Branched polyether with multiple primary hydroxyl groups: polymerization of 3-ethyl-3-hydroxymethyloxetane

Cationic polymerization of 3-ethyl-3-hydroxymethyloxetane gives branched, soluble macromolecules with multiple glycolic end groups. There are approximately 3–4 “normal” units per one branched unit.     

Diastereoselective synthesis of tetrahydrofurans via reaction of gamma,delta-epoxycarbanions with aldehydes

[reaction: see text] Hydroxymethyl-substituted tetrahydrofurans were prepared with high diastereoselectivity by reaction of the carbanion derived from 3,4-epoxybutyl phenyl sulfone with aldehydes in the presence of a mixture of lithium and potassium tert-butoxides. Initial formation of aldol-type adducts is a nondiastereoselective but reversible process; thus, subsequent formation of one main diastereoisomer is controlled by the relative rates of cyclization. The configuration of the carbon stereocenter at the oxirane ring is inverted in the course of the S(N)2 process, and two new centers are created diastereoselectively.     

Alterations of ciliate phosducin phosphorylation in Blepharisma japonicum cells

We have previously reported that motile photophobic response in ciliate Blepharisma japonicum correlates with dephosphorylation of a cytosolic 28 kDa phosphoprotein (PP28) exhibiting properties similar to those of phosducin. Here we demonstrate in in vivo phosphorylation assay that the light-elicited dephosphorylation of the PP28 is significantly modified by cell incubation with substances known to modulate protein phosphatase and kinase activities. Immunoblot analyses showed that incubation of ciliates with okadaic acid and calyculin A, potent inhibitors of type 1 or 2A protein phosphatases, distinctly increased phosphorylation of PP28 in dark-adapted cells and markedly weakened dephosphorylation of the ciliate phosducin following cell illumination. An enhancement of PP28 phosphorylation was also observed in dark-adapted ciliates exposed to 8-Br-cAMP and 8-Br-cGMP, slowly hydrolysable cyclic nucleotide analogs and 3-isobutyryl-1-methylxanthine (IBMX), a non-specific cyclic nucleotide phosphodiesterase (PDEs) inhibitor. Only slight changes in light-evoked dephosphorylation levels of PP28 were observed in cells treated with the cyclic nucleotide analogs and IBMX. Incubation of ciliates with H 89 or KT 5823, highly selective inhibitor of cAMP-dependent protein kinase (PKA) and cGMP-dependent protein kinase (PKG), respectively, decreased PP28 phosphorylation levels in dark-adapted cells, whereas the extent of light-evoked dephosphorylation of the phosphoprotein was only slightly influenced. Cell treatment with higher Ca2+ concentration together with ionophore A23187 in culture medium resulted in marked increase in PP28 phosphorylation levels, while quite an opposite effect was observed in cells exposed to Ca2+ chelators, EGTA or BAPTA/AM as well as calmodulin antagonists, such as trifluoperazine (TFP), W-7 or calmidazolium. Light-dependent dephosphorylation was not considerably affected by these treatments. The experimental findings presented here suggest that an endogenous light-dependent protein kinase-phosphatase system may be engaged in the alteration of phosducin phosphorylation in ciliate B. japonicum thereby to modulate the cell motile photophobic behavior.     

Determination of dipole moment in the ground and excited state by experimental and theoretical methods of N-nonyl acridine orange

The absorption and fluorescence spectra of N-nonyl acridine orange are determined at room temperature (298 K) in cyclohexane, benzene, carbon tetrachloride, chloroform, chlorobenzene and dichloromethane. The ground state of dipole moment was obtained by impedance measurements using Guggenheim-Debeye's method. The experimental excited state dipole moment of N-nonyl acridine orange was determined using Bakhshiev's and Kawski-Chamma-Viallet's formulae and solvent polarity parameter proposed by Reichardt. These experimental results were completed with theoretical results using quantum chemical methods. The experimental (muexp=10.76 D) and theoretical (mucal=9.9 D) dipole moments in the ground and excited state (muexp*=14.56 D) were compared.     

Thiyl radical interaction with pyrimidine C5-C6 double bond

Addition and elimination interaction of thiyl radicals with the C5-C6 double bond in pyrimidines was studied by the pulse radiolysis technique in aqueous solution with the use of different monitoring systems. For this purpose, p-thiocresol, cysteamine hydrochloride, and mercaptoethanol were used. The rate constants of addition and elimination of thiyl radicals were determined by applying the modified version of ACUCHEM (computer program for modeling complex reaction systems). Aliphatic thiyl radicals add to the pyrimidine C5-C6 double bond with k = 1.0-3.0 x 10(7) dm3 mol(-1) s(-1), whereas elimination takes place with k = 0.7-2.0 x 10(5) s(-1). Quantum chemical calculations at the B3LYP/6-31G(d)/PCM level show that the addition should occur at the C6 position of the pyrimidine ring and that the energy of interaction between thiyl radicals and the pyrimidine double bond C5-C6 is low.     

