Electrostatic Interactions That Determine the Rate of Pseudorotation Processes in Oxyphosphorane Intermediates: Implications with Respect to the Roles of Metal Ions in the Enzymatic Cleavage of RNA

The enzymatic cleavage of RNA takes place via a cyclic pentacoordinate oxyphosphorane intermediate/transition state. We carried out ab initio investigations on the neutral cyclic oxyphosphorane, which exists as a stable intermediate. As a consequence of the conformational preferences of the pentacoordinate trigonal bipyramidal intermediates, the rotation of the P-OH bonds is strongly coupled with the reaction coordinate for the pseudorotation process. In addition, the neutral PF(4)OH species has a higher barrier to pseudorotation than the corresponding anionic species PF(4)O(-). These findings are related to the positive charge of the hydrogen atoms on the equatorial oxygens in the trigonal bipyramidal structures: the hydrogen atoms preferably adopt eclipsed positions relative to the axial ligands. Fixing the cationic species in these regions causes an increase in the barrier heights for pseudorotation processes and, thus, prevents isomerization by pseudorotation. Consequently, metal coordination in the double-metal ion mechanism for enzymatic cleavage of RNA should serve to exclusively stabilize the trigonal bipyramidal intermediate/transition state for the in-line attack and departure process.     

On reflection from interfaces with some spatially dispersive metamaterials

Plane-wave reflection from interfaces with single and double wire media is considered. Such media exhibit strong spatial dispersion even at very low frequencies which causes appearance of additional waves. The problem of additional boundary conditions (ABC) in application to wire media is discussed and an ABC-free approach, known in solid state physics, is used. Expressions for the fields and Poynting vectors of refracted waves are derived. The directions and values of the power density flow of refracted waves are found and conservation of the power flow through the interface is checked.     

Plane wave propagation in a uniaxial bianisotropic medium with an application to a polarization transformer

Uniaxial bianisotropic medium is a generalization of the well-studied bi-isotropic and chiral media. It is obtained, for example, when microscopic helices with parallel axes are positioned in a host dielectric in random locations. Plane wave propagation in such a medium is studied and a simple solution for the dispersion equation and for the eigenwaves are found. As a numerical example, polarization properties of a transverse wave propagating in a uniaxial bianisotropic medium is considered. The results give a simple possibility to construct a polarization transformer with a transversely uniaxial chiral medium for changing the polarization of a propagating plane wave.     

Oxidomolybdenum(VI) complexes with atrane-type [O3N] ligands

Dioxomolybdenum(VI) complex [MoO₂Cl₂(dmso)₂] reacts with a series of tetradentate O₃N-type aminoalcohol–bisphenol ligands to form oxomolybdenum(VI) complexes of type [MoOCl(Lⁿ)]. The reaction of H₃L¹ produces [MoOCl(L¹)] as two separable isomers, whereas the reaction of H₃L² or H₃L³ yields a single product. The X-ray analyses of cis- and trans-[MoOCl(L¹)] reveal that the complexes are formed of monomeric molecules. The ligands have tetradentate coordination through three oxygen donors and one nitrogen donor, which is located trans to the terminal oxo group. The sixth coordination site is occupied by a chloro ligand.     

Impact of cavity symmetry on mode suppression and increase of free spectral range in solid-state dye microlaser

We describe modeling the solid-state dye laser with the microcavity size comparable to light wavelength.Certain symmetry in the allocation of gain material leads to depletion of odd longitudinal modes that,in turn, increases the tunability range of the microlaser. We provide simple physical explanation for the modeling results.     

