Local dissipation and coupling properties of cellular oscillators: a case study on calcium oscillations

Synchronised signal transduction between cells is crucial, since it assures fast and immutable information processing, which is vital for flawless functioning of living organisms. The question arises how to recognise the ability of a cell to be easily coupled with other cells. In the present paper, we investigate the system properties that determine best coupling abilities and assure the most efficient signal transduction between cells. A case study is done for intercellular calcium oscillations. For a particular diffusion-like coupled system of cellular oscillators, we determined the minimal gap-junctional permeability that is necessary for synchronisation of initially asynchronous oscillators. Our results show that dissipation is a crucial system property that determines the coupling ability of cellular oscillators. We found that low dissipation assures synchronisation of coupled cells already at very low gap-junctional permeability, whereas highly dissipative oscillators require much higher gap-junctional permeability in order to synchronise. The results are discussed in the sense of their biological importance for systems where the synchronous responses of cells were recognised to be indispensable for appropriate physiological functioning of the tissue.     

Study of the drying zirconia gel-precipitates using thermal analysis

Thermoanalytical techniques (TG, DTG, DTA and EGA) can be helpful in studying gel compositions and relating the chemical history and the role of the precipitant to the chemical properties of gels. The objective of our work was to determine the influence of the initial conditions in the reaction mixture on the product characteristics. Zirconia gels were prepared by the gelprecipitation method by the hydrolysis of zirconium tetrachloride dissolved in methanol. The substitution of water by methanol was chosen in order to obtain a reaction medium in which better control of the hydrolysis and condensation reactions of the zirconium precursor were achieved and thus also better control of the final properties of the dried zirconia gel-precipitates could be obtained. The nature of the hydrated zirconia gels obtained during the gelation process is strongly influenced by the conditions of the reaction mixture, e.g. concentration of the zirconium precursor, the mixing rate and particularly by the amount of water added. To distinguish between various types of water in the gel-precipitates, the furnace atmosphere and the partial water pressure were altered appropriately. It was shown that initial zirconium to water molar ratio has a significant effect on the properties of the final products. It was assumed that, according to the preparation conditions, three different types of water are present in the formed zirconia gel-precipitates. Modification of the dehydration processes of zirconia gel-precipitates enables control of the final microstructural and surface properties of the dried gels which are suitable for further catalysts support as well as mixed oxide preparation.     

Migration of radiocesium in a zeolite-solution system

Some properties of natural zeolite from Zaloka gorica, Slovenia, Yugoslavia were investigated to establish its applicability in solidification and for storage purposes of radioactive waste. It was found that this material is a rather good sorber for cesium, with a capacity of about 0.6 meq g^–1. The migration rate of Cs⁺ in a system ion exchanger-aqueous solution was investigated and correlated with the sorption behaviour of cesium in a system. The leaching rate of cesium from concrete containing zeolite was measured.     

Paradigms and paradoxes: patterns and estimation of the entropy of formation of aqueous hydrogen containing mono and polynuclear oxyanions

“Simple” energetic patterns, where simple means the use of parameters derived only from the stoichiometry of these species, are relatively rarely discussed in the literature. In addition, entropy studies have been dominated by derivation of the absolute quantity S° rather than the entropy of formation (TΔ_f S ^o). Relationships between the entropy of formation and different parameters such as negative value of the charge of the species, the number of oxygen atoms, the natural logarithm of the molecular weight, the total number of atoms and the number of central atoms that are gases were recently discussed by us for aqueous polynuclear oxyanions. As shown here hydrogen containing anions do not follow this pattern. In this study, new approaches for the estimation of the entropy of formation of aqueous hydrogen containing mono and polynuclear oxyanions are suggested, evaluated and recommended.     

Ferromagnetism in Metallocene-Doped Fullerenes

 Ferromagnetism in fullerene-based systems doped with metallocenes is reviewed. These compounds form a ferromagnetic state by spin-coupling between π electrons on fullerene units, while the metallocene molecules do not contribute to the spin ordering. One of these compounds has the highest critical temperature (19 K) for this class of compound. The magnetic properties of these materials are very strongly dependent on the crystallization conditions. Corresponding author. E-mail: Dragan.Mihailovic@ijs.si Received September 4, 2002; accepted September 6, 2002     

Syntheses and crystal structures of [Mg(HF)2](SbF6)2 and [Ca(HF)2](SbF6)2: new examples of HF acting as a ligand to metal centres

