Poly(ethylene oxide)/poly(2vinylpyridne)/lithium perchlorate blends as solid polymer electrolytes: Composition/property/structure interrelationship

Poly(ethylene oxide) (MW 600,000)/poly(2vinylpyridine) (MW 200,000)/LiClO₄ blends have been prepared by the solution blending process. The ionic conductivities of the blends containing lower weight fractions (15, 17.5, 20 and 22.5%) of poly (2vinylpyridine) initially increases as the salt content is increased, reaches a maximum at an ethylene oxide/Li⁺ mole ratio of 10 and decreases as the salt content is further increased. Blends, which have higher weight fractions of poly(2vinylpyridine) (25 and 35%) display different electric behavior, i.e., the ionic conductivity continously increased as the salt content is increased to an ethylene oxide/Li⁺ mole ratio of 2. Thermal, ⁷Li solidstate NMR and semiempirical MNDO molecular orbital studies indicate that this contrasting behavior may be explained by the structure and ratios of the solvates (mixed solvate or homosolvate) of LiClO₄ present in the blends. © 1995 John Wiley & Sons, Inc.     

Solid-phase synthesis of O-linked glycopeptide analogues of enkephalin

The synthesis of 18 N-alpha-FMOC-amino acid glycosides for solid-phase glycopeptide assembly is reported. The glycosides were synthesized either from the corresponding O'Donnell Schiff bases or from N-alpha-FMOC-amino protected serine or threonine and the appropriate glycosyl bromide using Hanessian's modification of the Koenigs-Knorr reaction. Reaction rates of D-glycosyl bromides (e.g., acetobromoglucose) with the L- and D-forms of serine and threonine are distinctly different and can be rationalized in terms of the steric interactions within the two types of diastereomeric transition states for the D/L and D/D reactant pairs. The N-alpha-FMOC-protected glycosides [monosaccharides Xyl, Glc, Gal, Man, GlcNAc, and GalNAc; disaccharides Gal-beta(1-4)-Glc (lactose), Glc-beta(1-4)-Glc (cellobiose), and Gal-alpha(1-6)-Glc (melibiose)] were incorporated into 22 enkephalin glycopeptide analogues. These peptide opiates bearing the pharmacophore H-Tyr-c[DCys-Gly-Phe-DCys]- were designed to probe the significance of the glycoside moiety and the carbohydrate-peptide linkage region in blood-brain barrier (BBB) transport, opiate receptor binding, and analgesia.     

Determination of rhizosphere 13C pulse signals in soil thin sections by laser ablation isotope ratio mass spectrometry

In grassland ecosystems, soil animals act as key soil engineers and architects. The diversity of soil animals is also a regulator of ecosystem carbon flow. However, our understanding of the link between soil animals, carbon fluxes and soil physical organisation remains poor. An integrated approach based on soil micromorphology and laser ablation stable isotope ratio mass spectrometry (LA-IRMS) was developed to provide spatially distributed data of pulse-derived (13)C tracer from roots in the soil environment. This paper describes the development and testing of a LA-IRMS (13)C/(12)C analytical method on soil thin sections as a means to determine the fate of root carbon derived from photosynthesis into soil. Results from this work demonstrated (1) that micro-scale delta(13)C (per thousand) analysis could be made on targeted features located within a soil thin section and (2) that LA-IRMS delta(13)C (per thousand) measurements made on samples obtained from (13)CO(2) pulse labelled plant-soil blocks confirmed the presence of recent photosynthates in the rhizosphere (1 and 4 weeks post-pulse).     

