Synthesis of a novel, highly symmetric bis-oxa-bridged compound

A highly oxygenated, novel pentacyclic bis-oxa-bridged compound 8 was synthesized with remarkable efficiency starting from readily available tetrachloro-5,5-dimethoxyclopentadiene and 1,4-cyclohexadiene in three steps. The ruthenium-catalyzed oxidation of 2:1 bis-adduct 1 followed by a one-pot transformation of the resulting bis-alpha-diketone 3 furnished (after esterification) the title compound in an overall yield of 29.1%. The versatility of this simple method was further demonstrated with other norbornyl alpha-diketones to obtain the corresponding strained oxa-bridged derivatives.     

Anion-exchange initiation of reactions: Detection and spectrophotometric determination of aliphatic amines with 2,4-dinitrophenylhydrazine

The role of anion-exchange resin beads in the initiation of reactions of tertiary amines with 2,4-dinitrophenylhydrazine has been explored. This reagent has been used for the selective detection and determination of aliphatic amines. Radiochemical studies have been performed to show that the coloured species is adsorbed but not exchanged on ion-exchange beads. A model for the interaction is proposed.     

Rydberg states of the strontium ion

We report on the spectroscopy of highly excited strontium ions after resonant multistep laser excitation. The states observed belonged to then s (26≦n≦79),n d (25≦n≦83),n f (28≦n≦86) andn g (30≦n≦81) series of Sr⁺. A least squares fit has been applied to determine the quantum defects and their linear energy dependence in each series, together with the ionisation limit of Sr⁺. The analysis of our data lead to a revised value for this ionisation limit of 88 965.18±0.02 cm^?1, with respect to the ground state of the Sr⁺ ion. Analysis of the non core-penetratingn g states yielded experimental values for the dipole and quadrupole polarizability of Sr⁺⁺, which are in satisfactory agreement with previous calculations.     

HPTLC Method for Determination of 20-Hydroxyecdysone in Sida rhombifolia L. and Dietary Supplements

Naturally occurring 20-hydroxyecdysone is an important anabolic ecdysteroid. A simple thin-layer chromatography method to quantitate 20-hydroxyecdysone in methanolic extract of the whole plant material of Sida rhombifolia L. was developed. This method was successfully applied for quantitative evaluation of dietary supplements. The separation was achieved on glass TLC plates coated with silica gel 60F254, using chloroform: methanol (8:2 v/v) as developing solvent. Densitometric evaluation of 20-hydroxyecdysone was performed at 250 nm in reflectance/absorbance mode. The calibration was in the range of 200–1,000 ng spot^?1 and correlation coefficient for the calibration curve was >0.999. In addition, for six different Sida species unique fingerprints were obtained on the HPTLC plate.     

Selective oxidation of cyclohexane by a Ru(III) analogue of the gif-system. RuIIIacetic acid-pyridine-KHSO5

Selective oxidation of cyclohexane to cyclohexanone was carried out in a RuCl₃-pyridine-acetic acid-KHSO₅ mixture. This system yields 2.8% of cyclohexanone (based on oxone concentration) under the conditions employed. Mechanistic postulate for the oxidation reaction involves the formation of a carbene intermediate (Ru=C) prior to the ketone formation.     

Phenomenology of flow disappearance in intermediate-energy heavy ion collisions

The disappearance of collective flow effects in heavy ion collisions is investigated using a microscopic optical model formalism for estimating collision momentum transfers. Phenomenological expressions for the balance energy are obtained which agree very well with measurements for various experimental collision pairs and with results obtained from Boltzmann-Uehling-Uhlenbeck simulations.     

Mixed-Metal Oxide Phases Containing Decavanadate Clusters: Synthesis and Crystal Structures of {{(H2O)2K-μ-(H2O)3-M(H2O)3}2[V10O28] (M=Co, Ni)

The synthesis and structures and thermal properties of two compounds: {(H₂O)₂K--(H₂O)₃-Co(H₂O)₃}₂[V₁₀O₂₈] (1) and {(H₂O)₂K--(H₂O)₃-Ni(H₂O)₃}₂[V₁₀O₂₈] (2) are described. These compounds have been prepared by the reaction of aqueous solutions (pH=3.5) of KVO₃with MCl₂·6H₂O (M=Co, Ni) at 70–72°C. The isomorphous structures of the two compounds consist of interlinked chains composed of arrays of {V₁₀O₂₈} clusters which are joined through {(H₂O)₂K--(H₂O)₃-M(H₂O)₃} bridges. Thermogravimetric studies revealed the complete removal of all water molecules in multiple steps in the temperature range 90–208°C.     

Radiochemical separation of radiothallium from proton-irradiated lead

Absorption of carrier-free T1 from nitric acid solutions of lead by ammonium 12-molybdophosphate fixed in the matrix of porous Teflon (AMP-sorbent) has been investigated. Effective separation of T1 and Pb is shown to take place. Elution processes of T1 from AMP-sorbent have been investigated. It is found that complete extraction of T1 is achieved upon dissolving AMP in concentrated ammonia. Further purification and concentration of T1 are performed by means of cation exchange chromatography on Dowex-50 or KU-2 resins. Investigation of high temperature behaviour of T1 ultramicroamounts in Pb melt showed that T1 is quantitatively separated out into the gas phase when fluorinating additions of PbF₂ or NaF solid salts covering the melt surface are used. The volatile compounds of radiothallium formed were transported by a stream of inert gas (He or N₂) from the evaporation zone to the thermochromatographic column, where they were sorbed on the surface in a limited zone with the maximum at 240 °C. Liquid and gas thermochromatographic methods for separation of carrier free radiothallium from protonirradiated lead material have been developed. The radiochemical, chemical and radionuclidic purity of T1 samples complies with requirements of nuclear medicine for²⁰¹T1 product. Both methods ensure 95% chemical yield of T1 and take about two hours each.