Interaction of anti-inflammatory drug naproxen with essential amino acids: Quantitative thermodynamic insights

A combination of ultrasensitive isothermal titration calorimetry and uv-visible spectroscopy has been employed to unravel interaction of anti-inflammatory drug naproxen with five essential amino acids L-arginine, L-lysine, L-phenylalanine, L-valine and L-tryptophan. The nature of interaction in each case has been examined based on standard molar enthalpy of interaction (Delta H-m(o)) and changes in the spectral properties. The values and sign of Delta H-m(o) m have been related with the nature of interacting groups and solvent reorganization as a result of drug-amino acid association. Exothermic standard molar enthalpy of interaction of naproxen with L-arginine indicated significant of polar interactions, and endothermic heat effects with all other amino acids suggested dominance of hydro-phobic effect and desolvation penalty in the association process. The overall value of enthalpy of interaction for all the studied amino acids is less than 2 kJ mol(-1) suggesting that these interactions are not very strong. The uv-visible results provided support to ITC results in obtaining mechanistic insights into the nature of in-teractions. The results derive significance from the fact that sometimes anti-inflammatory drug naproxen may be administrated along with supplements of essential amino acids. In case there is a strong drug-amino acids interaction, efficacy of each one may be affected.