Voracious planktonic hydroids: unexpected predatory impact on a coastal marine ecosystem

Hydroids are typically attached, benthic cnidarians that feed on a variety of small prey. During sampling on Georges Bank in spring 1994, we found huge numbers of hydroids suspended in the plankton. They fed on young stages of copepods that are an important prey for fish, as well as on young fish themselves. Two independent methods were used to estimate feeding rates of the hydroids; both indicate that the hydroids are capable of consuming from 50% to over 100% of the daily production of young copepods. These results suggest that hydroids can have a profound effect on the population dynamics of zooplankton and young fish on Georges Bank

Liquid-core polymer nanocapsules prepared using flash nanoprecipitation

Hypothesis: Nanocapsules, consisting of a solid shell and a liquid core, are an interesting class of materials with numerous applications and various methods of synthesis. One common method for synthesis of nanoparticles is flash nanoprecipitation. For a multicomponent system consisting of a liquid (n-hexadecane) and solid (polystyrene), we hypothesize that nanocapsules will form from droplets created by the turbulent mixing in the nanoprecipitation process. We anticipate n-hexadecane molecules should phase-separate more rapidly from the non-solvent, thus becoming the core, while the more slowly diffusing polystyrene forms the shell. Additionally, we predict that the amount of both n-hexadecane and polystyrene used in creating these nanocapsules will influence capsule size. Experiments: Using flash nanoprecipitation, we synthesized nanocapsules of a polystyrene shell and liquid core of n-hexadecane. We varied the concentrations of both polystyrene and n-hexadecane and characterized the resulting dispersions using dynamic light scattering and scanning electron microscopy. Findings: Our experiments demonstrate that flash nanoprecipitation can be employed to create nanocapsules with radii ranging from 50 to 200 nm, with radii of the n-hexadecane cores between 35 and 175 nm and polystyrene shells with thickness ranging from 7 to 62 nm. We used various methods of analysis to confirm this core/shell morphology and applied a droplet model to explain the dependence of particle size on initial concentrations of n-hexadecane and polystyrene

Magnetic Nanobeads as Potential Contrast Agents for Magnetic Resonance Imaging

Metal-oxo clusters have been used as building blocks to form hybrid nanomaterials and evaluated as potential MRI contrast agents. We have synthesized a biocompatible copolymer based on a water stable, nontoxic, mixed-metal-oxo cluster, Mn₈Fe₄O₁₂(L)₁₆(H₂O)₄, where L is acetate or vinyl benzoic acid, and styrene. The cluster alone was screened by NMR for relaxivity and was found to be a promising <i>T</i>₂ contrast agent, with <i>r</i>₁ = 2.3 mM^–1 s^–1 and <i>r</i>₂ = 29.5 mM^–1 s^–1. Initial cell studies on two human prostate cancer cell lines, DU-145 and LNCap, reveal that the cluster has low cytotoxicity and may be potentially used <i>in vivo</i>. The metal-oxo cluster Mn₈Fe₄(VBA)₁₆ (VBA = vinyl benzoic acid) can be copolymerized with styrene under miniemulsion conditions. Miniemulsion allows for the formation of nanometer-sized paramagnetic beads (∼80 nm diameter), which were also evaluated as a contrast agent for MRI. These highly monodispersed, hybrid nanoparticles have enhanced properties, with the option for surface functionalization, making them a promising tool for biomedicine. Interestingly, both relaxivity measurements and MRI studies show that embedding the Mn₈Fe₄ core within a polymer matrix decreases <i>r</i>₂ effects with little effect on <i>r</i>₁, resulting in a positive <i>T</i>₁ contrast enhancement

Solution and Solid State Structural Chemistry of Th(IV) and U(IV) 4‑Hydroxybenzoates

Organic ligands with carboxylate functionalities have been shown to affect the solubility, speciation, and overall chemical behavior of tetravalent metal ions. While many reports have focused on actinide complexation by relatively simple monocarboxylates such as amino acids, in this work we examined Th­(IV) and U­(IV) complexation by 4-hydroxybenzoic acid in water with the aim of understanding the impact that the organic backbone has on the solution and solid state structural chemistry of thorium­(IV) and uranium­(IV) complexes. Two compounds of the general formula [An₆O₄(OH)₄(H₂O)₆(4-HB)₁₂]·<i>n</i>H₂O [An = Th (<b>Th-1</b>) and U (<b>U-1</b>); 4-HB = 4-hydroxybenzoate] were synthesized via room-temperature reactions of AnCl₄ and 4-hydroxybenzoic acid in water. Solid state structures were determined by single-crystal X-ray diffraction, and the compounds were further characterized by Raman, infrared, and optical spectroscopies and thermogravimetry. The magnetism of <b>U-1</b> was also examined. The structures of the Th and U compounds are isomorphous and are built from ligand-decorated oxo/hydroxo-bridged hexanuclear units. The relationship between the building units observed in the solid state structure of <b>U-1</b> and those that exist in solution prior to crystallization as well as upon dissolution of <b>U-1</b> in nonaqueous solvents was investigated using small-angle X-ray scattering, ultraviolet–visible optical spectroscopy, and dynamic light scattering. The evolution of U solution speciation as a function of reaction time and temperature was examined. Such effects as well as the impact of the ligand on the formation and evolution of hexanuclear U­(IV) clusters to UO₂ nanoparticles compared to prior reported monocarboxylate ligand systems are discussed. Unlike prior reported syntheses of Th and U­(IV) hexamers where the pH was adjusted to ∼2 and 3, respectively, to drive hydrolysis, hexamer formation with the HB ligand appears to be promoted only by the ligand