Effect of pre-heat treatment on a Fischer-Tropsch iron catalyst

Mössbauer spectroscopy was used to investigate the effect of heating the Fischer-Tropsch catalyst 100 Fe/5 Cu/4.2 K/24 SiO₂ in two different atmospheres while ramping the temperature of the catalyst from room temperature to 280 °C in 5.5 h prior to pretreatment of the catalyst. Preheating in H₂/CO=0.7 gave rise to an iron (Fe²⁺) silicate, while preheating in helium resulted in the formation of -carbide Fe_2.2C. Iron oxides and -carbide Fe₅C₂ were also formed in both preheat treatments.     

Colorimetric determination of ascorbic acid in pharmaceutical preparations and biological samples

A simple and rapid method is described for the determination of L-ascorbic acid, based on its reduction of iron (III). The iron(II) thus formed is complexed with quinaldic acid and pyridine. The absorbance is measured at 380 nm after extracting the complex into chloroform. Beer's law is obeyed over the concentration range 2.5–25 g ml^–1 ascorbic acid. The results obtained are accurate and reproducible with the standard deviation of 0.0076. The method has been applied to the analysis of pharmaceuticals and biological samples with satisfactory results.     

Estimation of degree of counterion binding and related parameters of monomeric and dimeric cationic surfactants from cloud point measurements by using triblock polymer as probe

The cloud point (C _P) measurements of aqueous solutions of a triblock polymer (TBP) [(PEO)_2.5(PPO)₃₁(PEO)_2.5], in the presence of varying amounts of cationic surfactants (monomeric and dimeric alkylammoniumbromides) covering premicellar to postmicellar regions, have been carried out. A plot of C _P vs surfactant concentration allowed us to evaluate apparent critical micelle concentration (cmc*), which has been found to decrease with an increase in the amount of salt. The cmc* values thus obtained in the absence and presence of salt allowed us to evaluate counterion binding (β) by using the Corrin–Harkins method. β values have been further used to evaluate the thermodynamic parameters of these ionic surfactants. The results suggest that the β values evaluated using this method, especially at low [TBP], are in good agreement with those already reported in the literature.     

FLUORESCENCE AND CIRCULAR DICHROISM STUDIES ON THE PHYCOERYTHROCYANINS FROM THE CYANOBACTERIUM

Two phycoerythrocyanin (PEC) fractions have been obtained from the phycobilisomes of the cyanobac-terium Westiellopsis prolifica ARM 365. They have been characterized by absorption, fluorescence and circular dichroism spectroscopy. One of them is spectroscopically similar to a PEC trimer known from other organisms. Whereas efficient energy transfer from its violin (α-84) to the cyanin (β-84, 155) chromophores is efficient in the trimer (αβ it is impeded after dissociation to the monomer (α,β). A second fraction of PEC which we earlier termed PEC(X) (Maruthi Sai et al., Photochem. Photobiol. 55 ,119–124, 1992), exhibited the spectral properties similar to that of the α-subunit of PEC from Mastigocladus laminosus. With this highly photoactive fraction, the circular dichroism spectra of the violobilin chromophore in both photoreversible states were obtained.     

Metal-phosphine chalcogenide interactions. Crystal and molecular structures of [di-μ-iodo-bis{(methyl cyanide-N)(triphenylthiophosphorane-S)copper(I)}] and [di-μ-chloro-bis{μ-1,2-ethylenebis(diphenylphosphine selenide-Se,Se)} dicopper(I)]

