Temperature dependence of the interaction of cholate and deoxycholate with fluid model membranes and their solubilization into mixed micelles

The interaction of bile salts with model membranes composed of soybean phosphatidylcholine (SPC) and synthetic 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) was investigated using high sensitivity isothermal titration calorimetry (ITC). The partitioning and incorporation of the bile salts sodium cholate (NaC) and sodium deoxycholate (NaDC) from an aqueous phase (pure water or 0.1 M NaCl) into fluid bilayer vesicles was studied as a function of temperature and ionic strength. The thermodynamic parameters of partitioning were determined with a model taking electrostatic interactions into account. In addition, the solubilization of SPC and POPC vesicles with NaC and NaDC as a function of temperature was also studied by ITC and the phase diagrams for the vesicle to micelle transition at two different temperatures were established. Unsaturated phospholipids require higher amounts of detergent to be transformed into micelles compared to saturated phospholipids. In addition, the width of the coexistence region of mixed micelles and mixed vesicles is larger for phosphatidylcholines with unsaturated chains. A comparison of NaDC with NaC shows the higher solubilization effectiveness of NaDC in agreement with its lower cmc. Furthermore, increasing the ionic strength decreases the amount of bile salt necessary for the formation of mixed micelles, which is also expected from the decrease of the cmc with ionic strength due to the shielding of the charges of the bile salts.     

Wing-triangulated graphs are perfect

The wing-graph W(G) of a graph G has all edges of G as its vertices; two edges of G are adjacent in W(G) if they are the nonincident edges (called wings) of an induced path on four vertices in G. Hoàng conjectured that if W(G) has no induced cycle of odd length at least five, then G is perfect. As a partial result towards Hoàng's conjecture we prove that if W(G) is triangulated, then G is perfect. © 1997 John Wiley & Sons, Inc.     

N–O-Bindungsspaltung in O-silylierten Oximen bei der Reaktion mit einem Titanocen-Alkin-Komplex

N–O Bond Cleavage in O-silylated Oximes by Reaction with a Titanocene-Alkyne Complex Cp₂Ti(Me₃SiC₂SiMe₃) 1 reacts with alicyclic and aliphatic O-silylated ketoximes of type R¹R²C=NOSiMe₃ ( 2 : R¹R² = (CH₂)₅; 3 : R¹ = R² = Me) under N–O bond breaking to the titanocene complexes Cp₂Ti(OSiMe₃)(N=CR¹R²) 6 (R¹R² = (CH₂)₅) and 7 (R¹ = R² = Me). The structure of 6 was obtained by X-ray crystal structure analysis ( 6 : triclinic, space group P1, Z = 2, a = 9.486(1), b = 9.865(1), c = 12.305(2) Å, α = 107.19(1), β = 96.08(1), γ = 111.08(1)°).     

A mathematical approach to solve the network reconstruction problem

The reconstruction of biochemical and genetic networks from experimental data is an important challenge in biology and medical basic research. We formalize this problem mathematically and present an exact algorithm for its solution. Our procedure yields either a complete list of all alternative network structures that explain the observed phenomena or proves that no solution exists using the given data set. This work was supported by the German Ministry of Education and Research (BMBF) through the FORSYS initiative.     

Struktur,Eigenschaften und NMR-spektroskopische Charakterisierung von Cp2Zr(Pyridin)(Me3SiCCSiMe3)

Structure, Properties, and NMR Spectroscopical Characterization of Cp₂Zr(pyridine)(Me₃SiC?CSiMe₃) Displacement of the THF ligand in Cp₂Zr(THF)(Me₃SiC?CSiMe₃) ( 1 ) with pyridine yields Cp₂Zr(η¹-NC₅H₅)(Me₃SiC?CSiMe₃) (3). Unlike 1 , the complex 3 is stable in hydrocarbon solvents. According to the temperature dependent ¹H and ¹³C NMR spectra, the structure of complex 3 in solution is dynamic due to a rotation of the alkyne ligand. In addition, when 3 is dissolved in pyridine an easy exchange between coordinated and free molecules of pyridine takes place. In the solid state complex 3 displays a tetrahedral coordination sphere at the zirconium center composed of Cp ligands, alkyne and pyridine as shown by an X-ray structure analysis. The complex 3 reacts readily with water and carbon dioxide giving the same products as in the case of 1 .     

UV-spectroscopic quantitative determination of non-aromatic amines in ionic liquids.

In the last decade, ionic liquids have shown great promise in a plethora of applications. Nevertheless, little attention has been paid to the characterization of the purity of these fluids, which ultimately lead to non-reproducible data in the literature. Derivatization with carbon disulfide is used to quantitatively determine primary and secondary non-aromatic amines (detection limit: 0.2 wt%), such as 1-butylamine, morpholine or pyrrolidine, in ionic liquids. The corresponding dithiocarbamates formed are analyzed by ultraviolet spectroscopy at wavelengths between 277 and 285 nm.