Complementary Methods of Processing diS-C3(3) Fluorescence Spectra Used for Monitoring the Plasma Membrane Potential of Yeast: Their Pros and Cons

Carbocyanine dye diS-C₃(3) was repeatedly employed in monitoring the plasma membrane potential of yeast and other living cells. Four methods of measuring and evaluating probe fluorescence signal were used in different studies, based on following fluorescence parameters: fluorescence intensity emitted within a certain spectral interval, F(580)/F(560) fluorescence emission ratio, wavelength of emission spectrum maximum, and the ratio of respective fluorescence intensities corresponding to the diS-C₃(3) bound to cytosolic macromolecules and remaining dissolved in the aqueous cell medium (i.e., unbound, or free). Here we show that data corresponding to the three latter spectral assessments of diS-C₃(3) accumulation in cells is mutually convertible, which means that their alternative use cannot lead to ambiguities in the interpretation of the results of biological experiments. On the other hand, experiments based on the effortless measurements of fluorescence intensities should be interpreted cautiously because controversial results can be obtained, depending on the particular choice of cell-to-dye concentration ratio and emission wavelength.     

Solvatochromic Effect in the Optical Spectra of Calcofluor and its Relation to Fluorescent Staining of Yeast Cell Walls

Fluorescence spectral properties of calcofluor (a popular stain used to visualize cell walls of bacteria, yeast and fungi) has been studied. The analysis of calcofluor fluorescence emission spectra measured in a wide range of solvents (including media containing chitin), and in yeast cell suspensions has revealed that the solvatochromic properties of calcofluor ensue essentially from the by solvent-solute hydrogen bonding, or from the hydrogen bonding to cell wall polysaccharides with an eventual contribution of calcofluor aggregation at the cell surface. Preliminary data suggest that calcofluor emission spectra can be employed as a practical marker of variations in the quality of yeast cell wall.     

Polyoxomolybdate‐Stabilized Ru0 Nanoparticles Deposited on Mesoporous Silica as Catalysts for Aromatic Hydrogenation

We use polyoxometalates as precursors for the preparation of heterogeneous catalysts. In the starting molecular precursor [{Ru(C₆Me₆)}₂Mo₅O₁₈{Ru(C₆Me₆)(H₂O)}], three ruthenium arene fragments are supported on a formally lacunary Lindqvist‐type polyoxomolybdate. This species was introduced by incipient wetness impregnation into the porosity of a SBA‐15‐type mesoporous silica. The evolution of the system under reducing atmosphere is followed by several methods, such as temperature‐programmed reduction (TPR), Raman, and X‐ray absorption spectroscopy (XAS). The results indicate that the polyoxometalate structure is retained after grafting on silica and allows the stabilization of Ru⁰ nanoparticles after reduction. The resulting system exhibits interesting catalytic activity in benzene hydrogenation.     

Co-melting of solid sucrose and multivalent cation soaps for solvent-free synthesis of sucrose esters

Sucrose fatty acid esters, useful as mild surfactants, have been synthesised in good yields in a solvent-free medium. High contents of monoesters and low saponification rate have been observed. The co-melting of sucrose and a multivalent cation soap such as magnesium or zinc soaps, under basic conditions, allowed the formation of a homogeneous reaction mixture, where solid sucrose was fully dissolved. The kinetic monitoring profiles are similar to reactions in homogeneous solutions, with fast initial formation of monoesters. As a consequence, conversion of sucrose in sucrose esters occurred in good yields. The specificity of multivalent cation soaps compared to monovalent cation soaps, for example, potassium stearate, was pointed out.     

Membrane electrodes sensitive to doubly charged surfactants. Application to a cationic gemini surfactant

The response of a membrane electrode is not always identical to that of a redox electrode. Indeed, in the case of membrane electrode the response is not due to a redox equilibrium but to a cross-membrane potential. So, the membrane electrode's response depends mainly on the carrier system and the nature of the membrane. The properties of the membrane can favour several reactions giving rise to different ionic species diffusing in the membrane. The expression of the cross-membrane potential thus depends on the number and quantities of these ionic species. To illustrate this, we established the equations for the case of a two-charge cation detected by a univalent charged carrier. We show that the Nernstian response is not applicable to membrane electrodes. This approach allowed us to interpret results obtained with a cationic gemini surfactant-selective electrode prepared in the laboratory. To prove the well working of this electrode, we determined the critical micelle concentration in water and several NaBr solutions (0.004, 0.006, 0.01 and 0.02 M) from which the counterion binding has been determined.     

A generalization of the cosine-sine functional equation on groups

The functional equation f(xy)=f(x)g(y)+g(x)f(y)+h(x)h(y) is solved where f, g, h are complex functions defined on a group.     

A linear programming formulation of a semi-Markov model to design pig facilities

Housing facilities design represents the main strategic decision in pig farms. This paper introduces a linear programming formulation of a semi-Markov process to approach the facilities design. Thus, the Linear Programming formulation determines the optimum replacement policy and provides the equilibrium distribution of the herd along pig facilities. Then, the calculation of the associated needs of room for each sow facility is derived from sow herd distribution at equilibrium. Results show the flexibility of the model for designing pig facilities and computational advantages in the solving procedure compared to previous proposals. Furthermore, the robustness of the optimal solution is studied by means of sensitivity analysis.     

Determination of light elements using cyclotron-accelerated particles

We present results on the determination of phosphorus, sulfur, fluorine and chlorine in various matrices and some consideration about the possbility of using fast neutrons in elemental analysis based on the variable energy U-120 Cyclotron of the Institute of Atomic Physics (IAP).     

Ratchet effect in faceting

The paper deals with a new phenomenon, named ratchet effect, envisioned theoretically as a likely consequence of metastability of crystal facets and expected to occur upon a temperature cycling. In experiments, Pn3m lyotropic crystals surrounded by the isotropic L1 phase in the mixture C₁₂EO₂/water are used. At equilibrium, the Pn3m/L1 interface contains small (111)-type facets in coexistence with rough surfaces. In agreement with theoretical expectations, it is shown that upon a saw-tooth-shaped temperature cycling, facets are growing until the rough surfaces are completely eliminated. A model of the ratchet effect is proposed.Received: 8 January 2004, Published online: 25 March 2004PACS: 64.70.Md Phase transitions in liquid crystals - 68.35.Md Surface thermodynamics, surface energies - 61.30.-v Liquid crystals