Free radical scavenging potency of phloretic acid: thermodynamics of 2H+/2e processes

Phloretic acid (3-(4’-hydroxyphenyl)propanoic acid) is one of the most abundant colon metabolites of various classes of polyphenols (e.g., polymeric proanthocyanidins, tea catechins, and ellagitannins). Its concentration in fecal water may reach value of 210mol/L [1], which could be high enough to exert at least in situ antioxidant activity [2]. Thermodynamics of 2H+/2e free radical scavenging mechanisms of phloretic acid was studied by DFT method using Gaussian 09 package [3]. Geometry optimizations and frequency calculations were carried out using the M06-2X/6-311++G(d, p) level of theory, in conjunction with the SMD continuum solvation model. For the first time direct involvement of carboxylic group in free radical scavenging mechanisms was investigated considering double hydrogen atom transfer (HAT), double single electron transferproton transfer (SET-PT) and double sequential proton loss electron transfer (SPLET) processes producing dienone lactone [4]. Obtained results indicate that phloretic acid possesses potential for inactivating free radicals of different characteristics (HO•, HOO•, CH3O•, CH3OO•, CH2=CH–O–O•, PhO•, Cl3COO• etc.) by direct scavenging via double HAT and double SPLET mechanisms. In this way, because phloretic acid is produced in highM concentrations and it is usually better absorbed than its precursor molecules, it may contribute to health benefits associated with regular intake of polyphenol-rich diet. References: [1] B. Halliwell, J. Rafter, A. Jenner, Am. J. Clin. Nutr. 81 (2005) 268S−276S. [2] M. Galleano, S.V. Verstraeten, P.I. Oteiza, C.G. Fraga, Arch. Biochem. Biophys. 501 (2010) 23−30. [3] M.J. Frisch, G.W. Trucks, H.B. Schlegel et al., Gaussian 09, Wallingford, CT, 2009. [4] H. Iwasaki, L.A. Cohen, B. Witkop, J. Am. Chem. Soc. 85 (1963) 3701-3702.