A nuclear forensics investigation involving a uranium ore concentrate relies on accurate and precise analysis of impurities. Analytical data defensibility requires the use of reference materials as ...part of quality control. This study presents a compilation of trace element concentration results of the CUP-2 Uranium Ore Concentrate Standard measured by 11 different laboratories. The laboratories employed various dissolution methods, analytical preparation methods, and instrumental platforms. The data presented here contain concentrations of 66 impurities with up to 138 individual data points for each impurity. Consensus values have been assigned to each impurity following a statistical analysis of the data set.
The lowest-observed-adverse-effect and no-observed-adverse-effect concentrations of sarin were determined in soils typical to Canada and Russia. Maximum acceptable concentrations were established to ...be 3.0 × 10
−4
mg kg
−1
for the standard reference soil, 2.0 × 10
−3
mg kg
−1
for prairie soil, and 1.0 × 10
−2
mg kg
−1
for forest soil.
Structural and mechanistic aspects of orthoplatination of acetophenone and benzaldehyde oximes by the platinum(II) sulfoxide and sulfide complexes PtCl2L2 (2, L = SOMe2 (a), rac-SOMePh (b), ...R-SOMe(C6H4Me-4) (c), and SMe2 (d)) to afford the corresponding platinacycles cis-(C,S)-PtII(C6H3-2-CR‘NOH-5-R)Cl(L) (3, R, R‘ = H, Me) have been investigated. The reaction of acetophenone oxime with sulfoxide complex 2a in methanol solvent occurs noticeably faster than with sulfide complex 2d due to the fact that the sulfoxide is a much better platinum(II) leaving ligand than the sulfide. Evidence is presented that the orthoplatination is a multistep process. The formation of unreactive dichlorobis(N-oxime)platinum(II) cations accounts for the rate retardation by excess acetophenone oxime and suggests the importance of pseudocoordinatively unsaturated species for the C−H bond activation by PtII. A comparative X-ray structural study of dimethyl sulfoxide platinacycle 3b (R = R‘ = Me) and its sulfide analogue 3e (R = H, R‘ = Me), as well as of SOMePh complex 3c (R = H, R‘ = Me), indicated that they are structurally similar and a sulfur ligand is coordinated in the cis position with respect to the σ-bound phenyl carbon. The differences concern the Pt−S bond distance, which is notably longer in the sulfide complex 3e (2.2677(11) Å) as compared to that in sulfoxide complexes 3b (2.201(2)−2.215(2) Å) and 3c (2.2196(12) Å). Whereas the metal plane is practically a plane of symmetry in 3b due to the H-bonding between the sulfoxide oxygen and the proton at carbon ortho to the Pt−C bond, an S-bonded methyl of SOMePh and SMe2 is basically in the platinum(II) plane in complexes 3c and 3e, respectively. There are intra- and intermolecular hydrogen bond networks in complex 3b. An interesting structural feature of complex 3c is that the two independent molecules in the asymmetric unit of the crystal reveal an extremely short Pt−Pt contact of 3.337 Å.
Orthometalated aryl oxime complexes cis-(C,S)-PtII(C6H3-2-CMeNOH-5-R)Cl(Me2SO) (1, R = H (a), MeO, Me, F, and Cl) undergo deoxygenation of dimethyl sulfoxide (DMSO) in methanol in the presence of ...HCl to afford the Pt(IV) dimethyl sulfide complexes fac-PtIV(C6H3-2-CMeNOH-5-R)Cl3(Me2S) (2), the composition of which was confirmed by an X-ray structural study of 2a. The mechanism of the deoxygenation coupled with the oxidation of Pt(II) to Pt(IV) was investigated using cyclic voltammetry, UV−vis, and 1H NMR spectrometry techniques at 40−60 °C in the presence of HCl, LiCl, and NaClO4. The conversion of 1 into 2 does not occur intramolecularly and involves two time-resolved phases which were studied independently. The first is the substitution of chloride for DMSO to afford the anionic reactive complexes cis-Pt(C6H3-2-CMeNOH-5-R)Cl2- (1 Cl), which are involved in the acid-promoted interaction with free DMSO in the second phase. The formation of 1 Cl follows the usual two-term rate law k obs1 = k s + k ClLiCl, the k Cl-driven pathway being negligible for the electron-rich complex with R = MeO. Thus-generated complexes 1 Cl, in contrast to their precursors 1, are more susceptible to oxidation, and the irreversible peak for 1 Cl, E(p1), is observed ca. 300 mV more cathodically compared to that of 1. The second phase is acid-catalyzed and at low LiCl concentrations follows the rate expression k obs2H+-1 = k 10‘ + k 10LiCl. The complexes with the electron-withdrawing substituents R react faster, and there is a linear correlation between log k 10 and E(p1). The first-order in the acid is discussed in terms of two kinetically indistinguishable mechanisms involving the rate-limiting either electron transfer from 1 Cl to protonated DMSO (mechanism 1) or insertion of the SO bond of free DMSO into the platinum−hydride bond of the reactive hydride complex of Pt(IV), cis-Pt(C6H3-2-CMeNOH)(H)Cl2, to afford a {Pt−SMe2−OH} fragment. Its protonation by HCl and dissociation of water gives the final product 2 (mechanism 2). 1H NMR evidence is presented for the formation of the hydride species on protonation of a Pt(II) complex, whereas a density functional study of the two mechanisms indicates that mechanism 2 is less energy demanding. The system studied is viewed as a functioning mimetic of the Mo-dependent enzyme DMSO reductase because of several common features observed in catalysis.
