3-O-Sulfation of Heparan Sulfate Enhances Tau Interaction and Cellular Uptake

Prion-like transcellular spreading of tau in Alzheimer's Disease (AD) is mediated by tau binding to cell surface heparan sulfate (HS). However, the structural determinants for tau–HS interaction are not well understood. Microarray and SPR assays of structurally defined HS oligosaccharides show that a rare 3-O-sulfation (3-O-S) of HS significantly enhances tau binding. In Hs3st1^−/− (HS 3-O-sulfotransferase-1 knockout) cells, reduced 3-O-S levels of HS diminished both cell surface binding and internalization of tau. In a cell culture, the addition of a 3-O-S HS 12-mer reduced both tau cell surface binding and cellular uptake. NMR titrations mapped 3-O-S binding sites to the microtubule binding repeat 2 (R2) and proline-rich region 2 (PRR2) of tau. Tau is only the seventh protein currently known to recognize HS 3-O-sulfation. Our work demonstrates that this rare 3-O-sulfation enhances tau–HS binding and likely the transcellular spread of tau, providing a novel target for disease-modifying treatment of AD and other tauopathies.     

Structure and gas transport characteristics of triethylene oxide-grafted polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene

Polymeric membrane-based gas separation technology has significant advantages compared with traditional amine-based CO₂ separation method. In this work, SEBS block copolymer is used as a polymer matrix to incorporate triethylene oxide (TEO) functionality. The short ethylene oxide segment is chosen to avoid crystallization, which is confirmed by differential scanning calorimetry and wide-angle X-ray scattering characterizations. The gas permeability results reveal that CO₂/N₂ selectivity increased with increasing content of TEO functional group. The highest CO₂ permeability (281 Barrer) and CO₂/N₂ selectivity (31) were obtained for the membrane with the highest TEO incorporation (57 mol%). Increasing the TEO content in these copolymers results in an increase in CO₂ solubility and a decrease in C₂H₆ solubility. For example, as the grafted TEO content increased from 0 to 57 mol%, the CO₂ solubility and CO₂/C₂H₆ solubility selectivity increased from 0.72 to 1.3 cm³(STP)/cm³ atm and 0.47 to 1.3 at 35°C, respectively. The polar ether linkage in TEO-grafted SEBS copolymers exhibits favorable interaction with CO₂ and unfavorable interaction with nonpolar C₂H₆, thus enhancing CO₂/C₂H₆ solubility selectivity.     

Stokes flow solutions in infinite and semi-infinite porous channels

We derive a class of exact solutions for Stokes flow in infinite and semi-infinite channel geometries with permeable walls. These simple, explicit, series expressions for both pressure and Stokes flow are valid for all permeability values. At the channel walls, we impose a no-slip condition for the tangential fluid velocity and a condition based on Darcy's law for the normal fluid velocity. Fluid flow across the channel boundaries is driven by the pressure drop between the channel interior and exterior; we assume the exterior pressure to be constant. We show how the ground state is an exact solution in the infinite channel case. For the semi-infinite channel domain, the ground-state solutions approximate well the full exact solution in the bulk and we derive a method to improve their accuracy at the transverse wall. This study is motivated by the need to quantitatively understand the detailed fluid dynamics applicable in a variety of engineering applications including membrane-based water purification, heat and mass transfer, and fuel cells.     

Stress-resultant plasticity theories for composite laminated plates

Constitutive laws are presented for the inelastic analysis of laminated composite plates. The implications of using an elastoplastic theory, applied in a stress-resultant formulation, are discussed and investigated. Two different stress-resultant plasticity theories are proposed, both of which overlook the matrix and fiber inelastic behavior and describe the inelastic response of the laminate as a function of overall laminate properties. Results from numerical experiments with the proposed models are compared with results obtained using a micromechanical elastoplastic composite constitutive model.     

Heat transfer during dry spinning of fibers

Summary Heat transfer to fibers formed in dry spinning has been subjected to fundamental analysis. Solutions of the equation of energy have been derived and tested with experimental data. Results were deemed satisfactory in view of the accuracy of the experimental data. The present work is believed to yield a good representation of the heat transfer in the dry spinning process.Nomenclature h heat transfer coefficient, cal/cm² °C sec - k thermal conductivity, cal/cm °C sec - r radial distance, cm - t time, sec - Z axial distance, cm - A surface area, cm² - A _n or n-th root of - A ₀ energy required for solvent evaporation, cal/sec cm³ - C _p specific heat cal/gm °C - J ₀ Bessel function of first kind, order zero - J ₁ Bessel function of first kind, order one - J ₂ Bessel function of first kind, order two - N k/(R ² C _p V) - Q volumetric flow rate cm³/sec - R outside radius, cm - T point temperature, °C - T _S surface temperature °C - T ₀ initial fiber temperature °C - T ambient air temperature, °C - average fiber temperature, °C - ₁ average fiber temperature of preceding segment, °C - V average fiber velocity relative to air strean, cm/sec - V _r radial velocity component, cm/sec - V _z axial velocity components, cm/sec - V direction velocity component cm/sec - W weight of solvent evaporated in a given fiber segment, gms - _n a solution of the equation J ₀(X)=0 - heat of vaporization of solvent, cal/gm - dimension - r/R - density, gms/cc     

