Influence of water in the lamellar rearrangement of internal wool lipids

Small angle X-ray scattering (SAXS) was applied to a new lipid model arrangement, which was achieved by concentrating or diluting internal wool lipid liposome suspensions in varying water concentrations. The influence of the water content in the lamellar structure of the internal wool lipids is compared with the lamellar structure of phosphatidylcholine bilayers present in the membranes of the living cells. The high increase in the lamellar distances with the water content indicates that large amounts of water can be retained in the lipid wool membrane in contrast to the case of phosphatidylcholine liposomes. A transition temperature between 40 and 50 degrees C tends to eliminate the ordered lamellar structure when more than 60% of water is present in the bilayer structure. This could account for the increase in the permeability of the wool fibres when these are soaked in water at temperatures exceeding 40 degrees C.     

Surface tension and adsorption behavior of mixtures of diacyl glycerol arginine-based surfactants with DPPC and DMPC phospholipids

The binary surface interactions of some novel cationic diacyl glycerol arginine-based surfactants with model phospholipids, which are often used as model membrane components, are studied at 25 °C in aqueous solutions of 0.1 M sodium chloride. The surfactants are 1,2-dimyristoyl-rac-glycero-3-O-(N^α-acetyl-l-arginine) hydrochloride (1414RAc) and 1,2-dilauroyl-rac-glycero-3-O-(N^α-acetyl-l-arginine) hydrochloride (1212RAc), and they are important as potential antimicrobial agents which are biodegradable and with less toxicity than other cationic surfactants. The phospholipids are 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC). The equilibrium and dynamic surface tension of each surfactant, each phospholipid, and some of their binary mixtures are studied using the bubble surfactometry method at constant area or pulsating area conditions. In addition, the surface densities of pure and mixed monolayers of these compounds at the air/water interface are probed with infrared reflection–absorption spectroscopy (IRRAS). Steady state and dynamic surface tension synergism, or antisynergism in one case, and synergistic adsorption effects are detected for the mixed dispersions studied. The enhanced adsorption detected with IRRAS, and the enhanced dynamic and steady state surface tension lowering indicate strong miscibility and net attractive interactions between the compounds in the adsorbed mixed monolayers.     

Synthesis, Structural Characterization and Spectroscopic Properties of 1,2-Bis[4-(3,5-dimethyl-1H-pyrazol-1-yl)-2-oxobutyl]benzene

Abstract  

The crystal structure of the title compound C₂₂H₃₀N₄O₂·H₂O (L), has been determined using X-ray diffraction at 293 K. The crystal of 1,2-bis[4-(3,5-dimethyl-1H-pyrazol-1-yl)-2-oxobutyl]benzene is in triclinic crystal system with space group P(−1) (Z = 2), lattice parameters a = 8.225(6) ?, b = 10.967(6) ?, c = 12.903(6) ?, V = 1119.1(11) ?³. Analyses of single crystals of L, crystallized from dichloromethane/diethyl ether (1:1), revealed that the molecules are arranged in couples, which adopt a pseudo chair conformation, by means of intermolecular O–H···N hydrogen bonding interactions. Moreover, the extended structure revealed a 1D chain caused by several C–H···N intermolecular interactions.     

Fast 2D NMR ligand screening using Hadamard spectroscopy

Fast 2D NMR-based screening can be achieved using Hadamard encoded spectroscopy to focus on the signals of interest (e.g., enzyme active or ligand recognition sites). By recording a set of Hadamard spectra (a "Hadamard constellation") with relative offsets comparable to the excitation bandwidth, quantitative ligand-induced shifts can be obtained from peak intensities.     

