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Results for “Photochemistry and Photobiology”

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USGS1993

Aquatic photolysis: photolytic redox reactions between goethite and adsorbed organic acids in aqueous solutions

Photolysis of mono and di-carboxylic acids that are adsorbed onto the surface of the iron oxyhydroxide (goethite) results in an oxidation of the organic material and a reduction from Fe(III) to Fe(II) in the iron complex. There is a subsequent release of Fe2+ ions into solution. At constant light flux and constant solution light absorption, the factors responsible for the degree of photolytic reaction include: the number of lattice sites that are bonded by the organic acid; the rate of acid readsorption to the surface during photolysis; the conformation and structure of the organic acid; the degree of oxidation of the organic acid; the presence or absence of an ??-hydroxy group on the acid, the number of carbons in the di-acid chain and the conformation of the di-acid. The ability to liberate Fe(III) at pH 6.5 from the geothite lattice is described by the lyotropic series: tartrate>citrate> oxalate > glycolate > maleate > succinate > formate > fumarate > malonate > glutarate > benzoate = butanoate = control. Although a larger amount of iron is liberated, the series is almost the same at pH 5.5 except that oxalate > citrate and succinate > maleate. A set of rate equations are given that describe the release of iron from the goethite lattice. It was observed that the pH of the solution increases during photolysis if the solutions are not buffered. There is evidence to suggest the primary mechanism for all these reactions is an electron transfer from the organic ligand to the Fe(III) in the complex. Of all the iron-oxyhydroxide materials, crystalline goethite is the least soluble in water; yet, this study indicates that in an aqueous suspension, iron can be liberated from the goethite lattice. Further, it has been shown that photolysis can occur in a multiphase system at the sediment- water interface which results in an oxidation of the organic species and release of Fe2+ to solution where it becomes available for further reaction. ?? 1993.

Journal of Photochemistry and Photobiology A: Chem↗

USGS2007

TiO 2 as a photocatalyst for control of the aquatic invasive alga, Cladophora, under natural and artificial light

Cladophora, a nuisance and invasive, filamentous algae (Chlorophyta), massively accumulates along the shores of the lower Great Lakes each summer causing great economic damage and compromising recreational opportunity and perhaps public health. In vitro experiments showed that Cladophora samples were physically and biologically degraded when subjected to TiO 2 -mediated photocatalysis. For the most successful photocatalytic process, TiO 2 was immobilized on a glass surface and used in combination with either sunlight or artificial UV light. The loss of vital algal pigments was monitored using UV–vis spectrophotometry, and cell structural changes were determined by microscopic observation. Cladophora, in the presence of TiO 2 -covered glass beads, experienced a loss of chloroplast pigments after 2 h of UV lamp light irradiation. In a separate experiment, sunlight exposure over 4 days (&sim;24 h) resulted in the complete oxidative degradation of the green chloroplast pigments, verified by the UV spectra of the algal extracts. These results suggest that TiO 2 , mobilized on sunlit silicates may be useful in controlling growth and survival of this alga in the Great Lakes, thus mitigating many of the economic, aesthetic ecological impacts of this invasive alga.

Journal of Photochemistry and Photobiology A: Chem↗

USGS2008

The aqueous photolysis of ethylene glycol adsorbed on geothite

Suspensions of goethite (α-FeOOH) were photolyzed in aerated ethylene glycol-water solutions at pH 6.5, with ultraviolet light in the wavelength range300–400 nm. Under these conditions, formaldehyde and glycolaldehyde were detected as photoproducts. Quantum yields of formaldehyde production ranged from 1.9 7times; 10 -5 to 2.9 × 10 -4 over the ethylene glycol concentration range of 0.002-2.0 mol/ℓ, and gave evidence that the reaction occurred at the goethite surface. Quantum yields of glycolaldehyde were 20% less than those of formaldehyde, and displayed a concentration-dependent relationship with ethylene glycol similar to that of formaldehyde. Immediately after photolysis, Fe 2+ was measured to be 4.6 × 10 -7 mol/ℓ in an aerated suspension containing 1.3 mol/ℓ ethylene glycol, and 8.5 × 10 -6 mol/ℓ in the corresponding deoxygenated suspension. Glycolaldehyde was not generated in the deoxygenated suspensions. These results are consistent with a mechanism involving the transfer of an electron from an adsorbed ethylene glycol molecule to an excited state of Fe 3+ (Iron[III]) in the goethite lattice, to produce Fe 2+ and an organic cation. In a series of reactions involving O 2 , FeOOH, and Fe 2+ , the organic cation decomposes to form formaldehyde and the intermediate radicals “OH and” CH 2 OH. OH reacts further with ethylene glycol in the presence of O 2 to yield glycolaldehyde. Aqueous photolysis of ethylene glycol sorbed onto goethite is typical of reactions that can occur in the aquatic environment.

Photochemistry and Photobiology↗

USGS2001

Resistance of a lizard (the green anole, Anolis carolinensis ; Polychridae) to ultraviolet radiation-induced immunosuppression

The green anole ( Anolis carolinensis ) is the most northerly distributed of its Neotropical genus. This lizard avoids a winter hibernation phase by the use of sun basking behaviors. Inevitably, this species is exposed to high doses of ambient solar ultraviolet radiation (UVR). Increases in terrestrial ultraviolet-B (UV-B) radiation secondary to stratospheric ozone depletion and habitat perturbation potentially place this species at risk of UVR-induced immunosuppression. Daily exposure to subinflammatory UVR (8 kJ/m 2 /day UV-B, 85 kJ/m 2 /day ultraviolet A [UV-A]), 6 days per week for 4 weeks (total cumulative doses of 192 kJ/m 2 UV-B, 2.04 × 10 3 kJ/m 2 UV-A) did not suppress the anole's acute or delayed type hypersensitivity (DTH) response to horseshoe crab hemocyanin. In comparison with the available literature UV-B doses as low as 0.1 and 15.9 kJ/m 2 induced suppression of DTH responses in mice and humans, respectively. Exposure of anoles to UVR did not result in the inhibition of ex vivo splenocyte phagocytosis of fluorescein labeled Escherichia coli or ex vivo splenocyte nitric oxide production. Doses of UV-B ranging from 0.35 to 45 kJ/m 2 have been reported to suppress murine splenic/peritoneal macrophage phagocytosis and nitric oxide production. These preliminary studies demonstrate the resistance of green anoles to UVR-induced immunosuppression. Methanol extracts of anole skin contained two peaks in the ultraviolet wavelength range that could be indicative of photoprotective substances. However, the resistance of green anoles to UVR is probably not completely attributable to absorption by UVR photoprotective substances in the skin but more likely results from a combination of other factors including absorption by the cutis and absorption and reflectance by various components of the dermis.

Photochemistry and Photobiology↗