The adsorption and photolysis of the herbicide bensulfuron-methyl [2-(4, 6-dimethoxypyrimidm-2-carbamoylsulfamoyl)-o-toluic acid methyl ester] on homoionic Na+-, Ca2+- and Fe3+-montmorillonite and kaolinite clays were studied. The Freundlich adsorption coefficient, Kf, measured from isotherms on clays followed the order Na+ < Ca2+ < Fe3+. Montmorillonite showed a greater adsorptive capacity than kaolinite. Analysis of Fourier transform infrared spectra of bensulfuron-methyl adsorbed on clay suggested probable bonding interactions between bensulfuron-methyl and homoionic clays. The photolysis rate of herbicide adsorbed on homoionic clay surfaces was quite slow to its free state and decreased in the order Na+ > Ca2+ > Fe3+, indicating that adsorption may have prevented photolysis.

The newly developed herbicide buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadizol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} was studied with respect to its interaction with soils and homoionic clay minerals and its response to irradiation with ultraviolet light. Results showed that it could enter the interlamellar spaces of swelling clays such as smectite. Isothermic adsorption studies indicated that Cu+2-smectite adsorbed more buthidazole than Cu+2-kaolinite. The Cu+2-clay adsorption isotherm fitted the Langmuir model. The effect of exchangeable cations on adsorption was not significant in soils of high organic matter content. Bioassay studies indicated that buthidazole's phytotoxicity was not decreased in either clays or in organic soils. Infrared spectroscopic studies showed the coordination of buthidazole with Cu+2 through C=O Cu interaction with buthidazole resulted in a ligand-to-metal ratio to 1:1. Protonation of buthidazole occurred in Al+3-and H+-smectite. The herbicide was labile to UV-light irradiation at 254 nm but not at 366 nm. The photoconversion indicated a first-order reaction. The photolytic product(s) included the –N=C=O structure. Copper(II) ions, which form complexes, retarded photolysis of buthidazole in UV-light, but the Ca+2 ion, which is unable to form complexes, did not.

Norflurazon applied for weed control in cotton, as well as some other herbicides, sometimes persists in soil from one growing season to the next at levels phytotoxic to the following crop. Dissipation modes of norflurazon were characterized by using 14C-labeled herbicides for adsorption, mobility, photolysis, and volatility studies to aid in the prediction of conditions influencing herbicide carryover problems. A direct soil-counting technique modified for use in these studies yielded a norflurazon recovery as high as 83% of the applied radioactivity. Relative mobility of the herbicides on soil thin-layer chromatography plates was fluometuron ≥ atrazine > norflurazon. Norflurazon adsorption increased and mobility decreased as soil organic matter and clay content increased. Considerable upward movement of norflurazon and atrazine occurred in subirrigated columns containing herbicide-treated Hebert silt loam. Upward movement in excess of 5 cm occurred in 10 days and 8 weeks for atrazine and norflurazon, respectively. Photolysis and volatilization studies with norflurazon and atrazine revealed low volatilization but significant photolytic losses for norflurazon when herbicide-treated soil-coated slides were exposed to ultraviolet or sunlight. After 98 h atrazine volatilization was greater and photolysis in sunlight less than that observed for norflurazon. Laboratory studies showing upward movement of norflurazon and atrazine, in conjunction with dissipation losses occurring at the soil surface, suggested that losses of norflurazon and atrazine are facilitated by movement in capillary water referred to as the “wick” effect.

Aminocyclopyrachlor (AMCP) is a newly developed synthetic auxin herbicide for broadleaf weed control in turfgrass systems. AMCP has been observed to undergo rapid photodecomposition in shallow water when exposed to sunlight. Most herbicide applications on golf courses occur during the morning when dew is still present on the turfgrass canopy. These conditions could result in efficacy loss if photolysis occurred while AMCP is suspended in dew droplets. Research was conducted to determine the effect of ambient moisture on AMCP efficacy. AMCP (79 and 105 g ae ha−1), aminopyralid (280 g ae ha −1), and two AMCP granular formulations (84 g ha−1) were applied to dew-covered (WET) and dew-excluded (DRY) ‘Tifway' bermudagrass plots. Herbicide treatments applied to WET plots had greater visually rated bermudagrass injury than respective treatments applied to DRY plots at 7 and 21 d after treatment (DAT), with the exception of aminopyralid at 21 DAT. Normalized difference vegetative index on turfgrass quality complemented visual ratings, indicating greater turfgrass quality reductions when applied to WET vs. DRY plots. These results indicate that AMCP applications made to dew-covered turfgrass can increase herbicidal efficacy, and no significant losses due to photodegradation were observed.