Tetra­kis(1‐eth­yl‐1H‐1,2,4‐triazole‐κN4)bis­(nitrato‐κO)copper(II) and bis­(nitrato‐κO)tetra­kis­(1‐prop­yl‐1H‐1,2,4‐triazole‐κN4)copper(II)

The copper(II) environments for tetra­kis­(1‐eth­yl‐1,2,4‐triaz­ole)­dinitratocopper(II), [Cu(NO₃)₂(C₄H₇N₃)₄], and tetrakis­(1‐prop­yl‐1,2,4‐triazole)dinitratocopper(II), [Cu(NO₃)₂(C₅H₉N₃)₄], are distorted square bipyramidal. Both structures are centrosymmetric, with the copper(II) ions located at inversion centers coordinated by four N atoms of four triazole mol­ecules and by two O atoms of two nitrate ions in an elongated octa­hedral geometry. This elongation is a result of the Jahn–Teller effect. The largest distortion is that of the N—Cu—O angles, which differ from 90° by 5.68 (10)° in the eth­yl and 5.59 (8)° in the prop­yl derivative.     

Solvatochromism of 3-[2-(aryl)benzoxazol-5-yl]alanine derivatives

The photophysical properties of N-Boc-3-[2-(9-anthryl)benzoxazol-5-yl]-l-alanine methyl ester (BoxAnt) and N-Boc-3-[2-[4-(9′-(10′-butyl)anthryl)phenyl]benzoxazol-5-yl]-l-alanine methyl ester (BoxPhAnt) were studied in a series of solvents. Their absorption spectra are less sensitive to the solvent polarity than the corresponding fluorescence spectra which show a pronounced solvatochromic effect leading to large Stokes shifts. Using an efficient solvatochromic method, based on the empirical solvent polarity parameter , a large change of the dipole moment on excitation for BoxPhAnt has been found. From an analysis of the solvatochromic behaviour of the absorption and fluorescence spectra in terms of bulk solvent polarity functions, f(_r, n) and g(n), a larger excited-state dipole moment (about 8 D, ψ = 56) was obtained for BoxPhAnt than for BoxAnt (about 3 D, ψ = 0). Both applied methods gave similar values of the excited-state dipole moments for both compounds studied.     

Spectrum analysis of U-doped LaBr3 single crystals. Part 1: crystal-field analysis

Single crystals of U³⁺:LaBr₃ were grown by the Bridgman-Stockbarger technique. High-resolution polarized absorption spectra of the crystals were recorded at 4.2 K in the 4000-50,000 cm⁻¹ range. Sixty-four experimental crystal-field energy levels of the U³⁺ ion were fitted to a semiempirical Hamiltonian employing free-ion, one-electron crystal-field as well as two-particle correlation crystal-field (CCF) operators with an r.m.s. deviation of 28 cm⁻¹. The performed analysis of the spectra enabled the determination of crystal-field parameters and assignment of the observed 5f³→5f³ transitions. The effects of selected CCF operators on the splitting of some specific U³⁺ multiplets have been investigated and the obtained values of Hamiltonian parameters are discussed and compared with those reported in previous analyses.     

Selective voltammetric determination of chromium (VI) with DTPA and nitrate

A voltammetric determination of Cr(VI) in a flow system is described based on the selective accumulation of the reduction product of Cr(VI) on an HMDE, its complexation with DTPA and subsequent reduction of the complex in presence of nitrate. The calibration graphs were linear up to 100 and 5 nmol/L for deposition times 120 and 600 s, respectively. The relative standard deviation was 2.8% (n = 5) for Cr(VI) concentrations of 5 × 10^–8 mol/L. The detection limits (3 σ) for Cr(VI) were 1.0 and 0.12 nmol/L at deposition times of 120 and 600 s, respectively. Typical interferences derived from real water samples are discussed. The method has been applied for the determination of Cr(VI) in spiked natural water samples. Received: 18 June 1998 / Revised: 28 September 1998 / Accepted: 5 October 1998     

Complexing properties of methyl and phenyl glycine derivatives in their compounds with H+, Ni(II), Cu(II), and Zn(II)

The influence of the solvent and the substituents on the complexing properties of methyl and phenyl glycine derivatives is discussed. On the basis of a computer analysis of potentiometric titration results, the composition and the stability constants of the complexes ofN-methylglycine,N,N-dimethylglycine,N-phenylglycine and phenylglycine with H⁺ and with Ni(II), Cu(II), Zn(II) were determined. The ligand-metal coordination mode as well as the zwitterion level in percent in ligand/proton systems were determined by spectral analyses and equilibria studies.

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Komplexbildung der Methyl- und Phenylglycin-Derivate in ihren Verbindungen mit dem Proton und Ni(II), Cu(II) und Zn(II)

Zusammenfassung Der Einfluß des Lösungsmittels und der Substituenten auf die komplexbildenden Eigenschaften der Methyl- und Phenylglycin-Derivate wird diskutiert. Anhand einer Computer-Analyse von potentiometrischen Daten wurden die Zusammensetzung und die Beständigkeitskonstanten der Komplexe vonN-Methylglycin,N,N-Dimethylglycin,N-Phenylglycin und Phenylglycin mit H⁺, Ni(II), Cu(II) und Zn(II) festgestellt. Mittels spektroskopischer Methoden und Gleichgewichtstudien wurde der Koordinationstyp des Liganden mit dem Metall festgestellt sowie der Prozentanteil des Zwitterions im Ligand/Proton-System.