Micrometrically scaled textured metallic hydrophobic interfaces validate the Cassie-Baxter wetting hypothesis

The possibility of forming a hydrophobic metallic interface is shown when it is micrometrically textured. On such surface obtained by gold coating the polymer honeycomb template, the apparent contact angle of water was observed to be close to or greater than 90 degrees . The metal hydrophobicity is explained by trapping air inside pores of pattern according to the Cassie-Baxter wetting model. The agreement between calculated and observed values of the apparent contact angle justifies the applicability of this model in the present case. Formation of the acute local (Young) angle on the pore surface is provided by its concave form.     

Determination of protein oxidation by mass spectrometry and method transfer to quality control

Characterization and quantitative analysis of oxidation plays an important role in biopharmaceutical development. This study demonstrates an approach to the assessment of susceptible to oxidation methionine residues in monoclonal antibodies and recombinant proteins. A method for the determination of oxidation levels by peptide mapping with mass spectrometric (MS) detection is described and its advantages compared to the UV detection are presented. Good linearity and reproducibility for determination of oxidation with MS detection are demonstrated (R2 > 0.99; RSDs of 4-9%). Aspects of method transfer to quality control group (QC) are discussed. As well, a quick and easy flow injection/MS method is proposed to substitute for peptide map analysis. Peptide coverage, linearity, reproducibility, robustness, sensitivity and quantitative oxidation results are compared for the flow injection/MS and LC/MS approaches.     

Variations of the antioxidant system during development of the cold-tolerant beetle, Tenebrio molitor

Data relating to the peculiarities of antioxidant enzyme activities, glutathione (GSH) level and lipid peroxidation (LP) intermediates specific to at each ontogenic stage of Tenebrio molitor are presented. Metamorphosis is accompanied by a shift of prooxidant-antioxidant balance towards oxidative processes, since pupae have the highest levels of lipid peroxidation intermediates. Cold acclimation (4 degree C) can promote oxidative stress at the cold sensitive developmental stage--imagoes, which enhance their levels of diene conjugates and ketodienes after a 2-week cold acclimation. This enhancement is accompanied by an increase in catalase (CAT) activity. GSH levels undergo no changes in imagoes after cold acclimation. Neither larval nor pupal T. molitor show significant changes in LP product contents after cold acclimation. Chilling results in a significant increase in CAT activities in pupae, but not in larvae. GSH levels are reduced both in larvae and pupae after cold exposure. However, cold acclimation does not affect superoxide dismutase (SOD) activity in any of the developmental stages of T. molitor.     

Hydrogen Bonding of Carboxylic Acids in Aqueous Solutions—UV Spectroscopy, Viscosity, and Molecular Simulation of Acetic Acid

The UV spectra of aqueous acetic acid solutions up to 2M were investigated. At these wavelengths, the carboxylic acids exhibit an absorption peak, attributed to the C=O group, which shifts when hydrogen bonds are formed.. The measured spectra were best fitted to several bands, either of Gaussian or Lorentzian shape, which can be explained as several types of structural units formed by hydrogen bonds established between acetic acid and water molecules and between acetic acid molecules themselves. Molecular dynamics simulation of these mixtures was also performed, confirming the occurrence of several types of hydrogen bonds and showing the presence of dimers at higher concentrations. The viscosity and density of these solutions were also measured at different concentrations and temperatures. These results give a more complete picture of the hydrogen bond network of the system.     

Thermotropic phase transition in soluble nanoscale lipid bilayers

The role of lipid domain size and protein-lipid interfaces in the thermotropic phase transition of dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) bilayers in Nanodiscs was studied using small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and generalized polarization (GP) of the lipophilic probe Laurdan. Nanodiscs are water-soluble, monodisperse, self-assembled lipid bilayers encompassed by a helical membrane scaffold protein (MSP). MSPs of different lengths were used to define the diameter of the Nanodisc lipid bilayer from 76 to 108 A and the number of DPPC molecules from 164 to 335 per discoidal structure. In Nanodiscs of all sizes, the phase transitions were broader and shifted to higher temperatures relative to those observed in vesicle preparations. The size dependences of the transition enthalpies and structural parameters of Nanodiscs reveal the presence of a boundary lipid layer in contact with the scaffold protein encircling the perimeter of the disc. The thickness of this annular layer was estimated to be approximately 15 A, or two lipid molecules. SAXS was used to measure the lateral thermal expansion of Nanodiscs, and a steep decrease of bilayer thickness during the main lipid phase transition was observed. These results provide the basis for the quantitative understanding of cooperative phase transitions in membrane bilayers in confined geometries at the nanoscale.     

