1.2- Dithiolenes oxygen atom transfer

Subsequently, RR was used to successfully detect structural changes between the oxidized and reduced forms of both DMSOR and BSOR that are consistent with the proposed oxygen atom transfer mechanism of the catalytic reaction (95, 97). These experiments make use of the readily measurable isotopic shifts in vibration frequency between ieO=Mo and lsO=Mo to follow the fate of the oxygen atom removed from DMSO (or BSO) by the Mo. In this way, the clean transfer of 180 from DMSlsO to Mo(IV) to yield the oxidized form of the active site as Mo(VI)=180 was directly observed as well as the substrate-bound intermediate, (DMS180)Mo(IV). Further discussion of the technique of RR applied to metal dithiolenes and dithiolene-containing enzymes is included in Chapter 4 in this volume (98). 

These complexes [MO(sdt)2] (M = Mo or W) represent minimal structural analogues of the active sites of the Mo and W oxo-transfer enzymes of the DMSO reductase type (Figure 3). Furthermore, their redox properties show similarities to those of the Mo and W centres of the enzymes (Figure 11). Thus, each complex possesses a reversible [MO(dithiolene)2] /[MO(dithiolene)2] couple and the potential of each WVW" couple is ca. 225 mV lower than that of the equivalent Mo /Mo couple cf the potential difference of ca. 325 mV observed for the MoVMo and Mo /Mo couples, with Mo > W, for the DMSO reductases of R. capsulatus (Section 3.2). Also, these systems M complexes are converted to their M " counterparts by oxygen-atom transfer from McjNO and the [M02(dithiolene)2] complexes are reduced to the... 

Figure 3.11 Oxygen atom transfer reactions of -oxides mediated by bis(dithiolene) W complexes.

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