Systematic front distortion and presence of consecutive fronts in a precipitation system

A new simple reaction-diffusion system is presented focusing on pattern formation phenomena as consecutive precipitation fronts and distortion of the precipitation front.The chemical system investigated here is based on the amphoteric property of aluminum hydroxide and exhibits two unique phenomena. Both the existence of consecutive precipitation fronts and distortion are reported for the first time. The precipitation patterns could be controlled by the pH field, and the distortion of the precipitation front can be practical for microtechnological applications of reaction-diffusion systems

Biological studies with comprehensive 2D-GC-HRMS screening: Exploring the human sweat volatilome

A key issue in GCxGC-HRMS data analysis is how to approach large-sample studies in an efficient and comprehensive way. We have developed a semi-automated data-driven workflow from identification to suspect screening, which allows highly selective monitoring of each identified chemical in a large-sample dataset. The example dataset used to illustrate the potential of the approach consisted of human sweat samples from 40 participants, including field blanks (80 samples). These samples have been collected in a Horizon 2020 project to investigate the capacity of body odour to communicate emotion and influence social behaviour. We used dy-namic headspace extraction, which allows comprehensive extraction with high preconcentration capability, and has to date only been used for a few biological applications. We were able to detect a set of 326 compounds from a diverse range of chemical classes (278 identified compounds, 39 class unknowns, and 9 true unknowns). Unlike partitioning-based extraction methods, the developed method detects semi-polar (log P < 2) nitrogen and oxygen-containing compounds. However, it is unable to detect certain acids due to the pH conditions of un-modified sweat samples. We believe that our framework will open up the possibility of efficiently using GCxGC-HRMS for large-sample studies in a wide range of applications such as biological and environmental studies

Potential physiological stress biomarkers in human sweat

Emotional sweating occurs in response to affective stimuli like fear, anxiety, or stress and is more evident in specific parts of the body such as the palms, soles, and axillae. During emotional sweating, humans release many volatile organic compounds (VOCs) that could play a crucial role as possible com-municative signals of specific emotions. In this preliminary study, we investigated seven volatiles belonging to the chemical class of acids and released from the armpit as possible stress biomarkers. To this aim, we processed sweat VOCs and physiological stress correlates such as heart rate variability (HRV), electrodermal activity, and thermal imaging during a Stroop color-word test. Particularly, we modelled the variability of well-known stress markers extracted from the physiological signals as a function of the acid VOCs by means of LASSO regression. LASSO results revealed that the dodecanoic acid was the only selected regressor and it was able to significantly explain more than 64 % of the variance of both the mean temperature of the tip of the nose (p=0.018, R2=0.64) and of the mean HRV (p=0.011, R2=0.67). Although preliminary, our results suggest that dodecanoic acid could be a marker of the sympathetic nervous system response to stress stimuli, opening for the detection of new biomarkers of stress

Bioavailability of organic contaminants in a changing climate

The effects of predicted future climate change was investigated with special emphasis on the association of organic contaminants with dissolved organic carbon (DOC) in the Baltic Sea. An automated method was developed for the measurements of DOC - water distribution constants at realistic DOC concentrations in brackish water. The method proved to be valid for 30 organic contaminants with different structural elements in the 5 – 100 mg car bon/L DOC concentration range. There were limitations of this method. Firstly, its applicability is limited towards contaminants with lower affinity to DOC. Secondly, at higher (>100 mg carbon/L) DOC concentrations the sorption of contaminants was underest imated. Afterwards, water samples were collected from 15 points within the Baltic Sea in a north - south gradient t o examine the spatial differences in DOC characteristics and sorption properties . The DOC samples were analyzed using proton nuclear magnetic resonance and ultraviolet spectroscopy. Results from both techniques indicated that the aromatic nature of the DOC pool increased towards the northern Baltic Sea. This was expected as the freshwater inflow has high significance in controlling the hydrograp hic conditions in the Bothnian Bay. Sorption of organic contaminants was subsequently measured in the same samples. The results showed decreased sorption from north to south for hydrophobic contaminants such as chlorinated benzenes but for contaminants lik e tributyl - phosphate no spatial tendencies were observed. The data generated was used to determine molecular descriptors of DOC using linear free energy relationships. The results indicated a higher significance of hy drogen bond donor/acceptor functional g roups of the DOC in the south. Changes in contaminant distribution were simulated in model pelagic ecosystems at possible endpoints predicted by future climate change scenarios. Separate and combined effects of temperature a nd DOC were studied in mesocosms. The results indicated interesting tendencies. Increased temperature resulted in increased losses in the amounts of organic contaminants. Increased DOC levels promoted sedimentation and sorption of contaminants to particulate matter and biota. Hi gher amounts of contaminants were retained. The combined effects of the two factors led to and overall decrease in dissolved amounts. Higher losses or increased sedimentation and sorption to particles were also observed depending on contaminant properties.EcoChang

