CYCLOTRIVERATRYLENE MODELS FOR [4FE-4S] PROTEINS - 3 1 SUBSITE DIFFERENTIATION AND MODULATION OF THE REDOX POTENTIAL/

The potential of cyclotriveratrylene (ctv) (2,3,7,8,12,13-hexamethoxy- 10, 15-dihydro-5H-tribenzo[a,d,g]cyclononene) trithiols as ligands tha t can easily be functionalised and show subsite differentiation in the ir complexes with [4Fe-4S] clusters has been explored. The cluster com plexes of tris(2-sulfanylethoxy)- and tris(3-sulfanylmethylbenzyloxy)- functionalised ctvs have been studied by core-extrusion experiments, s pectroscopy and electrochemical techniques. With [Fe4S4Cl4](2-) as sta rting material a cluster complex was obtained in which the unique Fe a nd its co-ordinating Cl was turned into the cavity and show no reactiv ity. Starting with the more bulky [Fe4S4(SBu(t))(4)](2-) the unique ir on points outwards and is susceptible to substitution reactions. The e ffects of hydrogen bonding and electron density on the redox potential of the cluster complex have been investigated. The redox potential be comes more negative when the length of the spacer between the ctv and cluster core is increased, which is explained by the longer distance b etween the cluster and the electron-withdrawing phenoxy moiety of the ctv. The synthesis of ctv derivatives with one thiol and one alcohol f unctionality per phenyl unit, and comparison with corresponding deriva tives where hydrogen bonding is not possible, showed that no significa nt differences were found. The effects of a substituent in an aromatic amide group that could hydrogen bond to the co-ordinated thiol were i nvestigated. A weak effect, in the direction expected, was found upon substitution of methyl for H.