Efficient photoinduced conversion of an azo dye on hexachloroplatinate(IV)-modified TiO2 surfaces under visible light irradiation-A photosensitization pathway

The titanium dioxide photocatalyst is employed to examine the influence of chemisorbed hexachloroplatinate(IV) anions (PtCl(6) (2-)) on the surface of P-25 TiO(2) particles on the photoinduced conversion of the azo dye Ethyl Orange (EO) in visible light-illuminated Pt(IV)/TiO(2) dispersions. Spin-trap electron spin resonance (ESR) spectral results, measurement of quantities of organoperoxides formed, total organic carbon (TOC) and chemical oxygen demand (COD(Cr)) assays, together with XPS evidence show that the self-sensitized transformation dynamics of the EO dye mediated by Pt(IV)/TiO(2) are much faster than those occurring on naked TiO(2) under otherwise identical conditions of visible light irradiation. X-ray photoelectron spectral data also show that under the experimental conditions used, no Pt(0) formed on the titania particles during visible light irradiation. We propose a reaction mechanism in which the more rapid conversion of EO in the presence of PtCl(6) (2-) is caused principally by photoexcitation of the dye and not by localized excitation of the tetrachloroplatinate(IV)/TiO(2) particles.     

Deconvoluting the functions of polypeptide N-alpha-acetylgalactosaminyltransferase family members by glycopeptide substrate profiling

The polypeptide N-alpha-acetylgalactosaminyltransferases (ppGalNAcTs) play a key role in mucin-type O-linked glycan biosynthesis by installing the initial GalNAc residue on the protein scaffold. The preferred substrates and functions of the >20 isoforms in mammals are not well understood. However, current data suggest that glycosylated mucin domains are created by the successive, often hierarchical, action of several specific ppGalNAcTs. Herein we analyzed the glycopeptide substrate preferences of several ppGalNAcT family members using a library screening approach. A 56-member glycopeptide library designed to reflect a diversity of glycan clustering was assayed for substrate activity with ppGalNAcT isoforms using an azido-ELISA. The data suggest that the ppGalNAcTs can be classified into at least four types, which working together, are able to produce densely glycosylated mucin glycoproteins.     

Guest-framework interaction in type I inorganic clathrates with promising thermoelectric properties: on the ionic versus neutral nature of the alkaline-earth metal guest A in A8Ga16Ge30 (A=Sr, Ba)

Periodic density functional calculations using pseudopotentials and a local basis set were performed on the type I clathrates A(8)Ga(16)Ge(30) (A=Sr, Ba). Both are known to show promising thermoelectric properties. Ab initio wave functions were analyzed within the framework of the quantum theory of atoms in molecules. This enabled us to analyze both the charge transfer and bonding properties of the clathrate from a rigorous quantum mechanical viewpoint. The Ba and Sr centers were found to be largely ionic (charge: ca. +1.7 e) both in the smaller 20-atom and in the larger 24-atom cages, consistent with a Zintl-phase view of these type I clathrates. The assertion that the Sr atoms in the different cages have similar oxidation states is shown to be consistent with multiwavelength diffraction experiments on Sr(8)Ga(16)Ge(30); while the assertion of ionicity of the Sr center is supported by the observation that the adsorption edge lies close to that previously found in the Sr K-edge XANES spectra of Sr(OH)(2).8 H(2)O. As such, this work contradicts previous experimental and theoretical studies that claim that the guest atoms are neutral. We show that the discrepancy is related to the definitions used for electron transfer. Definitions based on electron displacement (rearrangement) in space, as in previous works, do not account for the variation in shape and volume of the atomic catchment regions upon change in the number and average locations of the particles in the system. Eventually, such definitions lead to underestimation of charge transfer. The large binding energy found in earlier work for Ba and Sr in these materials is found to be consistent with a simple picture of charge transfer from the guest to the frame. Preliminary investigations on a clathrate of perfect stoichiometry appear to rule out any important relationship between the observed increase in the thermoelectric figure of merit with increasing external pressure and host-guest charge transfer.     

