Degeneracy of rotational viscosities at the chiral smectic C-smectic A transition in DOBAMBC

From measurements of the electroclinic effect and the dielectric strength of the soft mode close to the chiral smectic C-smectic A transition we show that the rotational viscosities associated with the Goldstone and soft modes are degenerate at T_c, in agreement with the predictions of the theoretical model.     

An ultrasonic investigation of the critical behaviour of the elastic moduli near the smectic C-smectic A phase transition

Results for the frequency-temperature dependence of the elastic moduli and the longitudinal sound velocity near the S_C-S_A transition are reported. The measurements were made at frequencies in the range 0.15-27 MHz. The interpretation of the results obtained was made using the theory of critical dynamics taking into consideration the bare anisotropy.     

Smectic A and smectic C materials: partially deuteriated chiral liquid crystals (S)-(-)-2-methylbuty 4-(4-(d13)-hexyloxyphenyl)benzoate and (S)-(-)-2-methylbutyl 4-(4-(d17)-octyloxyphenyl)benzoate

In order to study the difference in microscopic orientation of ferro- and antiferroelectric liquid crystalline molecules, we synthesized the partially deuteriated chiral compounds, (S)-(^-)-2-methylbutyl 4-(4-(d₁₃)-hexyloxy- and (S)-(^-)-2-methylbutyl 4-(4-(d₁₇)-octyloxy-phenyl)benzoates. Fundamental physical properties such as phase transition temperatures, spontaneous polarization and tilt angle were determined. Polarized FTIR measurements were also made to provide information on molecular structure and orientation.     

Smectic A and smectic C materials: partially deuteriated chiral liquid crystals (S)-(-)-2-methylbuty 4-(4-(d13)-hexyloxyphenyl)benzoate and (S)-(-)-2-methylbutyl 4-(4-(d17)-octyloxyphenyl)benzoate

In order to study the difference in microscopic orientation of ferro- and antiferroelectric liquid crystalline molecules, we synthesized the partially deuteriated chiral compounds, (S)-(^-)-2-methylbutyl 4-(4-(d₁₃)-hexyloxy- and (S)-(^-)-2-methylbutyl 4-(4-(d₁₇)-octyloxy-phenyl)benzoates. Fundamental physical properties such as phase transition temperatures, spontaneous polarization and tilt angle were determined. Polarized FTIR measurements were also made to provide information on molecular structure and orientation.     

Diastereoselective formation of chiral iridium hydrides containing the chiral P,N-chelate ligand (4S)-2-(2-(diphenylphosphino)phenyl)-4-isopropyl-1,3-oxazoline

The iridium complex [Ir(mu-Cl)(PN)(PPh3)]2 (1) reacts with H2 affording only the kinetic isomer OC-6-55-C of the dihydride [IrClH2(PN)(PPh3)] (2) and with methanol yielding, also exclusively, the thermodynamic isomer OC-6-53-C (2b) of the same dihydride; complex 2b has been characterised by X-ray diffractometric methods.     

A new approach to (S)-4-hydroxy-2-pyrrolidinone and its 3-substituted analogues

Successive treatment of a phenyl thioether derived from (S)-malic acid with n-BuLi, lithium naphthalenide (LN), and electrophiles led to 4-hydroxy-3-substituted 2-pyrrolidinones in one-pot and in high regio- and diastereoselectivity at C-3. N-Debenzylation of 1-benzyl-4-hydroxy-2-pyrrolidinone using LN afforded naturally occurring (−)-(S)-4-hydroxy-2-pyrrolidinone. (−)-(3S,4S)-4-Hydroxy-3-methyl-2-pyrrolidinone, the lactam form of the γ-amino acid residue found in marine natural products, bistramides, was prepared by the same method.     

Spectrophotometric studies of 4-(2-hydroxy-4-substituted-azobenzene)-2-methyl-quinolines as reagents for the determination of silver

Summary The spectroscopic behaviour of some quinoline azo dyes has been studied. A simple, rapid, accurate, and sensitive method for the spectrophotometric microdetermination of Ag(I) ions using the title compounds is given. The conditions for the formation of the coloured complexes are obeyed up to 26 µg·ml^–1; the optimum concentration range for application of theRingbom method is 2.5–23 µg·ml^–1. The molar absorptivity and theSandell sensitivity have also been calculated. The method proved to be successful in determining Ag⁺ in photography fixing solutions. The results agreed satisfactorily with those obtained using standard atomic absorption spectroscopy.

