λ -Benzyl-L-Glutamate Graft Copolymers of Cellulose and Poly[Arylene Ether Sulfone]

Macroinitiators with primary amino substituents were synthesized by one of the following techniques: a) cyanoethylation of cellulose followed by diborane reduction to produce aminopropylcellulose, 1; b) nitration, then SnCl₂ reduction of poly(arylene ether sulfone), 5, to produce poly(2-aminoarylene ether sulfone), 2; c) phthalimidation of 5 followed by hydrazinolysis to yield poly(2-aminomethylarylene ether sulfone), 3; and d) LiAlH₄ reduction of poly(cyanophenylene arylene ether) to poly(aminomethylphenylene arylene ether), 4. Heterogeneous grafting of Λ-benzyl-L-glutamate-N-carboxyanhydride, 8, to Polymer 1 resulted in a nonrandom distribution of amino acid residues; α-helical conformations were detected at low BLG-NCA/NH₂ ratios (<5 amino acids). Using molar ratios ranging from 1 to 100 of 8, relative to the amine concentration, grafting to Polymers 3 and 4 was effected in anhydrous THF at room temperature under homogeneous conditions. If reaction times between 24 and 48 h are utilized, high grafting efficiencies (>80%) are obtained. The conformation of the polypeptide chain was evaluated by NMR and infrared spectroscopy. Polypeptides grafted to Polymers 3 and 4 appeared to adopt the expected conformation for the chain length predicted, i.e., a progression from random coil (<8 amino acids) to β-pleated sheet (8–13 amino acids) to α-helix (> 13 amino acids). The benzyl ester functions on the BLG grafts are subject to direct modification with amine nucleophiles; studies with butylamine correlate reaction conditions with extent of ester vs peptide cleavage. In the presence of 1-hydroxybenzotriazole, aminolysis of the ester is favored and conversions to Λ-amides up to 75% without peptide cleavage are achieved.     

The level structure of 184W FROM THE β− decay of 184Ta

Levels of ¹⁸⁴W populated in the decay of 8.7 h ¹⁸⁴Ta have been studied by a variety of experimental techniques. As a result of β and γ-ray energy and intensity determinations and extensive β-γ and γ-γ coincidence measurements, a detailed ¹⁸⁴Ta decay scheme accommodating more than 99.5% of the decay intensity has been established. Intense β-ray groups of end-point energies 1165±26 and 1123±26 keV populate levels in ¹⁸⁴W at 1699 and 1746 keV, which de-excite predominantly to the 8.3 μs isomeric level at 1285 keV, recently identified as the $\text{1}\text{2}{}^{\mathrm{?}}\text{[510]ν?}\text{11}\text{2}{}^{\mathrm{+}}\text{[615]ν K}{}^{\mathrm{\pi }}\text{= 5}{}^{\mathrm{?}}$ band origin. The 1699 keV level also de-excites to members of a $\text{1}\text{2}{}^{\mathrm{?}}\text{[510]ν?}\text{7}\text{2}\text{[503]ν K}{}^{\mathrm{\pi }}\text{= 3}{}^{\mathrm{+}}$ band based at 1425 keV. New information about the properties of the γ-vibrational and K = 2 octupole bands in ¹⁸⁴W is presented and the possible configurations of the levels directly populated in the β^? decay are discussed. The configuration $\text{7}\text{2}{}^{\mathrm{+}}\text{[404]π ?}\text{3}\text{2}{}^{\mathrm{?}}\text{[512]ν K}{}^{\mathrm{\pi }}\text{= 5}{}^{\mathrm{?}}$ is indicated for the ¹⁸⁴Ta ground state.     

Europium-directed self-assembly of a luminescent supramolecular gel from a tripodal terpyridine-based ligand

Eu(III), the last piece in the puzzle: Europium-induced self-assembly of ligands having a C(3)-symmetrical benzene-1,3,5-tricarboxamide core results in the formation of luminescent gels. Supramolecular polymers are formed through hydrogen bonding between the ligands. The polymers are then brought together into the gel assembly through the coordination of terpyridine ends by Eu(III) ions (blue dashed arrow: distance between two ligands in the strand direction).     