Interactions of Ni(II) and Cu(II) ions with the hydrolysis products of the C-terminal -ESHH- motif of histone H2A model peptides. Association of the stability of the complexes formed with the cleavage of the -E-S- bond

We studied the interactions of Ni(II) and Cu(II) ions with the synthetic tetrapeptides SHHK- and SAHK-, which were blocked by amidation making them more realistic models of the hydrolysis peptidic products of the hexapeptides models of H2A histone. A combination of potentiometric and spectroscopic techniques (UV/Vis, CD, NMR and EPR) suggested that at pH > 7 both tetrapeptides coordinated equatorially through the imidazole ring of His in position 3, the N-terminal amino group and the two amide nitrogens existing between these groups {NH2, 2N-, NIm} forming 4N square-planar complexes. While in the case of the CuH(-1)L complex with SHHK- a possible axial coordination of the imidazole ring of His in position 2 was suggested, in the case of the analogous NiH(-1)L complex a completely different interaction of the same ring with metal ions was observed. As expected these complexes have the same structures with the hydrolysis products produced from the Ni(II)- or Cu(II)-assisted hydrolysis of previously studied hexapeptide models of the C-terminal of histone H2A, due to their predominance at pH > 7.4. In addition, the competition plots presented herein showed that the synthetic tetrapeptides SHHK- and SAHK- have higher affinity towards Ni(II) and Cu(II) ions than the previously studied hexapeptides, suggesting that metal ions remain bound to the peptidic products during the hydrolysis cleavage. Thus, it can be concluded that the stability of Ni(II) or Cu(II) complexes with the synthetic tetrapeptides and consequently with the real hydrolysis peptidic products is the driving force of the hydrolysis reaction of H2A histone blocked hexapeptide models, presented in previous studies.     

Photoionization of excited molecular states. H2 C 1Πu

We present photoelectron spectra for H₂ in the excited C ¹Π_u, υ = 0–4.J = 1 levels prepared by multiphoton excitation. In accordance with the Franck-Condon principle, the H₂⁺ vibrational state distribution is dominated by Δυ = 0 transitions from the C ¹Π_u state, illustrating a useful method for preparing vibrationally state-selected molecular ions. Equally important observed systematic departures from Franck-Condon factors, which provide detailed information on excited-state photoionization dynamics of molecules.     

Radiological characterization of spent control rod assemblies

Three different spent control rods were obtained for direct-assay measurements and empirical sampling and analysis. They were: 1) a BWR cruciform control rod, 2) a PWR rod-cluster control assembly, and 3) a burnable poison-rod assembly. The dominant activity of the BWR cruciform control rod and the PWR burnable poison-rod assembly is⁶⁰Co, whereas the PWR rod-cluster control assembly is dominated not only by⁶⁰Co, but also by^108mAg and^110mAg, which are found in the Ag–In–Cd alloy of the absorber rods. The radionuclide inventories calculated for the three spent control rods from the empirical sampling data agree very well with data determined from the two direct assay methodologies. The concentration of^108mAg in the rod-cluster control assembly will have to be considered when these types of spent control rods are prepared for waste disposal.     

WAVELENGTH DEPENDENCY OF THE RATE OF IODINE CATALYZED PHOTOISOMERIZATION OF RETINOL and RETINAL

In separate experiments, hydrocarbon solutions of the 11-cis isomers of retinol and retinal containing catalytic amounts of iodine were irradiated with monochromatic light. Changes in absorbance were followed spectroscopically for each wavelength of light and measured as a function of time. The curve obtained by plotting the change in absorbance (delta A) vs time (t) is a hyperbola, and thus the plot of 1/delta A vs 1/t forms a straight line. The half reaction time, t1/2, was extracted from this equation, giving a value for each wavelength of light. The parameter 1/t1/2 is adjusted to compensate for variation of light quanta from the xenon source, and it is plotted vs wavelength. A response spectrum is obtained that is a Gaussian. The lambda max is 510 nm for retinol and 519 nm for retinal. This shows that in the photoisomerization iodine is the absorbing species and not the carbocation, which absorbs at 589 nm.