Spatial and temporal patterns of dissolved nitrogen and phosphorus in surface waters of a multi-land use basin.

Research on relationships between dissolved nutrients and land-use at the watershed scale is a high priority for protecting surface water quality. We measured dissolved nitrogen (DN) and ortho-phosphorus (P) along 130 km of the Calapooia River (Oregon, USA) and 44 of its sub-basins for 3 years to test for associations with land-use. Nutrient concentrations were analyzed for spatial and seasonal patterns and for relationships with land-use and stream discharge. Ortho-P and DN were higher in lower-elevation sub-basins dominated by poorly drained soils and agricultural production compared with higher-elevation sub-basins dominated by well-drained soils and forests. Eight lower basins had at least one sample period with nitrate-N > 10 mg L(-1). The Calapooia River had lower concentrations of dissolved nutrients compared with lower sub-basins, often by an order of magnitude. Dissolved organic N represented a greater proportion of DN in the upper forested sub-basins. Seasonal nutrient concentrations had strong positive correlations to the percent of a sub-basin that was managed for agriculture in all seasons (p values ≤ 0.019) except summer. Results suggest that agricultural lands are contributing to stream nutrient concentrations. However, poorly drained soils in agricultural areas may also contribute to the strong relationships that we found between dissolved nutrients and agriculture.

Hydrology Predominates Over Harvest History and Landscape Variation to Control Water Quality and Disinfection Byproduct Formation Potentials in Forested Pacific Coast Watersheds.

Despite the global importance of forested watersheds as sources of drinking water, few studies have examined the effects of forestry on drinking water treatability. Relatively little is known about how the interaction between landscape variation and flow impacts source water quality and what this interaction means for drinking water treatability. To address this knowledge gap, we examined variability in sediments, dissolved organic matter, and disinfection byproduct formation potentials (DBP-FPs) across a range of flow conditions in four small watersheds with contrasting forest harvest histories and soil characteristics on Vancouver Island. Storm event-driven change in streamflow was the primary driver of water quality and DBP-FPs at our sites, with greater changes during stormflow (e.g., a 3-fold increase in dissolved organic carbon concentrations) than those across contrasting watersheds. Flow-driven changes in water quality and DBP-FPs were not significantly different across watersheds with different harvest histories; muted responses may be attributed to widespread second growth forests (i.e., recent harvesting effects may be confounded by historical harvest), forestry practices (e.g., slash burning), or soils with low organic carbon storage. This study suggests that variation in hydrology predominates over harvest history and soil characteristics to drive water quality and DBP-FPs on the east coast of Vancouver Island.

Evaluation of a carbonic anhydrase mimic for industrial carbon capture.

Zinc(II) cyclen, a small molecule mimic of the enzyme carbonic anhydrase, was evaluated under rigorous conditions resembling those in an industrial carbon capture process: high pH (>12), nearly saturated salt concentrations (45% K2CO3) and elevated temperatures (100-130 °C). We found that the catalytic activity of zinc cyclen increased with increasing temperature and pH and was retained after exposure to a 45% w/w K2CO3 solution at 130 °C for 6 days. However, high bicarbonate concentrations markedly reduced the activity of the catalyst. Our results establish a benchmark level of stability and provide qualitative insights for the design of improved small-molecule carbon capture catalysts.

Toward a small molecule, biomimetic carbonic anhydrase model: theoretical and experimental investigations of a panel of zinc(II) aza-macrocyclic catalysts.

A panel of five zinc-chelated aza-macrocycle ligands and their ability to catalyze the hydration of carbon dioxide to bicarbonate, H(2)O + CO(2) → H(+) + HCO(3)(­), was investigated using quantum-mechanical methods and stopped-flow experiments. The key intermediates in the reaction coordinate were optimized using the M06-2X density functional with aug-cc-pVTZ basis set. Activation energies for the first step in the catalytic cycle, nucleophilic CO(2) addition, were calculated from gas-phase optimized transition-state geometries. The computationally derived trend in activation energies was found to not correspond with the experimentally observed rates. However, activation energies for the second, bicarbonate release step, which were estimated using calculated bond dissociation energies, provided good agreement with the observed trend in rate constants. Thus, the joint theoretical and experimental results provide evidence that bicarbonate release, not CO(2) addition, may be the rate-limiting step in CO(2) hydration by zinc complexes of aza-macrocyclic ligands. pH-independent rate constants were found to increase with decreasing Lewis acidity of the ligand-Zn complex, and the trend in rate constants was correlated with molecular properties of the ligands. It is suggested that tuning catalytic efficiency through the first coordination shell of Zn(2+) ligands is predominantly a balance between increasing charge-donating character of the ligand and maintaining the catalytically relevant pK(a) below the operating pH.

Conjugation to Biocompatible Dendrimers Increases Lanthanide T2 Relaxivity of Hydroxypyridinone (HOPO) Complexes for Magnetic Resonance Imaging (MRI).

