Elasticity, strength and resilience: A comparative study on mechanical signatures of α-Helix, β-sheet and tropocollagen domains

In biology, structural design and materials engineering is unified through formation of hierarchical features with atomic resolution, from nano to macro. Three molecular building blocks are particularly prevalent in all structural protein materials: alpha helices (AHs), beta-sheets (BSs) and tropocollagen (TC). In this article we present a comparative study of these three key building blocks by focusing on their mechanical signatures, based on results from full-atomistic simulation studies. We find that each of the basic structures is associated with a characteristic material behavior: AH protein domains provide resilience at large deformation through energy dissipation at low force levels, BS protein domains provide great strength under shear loading, and tropocollagen molecules provide large elasticity for deformation recovery. This suggests that AHs, BSs, and TC molecules have mutually exclusive mechanical signatures. We correlate each of these basic properties with the molecule’s structure and the associated fundamental rupture mechanisms. Our study may enable the use of abundant protein building blocks in nanoengineered materials, and may provide critical insight into basic biological mechanisms for bio-inspired nanotechnologies. The transfer towards the design of novel nanostructures could lead to new multifunctional and mechanically active, tunable, and changeable materials.     

Anticipatory stress influences decision making under explicit risk conditions.

Recent research has suggested that stress may affect memory, executive functioning, and decision making on the basis of emotional feedback processing. The current study examined whether anticipatory stress affects decision making measured with the Game of Dice Task (GDT), a decision-making task with explicit and stable rules that taps both executive functioning and feedback learning. The authors induced stress in 20 participants by having them anticipate giving a public speech and also examined 20 comparison subjects. The authors assessed the level of stress with questionnaires and endocrine markers (salivary cortisol and alpha-amylase), both revealing that speech anticipation led to increased stress. Results of the GDT showed that participants under stress scored significantly lower than the comparison group and that GDT performance was negatively correlated with the increase of cortisol. Our results indicate that stress can lead to disadvantageous decision making even when explicit and stable information about outcome contingencies is provided. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Donor Atom‐Stabilized Aluminum Alkyls as Cocatalysts for the Ziegler–Natta Polymerization of Propene

A number of organoaluminum compounds, stabilized with intramolecular nitrogen‐ or oxygen‐donor functions, have been used as cocatalysts for the MgCl₂/TiCl₄‐catalyzed homopolymerization of propene as well as for the copolymerization of ethene with propene. The polymerization behavior of these aluminum alkyls was examined at different Al/Ti ratios within the range of 2 to 50 and compared with the reference of triethylaluminum (TEA). Especially the alkyls [2‐(N,N‐dimethylaminomethyl)phenyl]dimethylaluminum ( 1 ) and [2‐(N,N‐dimethylaminomethyl)phenyl]diethylaluminum ( 2 ) show the highest activities at very low Al/Ti ratios in the homopolymerization of propene, whereas TEA is almost inactive. The species [8‐(N,N‐dimethylamino)naphthyl]dimethylaluminum ( 4 ) reaches the highest activity of all examined alkyls and is very close to the highest value obtained with TEA. Bulky iso‐butyl groups at the aluminum center are responsible for the very poor performance of the nitrogen stabilized cocatalysts [8‐(N,N‐dimethylamino)naphthyl]diisobutylaluminum ( 5 ) and [2‐(N,N‐dimethylaminomethyl)phenyl]diisobutylaluminum ( 3 ). The properties of the polypropenes synthesized with the stabilized organoaluminum species are similar to those produced with TEA but with a distinctly higher molar mass. In the case of 1 , it was possible to increase the molar mass by a factor of three. For the copolymerizations, the compounds [2‐(N,N‐diethylaminomethyl)phenyl]diethylaluminum ( 7 ) and (2‐methoxybenzyl)diisobutylaluminum ( 8 ) were found to be most suitable, producing polymers with significantly higher activities than TEA. For all copolymers two fractions were obtained, one crystalline fraction with a low and an amorphous part with a high amount of comonomer. In both fractions, 7 and 8 provide a higher comonomer incorporation than TEA.     

A Comparison of Organically and Conventionally Grown Foods—Results of a Review of the Relevant Literature

This review is concerned with the summary and evaluation of the results from more than 150 investigations comparing the quality of conventionally and organically produced food or of foods produced with the aid of different fertilisation systems. Cereals, potatoes, vegetables, fruits, wine, beer, bread, cakes and pastries, milk, meat, eggs and honey, as well as products made from them, have been included in the review. Most of the studies evaluated are physico-chemical investigations of concentrations of desirable and undesirable ingredients, pesticide residues, contaminants, sensory analyses and feed experiments with animals. Nutritional studies in humans and experiments which used holistic methods of analysis are also included. Since different methods of sampling were used in the investigations, a summary evaluation of individual results is extremely difficult. Even when the sampling methods are of the same type, a great many factors have to be taken into consideration which are not directly related to the production system but which do influence food quality to a large degree. Despite the heterogeneity of the sample material, some differences in quality between products from conventional and organic farming or foods produced with the aid of different fertilisation systems have been identified. © 1997 SCI     

Reactive surfactants in heterophase polymerization. VI. Synthesis and screening of polymerizable surfactants (surfmers) with varying reactivity in high solids styrene—butyl acrylate—acrylic acid emulsion polymerization

