Do Liposome‐binding Constants of Porphyrins Correlate with Their Measured and Predicted Partitioning Between Octanol and Water?¶

We tested correlations between lipophilicity parameters and the partitioning of sensitizers into membranes. For this purpose we investigated 17 porphyrins and two chlorins having various chemical structures. Some of these compounds possess an amphiphilic structure (including hematoporphyrin, deuteroporphyrin, mesoporphyrin, chlorin e6 and more). The others are very symmetrical sensitizers [meso-tetra(N-methyl-4-pyridyl)porphyrin, tetra-benzoporphyrin, coproporphyrin I dihydrochloride (CP), meso-tetra(4-carboxyphenyl)porphyrin (TCP) and meso-tetra(m-hydroxyphenyl)chlorin]. Our investigation also included two series of hematoporphyrins and protoporphyrins with varying lengths of alkylcarboxylate side groups. The partitioning of these compounds between the bulk aqueous phase and liposomes was studied by fluorescence methods, and a liposome-binding constant, Kb, was obtained. It was found that CP and TCP do not incorporate into the lipid phase at pH 7.3. An n-octanol-water partition coefficient (log P) and a distribution coefficient (log D) were predicted with a modeling software. The values of log D were also obtained experimentally. We found that for the studied molecules, the predicted log D correlated well with the measured values. The values of log D as well as log P, in turn, did not correlate nicely, for the whole group of studied compounds, with the binding constants to liposomes. However, in the case of porphyrins that share a similar structure, the Kb showed good linear correlation with both log P and log D. For the series of hematoporphyrins and protoporphyrins with different lengths of alkylcarboxyl groups, it was shown that prolongation of this group caused an increase in the lipophilicity and the liposome-binding constant. This effect is more pronounced for the proto- than for the hematoporphyrin series. The results highlight the possible use, as well as limitations, of lipophilicity parameters for the prediction of membrane binding.     

Redetermination of iron dialuminide,FeAl2

The crystal structure of iron dialuminide [Corby & Black (1973). Acta Cryst. B 29 , 2669–2677] has been redetermined on a single crystal synthesized from the elements by arc melting. The compound crystallizes in the triclinic space group P with 19 atoms per unit cell, one Fe site being on an inversion centre. The crystal structure can be described as an inclusion‐plus‐deformation derivative of the orthorhombic YPd₂Si structure type.     

Oxygen nonstoichiometry of tetragonal La2-xSr(x)CuO4-δ (x = 0.15-1.2) and in situ XPS studies at elevated temperatures

The peculiarities of oxygen nonstoichiometry (δ) in tetragonal La(2-x)Sr(x)CuO(4-δ) solid solution with x(Sr) = 0.15-1.2 were studied by XRD, NPD, in situ high-temperature XPS, and chemical analysis. Temperature dependences of oxygen nonstoichiometry, δ = δ(T), were obtained for different Sr contents at 1 bar of O(2). Two types of charge compensation during replacement of lanthanum by strontium are discussed: an increase of the average copper oxidation state and a formation of oxygen vacancies. The average copper oxidation state V(Cu) exhibits a maximum of 2.32 at x(Sr) = 0.6, while δ increases with x(Sr). Oxygen vacancies are unambiguously located on the 4c site ({CuO(2)} plane) for compositions with different strontium contents, which electronic state is described by the O 2p core electron peak at about 531 eV. Thermal stability of the solid solution in a vacuum is associated with the extraction of practically the entire oxygen from CuO(2) layers and the formation of Cu(+) at least in the near-surface region. The higher average copper oxidation state after synthesis in the Sr-rich phases in comparison with the Sr-poor compositions prevents oxygen removal and the formation of Cu(+) and, therefore, stabilizes the structure during heating in a vacuum.     

Bistable bacterial growth rate in response to antibiotics with low membrane permeability

We demonstrate that growth rate bistability for bacterial cells growing exponentially at a fixed external antibiotic concentration can emerge when the cell wall permeability for the drug is low and the growth rate sensitivity to the intracellular drug concentration is high. Under such conditions, an initially high growth rate can remain high, due to dilution of the intracellular drug concentration by rapid cell volume increase, while an initially low growth rate can remain low, due to slow cell volume increase and insignificant drug dilution. Our findings have implications for the testing of novel antibiotics on growing bacterial strains.     

Absolute spectroscopic determination of cross-membrane potential

Spectroscopic determination of the cross-membrane electric potential has been used for more than 20 years. This method, which usually employs absorption or fluorescence measurements, allows for a rapid and noninvasive study of the electrical properties of the membranes of cells and liposomes. However, the usual fluorescence techniques preferably allow monitoring changes in the potential on triggerable or excitable membranes, and not the absolute value of the potential. They also do not provide means for measuring the potential on single cells. This paper reviews three methods that solve these issues. Nernstian dyes which partition between intra-and extracompartmental volumes enable a fluorescence microscopic determination of a single cell and even a single organelle. Dual-wavelength ratiometric recording from membrane-staining dyes also provides means for measuring the field on a single cell. Resonance Raman probes provide a spectroscopic method with a natural internal standard for the absolute measurement of membrane potential.     

