Singlet Oxygen Reactions with Flavonoids. A Theoretical – Experimental Study

Abstract

Detection of singlet oxygen emission, λmax = 1270 nm, following laser excitation and steady-state methods were employed to measure the total reaction rate constant, kT, and the reactive reaction rate constant, kr, for the reaction between singlet oxygen and several flavonoids. Values of kT determined in deuterated water, ranging from 2.4×107 M−1s−1 to 13.4×107 M−1s−1, for rutin and morin, respectively, and the values measured for kr, ranging from 2.8×105 M−1s−1 to 65.7×105 M−1s−1 for kaempferol and morin, respectively, being epicatechin and catechin chemically unreactive. These results indicate that all the studied flavonoids are good quenchers of singlet oxygen and could be valuable antioxidants in systems under oxidative stress, in particular if a flavonoid-rich diet was previously consumed. Analysis of the dependence of rate constant values with molecular structure in terms of global descriptors and condensed Fukui functions, resulting from electronic structure calculations, supports the formation of a charge transfer exciplex in all studied reactions. The fraction of exciplex giving reaction products evolves through a hydroperoxide and/or an endoperoxide intermediate produced by singlet oxygen attack on the double bond of the ring C of the flavonoid.

Morin Flavonoid Adsorbed on Mesoporous Silica, a Novel Antioxidant Nanomaterial

“…The sum of the physical quenching ( k q ) and chemical reaction ( k R ) constants correspond to the total rate constant ( k T ) [38, 39]. In this work, k T values for the deactivation of singlet oxygen by AMSNPs-MOR dispersed in D 2 O were obtained by measuring the first-order rate of singlet oxygen of luminescence decay in the presence and absence of morin (Eq 11).…”

Towards Screening the Enhance of Luminescence Properties of Modified Tannins in Alkaline Solution by a Fenton-Like Reaction

“…Occurrence of intermediary peroxide dianion form (ToxO 2 2-, Eq. (20)) is due to the chemical type addition of O 2 (a 1 Δ g ) by fl avonol (Tox) mainly responsible for oxygen attack on C-ring, with C4-oxy-group and C2-C3 double bond [32][33][34][35].…”

Flavonoids as a scaffold for development of novel anti-angiogenic agents: An experimental and computational enquiry

“…Recent experimental study involving detection of oxygen emission using laser excitation and steady-state methods elucidated few requirements for flavonoid's ability to react with ROS. One of the major requirements was the presence of 2-3 double bond in C-ring [76]. Careful structural observation of compounds that did not respond in DPPH assay indicate complete absence of such double bond; indeed, the lack of such structural requirement in case of 7HFN, silibinin, naringenin and 4 0 MF might be a possible reason for absence of antioxidant abilities.…”