Axial dispersion in fluid flow through porous plates in parallel and through a porous tube

Summary Effects of axial diffusion on liquid-liquid displacement in fluid flow through porous plates in parallel and through a porous tube are considered as problems of two zones in unsteady state mass transfer. The solutions of the differential equations of the system in terms of the Laplace transformed variable contain an infinite number of essential singularities in a complicated form. Therefore approximate solutions are obtained by numerical inversion of the Laplace transform. Some of the numerical results are presented and discussed.Nomenclature C ₁ concentration of solute in Zone 1 - C ₂ concentration of solute in Zone 2 - C ₀ initial concentration of solute in Zone 2 - D _e effective diffusivity - D* axial dispersion (mixing) coefficient - K ratio D*/D _e - P _e Péclet number, Xv/D _e, Rv/D _e - P _e * longitudinal Péclet number, Xv/D*, Rv/D* - R inner radius of a porous tube - t time - v average velocity of fluid flow through Zone 1 - W width of a porous plate - Y length of a porous plate (tube) - porosity - ₁ dimensionless concentration of solute in Zone 1, C ₁/C ₀ - ₂ dimensionless concentration of solute in Zone 2, C ₂/C ₀ - Laplace transform of ₁ - Laplace transform of ₂ - ₁ dimensionless distance in porous plate, x/X - ₂ dimensionless distance in a porous tube, r/R - ₁ dimensionless axial distance in porous plate, y/X - ₂ dimensionless axial distance in a porous tube, y/R - ₁ dimensionless time in porous plate, tD _e/X ² - ₂ dimensionless time in a porous tube, tD _e/R ² - Units CGS system     

Thermal and optical properties of highly fluorinated copolymers of methacrylates

Copolymers of pentafluorophenylhexafluoroisopropyl methacrylate (FPPMA) with trifluoroethyl methacrylate (TFEMA) were prepared in THF solution and in bulk using azobisisobutyronitrile as a free radical initiator. The monomer reactivity ratios of TFEMA (M₁) and FPPMA (M₂) were calculated as r₁ = 0.55 and r₂ = 0.07. The refractive indices of poly(TFEMA) and poly(FPPMA) are very similar as 1.435 and 1.430, respectively, at 532 nm, and the copolymer films were transparent. The glass transition temperatures (T_g) of the copolymers were in the range of 80–90°C and showed a negative deviation from the Gordon–Taylor equation. The thermal decomposition temperature (T_d) was increased with the content of FPPMA in copolymers. Low water absorption for 1:1 FPPMA/TFEMA copolymer was detected. Copolymers of FPPMA with hexafluoroisopropyl methacrylate (HFPMA) were also prepared. The monomer reactivity ratios of HFPMA (M₁) and FPPMA (M₂) were calculated as r₁ = 0.43 and r₂ = 0.10. The T_gs of the copolymers were in the range of 88–95°C and showed also a negative deviation from the Gordon–Taylor equation. T_g and T_d of the copolymers were increased with the content of FPPMA. The refractive index of poly(HFPMA) (1.384 at 532 nm) is much lower than that of FPPMA homopolymer, but copolymer films obtained were clear and transparent. Copyright © 2013 John Wiley & Sons, Ltd.     

On-Surface Synthesis and Characterization of Acene-Based Nanoribbons Incorporating Four-Membered Rings

A bottom up method for the synthesis of unique tetracene-based nanoribbons, which incorporate cyclobutadiene moieties as linkers between the acene segments, is reported. These structures were achieved through the formal [2+2] cycloaddition reaction of ortho-functionalized tetracene precursor monomers. The formation mechanism and the electronic and magnetic properties of these nanoribbons were comprehensively studied by means of a multitechnique approach. Ultra-high vacuum scanning tunneling microscopy showed the occurrence of metal-coordinated nanostructures at room temperature and their evolution into nanoribbons through formal [2+2] cycloaddition at 475 K. Frequency-shift non-contact atomic force microscopy images clearly proved the presence of bridging cyclobutadiene moieties upon covalent coupling of activated tetracene molecules. Insight into the electronic and vibrational properties of the so-formed ribbons was obtained by scanning tunneling microscopy, Raman spectroscopy, and theoretical calculations. Magnetic properties were addressed from a computational point of view, allowing us to propose promising candidates to magnetic acene-based ribbons incorporating four-membered rings. The reported findings will increase the understanding and availability of new graphene-based nanoribbons with high potential in future spintronics.     

Heat capacities of solid polymers

The heat capacity of a solid polymer is governed by the manner in which the internal energy is distributed over the various degrees of freedom. If the internal energy manifests itself in harmonic oscillatory motions, the heat capacity is the sum of contributions of the normal modes of motion. In practice, full frequency data are not generally available for polymers. This paper proposes an empirical method for determining the heat capacities of linear high polymers by the addition of contributions from different chain segments. A survey of heat capacity data for 30 linear high polymers and several copolymer systems has revealed that additivity is usually valid for a temperature range from about 60°K to the glass-transition temperature. A table of heat capacity contributions of a number of polymer constituents is derived which permits the calculation of unknown heat capacities to an accuracy of ±5% or better. In addition, δC_p data for the increase of the heat capacity at the glass-transition temperature were found to agree with the rule of constant heat capacity increase per mole of “bead” proposed 8 years ago.