Glyphosate (N-(phosphonomethyl)glycine) is the most widely used herbicide on earth. A simple assay to quantify glyphosate concentrations in environmental samples was developed as part of an interdisciplinary effort linking introductory laboratory courses in chemistry, biology, and microbiology. In this 3 h laboratory experiment, students used UV−vis spectroscopy to quantify glyphosate in prepared unknowns and supernatants from glyphosate-treated soil samples. Regression analysis indicated that the assay is linear up to 20.0 ppm, making it particularly useful for detection of low levels of glyphosate in environmental samples. The assay can be used to quantify the activity of glyphosate-degrading soil microorganisms by comparing glyphosate levels between autoclaved and nonautoclaved soil slurries.
Single-crystal X-ray diffraction
studies of pristine and γ-irradiated
Ca2[UO2(O2)3]·9H2O reveal site-specific atomic-scale changes during the solid-state
progression from a crystalline to X-ray amorphous state with increasing
dose. Following γ-irradiation to 1, 1.5, and 2 MGy, the peroxide
group not bonded to Ca2+ is progressively replaced by two
hydroxyl groups separated by 2.7 Å (with minor changes in the
unit cell), whereas the peroxide groups bonded to Ca2+ cations
are largely unaffected by irradiation prior to amorphization, which
occurs by a dose of 3 MGy. The conversion of peroxide to hydroxyl
occurs through interaction of neighboring lattice H2O molecules
and ionization of the peroxide O–O bond, which produces two
hydroxyls, and allows isolation of the important monomer building
block, UO2(O2)2(OH)2
4–, that is ubiquitous in uranyl capsule polyoxometalates.
Steric crowding in the equatorial plane of the uranyl ion develops
and promotes transformation to an amorphous phase. In contrast, γ-irradiation
of solid Li4[(UO2)(O2)3]·10H2O results in a solid-state transformation to
a well-crystallized peroxide-free uranyl oxyhydrate containing sheets
of equatorial edge and vertex-sharing uranyl pentagonal bipyramids
with likely Li and H2O in interlayer positions. The irradiation
products of these two uranyl triperoxide monomers are compared via
X-ray diffraction (single-crystal and powder) and Raman spectroscopy,
with a focus on the influence of the Li+ and Ca2+ countercations. Highly hydratable and mobile Li+ yields
to uranyl hydrolysis reactions, while Ca2+ provides lattice
rigidity, allowing observation of the first steps of radiation-promoted
transformation of uranyl triperoxide.
Seven
novel uranyl sulfate compounds were crystallized by ionothermal
synthesis methods through systematic changes in experimental conditions.
The parameters explored were temperature, soak time, cooling rate,
and reactants, including uranium(VI) salt, a uranium(VI) concentration
in the ionic liquid, and the pH by cosolvent addition. The ionic liquid
1-ethyl-3-methylimidazolium ethyl sulfate (EMIm-EtSO4)
was used in each experiment. Although the seven uranyl sulfate compounds
all contained the EMIm organic cation of the ionic liquid, the different
synthetic conditions produced varying uranyl coordination environments
that resulted in discrete crystal structures. The impact of the ionothermal
synthetic conditions on the resulting crystal structures is discussed.
Aqueous solutions of lithium uranyl triperoxide, Li4[UO2(O2)3] (LiUT), were irradiated
with gamma rays at room temperature and found to form the uranyl peroxide
cage cluster, Li24[(UO2)(O2)(OH)]24 (Li–U24). Raman spectroscopy and 18O labeling were used to identify the Raman-active vibrations
of LiUT. With these assignments, the concentration of LiUT was tracked
as a function of radiation dose. A discrepancy between monomer removal
and cluster formation suggests that the reaction proceeds by the assembly
of an intermediate. Non-negative matrix factorization was used to
separate Raman spectra into components and resulted in the identification
of a unique intermediate species. Much of the conversion appears to
be driven by water radiolysis products, particularly the hydroxyl
radical. This differs from the 18O-labeled copper-catalyzed
formation of U24, which progresses at a steady rate with
no observation of intermediates. Li–U24 in solution
decomposes at high radiation doses resulting in a solid insoluble
product similar to Na-compreignacite, Na2(UO2)6O4(OH)6·7H2O,
which contains uranyl oxyhydroxy sheets.
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