Icosahedral Cobalt Bis(dicarbollide) Ions with Bridge Linker and Their Electrochemistry in Aqueous Media

Abstract

Boron cluster compounds (BCC) proved recently promising properties for use in drug design and molecular probes. Their applications in medicine are inherently connected with use of water-based environments. Up to now, the BCC were predominantly characterized in non-aqueous milieus. Therefore, we decided to perform electrochemical research of BCC in water-based electrolytes. We have focused on several boron clusters with structures that follow our previous study on icosahedral cobalt bis(dicarbollide) ions with a central coordination Co(III) atom in phosphate buffers, where we have found the best response for bridge type of exo-skeletal substituent. Therefore, in present study, we decided to focus on the promising structures, in which two 11 vertexes C2B9 dicarbollide ligands are interconnected via short bridge. Such structures may contain side chains usable for bioconjugation experiments.For our electrochemical experiments, we have used phosphate buffers of different pHs (2-10) and polished glassy carbon electrode. As the bridge structure served these exo-skeletal substituents: sulfur, amino group, tolylene, chlorpehenylene, phenylene, xylylene, byphenylene, phosphoric groups.The effect of various exo-skeletally substituted cobaltacarboranes (differing in type and length of the side chain) on the electrochemical response was studied. The results show that all parameters, the peak shape, the potential position and the peak current density height are significantly altered by the endo- and exo- skeletal substituents. Within the range of studied substitution, we were able to detect the signals in a broad potential range from E = -1.38 V to E = 1.73 V. From this follows clear possibilities to tune the position of two potential types in the electrochemical window that alternatively correspond either to the oxidation of the core structure of boron polyhedra or the central Co(III). The results also show that the electrochemical methods represent another tool for fast tracking the aggregation phenomena connected with non-classical amphiphilic behavior of boron clusters in aqueous solutions