Lanthanide N,N-dimethylaminodiboranates as a new class of highly volatile chemical vapor deposition precursors

New lanthanide N,N-dimethylaminodiboranate (DMADB) complexes of stoichiometry Ln(H(3)BNMe(2)BH(3))(3) and Ln(H(3)BNMe(2)BH(3))(3)(thf) have been prepared, where Ln = yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, and lutetium, except that isolation of the desolvated complexes proved difficult for Eu and Yb. The tetrahydrofuran (thf) complexes are all monomeric, and most of them adopt 13-coordinate structures in which each DMADB group chelates to the metal center by means of four B-H···Ln bridges (each BH(3) group is κ(2)H; i.e., forms two B-H···Ln interactions). For the smallest three lanthanides, Tm, Yb, and Lu, the metal center is 12 coordinate because one of the DMADB groups chelates to the metal center by means of only three B-H···Ln bridges. The structures of the base-free Ln(H(3)BNMe(2)BH(3))(3) complexes are highly dependent on the size of the lanthanide ions: as the ionic radius decreases, the coordination number decreases from 14 (Pr) to 13 (Sm) to 12 (Dy, Y, Er). The 14-coordinate complexes are polymeric: each metal center is bound to two chelating DMADB ligands and to two "ends" of two ligands that bridge in a Ln(κ(3)H-H(3)BNMe(2)BH(3)-κ(3)H)Ln fashion. In the 13-coordinate complexes, all three DMADB ligands are chelating, but the metal atom is also coordinated to one hydrogen atom from an adjacent molecule. The 12-coordinate complexes adopt a dinuclear structure in which each metal center is bound to two chelating DMADB ligands and to two ends of two ligands that bridge in a Ln(κ(2)H-H(3)BNMe(2)BH(3)-κ(2)H)Ln fashion. The complexes react with water, and the partial hydrolysis product [La(H(3)BNMe(2)BH(3))(2)(OH)](4) adopts a structure in which the lanthanum and oxygen atoms form a distorted cube; each lanthanum atom is connected to three bridging hydroxyl groups and to two chelating DMADB ligands. One B-H bond of each chelating DMADB ligand forms a bridge to an adjacent metal center. Field ionization MS data, melting and decomposition points, thermogravimetric data, and NMR data, including an analysis of the paramagnetic lanthanide induced shifts (LIS), are reported for all of the complexes. The Ln(H(3)BNMe(2)BH(3))(3) compounds, which are highly volatile and sublime at temperatures as low as 65 °C in vacuum, are suitable for use as chemical vapor deposition (CVD) and atomic layer deposition (ALD) precursors to thin films.     

NMR spectroscopy and structural characterization of dithiophosphinate ligands relevant to minor actinide extraction processes