Concomitant length and diameter separation of single-walled carbon nanotubes

Gel electrophoresis and column chromatography conducted on individually dispersed, ultrasonicated single-walled carbon nanotubes yield simultaneous separation by tube length and diameter. Electroelution after electrophoresis is shown to produce highly resolved fractions of nanotubes with average lengths between 92 and 435 nm. Separation by diameter is concomitant with length fractionation, and nanotubes that have been cut shortest also possess the greatest relative enrichments of large-diameter species. Longer sonication time causes increased electrophoretic mobility in the gels; thus, ultrasonic processing determines the degree of both length and diameter separation of the nanotubes. The relative quantum yield decreases nonlinearly as the nanotube length becomes shorter. These techniques constitute a preparative, scalable method for separating nanotubes by two important attributes required for electronic and sensor applications.     

Opposite trends in thermodynamic compatibility between copolyamide and chitosan in their binary blend

Gibbs energy, enthalpy, and entropy of mixing in binary blends of chitosan with ter‐copolyamide 6/66/610 at ambient conditions have been determined over the entire concentration range using thermodynamic cycle based on dissolution of individual polymers and their blends of different composition in a common solvent – formic acid. Experimental procedure included stepwise equilibrium vapor sorption of glacial formic acid on the cast films and isothermal microcalorimetry of dissolution of these films in liquid glacial formic acid at 25 °C. Formic acid appeared to be a very good solvent for individual polymers and their blends. Flory‐Huggins interaction parameter determined from sorption isotherms was negative and varied from ?2.56 to ?1.79 depending upon blend composition. The enthalpies of dissolution of individual polymers and their blends were strongly exothermic and varied from ?200 to ?40 Joule/g. Independent thermodynamic cycles for Gibbs free energy and enthalpy remarkably revealed similar trends in concentration dependence of different thermodynamic functions of mixing between chitosan and copolyamide. At high chitosan content, the binary blend is characterized by large and negative values of Gibbs free energy, enthalpy, and entropy of mixing that provide high polymer compatibility. On the contrary, at high copolyamide content the blends are incompatible and are characterized by positive values of enthalpy, entropy, and Gibbs free energy of mixing. Such complicated thermodynamic behavior is the result of the superposition of strong molecular interactions (H‐bonds) between polymers in the blend and isothermal fusion of copolyamide crystallites. Thermodynamic analysis correlates well with the data obtained by polarized microscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2603–2613, 2007     

Modeling viscoelastic properties of triblock copolymers: A DPD simulation study

Gel systems based on self‐assembled, amphiphilic ABA triblock copolymers in midblock‐selective solvent form stable, spatially extended networks with controllable morphology and tunable viscoelastic behavior. In this work, we systematically evaluate the mechanical properties of these gels using morphology calculations, and a nonequilibrium oscillatory shear technique based on the dissipative particle dynamics (DPD) method. Our simulations demonstrate that low molecular weight triblock copolymers with incompatible blocks self‐assemble into micelles connected with bridges and loop‐like chains comprised of the solvent‐selective polymer midblocks. The fraction of bridges, ?_b, generally increases with increasing relative volume of the midblock, x, defined as the ratio of midblock and endblock volumes ( ). For our model, ?_b reaches a plateau at approximately x > 9 for a strongly selective solvent. At this limit, the value of ?_b increases from 0.40 to about 0.66 as the copolymer concentration, c, increases from 0.2 to 0.5; however, this increase is less significant at higher concentrations. The elastic response of the gel studied here is comparable with the Rouse modulus. The elastic modulus increases with polymer concentration, and it exhibits a broad peak within 6 < x < 12. Finally, we present an approximate method to predict the elastic modulus of unentangled ABA triblock copolymers based solely on the morphology of the micellar gel, which can be gleaned from equilibrium DPD simulations. We demonstrate that our simulation results are in good qualitative agreement with other theoretical predictions and experimental data. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 15–25, 2010