Dissipation of imidazolinone herbicides imazaquin and imazethapyr under no-till field conditions was not affected by straw mulch level (1,300, 3,600, or 5,900 kg/ha) in either of 2 yr of field data. Half-lives averaged 7 d for imazaquin and 8 d for imazethapyr. Chlorimuron half-lives averaged 5 d. Imazaquin and imazethapyr residues did not injure corn (Zea mays) the growing season following application. Injury from chlorimuron to corn planted the next year was greatest where applications were made to the highest straw level, reducing corn yield 6%. In laboratory experiments, uniformly cut wheat (Triticum aestivum) straw placed over sand intercepted all three herbicides equally. Herbicide interception was 16, 43, 69, and 89% for straw levels of 840, 1,680, 3,360, and 6,720 kg/ha, respectively. In the laboratory, simulated rainfall removed more imazaquin and imazethapyr from straw than chlorimuron, and approximately 10% of the applied imazaquin or imazethapyr and 20% of the applied chlorimuron remained on the straw after application of 1.0 cm of water. Imazaquin and imazethapyr dissipated 59 and 20%, respectively, during a 7-d incubation period in the greenhouse. Imazaquin dissipation was equal between sand and straw, whereas imazethapyr dissipation was primarily from sand. Chlorimuron did not dissipate from either straw or sand. This indicated that chlorimuron, a sulfonylurea, was more stable than either imidazolinone under these conditions.

Herbicides applied to container plants in nurseries are transported in runoff water to on- and off-site ponds and retention basins. This study was conducted to determine biotic and abiotic effects on isoxaben dissipation in model flow-through retention basins to maximize aqueous isoxaben degradation. Field studies were conducted in 1999 and 2000 to evaluate the effects of gravel and pine bark amendments and water retention times on isoxaben persistence in holding basins. In 1999, total isoxaben discharge into flow-through gravel-filled basins was greater than isoxaben losses from gravel and nongravel basins in which water was retained. Photodegradation appeared to be greater in basins without gravel, indicating that gravel protected isoxaben from photolysis. Further studies determined the effect of water retention time and the presence of aged pine bark amendment on isoxaben discharge from basins. Isoxaben discharge level was reduced when water retention time was increased from 3 to 5 d. In the 3-d retention time treatment, added pine bark reduced peak isoxaben discharge by 45% and total isoxaben by 53% at 14 d after treatment. In treatments containing pine bark within the retention basins, isoxaben was released over a longer period of time. No differences were observed in 5-d water retention time treatments with and without pine bark. Analysis of gravel from isoxaben-treated retention basins indicated the presence of several genera of bacteria including Pseudomonas, Arthrobacter, and Cellulomonas. Some isolates of Pseudomonas, Rahnella, Methobacterium, and Paenibacillus from the basins grew on M9 medium with isoxaben as the sole carbon and energy source, indicating their ability to metabolize isoxaben. Results indicate that retention basins are helpful in reducing isoxaben levels before release or reuse of runoff water from a container nursery, and that retention time of runoff water in basins is the most important factor in reducing isoxaben discharge.

The ORGANIC experiment on EXPOSE-R spent 682 days outside the International Space Station, providing continuous exposure to the cosmic-, solar- and trapped-particle radiation background for fourteen samples: 11 polycyclic aromatic hydrocarbons (PAHs) and three fullerenes. The thin films of the ORGANIC experiment received, during space exposure, an irradiation dose of the order of 14 000 MJ m−2 over 2900 h of unshadowed solar illumination. Extensive analyses were performed on the returned samples and the results compared to ground control measurements. Analytical studies of the returned samples included spectral measurements from the vacuum ultraviolet to the infrared range and time-of-flight secondary ion mass spectrometry. Limited spectral changes were observed in most cases pointing to the stability of PAHs and fullerenes under space exposure conditions. Furthermore, the results of these experiments confirm the known trend in the stability of PAH species according to molecular structure: compact PAHs are more stable than non-compact PAHs, which are themselves more stable than PAHs containing heteroatoms, the last category being the most prone to degradation in the space environment. We estimate a depletion rate of the order of 85 ± 5% over the 17 equivalent weeks of continuous unshadowed solar exposure in the most extreme case tetracene (smallest, non-compact PAH sample). The insignificant spectral changes (below 10%) measured for solid films of large or compact PAHs and fullerenes indicate a high stability under the range of space exposure conditions investigated on EXPOSE-R.

