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911.
Steven van Terwingen Daniel Brüx Ruimin Wang Ulli Englert 《Molecules (Basel, Switzerland)》2021,26(13)
In the hydrochloride of a pyrazolyl-substituted acetylacetone, the chloride anion is hydrogen-bonded to the protonated pyrazolyl moiety. Equimolar co-crystallization with tetrafluorodiiodobenzene (TFDIB) leads to a supramolecular aggregate in which TFDIB is situated on a crystallographic center of inversion. The iodine atom in the asymmetric unit acts as halogen bond donor, and the chloride acceptor approaches the -hole of this TFDIB iodine subtending an almost linear halogen bond, with Cl···I = Å and Cl···I–C = 179.32(6)°. This contact is roughly orthogonal to the N–H···Cl hydrogen bond. An analysis of the electron density according to Bader’s Quantum Theory of Atoms in Molecules confirms bond critical points (bcps) for both short contacts, with = 0.129 for the halogen and e for the hydrogen bond. Our halogen-bonded adduct represents the prototype for a future class of co-crystals with tunable electron density distribution about the -hole contact. 相似文献
912.
Scarlett Puebla-Barragan Emiley Watson Charlotte van der Veer John A. Chmiel Charles Carr Jeremy P. Burton Mark Sumarah Remco Kort Gregor Reid 《Molecules (Basel, Switzerland)》2021,26(15)
Lactobacillus crispatus is the dominant species in the vagina of many women. With the potential for strains of this species to be used as a probiotic to help prevent and treat dysbiosis, we investigated isolates from vaginal swabs with Lactobacillus-dominated and a dysbiotic microbiota. A comparative genome analysis led to the identification of metabolic pathways for synthesis and degradation of three major biogenic amines in most strains. However, targeted metabolomic analysis of the production and degradation of biogenic amines showed that certain strains have either the ability to produce or to degrade these compounds. Notably, six strains produced cadaverine, one produced putrescine, and two produced tyramine. These biogenic amines are known to raise vaginal pH, cause malodour, and make the environment more favourable to vaginal pathogens. In vitro experiments confirmed that strains isolated from women with a dysbiotic vaginal microbiota have higher antimicrobial effects against the common urogenital pathogens Escherichia coli and Enterococcus faecium. The results indicate that not all L. crispatus vaginal strains appear suitable for probiotic application and the basis for selection should not be only the overall composition of the vaginal microbiota of the host from which they came, but specific biochemical and genetic traits. 相似文献
913.
&#x;ukasz Orze&#x; Maria Oszajca Justyna Polaczek Dominika Por&#x;bska Rudi van Eldik Grayna Stochel 《Molecules (Basel, Switzerland)》2021,26(16)
Pressure is one of the most important parameters controlling the kinetics of chemical reactions. The ability to combine high-pressure techniques with time-resolved spectroscopy has provided a powerful tool in the study of reaction mechanisms. This review is focused on the supporting role of high-pressure kinetic and spectroscopic methods in the exploration of nitric oxide bioinorganic chemistry. Nitric oxide and other reactive nitrogen species (RNS) are important biological mediators involved in both physiological and pathological processes. Understanding molecular mechanisms of their interactions with redox-active metal/non-metal centers in biological targets, such as cofactors, prosthetic groups, and proteins, is crucial for the improved therapy of various diseases. The present review is an attempt to demonstrate how the application of high-pressure kinetic and spectroscopic methods can add additional information, thus enabling the mechanistic interpretation of various NO bioinorganic reactions. 相似文献
914.
