Conformational Properties of Arenicins: From the Bulk to the Air–Water Interface

The structures of two antimicrobial peptides (arenicin Ar‐1 and its linear derivative C/S‐Ar‐1) are studied in different solutions and at the air–water interface using spectroscopic methods such as circular dichroism (CD) and infrared reflection absorption spectroscopy (IRRAS) as well as grazing incidence X‐ray diffraction (GIXD) and specular X‐ray reflectivity (XR). Both peptides exhibit similar structures in solution. In the buffer used for most of the experiments the main secondary structure elements are 22 % β‐turn, 38 % β‐sheet and 38 % random coil. The amphiphilic peptides are surface‐active and form a Gibbs monolayer at the air–buffer interface. The surface activity is drastically increased by increasing the ionic strength of the subphase. The β‐sheet layer is quite stable and can be compressed to higher surface pressures. This adsorption layer is very crystalline. Bragg peaks corresponding to an interstrand distance of 4.78 Å and to an end‐to‐end distance have been observed. This end‐to‐end distance can be connected with the observed differences in the layer thickness leading to the assumption that the peptides form a hairpin which is bended depending on the interactions with the counterions.     

Randomization of Amyloid‐β‐Peptide(1‐42) Conformation by Sulfonated and Sulfated Nanoparticles Reduces Aggregation and Cytotoxicity

The amyloid‐β peptide (Aβ) plays a central role in the mechanism of Alzheimer's disease, being the main constituent of the plaque deposits found in AD brains. Aβ amyloid formation and deposition are due to a conformational switching to a β‐enriched secondary structure. Our strategy to inhibit Aβ aggregation involves the re‐conversion of Aβ conformation by adsorption to nanoparticles. NPs were synthesized by sulfonation and sulfation of polystyrene, leading to microgels and latexes. Both polymeric nanostructures affect the conformation of Aβ inducing an unordered state. Oligomerization was delayed and cytotoxicity reduced. The proper balance between hydrophilic moieties and hydrophobic chains seems to be an essential feature of effective NPs.

     

Distillation of fermented sugarcane juice: fractions characterized by electrospray ionization mass spectrometry and multivariate data treatment

Direct infusion electrospray ionization mass spectrometry in the negative ion mode (ESI(?)‐MS) was employed to discriminate among fractions arising from the distillation of fermented sugarcane juice during the production of cachaça, a typical Brazilian alcoholic beverage. Aliquots were collected in the course of distillation and their ESI(?)‐MS shown to be almost indistinguishable by a simple visual inspection. However, when the ESI(?)‐MS data were treated by the principal component analysis (PCA) and hierarchical clustering analysis (HCA) statistical methods, four major groups were clearly determined, the so‐called head (two distinct clusters), heart and tail fractions. Furthermore, the recognition of diagnostic ions (and their respective intensities) enabled a more confident establishment of the cutoff position (i.e. the initial and final points of each fraction). In conclusion, ESI‐MS, in conjunction with PCA or HCA approaches, proved to be a quite efficient method that allowed for a prompt characterization of each fraction derived from the distillation of brewed sugarcane. The results described herein can, therefore, be useful not only to optimize the production of cachaça but also to improve the quality of the final product. Copyright © 2012 John Wiley & Sons, Ltd.     

Redox processes of cytochrome c immobilized on solid supported polyelectrolyte multilayers

The heme protein cytochrome c (Cyt-c), immobilized on polyelectrolyte multilayers on a silver electrode, was studied by stationary and time-resolved surface-enhanced resonance Raman (SERR) spectroscopy to probe the redox site structure and the mechanism and dynamics of the potential-dependent interfacial processes. The layers were built up by sequential adsorption of polycations (poly[ethylene imine] (PEI); polyallylamine hydrochloride (PAH)) and polyanions (poly[styrene sulfonate] (PSS)). All multilayers terminated by PSS electrostatically bind Cyt-c. On PEI/PSS coatings, Cyt-c is peripherally bound and fully redox-active. Due to the interfacial potential drop, the apparent redox potential is lowered by 40 mV compared to that in solution. The rate constant for the heterogeneous electron transfer (ET) of ca. 0.1 s(-1) is consistent with electron tunneling through largely ordered PEI/PSS layers. ET is coupled to a reversible conformational transition of Cyt-c that involves a change of the coordination pattern of the heme. Additional (PAH/PSS) double layers cause a broadening of the redox transition and a drastic negative shift of the redox potential, which is attributed to the formation of PSS/Cyt-c complexes. It is concluded that Cyt-c can effectively compete with PAH for binding of PSS, resulting in a rearrangement of the layered structure and a penetration of the PSS-bound Cyt-c into the PAH/PSS double layers. This conclusion is consistent with SERR intensity and quartz microbalance measurements. ET was found to be overpotential-independent and faster than that for PEI/PSS coatings, which is interpreted in terms of specific PSS/Cyt-c complexes serving as gates for the heterogeneous ET.     

High-speed microcontact printing

We have demonstrated microcontact printing (muCP) of self-assembled monolayers in the millisecond regime. The contact formation and separation of the stamp and substrate was studied with high-speed video recordings. Using high ink concentrations and contact times as short as 1 ms, we printed monolayers of hexadecanethiol on Au, which served as a selective etch resist. High-speed muCP yields defect-free monolayers that are independent of the dimensions of the printed patterns, have high contrast between printed and unprinted areas, and enable perfect reproducibility of prints.     

