The effect of heating on background and radiation-induced EPR signals in tooth enamel

The presented study is a continuation of our work performed during participation in the Third International Intercomparison on EPR Tooth Dosimetry. During the process of samples preparation, all 22 enamel samples were accidentally exposed for about 30 min to 150 degrees C temperature. This considerably affected shape of their EPR spectra mainly due to substantial increase in the background signal, which approximately doubled its contribution to the spectra. These effects were studied closer under controlled conditions of the delivered dose and heating temperature using another enamel samples. The observed changes in the spectra shape partially faded within a few days after heating. The heating resulted also in a noticeable generation of a spectral component similar to the dosimetric signal induced in enamel by radiation. The temperature-induced dosimetric component in EPR spectra of the heated samples remained constant for 32 days. Deviations in calculated contributions of the dosimetric signal into total EPR spectra of irradiated sample varied from -12 to +15% of its initial contribution in the non-heated enamel, depending on type of the background spectrum applied in numerical processing of the spectra.     

A new selective approach to 1,1-bis(silyl)-2-arylethenes and 1,1-bis(silyl)-1,3-butadienes via sequential silylative coupling-Heck coupling reactions

A novel selective route to 1,1-bis(silyl)-1-alkenes has been developed. Sequential one-pot silylative coupling exo-cyclization of 1,2-bis(dimethylvinylsiloxy)ethane followed by the reaction with Grignard reagents leads to the desired 1,1-bis(silyl)ethenes, which are then efficiently coupled in the presence of silver nitrate and palladium acetate with aryl or alkenyl idodides to give the corresponding 1,1-bis(silyl)-2-arylethenes or 1,1,4-trisubstituted 1,3-butadienes with high yield.     

Two Crystal Forms of 4-{(2<Emphasis Type="Italic">E</Emphasis>)-2-[1-(4-Methoxyphenyl)ethylidene] hydrazinyl}-8-(trifluoromethyl)quinoline

Abstract  

The Schiff base, 4-{(2E)-2-[1-(4-methoxyphenyl)ethylidene] hydrazinyl}-8-(trifluoromethyl)quinoline, crystallizes in two polymorphic forms depending on the solvent. One of these forms is monoclinic (1M), space group P2₁/c with a = 10.2906(10) ?, b = 8.9211(7) ?, c = 18.4838(15), β = 97.271(8)°, and the other is orthorhombic (1O), space group Pbca, unit-cell parameters: a = 13.6485(12) ?, b = 9.0588(9) ?, c = 27.400(2) ?. The molecules in either crystalline form have similar bond lengths and angles, but one is nearly planar while the other has a significant twist. In monoclinic form the dihedral angle between terminal ring planes is 17.26(8)° while in the orthorhombic one it is 26.11(5)°, and in this latter case the central chain is almost coplanar with the quinoline ring system while in the former these two planes are significantly twisted. The crystal structures of both forms are determined by the interplay of van der Waals forces and weak directional interactions C–H···F, π···π stacking, and—in the case of 1M—short intermolecular C–F···N contact. The crystals of 1M decomposes slowly into the powder while the other form is stable. The powder diffraction pattern of the product of decomposition of 1M is similar to that calculated for 1O. This suggests that the decomposition is a consequence of the phase transition of the less stable monoclinic into more stable orthorhombic form.     

N-Skatyltryptamines—Dual 5-HT6R/D2R Ligands with Antipsychotic and Procognitive Potential

A series of N-skatyltryptamines was synthesized and their affinities for serotonin and dopamine receptors were determined. Compounds exhibited activity toward 5-HT_1A, 5-HT_2A, 5-HT₆, and D₂ receptors. Substitution patterns resulting in affinity/activity switches were identified and studied using homology modeling. Chosen hits were screened to determine their metabolism, permeability, hepatotoxicity, and CYP inhibition. Several D₂ receptor antagonists with additional 5-HT₆R antagonist and agonist properties were identified. The former combination resembled known antipsychotic agents, while the latter was particularly interesting due to the fact that it has not been studied before. Selective 5-HT₆R antagonists have been shown previously to produce procognitive and promnesic effects in several rodent models. Administration of 5-HT₆R agonists was more ambiguous—in naive animals, it did not alter memory or produce slight amnesic effects, while in rodent models of memory impairment, they ameliorated the condition just like antagonists. Using the identified hit compounds 15 and 18, we tried to sort out the difference between ligands exhibiting the D₂R antagonist function combined with 5-HT₆R agonism, and mixed D₂/5-HT₆R antagonists in murine models of psychosis.     

Effect of weak anchoring on the electric field induced deformations of nematic layers

The stationary deformations of nematic layers with a twisted structure are analysed by means of the Taylor expansion method based on catastrophe theory. The role of weak anchoring is investigated. Variations of the polar and azimuthal angles describing the surface director orientation are allowed. The stability of two equilibrium states, the twisted and the homeotropic, is studied. Several types of continuous and discontinuous transitions between them are revealed. The threshold voltages are calculated.     

Zebra Factorizations in Free Semigroups

Let $S$ be a semigroup of words over an alphabet $A$. Let $\Omega(S)$ consist of those elements $w$ of $S$ for which every prefix and suffix of $w$ belongs to $S$. We show that $\Omega(S)$ is a free semigroup. Moreover, $S$ is called separative if also the complement $S^c = A^+\setminus S$ is a semigroup. There are uncountably many separative semigroups over $A$, if $A$ has at least two letters. We prove that if $S$ is separative, then every word $w \in A^+$ has a unique minimum factorization $w = z_1z_2 \cdots z_n$ with respect to $\Omega(S)$ and $\Omega(S^c)$, where $z_i \in \Omega(S) \cup \Omega(S^c)$ and $n$ is as small as possible.     

Specific binding of a biotinylated,metallocarbonyl‐labelled dendrimer to immobilized avidin detected by diffuse‐reflectance infrared Fourier transform spectroscopy

Molecular recognition between avidin covalently immobilized at the surface of acrylic resin beads and a transition metallocarbonyl tracer of the biotin ligand was detected using diffuse reflectance infrared Fourier transform spectroscopy. Copyright © 2004 John Wiley & Sons, Ltd.     

Thermal and photochemical production of chromate(VI) ions from some complexes containing the “CrNO”2+ group

Results are reported for the oxidation of complexes of the type [Cr(CN)_5?x(H₂O)_xNO]^x?3 by molecular oxygen in alkaline medium. In the case of the [Cr(CN)₅NO]^3? complex the reaction proceeded photochemically, whereas in othe cases the thermal oxidation was also observed. The influence of pH, CN^? concentration and energy of radiation was investigated.