Complexes of Cu^I with tertiary phosphine chalcogenides are described. CuI reacts with Ph₃PS in MeCN/CH₂Cl₂ to form {CuI(Ph₃PS)(MeCN)} and CuCl reacts with 1,2-ethylene-bis(tertiary phosphine selenide) {dpeSe₂} in MeCN to yield {CuCl(dpeSe₂)}. Both compounds exist as halogen-bridged centrosymmetric dimers: [Cu₂(-I)₂-(Ph₃PS)₂(MeCN)₂] (1) and [Cu₂(-Cl)₂(dpeSe₂)₂] (2) respectively. Compound (1) has almost symmetric Cu—I bonds, d(Cu—I) = 2.6503(8) Å and d(Cu—I) = 2.7196(9) Å, and each Cu is further bonded to a S atom [d(Cu—S) = 2.3444(13) Å] from Ph₃PS and to a N atom [d(Cu—N) = 2.030(5) Å] from MeCN. Compound (2) has unequal Cu—Cl bonds, 2.6390(19) and 2.2806(18) Å and nearly equal Cu—Se bonds [2.4042(11) and 2.4060(11) Å]. The geometry about each Cu center in both cases is distorted tetrahedral. The Cu—Cu bond distance in (2) is 3.249(2) Å as compared with 3.4141(16) Å in (1). MeCN is bonded strongly to Cu^I as the excess of Ph₃PS failed to remove it from the coordination sphere. Compound (2) represents the first structurally characterised example of copper(I) with a bis(tertiary phosphine selenide) (dpeSe₂) acting as a bridging ligand.     

Effect of adding glycols to the micellar properties of Tween: small-angle neutron scattering and turbidity measurements

Small-angle neutron scattering (SANS) and turbidity measurements have been carried out on the nonionic surfactants Tween 20 and Tween 80, in the presence of diethyleneglycol (DEG), triethyleneglycol (TEG), ethylene glycol monoethyl ether (EGMEE), and ethyleneglycol mono butyl ether (EGMBE). SANS measurements show that the shapes of the Tween 20 and Tween 80 micelles are oblate ellipsoidal, which do not change predominantly in the presence of DEG and TEG. However, the presence of EGMBE and EGMEE reduces the aggregation number of Tween. This has been attributed to the solubilization of EGMBE and EGMEE in the Tween micelles, providing them with additional hydrophobicity.     

Modified pyrohydrolysis apparatus for the separation of fluorine and chlorine trace impurities from nuclear fuel samples for quality control analysis

A quartz pyrohydrolysis apparatus designed for the safe handling of pyrophoric carbide nuclear fuel samples while separating C1 and F trace impurities for quality control analysis is described. It has several advantages over the commonly used pyrohydrolysis apparatus. Performance of the apparatus during routine analysis of a large number of nuclear fuel samples has been found to be quite satisfactory.     

Spectroscopic studies of rhodamine 6G dispersed in polymethylcyanoacrylate

We report here electronic absorption, fluorescence and resonance Raman studies of rhodamine 6G laser dye dispersed in the polymethylcyanoacrylate matrix. In the electronic absorption and fluorescence spectra of dispersed rhodamine 6G, band maxima are red shifted compared to solution. Raman spectra show some new bands. These spectral changes arise due to matrix effect and interaction between rhodamine 6G and the host material involving amine group of rhodamine.     

Suspension ring-opening metathesis polymerization: the preparation of norbornene-based resins for application in organic synthesis

A series of norbornene-based resin beads were obtained by aqueous suspension ring-opening metathesis polymerization (ROMP) and used as polymeric supports for organic synthesis. These resins were prepared from norbornene, norborn-2-ene-5-methanol, and cross-linkers such as bis(norborn-2-ene-5-methoxy)alkanes, di(norborn-2-ene-5-methyl)ether, and 1,3-di(norborn-2-ene-5-methoxy)benzene. The resulting unsaturated ROMP (U-ROMP) resins containing olefin repeat units were chemically modified using hydrogenation, hydrofluorination, chlorination, and bromination reactions to produce saturated ROMP resins with different chemical and physical properties. The hydrogenated ROMP (H-ROMP) resin was found to be highly resistant to acidic, basic, Lewis acid, and Birch reduction conditions and was assessed as a polymeric support in a series of solid-phase synthetic applications. The H-ROMP resin was found to have superior performance compared to polystyrene-divinylbenzene (PS-DVB) copolymers in aromatic nitration and acylation reactions. In a conventional five-step solid-phase synthesis of a hydantoin, similar results were obtained for both the H-ROMP and PS-DVB resins. The U-ROMP resin was also shown to be effective in the solid-phase syntheses of benzimidazoles and benzimidazolones.