Magnetic resonance imaging (MRI) contrast agents represent a worldwide billion-dollar market annually. While T1 relaxivity enhancement contrast agents receive greater attention and a significantly larger market share, the commercial potential for T2 relaxivity enhancing contrast agents remains a viable diagnostic option due to their increased relaxivity at high field strengths. Improving the contrast and biocompatibility of T2 MRI probes may enable new diagnostic prospects for MRI. Paramagnetic lanthanides have the potential to decrease T1 and T2 proton relaxation times, but are not commercially used in MRI diagnostics as T2 agents. In this article, oxygen donor chelates (hydroxypyridinone, HOPO, and terephthalamide, TAM) of various lanthanides are demonstrated as biocompatible macromolecular dendrimer conjugates for the development of T2 MRI probes. These conjugates have relaxivities up to 374 mm-1s-1 per dendrimer, high bioavailability, and low in vitro toxicity.

Conjugation effects of various linkers on Gd(III) MRI contrast agents with dendrimers: optimizing the hydroxypyridinonate (HOPO) ligands with nontoxic, degradable esteramide (EA) dendrimers for high relaxivity.

One essential requirement for more sensitive gadolinium-based MRI contrast agents is to slow the molecular tumbling of the gadolinium(III) ion, which increases the gadolinium's relaxivity (i.e., its ability to speed up the NMR relaxation of nearby water molecules). One route to this is through conjugation to high-molecular-weight polymers such as dendrimers. In this work, amine-functionalized TREN-bis(1,2-HOPO)-TAM-ethylamine and TREN-bis(1-Me-3,2-HOPO)-TAM-ethylamine ligands have been synthesized and attached to biocompatible 40 kDa esteramide (EA)- and poly-l-lysine (PLL)-based dendrimers capable of binding up to eight gadolinium complexes. These conjugates have T(1) relaxivities of up to 38.14 ± 0.02 mM(-1) s(-1) per gadolinium at 37 °C, corresponding to relaxivities of up to 228 mM(-1) s(-1) per dendrimer molecule. This relaxivity expressed on a "per Gd" basis is several times that of the small-molecule complexes and an order of magnitude higher than that of current commercial agents. Because of their high performance and low toxicity, these macromolecules may constitute an attractive complement to currently available gadolinium(III)-based contrast agents.

Synthesis and properties of star-comb polymers and their doxorubicin conjugates.

We describe a six-step synthesis to water-soluble doxorubicin (DOX)-loaded biodegradable PEGylated star-comb polymers with favorable pharmaceutical properties by atom transfer radical polymerization (ATRP) starting with a commercially available tripentaerythritol carrying eight reactive sites. The low polydispersity polymers degrade in a stepwise manner into lower molecular weight (MW) fragments by 15 days at 37 °C at either pH 5.0 or pH 7.4. The half-life of the star-comb polymers in blood is dependent upon the molecular weight; the 44 kDa star-comb has a t(1/2, ß) of 30.5 ± 2.1 h, which is not significantly changed (28.6 ± 2.7 h) when 6.6 wt % of DOX is attached to it via a pH-sensitive hydrazone linker. The star-comb polymers have low accumulation in organs but a high accumulation in C26 flank tumors implanted in Balb/C mice. The hydrodynamic diameter of polymer-DOX conjugates measured by dynamic light scattering increases from 8 to 35 to 41 nm as the loading is increased from 6.6 to 8.4 to 10.2 wt %. Although there is no significant difference in the t(1/2, ß) or in the accumulation of polymer-DOX in C-26 tumors, the uptake of polymer in the spleen is significantly higher for polymers with DOX loadings greater than 6.6 wt %. Polymer accumulation in other vital organs is independent of the DOX loading. The facile synthesis, biodegradability, long circulation time, and high tumor accumulation of the attached drug suggests that the water-soluble star-comb polymers have promise in therapeutic applications.

Design, synthesis, and biological evaluation of a robust, biodegradable dendrimer.

PEGylated dendrimers are attractive for biological applications due to their tunable pharmacokinetics and ability to carry multiple copies of bioactive molecules. The rapid and efficient synthesis of a robust and biodegradable PEGylated dendrimer based on a polyester-polyamide hybrid core is described. The architecture is designed to avoid destructive side reactions during dendrimer preparation while maintaining biodegradability. Therefore, a dendrimer functionalized with doxorubicin (Dox) was prepared from commercial starting materials in nine, high-yielding linear steps. Both the dendrimer and Doxil were evaluated in parallel using equimolar dosage in the treatment of C26 murine colon carcinoma, leading to statistically equivalent results with most mice tumor-free at the end of the 60 day experiment. The attractive features of this dendritic drug carrier are its simple synthesis, biodegradability, and versatility for application to a variety of drug payloads with high drug loadings.

