General method for the synthesis of 2′-O-carboranyl-nucleosides

The carboranyl cage is a new modifying entity for nucleosides, DNA oligonucleotides, and other biomolecules. Herein, the first reliable method for the synthesis of nucleosides modified with a carborane cluster at the 2′-position is described.     

Synthesis and Characterization of Polyether Adducts of Barium and Strontium Carboxylates and Their Use in the Formation of MTiO(3) Films

The synthesis, characterization, and reactivity of new polyether adducts of strontium and barium carboxylates of general composition M(O(2)CCF(3))(n)()(L) (M = Ba, L = 15-crown-5, (1); M = Ba (2), Sr (3), respectively, with L = tetraglyme are reported. The compounds were synthesized by reaction of BaCO(3) or MH(2) (M = Sr or Ba) with organic acids in the presence of the polyether ligands. These compounds have been characterized by IR and (13)C and (1)H NMR spectroscopies, elemental analyses, and thermogravimetric analysis. The species Ba(2)(O(2)CCF(3))(4)(15-crown-5)(2) (1) and [Ba(2)(O(2)CCF(3))(4)(tetraglyme)](infinity) (2), were also characterized by single-crystal X-ray diffraction. Ba(2)(O(2)CCF(3))(4)(15-crown-5)(2) (1) crystallizes in the orthorhombic space group Cccm with cell dimensions of a = 13.949(1) ?, b = 19.376(2) ?, c = 16.029(1) ?, and Z = 8. [Ba(2)(O(2)CCF(3))(4)(tetraglyme)](infinity) (2) crystallizes in the monoclinic space group C2/c with cell dimensions of a = 12.8673(12) ?, b = 16.6981(13) ?, c = 15.1191(12) ?, beta = 99.049(8) degrees, and Z = 4. Compounds 1-3 thermally decompose at high temperatures in the solid state to give MF(2). However, solutions of compounds 1-3 dissolved in ethanol with Ti(O-i-Pr)(4) give crystalline perovskite phase MTiO(3) films, or in the case of mixtures of 2 and 3, Ba(1)(-)(x)()Sr(x)()TiO(3) films below 600 degrees C when spin coated onto silicon substrates and thermally treated. The crystallinity, purity, and elemental composition of the films was determined by glancing angle X-ray diffraction and Auger electron spectroscopy.     

Complex compounds of ferrocene in a biacceptor system

Summary Three-component systems of ferrocene (FcH): carbon tetrachloride: tetranitromethane have been investigated spectrally in the 290–800 nm range. Quantitative relationships were investigated between electron-donor acceptor (EDA) complexes of ferrocene and CCl₄ (FcH · CCl₄) and C(NO₂)₄ [FcH · C(NO₂)₄] and the ferricenium cation (FcH⁺) which is formed as a result of dissociation of complexes and which depends upon the initial concentration of C(NO₂)₄ and duration the reaction. The results prove the destabilizing influence of C(NO₂)₄ on the EDA complex of ferrocene and CCl₄.     

The thermal decompositions of some transition metal acrylates and polyacrylates

The thermal behaviours of zinc, cobalt, nickel and copper acrylates and their polymers were investigated. It was found that the decompositions of these compounds are complex processes. The main decomposition of the monomer was preceded by thermal polymerization. The thermal effect of this reaction was greater for zinc acrylate than for the other salts. The reaction orders and activation energies of decomposition of the monomers and the polymers were calculated and the differences discussed.

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Zusammenfassung Das thermische Verhalten der Acrylate von Zink, Kobalt, Nickel und Kupfer und das der entsprechenden Polymere wurde untersucht. Es wurde festgestellt, dass die Zersetzung dieser Verbindungen komplexe Prozesse sind.Der Zersetzung der Monomeren ging eine thermische Polymerisation voraus. Der thermische Effekt dieser Reaktion war im Falle des Zinkacrylats grösser als bei den anderen Salzen. Die Reaktionsordnungen und Aktivierungsenergien der Zersetzung der Monomeren und Polymeren wurden berechnet und die Unterschiede diskutiert.