Weak first-order tilting transition in monolayers of mono- and bipolar docosanol derivatives

A systematic analysis of pressure-area isotherms and grazing incidence X-ray diffraction (GIXD) data of 22-methoxydocosan-1-ol (H3C-O-(CH2)22-OH, MDO), docosan-1-ol (H3C-(CH2)21-OH, DO), and docosyl methyl ether (H3C-(CH2)21-O-CH3, DME) monolayers on pure water between 10 and 35 degrees C is presented. All monolayers form fully condensed phases in the investigated temperature region. The GIXD data reveal that the monolayers exhibit the phase sequence -S at lower temperature and -LS at higher temperature. Phase diagrams have been established. Inserting a second hydrophilic group at the opposite end of the molecule (bipolar MDO) shifts the S/LS boundary to higher temperatures. All monolayers exhibit herringbone (HB) packing at lower temperatures. The "kink" in the isotherms observed at lower temperatures is replaced by a very small plateau region at higher temperatures. The entropy changes connected with this weak first-order tilting transition are much smaller compared with the first-order transition from liquid-expanded (LE) to condensed (LC). Additionally, this transition is endothermic in contrast to the LE/LC transition. The reason for the endothermic transition is the weaker positional correlation in the nontilted state compared with the tilted one. The appearance of the weak first-order endothermic transition can be connected with the changed phase sequence. X-ray photoelectron spectroscopy (XPS) measurements provide information about the polar group orientation. Considerations based on GIXD and XPS data as well as adhesion energy of the different terminal end groups lead to the conclusion that the hydroxyl group of the bipolar MDO is attached to the water surface while the methoxy group is in contact with air. The presented results show that the second hydrophilic group influences the monolayer properties in a mild way.     

Equilibrium distribution of permeants in polyelectrolyte microcapsules filled with negatively charged polyelectrolyte: the influence of ionic strength and solvent polarity

The effects of ionic strength and solvent polarity on the equilibrium distribution of fluorescein (FL) and FITC-dextran between the interior of polyelectrolyte multilayer microcapsules filled with negatively charged strong polyelectrolyte and the bulk solution were systematically investigated. A negatively charged strong polyelectrolyte, poly(styrene sulfonate) (PSS), used for CaCO3 core fabrication, was entrapped inside the capsules. Due to the semipermeability of the capsule wall, a Donnan equilibrium between the inner solution within the capsules and the bulk solution was created. The equilibrium distribution of the negatively charged permeants was investigated by means of confocal laser scanning microscopy as a function of ionic strength and solvent polarity. The equilibrium distribution of the negatively charged permeants could be tuned by increasing the bulk ionic strength to decrease the Donnan potential. Decreasing the solvent polarity also could enhance the permeation of FL, which induces a sudden increase of permeation when the ethanol volume fraction was higher than 0.7. This is mainly attributed to the precipitation of PSS. A theoretical model combining the Donnan equilibrium and Manning counterion condensation was employed to discuss the results.     

Thermal behavior of polyelectrolyte multilayer microcapsules: 2. Insight into molecular mechanisms for the PDADMAC/PSS system

Polyelectrolyte multilayer capsules consisting of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) were used as a model system to study the temperature-dependent behavior of polyelectrolyte multilayer films in aqueous media. Shells terminated with PSS shrink upon heating, whereas PDADMAC-terminated ones swell, independent of the nature of the first layer, as measured by means of confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Elemental analysis shows that the initial exponential layer growth of the film leads to a nearly neutral overall charge in the first case or a high positive excess charge in the latter. Depending on this overall charge either surface tension, due to an unfavorable polymer-solvent interaction, or electrostatics dominates, resulting in a shrinkage or expansion of capsules, respectively. Thus, it is possible to swell temperature-shrunk capsules by coating them with an additional PDADMAC layer. Micro-DSC measurements prove that polyelectrolyte multilayers undergo a glass transition in water at which the wall material softens, allowing the rearrangements to occur. It is found that the thermal history has an influence on the temperature behavior of capsules, especially on those ones terminated with PDADMAC. Also, the molecular weight of the polyelectrolytes affects the rearrangement of capsules. The lower the molecular weight and thus the smaller the entanglement of chains, the easier polyelectrolytes can rearrange.     

Research reactors as sources of atmospheric radioxenon

Radioxenon emissions of the TRIGA Mark II research reactor in Vienna were investigated with respect to a possible impact on the verification of the Comprehensive Nuclear Test-Ban-Treaty. Using the Swedish Automatic Unit for Noble Gas Acquisition (SAUNA II), five radioxenon isotopes ¹²⁵Xe, ^131mXe, ^133mXe, ¹³³Xe and ¹³⁵Xe were detected, of which ¹²⁵Xe is solely produced by neutron capture in stable atmospheric ¹²⁴Xe and hence acts as an indicator for neutron activation processes. The other nuclides are produced in both fission and neutron capture reactions. The detected activity concentrations ranged from 0.0010 to 190 Bq/m³. The source of the radioxenon is not yet fully clarified, but it could be micro-cracks in the fuel cladding, fission of ²³⁵U contaminations on the outside of the fuel elements or neutron activation of atmospheric Xe. Neutron deficient ¹²⁵Xe with its highly complex decay scheme was seen for the first time in a SAUNA system. In many experiments the activity ratios of the radioxenon nuclides carry the signature of nuclear explosions, if ^131mXe is omitted. Only if ^131mXe is included into the calculations of the isotopic activity ratios, the majority of the measurements revealed a “civil” signature (typical for a NPP). A significant contribution of the TRIGA Vienna to the global or European radioxenon inventory can be excluded. Due to the very low activities, the emissions are far below any concern for human health.