Nitrate-nitrogen, land use/land cover, and soil drainage associations at multiple spatial scales.

Managing non-point-source pollution of water requires knowledge of land use/land cover (LULC) influences at altering watershed scales. To gain improved understanding of relationships among LULC, soil drainage, and dissolved nitrate-N dynamics within the Calapooia River Basin in western Oregon, we selected 44 watersheds ranging in size between 3 and 33 km(2) for monthly synoptic sampling of surface water quality between October 2003 and September 2004. Seasonal associations were examined between dissolved nitrate-N and proportion of woody vegetation or poorly drained soils at differing scales (10, 20, 30, 60, 90, 150, 300 m, and entire watershed), which we defined as influence zones (IZs), surrounding stream networks. Correlations between nitrate-N and proportion woody vegetation or poorly drained soil at each IZ were analyzed for differences using the Hotelling-Williams test. We observed negative correlations (r = -0.81 to -0.94) between nitrate-N and proportion of woody vegetation during winter and spring. Poorly drained soils had positive correlations (r = 0.63-0.87) with nitrate-N. Altering the scale of analysis significantly changed correlations between nitrate-N and woody vegetation, with IZs <150 m being stronger than the watershed scale during winter. However, absolute differences in correlation values were small, indicating minimal ecological consequence for significant differences among scales. In contrast, nitrate-N correlations with poorly drained soil were stronger at the watershed scale than the 10- through 90-m IZs during winter and spring, and absolute differences were sufficient to suggest that scale is ecologically important when determining associations between dissolved nitrate-N and poorly drained soils.

Encapsulated liquid sorbents for carbon dioxide capture.

Drawbacks of current carbon dioxide capture methods include corrosivity, evaporative losses and fouling. Separating the capture solvent from infrastructure and effluent gases via microencapsulation provides possible solutions to these issues. Here we report carbon capture materials that may enable low-cost and energy-efficient capture of carbon dioxide from flue gas. Polymer microcapsules composed of liquid carbonate cores and highly permeable silicone shells are produced by microfluidic assembly. This motif couples the capacity and selectivity of liquid sorbents with high surface area to facilitate rapid and controlled carbon dioxide uptake and release over repeated cycles. While mass transport across the capsule shell is slightly lower relative to neat liquid sorbents, the surface area enhancement gained via encapsulation provides an order-of-magnitude increase in carbon dioxide absorption rates for a given sorbent mass. The microcapsules are stable under typical industrial operating conditions and may be used in supported packing and fluidized beds for large-scale carbon capture.

Improving T1 and T2 magnetic resonance imaging contrast agents through the conjugation of an esteramide dendrimer to high-water-coordination Gd(III) hydroxypyridinone complexes.

Commercial gadolinium magnetic resonance imaging (MRI) contrast agents are limited by low relaxivity (r1) and coordination to only a single water molecule (q = 1). Consequently, gram quantities of these agents must be injected to obtain sufficient diagnostic contrast. In this study, MRI contrast agents for T(1) and T2 relaxivity were synthesized using hydroxypyridinone and terephthalamide chelators with mesityl and 1,4,7-triazacyclononane capping moieties. When covalently conjugated to a highly biocompatible esteramide dendrimer, T2 relaxation rates up to 52 mm(-1) s(-1) and T1 relaxation rates up to 31 mm(-1) s(-1) per gadolinium were observed under clinically relevant conditions. These values are believed to be brought about by using a dendritic macromolecule to decrease the molecular tumbling time of the small molecule complexes. These agents also show high aqueous solubility and low toxicity in vitro. In this study we report six new compounds: three discrete complexes and three dendrimer conjugates.

Analysis of Lanthanide Complex Dendrimer Conjugates for Bimodal NIR and MRI Imaging.

Advances in clinical diagnostic instrumentation have enabled some imaging modalities to be run concurrently. For diagnostic purposes, multimodal imaging can allow for rapid location and accurate identification of a patient's illness. The paramagnetic and near Infra-red (NIR) properties of Dy(III) and Yb(III) are interesting candidates for the development of bimodal NIR and magnetic resonance imaging (MRI) contrast agents. To enhance their intrinsic bimodal properties, these lanthanides were chelated using the hexadentate-all-oxygen-donor-ligand TREN-bis-(1-Me)-3,2-HOPO-TAM-NX (NX, where X = 1, 2 or 3) and subsequently conjugated to the esteramide dendrimer (EA), to improve bioavailability, solubility, and relaxivity. Of these new complexes synthesized and evaluated, DyN1-EA had the largest ionic T(1) relaxivity, 7.60 mM(-1) s(-1), while YbN3-EA had the largest ionic T(2) relaxivity with a NIR quantum yield of 0.17 % when evaluated in mouse serum. This is the first Yb(III) bimodal NIR/T(2) MRI contrast agent of its kind evaluated.