Analysis of volatile organic compounds in indoor environments using thermal desorption with comprehensive two-dimensional gas chromatography and high-resolution time-of-flight mass spectrometry

Building-related health effects are frequently observed. Several factors have been listed as possible causes including temperature, humidity, light conditions, presence of particulate matter, and microorganisms or volatile organic compounds. To be able to link exposure to specific volatile organic compounds to building-related health effects, powerful and comprehensive analytical methods are required. For this purpose, we developed an active air sampling method that utilizes dual-bed tubes loaded with TENAX-TA and Carboxen-1000 adsorbents to sample two parallel air samples of 4 L each. For the comprehensive volatile organic compounds analysis, an automated thermal desorption comprehensive two-dimensional gas chromatography high-resolution time-of-flight mass spectrometry method was developed and used. It allowed targeted analysis of approximately 90 known volatile organic compounds with relative standard deviations below 25% for the vast majority of target volatile organic compounds. It also allowed semiquantification (no matching standards) of numerous nontarget air contaminants using the same data set. The nontarget analysis workflow included peak finding, background elimination, feature alignment, detection frequency filtering, and tentative identification. Application of the workflow to air samples from 68 indoor environments at a large hospital complex resulted in a comprehensive volatile organic compound characterization, including 178 single compounds and 13 hydrocarbon groups

Isolation of single molecules from complex GCxGC chromatograms

We developed a novel approach capable of isolating and recollecting nearly any molecule from complex GCxGC chromatograms. This was achieved by modifying a GCxGC-Q-TOF system with a Deans switch, a passive splitter, and careful adjustments of flows and capillary dimensions. The setup was evaluated with more than a hundred standard chemicals covering a wide range of volatility (boiling points: 56 – 343 ⁰C) and polarity (log P: -0.2 – 9.4). We found that recovery from tube to tube can become highly efficient if a custom-made adapter is attached directly on the FID port (average recovery rate of 76 ± 7%). Furthermore, we could achieve an isolation down to a minimum distance of 50 ms between baseline separated eluting peaks. In addition, the setup was designed for easy adaptation by repurposing existing instrument control software to define the isolation windows for the compounds of interest (first and second column retention time windows). We expect this novel development to allow several new applications, e.g., the isolation or selective enrichment of molecules in food and flavour analysis; the investigation of suspect chemicals (incl. unknowns) for effect directed analysis (e.g., bioassays), and the isolation of chemicals for further chemical analysis

The Liesegang eyes phenomenon

Radially symmetric pattern formation phenomena were investigated experimentally and numerically in 2D using a new experimental arrangement in a precipitation system. We examined the dependence of the pattern structure and the evolution of the precipitation front on its curvature. Depending on the radius of the reaction medium, two types of precipitation patterns has been observed: (a) pattern with a continuously distributed precipitate and a well detectable precipitation-free domain (Liesegang eyes phenomenon); (b) pattern with a continuous precipitation zone and discrete ring formation. Results of our simulations are in a good agreement with the experimental observations

Breaking the Rules: On the Relative Stability of Some Methylencyclopropane and Methylcyclopropene Derivatives

The structure of the spirocyclic product obtained by reacting catechol with 1,1-dichloro-2-(chloromethyl)cyclopropane is shown by NMR and X-ray analysis to be that of a 2-methylcyclopropene (MeCP), instead of the previously reported 2-methylenecyclopropane (MCP) one. The study of the equilibration between the two isomeric forms by experimental and computational means (including both Density Functional Theory – DFT – and Coupled Cluster with single, double, and perturbative triple excitations – CCSD(T) – calculations) revealed that, at variance with most of the alkylidenecyclopropane/alkylcyclopropene systems described to date, for the compounds of the present study the MeCP derivative is more stable by≈ 2.5–3.0 Kcal mol−1 than the MCP one. The extension of the DFT and CCSD(T) study to other spiro-MCP/MeCP pairs suggests that the origin of the unexpected shift of the equilibrium position can be tracked back to a combination of electronic and ring-strain effects. These findings lead to re-think a long-standing, and substantially undisputed belief in the area of unsaturated cyclopropane derivatives