Dielectric study of the alpha and beta processes in supercooled ethylene glycol oligomer-water mixtures

Broadband dielectric measurements for 65 wt % ethylene glycol oligomer (EGO)-water mixtures with one to six repeat units of EGO molecules were performed in the frequency range of 10 microHz-10 GHz and the temperature range of 128-298 K. In the case of the water-EGO mixtures with one and two repeat units of the EGO molecule (small EGO), the shape of the dielectric loss peak of the primary process is asymmetrical about the logarithm of the frequency of maximum loss above the crossover temperature, T(C). The asymmetric process continues to the alpha process at a low frequency, and an additional beta process appears in the frequency range higher than that of the alpha process below T(C). In contrast, the water-EGO mixtures with three or more repeat units of the EGO molecule (large EGO) show a broad and symmetrical loss peak of the primary process above T(C). The symmetric process continues to the beta process, and an additional alpha process appears in the frequency range lower than that of the beta process below T(C). These different scenarios of the alpha-beta separation related to the shape of the loss peak above T(C) are a result of the difference in the cooperative motion of water and solute molecules. The solute and water molecules move cooperatively in the small EGO-water mixtures above T(C), and this cooperative motion leads to the asymmetric loss peak above T(C) and the alpha process below T(C). For the large EGO-water mixtures, the spatially restricted motion of water confined by solute molecules leads to the symmetric loss peak above T(C) and the beta process below T(C).     

Weak and Strong Convergence for Fixed Points of Asymptotically Non-expansive Mappings

A few weak and strong convergence theorems of the modified three-step iterative sequence with errors and the modified Ishikawa iterative sequence with errors for asymptotically non-expansive mappings in any non-empty closed convex subsets of uniformly convex Banach spaces are established. The results presented in this paper substantially extend the results due to Chang (2001), Osilike and hniagbosor (2000), Rhoades (1994) and Schu (1991).     

Fermi surface reconstruction in the CDW state of CeTe3 observed by photoemission

CeTe3 is a layered compound where an incommensurate charge density wave (CDW) opens a large gap ( approximately 400 meV) in optimally nested regions of the Fermi surface (FS), whereas other sections with poorer nesting remain ungapped. Through angle-resolved photoemission, we identify bands backfolded according to the CDW periodicity. They define FS pockets formed by the intersection of the original FS and its CDW replica. Such pockets illustrate very directly the role of nesting in the CDW formation but they could not be detected so far in a CDW system. We address the reasons for the weak intensity of the folded bands, by comparing different foldings coexisting in CeTe3.     

Resonant Brewster filters with absentee layers

A method for lowering the sideband levels associated with the spectral response of resonant waveguide-grating filters is presented. With a TM-polarized incident wave near the Brewster angle, the filter sidebands are suppressed by application of a half-wavelength absentee waveguide layer and an arbitrary-thickness grating layer. Adjusting the thickness of the grating layer permits control of the filter linewidth without appreciably affecting the sideband features. To verify the theoretical prediction, we fabricated and tested a double-layer waveguide-grating filter. It exhibited a peak efficiency of 82.4%, with sideband reflection levels below 0.6%, over a 95-nm spectral range.     

Total synthesis of (+)-Brefeldin A

The total synthesis of (+)-brefeldin A has been accomplished via 15 linear steps in a 7.9% overall yield from the known Weinreb amide 6. The key parts of this approach include the stereoselective construction of the cis-disubstituted hydroxycyclopentane skeleton and the direct introduction of the C1-C3 acrylate moiety using a new variant of a trans-vinylogous acyl anion equivalent.     

Facile synthesis of plasmalogens via Barbier-type reactions of vinyl dioxanes and vinyl dioxolanes with alkyl halides in LiDBB solution

Plasmalogens (i.e. plasmenylcholines or plasmenylethanolamines) are a biologically important class of glycerophospholipids that have been difficult to synthesize due to the presence of an acid and oxidatively labile (Z)-vinyl ether substituent at the sn-1 position and a base-labile sn-2 acyl substituent that easily migrates during silica gel purification. We report two facile synthetic methods for the preparation of racemic plasmenylcholines via a tandem reductive vinyl dioxane/dioxolane ring opening and alkyliodide coupling process that proceeds in a single pot reaction. The key step in the formation of (Z)-vinyl ether precursors for the production of plasmenylcholines is accomplished using LiDBB under Barbier-type conditions to give the corresponding TBDMS-protected 1-O-Z'-vinylglycerol intermediate in moderate yields. This pathway is the most direct synthetic route for the formation of plasmenylcholines to date, requiring a total of six transformations from acrolein and glycerol or solketal as inexpensive starting materials, to generate glycerophosphocholine-type plasmalogens in 4% overall yield.     

Stereoselective synthesis of a novel apio analogue of neplanocin A as potential S-adenosylhomocysteine hydrolase inhibitor

A total synthesis of apio-neplanocin A, which combines properties of apio nucleoside and neplanocin A and is a potential inhibitor of S-adenosylhomocysteine hydrolase, was accomplished starting from D-ribose via stereoselective hydroxymethylation and RCM reaction. [reaction: see text]     

Solution-phase synthesis of aminooxy peptoids in the C to N and N to C directions

[structure: see text] Aminooxy peptoids, which are potential peptidomimetics, were synthesized by a stepwise monomer assembly. Ns-protected N-substituted aminooxyacetate tert-butyl esters were used as a monomer in both the C to N and the N to C directions. Submonomer synthesis of aminooxy peptoids is also described.