Estimated formation constants for the complexation of methylmercury(II) by captopril {1-[(2S)-3-mercapto-2-methyl-1-oxopropyl]-L-proline}: evidence of stronger binding to the cis isomer of the drug

Abstract

Complexation of CH₃Hg¹¹ by captopril {1-[(2S)-3-mercapto-2-methyl-1-oxopropyl]-L-proline} has been studied by ¹H and ¹³C NMR spectroscopy. Very little changes were observed in the equilibrium constants of the cis and trans isomers of CH₃Hg^II–captopril at a 1 : 1 ratio and free captopril as a function of pH*. However, in the ¹³C NMR spectrum the chemical shift of the HSCH₂ resonance was greater for the cis than for the trans form at a 1 : 1 ratio. The formation constants (log K_f) constants for the cis and trans isomers are estimated to be 16.85 and 16.57 based on the equation log K_f= pK_SH+ 6.86.