Multi-pumping flow system for the determination of dissolved orthophosphate and dissolved organic phosphorus in wastewater samples

A multi-pumping flow system (MPFS) for the spectrophotometric determination of dissolved orthophosphate and dissolved organic phosphorus in wastewater samples is proposed. The determination of orthophosphate is based on the vanadomolybdate method. In-line ultraviolet photo-oxidation is employed to mineralise organic phosphorus to orthophosphate prior to detection. A solenoid valve allows the deviation of the flow towards the UV-lamp to carry out the determination of organic phosphorus.Calibration was found to be linear up to 20 mg P L⁻¹, with a detection limit (3s_b/S) of 0.08 mg P L⁻¹, an injection throughput of 75 injections h⁻¹ and a repeatability (R.S.D.) of 0.6% for the direct determination of orthophosphate. On the other hand, calibration graphs were linear up to 40 mg P L⁻¹, with a detection limit (3s_b/S) of 0.5 mg P L⁻¹, an injection throughput of 11 injections h⁻¹ and a repeatability (R.S.D.) inferior to 2.3% for the procedures involving UV photo-oxidation.     

Nitrene Chemistry in Organic Synthesis: Still in Its Infancy?

The element nitrogen is essential to life. Considerable attention is thus paid to the development of synthetic methods for its introduction into molecules. Nitrenes, long regarded as highly reactive but poorly selective species, have recently emerged as useful tools for the formation of C-N bonds. Practical metal-catalyzed protocols are now available for the preparation of amines through either the aziridination of alkenes or the C-H amination of alkanes. Recent results highlighted in this Minireview suggest that synthetic nitrene chemistry is maturing with a wider scope not limited to these two reactions.     

Protoneutron star cooling with convection: the effect of the symmetry energy

We model neutrino emission from a newly born neutron star subsequent to a supernova explosion to study its sensitivity to the equation of state, neutrino opacities, and convective instabilities at high baryon density. We find the time period and spatial extent over which convection operates is sensitive to the behavior of the nuclear symmetry energy at and above nuclear density. When convection ends within the protoneutron star, there is a break in the predicted neutrino emission that may be clearly observable.     

Tuning the hemilabile behaviour of a thioether–pyrazole ligand on Pd(II) complexes with diphosphines

The coordination mode of thioether–pyrazole ligand, 1,5-bis(3,5-dimethyl-1-pyrazolyl)-3-thiapentane (bdtp) and 1,8-bis-(3,5-dimethyl-1-pyrazolyl)-3,6-dithiaoctane (bddo) ligands, in Pd(II) complexes containing a diphosphine ligand is determined by subtle changes in size of the bridge between the two phosphorus atoms. The ¹H NMR and ³¹P{¹H} NMR at variable temperature in acetonitrile solution prove that the hemilabile character of the bdtp ligand depend on the diphosphine ligand. Thus, while in [Pd(bdtp)(dppe)](BF₄)₂ [1](BF₄)₂ the thioether group not participate in the Pd(II) coordination sphere, two isomers with different coordination (P₂N₂ vs P₂NS) are in equilibrium in [Pd(bdtp)(dppp)](BF₄)₂ [2](BF₄)₂ acetonitrile solution. For complexes [Pd(bddo)(dppe)](BF₄)₂ [3](BF₄)₂ and [Pd(bddo)(dppp)](BF₄)₂ [4](BF₄)₂, only the coordination N,N is observed.     

On the equivalence of the Einstein–Hilbert and the Einstein–Palatini formulations of general relativity for an arbitrary connection

In the framework of the Einstein–Palatini formalism, even though the projective transformation connecting the arbitrary connection with the Levi-Civita connection has been floating in the literature for a long time and perhaps the result was implicitly known in the affine gravity community, yet as far as we know Julia and Silva were the first to realise its gauge character. We rederive this result by using the Rosenfeld–Dirac–Bergmann approach to constrained Hamiltonian systems and do a comprehensive self contained analysis establishing the equivalence of the Einstein–Palatini and the metric formulations without having to impose the gauge choice that the connection is symmetric. We also make contact with the the Einstein–Cartan theory when the matter Lagrangian has fermions.