EuII-containing complexes were studied with respect to properties relevant to their use as contrast agents for magnetic resonance imaging. The influences of molecular parameters and field strength on relaxivity were studied for a series of EuII-containing cryptates and their adducts with β-cyclodextrins, poly-β-cyclodextrins, and human serum albumin. Solid- and solution-phase characterization of EuII-containing complexes is presented that demonstrates the presence of inner-sphere molecules of water. Additionally, relaxivity, water-exchange rate, rotational correlation time, and electronic relaxation time were determined using variable-temperature 17O-NMR, nuclear magnetic relaxation dispersion, and electron paramagnetic resonance spectroscopic techniques. We expect that our results will be instrumental in the design of future EuII-based contrast agents.
Specific pore size distributions of synthesized methylsilsesquioxane-based network materials stem from a combination of the solvation of monomers and growing oligomers, as well as miscibility of water in tested solvents; enabling specific analyte uptake materials.
AbstractThe “greening” of silicon chemistry is fundamentally important for the future of the field. Traditional methods used to make silicon-based materials rely on carbon rich processes that are highly energy intensive, cause pollution, and are unsustainable. Researchers have taken up the challenge of developing new chemistries to circumvent the difficulties associated with traditional silicon material synthesis. Most of this work has been in the conversion of the “green” carbon neutral biogenic silica source rice hull ash (RHA, ~85 % silica) into useful silicon building blocks such as silica’s, silicon, and alkoxysilanes by using the inherently higher surface area and reactivity of RHA to sidestep the low reactivity of mined silica sources. This is a review of the work that has been done in the area of developing more environmentally benign methods for the synthesis and use of silicon containing materials to eliminate the negative impact on the environment.
A 2,6-bis(2-benzimidazolyl)
pyridine-linked silsesquioxane-based
semi-branched polymer was synthesized, and its photophysical and metal-sensing
properties have been investigated. The polymer is thermally stable
up to 285 °C and emits blue in both solid and solution state.
The emission of the polymer is sensitive to pH and is gradually decreased
and quenched upon protonation of the linkers. The initial emission
color is recoverable upon deprotonation with triethylamine. The polymer
also shows unique spectroscopic properties in both absorption and
emission upon long-term UV irradiation, with red-shifted absorption
and emission not present in a simple blended system of phenylsilsesquioxane
and linker, suggesting that a long-lived energy transfer or charge
separated state is present. In addition, the polymer acts as a fluorescence
shift sensor for Zn(II) ions, with red shifts observed from 464 to
528 nm, and reversible binding by the introduction of a competitive
ligand such as tetrahydrofuran. The ion sensing mechanism can differentiate
Zn(II) from Cd(II) by fluorescence color shifts, which is unique because
they are in the same group of the periodic table and possess similar
chemical properties. Finally, the polymer system embedded in a paper
strip acts as a fluorescent chemosensor for Zn(II) ions in solution,
showing its potential as a solid phase ion extractor.
Dissociation rates of five Eu II -containing cryptates in water were measured using UV-visible spectroscopy and murexide at pH 6.5, 7, 7.5, 8, and 9. Murexide was used as a coordinating dye for Eu II . Results for a known cryptate were within experimental error of the value obtained using other methods, and enabled measurement of other cryptates. This validation of the use of murexide to study the dissociation of Eu II -containing cryptates enables use with other complexes of Eu II .
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