Singlet oxygen generation of a natural anthraquinone

COMINI LR .; MARIONI J; NÚÑEZ MONTOYA SC; FERNÁNDEZ I; RIVAROLA V; GARAGIOLA B; BORSARELLI C; CABRERA JL.

Córdoba

Encuentro; XI ENCUENTRO LATINOAMERICANO DE FOTOQUÍMICA Y FOTOBIOLOGÍA.; 2012

Comite Organizador del Evento

Many photosensitizers molecules (PS) possess the ability to interact with triplet molecular oxygen and absorb visible light to produce reactive oxygen species (ROS), such as superoxide anion (O2.-) and singlet molecular oxygen (1O2) by means of different mechanisms: electrons transfer (Type I) and energy transfer (Type II), respectively. Because of this property to generate ROS by photoinduction, these compounds are classified as photodynamic PS [1]. It has been shown that several natural photodynamic PS were bioactive, exhibiting antibiotic, antifungal, antitumoral and antiviral properties, and thus could be used in photodynamic therapy (PDT) [2]. From the aerial parts of Heterophyllaea pustulata Hook f (Rubiáceas, "cegadera"), ten anthraquinone derivatives were isolated [3,4]; and their Type I and/or Type II photosensitizing properties were demonstrated by our research group, as well as their photodynamic antibacterial and anticancer activity in vitro of some of them [5,6]. Continuing the phytochemical studies of this vegetal specie, a new anthraquinone was isolated and identified from its roots: lucidin ω-metil ether (LC), which has demonstrated its ability as PS Type I [7]. In the present work, we report its capability as PS Type II. Therefore, the quantum yield of 1O2 production was determined using a comparative method based on detection of the NIR phosphorescence dynamic emission of 1O2 produced by a pulsed laser excitation. The third harmonic 355 nm from a Q-switched Nd:YAG (Continuum Minilite II) laser, shooting pulses 5 mJ and half-width of 10 ns, was used to excite the AQ and the reference (perinaphthenone), both dissolved in chloroform. The NIR phosphorescence of 1O2 (long de onda max = 1270 nm), previously filtered with a bandpass filter (Spectrogon BP-1260) was obtained in a right angle with a germanium photodiode detector Judson J16TE2-66 G, Peltier cooled to -30ºC. The decay curves of 1O2 phosphorescence vs. incident laser energy were collected with a Tektronix TDS3032B digital oscilloscope and analyzed with the software Microcal Origin 8.0. The quantum yield value of 1O2 production for LC was 0.28 ± 0.03, which is in the range of quantum yield found for other AQs obtained from the aerial parts of this vegetal species. Thus, we confirm its effect as PS type II. Based on this result and in the fact that this AQ also exhibits Type I photosensitizing properties, this compound could be considered as a good candidate for use in PDT.