Search results for "Salt"
showing 10 items of 1157 documents
Charge Pair Interactions in Transmembrane Helices and Turn Propensity of the Connecting Sequence Promote Helical Hairpin Insertion
2013
alpha-Helical hairpins, consisting of a pair of closely spaced transmembrane (TM) helices that are connected by a short interfacial turn, are the simplest structural motifs found in multi-spanning membrane proteins. In naturally occurring hairpins, the presence of polar residues is common and predicted to complicate membrane insertion. We postulate that the pre-packing process offsets any energetic cost of allocating polar and charged residues within the hydrophobic environment of biological membranes. Consistent with this idea, we provide here experimental evidence demonstrating that helical hairpin insertion into biological membranes can be driven by electrostatic interactions between clo…
Structural studies of five novel bile acid-4-aminopyridine conjugates
2012
Abstract Synthesis and solid-state structural characterization of five bile acid amides of 4-aminopyridine (4-AP) are reported. Systematic crystallization experiments revealed a number of structural modifications and/or solvate/hydrate systems for these conjugates. Particularly, cholic acid conjugate exhibited five distinct structure modifications, including one anhydrous form, mono- and dihydrates, as well as ethanol and 2-butanol solvates. The obtained crystal forms were examined extensively with various analytical methods, including solid-state NMR, Raman, and IR spectroscopies, powder and single crystal X-ray diffraction methods, thermogravimetry, and differential scanning calorimetry. …
An efficient dissipative particle dynamics-based algorithm for simulating electrolyte solutions
2015
We propose an efficient simulation algorithm based on the dissipative particle dynamics (DPD) method for studying electrohydrodynamic phenomena in electrolyte fluids. The fluid flow is mimicked with DPD particles while the evolution of the concentration of the ionic species is described using Brownian pseudo particles. The method is designed especially for systems with high salt concentrations, as explicit treatment of the salt ions becomes computationally expensive. For illustration, we apply the method to electro-osmotic flow over patterned, superhydrophobic surfaces. The results are in good agreement with recent theoretical predictions.
Syntheses and structural study of bile acid amidoalcohols.
2008
Preparation, structural and thermoanalytical characterization of fourteen N-hydroxyalkyl 5beta-cholan-24-amides have been performed in this study. The utilized techniques include liquid state and CP-MAS 13C NMR spectroscopy, thermogravimetry, differential scanning calorimetry, and also powder and single crystal X-ray crystallography. The results were discussed and compared to each other and also to previous findings on similar compounds. One pure hydrate form was obtained. Six new single crystal structures were determined, including one hydrated chloroform solvate. Decomposition temperatures were found to correlate with the side chain length, and the number of the hydroxyl groups. The spati…
Ion-Pair Recognition of Tetramethylammonium Salts by Halogenated Resorcinarenes
2011
The non-covalent interactions of different upper-rim-substituted C(2)-resorcinarenes with tetramethylammonium salts were analyzed in the gas phase in an Electrospray Ionization Fourier-transform ion-cyclotron-resonance (ESI-FTICR) mass spectrometer and by (1)H NMR titrations. The order of binding strengths of the hosts towards the tetramethylammonium cation in the gas phase reflects the electronic nature of the substituents on the upper rim of the resorcinarene. In solution, however, a different trend with particularly high binding constants for halogenated resorcinarenes has been observed. This trend can be explained by a synergetic effect originating from the interaction of the halogenate…
Characterization of isomeric 1,2,4-oxadiazolyl-N-methylpyridinium salts by electrospray ionization tandem mass spectrometry.
2007
The mass spectrometric behavior of 1,2,4-oxadiazolyl- N-methylpyridinium salts has been investigated. These substances are of current interest as perspective ionic liquids, compounds used as green solvents for synthesis, and for their catalytic properties. The studies have been developed through electrospray ionization tandem mass spectrometry (ESI-MS/MS) experiments. The obtained results demonstrate a ready distinction between the two isomeric classes, 3- N-methylpyridinium- and 5- N-methylpyridinium-1,2,4-oxadiazoles, is possible through ESI-MS/MS experiments. A deeper investigation on the principal fragmentation pathways of characteristic ions has been also developed.
Novel Hexanuclear Copper(II) Complex Built from a Simple Tetrachelating Triazole Ligand: Synthesis, Structure, and Magnetism
2013
A new easy symmetric 3,5-disubstituted 1,2,4-triazole ligand (H3diV) by reaction with an excess of copper(II) salt has afforded a novel hexanuclear compound (Cu/HdiV ratio of 6:2) through a bis(trans-cis-cis-trans) binding mode, exhibiting two types of Cu(II) centers and two clearly distinguishable antiferromagnetic J1 (-234 cm(-1)) and J2 (-35 cm(-1)) coupling constants.
Apparent molar volumes of strontium chloride in ethanol + water at 298.15 K
1997
Densities of ethanol + water + strontium chloride mixtures have been measured with an oscillating-tube densimeter over a large range of concentrations of the salt and ethanol, at 298.15 K. From these densities, apparent molar volumes of the electrolyte in these mixtures have been calculated, and partial molar volumes at infinite dilution have been evaluated.
Indication of drier periods on Mars from the chemistry and mineralogy of atmospheric dust
2005
The cover shows part of the Larry's Lookout panorama, seen from the Mars Exploration Rover (MER) Spirit during its drive up Husband Hill: the summit is about 200 metres from the rover. Six papers this week report in detail on the MER mission. An Analysis compares predictions used to select a landing site with the conditions actually encountered. This ‘ground truth’ will be invaluable for interpreting future remote-sensing data. Surface chemistry suggests that the upper layer of soil may contain 1% meteoritic material. MER provides a unique glimpse of solar transits of the moons Phobos and Deimos. Rover Opportunity examined wind-related processes, and spectroscopy indicates a dry origin for …
Organic salts and aromatic substrates in two-component gel phase formation: the study of properties and release processes
2015
To identify gel phases able to act as confined reaction media or materials for the removal of organic pollutants, we studied two-component gel phases formed by naphthalenedisulfonate diimidazolium salts in the presence of some organic guests, in 1-propanol solution. Guests differing in π-surface area, bulkiness and electronic properties were taken into account. Soft materials obtained were investigated for their thermal stability, self-repairing ability and morphology. Furthermore, two-component gel phase formation was studied using resonance light scattering (RLS) measurements. Guest release processes from the gel phase were also studied. These processes were monitored as a function of tim…