Specificity of metal ion cross-linking in marine mussel adhesives

In an effort to understand the formation of marine bioadhesives, mussel protein extracts were cured with various reagents and the enhanced cross-linking ability of Fe3+ was found.     

Possible resonance structure in the elastic scattering of neutrons by Y near En = 1 MeV

The total cross section as well as the differential cross section and polarization in the elastic scattering of 0.8–1.4 MeV neutrons by Y have been measured with neutron beams of energy spread less than 20 keV. Rather weak structure with widths ≈ 50 keV was observed at a few energies within this range. The data were analyzed by use of a model in which the scattering process is described in terms of resonance amplitudes superimposed on an optical-potential background. Although not completely definitive, this analysis indicates the existence of three intermediate-width resonances (two 1^? and one 1⁺) at neutron energies between ≈ 1.0 and 1.2 MeV. The properties of the 1^? resonances suggest that these are the parent states of the proposed T_> components of the El giant resonance observed near 21 MeV excitation energy in ⁹⁰Zr produced in the ⁸⁹Y(p,γ₀) reaction. The resolved resonance structure in this energy region is in reasonable agreement with a recent calculation of the energies and widths of negative-parity states in ⁹⁰Y.     

Bismuth trichloride–mediated cleavage of phenolic methoxymethyl ethers

A simple and efficient method for removal of phenolic methoxymethyl ethers in the presence of 30 mol% of bismuth trichloride in acetonitrile/water is described. Notable features of the cleavage protocol entail use of an ecofriendly bismuth reagent, ease of handling, low cost, operational simplicity, and good functional group compatibility. A number of structurally varied phenolic methoxymethyl ethers were cleaved in good to excellent yields.     

Microbicides for HIV/AIDS. 2. Electrophoretic fingerprinting of CD4+ T-cell model systems

New measurements of the dependence of the surface charge on the pH and electrolyte concentration for three living human white blood cell lines that are the principal targets of the HIV-1 virus are reported. Comparison of the electrophoretic fingerprint (EF) pattern, especially the line of zero mobility, with that of reference colloids establishes the separate individual identities and shows that all three exhibit a zwitterionic surface. With the EF results as a guide, preliminary biological infectivity measurements showed that small polyvalent cations modulate the negative charge on the T-cell surface in a way that strongly affects the infection kinetics. H9 cells were exposed to an infectious virus (X4), and the data showed that HIV interaction with target cells is enhanced by physiological fluids. The nondestructive methodology described is generally applicable to characterization of the surface charge and determination of the colloidal stability of any aqueous charged colloidal system without reference to any model of the double layer.     

Dramatic Effect of Magnetite Particles on the Dynamics of Photogenerated Free Radicals

Abstract— Polymeric particles of about 1 u.m in diameter and containing around 40% magnetite have a dramatic influence on the dynamics of triplet radical pair reactions occurring in micelles in their vicinity. The effect has been monitored with laser flash photolysis techniques and results in a decrease of the number of radicals that separate from their geminate partner and an acceleration of radical pair geminate reactions. The effect involves remote interactions because the solution contains ca 10¹¹micelles for each polymeric particle. Magnetite also perturbs the way in which the radicals interact with an external magnetic field.     

A split microchannel design and analytical model to compensate for electroosmotic instabilities in micro-separations

Organic polymers offer many advantages as materials for the construction of microfluidic devices but suffer frequently from the limitation that the electrodynamic flow they support can exhibit considerable instability. This article describes a split-channel microfluidic device that can be used to compensate for changes in electroosmotic flow. The design of the separation system divides an analyte plug after injection between two separation channels of differing length. The two channels are later recombined for single point detection, eliminating the need for a scanning optical detection system. The utility of this simple design lies in the fact that the migration time of any analyte can be referenced to its twin in the parallel separation channel. This eliminates the need for a separate electroosmotic marker and allows mobilities measured in multiple devices to be compared quantitatively. Using a model adopted from the literature, the data from the split channel system can be used to precisely account for the drift that characterizes electrophoretic separations made in a polymer chip. The relative standard deviations of the analyte mobilities measured for replicate runs on multiple devices were reduced from values as high as 20% to ca. 1% RSD. This internal standardization procedure also appears to address other sources of drift in the electroosmotic flow (EOF) supported by the polymer microchannel, eliminating the need for careful monitoring of either the temperature or reservoir pH between separation runs.     

Melt crystallization of zinc alkali phosphate glasses

Melt crystallization of two zinc alkali phosphate glasses was studied with X-ray diffraction (XRD) experiments to accelerate efforts to melt process these glasses with organic polymers. The inorganic glasses differed markedly in chemical durability (water sensitivity) and crystallization rates. They were studied at room temperature prior to and after melt processing with XRD experiments and in situ at melt temperatures without flow in a novel differential scanning calorimeter/XRD apparatus. The glasses were found to be amorphous at room temperature and semi-crystalline above their glass-transition temperatures. Higher temperatures and shear (mixing) rates increased the crystallization rate of the glasses. The non-durable (water-sensitive) glass was observed to contain significant levels of crystalline matter after melt processing at 400°C. This process-induced crystallization of the glasses must be controlled, possibly during processing and/or glass formulation, otherwise it may lead to formation of unwanted phase-separated defects in the glass. If high levels of the crystalline matter are present during melt processing, they may lead to irreversible plugging of the processing equipment.     

Photolysis of poly(tert-butyl acrylate) in the region of the glass transition temperature

The thin film (1 × 10^?5 cm.) photolysis (2537 A.) of poly(tert-butyl acrylate) under 1 atm. helium pressure has been investigated in detail. Isobutene was the only significant volatile product in the temperature range 20–110°C. The reaction was demonstrated to be initially a first-order decomposition with an energy of activation of 3.3 kcal./mole in the glassy state. Above the glass transition temperature a value of 1.8 kcal./mole was found. The rate of isobutene formation is autoaccelerated when a minimum of one acrylic acid unit is generated per chain. The initial quantum yield for the formation of isobutene varies from 0.083 to 0.17 over the temperature range studied. There was no dependence of quantum yield on the exciting wavelength using sources of 1849, 2537, and 3660 A. The intensity exponent was found to be unity, consistent with first-order decomposition kinetics.