Use of Melatonin Derivatives as Spin Traps for Hydroxyl Radicals: A Computational Studies. Aaron Teye Caesar and Dr. Scott Jeffery Kirkby, Department of Chemistry, College of Arts and Sciences, East Tennessee State University, Johnson City, TN. Free radicals, especially reactive oxygen species, have been implicated in several deleterious processes which result in degenerative and cardiovascular diseases. Melatonin (N-acetyl-5-methoxytryptamin, MLT) is a naturally occurring antioxidant which has shown some potential for use as a spin trap. Spin traps react with short lived radicals such as hydroxy (.OH) or superoxide (O2-) to produce more stable products called spin adducts which may be characterized by electron paramagnetic resonance spectroscopy. This work examines whether MLT derivatives show improved spin adduct stability which may enhance their spin trapping characteristics. Electronic structure calculations of MLT, selected derivatives and 2-OH radical products were performed at the HF/6-31G(d), cc-pVDZ and DFT/B3LYP/6-31G(d) and cc-pVDZ levels of theory using NWChem. The stabilization energy was calculated using; ∆Estabilization = Espin adduct – (Espin trap + Ehydroxy radical). In units of hartrees, the results of 2-OHMLT, 2-OHMLT-Me and 2-OHMLT-CN are -0.43738, -1.60054, -1.60380 for HF/6-31G(d); -1.46071, -1.44788 and -1.46173 for DFT/6-31G(d) respectively. Also, HF/cc-pVDZ and DFTB3LYP/cc-pVDZ respectively gave -1.61268, -1.60233, -1.61409 and -1.44929, -0.26318, -1.45521.