For the first time the kinetic rate constants of the UV photolysis of polyynes C6H2, C8H2, C10H2, C12H2 and C14H2 under rigorously inert atmosphere have been determined in three different solvents: n-hexane, n-heptane and decalin. First- or pseudofirst-order kinetics appear suitable to describe the photolysis of these molecules and k values in the range between 3.0×10−3 s−1 and 4.6×10−3 s−1 have been determined. The unique exception is represented by C6H2 which photolyses more slowly with k=3.2×10−4 s−1. Two different UV sources have been used in the present study: a low-pressure mercury lamp having a monochromatic emission at 253.7 nm and a medium-to high-pressure lamp with a continuous emission between 222 nm and 580 nm. The results are of interest in the understanding, and also the modelling, of the fate of polyynes released by carbon-rich stars in the interstellar medium or the polyynes released by comets in their active phase.

The photolysis of dilute solutions of octacyclosulphur or hexacyclosulphur in n-hexane with 253.6 nm UV radiation produces S and possibly S2. The ‘ring-opening’ yields of these sulphur molecules range from 0.2 to 0.7. When the hydrogen end-capped polyyne C10H2 is irradiated in n-hexane, it transforms into unidentified products with a quantum yield of 3×10−5. When octacyclosulphur is added to the solution, the yield rises to 7×10−3. The putative sulphur-bearing product(s) could not be identified. It is suggested that sulphur-bearing molecules might be formed in astronomical settings by reactions of carbon molecules having triple or double C—C bonds with photolytically produced S and/or S2.

Little is known about the functional connectivity between astrocytes in the CNS. To explore this issue we photo-released glutamate onto a single astrocyte in murine hippocampal slices and imaged calcium responses. Photo-release of glutamate causes a metabotropic glutamate receptor (mGluR)-dependent increase in internal calcium in the stimulated astrocyte and delayed calcium elevations in neighboring cells. The delayed elevation in calcium was not caused by either neuronal activity following synaptic transmission or by glutamate released from astrocytes. However, it was reduced by flufenamic acid (FFA), which is consistent with a role for adenosine triphosphate (ATP) release from astrocytes as an intercellular messenger. Exogenous ligands such as ATP (1 µM) increased the number of astrocytes that were recruited into coupled astrocytic networks, indicating that extracellular accumulation of neurotransmitters modulates neuronal excitability, synaptic transmission and functional coupling between astrocytes.

We report on non-particulate titania photoelectrodes with a unique highly-ordered nanotube-array architecture prepared by an anodization process that enables precise control over array dimensions. Under 320–400 nm illumination titania nanotube-array photoanodes, pore size 110 nm, wall thickness 20 nm, and 6 μm length, generate hydrogen by water photoelectrolysis at a normalized rate of 80 mL/W•hr, to date the most efficient titania-based photoelectrochemical device, with a conversion efficiency of 12.25%. The highly-ordered nanotubular architecture allows for superior charge separation and charge transport, with a calculated quantum efficiency of nearly 100% for incident photons with energies larger than the titania bandgap.

A fast-scanning dichroic microspectrophotometer was used to trace products of rhodopsin photolysis (metarhodopsins I/II/III and later) in structurally intact amphibian rod outer segments (ROSs) and metabolically active rods. The instrument allows the recording of absorbance spectra with a time resolution better than 1 s, and to discriminate between products with similar absorbance spectra that differ with respect to the orientation of their chromophore in the photoreceptor membrane. We demonstrate that metarhodopsin III is in a pH-reversible equilibrium with metarhodopsin II and that the metarhodopsin III chromophore is orientated with respect to the membrane plane even more strictly than the 11-cis retinal in “dark” rhodopsin. This indicates that all-trans retinal in metarhodopsin III is still attached to its native binding site on opsin. The kinetic scheme of the decay of metarhodopsins is presented in which metarhodopsin III lies in a shunt pathway from metarhodopsin II to retinal. Formation of metarhodopsin III was detected at bleaches as low as ≈ 3%, contrary to previous reports that it is not formed at below 10% bleaches. Another product that is spectrally similar to metarhodopsin III, termed P440, appears at later stages of photolysis as the result of the decay of metarhodopsin II and metarhodopsin III. The chromophoric group in P440 is orientated preferentially across the disk membrane. The final product(s) in isolated ROS, where the reduction of retinal to retinol is blocked, consists of a mixture of a free retinal and retinal possibly attached to different binding sites in the membrane. In metabolically active rods the later products are quickly converted to retinol. We conclude that metarhodopsin III represents a specific conformational state of metarhodopsin where the chromophoric binding site is still occupied by all-trans retinal. Hence, the formation and decay of metarhodopsin III may be limiting for the rate of rhodopsin regeneration and photoreceptor dark adaptation.