Browsing by Author "Fuentes Lemus, Eduardo"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Complexation of AAPH (2,2′-azobis(2-methylpropionamidine) dihydrochloride) with cucurbit[7]uril enhances the yield of AAPH-derived radicals
    (2023) Forero Girón, Angie; Fuentealba Patiño, Denis Alberto; Mariño Ocampo, Nory Johana; Gutiérrez Oliva, Soledad; Herrera Pisani, Bárbara Andrea; Toro Labbé, Alejandro; Fuentes Lemus, Eduardo; Davies, Michael J.; Aliaga Miranda, Margarita Elly; López Alarcón, Camilo Ignacio
    AAPH (2,2′-azobis(2-methylpropionamidine) dihydrochloride), a water-soluble azo compound is widely employed to produce peroxyl radicals for chemical and biological studies. This compound is shown herein to form a stable inclusion complex with cucurbit[7]uril (CB7), a well-established supramolecular host. Competitive binding assays using berberine dye, isothermal titration calorimetry (ITC), and nuclear magnetic resonance (1H-NMR) experiments, provided evidence for the inclusion of AAPH inside the CB7 cavity with a binding constant of 2.5 ± 0.8 x 105 L mol-1 (determined by ITC). Computational analysis at B3LYP-D3BJ/6-311G(d,p) of the complex (AAPH@CB7) showed interactions of the positively-charged amino groups of AAPH with carbonyl functions at the CB7 entrances. Photolysis of AAPH@CB7 by illumination at 365 nm, gave a higher yield of carbon-centered radicals when compared to the absence of CB7, as evidenced by electron paramagnetic resonance spin trapping using α-phenyl-N-t-butylnitrone. Enhanced radical formation was corroborated by increased consumption of pyrogallol red, free Trp and Trp-containing peptides when these were exposed to AAPH@CB7 in the presence of light. The increased yield of radicals generated by AAPH@CB7 is believed to arise from a pull effect of CB7 portals on initial AAPH-derived carbon-centered radicals generated by photolysis. It is proposed that these radicals are exposed and released to the bulk solution and react with O2 to give peroxyl radicals. These results suggest that the AAPH@CB7 complex can be used to generate high yields of peroxyl radicals for their use in studying these species in material, environmental and biomedical sciences amongst others.
  • Thumbnail Image
    Item
    Iodide influences the sensitized one-electron photo-oxidation of Tyr and Trp residues by competition reaction
    (2025) Ignasiak, M.; Frąckowiak, K.J.; Fuentes Lemus, Eduardo; Hägglund, P. M.; Gamon, L.; Davies, M. J.; Marczak, Ł.; Marciniak, B.
    3-carboxybenzophenone (CB) is an efficient photosensitizer that can oxidize multiple amino acid side chains in peptides and proteins via electron transfer (ET) reactions yielding various radicals and radical ions. Recombination reactions of these species can yield CBH-adducts and cross-links, whereas secondary reactions can give radicals on other side chains and further products. Prevention of initial radical formation, or interception of intermediate radicals is predicted to modulate the extent of protein damage. Consequently, in this work the effect of iodide ions (I‾) on CB-photosensitized oxidation was investigated with Trp and TyrOH, as these moieties are prone to photooxidation. A scavenging effect of I‾ on the formation of TyrO• radicals was readily detected in kinetic experiments using laser flash photolysis, whilst effects on TrpN• radical formation remain ambiguous (due to overlap of the absorptions of transient absorption spectra of TrpN• and CBH• radicals). Addition of I‾ suppresses oxidation of Trp and TyrOH, with this resulting in lower concentrations of di-Trp, di-Tyr and adducts with CBH, without formation of additional products involving I‾. The effect of I‾ was also analysed for a model protein – lysozyme – with a protective effect observed against loss of activity on illumination with CB. Multiple products were identified, including adducts of CBH to Trp, TyrOH or Met. The formation of crosslinks arising from CB-mediated photo-oxidation of lysozyme was limited in the presence of I‾. Together these data indicate that I‾ modulates photodamage induced by CB to peptide and protein targets.