The interactions between the new organometallic complexes, ferrocene-substituted dithio-o-carborane conjugates (denoted as FcSB1, FcSB2 and FcSBCO) and hemoglobin (Hb) are investigated by electrochemistry, fluorescence and UV-vis absorption spectroscopy. The results demonstrate that FcSB1, FcSB2 and FcSBCO can bind to the heme iron center through the replacement of the weakly bound H2O/O2 in the distal heme pocket of Hb by their sulfur donor atoms, inducing the allosteric change from the R state (oxygenated conformation, relax) to T state (deoxygenated conformation, tense). The binding affinity is in the order of FcSBCO>FcSB2>FcSB1. Moreover, the fluorescence study illustrates that the three ferrocene-carborane conjugates differently affect the quarterly and tertiary structures as well as the polarity in the surrounding of the Trp and Tyr residues in Hb. Typically, FcSB2 mainly induces alterations of the microenvironment around the β37Trp residue which is located on the α1β2 interface of Hb. Such distinct influences are attributed to the structural features of FcSB1, FcSB2 and FcSBCO containing hydrophobic ferrocenyl and carboranyl units as well as C=O group. Screening the protein-binding behavior can signify the potential bioactivity of such molecules and may be helpful in the future development of promising multifunctional metallodrugs.
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