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

• Published in: Inorganic chemistry 2003-04, Vol.42 (8), p.2774-2782
• Main Authors: Diven, Conrad F, Wang, Fei, Abukhdeir, Abde M, Salah, Wajeeh, Layden, Brian T, Geraldes, Carlos F. G. C, Mota de Freitas, Duarte
• Format: Article
• Language: English
• Subjects: Cells, Cultured - drug effects; Chlorides - chemistry; Cobalt - chemistry; Fibroblasts - drug effects; Glycine - chemistry; Humans; Hydrogen-Ion Concentration; Indicators and Reagents - chemistry; Isotopes - chemistry; Magnetic Resonance Spectroscopy; Thermodynamics
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic0258680

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) less for Co(II)/gly than for Co2+ (aq) at ρ values in the range 0.066−0.40. Intracellular chloride was clearly detectable by 35Cl NMR spectroscopy in human skin fibroblast cells suspended in medium containing 40 mM Co(II)/gly SR. We determined that, although Co2+ (aq) provides a larger shift than Co(II)/gly at the same ρ value, there are significant advantages for using Co(II)/gly, such as pH stability, ionic strength independent chemical shifts, narrow 35Cl- NMR resonances, and reduced cellular toxicity, as a SR in biological systems.