Several polymerizable surfactants (surfmers) have been used in the semi-continuous emulsion copolymerization of styrene, butyl acrylate, and acrylic acid. Three of the (anionic) surfmers (sodium 11-crotonoyl undecan-1-yl sulfate, sodium 11-methacryloyl undecan-1-sulfate, and sodium sulfopropyl tetradecyl maleate) were prepared in house with purities between 53 and 82%. Physicochemical properties such as the critical micelle concentration, the adsorption isotherm, and the specific adsorption area were determined. The surfmers were then used with constant addition profiles in semicontinuous reactions, and the instantaneous conversions of the main monomers determined. The particle size, amount of coagulum, surface tension, and stability against electrolyte solutions of the latices were evaluated. Films were cast of some of the latices, and the visual appearance and water adsorption were assessed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 183–1820, 1997     

Isothiazol-1,1-dioxide – vom Süßstoff zum chiralen Auxiliar in der stereoselektiven Synthese

Isothiazole 1,1-dioxides – From Sweeter to Chiral Auxiliar in the Stereoselective Synthesis This review gives a report of the last ten years on the new synthetic methods, reactions and biological applications of isothiazole 1,1-dioxide derivatives. the formation of monocyclic and heterocyclic annelated isothiazole 1,1-dioxides by oxidation of isothiazoles, cyclocondensation of sulfonamides and cycloaddition of isothiazol-3(2H)-one 1,1-dioxides are discussed in more detail. Furthermore, the preparation of pharmacologically important N-substituted saccharines is reported. New saccharine-derived chiral N-enoyl-and N-acyl-2,3-dihydro-1,2-benzisothiazole 1,1-dioxides serve as advantageous stereoface-directing dienophile and dipolarophile auxiliaries in Diels-Alder-reactions and 1,3-dipolar cycloadditions. Asymmetric alkylations, acylations and aldolizations are also described.     

Field-deployable, high-resolution, time-of-flight aerosol mass spectrometer

The development of a new high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is reported. The high-resolution capabilities of this instrument allow the direct separation of most ions from inorganic and organic species at the same nominal m/z, the quantification of several types of organic fragments (CxHy, CxHyOz, CxHyNp, CxHyOzNp), and the direct identification of organic nitrogen and organosulfur content. This real-time instrument is field-deployable, and its high time resolution (0.5 Hz has been demonstrated) makes it well-suited for studies in which time resolution is critical, such as aircraft studies. The instrument has two ion optical modes: a single-reflection configuration offers higher sensitivity and lower resolving power (up to approximately 2100 at m/z 200), and a two-reflectron configuration yields higher resolving power (up to approximately 4300 at m/z 200) with lower sensitivity. The instrument also allows the determination of the size distributions of all ions. One-minute detection limits for submicrometer aerosol are <0.04 microg m(-3) for all species in the high-sensitivity mode and <0.4 microg m(-3) in the high-resolution mode. Examples of ambient aerosol data are presented from the SOAR-1 study in Riverside, CA, in which the spectra of ambient organic species are dominated by CxHy and CxHyOz fragments, and different organic and inorganic fragments at the same nominal m/z show different size distributions. Data are also presented from the MIRAGE C-130 aircraft study near Mexico City, showing high correlation with independent measurements of surrogate aerosol mass concentration.     

Metabolism of quercetin and rutin by the pig caecal microflora prepared by freeze-preservation

Several studies confirm a protection of cardiovascular diseases and certain forms of cancer by dietary flavonoid intake. The bioavailability of flavonoids is influenced by the metabolism of the microflora in the intestine. Using a new in vitro model system the deglycosylation of the flavonol rutin and the degradation of its aglycone quercetin were investigated by using fresh pig caecal inocula in comparison to inocula prepared before by freeze-preservation between 6 wk and 5 months. The incubation experiments led to the same pattern of phenolic degradation products in comparable amounts in both preparations using HPLC-DAD and GC-flame ionization detection (GC-FID) or GC-MS detection within 24-48 h of incubation. With the preservation of the microbial vitality and the metabolic efficiency by freeze-preparation over several months the experimental design of microbial metabolism studies will be independent in time and locality.     

Studies on acrylamide levels in roasting, storage and brewing of coffee

The content of acrylamide in coffee reaches a peak early in the roasting process, reflecting occurrence of both formation and destruction of acrylamide during roasting. Levels of acrylamide in the fully roasted product are a small fraction of the peak reached earlier. Glucose and moisture in green coffee do not show a significant correlation with acrylamide in roasted coffee. Pre-roasting levels of asparagine show a correlation only in Arabica coffee. The main factors affecting the level of acrylamide in roasted coffee appear to be the Arabica/Robusta ratio, with Robusta giving higher levels; time and degree of roast, with both shorter and lighter roasting at the edges of the normal roasting range giving higher levels; storage condition and time, with clear reduction at ambient storage. This storage reduction of acrylamide followed second order reaction kinetics with an activation energy of 73 KJ/mole. The acrylamide in roasted coffee is largely extracted into the brew and stable within usual time of consumption. As these four main factors also substantially affect the sensorial characteristics of the brew, and as modifications of the process have to comply with the consumer-accepted boundaries of taste profiles, only small effects on the acrylamide level are expected to be achievable.