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Abstract-The rate of reaction of trace metal ions is an important consideration when studying the chemistry of trace metals in natural waters. The application of speciation models to natural water systems requires knowledge of kinetics if reactions are slow. Most bioassay and toxicity tests conducted in static and flow-through systems have not taken reaction kinetics into account. Therefore, results from these studies may overestimate the toxicity in the receiving waters. In the present study, the kinetics of the interaction of Cu(II) with humic acid (HA) and its influence on the toxicity of copper to Ceriodaphnia dubia were investigated by both chemical kinetic studies using a copper ion selective electrode and bioassay tests using a continuous flow-through bioassay system. A two-ligand site with first-order rate constants model gave a very good description of experimental kinetic data of the change of free Cu 2ϩ concentration. Average k 1 was 1.85/h and average k 2 was 0.094/h. Bioassay tests indicated that different reaction times of copper with HA solution produced different toxic effects to organisms. We determined the hydrodynamic characteristics of the bioassay chambers to better describe the exposure of the organisms to free Cu 2ϩ . The bioassays supported the free ion activity model that the bioavailability and therefore toxicity of copper was directly correlated to the free Cu 2ϩ concentration rather than to the total copper concentration. It was further shown that conventional chemical kinetics can be used to predict the toxicity of copper in these bioassays. This study supports the importance of considering reaction kinetics when studying the chemistry of trace metals in natural waters.

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The development of high specific surface area amidoxime-based polymeric (H-ABP) fibers presents a new technology for the synthesis of highly efficient adsorbents for uranium extraction from seawater (UES), thus opening a whole new means of nuclear fuel production from the ocean.

A large area and controllable synthesis of well-aligned CN x nanotubes with a high content of nitrogen (xE9%) was carried out by pyrolyzing metal phthalocyanine on an n-type Si(100) substrate. The diameters of the CN x nanotubes range widely from 20 to 200 nm, and the lengths range from 1 to 100 µm. The impressive bamboolike CN x nanotubes consist of a few uniform, small, and well-ordered compartments. Investigation on morphology and elemental composition of the CN x nanotubes suggests that the overall tube morphology depends strongly on the nitrogen concentration. The higher the N content, the more compartmentalized of nanotubes become, which results in the formation of more curved CN x nanotubes. Our studies show that three different types of N atoms can be present in these materials. These are "pyridinic", "pyrrolic", and "graphitic" nitrogen with binding energies of 398.1, 401.0, and 405.1 eV, respectively. Field emission measurements suggest that the CN x nanotubes began to emit electrons at an electric field of 1.5 V/µm, and current densities of 80 µA/cm 2 have been realized at an applied field as low as 2.6 V/µm. Doping carbon nanotubes with N enhances their electron-conducting properties because of the presence of additional lone pairs of electrons that act as donors with respect to the delocalized π system of the hexagonal framework. The controllable synthesis of well-aligned CN x nanotubes with high N ratio may open a route to improve the field emission properties of nanotubes.

The amyloid precursor protein (APP) undergoes sequential cleavages to generate various polypeptides, including the amyloid-␤ protein (A␤), which forms amyloid plaques in Alzheimer's disease (AD), secreted APP␣ (sAPP␣) which enhances memory, and the APP intracellular domain (AICD), which has been implicated in the regulation of gene transcription and calcium signaling. The ␤-site APP cleaving enzyme 1 (BACE1) cleaves APP in an activity-dependent manner to form A␤, AICD, and secreted APP␤. Because this neural activity was shown to diminish synaptic transmission in vitro [Kamenetz F, Tomita T, Hsieh H, Seabrook G, Borchelt D, Iwatsubo T, Sisodia S, Malinow R (2003) Neuron 37:925-937], the prevailing notion has been that this pathway diminishes synaptic function. Here we investigated the role of this pathway in vivo. We studied transgenic mice overproducing APP that do not develop AD pathology or memory deficits but instead exhibit enhanced spatial memory. We showed enhanced synaptic plasticity in the hippocampus that depends on prior synaptic activity. We found that the enhanced memory and synaptic plasticity are abolished by the ablation of one or both copies of the BACE1 gene, leading to a significant decrease in AICD but not of any other APP cleavage products. In contrast to the previously described negative effect of BACE1-mediated cleavage of APP on synaptic function in vitro, our in vivo work indicates that BACE1-mediated cleavage of APP can facilitate learning, memory, and synaptic plasticity.transgenic ͉ learning A myloid precursor protein (APP) undergoes proteolysis at ␣-, ␤-, ␥-, and -secretase sites to release amino-terminal, internal, and carboxyl-terminal polypeptides, including APP intracellular domain (AICD) [another name for carboxyl-terminal fragment (CTF )] (Fig. 1a). Activity-related regulation of APP cleavage has been proposed at the ␣-and ␤-secretase sites (1, 2), suggesting a physiological role of APP and APP cleavage in the brain. The activation of M1 and M3 muscarinic acetylcholine receptors stimulates ␣-secretase activity and releases secreted APP␣ (sAPP␣) (1), which has been reported to enhance synaptic plasticity and memory (3, 4). Synaptic activity triggers the regulated cleavage of APP through another pathway, by way of ␤-site APP cleaving enzyme 1 (BACE1), followed by ␥-and -secretase, releasing amyloid-␤ protein (A␤) (2, 5) and AICD. Genetic ablation of APP, BACE1, or presenilin-1, the catalytic component of the ␥-and -secretase complexes, profoundly reduces or eliminates A␤ and AICD production and can lead to impaired memory in mice (6-9). Although the molecular basis of impaired memory in mice lacking APP, BACE1, or presenilin-1 has not been defined, the ablation studies implicate a possible role for A␤ or AICD in normal brain function.Here we address the neuronal function of APP and its cleavage products by characterizing transgenic mice that over express APP but do not develop Alzheimer-like pathology or memory deficits. In mice expressing different amounts of BACE1, we found that...

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