Characterization of interactions between organotin compounds and human serum albumin by capillary electrophoresis coupled with inductively coupled plasma mass spectrometry

Thermodynamic data such as the binding constants are vital parameters describing interactions between exotic trace compounds and biomolecules in biochemical property modeling. In this study, the stability constants of organometallic compound and protein complexes were studied by using capillary electrophoresis coupled with inductively coupled plasma mass spectrometry (CE-ICP-MS), considering its low detection limits and low sample demand. Four organotin compounds (trimethyltin (TMT), tripropyltin (TPrT), tributyltin (TBT), triphenyltin (TPhT)) and human serum albumin (HSA) were used as model organometallic compounds and protein, respectively. Affinity capillary electrophoresis (ACE) and nonequilibrium capillary electrophoresis assays of equilibrium mixtures (NECEEM) were performed and compared by using ICP-MS as the detector to determine the binding constants of organotin compounds and HSA in 1:1 molar ratio assumption. Constant measurements of the two methods were both simple, however, ACE assays were more accurate and more appropriate for the constant determination of the organotin–HSA complexes, considering the errors of the NECEEM method. A good precision of the binding constants (log Kb) using the ACE method was proved by different mathematical calculations, and the values were 6.13 ± 0.51 (TMT), 5.72 ± 0.38 (TPrT), 5.68 ± 0.34 (TBT), 6.05 ± 0.38 (TPhT) respectively for each of the organotin–HSA complexes, showing non-covalent interaction between organotin compounds and HSA. Meanwhile, this study also confirms the suitability of CE-ICP-MS method for further studies on organometallic complexation.