Messung von Intensit?tskorrelationsfunktionen bei Laserlicht

Ohne Zusammenfassung     

Fluorescent Dynamic Covalent Polymers for DNA Complexation and Templated Assembly

Dynamic covalent polymers (DCPs) offer opportunities as adaptive materials of particular interest for targeting, sensing and delivery of biological molecules. In this view, combining cationic units and fluorescent units along DCP chains is attractive for achieving optical probes for the recognition and delivery of nucleic acids. Here, we report on the design of acylhydrazone-based DCPs combining cationic arginine units with π-conjugated fluorescent moieties based on thiophene-ethynyl-fluorene cores. Two types of fluorescent building blocks bearing neutral or cationic side groups on the fluorene moiety are considered in order to assess the role of the number of cationic units on complexation with DNA. The (chir)optical properties of the building blocks, the DCPs, and their complexes with several types of DNA are explored, providing details on the formation of supramolecular complexes and on their stability in aqueous solutions. The DNA-templated formation of DCPs is demonstrated, which provides new perspectives on the assembly of fluorescent DCP based on the nucleic acid structure.     

Laminar flame speed and shock-tube multi-species laser absorption measurements of Dimethyl Carbonate oxidation and pyrolysis near 1 atm

Dimethyl Carbonate (DMC) is a carbonate ester that can be produced in an environment-friendly way from methanol and CO₂. DMC is one of the main components of the flammable electrolyte used in Li-ion batteries, and it can also be used as a diesel fuel additive. Studying the combustion chemistry of DMC can therefore improve the use of biofuels and help developing safer Li-ion batteries. The combustion chemistry of DMC has been investigated in a limited number of studies. The aim of this study was to complement the scarce data available for DMC combustion in the literature. Laminar flame speeds at 318 K, 363 K, and 463 K were measured for various equivalence ratios (ranging from 0.7 to 1.5) in a spherical vessel, greatly extending the range of conditions investigated. Shock tubes were used to measure time histories of CO and H₂O using tunable laser absorption for the first time for DMC. Characteristic reaction times were also measured through OH* emission. Shock-tube spectroscopic measurements were performed under dilute conditions, at three equivalence ratios (fuel-lean, stoichiometric, and fuel-rich) between 1260 and 1660 K near 1.3 ± 0.2 atm, and under pyrolysis conditions (98%+dilution) ranging from 1230 to 2500 K near 1.3 ± 0.2 atm. Laminar flame speed experiments were performed around atmospheric pressure. Detailed kinetics models from the literature were compared to the data, and it was found that none are capable of predicting the data over the entire range of conditions investigated. A numerical analysis was performed with the most accurate model, underlining the need to revisit at least 3 key reactions involving DMC.     

Multiscale Approach of Spin Crossover Materials: A Concept Mixing Russian Dolls and Domino Effects

The spin crossover (SCO) phenomenon corresponds to a modification that originates at the atomic scale. However, the simple consideration of the transformations that occur following the SCO at this scale or in its close vicinity does not allow anyone to truly understand, anticipate and thus take advantage of what happens at the scale of the material, and even less at the device one. As the fruit of years of work and experience on this phenomenon, we formalize here the concept of the multiscale understanding of SCO. Clearly, the deflagration generated by the initial impressive atomic modification on all the physical scales of the solid must be understood in terms of structure-properties relationships that fit together, like Russian dolls, and propagate according to a kind of domino effect. Each scale can both give different and independent consequences from those of the other scales but at the same time can influence those of a larger or smaller scale, the whole being imperatively to take into account. The concept appears well illustrated by the volume modification, always the same at the atomic level but drastically different and adaptable, in amplitude and sense, at any other physical scale. This approach results in a much wider range of potential applications than the atomic level alone initially suggests, including one serious path to shape memory materials.     

Moisture uptake in nanocellulose: the effects of relative humidity,temperature and degree of crystallinity

Cellulose - Foams made from cellulose nanomaterials are highly porous and possess excellent mechanical and thermal insulation properties. However, the moisture uptake and hygroscopic properties of...     

Specific Versus Non-specific Response in Exponential Molecular Amplification from Cross-Catalysis: Modeling the Influence of Background Amplifications on the Analytical Performances

Molecule based signal amplifications relying on an autocatalytic process may represent an ideal strategy for the development of ultrasensitive analytical or bioanalytical assays, the main reason being the exponential nature of the amplification. However, to take full advantage of such amplification rates, high stability of the starting co-reactants is required in order to avoid any undesirable background amplification. Here, on the basis of a simple kinetic model of cross-catalysis including a certain degree of intrinsic instability of co-reactants, we highlight the key parameters governing the analytical response of the system and discuss the analytical performances that are expected from a given kinetic set. In particular, we show how the detection limit is directly related to the relative instability of reactants within each catalytic loop. The model is validated with an experimental dataset and is intended to serve as a guide in the design and optimization of autocatalytic molecular-based amplification systems with improved analytical performances.     

MCH-R1 Antagonist GPS18169, a Pseudopeptide,Is a Peripheral Anti-Obesity Agent in Mice

Melanin-concentrating hormone (MCH) is a 19 amino acid long peptide found in the brain of animals, including fishes, batrachians, and mammals. MCH is implicated in appetite and/or energy homeostasis. Antagonists at its receptor (MCH-R1) could be major tools (or ultimately drugs) to understand the mechanism of MCH action and to fight the obesity syndrome that is a worldwide societal health problem. Ever since the deorphanisation of the MCH receptor, we cloned, expressed, and characterized the receptor MCH-R1 and started a vast medicinal chemistry program aiming at the discovery of such usable compounds. In the present final work, we describe GPS18169, a pseudopeptide antagonist at the MCH-R1 receptor with an affinity in the nanomolar range and a Ki for its antagonistic effect in the 20 picomolar range. Its metabolic stability is rather ameliorated compared to its initial parent compound, the antagonist S38151. We tested it in an in vivo experiment using high diet mice. GPS18169 was found to be active in limiting the accumulation of adipose tissues and, correlatively, we observed a normalization of the insulin level in the treated animals, while no change in food or water consumption was observed.     

Transient Substrate‐Induced Catalyst Formation in a Dynamic Molecular Network

In biology enzyme concentrations are continuously regulated, yet for synthetic catalytic systems such regulatory mechanisms are underdeveloped. We now report how a substrate of a chemical reaction induces the formation of its own catalyst from a dynamic molecular network. After complete conversion of the substrate, the network disassembles the catalyst. These results open up new opportunities for controlling catalysis in synthetic chemical systems.