Stereochemistry of organic sulphur compounds. part 13. Configurational assignment of diastereoisomers of 2-methylsulphinyl-1,2-diphenylethanol and of their O-methyl and O-acetyl derivatives

The synthesis, isolation and conformational analysis of the diastereomeric 2-methylsulphinyl-1,2-diphenylethanol and of its $\text{O}$-methyl and $\text{O}$-acetyl derivatives are reported. Chemical correlations and the study of the influence of solvent polarity changes on the coupling constants have permitted the configurational assignment. Lanthanide shift reagents have been used also. to this effect. The role of hydrogen bonding in the hydroxysulphoxides has been evaluated in diluted solutions by IR and NMR spectroscopy. A donor-acceptor interaction between oxygen and sulphur has been invoked to explain the differences in conformational behaviour between epimeric sulphoxides at sulphur atom.     

The use of radium isotopic ratio in groundwater as a tool for pollution source identificatioin

Radium isotopes were measured in groundwater near a radioactive storage facility with contained pasty residues from monazite and industrial processing sealed in concerete reserouirs. The concentration of radium isotopes in the water was slightly higher than found in the normal drinking water. The measured²²⁸Ra to²²⁵Ra ratio in the groundwater is not compatible with calculations of radium isotopes ingrow and docay in cake II for different elapsed times, leaving mesothorium cake as the most likely source of contamination.     

High-pressure flow-injection assembly. Indirect determination of glycine by atomic absorption spectrometry

A procedure for the determination of glycine is described. The method is based on the reaction of the analyte with finely powdered, solid copper(II) carbonate in a continuous-flow assembly. The optimum experimental conditions of pH, temperature, sample volume, flow-rate, column length and internal diameter, and the linear range of calibration, were studied. Interference from foreign substances that accompany this amino acid in pharmaceutical formulations was studied, and the method was applied to the determination of glycine.     

Encapsulation of Hematite in Zircon by Microemulsion and Sol-Gel Methods

Microemulsion method has been applied and compared with sol-gel, coprecipitation and ceramic route with the purpose of encapsulating hematite into zircon crystals used as ceramic pigment. In the commercial synthesis of pink coral pigment, NaF flux agent is usually added in order to improve the reactivity of the system; therefore, the addition of flux agents (NaF or NaF · 2NaCl) has been investigated. Likewise, the effect of precipitating agent (NH₃ or NaOH) has been studied. Sol-gel becomes the more reactive method and produces the best red colours without fluorides addition, but does not give red colour in the presence of halides fired at 1000°C. Ammonia microemulsioned and coprecipitated powders give similar orange-brown colours without fluorides, and red colours with fluorides addition. The addition of NaF produces higher inclusion effectiveness than NaF · 2NaCl. The stabilization of sodium silicozirconate crystalline phases in NaOH coprecipitated or emulsioned samples avoids the zircon crystallization and then the hematite encapsulation.     

Design of a chiral mesoporous silica and its application as a host for stereoselective di-pi-methane rearrangements

[reaction: see text] A chiral periodic mesoporous organosilica (ChiMO) was prepared, in which a 1,2-bis-(ureido)cyclohexyl linker (38 wt %) is introduced into the walls of the hybrid organic-inorganic material. This silica was used as a host for 11-formyl-12-methyldibenzobarrelene (2), and the stereoselectivity of the di-pi-methane rearrangement of 2 within this host-guest complex was studied. At low conversions, the only product was the corresponding dibenzosemibullvalene. An enantiomeric excess of 24% at 11% conversion was obtained using the ChiMO as host. These values compare well with those achieved using a system based on conventional faujasites (LiY and NaY) as hosts incorporating a chiral auxiliary. We tested S-phenylglycine, S-proline, S-camphanic acid, and S-mandelic acid as chiral auxiliaries. In contrast to the behavior of the ChiMO material, adsorption of dibenzobarrelene in purely siliceous mesoporous MCM-41 silica (3.2 nm pore size) containing ephedrine failed, a failure that can be explained as arising from the large internal silanol population and high hydrophilicity of the siliceous MCM-41 sample.     

Development of an amperometric biosensor based on acetylcholine esterase covalently bound to a new support material

A new type of amperometric biosensor based on immobilised acetylcholine esterase was designed and constructed. The enzyme was immobilised on a flow-through working electrode, which was prepared from reticulated vitreous carbon (RVC) or from a composite material consisting of RVC and superporous agarose. The sensor was operated in FIA mode using acetylthiocholine as a substrate. The sensor responded to inhibitors such as paraoxon-10(-9) mol was detected by the sensor in a non-optimised configuration. The practical lifetime of the sensor was at least 1 month.     

Flunitrazepam induces geometrical changes at the lipid-water interface

Flunitrazepam (FNTZ) effects on molecular packing and surface curvature in artificial model membranes were investigated. FNTZ, from the subphase under dipalmitoylphosphatidylcholine (dpPC) monolayers at the air-water interface, expanded the surface pressure-area isotherm and induced an increment in the limiting area; in this conditions, the collapse pressure of dpPC decreased, indicating a lowering in the stability of the monolayer. Thermodynamic-geometric correlations based on molecular parameters predicted a decrement in the aggregation number and stability, and an increase in the curvature of the self-aggregated structure of dpPC in aqueous medium in the presence of FNTZ. Accordingly, negative-staining electron microscopy of dpPC aqueous dispersions showed that the mean diameter of dpPC vesicles decreased 2 and 2.87 times in the presence of 10 nM and 50 μM FNTZ, respectively, compared with control samples. The release of a soluble marker entrapped in dpPC liposomes increased slightly respect to the control in the presence of FNTZ. In dpPC-dpPE mixed liposomes 50 μM FNTZ induced a decrement in the amount of the aminophospholipid exposed to the outer monolayer. Concluding, an FNTZ-induced expansion of dpPC-water interface region affected the constraints imposed on the lipid-water system by the molecular geometry, interacting free energies and entropy that determine the shape of a multimolecular structure. In liposomes composed of a pure phospholipid, the bilayer expansion leaded, through a structure instability, to reduce the liposome size; in mixed liposomes, phospholipid molecules translocation could be observed as another compensating mechanism of the initial perturbation. These results may be relevant for understanding benzodiazepines' effects non-mediated by membrane receptors.     

Operating on the universe

Summary In spite of the fact that the Z.F. universe is not well-ordered, it behaves in some respects like the ordinals. It is possible to define on it the usual operations of addition, multiplication and exponentiation, which enjoy similar properties to those on the ordinals. Further when restricted to the ordinals, the operations coincide, so that ordinal arithmetic can be regarded as a restriction of the universe arithmetic. But more than that, rank which retracts the universe of sets onto the ordinals is a homomorphism between the universe arithmetical structure V,+,·,exp and the ordinal arithmetical structure Ord, +, ·,exp.     

Stationary axisymmetric solutions of the Jordan-Brans-Dicke equations with electromagnetic sources

Any stationary axisymmetric solution of the coupled JBD-Maxwell field equations such thatF _ab ^* t^ab vanishes, can be determined from a composition of any stationary axisymmetric Einstein-Maxwell spacetime with the Weyl class of metrics.     

Evaluation of the photocurrent value for poly(2,5-dicyano- p -phenylene-vinylene)-co-(p-phenylene-vinylene) (DCN-PPV/PPV)

Journal of Solid State Electrochemistry - A method to obtain poly(2,5-dicyano-p-phenylene-vinylene)-co-(p-phenylene-vinylene) (DCN-PPV/PPV) block copolymer was developed. The structural...