The cyclodimerisation of 3-methyl-2-butenenitrile

3-Methyl-2-butenenitrile (1) cyclodimerised on treatment with lithium diisopropylamide in dimethoxyethane at temperatures between ?78°C and 0°C to 3-amino-4-cyano-1,5,5-trimethyl-1,3-cyclohexadiene (2) the structure of which was established by acid hydrolysis to the known 4-cyano-1,5,5-trimethyl-1-cyclohexene-3-one (3).     

Siloxyaluminate and Siloxygallate Complexes as Models for Framework and Partially Hydrolyzed Framework Sites in Zeolites and Zeotypes

Anionic molecular models for nonhydrolyzed and partially hydrolyzed aluminum and gallium framework sites on silica, M[OSi(OtBu)₃]₄⁻ and HOM[OSi(OtBu)₃]₃⁻ (where M=Al or Ga), were synthesized from anionic chlorides Li{M[OSi(OtBu)₃]₃Cl} in salt metathesis reactions. Sequestration of lithium cations with [12]crown-4 afforded charge-separated ion pairs composed of monomeric anions M[OSi(OtBu)₃]₄⁻ with outer-sphere [([12]crown-4)₂Li]⁺ cations, and hydroxides {HOM[OSi(OtBu)₃]₃} with pendant [([12]crown-4)Li]⁺ cations. These molecular models were characterized by single-crystal X-ray diffraction, vibrational spectroscopy, mass spectrometry and NMR spectroscopy. Upon treatment of monomeric [([12]crown-4)Li]{HOM[OSi(OtBu)₃]₃} complexes with benzyl alcohol, benzyloxide complexes were formed, modeling a possible pathway for the formation of active sites for Meerwin–Ponndorf–Verley (MPV) transfer hydrogenations with Al/Ga-doped silica catalysts.     

Organoboranes. 52. The successful ring enlargement of boracyclanes via sequential one-carbon homologation: The first synthesis of boracyclanes in the strained medium-ring range

Previous attempts to synthesize boracyclanes in the medium-ring range (9-, 10-, 11-, and 12-ring members) via cyclic hydroboration of α,ω-dienes have failed. However, their synthesis via the sequential one-carbon homologation of B-methoxyboracyclanes has been achieved utilizing the successive reaction of B-methoxyboracyclanes with in situ generated (chloromethyl)lithium (LiCH₂Cl): MeOB(CH₂)₅ → MeOB(CH₂)₆ → MeOB(CH₂)₇ → MeOB(CH₂)₈ → MeOB(CH₂)₉ → MeOB(CH₂)₁₀ → MeOB(CH₂)₁₁. The yields achieved are in the range of 75–85%. In each case the products are identified by conversion via the DCME reaction into the known cycloalkanones. This development provides the first entry into boracyclanes of the strained medium ring range.     

Conical parametric scattering of a single extraordinary beam in BaTiO3 crystal

In this paper, the parametric scattering of a single extraordinary polarized beam of laser in BaTiO₃ photorefractive crystal has been investigated experimentally and theoretically. The resulting pattern consists of beam fanning, isotropic ring, and anisotropic one. Among all parts of scattering pattern, isotropic ring has not been studied as much as beam fanning and anisotropic ring, and there still are some differences in reports about it. Therefore, the study has mainly focused on this part. In this experimental configuration, isotropic ring is just visible in positive angles although the other parts of parametric scattering pattern can be visible from behind and in front of the crystal. In addition to steady state pattern in forward and backward directions, its transient behavior with the rotation of crystal has been studied. The results of experiments have been analyzed carefully, and their theoretical explanations have been presented based on the standard theory of parametric scattering in photorefractive crystals. It has been shown that this configuration corresponds to the so called parametric B-process scattering.     

Azelaic acid in model membranes: A thermodynamical and structural study

Summary We report a thermodynamical and structural investigation on the effect of a dicarboxylic acid, the azelaic acid, on a synthetic phosophatidylcholine in excess water condition. The results indicate that the drug interacts with the lipid headgroup region, near to the hydrocarbon chains: in particular, at higher concentrations investigated, an interdigitated ?gel phase?, with rigid chains, stiff and perpendicular to the lamellar planes, is induced. The experimental electron density profiles, obtained for samples containing low and high quantity of azelaic acid, support the proposed interaction. Moreover, step electron density models, used to confirm the selected sign combination of the observed structure factors, show the best agreement with the experimental data when the chain terminal methyl groups are frozen in fixed position. Work presented at the second USSR-Italy Bilateral Meeting on Liquid Crystals held in Moscow, September 15–21, 1988.     

Simultaneous RP-LC Determination of Artesunate and Amodiaquine in Pharmaceutical Preparations

A simple, fast and precise reversed phase liquid chromatographic method was developed for the simultaneous determination of artesunate (AS) and amodiaquine (AD) in combined pharmaceutical dosage form. Chromatographic separation of the two drugs was performed on a BDS Hypersil C18, 100 mm × 4.6 mm, 3 μm particle size column as stationary phase with a mobile phase comprising of phosphate buffer (pH 3.0 with orthophosphoric acid) and acetonitrile in the proportion of 50:40 (v/v), at a flow rate of 0.8 mL min^?1 and UV detection at wavelength 210 nm for AS and 300 nm for AD using photo diode array detection. The proposed method was validated for specificity, accuracy, linearity, range, precision and was successfully applied to the simultaneous determination of AS and AD in the combined fixed dosage form without any excipient’s interference.     

Some structural and dynamical properties of multilamellar vesicles incorporated with propranolol

Summary Spin labelling ESR, calorimetry and³¹P NMR have been used to investigate dipalmitoyl phosphatidylcholine dispersions incorporated with propranolol which is a β-adrenoceptor blocking drug, widely used in the treatment of arrhythmy. The drug appears to enter the lipid bilayer also at the lowest concentrations and to induce a progressive fluidification of multilamellar vesicles. In fact, the presence of drug reduces the temperature of chain melting transition and the corresponding cooperation number. Furthermore the phase transitionL _β′ −P _β′ is not observable also at the lowest drug concentrations. Work presented at the First USSR-Italy Bilateral Meeting on Liquid Crystals held in Portonovo, Ancona (Italy), September 30–October 2, 1987.