Herein, a nuclear forensics investigation involving a uranium ore concentrate relies on accurate and precise analysis of impurities. Analytical data defensibility requires the use of reference ...materials as part of quality control. This study presents a compilation of trace element concentration results of the CUP-2 Uranium Ore Concentrate Standard measured by 11 different laboratories. The laboratories employed various dissolution methods, analytical preparation methods, and instrumental platforms. The data presented here contain concentrations of 66 impurities with up to 138 individual data points for each impurity. Consensus values have been assigned to each impurity following a statistical analysis of the data set.
In a recent international exercise, 10 international nuclear forensics laboratories successfully performed radiochronometry on three low enriched uranium oxide samples, providing 12 analytical ...results using three different parent-daughter pairs serving as independent chronometers. The vast majority of the results were consistent with one another and consistent with the known processing history of the materials. In general, for these particular samples, mass spectrometry gave more accurate and more precise analytical results than decay counting measurements. In addition, the concordance of the
235
U–
231
Pa and
234
U–
230
Th chronometers confirmed the validity of the age dating assumptions, increasing confidence in the resulting conclusions.
The ester cleavage of
R- and
S-isomers
N-CBZ-leucine
p-nitrophenyl ester intermolecularly catalyzed by
R- (
a) and
S-stereoisomers (
b) of the Pd(II) metallacycle Pd(C
6H
4C
∗HMeNMe
2)Cl(py) (
3) ...follows the rate expression
k
obs =
k
o +
k
cat
3, where the rate constants
k
cat equal 25.8 ± 0.4 and 7.6 ± 0.5 dm
3 mol
−1 s
−1 for the
S- and
R-ester, respectively, in the case of
3a, but are 5.7 ± 0.6 and 26.7 ± 0.5 dm
3 mol
−1 s
−1 for the
S- and
R-ester, respectively, in the case of
3b (pH 6.23 and 25°C). Thus, the best catalysis occurs when the asymmetric carbons of the leucine ester and Pd(II) complex are
R and
S, or
S and
R configured, respectively. Molecular modeling suggests that the stereoselection results from the spatial interaction between the CH
2CHMe
2 radical of the ester and the α-methyl group of
3. A hydrophobic/stacking contact between the leaving 4-nitrophenolate and the coordinated pyridine also seems to play a role. Less efficient intramolecular enantioselection was observed for the hydrolysis of
N-t-BOC-
S-metthionine
p-nitrophenyl ester with
R- and
S-enantiomers of Pd(C
6H
4C∗HMeNMe
2)Cl coordinated to sulfur.
Throughout much of their history, enzymes secreted by microorganisms were used in the process of fermentation to produce and preserve food products. Fermented foods such as cheese, yogurt, and bread ...have been crucial to the development of modern civilization. Over time, advances in science and engineering have allowed the isolation of novel enzymes and characterization of their properties. As a result, applications of these biological molecules have increased dramatically in the past three decades as they are used routinely nowadays and form the cornerstone of all major industries of the 20th century. The use of enzymes in the manufacturing industries is not only beneficial for the consumers but it also replaces the use of harsh chemicals detrimental to the environment with green alternatives. In this chapter, we introduce the reader to pioneering omics approaches that aid in the discovery of new enzymes with unique functions or aid in optimizing current ones for higher yield, selectivity, and/or improved usage. Finally, we illustrate some examples of enzymes that were already targeted by molecular bioengineering and refined for commercial applications.
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