NMR investigation of magnesium chelation and cation-induced signal shift effect of testosterone.

We have previously reported that testosterone (Tes) is able to interact with magnesium chloride dissolved in methanol. In this study, we have applied H and C NMR spectroscopies to a series of Tes solutions containing Mg at various concentrations. High-resolution C NMR spectra of Tes/Mg revealed well-resolved C signals, and the intensities of those arising from C3, C5, C16, and C17 decreased linearly with increasing Mg concentration. The magnitude of the chelation affinity could be deduced from the slopes of the C intensity variations; typically, the greater the slope the higher the chelation affinity. The results revealed Tes/Mg chelation to be mediated by the oxygen atom attached to C3 in ring A, and the hydroxyl group attached to C17 in ring D. With regard to the chelation specificity, we showed that Tes chelates Mg, but not Ca or Zn. We also explored the cation-induced signal shift effects of Tes in the presence of Mg, Ca, or Zn. We demonstrate that high-resolution C NMR spectroscopy provides a better probe than H NMR for the detection of cation chelation and cation-induced signal shift effects for steroid compounds such as Tes.