Hamamelitannin Analogues that Modulate Quorum Sensing as Potentiators of Antibiotics against Staphylococcus aureus

The modulation of bacterial communication to potentiate the effect of existing antimicrobial drugs is a promising alternative to the development of novel antibiotics. In the present study, we synthesized 58 analogues of hamamelitannin (HAM), a quorum sensing inhibitor and antimicrobial potentiator. These efforts resulted in the identification of an analogue that increases the susceptibility of Staphylococcus aureus towards antibiotics in vitro, in Caenorhabditis elegans, and in a mouse mammary gland infection model, without showing cytotoxicity.     

Screening approach for chiral separation of pharmaceuticals. Part III. Supercritical fluid chromatography for analysis and purification in drug discovery

High-throughput and performance analysis and purification of enantiomers are important parts of drug discovery and provide high-quality compounds for pharmacological testing. We have previously reported two parts describing chiral chromatographic screens using normal-phase (NPLC) and reversed-phase (RPLC) liquid chromatography, in order to cope with increasing numbers of new compounds generated by chemistry programs. We present in this part the development and implementation of a third faster screen using supercritical fluid chromatography (SFC) to maximize chance in achieving rapid enantiomer resolution of large numbers of compounds in a minimum of time. The SFC screen utilizes a narrow combination of only four columns (Chirlapak AD and AS, and Chiralcel OD and OJ) and two solvent modifiers (methanol and isopropanol). A modifier and column-switching setup was employed to allow the entire screening process to be serially run in the order AD> OD > OJ > AS and methanol > isopropanol, so that the screening for a given molecule can be stopped when separation is achieved. The switching system was fully automated for unattended operation of multiple compounds. An optimization procedure was also defined, which can be performed if needed for unsuccessful separations in the screening step. The chiral SFC strategy proved its performance and robustness in resolution of hundreds proprietary chiral molecules generated by drug discovery programs, with a success rate exceeding 95%. In addition, the generic capability of the strategy was evaluated by applying the screen and optimization methodology to a test set comprising 40 marketed drugs differing from proprietary compounds in terms of chemical diversity, revealing a similar high success rate of 98%. Chiral separations developed at the analytical scale work easily and equally well at the semi-preparative level, as illustrated with an example. The SFC screen allows resolution of compounds that were partially separated by NPLC or not separated at all by RPLC, demonstrating the utility of implementing complementary chromatographic techniques. The SFC screen is currently an integral part of our analytical support to discovery chemical programs and is considered the first try for chiral separations of new compounds, because it offers a higher success rate, performance and throughput.     

Laser-induced breakdown spectroscopy of carbon in helium and nitrogen at high pressure

This work is devoted to the study of the gas pressure effect on the laser-induced breakdown spectroscopy signal intensity of carbon. Experiments are performed, using a 1064 nm Nd:YAG laser, with carbon solid samples placed inside a high pressure chamber filled with helium or nitrogen, the gas pressure varying from 1 to 80 atm. The signal intensity of the carbon line (247.86 nm) decreases with increasing pressure. As the plasma size strongly decreases with pressure, two collection optical setups are used, showing different raw results. To take into account the plasma size evolution with pressure, calculated corrections are applied to the collected light intensity. Carbon line emission is measured and corrected as a function of pressure in both gases. At 1 atm, the emission line is found to be greater in helium than in nitrogen by a factor of approximately 3, whereas the intensities in the two gases become close to each other at 80 atm.     

5‐Chloro‐3‐methylthio‐1,2,4‐thiadiazol‐2‐ium chlorides as useful synthetic precursors to a variety of 6aλ4‐thiapentalene systems

Title salts 3 were easily obtained by treatment of formimidoyl isothiocyanates 1 with a twofold excess of methanesulfenyl chloride. They showed interesting chemical behavior toward several nitrogen and carbon nucleophiles. Substitution reactions with isothioureas and acetamide in the presence of triethylamine gave the 1H, 6H‐6aλ⁴‐thia‐1,3,4,6‐tetraazapentalenes 7 and 6H‐6aλ⁴‐thia‐1‐oxa‐3,4,6‐triazapentalene 9 , respectively. Addition of p‐toluidine furnished the 5‐imino‐thiadiazole derivatives 10 , which reacted further with diverse heterocumulenes to yield the corresponding thiatriaza‐ and tetraazapentalene species 11 . The N,N′‐bis(1,2,4‐thiadiazol‐5‐ylidene)diaminobenzenes 13 were also prepared and reacted with phenyl isothiocyanate. Two stable rotational isomers were separated for the 1,2‐phenylene product 14b . Other π‐hypervalent sulfur compounds 16 were synthesized under similar conditions from salts 3 and methyl cyanoacetate or dimethyl malonate. The structural assignments were discussed on the basis of IR and NMR spectroscopic data and received additional support from X‐ray analysis of substrate 16a . © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:95–105, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10106     

Interrupted heating DTA for liquidus temperature determination of Ag–Cd–In alloys

Journal of Thermal Analysis and Calorimetry - An Ag–Cd–In alloy is used as the control rod material in most pressurized water reactors. Despite this important application, the phase...     

