Quenching of Singlet Molecular Oxygen, O₂(¹Δ_g), by Dipyridamole and Derivatives

Abstract

Dipyridamole (DIP) is known for its vasodilating and antiplatelet activity, exhibiting also a potent antioxidant effect, strongly inhibiting lipid peroxidation. This effect has been studied in mitochondria and a correlation between the DIP derivatives' structure, the ability to bind to micelles and biological activity has been suggested. In the present work, the quenching of singlet molecular oxygen, O(2)((1)Delta(g)), by DIP and RA47 and RA25 derivatives was analyzed in acetonitrile (ACN) and aqueous acid solutions. Laser flash photolysis excitation of methylene blue (MB) was made at 532 nm and monomol light emission of O(2)((1)Delta(g)) was monitored at 1270 nm. Bimolecular quenching constants in ACN are consistent with an efficient physical quenching, presenting values a bit lower than the diffusion limit (k(t) = 3.4-6.8 x 10(8) M(-1 )s(-1)). The quenching process probably occurs via reversible charge transfer with the formation of an exciplex. Calculation of DeltaG(et) associated with O(2)((1)Delta(g)) quenching corroborates with uncompleted electron transfer. In aqueous acid solutions (pH = 3.0), the k(t) values for DIP and derivatives are 20-fold smaller when compared with ACN. The electrochemical properties of DIP in ACN are characterized by two consecutive one-electron processes with half-wave oxidation potentials of 0.30 and 0.67 V vs saturated calomel electrode (SCE). However, in an aqueous acid medium, a single oxidation wave is observed involving a two-electron process (0.80 V vs SCE). Therefore, O(2)((1)Delta(g)) quenching is consistent with electrochemical data.

Antimicrobial mechanisms behind photodynamic effect in the presence of hydrogen peroxide

“…A cuvette containing 30 μM of MB in a deutered (D 2 O) solution or D 2 O plus H 2 O 2 solution was irradiated using a Nd:YAG laser (Surelite III, Continuum, Santa Clara, USA) at λ = 532 nm (pulse-energy of 30 mJ and pulse-length of 10 ns). The transient emission of singlet oxygen phosphorescence was accumulated and integrated over 20 pulses by a fluorimeter linked to an infrared photomultiplier tube 30. A D 2 O solution was used to enhance the lifetime of singlet oxygen and therefore increase its detection by the equipment.…”

“…The transient emission of singlet oxygen phosphorescence was accumulated and integrated over 20 pulses by a fluorimeter linked to an infrared photomultiplier tube. 30 A D 2 O solution was used to enhance the lifetime of singlet oxygen and therefore increase its detection by the equipment.…”

Biosilicate® and low-level laser therapy improve bone repair in osteoporotic rats

“…These effects are known to increase the synthesis of DNA, RNA and cell‐cycle regulatory proteins, therefore promoting cell proliferation (Renno et al , 2007). In vitro studies using osteoblastic cells showed that LLLT is capable of increasing mitochondrial activity (Renno et al , 2009), osteoblast DNA and RNA synthesis, bone nodule formation (Trelles and Mayayo 1987), osteocalcin and osteopontin gene expression and ALP activity (Oliveira et al , 2007). Also, the LLLT has demonstrated to be able of accelerating the process of fracture repair in rabbits and rats, increasing the callus volume and bone mineral density (Stein et al , 2005).…”

Novel (E)-1-(pyrrole-2-yl)-3-(aryl)-2-(propen-1-one) derivatives as efficient singlet oxygen quenchers: kinetics and quantum chemical calculations

“…Many heterocyclic compounds also act as quenchers of singlet oxygen. [45][46][47] The interest in obtaining this type of heterocyclic chalcone derivatives is due to their versatility as starting materials in the synthesis of a series of heterocyclic compounds. 48 However, a,b-unsaturated systems in combination with substituted aromatic rings with electron releasing groups (ERGs) and heterocyclic rings such as pyrrole (6 pe À in a 5-membered ring) can inuence the antioxidant properties of ).…”