lacking a disulfide bond normally found in the wild-type structure. This disulfide bond lies in the proposed hingebending region between the two domains of lysozyme. The refinement was carried out for each structure using 1.5 A data and sought to define the influence of this disulfide bond on the dynamic structure of the protein. The dynamic structure refinement was found to result in coordinates with rms variations of 0.06 and 0.07 A for all atoms relative to the structures refined by isotropic B factor refinement for the wild-type and mutant structures, respectively. The rms difference between wild-type and mutant structures was found to be 0.24 A for all atoms with B factors less than 20. 

---