Morphological origins of temperature and rate dependent mechanical properties of model soft thermoplastic elastomers

Thermoplastic elastomers (TPEs) combine high elasticity with melt processability due to their structural features being based on physical associations rather than chemical crosslinking. Their mechanical properties are governed by the interplay of the different dynamics present in the system (i.e., hard block associations and soft block mobility) combined with their morphology. Irrespective of their exact chemical structure or type of association (crystals, hydrogen bonds, or glassy domains), many soft TPEs show a reduction in toughness at elevated temperatures. In this study, we investigate the high-temperature mechanical properties of a model series of industrially relevant TPEs via systematically varying composition and molecular weight. The results show an increase in temperature resistance and in large-strain stress response as chain length increases. We underline the key parameters that influence the mechanical behavior and explain the observed effect of molecular weight on both the temperature- and rate-dependent large-strain response. A physical network-based model is presented that can explain the experimental findings assuming an improved network connectivity and extended lifetime of the entangled segments with increasing molecular weight.     

Synthesis and characterization of hydrogels containing redox-responsive 2,2,6,6-tetramethylpiperidinyloxy methacrylate and thermoresponsive N-isopropylacrylamide

Smart hydrogels containing 2,2,6,6-tetramethylpiperidinoxy methacrylate (TEMPO) and N-isopropylacrylamide (NIPAM) that undergo reversible redox behavior are prepared and investigated. Several polymer networks are first prepared by free-radical copolymerization of varying amounts of TEMPO, NIPAM, and a crosslinker (diethylene glycol diacrylate) and subsequently swelled with water to lead to hydrogels. In order to investigate the effects of the redox activity of TEMPO units and of the lower critical solution temperature of NIPAM on the hydrogel properties, a study of the swelling ratio of the polymer networks in distilled water at different temperatures is performed for the two forms of TEMPO, the reduced (TEMPO) and oxidized (TEMPO⁺) one. Moreover, the rheological properties are also measured for both hydrogel forms. Finally, the encapsulation abilities of the oxidized hydrogels are demonstrated via electrostatic interactions between positively charged TEMPO⁺ units and negatively charged guest molecules, supporting future application of our system in the biomedical and environmental fields.     

Molecular Dynamics Simulation of Small Molecules Interacting with Biological Membranes

Cell membranes protect and compartmentalise cells and their organelles. The semi-permeable nature of these membranes controls the exchange of solutes across their structure. Characterising the interaction of small molecules with biological membranes is critical to understanding of physiological processes, drug action and permeation, and many biotechnological applications. This review provides an overview of how molecular simulations are used to study the interaction of small molecules with biological membranes, with a particular focus on the interactions of water, organic compounds, drugs and short peptides with models of plasma cell membrane and stratum corneum lipid bilayers. This review will not delve on other types of membranes which might have different composition and arrangement, such as thylakoid or mitochondrial membranes. The application of unbiased molecular dynamics simulations and enhanced sampling methods such as umbrella sampling, metadynamics and replica exchange are described using key examples. This review demonstrates how state-of-the-art molecular simulations have been used successfully to describe the mechanism of binding and permeation of small molecules with biological membranes, as well as associated changes to the structure and dynamics of these membranes. The review concludes with an outlook on future directions in this field.     

Refinement of the inversion‐transfer NMR experiment for faster characterization of chemical exchange

It is shown theoretically that the inversion‐transfer experiment used to estimate the value of unidirectional rate constants in chemical exchange systems can be performed faster via a reduction of the recovery delay. The chemical exchange rate constants can then be estimated accurately with a formula close to that of standard inversion transfer and easy to use, after a justified approximation. A function was developed to determine the optimal value of the recovery delay for an optimal inversion‐transfer sequence. The validity of these theoretical results was checked experimentally with a solution of N,N‐dimethylacetamide in which chemical exchange arises from internal hindered rotation. Copyright © 2015 John Wiley & Sons, Ltd.