---

Spectrophotometrische Untersuchungen von 4-(2-Hydroxy-4-subst.-azobenzol)-2-methylchinolinen als Reagentien zur Silberbestimmung

Zusammenfassung Das spektroskopische Verhalten einiger Chinolin-Azofarbstoffe wurde untersucht. Eine einfache, rasche, genaue und empfindliche Methode zur spektrophotometrischen Mikrobestimmung von Silbert(I)-Ionen mittels der Titelverbindungen wird vorgestellt. Die Bedingungen zur Bildung der gefärbten Komplexe werden bis zu einer Maximalkonzentration von 26 µg·ml^–1 erfüllt; der optimale Konzentrationsbereich zur Anwendung derRingbom-Methode liegt zwischen 2.5 und 23 µg·ml^–1. Die molare Absorption und die Empfindlichkeit nachSandell wurden ebenfalls berechnet. Die Methode wurde erfolgreich zur Bestimmung von Ag⁺ in photographischen Fixierlösungen eingesetzt. Die Ergebnisse stimmen in zufriedenstellender Weise mit durch Atomabsorptionsspektroskopie erhaltenen überein.

     

Dielectric relaxation spectroscopy and electro-optical studies of phase behaviour of a chiral smectic liquid crystal

Dielectric relaxation processes in various phases of a chiral smectic liquid crystal compound have been investigated over a wide range of frequencies from 10 to 300 kHz. Dielectric spectroscopy reveals the existence of two relaxation frequencies corresponding to the ferroelectric and ferrielectric Goldstone modes in the range of temperature where two different phases coexist. This phenomenon of coexistence is examined with respect to the cell thickness and reversal temperature.     

Synthesis of (+)-(S)-Streptenol A and Biomimetic Synthesis of (2R,4S)- and (2S,4S)-2-(Pent-3-enyl)piperidin-4-ol

(+)-(S)-Streptenol A is synthesized by coupling a 1,3-dithiane with an optically pure epoxide. The absolute configuration of (+)-(S)-streptenol A is thereby correlated with that of (S)-malic acid. Stereoselective reduction of an oxime that could easily be prepared from streptenol A gave the (3S,5R)- and (3S,5S)-aminostreptenols, and after cyclization, configurationally pure 2,4-functionalized piperidine alkaloids.     

New,highly efficient syntheses of rac-, (R)- and (S)-4-hydroxy-2-cyclohexenone

Both enantiomers of 4-hydroxy-2-cyclohexenone have been synthesised from chiral p-benzoquinone equivalents through very short and simple sequences in good overall yields.     

Enantioselective synthesis of ethyl (S)-2-hydroxy-4-phenylbutyrate by recombinant diketoreductase

Recombinant diketoreductase showed excellent stereoselectivity in the double reduction of β,δ-diketo esters. To investigate the substrate specificity and to broaden the applications of this new biocatalyst, a number of ketone substrates were used to evaluate the substrate spectrum and enantioselectivity of this enzyme in the present study. Among the ketone substrates tested, only this enzyme displayed high efficiency and excellent enantioselectivity in the reduction of ethyl 2-oxo-4-phenylbutyrate to ethyl (S)-2-hydroxy-4-phenylbutyrate. After optimizing the reaction conditions, the bio-reduction of ethyl 2-oxo-4-phenylbutyrate at a substrate concentration of 0.8 M (164.8 g/L) was achieved by the recombinant diketoreductase in an aqueous-toluene biphasic system coupled with formate dehydrogenase for the regeneration of cofactor, resulting in an overall hydroxyl product yield of 88.7% (99.5% ee). This new enzymatic transformation may offer a practical method for the preparation of this important chiral building block.     

Synthesis of (S,S)-1,5-bis(4-alkyl-5-hydroxy-2-oxo-3-azapentyl)-1,5-diazacyclooctane

Crown ether derivatives have been extensively developed to provide enhanced structural recognition of substrate alkyl-ammonium cations. In particular a number of investigations of complexation of chiral alkylammonium salts by chiral crown ethers have been reported. The enantioselectivity has been applied in the chromatographic resolution of amino acid perchlorates. In general the crown ethers used in these studies have been based upon derivatives of 2, 2′-dihydroxy-1, 1′-binaphthyl1 or deriv…