Karen A. Marley

Sanguinarine, a phototoxic H2O2-producing alkaloid.

Abstract— Sanguinarine chloride, a quaternary salt of a benzophenanthrene alkaloid, was phototoxic to catalase‐deficient strains of Escherichia coli but not to Trichoplusia ni (cabbage looper moth larvae), an insect with high levels of catalase activity. Chemical analyses confirm that sanguinarine is an efficient producer of H2O2. This differential toxicity suggests that the mode of phototoxic action involves production of H2O2 which could be detoxified in many organisms by catalase.

Quenching of singlet oxygen by alkaloids and related nitrogen heterocycles

Abstract Fifteen plant alkaloids and related heterocyclic compounds were tested for their ability to quench singlet oxygen. Most of the compounds showed high activity; brucine and strychnine were especially efficient quenchers. Brucine, at a concentration of ca 2.6 x 10 −5 M, is capable of inactivating half the singlet oxygen molecules it encounters. This quenching may serve in nature to protect plants from the deleterious effects of singlet oxygen or other reactive oxidants.

Ferric-ion-photosensitized damage to DNA by hydroxyl and non-hydroxyl radical mechanisms

Iron(III) and UVA (320-400 nm) light strongly diminished the transforming activity of Haemophilus influenzae DNA in the presence of oxygen. Iron(III) alone in the absence of light had no measurable effect on the transforming activity. The chelating agent ethylenediaminetetraacetic acid (EDTA) conferred virtually complete protection, but hydroxyl radical scavengers (mannitol, methanol, ethanol, isopropanol and dimethyl sulfoxide) inhibited only a small fraction of the inactivation. Treatment of plasmid DNA (pBR322) with iron(III) results in the conversion of the covalently closed circular form of the plasmid to open circles and ultimately to the linear form. Concomitant with the alteration in the conformation of the plasmid, the ability to transform Escherichia coli was reduced. In model systems, iron(III) photoreacted with the DNA backbone causing nicking and double-strand breakage. The results are consistent with a mechanism involving a preliminary complexation of iron(III) by DNA followed by the generation of reactive free radicals other than .OH. We suggest that bound iron, or other UV-absorbing transition metal complexes, may be chromophores capable of causing DNA damage in the long-wave near-UV region.

Surfactant-assisted UV-photolysis of nitroarenes.

Photochemical transformations (lambda-254 nm) of 2,4-dinitrotoluene (2,4-DNT) in aqueous solutions containing the cationic surfactant cetyltrimethylammonium (CTA) and the anionic nucleophile borohydride (BH4-) were investigated. The overall decay rate was enhanced at CTA concentrations above the critical micelle concentration (cmc) when stoichiometric excess BH4- was present in solution. A kinetic model that separates the overall reaction rate into micellar and aqueous pseudo-phase components indicates transformation in micelles is 17 times faster that in the homogeneous water phase under those conditions investigated. Intermediate products were identified by comparing the HPLC retention times and ultraviolet-visible absorption spectra of product peaks to those of analytical standards. 2-Methyl-5-nitroaniline, 4-nitrotoluene, 2-nitrotoluene, 4-methyl-3-nitroaniline, 2,4-diaminotoluene, o-toluidine, 1,3-dinitrobenzene, 3-nitroaniline, p-cresol, and 2,4-diaminophenol were identified as photo-transformation intermediates or products.

A NEW PHOTOPRODUCT FROM FUROCOUMARIN PHOTOLYSIS IN DILUTE AQUEOUS SOLUTION: 5‐FORMYL‐6‐HYDROXYBENZOFURAN

Abstract— This paper presents the analysis and identification of an unstable product previously undescribed from furocoumarin photolysis, 5‐formyl‐6‐hydroxybenzofuran. Reverse‐phase chromatography and solid‐phase extraction techniques allowed its isolation.

Photochemistry in Hoagland's Nutrient Solution

Abstract Atrazine photodegraded (in the absence of plants) in Hoaglands hydroponic medium in sunlight. The medium contained two important solar UV absorbing species, complexed iron and nitrate. Increasing the concentrations of iron or of nitrate resulted in increased rates of atrazine loss. Increasing the concentration of trace elements copper, manganese, and zinc had little effect on the photodegradation rate. The pathway may involve the reaction of hydroxyl radicals produced by the photolysis of nitrate and/or iron with atrazine.

Singlet Oxygen in the Environment

Singlet oxygen (1O2) is produced in the environment almost exclusively by photochemical pathways. Although it can be detected in many environmental compartments, its potential roles in chemical reactions under environmental conditions are not completely understood. For example, in the atmosphere, it is formed at lower elevations (<40km) by photolysis of ozone and by energy transfer to ground-state oxygen from photoexcited donor species. In the ionosphere, 1O2 participates in emission processes that contribute to the airglow, but in the stratosphere and troposphere its importance appears to be negligible. In natural surface waters, it is formed with about 1% efficiency from dissolved humic materials, but its deactivation by water molecules is so rapid that very few chemical reactions are able to compete. Its steady-state concentrations in most natural waters appear to center around 10-13 M. In water bodies polluted by light-absorbing chemicals such as dyestuffs, it is possible that it might be somewhat more important. In hydrophobic environments such as aquatic surface layers, especially those containing aromatic petroleum derivatives, lO2 might play a quite significant role due to its increased concentration and lifetime. Some solid phases, such as plant, soil, and mineral surfaces, could be sites where lO2 is formed, but little is known about its importance; and similar statements could be made about 1O2 in living cells, despite many decades of investigation of the mechanisms of “photodynamic toxicity.”

Sunlight photochlorination and dark chlorination of monoterpenes

Abstract The aqueous chlorination of the monoterpenes camphene, limonene, α-pinene and β-pinene produced complex polychlorinated product mixtures. The extent of chlorination was primarily dependent on pH and light conditions. At pH2 and exposure to sunlight, product mixtures were obtained that had striking similarities to Toxaphene. At higher pH or in the dark, less extensive but still substantial chlorination took place; these lower chlorinated compounds could be mistaken for biologically degraded Toxaphene in environmental samples.

Preparation and photoisomerization of 2-formylcinnamaldehyde in solution

Abstract Naphthalene, in dilute aqueous solution, reacts with ozone to form one or both isomers of 2-formylcinnamaldehyde an equilibrium mixture of the isomers also results upon irradiation of the E-isomer with long wavelength ultraviolet light.