Color Indicator for Supramolecular Polymer Chemistry: Phenolphthalein‐Containing Thermo‐ and pH‐Sensitive N‐(Isopropyl)acrylamide Copolymers and β‐Cyclodextrin Complexation

The copolymerization parameters of N‐(isopropyl)acrylamide ( 1 ) and N‐(2‐hydroxy‐5‐(1‐(4‐hydroxyphenyl)‐3‐oxo‐1,3‐dihydroisobenzofuran‐1‐yl)benzyl)acrylamide ( 2 ) are determined. For both monomers, the homoaddition proceeds slightly faster than the heteroaddition step; however, the polymer formation occurs in a statistic fashion. Copolymers of different compositions are prepared and the cloud points are determined. Thereby, a significant influence of the concentration of monomer 2 and the pH value is found. For the first time, the complexation of polymer attached phenolphthalein by β‐cyclodextrins is shown. Furthermore, it is possible to achieve a decomplexation by the addition of suitable guest molecules. Both procedures can be followed with the naked eye.

     

Human and climate impact on 15N natural abundance of plants and soils in high-mountain ecosystems: a short review and two examples from the Eastern Pamirs and Mt. Kilimanjaro

Population pressure increasingly endangers high-mountain ecosystems such as the pastures in the Eastern Pamirs and the mountain forests on Mt. Kilimanjaro. At the same time, these ecosystems constitute the economic basis for millions of people living there. In our study, we, therefore, aimed at characterising the land-use effects on soil degradation and N-cycling by determining the natural abundance of ¹⁵N. A short review displays that δ¹⁵N of plant–soil systems may often serve as an integrated indicator of N-cycles with more positive δ¹⁵N values pointing towards N-losses. Results for the high-mountain pastures in the Eastern Pamirs show that intensively grazed pastures are significantly enriched in ¹⁵N compared to the less-exploited pastures by 3.5 ‰, on average. This can be attributed to soil organic matter degradation, volatile nitrogen losses, nitrogen leaching and a general opening of the N-cycle. Similarly, the intensively degraded savanna soils, the cultivated soils and the soils under disturbed forests on the foothill of Mt. Kilimanjaro reveal very positive δ¹⁵N values around 6.5 ‰. In contrast, the undisturbed forest soils in the montane zone are more depleted in ¹⁵N, indicating that here the N-cycle is relatively closed. However, significantly higher δ¹⁵N values characterise the upper montane forest zone at the transition to the subalpine zone. We suggest that this reflects N-losses by the recently monitored and climate change and antropogenically induced increasing fire frequency pushing the upper montane rainforest boundary rapidly downhill. Overall, we conclude that the analysis of the ¹⁵N natural abundance in high-mountain ecosystems is a purposeful tool for detecting land-use- or climate change-induced soil degradation and N-cycle opening.     

Finite Element Simulation of Frost Wedging in Ice Shelves

Break-up events in ice shelves have been studied extensively during the last years. One popular assumption links disintegration events to surface melting of the ice shelf in conjunction with growing melt-water ponds, leading to hydro-fracture. As this explanation only holds during warm seasons [1], the possibility of frost wedging as forcing mechanism for autumn and winter break-up events is considered. Frost wedging can only occur if a closed ice lid seals the water inside the crack. Hence, the present study of frost wedging in a single crack uses ice lid thicknesses to evaluate the additional pressure on the crack faces. The investigation of the resulting stress intensity factor as a measure of crack criticality follows consequently. The results show that freezing water inside a crack can result in unstable crack growth of an initially stable water filled crack. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A proximal gradient method for control problems with non-smooth and non-convex control cost

Computational Optimization and Applications - We investigate the convergence of the proximal gradient method applied to control problems with non-smooth and non-convex control cost. Here, we focus...     