Chantelle Human Dalene de Beer Magdalena Muller Marieta van der Rijst Marique Aucamp Andreas Tredoux Andr de Villiers Elizabeth Joubert 《Molecules (Basel, Switzerland)》2021,26(17)
Green rooibos extract (GRE), shown to improve hyperglycemia and HDL/LDL blood cholesterol, has potential as a nutraceutical beverage ingredient. The main bioactive compound of the extract is aspalathin, a C-glucosyl dihydrochalcone. The study aimed to determine the effect of common iced tea ingredients (citric acid, ascorbic acid, and xylitol) on the stability of GRE, microencapsulated with inulin for production of a powdered beverage. The stability of the powder mixtures stored in semi-permeable (5 months) and impermeable (12 months) single-serve packaging at 30 °C and 40 °C/65% relative humidity was assessed. More pronounced clumping and darkening of the powders, in combination with higher first order reaction rate constants for dihydrochalcone degradation, indicated the negative effect of higher storage temperature and an increase in moisture content when stored in the semi-permeable packaging. These changes were further increased by the addition of crystalline ingredients, especially citric acid monohydrate. The sensory profile of the powders (reconstituted to beverage strength iced tea solutions) changed with storage from a predominant green-vegetal aroma to a fruity-sweet aroma, especially when stored at 40 °C/65% RH in the semi-permeable packaging. The change in the sensory profile of the powder mixtures could be attributed to a decrease in volatile compounds such as 2-hexenal, (Z)-2-heptenal, (E)-2-octenal, (E)-2-nonenal, (E,Z)-2,6-nonadienal and (E)-2-decenal associated with “green-like” aromas, rather than an increase in fruity and sweet aroma-impact compounds. Green rooibos extract powders would require storage at temperatures ≤ 30 °C and protection against moisture uptake to be chemically and physically shelf-stable and maintain their sensory profiles. 相似文献
915.
916.
This paper introduces a semi‐discrete implicit Euler (SDIE) scheme for the Allen‐Cahn equation (ACE) with fidelity forcing on graphs. The continuous‐in‐time version of this differential equation was pioneered by Bertozzi and Flenner in 2012 as a method for graph classification problems, such as semi‐supervised learning and image segmentation. In 2013, Merkurjev et. al. used a Merriman‐Bence‐Osher (MBO) scheme with fidelity forcing instead, as heuristically it was expected to give similar results to the ACE. The current paper rigorously establishes the graph MBO scheme with fidelity forcing as a special case of an SDIE scheme for the graph ACE with fidelity forcing. This connection requires the use of the double‐obstacle potential in the ACE, as was already demonstrated by Budd and Van Gennip in 2020 in the context of ACE without a fidelity forcing term. We also prove that solutions of the SDIE scheme converge to solutions of the graph ACE with fidelity forcing as the discrete time step converges to zero. In the second part of the paper we develop the SDIE scheme as a classification algorithm. We also introduce some innovations into the algorithms for the SDIE and MBO schemes. For large graphs, we use a QR decomposition method to compute an eigendecomposition from a Nyström extension, which outperforms the method used by, for example, Bertozzi and Flenner in 2012, in accuracy, stability, and speed. Moreover, we replace the Euler discretization for the scheme's diffusion step by a computation based on the Strang formula for matrix exponentials. We apply this algorithm to a number of image segmentation problems, and compare the performance with that of the graph MBO scheme with fidelity forcing. We find that while the general SDIE scheme does not perform better than the MBO special case at this task, our other innovations lead to a significantly better segmentation than that from previous literature. We also empirically quantify the uncertainty that this segmentation inherits from the randomness in the Nyström extension. 相似文献
917.
Fuxi Bao Dr. Erno Kemppainen Iris Dorbandt Radu Bors Dr. Fanxing Xi Prof. Dr. Rutger Schlatmann Prof. Dr. Roel van de Krol Dr. Sonya Calnan 《ChemElectroChem》2021,8(1):195-208
Nickel-molybdenum (NiMo) alloys can be a possible alternative to platinum as hydrogen evolution reaction (HER) catalysts because of the superior HER activity. However, the superior HER activity and the pH-dependent kinetics are not currently fully understood. Herein, we present a study of HER kinetics and mechanisms of NiMo in alkaline, near-neutral and acidic media by combining voltammetry measurements with electrochemical impedance spectroscopy and a microkinetic model. The results indicate that, compared to Ni, NiMo has significantly higher active surface area and intrinsic HER activity. In the subsequent measurements, we demonstrated that different from the existing explanations to the HER mechanisms for NiMo, the HER process in acidic, near-neutral, and alkaline media is controlled by the Heyrovsky step. Our results show that increasing pH increases the hydrogen coverage, which increases the Tafel-slope at low overpotentials, eventually resulting in only a single Tafel slope, which would commonly be interpreted as a Volmer-limited reaction. Furthermore, the studies of thickness effect on HER kinetics show that the HER kinetics of NiMo are thickness-dependent. In phosphate buffer, the increase in thickness did not significantly increase the double-layer capacitance, but simulations with the microkinetic model indicate that the active surface area still increased similarly to other electrolytes, which is likely related to the type of electrolyte used. 相似文献
918.
