Urocanic acid as an efficient hydroxyl radical scavenger: a quantum theoretical study

Abstract

The photoisomerization of urocanic acid (UCA)--which is present in human skin epidermis, where it acts as a sunscreen--from its trans isomer to its cis isomer upon exposure to UV-B radiation is known to cause immunosuppression. In recent years, the antioxidant properties of UCA (it acts as a hydroxyl radical scavenger) have also been recognized. In view of this, the mechanisms of stepwise reactions of trans-UCA with up to four hydroxyl radicals were investigated. The molecular geometries of the different species and complexes involved in the reactions (reactant, intermediate and product complexes, as well as transition states) were optimized via density functional theory in the gas phase. Solvation in aqueous media was treated with single point energy calculations using DFT and the polarizable continuum model. Single point energy calculations in the gas phase and aqueous media were also carried out using second-order Møller-Plesset perturbation theory (MP2). The AUG-cc-pVDZ basis set was employed in all calculations. Corrections for basis set superposition error (BSSE) were applied. Vibrational frequency analysis was performed for each optimized structure to ensure the validity of the optimized transition states. It was found that the binding of the first OH· radical to UCA involves a positive energy barrier, while subsequent reactions of OH· radicals are exergonic. Transition states were successfully located, even in those cases where the barrier energies were found to be negative. The cis-trans isomerization barrier energy of UCA and that of the first OH· radical addition to UCA are comparable, meaning that both processes can occur simultaneously. It was found that UCA could serve as an antioxidant in the form of an efficient OH· radical scavenger.

Angiotensin-converting enzyme 2, angiotensin-(1–7) and Mas: new players of the renin–angiotensin system

“…Besides its physiological relevance for kidney homeostasis, the ACE2/Ang-(1-7)/Mas axis also has an important and controversial role in renal diseases, acting as a renoprotective (Oudit et al 2006, 2010, Soler et al 2007, Pinheiro et al 2009, Burns et al 2010, Dilauro et al 2010, Zhang et al 2010, Giani et al 2011, Liu et al 2011b, Moon et al 2011, Stegbauer et al 2011, Zhong et al 2011, Barroso et al 2012, Kim et al 2012, Nadarajah et al 2012 or a proinflammatory (Esteban et al 2009, Velkoska et al 2011 agent. Briefly, Pinheiro et al (2009) reported that mice with genetic deletion of Mas developed renal dysfunction with an increase of glomerular tuft diameter and enhancement of fibronectin and collagen IV and III deposition, besides an increase of AT 1 and TGF-b expression.…”

Two‐dimensional imaging of spontaneous ultra‐weak photon emission from the human skin: role of reactive oxygen species

“…Our observation that the topical application of Fenton reagent system on the dorsal side of the hand results in an enhancement in ultra-weak photon emission indicates that HO is involved in photon emission ( Figure 6E). The non-enzymatic antioxidant system consists of urocanic acid, a metabolite of histidine present in the upper layer of human skin epidermis [45]. In contrast to O À 2 and H 2 O 2 , there is no efficient enzyme system that can scavenge the excess of HO .…”

Repair of Oxidizing Hydroxyl Adduct Radicals of DNA Bases by Hydroxyl‐trans‐Stilbenes via Single Electron Transfer

“…Gibbs free energy G was calculated as following equation: G = E HF + G 0 , where E HF represents the total calculated electronic energy at the M06‐2X / ma‐TZVP // 6–311G (d, p) level and G 0 is the thermal correction to Gibbs free energy at the M06‐2X / 6–311G (d, p) level. The method used for calculating Gibbs free energy in this study has been applied in the literature ,,…”