Photosensory transduction in unicellular eukaryotes: a comparison between related ciliates Blepharisma japonicum and Stentor coeruleus and photoreceptor cells of higher organisms

Blepharisma japonicum and Stentor coeruleus are related ciliates, conspicuous by their photosensitivity. They are capable of avoiding illuminated areas in the surrounding medium, gathering exclusively in most shaded places (photodispersal). Such behaviour results mainly from motile photophobic response occurring in ciliates. This light-avoiding response is observed during a relatively rapid increase in illumination intensity (light stimulus) and consists of cessation of cell movement, a period of backward movement (ciliary reversal), followed by a forward swimming, usually in a new direction. The photosensitivity of ciliates is ascribed to their photoreceptor system, composed of pigment granules, containing the endogenous photoreceptor -- blepharismin in Blepharisma japonicum, and stentorin in Stentor coeruleus. A light stimulus, applied to both ciliates activates specific stimulus transduction processes leading to the electrical changes at the plasma membrane, correlated with a ciliary reversal during photophobic response. These data indicate that both ciliates Blepharisma japonicum and Stentor coeruleus, the lower eukaryotes, are capable of transducing the perceived light stimuli in a manner taking place in some photoreceptor cells of higher eukaryotes. Similarities and differences concerning particular stages of light transduction in eukaryotes at different evolutional levels are discussed in this article.     

Spectral studies of N-nonyl acridine orange in anionic, cationic and neutral surfactants

The spectroscopic and photophysical properties of N-nonyl acridine orange - a metachromatic dye useful as a mitochondrial probe in living cells - are reported in water and microheterogeneous media: anionic sodium dodecylsulfate (SDS), cationic cetyltrimethylammonium bromide (CTAB) and neutral octylophenylpolyoxyethylene ether (TX-100). The spectral changes of N-nonyl acridine orange were observed in the presence of varying amount of SDS, CTAB and TX-100 and indicated formation of a dye-surfactant complex. The spectral changes were also regarded to be caused by the incorporation of dye molecules to micelles. It was proved by calculated values K(b) and f in the following order: K(bTX-100)>K(bCTAB)>K(bSDS) and f(TX-100)>f(CTAB)>f(SDS). NAO binds to the micelle regardless the micellar charge. There are two types of interactions between NAO and micelles: hydrophobic and electrostatic. The hydrophobic interactions play a dominant role in binding of the dye to neutral TX-100. The unexpected fact of the binding NAO to cationic CTAB can be explained by a dominant role of hydrophobic interactions over electrostatic repulsion. Therefore, the affinity of NAO to CTAB is smaller than TX-100. Electrostatic interactions play an important role in binding of NAO to anionic micelles SDS. We observed a prolonged fluorescence lifetime after formation of the dye-surfactant complex tau(SDS)>tau(TX-100)>tau(CTAB)>tau(water), the dye being protected against water in this environment. TX-100 is found to stabilize the excited state of NAO which is more polar than the ground state. Spectroscopic and photophysical properties of NAO will be helpful for a better understanding of the nature of binding and distribution inside mammalian cells.     

Equation of state of nitrogen (N2) at high pressures and high temperatures: molecular dynamics simulation

Nitrogen equation of state at pressures up to 30 GPa (300 kbars) and temperatures above 800 K was studied by molecular dynamics (MD) simulations. The dynamics of the N(2) molecules is treated in hard rotor approximation, i.e., it accounts both translational and rotational degrees of freedom. The rotational motion of the N(2) molecule is treated assuming constant moment of inertia of the nitrogen molecule. The new MD program fully accounts anisotropic molecular nitrogen interaction. The N(2)-N(2) interaction potential has been derived by van der Avoird et al. [J. Chem. Phys. 84, 1629 (1986)] using the results of high precision Hartree-Fock ab initio quantum mechanical calculations. The potential, fully accounts rotational symmetry of the N(2)-N(2) system, by employing 6-j Wigner symbols, i.e., preserving full rotational symmetry of the system. Various numerical algorithms were tested, in order to achieve the energy preservation during the simulation. It has been demonstrated that the standard Verlet algorithm was not preserving the energy for the standard MD time step, equal to 5x10(-16) s. Runge-Kutta fourth order method was able to preserve the energy within 10(-4) relative error, but it requires calculation of the force four times for each time step and therefore it is highly inefficient. A predictor-corrector method of the fifth order (PC5) was found to be efficient and precise and was therefore adopted for the simulation of the molecular nitrogen properties at high pressure. Singer and Fincham algorithms were tested and were found to be as precise as PC5 algorithm and they were also used in the simulation of the equation of state. Results of MD simulations are in very good agreement with the experimental data on nitrogen equation of state at pressures below 1 GPa (10 kbars). For higher pressures, up to 30 GPa (300 kbars), i.e., close to molecular nitrogen stability limit, determined by Nellis et al. [Phys. Rev. Lett. 85, 1262 (1984)], the obtained numerical results provide new data of the experimentally unexplored region. These data were formulated in the analytical form of pressure-density-temperature equation of state.     