[Mg(HF)₂](SbF₆)₂ and [Ca(HF)₂](SbF₆)₂ monocrystals were grown from the corresponding hexafluoroantimonates(V) dissolved in anhydrous hydrogen fluoride. [Mg(HF)₂](SbF₆)₂ crystallizes in the space group Pnma (no. 62) with a=1249.1(4) pm, b=1230.2(4) pm, c=699.1(2) pm, V=1.0742(6) nm³, Z=4. Magnesium is octahedrally coordinated by six fluorine atoms from which two belong to two HF molecules. The structure can be represented by alternating rows of magnesium and antimony atoms running parallel to the c-axis. Magnesium atoms are connected by cis bridging Sb(2)F₆ units along the a-axis and by trans bridging Sb(1)F₆ units along the b-axis. In this way a three-dimensional network is formed.[Ca(HF)₂](SbF₆)₂ crystallizes in the space group P2₁/n (no. 14) with a=935.2(3) pm, b=1088.7(3) pm, c=1104.8(3) pm, β=106.697(5)°, V=1.0774(5) nm³, Z=4. The coordination sphere around the calcium atom consists of eight fluorine atoms which define the vertices of an Archimedean antiprism. The two HF molecules directly coordinate the calcium atom and their fluorine atoms are placed in the corners of different square faces of the Archimedean antiprism. The Ca-F(HF) distances are shorter than the Ca-F(Sb) distances. The Sb(1)F₆ and Sb(2)F₆ groups have four equatorial bridging fluorine atoms, while the Sb(3)F₆ groups have only two bridging trans F ligands. The Ca atoms in the [−1,0,1] plane are connected by equatorial F ligands of Sb(1)F₆ and Sb(2)F₆ units, forming a [Ca(SbF₆)⁺]_n layer. These layers are connected by trans bridging Sb(3)F₆ groups. HF molecules occupy the space between these layers and additionally contribute to the connection between the layers by hydrogen bonding.     

Minimization of mass interferences in quadrupole inductively coupled plasma mass spectrometric (ICP-MS) determination of palladium using a flow injection on-line displacement solid-phase extraction protocol

A flow injection on-line displacement solid-phase extraction protocol was employed to minimize mass interferences with determination of palladium by inductively coupled plasma mass spectrometry (ICP-MS). The developed method involved in on-line complexing of Ag⁺ with pyrrolidine dithiocarbamate (PDC), presorption of the resultant Ag–PDC onto a microcolumn packed with the cigarette filter, displacement sorption of Pd²⁺ through loading the sample solution onto the microcolumn due to on-line displacement reaction between Pd²⁺ and the presorbed Ag–PDC, elution of the retained Pd²⁺ with 50 μL of ethanol for on-line ICP-MS detection. Interferences from co-existing heavy metal ions with lower stability of their PDC complexes relative to Ag–PDC were minimized/eliminated. No interferences from 5 mg L^− 1 Zn and 3 mg L^− 1 Pb for ¹⁰⁴Pd, 0.4 mg L^− 1 Cu for ¹⁰⁵Pd, 6 mg L^− 1 Zn and 2 mg L^− 1 Cd for ¹⁰⁶Pd, 6 mg L^− 1 Zn and 3 mg L^− 1 Cd for ¹⁰⁸Pd, and 2 mg L^− 1 Cd for ¹¹⁰Pd were observed for the determination of 100 ng L^− 1 Pd. The enhancement factors of 71–75, sample throughput of 23 samples h^− 1 and detection limits of 2.8–3.5 ng L^− 1 were achieved with the consumption of 3.0 mL of sample solution. The precision (RSD) for eleven replicate determinations of Pd at the 100 ng L^− 1 level was 1.8–2.7%. The developed method was applied to the determination of palladium in rock samples.     

Thermal electron capture by some halopropanes

Thermal electron attachment rate constants for CF₃CHClCH₃, CF₂ClCFClCF₃ and CBrF₂CH₂CH₂Br have been measured with electron swarm method. Corresponding rate constants are equal to 7.6×10⁻¹¹, 5.5×10⁻⁹ and 1.5×10⁻⁸ cm³ molecule⁻¹ s⁻¹, respectively. The dissociative electron attachment (DEA) spectra for nine haloalkanes have been determined using negative ion mass spectrometry. The correlation between rate constants, position of the DEA peaks and vertical attachment energy (VAE) available in literature has been demonstrated.     

Computer simulation of ion chromatography separation: an algorithm enabling continuous monitoring of anion distribution on an ion-exchange chromatography column

A computer algorithm for the calculation of ion chromatography separation is presented. It is based on the calculation of equilibrium concentrations of present analyte in discrete column segments. The continuous column is treated as a number of discrete cells or segments where the equilibration process between the stationary phase and the eluent is simulated. The ion-exchange equilibration process is supposed to be instantaneous and quantitative. The continuous flow of the eluent is rendered by discrete transfers. The size of each transfer of the eluent corresponds to a portion of the volume contained in one column segment. The equilibrium calculations in all column segments are repeated for each transfer of the eluent, through all the stages of the chromatographic process. The distribution of the analytes between the stationary phase and the eluent can be monitored at any step and in any column segment which means that the described algorithm provides the spatial and time concentration profiles. The simulated chromatogram is acquired as a time-concentration profile in the last column segment. The obtained chromatograms are in good agreement with the experimental ones. The distribution of ions between the stationary phase and the eluent in the early stages of the ion chromatographic process can thus be studied with confidence.