Interfacial layers from the protein HFBII hydrophobin: dynamic surface tension, dilatational elasticity and relaxation times

The pendant-drop method (with drop-shape analysis) and Langmuir trough are applied to investigate the characteristic relaxation times and elasticity of interfacial layers from the protein HFBII hydrophobin. Such layers undergo a transition from fluid to elastic solid films. The transition is detected as an increase in the error of the fit of the pendant-drop profile by means of the Laplace equation of capillarity. The relaxation of surface tension after interfacial expansion follows an exponential-decay law, which indicates adsorption kinetics under barrier control. The experimental data for the relaxation time suggest that the adsorption rate is determined by the balance of two opposing factors: (i) the barrier to detachment of protein molecules from bulk aggregates and (ii) the attraction of the detached molecules by the adsorption layer due to the hydrophobic surface force. The hydrophobic attraction can explain why a greater surface coverage leads to a faster adsorption. The relaxation of surface tension after interfacial compression follows a different, square-root law. Such behavior can be attributed to surface diffusion of adsorbed protein molecules that are condensing at the periphery of interfacial protein aggregates. The surface dilatational elasticity, E, is determined in experiments on quick expansion or compression of the interfacial protein layers. At lower surface pressures (<11 mN/m) the experiments on expansion, compression and oscillations give close values of E that are increasing with the rise of surface pressure. At higher surface pressures, E exhibits the opposite tendency and the data are scattered. The latter behavior can be explained with a two-dimensional condensation of adsorbed protein molecules at the higher surface pressures. The results could be important for the understanding and control of dynamic processes in foams and emulsions stabilized by hydrophobins, as well as for the modification of solid surfaces by adsorption of such proteins.     

Microwave Assisted Graft Copolymerization of N-Isopropyl Acrylamide and Methyl Acrylate on Cellulose: Solid State NMR Analysis and CaCO3 Crystallization

Summary: Graft copolymerization of N-isopropyl acrylamide and methyl acrylate on α-cellulose was carried out under microwave irradiation at specific cut off temperatures with cerium (IV) ammonium nitrate and potassium persulfate (KPS) as the initiating system. The role of KPS was to oxidize Ce (III) to Ce (IV) which is the active species in radical formation. The reactions at a temperature cut off of 60 °C were confirmed by ¹³C nuclear magnetic resonance cross-polarization with magic- angle spinning (¹³C NMR CP/MAS) and Fourier-transform infrared spectroscopy (FTIR). The extent of grafting was calculated from weight gain and ¹³C resonances. The grafted cellulose was thermally more stable than the parent cellulose. An attempt to do grafting at a higher cut off temperature of 80 °C was made, however, no grafting was observed from ¹³C NMR CP/MAS but TGA results showed that a cellulose having more thermal stability resulted which was attributed to cross linking. Crystallization of CaCO₃ was carried out using the grafted materials as templates showed better nucleation and different crystal structure was observed.     

Change in Physico-chemical Properties of PMMA and PS by Copolymerization with an Anionic Amphiphilic Comonomer: Sodium 11-(methacryloyloxy) undecanylsulfate (MET)

Sodium 11-(methacryloyloxy) undecanylsulfate (MET) monomer units were incorporated in polystyrene (PS) and poly(methyl methacrylate) (PMMA) by free radical copolymerization in solution with styrene and methyl methacrylate, respectively. Experimental compositions, thermal degradations, average molecular weights, glass transitions and affinities for moisture were experimentally determined for copolymers of various compositions. Both styrene and methyl methacrylate copolymerized well with MET. An increase in the moisture affinity and a change in the glass transition were observed with increasing MET content in the respective copolymers.     

Synthesis and characterization of laser ablated TiNi films

TiNi thin films with BaTiO₃ and PbZr_0.52Ti_0.48O₃ (PZT) as buffer layers were deposited on Si(100) substrates by the pulsed laser deposition (PLD) method. Buffer layers (BaTiO₃ and PZT) were deposited at 600 °C in oxygen (O₂) environment and TiNi films were deposited on the top of the buffer layer in presence of 15 mTorr nitrogen (N₂) at various deposition temperatures (50, 300, and 500 °C). Synthesis and characterization of TiNi films were investigated from the crystallographic point of view by using X-ray diffractometer (XRD) and atomic force microscope (AFM) techniques. It is found that buffer layer of BaTiO₃ and PZT have improved the crystallinity of TiNi films deposited at higher temperatures. The TiNi/PZT film was uniform compared to TiNi/BaTiO3 film with the exception of agglomerates that appeared throughout the layer.     

The copolymerization of propylene with higher,linear α‐olefins

Propylene was copolymerized with the linear α‐olefins 1‐octene, 1‐decene, 1‐tetradecene, and 1‐octadecene. The metallocene catalyst Me₂Si(2‐Me Benz[e]Ind)₂ZrCl₂, in conjunction with methylalumoxane as a cocatalyst, was used to synthesize the copolymers. The copolymers were characterized by ¹³C and ¹H NMR with a solvent mixture of 1,2,4‐trichlorobenzene (TCB) and benzene‐d₆ (9/1) at 100 °C. Thermal analyses were carried out to determine the melting and crystallization temperatures, whereas the molecular weights and molecular weight distributions were determined by gel permeation chromatography with TCB at 140 °C. Glass‐transition temperatures were determined with dynamic mechanical analysis. Relationships among the comonomer type and amount of incorporation and the melting/crystallization temperatures, glass‐transition temperature, crystallinity, and molecular weight were established. Moreover, up to 3.5% of the comonomer was incorporated, and there was a decrease in the molecular weight with increased comonomer content. Also, the melting and crystallization temperatures decreased as the comonomer content increased, but this relationship was independent of the comonomer type. In contrast, the values for the glass‐transition temperature also decreased with increased comonomer content, but the extent of the decrease was dependent on the comonomer type. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4110–4118, 2000     

Geometric analysis of a two-body problem with quick loss of mass

Nonlinear Dynamics - We consider a two-body problem with quick loss of mass which was formulated by Verhulst (Verhulst in J Inst Math Appl 18: 87–98, 1976). The corresponding dynamical system...     

Prevention and medication of HIV/AIDS: the case of Botswana

In this paper we developed a mathematical model which allows estimating and projecting the effects of prevention and treatment programs on the total population size, HIV-induced deaths, and life expectancies. Considering only the female population we project the changes of the demographic developments and the situation of HIV/AIDS for Botswana up to 2060. Our mathematical model is used to project the female population development considering their age-structure. Treatment programs are included through selecting a price for medication (or giving it for free). Prevention programs consist of two parts: school-based programs which try to change risky behavior and instantaneous prevention (e.g., free condoms) which has only a short-time effect on the infection risk. The main conclusions drawn from our results are that prevention-only programs always yield the fastest decrease in HIV/AIDS prevalence. Adding a medication program reduces the efficiency of the prevention interventions regarding prevalence, but it reduces the number of HIV-induced deaths and increases life expectancies. This research was partly financed by the Austrian Science Foundation (FWF) under grant No P18161-N13.     

Facile preparation of bis(thiocarbonyl)disulfides via elimination

A robust facile synthetic preparation of bis(thiocarbonyl)disulfides is presented. The route follows an elimination mechanism rather than the more common oxidation. Addition of p-tosyl chloride to a thiocarbonyl thiolate results in the elimination of the chloride by the trithiocarbonate anion and subsequent elimination of the tosyl leaving group (by a second thiocarbonyl thiolate). The side products of the reaction are bis(4-methylphenyl)disulfone and tosylate salts/acids.