Transition metal complexes as electrochemical markers for steroids

The electrochemical behaviour of few Co₂(CO)₆(alkyne-estradiol) and Mo₂Cp₂(CO)₄(alkyne-estradiol) complexes is described. For purposes of comparison the electrochemical responses of free estradiols and of the model compound Co₂(CO)₆(HC₂H) have also been investigated. From the cyclic voltammetric responses of the estradiol-organometallic derivatives, it is clear that the two constituent units, i.e. Co₂″₆CC″ and the estradiol frame, undergo relatively independent electrochemical processes. Significantly the labelling of steroids by means of bimetallic fragments (having an accessible LUMO) increases their electrochemical activity by adding a well-defined reduction process which makes the molecules cathodically detectable at stationary electrodes. This approach suffers from adsorption and filming problems, but these can be overcome by careful pretreatment of the solid electrodes. A method of evaluating the molecular mobility of such complexes from the ¹³C-NMR line-width analysis is described.