Synthetic routes to alkyl and aryl substituted dithiophosphinate salts that contain non-coordinating PPh(4)(+) counter cations are reported. In general, these compounds can be prepared via a multi-step procedure that starts with reacting secondary phosphines, i.e. HPR(2), with two equivalents of elemental S. The synthetic transformation proceeds by oxidation of the phosphine followed by insertion of S into the H-P bond. This approach was used to synthesize a series of dithiophosphinic acids that were fully characterized, namely HS(2)P(p-CF(3)C(6)H(4))(2), HS(2)P(m-CF(3)C(6)H(4))(2), HS(2)P(o-MeC(6)H(4))(2) and HS(2)P(o-MeOC(6)H(4))(2). Although the insertion step was found to be much slower than the oxidation reaction, the formation of (NH(4))S(2)PR(2) from HPSR(2) occurred rapidly upon addition of NH(4)OH. Subsequent cation exchange reactions proceeded readily with PPh(4)Cl in water, under air and at ambient conditions to provide analytically pure samples of [PPh(4)][S(2)PR(2)] (R = p-CF(3)C(6)H(4), m-CF(3)C(6)H(4), o-CF(3)C(6)H(4), o-MeC(6)H(4), o-MeOC(6)H(4), Ph, and Me, 1b-7b, respectively), which were characterized by elemental analysis, multinuclear NMR, and IR spectroscopy. In addition, S(2)PPh(2)(-) and dithiophosphinates with ortho-substituted aryl groups (3b-6b) were characterized by X-ray crystallography. As opposed to the acids, which have short P=S double bonds and long P-SH single bonds, the metric parameters for the S atoms in S(2)PR(2)(-) are equivalent. In addition, the presence of large non-coordinating PPh(4)(+) cations guard against intermolecular P-S···X interactions and ensure that the P-S bond is isolated. These S(2)PR(2)(-) anions, which can be prepared in large quantities and isolated in crystalline form, are attractive for spectroscopic and theoretical studies because the P-S interaction can be probed independently in the absence of intermolecular interactions.     

Photorefractive control of surface plasmon polaritons in a hybrid liquid crystal cell

We present a photorefractive hybrid liquid crystal system that allows strong photorefractive effects on surface plasmon polaritons. We demonstrate its capability to couple energy between two 1.03 eV surface plasmon polariton modes with an efficiency of 25.3±2.3%. We present the energy and grating pitch dependence of the diffraction and a model that can qualitatively explain them.     

Cross Polarization for Improved Digital Image Correlation

Digital image correlation (DIC) is a surface deformation measurement technique for which accuracy and precision are sensitive to image quality. This work presents cross polarization, the use of orthogonal linear polarizers on light source(s) and camera(s), as an effective method for improving optical DIC measurements. The benefits of cross polarization are characterized through quantitative and statistical comparisons from two experiments: rigid body translation of a flat sample and uniaxial tension of a superelastic shape-memory alloy (SMA). In both experiments, cross polarization eliminated saturated pixels that degrade DIC measurements, and increased image contrast, which enabled higher spatial precision by using smaller subsets. Subset sizes are usually optimized for correlation confidence interval (typically with subsets of 21×21 px or larger), but can be decreased to achieve the highest possible spatial precision at the expense of increased correlation confidence intervals. Smaller subset sizes (such as 9×9 px) require better images to maintain correlation within error thresholds. By comparing DIC results from a uniaxial SMA tension test with unpolarized and cross-polarized images, we show that for 9×9 px subsets, the loss of valid DIC data points was reduced almost ten-fold with cross polarization. The only disadvantage we see to cross polarization is the decrease in specimen illumination due to transmission losses through the polarizers, which can easily be accommodated with sufficiently intense light sources. With the installation of relatively inexpensive linear polarizing filters, an optimum optical DIC setup can provide even better DIC measurements by delivering images without saturated pixels and with higher contrast for increased DIC spatial precision.     

Quantifying the Interdependence of Metal–Ligand Covalency and Bond Distance Using Ligand K‐edge XAS

Bond distance is a common structural metric used to assess changes in metal–ligand bonds, but it is not clear how sensitive changes in bond distances are with respect to changes in metal–ligand covalency. Here we report ligand K‐edge XAS studies on Ni and Pd complexes containing different phosphorus(III) ligands. Despite the large number of electronic and structural permutations, P K‐edge pre‐edge peak intensities reveal a remarkable correlation that spectroscopically quantifies the linear interdependence of covalent M?P σ bonding and bond distance. Cl K‐edge studies conducted on many of the same Ni and Pd compounds revealed a poor correlation between M?Cl bond distance and covalency, but a strong correlation was established by analyzing Cl K‐edge data for Ti complexes with a wider range of Ti?Cl bond distances. Together these results establish a quantitative framework to begin making more accurate assessments of metal–ligand covalency using bond distances from readily‐available crystallographic data.