A dynamic frictional contact problem for piezoelectric materials

We consider a mathematical model which describes the frictional contact between a piezoelectric body and an electrically conductive foundation. The process is dynamic, the material's behavior is modeled with an electro-viscoelastic constitutive law and the contact is described by subdifferential boundary conditions. We derive the variational formulation of the problem which is in the form of a system involving a second order evolutionary hemivariational inequality for the displacement field coupled with a time-dependent hemivariational inequality for the electric potential field. Then we prove the existence of a unique weak solution to the model. The proof is based on arguments of abstract second order evolutionary inclusions with monotone operators.     

Periodic mesoporous organosilicas with Im3m symmetry and large isocyanurate bridging groups

Adsorption and structural properties of periodic mesoporous organosilica with Im3m symmetry (SBA-16) and large heterocyclic bridging groups in cage-like mesopores are studied. The core of this bridging group is an isocyanurate ring integrated with three trimethoxysilyls through flexible propyl chains.     

A class of differential hemivariational inequalities in Banach spaces

In this paper we investigate an abstract system which consists of a hemivariational inequality of parabolic type combined with a nonlinear evolution equation in the framework of an evolution triple of spaces which is called a differential hemivariational inequality [(DHVI), for short]. A hybrid iterative system corresponding to (DHVI) is introduced by using a temporally semi-discrete method based on the backward Euler difference scheme, i.e., the Rothe method, and a feedback iterative technique. We apply a surjectivity result for pseudomonotone operators and properties of the Clarke subgradient operator to establish existence and a priori estimates for solutions to an approximate problem. Finally, through a limiting procedure for solutions of the hybrid iterative system, the solvability of (DHVI) is proved without imposing any convexity condition on the nonlinear function \(u\mapsto f(t,x,u)\) and compactness of \(C_0\)-semigroup \(e^{A(t)}\).     

Synthesis and X-ray structure of N-phenyl phenylglyoxamide

The title compound (C₁₄H₁₁NO₂) is monoclinic with a = 13.579(2), b = 5.297(1), c = 16.455(2) Å, = 98.11(2)°, Z = 4, and space group P2₁/n. The significant structural features lie in the two carbonyl groups of the glyoxamide which are oriented antiperiplanar to each other [–163.6(3)°]. The central bond C(1)–C(2) is 1.545(4) Å. The observed conformation is stabilized by intramolecular hydrogen bonds.     

Synthesis and X-ray structure of new 5-amino-methyl-4-isoxazolecarboxylic acid azides

The syntheses of the new heterocyclic azides which open a number ways of obtaining interesting isoxazole derivatives has been described. Chemical, spectral and X-ray data giving the evidence of the structure of these compounds are presented. X-ray studies were carried out on compoundsI,II(C₅H₅N₅O₂, C₁₂H₉N₅O₃) witha=3.775(2), 7.179(3);b=11.593(3), 8.135(3);c=8.443(3), 11.610(3);Z=2, 2 and space group Pn, . The structure was established using direct methods and refined by weighted full-matrix least squares. The refinement, based on 687 reflections forI, and 1648 forII withI>/ 3.0 (I), converged to a finalR of 0.333, 0.034 andR _w=0.036, 0.032.     

Cleavage of 1,3-oxathiol-2-one rings withn-butyllithium a new route to alkyl thiolates

1,3-Oxathiol-2-ones are converted byn-butyllithium into alkynyl thiolates.

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Spaltung von 1,3-Oxathiazol-2-on-Ringen mitn-Butyllithium. Ein neuer Weg zu Alkylthiolaten (Kurze Mitteilung)

Zusammenfassung 1,3-Oxathiol-2-one werden mitn-Butyllithium zu Alkinylthiolaten umgesetzt.