The influence of substitution of Co for Mn on magnetism of the HoMn6−xCoxSn6 compounds (0⩽x⩽0.25)

We have studied the effects of Co substitution for Mn on the structure and magnetic properties of the HoMn_6−xCo_xSn₆ compounds (0?x?0.25) with HfFe₆Ge₆-type structure (space group P6/mmm) by X-ray powder diffraction and magnetization measurements. A monotonic decrease of the lattice parameters a and c is observed with increasing Co content. While the compounds with x=0 and 0.05 exhibit ferrimagnetism in the whole temperature range, the compounds with 0.1?x?0.15 show ferrimagnetism, helimagnetism and re-entrant ferrimagnetism with decreasing temperature. For the compounds with x=0 and 0.05, the spin reorientation temperature is observed. A metamagnetic transition from helimagnetic magnetic ordering to ferrimagnetism is observed for the compounds with x=0.1 and 0.2. The results are summarized in the HoMn_6−xCo_xSn₆ magnetic phase diagram.     

Electrochemical properties of Cr doped V2O5 between 3.8 V and 2.0 V

Cr_0.1V₂O_5.15 was prepared by an oxalic acid assisted sol–gel method. X-ray diffraction showed that Cr doping induced a slight expansion (ΔV/V ≈ 2.3%) in the crystal lattice of V₂O₅. The electrochemical properties of Cr_0.1V₂O_5.15 in the potential range of 3.8–2.0 V were studied by cyclic voltammetry, galvanostatic charge–discharge cycling and potentiostatic intermittent titration technique. Cyclic voltammetry showed that the irreversible phase transition of V₂O₅ during the first cycle was effectively prevented by Cr doping. This caused the good charge–discharge cycling performance of the doped material. The discharge capacities were recorded to be 200, 170 and 120 mAhg^− 1 after fifty cycles at the C/10, C/2 and 1C rates, respectively. However, ex-situ X-ray diffraction showed that the crystal structure of the material was destroyed after long-term cycling. The lithium diffusion coefficient of Cr_0.1V₂O_5.15 varied between 10^− 11 and 10^− 12 cm² s^− 1, which was larger than that of crystalline V₂O₅, and was close to those of metal doped V₂O₅ in previous reports. The improvement in lithium diffusion kinetics was regarded as an important reason for the good electrochemical performance of Cr_0.1V₂O_5.15.     

Anatase TiO<Subscript>2</Subscript> nanoparticles for lithium-ion batteries

Anatase TiO₂ nanoparticles were prepared by a simple sol-gel method at moderate temperature. X-ray powder diffraction (XRD) and Raman spectroscopy revealed the exclusive presence of anatase TiO₂ without impurities such as rutile or brookite TiO₂. Thermogravimetric analysis confirmed the formation of TiO₂ at about 400 °C. Particle size of about 20 nm observed by transmission electron microscopy matches well with the dimension of crystallites calculated from XRD. The electrochemical tests of the sol-gel-prepared anatase TiO₂ show promising results as electrode for lithium-ion batteries with a stable specific capacity of 174 mAh g^?1 after 30 cycles at C/10 rate. The results show that improvement of the electrochemical properties of TiO₂ to reach the performance required for use as an electrode for lithium-ion batteries requires not only nanosized porous particles but also a morphology that prevents the self-aggregation of the particles during cycling.     

On the Membrane Binding of the Potentiometric Probe Di-4-ANEPPS: A Fluorescence and Resonance Raman Study

Di-4-ANEPPS is a dye molecules which has been used to probe membrane electric potentials by its electrochromic response. The dye has an unusual blue shift in the absorption spectrum upon partitioning to lipid membranes. We studied its binding properties to membranes by absorption, fluorescence and resonance Raman spectroscopy. The latter technique provided evidence for the differential solubilization of the dye in the membrane, where the polar head of the molecule protrudes out of the lipid environment and is responsible for the spectral behavior.     

Li12Cu12.60Al14.37: a new ternary derivative of the binary Laves phases

New ternary dodecalithium dodecacopper tetradecaaluminium, Li₁₂Cu_12.60Al_14.37 (trigonal, Rm, hR39), crystallizes as a new structure type and belongs to the structural family that derives from binary Laves phases. The Li atoms are enclosed in 15‐ and 16‐vertex and the Al3 atom in 14‐vertex pseudo‐Frank–Kasper polyhedra. The polyhedra around the statistical mixtures of (Cu,Al)1 and (Al,Cu)2 are distorted icosahedra. The electronic structure was calculated by the TB–LMTO–ASA (tight‐binding linear muffin‐tin orbital atomic spheres approximation) method. The electron localization function, which indicates bond formation, is mostly located at the Al atoms. Thus, Al—Al bonding is much stronger than Li—Al or Cu—Al bonding. This indicates that, besides metallic bonding which is dominant in this compound, weak covalent Al—Al interactions also exist.