22 research outputs found
A novel method to determine the elastic modulus of extremely soft materials
Determination of the elastic moduli of extremely soft materials that may deform under their own weight
is a rather difficult experimental task. A new method has been elaborated by means of which the elastic
modulus of such materials can be determined. This method is generally applicable to all soft materials
with purely neo-Hookean elastic deformation behaviour with elastic moduli lower than 1 kPa. Our novel
method utilises the self-deformation of pendent gel cylinders under gravity. When suspended, the
material at the very top bears the weight of the entire gel cylinder, but that at the bottom carries no
load at all. Due to the non-uniform stress distribution along the gel sample both the stress and the
resulting strain show position dependence. The cross-sectional area of the material is lowest at the top
of the sample and gradually increases towards its bottom. The equilibrium geometry of the pendant gel
is used to evaluate the elastic modulus. Experimental data obtained by the proposed new method were
compared to the results obtained from underwater measurements. The parameters affecting the
measurement uncertainty were studied by a Pareto analysis of a series of adaptive Monte Carlo
simulations. It has been shown that our method provides an easily achievable method to provide an
accurate determination of the elastic modulus of extremely soft matter typically applicable for moduli
below 1 kPa
Effect of temperature and substitution on cope rearrangement : A symmetry perspective
Many reactions feature symmetry variation along the reaction path on the potential energy surface. The interconversion of the point group symmetry of the stationary points can be characteristic of these processes. Increasing the temperature, however, leads to the loss of symmetry in its traditional yes-no language. We find that in such cases the instantaneous distance of the molecular structure from its symmetric counterpart is a suitable collective variable that can describe the reaction process. We show that this quantity, the continuous symmetry measure (CSM) has a positive linear relationship with temperature, implying that even highly symmetric molecules should be considered as asymmetric above 0K. Using ab initio molecular dynamics we simulate the temperature induced Cope rearrangements of several fluxional molecules and employ different CSM-s to follow the reaction progress. We use this methodology to demonstrate the validity of important concepts governing these reactions: Woodward-Hoffmann rules and TS aromaticity. Statistical analysis of the CSM distributions reveals that ligands connected to the carbon frame have profound effect on the reaction course. In particular our results show that lower temperatures tend to enhance the differences between the TS-stabilizing effect of the substituents
Pyrite in contact with supercritical water: the desolation of steam
The supercritical water and pyrite interface has been studied by DFT calculations. A surprisingly dry surface has been found which points to a new reactivity under extreme conditions which has relevance in the iron–sulfur world prebiotic chemistry of the early Earth.</p
webchem: An R Package to Retrieve Chemical Information from the Web
A wide range of chemical information is freely available online, including identifiers, experimental and predicted chemical properties. However, these data are scattered over various data sources and not easily accessible to researchers. Manual searching and downloading of such data is time-consuming and error-prone. We developed the open-source R package webchem that allows users to automatically query chemical data from currently 14 web sources. These cover a broad spectrum of information. The data are automatically imported into an R object and can directly be used in subsequent analyses. webchem enables easy, structured and reproducible data retrieval and usage from publicly available web sources. In addition, it facilitates data cleaning, identification and reporting of substances. Consequently, it reduces the time researchers need to spend on chemical data compilation
How Does Experimental Design Modify the Result of Daphnia magna Heartbeat Rate Test? ─ Analyses of Factors Affecting the Sensitivity of the Test System
Development of an unconventional test method involves usually the comparison of biological responses under a variety of test conditions. The quality of these biological methods relies on an appropriate experimental design. The Daphnia magna heartbeat rate as a physiological endpoint for assessing aquatic pollution has been of minor interest so far; nonetheless, this could be an early and sensitive indicator of the harmful effect of micropollutants. Our aim was to set up the optimal experimental design of the heartbeat rate test. The studied factors were the composition of the test medium, the age of the test organism, and the exposure time, at triclosan concentrations between 0.2–2000 μg/L. According to the evaluation of test results the optimal test condition for the heartbeat rate test assumes tap water as test medium, 10-day-old test organisms and 48 h exposure time
Efficient direct 2,2,2-trifluoroethylation of indoles via C-H functionalization
A novel highly C3 selective metal free trifluoroethylation of indoles using 2,2,2-trifuoroethyl(mesityl)-iodonium triflate was developed. The methodology enables the introduction of a trifluoroethyl group in a fast and efficient reaction under mild conditions with high functional group tolerance. Beyond the synthetic developments, quantum chemical calculations provide a deeper understanding of the transformation. This journal i
Direct ortho-Trifluoroethylation of Aromatic Ureas by Palladium Catalyzed C-H activation: A Missing Piece of Aromatic Substitutions
Understanding and Exploitation of Neighboring Heteroatom Effect for the Mild N-arylation of Heterocycles with Diaryliodonium Salts under Aqueous Conditions: A Theoretical and Experimental Mechanistic Study.
The mechanism of
arylation of N-heterocycles with unsymmetric diaryliodonium
salts is elucidated. The fast and efficient N-arylation reaction is
interpreted in terms of the bifunctionality of the substrate: The
consecutive actions of properly oriented Lewis base and Brønsted
acid centers in sufficient proximity result in the fast and efficient
N-arylation. The mechanistic picture points to a promising synthetic
strategy where suitably positioned nucleophilic and acidic centers
enable functionalization, and it is tested experimentally