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Previous work has demonstrated that several transition metals and their anions, including cadmium, arsenite, and selenite, can inhibit glucocorticoid binding to glucocorticoid receptors in vitro. In this study, we demonstrated that in vitro zinc can also inhibit the binding of glucocorticoids to their receptor at relatively modest concentrations (10 to 100 microM). This inhibition was demonstrated in both crude and immunopurified receptor preparations and was reversible following removal of zinc. Inhibition could also be reversed by addition of the reducing agent dithiothreitol (DTT). This suggested that zinc might be acting by interacting with the vicinal dithiols in the steroid binding region of the receptor as previously described for other transition metals and anions. The ability of a biologically important trace metal to block steroid binding suggests a role for zinc in the regulation of glucocorticoid receptor-ligand interactions and may explain the ability of zinc to block glucocorticoid-induced apoptosis.

The interaction between metals in homo-and heterometallic complexes are known as metallophilic interactions. The photoluminescent study of metal complexes with metallophilic interactions produces promising results. [1, 2] Bis(diphenylphosphine)amine (PNP) ligand systems were identified as the ligands of choice because they consist of a parameter for the measurement of its steric bulk on the nitrogen atom. The parameter is known as the Tolman based cone angle as introduced by Cloete et al. [3] The influence of the steric bulk on the catalytic activity of the ligand was investigated by Cloete et al.[3] A wide range of steric substituents are identified and a collection of dimeric metal complexes synthesised. The photoluminescent properties of these complexes were compared as a parameter for the metallophilic interactions present in the complexes. The influence of solvents is investigated and solid state luminescence is used for the luminescence study. The formation of exciplexes are possible with a semi-coordination between the solvent and the complex. [4] The solvent interaction and quenching effects correlate to photoluminescent data from other studies. [5,6] The structural aspects are compared using single crystal X-ray diffraction analysis and DFT calculations. This makes the comparison between theoretical and experimental data possible. The manipulation of the metal to metal distance is observed and a correlation drawn between the metal to metal distance and the steric bulk of the ligand system. Figure 1 illustrates two metal complexes with metallophilic interactions.