Evaluation of [Co(gly)3]- as a 35Cl- NMR Shift Reagent for Cellular Studies

We studied the efficacy of the tris-glycinatocobaltate(II) complex ([Co(gly)3]-) as a shift reagent (SR) for chloride by 35Cl NMR spectroscopy and compared to that of Co2+(aq). Due to the relatively low thermodynamic stability of [Co(gly)3]-, a 1:3 Co(II)/gly stoichiometric solution at physiological pH is approximately a 2:1 mixture of [Co(gly)2(H2O)2] and [Co(gly)(H2O)4]+. This SR was found to be stable up to higher pH values than Co2+(aq), better preventing Co(OH)2 formation at alkaline pH. No significant differences in the 35Cl- NMR chemical shift induced by Co(II)/gly or Co2+(aq) were observed in the presence of physiological concentrations of either Ca2+ or Mg2+, or of either Na+ or K+. Although Co2+(aq) was almost twice as effective as Co(II)/gly in shifting the 35Cl- NMR resonance at the same high ρ ([SR]/[Cl-]) value and low ionic strength, Co2+(aq) showed a significant decrease (p < 0.05) in the 35Cl- chemical shift at higher ionic strength. Line widths at half-height were significantly (p < 0.05...