Interactions in solution of cobalt(II) and nickel(II) with nicotinamide adenine dinucleotide: A potentiometric and calorimetric study

Abstract

The equilibrium constants and the thermodynamic parameters enthalpy and entropy of the interaction between Ni(II) and Co(II) with NAD+ in aqueous solution were determined by calorimetry and potentiometry methods (ionic strength adjusted to 0.1 with sodium nitrate at 25 °C). The macrochelation of the systems was also studied. All the data, including the protonation enthalpy data of NAD+ (very similar to the protonation enthalpy of 5′-AMP) suggest a less restrictive model for the NAD+ "folded" conformation without intramolecular stacking between the bases, in agreement both with recent theoretical calculations and with the X-ray structure of trimethylene-bisadeninium or the free acid form of NAD+.