Synthesis of [MoS 4] 2--M (M = Cu and Cd) clusters: Potential NMR spectroscopic structural probes for the orange protein

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Abstract

Two synthetic strategies of tetrathiomolybdate-metal clusters with the potential to be used as NMR structural probes for the location of the metal cofactor in the orange protein (ORP) are described. The first strategy is based on the substitution reaction in which small organic ligands bind directly to the metal centre in a molybdenum-copper hetero-dinuclear cluster. Interaction between [PPh 4] 2[MoS 4CuCl] and either aliphatic [β-mercaptoethanol (b-me)] or aromatic [o-aminobenzenethiol (abt)] thiols in the presence of a strong base resulted in the formation of [Ph 4P] 2[S 2MoS 2Cu(b-me)] (1a) and [Et 4N] 2[S 2MoS 2Cu(abt)]·H 2O·0.25DMF (1b), which can be used to obtain intermolecular NOEs. The compound 1a readily hydrolyzed to [Ph 4P] 2[OSMoS 2Cu(b-me)] (1a hydro) in contact with a protic solvent. The second strategy consisted of the incorporation of cadmium into tetrathiomolybdate ([MoS 4] 2-), which gives rise to the trinuclear cluster compound [PPh 4] 2[(MoS 4) 2Cd] (2). All clusters were characterized spectroscopically and their structure determined by X-ray diffraction. The NMR spectroscopic data are consistent with the formation of a complex with a 1:1 ratio of {MoS 4Cu} and thiol. The 113Cd NMR chemical shift of compound 2 is consistent with the cadmium having a tetrahedral geometry and coordinated by four sulfur ligands. The tetraphenylphosphonium cation in compound 1a was replaced by a tetramethylammonium countercation originating in the water-soluble compound [Me 4N-1a]. Solubility in aqueous buffers is a requirement for incorporating this cluster into apo-ORP. These compounds will be used to identify the exact location of the ORP heterometallic cluster using NMR methodologies.

Original languageEnglish
Pages (from-to)4159-4166
Number of pages8
JournalEuropean Journal of Inorganic Chemistry
Issue number26
DOIs
Publication statusPublished - 1 Sep 2012

Keywords

  • Cd NMR spectroscopy
  • Bioinorganic chemistry
  • Cadmium
  • Cluster compounds
  • Copper
  • Metalloproteins
  • Molybdenum
  • Orange protein
  • Proteins

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