A [H-1,N-15] Heteronuclear Single Quantum Coherence NMR Study of the Solution Reactivity of the Ruthenium-Based Mitochondrial Calcium Uniporter Inhibitor Ru265

The synthesis and characterization of the N-15-labeled analogue of the mitochondrial calcium uptake inhibitor [Cl(NH3)(4)Ru(mu-N)Ru(NH3)(4)Cl](3+) (Ru265) bearing [N-15]NH3 ligands is reported. Using [H-1,N-15] HSQC NMR spectroscopy, the rate constants for the axial chlorido ligand aquation of [N-15]Ru265 in pH 7.4 buffer at 25 degrees C were found to be k(1)=(3.43 +/- 0.03)x10(-4) s(-1) and k(2)=(4.03 +/- 0.09)x10(-3) s(-1). The reactivity of [N-15]Ru265 towards biologically relevant small molecules was also assessed via this method, revealing that this complex can form coordination bonds to anionic oxygen and sulfur donors. Time-based studies on these ligand-binding reactions reveal this process to be slow relative to the time required for the complex to inhibit mitochondrial calcium uptake, suggesting that hydrogen-bonding interactions, rather than the formation of coordination bonds, may play a more significant role in mediating the inhibitory properties of this complex.