Method for the simultaneous characterization of texture,orientation of electric field gradient,and/or magnetic field from the57Fe/57Co Mössbauer spectrum of pellets having a cylindrical texture typical of YBa2Cu3O7−x superconductors

A method using Mössbauer spectroscopy has been developed for estimating the degree of cylindrical texture in pellets of materials exemplified by the superconductor YBa₂Cu₃O_7–x.The procedure can also be used to determine unambiguously the sign and orientation of the electric field gradient of a nonmagnetic species coexisting with a magnetically ordered one (or coexisting with another nonmagnetic species for which the sign and the orientation of the electric field gradient are known).     

The potential of arsenic speciation in molluscs for environmental monitoring

This paper reports the assessment of total arsenic and six arsenic species (As(III), As(V), MMA, DMA, AsBet, AsCol) as contaminants of mussel samples collected around the island of Sardinia and in the Gulf of Venice. The samples were analysed using cation- and anion-exchange HPLC-HG-AFS for speciation and ICP-AES for the total As determination. To ensure the robustness of the routine analytical method, the technique was validated using a candidate reference material, BCR-710, and good agreement was obtained. It was recognised that higher total arsenic concentration in mussels does not necessarily result in higher toxicity of mussel samples.     

Electron diffraction study of the trichloromethyltrichlorogermane molecular structure and estimation for torsional barrier

The molecular geometry (in terms of r_a and r_g internuclear distances) and mean amplitudes of vibration of CCl₃GeCl₃ have been determined by electron diffraction. The bond lengths are similar to those found in analogous molecules. Although bond angles of unambiguous physical definition have not been determined it is established that the carbon and germanium bond configurations deviate little from the regular tetrahedral arrangement. The molecule performs large amplitude motion around the carbon-germanium bond. The torsional barrier was estimated to be 1.1 kcal mole^?1 using J. Karle's method [8].     

Influence of a crown ether comonomer on the temperature-induced phase transition of poly(N-isopropylacrylamide) hydrogels

Copolymerization of thermosensitive hydrogels based on poly(N-isopropylacrylamide) (PNIPA) is a possible route to enhanced storage capacity of guest molecules. This article describes the synthesis of the amphiphilic crown ether N9-propenoyl-3,6,12,15-tetraoxa-9,21-diazabicyclo[15.3.1]heneicosa-1(21),17,19-triene (CE) and its incorporation into a PNIPA hydrogel (PNIPA/CE). Mechanical measurements on the gel show that the CE units contribute to the elasticity of the network, but the swelling ratio in water is reduced compared to the unmodified system. The comonomer reduces the temperature of the volume phase transition (VPT), TVPT, and broadens the transition. Both the enthalpy and the entropy associated with the VPT decrease. Scattering measurements indicate that the local structural features on the scale of 10 A are unchanged, but the CE units form large clusters, the size of which increases with rising temperature. In the phase-separated state above TVPT these clusters are distributed on the polymer-water interface.     

Mechanism for hydrotalcite decomposition: a controlled rate thermal analysis study

The mechanism for the decomposition of hydrotalcite remains unsolved. Controlled rate thermal analysis enables this decomposition pathway to be explored. Hydrotalcites containing carbonate, vanadate and molybdate were prepared by coprecipitation. The resulting materials were characterised by XRD, simultaneous TG-DTG-DTA and controlled rate thermal analysis (CRTA) to determine the stability and thermal decomposition pathway of the synthesised hydrotalcites. For the carbonate intercalated hydrotalcite dehydration takes place in three steps two of which are quasi-isothermal and one non-isothermal. Dehydroxylation and decarbonation occur separately over the 235-330 and 330-370 degrees C temperature range. A second non-isothermal decarbonation step is observed in the 371-541 degrees C range. In comparison the mixed carbonate-vanadate and carbonate-molybdate hydrotalcites show two dehydration steps and the dehydroxylation and decarbonation occur simultaneously. The observation of three dehydration steps is used to support the model of water molecules in three structurally distinct environments in the hydrotalcite interlayer. CRTA technology provides a mechanism for the decomposition of hydrotalcites.     

Synthesis of ether-linked [60]fullerene glycoconjugates by nucleophilic cyclopropanation

Ethyl acetoacetate-sugar derivatives were prepared by standard alkylation of primary or secondary hydroxyls of diacetonide-protected sugars with ethyl 4-chloroacetoacetate. The obtained D-fructose, D-galactose, D-glucose and D-allose derivatives were conjugated to C₆₀ using the Bingel reaction to afford hydrolytically stable, ether-linked fullerene-carbohydrates. Conjugation of an ester-protected mannose derivative to the C₆₀ scaffold was carried out by the combination of the acetoacetate chemistry with the azide-alkyne click reaction.     

Synthesis of n-butyl ester and n-butylamide of methyl-phenylphosphinic acid: Two case studies

n-Butyl methyl-phenylphosphinate and methyl-phenylphosphinic n-butylamide were synthesized by different methods: the reaction of methyl-phenylphosphinic chloride with ⁿBuOH or ⁿBuNH₂, respectively, the T3P®-promoted derivatization of methyl-phenylphosphinic acid with ⁿBuOH or ⁿBuNH₂, the microwave-assisted direct esterification of the model phosphinic acid, and finally the alkylating esterification with n-butyl bromide under phase-transfer-catalytic and microwave-assisted conditions. The different methods, mostly elaborated by us, were compared from practical and environmentally friendly points of view.     

Synthesis of cellulose derivative based superabsorbent hydrogels by radiation induced crosslinking

Hydrogels with high water uptake were prepared by ionizing radiation induced crosslinking in aqueous solutions of four cellulose derivatives (carboxymethylcellulose sodium salt—CMC-Na, methylcellulose—MC, hydroxyethylcellulose—HEC and hydroxypropylcellulose—HPC). The gel fraction increased with absorbed dose, while water uptake decreased. At high polymer concentrations lower gel fractions were found due to the lower polymer chain mobility and inhomogeneity at low water content. The swelling rate gradually slowed down after 4–5 h. CMC and HEC gels reached equilibrium after 24 h, while HPC and MC gels required longer immersion times. Gels showed second-order swelling kinetics in water. The mechanism of the water diffusion proved to be anomalous. In pure water, CMC gels showed the highest, while HPC and MC gels the lowest water uptake. The derivatives had different sensitivities to ionic strength in the swelling solution. The salt type also proved to be a significant factor at uniform ionic strength. Thus different cellulose derivative based gels may be preferred at various applications depending on the environment.