Diffusion coefficients of alkyl ureas in aqueous solution at 25°C

The free diffusion coefficients of aqueous solutions of methyl-, 1,3-dimethyl-, ethyl-, and 1,3-diethylurea have been measured at 25°C by the Gouy interferometric technique. With the help of literature activity data the thermodynamic diffusion and the frictional coefficients are computed and a qualitative discussion of their concentration dependence is attempted.     

An experimental investigation of fracture by cavitation of model elastomeric networks

A new methodology to investigate the failure of elastomers in a confined geometry has been developed and applied to model end-linked polyurethane elastomers. The experimental in situ observations show that the elastomers fail by the growth of a single cavity nucleated in the region of maximum hydrostatic stress. Tests carried out at different temperatures for the same elastomer show that the critical stress at which this crack grows is not proportional to the Young's modulus E but depends mainly on the ratio between the mode I fracture energy G_IC and E. A reasonable fit of the data can be obtained with a model of cavity expansion by irreversible fracture calculating the energy release rate by finite elements with a strain hardening constitutive equation. Comparison between different elastomers shows that the material containing both entanglements and crosslinks is both tougher in mode I and more resistant to cavitation relative to its elastic modulus. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48:1409–1422, 2010     

Improving adhesion of acrylic waterborne PSAs to low surface energy materials: Introduction of stearyl acrylate

The effect of incorporating stearyl acrylate (SA) in the polymer backbone of a pressure sensitive adhesive on its adhesion properties on low energy surfaces was investigated. The presence of SA did not affect the polymer microstructure (sol molecular weight, gel, and network density) but affected the compatibility with the low energy substrate and the elasticity of the adhesive. The combination of these effects resulted in an optimum SA content. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Adsorption of myoglobin onto porous zirconium phosphate and zirconium benzenephosphonate obtained with template synthesis

Porous zirconium phosphate (P-ZrP) and zirconium benzenephosphonate (P-ZrBP) were prepared in the presence of an anionic surfactant acting as a template. Poorly crystalline materials with a P/Zr molar ratio equal to 2 and having a relatively high surface area and micro/mesoporosity have been obtained. The interaction of myoglobin with the two types of surfaces, the hydrophobic P-ZrBP and the hydrophilic P-ZrP, was investigated, and the adsorption isotherms were determined at different pH and temperature values. A model was proposed for the mechanism of the interaction of the protein with the surface based on the shape of the adsorption isotherm and the physical-chemical properties of myoglobin. The pH has been found to be an important parameter for determining the maximum adsorption capacity of P-ZrBP and P-ZrP for myoglobin molecules because of the changes that occur in the type and net charge of the protein surface as the pH of the medium changes. Protein binding affinity and capacity increase when the temperature is increased. This phenomenon occurs because myoglobin varies its conformation at high temperature with an increase in the exposed hydrophobic region. This process causes a stronger hydrophobic interaction between the protein and the adsorbent and reduces the repulsion between the adsorbed molecules. Studies on the activities of the obtained biocomposites are in progress.     

Thermodynamic features and environmental effects in a two-states molecular device under strict electrochemical control

The thermodynamic features of a synthetic molecular thread, recently proposed acting as an electrochemically-driven two-states molecular device, have been systematically investigated by means of nanoseconds time-scale classical molecular dynamics (MD) simulations and basic statistical mechanics relations. Results clearly suggest that the accessible conformational space of such a potential molecular switch shows a strong environmental dependence: the reversible molecular switching mechanism observed in liquid solution is effectively suppressed when the synthetic thread is hypothesized working in vacuo. Such a result has been related to a subtle energetic/entropic balance experienced by the whole system (solute and solvent) during the intramolecular conformational transition of the molecular thread, in presence and in absence of the solvent.     

Group-velocity control by quadratic nonlinear interactions

We give direct experimental evidence that the group velocity of ultrashort pulses can be controlled through chi(2)-cascaded interactions, under the condition of large group-velocity mismatch. The group velocity can be finely tuned by acting on pulse intensity and phase mismatch. Group-delay shifts up to 50 fs are achieved by propagating 40 fs pulses around 1400 nm in a 25 mm long periodically poled stoichiometric lithium tantalate crystal.     

Glycolipids from sponges. 13. Clarhamnoside, the first rhamnosylated alpha-galactosylceramide from Agelas clathrodes. Improving spectral strategies for glycoconjugate structure determination

Reinvestigation of the glycosphingolipid composition of the marine sponge Agelas clathrodes revealed the presence of a new tetraglycosylated alpha-galactoglycosphingolipid (1a), containing an unusual l-rhamnose unit in the sugar head. The structure of the new compound was elucidated using extensive 2D NMR studies. Because of the strong overlapping of the signals of the sugar protons in the (1)H spectrum, (13)C-coupled and (13)C-decoupled phase-sensitive HMQC spectra were used to study the multiplicity of the overlapping signals. In addition, the absolute configuration of sugars was determined using a simple and efficient, yet underutilized CD method.     

Inorganic-organic hybrids of the p,p'-diphenylmethylenediphosphinate, pcp2-. Synthesis, characterization, and XRPD structures of [Sn(pcp)] and [Cu(pcp)

Two new inorganic-organic polymeric hybrids [Sn(pcp)] and [Cu(pcp)], pcp=CH2(PhPO2)2(2-), have been synthesized and structurally characterized. The tin derivative has been obtained by reaction of the p,p'-diphenylmethylenediphosphinic acid (H2pcp) in water with SnCl2.2H2O, while the copper derivative has been synthesized through a hydrothermal reaction from the same H2pcp acid and Cu(O2CMe)2.H2O. The structures of these compounds have been solved "ab initio" by X-ray powder diffraction (XRPD) data. [Sn(pcp)] has a ladder-like polymeric structure, with tin(II) centers bridged by diphenylmethylenediphosphinate ligands, and alternating six- and eight-membered rings. The hemilectic coordination around the metal shows the tin(II) lone pair to be operative, resulting in significant interaction mainly with a C-C bond of one phenyl ring. The [Cu(pcp)] complex displays a polymeric columnar structure formed by two intersecting sinusoidal ribbons of copper(II) ions bridged by the bifunctional phosphinate ligands. The intersections of the ribbons are made of dimeric units of pentacoordinated copper ions. Crystal data for [Sn(pcp)]: monoclinic, space group P2(1)/c, a=11.2851(1), b=15.4495(6), c=8.6830(1) A, beta=107.546(1) degrees, V=1443.44(9) A, Z=4. Crystal data for [Cu(pcp)]: triclinic, space group P, a=10.7126(4), b=13.0719(4), c=4.9272(3) A, alpha=92.067(5), beta=95.902(7), gamma=87.847(4) degrees, V=685.47(7), Z=2. The tin compound has been characterized by 119Sn MAS NMR (magic-angle spinning NMR), revealing asymmetry in the valence electron cloud about tin. Low-temperature magnetic measurements of the copper compound have indicated the presence of weak antiferromagnetic interactions below 50 K.