Dynamic MR imaging of brain tumors in low field using undersampled projection reconstruction

A new application of the projection reconstruction method was developed, enabling dynamic T(1)-weighted contrast-enhanced magnetic resonance image (MRI) of brain tumors in a low-field imager. Two undersampled projection reconstruction spin echo sequences were implemented in an open low-field (0.23-T) MR imager, one with 64 and another with 42 projections in [0,pi], repetition time 150 ms, echotime 15 ms, and six slices were used in both sequences. The possibility of using these sequences to image dynamic contrast enhancement of brain tumors was studied in laboratory experiments and in two patient cases, one with fibrotic and the other with meningothelial meningioma. The laboratory experiments showed a nearly linear response in signal intensity to the concentration of gadopentetate dimeglumine in purified water up to 1.25 mM. Increasing concentrations up to 5.0 mM did not significantly affect the signal intensity, though starting from 3.0 mM concentration T(2) shortening decreased intensities slightly. The patient cases showed results consistent with an earlier study performed in a high-field imager. The results show that the studied sequences can be used to follow dynamic contrast enhancement in a low-field imager.     

Synthesis and ion conductance behavior of a tetrameric alamethicin ion channel

[structure: see text] A porphyrin-tethered construct, containing four full-length alamethicin monomers, has been synthesized and characterized. The ion conductance data of the assembly in 1 M HCl display long-lived, albeit noisy, channels that appear to be voltage-independent multiples of only one conductance state. The noise in the data is consistent with the molecular modeling studies, which indicate that the side chain of glutamine 7 of alamethicin does not fit well into the narrow pore of a parallel four-helix bundle.     

Optimization of passive optical network planning

Network planning problem typically involves large capital investment and can be formulated as an optimization problem where the objective is minimization of the first installed cost. We consider a passive optical network (PON) planning problem based on a residential area in Adana (Turkey). There are four possible primary node locations, twenty possible secondary node locations, and twenty-eight customers. We use genetic algorithm and mathematical modeling techniques to optimize the position of the primary and secondary nodes, their split levels and assigning customers to secondary nodes and secondary nodes to primary nodes under some constraints such as system’s attenuations and technical characteristics of all the equipment.     

Electrical properties of triple-doped bismuth oxide electrolyte for solid oxide fuel cells

In this study, the quaternary solid solutions of (Bi₂O₃)_(0.8?x)(Tb₄O₇)_0.1(Ho₂O₃)_0.1(Dy₂O₃)_x (x = 0.05, 0.10, 0.15, 0.20) as an electrolyte were synthesized for solid oxide fuel cells by the technique of solid-state synthesis.

The products were characterized by X-ray powder diffraction, differential thermal analysis/thermal gravimetry and the four-point probe technique (4PPT). The total electrical conductivity is measured on the temperature and the doped concentration by 4PPT.

All samples have been obtained as the δ-phase. According to the measurements of the 4PPT, the electrical conductivities of the samples increase with the temperature but decrease with the amount of doping rate. The value of the highest conductivity (σ) is found as 1.02?×?10^?1 S cm^?1 for the system of (Bi₂O₃)_0.75(Tb₄O₇)_0.1(Ho₂O₃)_0.1(Dy₂O₃)_0.05 at 850 °C. The thermal gravimetry (TG) curve shows that there is no mass loss of sample during the measurement. The analyses of differential thermal reveal that there are neither endothermic peaks nor exothermic peaks during the heating and cooling cycles (ranging from 30 to 1000 °C).     

Asymmetric logistic peak as a suitable function for the resolution of highly asymmetric voltammograms in non-bilinear systems

The asymmetric logistic peak is tested as a new function for the parametric signal fitting (PSF) of highly asymmetric electrochemical signals in non-bilinear datasets, such as those obtained in linear sweep voltammetry (LSV) or in the presence of irreversible electrochemical processes. This new multivariate curve resolution strategy (PSF-ALPA) is successfully applied to LS voltammograms measured for the Cd(II)-glutathione system with a hanging mercury drop electrode, where Cd(II) is reversibly reduced, and to differential pulse voltammograms (DPV) measured at a glassy carbon electrode, where Cd(II) reduction becomes irreversible. Matrix augmentation by using LS voltammograms measured at different scan rates provides good results and encourages the development of ALPA methodology for third order data.