Solid-phase peptide synthesis has been applied to the preparation of phosphonate-derivatized oligoproline assemblies containing two different RuII polypyridyl chromophores coupled via “click” ...chemistry. In water or methanol the assembly adopts the polyproline II (PPII) helical structure, which brings the chromophores into close contact. Excitation of the assembly on ZrO2 at the outer RuII in 0.1 M HClO4 at 25 °C is followed by rapid, efficient intra-assembly energy transfer to the inner RuII (k EnT = 3.0 × 107 s–1, implying 96% relative efficiency). The comparable energy transfer rate constants in solution and on nanocrystalline ZrO2 suggest that the PPII structure is retained when bound to ZrO2. On nanocrystalline films of TiO2, excitation at the inner RuII is followed by rapid, efficient injection into TiO2. Excitation of the outer RuII is followed by rapid intra-assembly energy transfer and then by electron injection. The oligoproline/click chemistry approach holds great promise for the preparation of interfacial assemblies for energy conversion based on a family of assemblies having controlled compositions and distances between key functional groups.
Three ethylene adducts to CuAlCl(4) have been characterized by single crystal and/or powder X-ray diffraction, (13)C, (27)Al and (63)Cu MAS NMR and diffuse reflectance UV-vis spectroscopy. ...(C(2)H(4))(2)CuAlCl(4), a = 7.1274(5) b = 12.509(1) c = 11.997(3) beta = 91.19 degrees, Pc, Z = 4; alpha-(C(2)H(4))CuAlCl(4), a =7.041(3) b = 10.754(8) c =11.742(9) beta = 102.48(6), P2(1), Z = 4 and beta-(C(2)H(4))CuAlCl(4), a = 7.306(2), b = 16.133(3), c = 7.094(1), Pna2(1), Z = 4. Up to 2 equiv of ethylene ( approximately 200 cm(3)/g relative to stp) are sorbed at room temperatures and pressures as low as 300 Torr. The ethylene ligands are bound to copper (I) primarily through a sigma-interaction, because the AlCl(4)(-) groups also bound to copper prevent any significant pi-back-bonding. The olefin binding is reversible and has been characterized by gravimetric and volumetric adsorption analysis and by time and pressure resolved synchrotron powder X-ray diffraction. Comparison of the parent crystal structure to those of the adduct phases provide an atomistic picture of the sorptive reconstruction reactions. These are proposed to proceed by a classic substitution mechanism that is directed by the van der Waals channels of the parent crystalline lattice.
Dichloroacetic acid (DCA) is formed from microbial action on the herbicide trichloroacetic acid. It is also used as a surfactant, disinfectant, and pharmaceutical agent. Therefore, it is a common ...contaminant of surface waters. The phytotoxicity of various concentrations of neutralized DCA on three species of aquatic macrophytes was investigated during a 21 day exposure period. Results indicated that of the two Myriophyllum species tested, M. sibericum was the more sensitive. Of the several endpoints studied, plant length and wet mass were the most sensitive. No differences in plant pigments, including chlorophyll-a, chlorophyll-b, and carotenoids were noted. Results indicated that levels of DCA found in the environments of Europe and North America, which are several orders of magnitude less than those used in these studies, is not a toxic risk for aquatic plants.
Monochloroacetic acid (MCA) is an environmental contaminant due its use in herbicide production and as a byproduct of chlorinating agents used for water disinfection. The effect of various ...concentrations of MCA in microcosms containing three species of aquatic macrophytes was investigated. Plants of the two Myriophyllum species were exposed for intervals up to 28 days. When MCA was introduced, Lemna gibba was introduced for three weeks of monitoring. L. gibba and M. spicatum were the least and most sensitive species, respectively. Effective concentrations were within one order of magnitude of each other for the species. The similarity of the toxic effects in the Myriophyllum species indicated that toxicity in one species predicted it in the other. Results showed that at concentrations commonly found in the environment, none of the species would be adversely affected.
In outdoor aquatic microcosms containing the rooted macrophytes, Myriophyllum spicatum and M. sibiricum, the toxicity of a binary mixture of trichloroacetic acid (TCA) and trifluoroacetic acid (TFA) ...was examined. The nominal TCA and TFA concentrations were 0.1, 1.0, 3.0, and 10 mg/l each. Plants were sampled 1 d prior to dosing and then at 2, 7, 14, 21, 35, and 49 d post-dosing. The plants exhibited clear signs of stress immediately after exposure to the mixture, as indicated by a decrease in pigment concentrations. Most biological endpoints, however, did not show any significant changes from control with exposure to the TCA/TFA mixture. Based on measured environmental concentrations, TCA/TFA mixtures were determined to represent no acute risk of toxicity to the plants.
Interdisciplinary time series observations are important for understanding and predicting ocean variability on time scales from seconds to decades. Plans are being made to implement open ocean ...observatories at key sites in the world ocean (e.g., OceanSITES and ORION). The Bermuda Testbed Mooring (BTM), located southeast of Bermuda (BATS site), and the HALE-ALOHA (H-A) mooring, north of Hawaii (HOT site) are prototypes for autonomous sampling interdisciplinary open ocean observatories. Both moorings are located in the deep sea (over 4500 m water depth) and provide fundamental measurements of meteorological, physical, biogeochemical, biological, and optical variables. Many of the present national and international ocean observatory plans have benefited from BTM and H-A research and development. Both programs provide stimuli for many forward-looking ideas concerning ocean technologies and the synergistic use of observations and models. New measurement systems and scientific results from the BTM and H-A projects are leading to improved sampling relevant to global biogeochemical cycling, ecosystem dynamics, and climate change as well as to improved predictive modeling in these areas along with air-sea interaction and hurricanes
Recent studies on the stages of change model Joekes, Katherine; Elderen, Thérèse Van; Schreurs, Karlein ...
Journal of health psychology,
01/2007, Letnik:
12, Številka:
1
Journal Article
The formation of aromatic and ketonic products from the treatment of 17β-acetoxy-3α,4α-epoxy-5α-hydroxyandrostane and its 3β,4β-epoxy-5β-hydroxy isomer with hydrobromic acid in glacial acetic acid is ...discussed in the context of the diaxial and diequatorial opening of the epoxide.
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