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Crystal structure and spectral characterization of hexanuclear oxo titanium(IV) clusters: [Ti6O6(OSi(CH3)3)6(OOCR)6] (R = Bu,CH2Bu,C(CH3)2Et)

Hexanuclear oxo titanium(IV) siloxo carboxylate complexes with the general formula [Ti₆O₆(OSi(CH₃)₃)₆(OOCR)₆] (R = Bu^t (1), CH₂Bu^t (2), C(CH₃)₂Et (3)) were synthesized in quantitative yield, by the reaction of Ti(OSiMe₃)₄ with the appropriate organic acid. Crystal structure determination revealed that molecules of 1–3 are composed of [Ti₆-(μ₃-O)₆] cores stabilized by six syn–syn carboxylato bridges and six terminal siloxide ligands. Each metal atom is surrounded by six oxo atoms, capping the triangular faces of the distorted octahedron. Spectral characterization (IR, NMR) of 1–3 revealed a significant non-equivalence of the carboxylate group interactions, resulting from the asymmetry of the Ti-μ-OOC bonds of the syn–syn bridges. The thermal stability of the studied compounds was determined from TGA/DTA analysis.     

Improvement of electrophoretic detection of antitrypsin activity in fish blood and seminal plasma

The original method of Uriel and Berges for detection of trypsin inhibitors lacks specificity due to masking effects of nonspecific esterases. We report a modification of this method based on inhibition of esterases in samples by phenylmethylsulfonyl fluoride (PMSF). This method can be particularly useful for characterization profiles of antitrypsin activity in seminal plasma of salmonid fish where esterases and inhibitors migrate at the same mobility.     

Synthesis,structural characterization,and thermal properties of zirconium(IV) <Emphasis Type="Italic">β</Emphasis>-ketodiester complexes

Mono- and bi-nuclear Zr(IV) β-ketodiester complexes of general formulas [Zr(dtbacdc)₄] (1), [Zr(dmacdc)₃(OⁱPr)]₂ (2), and [Zr(dtbacdc)₃(OⁱPr)]₂ (3), (dtbacdc = di-tert-butyl-1,3-acetonedicarboxylato and dmacdc = dimethyl-1,3-acetonedicarboxylato ligands) were successfully isolated, when zirconium(IV) isopropoxide reacted with the four- ((1)) or twofold ((2), (3)) excess of di-alkyl 1,3-acetonedicarboxylates (CO(CH₂COOR′)₂, R′ = Me, ^tBu). Analysis of single-crystal X-ray diffraction data showed that (1) crystallizes in the monoclinic system (C 2/c (no. 15)). The structure of this compound consists of monomers, which are composed of Zr(IV) ions surrounded by eight oxygen atoms derived from four chelating β-ketodiester ligands. The stoichiometry and the bi-nuclear structure of (2) and (3) using spectroscopic methods (IR and NMR), and mass spectrometry have been determined. Thermal analysis and variable temperature IR (VT-IR) spectroscopy have been used to study the thermal stability and thermal decomposition pathway of synthesized Zr(IV) compounds.     

Perception of across-frequency asynchrony and the role of cochlear delays

Cochlear filtering results in earlier responses to high than to low frequencies. This study examined potential perceptual correlates of cochlear delays by measuring the perception of relative timing between tones of different frequencies. A brief 250-Hz tone was combined with a brief 1-, 2-, 4-, or 6-kHz tone. Two experiments were performed, one involving subjective judgments of perceived synchrony, the other involving asynchrony detection and discrimination. The functions relating the proportion of "synchronous" responses to the delay between the tones were similar for all tone pairs. Perceived synchrony was maximal when the tones in a pair were gated synchronously. The perceived-synchrony function slopes were asymmetric, being steeper on the low-frequency-leading side. In the second experiment, asynchrony-detection thresholds were lower for low-frequency rather than for high-frequency leading pairs. In contrast with previous studies, but consistent with the first experiment, thresholds did not depend on frequency separation between the tones, perhaps because of the elimination of within-channel cues. The results of the two experiments were related quantitatively using a decision-theoretic model, and were found to be highly correlated. Overall the results suggest that frequency-dependent cochlear group delays are compensated for at higher processing stages, resulting in veridical perception of timing relationships across frequency.     

On some interfacial fundamental characteristics for a general model of giant magnetoresistance

We present an analytical model for introducing interface roughness into giant magnetoresistance. The roughness acts mainly on the spin currents via the mixing relaxation time, in such a way, that the theoretical results suggest a direct experimental procedure.