Dr. Sathiyaraj Kandhasamy Dr. Georgios Nikiforidis Dr. Gert Jan Jongerden Ferdy Jongerden Prof. Mauritius C. M. van de Sanden Dr. Mihalis N. Tsampas 《ChemElectroChem》2021,8(6):1156-1166
Based on the preliminary investigation of the intermediate temperature sodium-sulfur (IT-NaS) battery (150 °C), herein we advance this energy storage system, by retuning the catholyte formulation; namely i) concentration, ii) layer thickness, and iii) cut-off limits during galvanostatic charge-discharge cycling, lowering the operating temperature and improving cell design. The systematic implementation of these strategies boosted the cell performance significantly, delivering 112 mAh/g-sulfur, 90 % of its theoretical specific capacity (125 mAh/g-sulfur), and 50 deep reversible charge-discharge cycles with coulombic and round-trip energy efficiencies of 97±3 % and 73±4 %, respectively. Along with the stability and improvement of cycle life, this study demonstrates, for the first time, the practicality of the tubular IT-NaS technology at a temperature as low as 125 °C. 相似文献
919.
Marleen H. M. E. van Stevendaal Prof. Jan C. M. van Hest Dr. Alexander F. Mason 《ChemSystemsChem》2021,3(5):e2100009
Bottom-up synthetic cells, where diverse non-living materials are combined in creative ways in order to construct increasingly life-like and adaptive systems, are fast approaching a level of function that will enable significant advances in solving specific biomedical challenges. Over the last 10 years, we have seen a wide variety of synthetic cell based approaches to challenges in regulating antimicrobial activity, delivering cargo to mammalian cells, and “growth support”. Despite this progress, there has not been a widespread uptake of synthetic cell technologies in biomedical engineering. In this Review, we highlight both the strengths and limitations of these existing synthetic cell applications, as well as give an overview of the state-of-the-art of synthetic cell technology that has yet been applied to cellular contexts. In doing so we aim to identify opportunities for the advancement of this unique intersection of research fields. 相似文献
920.
Krska R Schubert-Ullrich P Josephs RD Emteborg H Buttinger G Pettersson H van Egmond HP Schothorst RC Macdonald S Chan D 《Analytical and bioanalytical chemistry》2007,388(5-6):1215-1226
This paper presents results from the European Commission-funded project Doncalibrant, the objective of which was to produce
calibrators with certified mass fractions of the Fusarium toxins deoxynivalenol (DON), 3-acetyldeoxynivalenol (3-Ac-DON), 15-acetyldeoxynivalenol (15-Ac-DON), and nivalenol (NIV),
in acetonitrile. The calibrators, available in ampoules, were sufficiently homogeneous, with between-bottle variations (s
bb) of less than 2%. Long-term stability studies performed at four different temperatures between −18 and 40 °C revealed no
significant negative trends (at a confidence level of 95%). Molar absorptivity coefficients (in L mol−1 cm−1) were determined for all four toxins (DON: 6805 ± 126, NIV: 6955 ± 205, 3-Ac-DON: 6983 ± 141, 15-Ac-DON: 6935 ± 142) on the
basis of a mini-interlaboratory exercise. The overall uncertainty of the calibrators’ target values for DON and NIV were evaluated
on the basis of gravimetric preparation data and include uncertainty contributions from possible heterogeneity, storage, and
transport. The Doncalibrant project resulted in the production of calibrators for DON (IRMM-315) and NIV (IRMM-316) in acetonitrile
with certified mass fractions of 25.1 ± 1.2 μg g−1 and 24.0 ± 1.1 μg g−1, respectively. Both CRMs became commercially available from the Institute for Reference Materials and Measurements (IRMM,
Geel, Belgium) at the beginning of 2007. 相似文献