Organopolysiloxanes as Chemically Sensitive Coatings for Optical Fibers

Various types of UV-curable organically modified siloxanes have been synthesized by the sol-gel method with the aim of fabricating chemically sensitive coatings for silica optical fibers. The refractive index of the coating material can be tailored in the range from 1.46 to 1.56 and sensitivity towards CO2 is achieved by incorporation of amino groups. The interaction of the cured layers with CO2 or with hydrocarbons has been studied in immersion experiments. Both the reaction of CO2 with incorporated amino groups and the penetration of hydrocarbons into the layer induce changes of the light absorption coefficient and the refractive index of the coating which are detected by measuring the output light intensity from the fiber.     

Enantioselective synthesis of 1-deoxy-d-gulonojirimycin from a phenylglycinol-derived lactam

Cyclocondensation of (R)-phenylglycinol with appropriately γ-substituted δ-oxo acid derivatives provides bicyclic lactams from which the enantioselective synthesis of 1-deoxy-d-gulonojirimycin has been reported.     

Synthesis and structure of [(Sn(mu-PCy))3(Na x PMDETA)2], containing an electron-deficient [(Sn(mu-PCy))3]2- dianion

The reaction of CyPHNa with Sn(NMe2)2 in the presence of PMDETA (= (Me2NCH2CH2)2NMe) gives the title compound [(Sn(mu-PCy))3(Na x PMDETA)2] (1), containing an electron-deficient [(Sn(mu-PCy))]3(2-) dianion with a novel two-electron, three centre (2e-3c) bonding arrangement.     

Enantiopure Chiral Macrocyclic Lanthanide Complexes Derived from (R)-2,2′-Diamino-1,1′-binaphthyl and 2,6-Diformylpyridine

The template condensation of (R)-2,2′-diamino-1,1′-binaphthyl and 2,6-diformylpyridine leads to lanthanide(III) complexes of the new chiral hexaaza macrocycle L that adopts highly twisted conformation in [LnL](NO₃)₃ complexes. The complexes have been characterised by ESI MS spectrometry and NMR spectroscopy. The analogous N₂O₄ chiral crown ether L2 that has the same carbon skeleton as L does not exhibit tendency to bind lanthanide(III) ions. The X-ray crystal structure of L2 exhibit squeezed conformation of the macrocycle and spatial disposition of donor atoms that does not predispose it for coordination of lanthanide(III) ions.     

One-pot palladium-catalyzed synthesis of 2,3-disubstituted bicyclo[2.2.1]heptanes and bicyclo[2.2.1]hept-5-enes

A new and highly stereoselective palladium-catalyzed synthesis is reported, based on two subsequent insertions of the bicyclo[2.2.1]heptene system into an aryl or vinylpalladium bond, formed in situ from aryl or vinyl bromides.     

Determination of terazosin by cloud point extraction-fluorimetric combined methodology

A new sensitive and selective preconcentration-fluorimetric method for determination of terazosin based on its native fluorescence was developed. The analyte, initially present in aqueous matrix, was treated with an extractive non-ionic surfactant solution and separated by the clouding phenomenon. The optimum analytical conditions for terazosin assay were established. Under these conditions, linear calibration curves were obtained over the range of 1 × 10⁻⁵ to 7.0 μg mL⁻¹ with detection and quantification limits of 1.11 × 10⁻⁵ and 3.7 × 10⁻⁵ μg mL⁻¹, respectively. Additionally, the binding constant (K_B) for the terazosin-PONPE 7.5 system was determined given a value of 1028 L mol⁻¹. The developed coupled methodology, which thoroughly satisfies the typical requirements for pharmaceutical control processes, was proved to be appropriate for monitoring terazosin in actual pharmaceutical formulations and biological fluid sample. The results were validated by recovery test and by comparison with other reported methods, being highly satisfactory.     

Structure of colloid silica determined by viscosity measurements

The viscosity of nanosized colloid silica suspensions, used as binders in the investment casting, was determined as a function of their weight fraction reaching 52%. A new capillary viscometer was used whose construction eliminated sedimentation effects. The experiments have been carried out at fixed pH 10.0 and controlled ionic strength. It was found that for a low silica concentration range (weight fraction below 5%) the suspension viscosity increased more rapidly than the Einstein theory predicts. This anomalous behavior could not be explained in terms of the primary electroviscous effect predicted to be a few orders of magnitude smaller as observed. This discrepancy was accounted for by postulating a fuzzy, gel-like structure of colloid silicas used in our experiments. Hence, the apparent hydrodynamic radius of silica particles in aqueous suspensions was found to be larger than the primary particle size in accordance with previous observations. Based on this postulate, an apparent density of the silica sols was found to be 1.32-1.37 g/cm(3) instead of 2.2-2.32 g/cm(3) as determined from the suspension dilution method. This behavior was interpreted in terms of the core/shell model with high shell porosity, reaching 85%. Similarly, for higher concentration ranges, silica viscosity increased more rapidly with increased sol concentration than predicted by the Batchelor model derived for hard particles. The deviation was attributed to the secondary electroviscous effect stemming from the electrostatic interactions among silica particles in sheared suspensions. This effect has quantitatively been interpreted in terms of Russel's theory. On the other hand, for the high concentration range the experimental results were well accounted for by the Dougherty-Krieger model. By exploiting our experimental findings a sensitive method of determining the structure and apparent density of silica sols in aqueous media was proposed.     

Pyrolysis-gas chromatography-mass spectrometry of cured phenolic resins

A previously described pyrolysis device with a movable reaction zone was used in the present work for thermal degradation of cured novolac and resol resins. After the pyrolysis the usual major components were identified, as well as relatively low-volatile aromatic compounds which were revealed after their separation in a capillary chromatographic column. Among the latter components, for both types of cured resins, xanthene and its methyl derivatives were found. The isomers of bis(hydroxyphenyl)methane were found in considerable quantities only in the case of partially cured novolac resins which contained any linear sequences in their structure.     

Studies on the conversions of diols and cyclic ethers—49: Stereochemistry of cyclodehydration of 1,4-diols on the action of brönsted and lewis acids: a comprehensive study

The stereochemistry of the cyclodehydration of (±)- and meso-2,5-hexanediol on the action of various dehydrating agents was investigated. The earlier assumed and confirmed intramolecular S_N2 mechanism for acid-catalysed ring-closure was found to hold in most cases. Various extents of racemisation can be observed on the action of certain Lewis acids, and the solvents concentrated H₂SO₄ and HMPT (hexamethyl phosporic acid triamide) under previously unexamined reaction conditions.