Indicator Supraparticles for Smart Gasochromic Sensor Surfaces Reacting Ultrafast and Highly Sensitive

The detection of toxic gases, such as NH₃ and CO, in the environment is of high interest in chemical, electronic, and automotive industry as even small amounts can display a health risk for workers. Sensors for the real‐time monitoring of these gases should be simple, robust, reversible, highly sensitive, inexpensive and show a fast response. The indicator supraparticles presented herein can fulfill all of these requirements. They consist of silica nanoparticles, which are assembled to supraparticles upon spray‐drying. Sensing molecules such as Reichardt's dye and a binuclear rhodium complex are loaded onto the microparticles to target NH₃ and CO detection, respectively. The spray‐drying technique affords high flexibility in primary nanoparticle size selection and thus, easy adjustment of the porosity and specific surface area of the obtained micrometer‐sized supraparticles. This ultimately enables the fine‐tuning of the sensor sensitivity and response. For the application of the indicator supraparticles in a gas detection device, they can be immobilized on a coating. Due to their microscale size, they are large enough to poke out of thin coating layers, thus guaranteeing their gas accessibility, while being small enough to be applicable to flexible substrates.     

A Cerberus‐Inspired Anti‐Infective Multicomponent Gatekeeper Hydrogel against Infections with the Emerging “Superbug” Yeast Candida auris

The pathogenic yeast Candida auris has received increasing attention due to its ability to cause fatal infections, its resistance toward important fungicides, and its ability to persist on surfaces including medical devices in hospitals. To brace health care systems for this considerable risk, alternative therapeutic approaches such as antifungal peptides are urgently needed. In clinical wound care, a significant focus has been directed toward novel surgical (wound) dressings as first defense lines against C. auris. Inspired by Cerberus the Greek mythological “hound of Hades” that prevents the living from entering and the dead from leaving hell, the preparation of a gatekeeper hybrid hydrogel is reported featuring lectin‐mediated high‐affinity immobilization of C. auris cells from a collagen gel as a model substratum in combination with a release of an antifungal peptide drug to kill the trapped cells. The vision is an efficient and safe two‐layer medical composite hydrogel for the treatment of severe wound infections that typically occur in hospitals. Providing this new armament to the repertoire of possibilities for wound care in critical (intensive care) units may open new routes to shield and defend patients from infections and clinical facilities from spreading and invasion of C. auris and probably other fungal pathogens.     

Use of Halley's Method in the Nonlinear Finite Element Analysis

Halley's method is a higher order iteration method for the solution of nonlinear systems of equations. Unlike Newton's method, which converges quadratically in the vicinity of the solution, Halley's method can exhibit a cubic order of convergence. The equations of Halley's method for multiple dimensions are derived using Padé approximants and inverse one-point interpolation, as proposed by Cuyt. The investigation of the performance of Halley's method concentrates on eight-node volume elements for nonlinear deformations using Staint Venant-Kirchhoff's constitutive law, as well as a geometric linear theory of von Mises plasticity. The comparison with Newton's method reveals the sensibility of Halley's method, in view of the radius of attraction but also demonstrates the advantages of Halley's method considering simulation costs and the order of convergence. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Defluorosilylation of Industrially Relevant Fluoroolefins Using Nucleophilic Silicon Reagents

A number of new magnesium and lithium silyl reagents were prepared and shown to be outstanding nucleophiles in reactions with industrially relevant fluoroolefins. These reactions result in a net transformation of either sp² or sp³ C?F bonds into C?Si bonds by two modes of nucleophilic attack (S_NV or S_N2′). The methods are mild, proceeding with high chemo‐ and regioselectivity. Mechanistic pathways are described that lead to new substitution patterns from HFO‐1234yf, HFO‐1234ze, and HFO‐1336mzz, previously inaccessible by transition metal catalyzed difluorosilylation routes.     

Suppression of the Verwey Transition by Charge Trapping

The Verwey transition in Fe₃O₄ nanoparticles with a mean diameter of 6.3 nm is suppressed after capping the particles with a 3.5 nm thick shell of SiO₂. By X‐ray absorption spectroscopy and its associated X‐ray magnetic circular dichroism this suppression can be correlated to localized Fe²⁺ states and a reduced double exchange visible in different site‐specific magnetization behavior in high magnetic fields. The results are discussed in terms of charge trapping at defects in the Fe₃O₄/ SiO₂ interface and the consequent difficulties in the formation of the common phases of Fe₃O₄. By comparison to X‐ray absorption spectra of bare Fe₃O₄ nanoparticles in course of the Verwey transition, particular changes in the spectral shape could be correlated to changes in the number of unoccupied d states for Fe ions at different lattice sites. These findings are supported by density functional theory calculations.