Comparing Branched versus Straight-chained Monoamide Extractants for Actinide Recovery

Separations of used nuclear fuel at the engineered scale have generally been completed using the Plutonium Uranium Redox Extraction (PUREX) process. The PUREX process uses tributyl phosphate (TBP) as an extractant to recover uranium and plutonium. While the TBP extractant has proven effective at recovering U and Pu at the engineered scale, TBP is potentially vulnerable to third phase formation and TBP degradation products (monobutyl and dibutyl phosphoric acids) which can complicate recovery of extracted metals from the organic phase. An alternative class of extractants, monoamides, has been considered for applications in thorium and uranium fuel cycles. When compared to TBP, monoamides tend to have higher separation factors for U or Pu from fission products, structural materials, and Th. This review summarizes the literature that explores actinide separations using monoamides by assessing the physiochemical properties between a broader library of branched and straight-chain monoamides than considered in previous reviews. An emphasis is placed on fine-tuning the selectivity of branched monoamides.     

On nonlinear stability of general undercompressive viscous shock waves

We study the nonlinear stability of general undercompressive viscous shock waves. Previously, the authors showed stability in a special case when the shock phase shift can be determined a priori from the total mass of the perturbation, using new pointwise methods. By examining time invariants associated with the linearized equations, we can now overcome a new difficulty in the general case, namely, nonlinear movement of the shock. We introduce a coordinate transformation suitable to treat this new aspect, and demonstrate our method by analyzing a model system of generic type. We obtain sharp pointwise bounds andL ^p behavior of the solution for allp, 1p.     

A non-affine network model for polymer melts

In this paper, a network model of polymer melts is proposed in which network junction points move non-affinely. In this non-affine motion, junction points follow particle paths as seen by an observer rotating at the fluid element's net rigid-rotation rate. The speed at which junction points move is reduced as the network segments near their maximum extensions. In order to maintain a frame invariant model, it is necessary that the vorticity be decomposed into two portions, such that, = _R + _D . The deformational vorticity, _D , arises from shear deformation and is frame invariant while the rigid vorticity, _R , is frame dependent. A constitutive equation based on this finitely extensible network strand (FENS) motion is developed. The model illustrates how rotations that cause changes in the relative orientation of a fluid element with its surroundings can be incorporated into a constitutive equation using the deformational vorticity. The FENS model predicts a shear-thinning viscosity, and the Trouton viscosity predicted by the model is finite for all elongation rates. Finally, stochastic simulation results are presented to justify a mathematical approximation used in deriving the constitutive equation.     

Database diversity assessment: New ideas, concepts, and tools

We present some new ideas for characterizing and comparing largechemical databases. The comparison of the contents of large databases is nottrivial since it implies pairwise comparison of hundreds of thousands ofcompounds. We have developed methods for categorizing compounds into groupsor series based on their ring-system content, using precalculatedstructure-based hashcodes. Two large databases can then be compared bysimply comparing their hashcode tables. Furthermore, the number of distinctring-system combinations can be used as an indicator of database diversity.We also present an indepen- dent technique for diversity assessment calledthe saturation diversity approach. This method is based on picking as manymutually dissimilar compounds as possible from a database or a subsetthereof. We show that both methods yield similar results. Since the twomethods measure very different properties, this probably says more about theproperties of the databases studied than about the methods.     

Conformational changes in a photosensory LOV domain monitored by time-resolved NMR spectroscopy

Phototropins are light-activated kinases from plants that utilize light-oxygen-voltage (LOV) domains as blue light photosensors. Illumination of these domains leads to the formation of a covalent linkage between the protein and an internally bound flavin chromophore, destabilizing the surrounding protein and displacing an alpha-helix from its surface. Here we use a combination of spectroscopic tools to monitor the kinetic processes that spontaneously occur in the dark as the protein returns to the noncovalent ground state. Using time-resolved two-dimensional (2D) NMR methods, we measured the rate of this process at over 100 independent sites throughout the protein, establishing that regeneration of the dark state occurs cooperatively within a 1.6-fold range of observed rates. These data agree with other spectroscopic measurements of the kinetics of protein/FMN bond cleavage and global conformational changes, consistent with these processes experiencing a common rate-limiting step. Arrhenius analyses of the temperature dependence of these rates suggest that the transition state visited during this regeneration has higher energy than the denatured form of this protein domain despite the fact that there is no global unfolding of the domain during this process.     

The heterogeneity of the glycosylation of alpha-1-acid glycoprotein between the sera and synovial fluid in rheumatoid arthritis

Alpha-1-acid glycoprotein (AGP) is a plasma glycoprotein produced by the liver that undergoes increased production and altered glycosylation in several physiological and pathological conditions including rheumatoid arthritis. To date, although present in the synovial fluid of rheumatoid arthritis patients, there has been no evidence for the separate extra-hepatic production of AGP. This study indicates that there could be a localized production of AGP in rheumatoid synovial fluid by demonstrating that the glycosylation patterns of AGP differed between the serum and synovial fluid in the same rheumatoid patient. Serum AGP was largely composed of fucosylated tri- and tetra-antennary oligosaccharide chains while the synovial fluid contained mainly bi-antennary chains that were fucosylated to a lesser extent. This structural heterogeneity of glycosylation resulted in functional diversity; serum but not synovial AGP is able to inhibit binding to the cell adhesion molecule E-selectin through expression of antigen sialyl Lewis X.     

DNA-based photonic logic gates: AND,NAND, and INHIBIT

Conventional microprocessors use elementary logic gates to perform complex computational tasks. Mimicking such computational processes using purely molecular systems has been limited in most cases by the lack of design generality or potential addressability of existing molecular logic gates. Herein we report that by employing the universal recognition properties of DNA simple photonic logic gates can be created that are capable of AND, NAND, and INHIBIT logic operations.     

Building functionalized peptidomimetics: new electroauxiliaries and the use of a chemical oxidant for introducing N-acyliminium ions into peptides

[reaction: see text] The removal of electroauxiliaries from peptide substrates with chemical oxidants has been examined as a method for inserting N-acyliminium ions into the peptides. To this end, it was found that both 4-methoxyphenyldimethylsilyl and 2,4-dimethoxyphenyldimethylsilyl electroauxiliaries were readily cleaved with the use of ceric ammonium nitrate. Of the two groups, the 2,4-dimethoxyphenyldimethylsilyl electroauxiliary was the most labile under the oxidative conditions. The oxidation reactions were shown to be compatible with the use of a solid-phase substrate.     

A photopatternable pentacene precursor for use in organic thin-film transistors

We demonstrate that modifying pentacene to incorporate an acid-labile moiety into its molecular structure leads to a new precursor that can be easily deposited, photopatterned, and processed via wet-chemical methods to produce organic semiconducting devices exhibiting good electrical characteristics. Acidic conditions produced by ultraviolet illumination of a co-deposited photoacid generator greatly accelerate the local conversion of this N-sulfinyl-tert-butylcarbamate pentacene adduct back to pentacene. Photopatterned thin-film transistors exhibit carrier mobilities in excess of 0.1 cm2 V-1 s-1, making this an attractive precursor for fabrication of large-area organic electronics via solution-phase methods.     

An asymmetric synthesis of both enantiomers of the indole alkaloid deplancheine

We report a novel, facile and asymmetric approach to both enantiomers of the indole alkaloid deplancheine from a readily available, nonracemic chiral template. The natural product and its antipode are isolated with >95% ee.