Photochemistry of Phytoalexins Containing Phenalenone‐like Chromophores: Photophysics and Singlet Oxygen Photosensitizing Properties of the Plant Oxoaporphine Alkaloid Oxoglaucine^¶

Abstract

Oxoglaucine (OG) is an oxoaporphine alkaloid, which has been linked to plant defense mechanisms. It contains a phenalenone (PN)–like chromophore, which suggests a role as singlet oxygen (1O2) photosensitizer. Indeed, OG is able to photosensitize 1O2 with 100% efficiency in nonpolar environments, similar to PN. However, this efficiency decreases in polar and protic media, although 1O2 is formed in all environments ranging from benzene to water. OG is a rather inefficient 1O2 quencher (kq= 8 × 105M−1 s−1) unlike the related alkaloids boldine and glaucine, for which an antioxidant role has been suggested. The results of this study contribute to the view that plant defense mediated by PN‐like secondary metabolites may have a photochemical component.

Two‐Photon Singlet Oxygen Microscopy: The Challenges of Working with Single Cells

“…when we quantify the total amount of O 2 (a 1 Δ g ) produced per excitation pulse], it is necessary to examine how both the signal and noise levels vary as a function of (1) the time window of data acquisition ( i.e. gate width on the photon counter); and (2) the number of independent laser shots employed in a given “accumulation” (see section). To address these issues, experiments were performed with one‐photon excitation (δ ex = 420 nm) of the sensitizer TMPyP in D 2 O (τΔ= 68 μs).…”

“…3. The instrument consists of three main parts: (1) a pulsed femtosecond (fs) laser system and associated optics that constitute our excitation source; (2) an inverted microscope; and (3) a detector plus related electronics. The names used for the lasers ( i.e.…”

“…For example, there is ample evidence that singlet oxygen is a byproduct of the photosynthetic pathway and that it can have detrimental effects on plant cells exposed to high intensity light (1). Alternatively, singlet oxygen also plays a role in defense mechanisms in both plant (2,3) and animal cells (4). For example, it has been shown that the myeloperoxidase system present in neutrophils can generate singlet oxygen in vitro , and there is evidence that this can occur in vivo as well (4).…”

Photoreduction of Azaoxoisoaporphines by Amines: Laser Flash and Steady‐State Photolysis and Pulse Radiolysis Studies

“…In Ar-saturated acetonitrile solutions containing AOIA, both, the radical anions and radical cations derived from them are generated by the reaction of solvated electrons or solvent radical anions and cations with a substrate (Eqs. [8][9][10][11][12]. On the other hand, in O 2 -saturated solutions only radical cations are formed (Eqs.…”

“…Oxoisoaporphines (OIA) alkaloids have been isolated from different families of plants such as Menispermaceae (1-3). These alkaloids that have been recognized as phototoxic phytoalexins, are synthesized by plants for the defense against pathogen agents or mechanical injuries (4)(5)(6)(7)(8)(9). Due to the planar structure of the oxoisoaporphine derivatives, it is expected that these compounds might intercalate into DNA.…”