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NMR investigations of Co(III) coordination compounds oriented in a dilute lyotropic liquid crystal
No full textExperimental evidences of counterion affinity in alginates: the case of nongelling ion Mg2+
No full textThe present contribution aims at testing experimentally the theoretical model previously devised (Donati, I.; Cesaro, A.; Paoletti, S.; Biomacromolecules 2006, 7, 281-287) for the description of the interaction between alginate and nongelling Mg2+ ions. The model, based on an extension of the counterion condensation theory, introduces a contribution of free energy of affinity, (Delta G) over bar (aff,0), which depends on the monomer composition of the polyuronate. In the present work, three different alginates separately mimicking the mannuronan (polyM), the guluronan (polyG), and the polyalternating (polyMG) components of alginate, together with a natural alginate isolated from Laminaria hyperborea (L. hyperborea), were examined. They were treated with Mg2+ ions, and relative variations in scattered light intensity, isothermal calorimetry (Delta H-mix) specific viscosity, and Na-23 NMR longitudinal relaxation rates were monitored with respect to samples at the same ionic strength but containing only Na+ ions. The fraction of condensed magnesium counterions was found to be strongly dependent on alginate composition, increasing along the series mannuronan < polyalternating similar to L. hyperborea < guluronan, thus in good agreement with the theoretical predictions
Exceptional Deshielding of 59Co Caused by Deuteration of the Hydrogen Bonds in Cobaloximes
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NMR parameters of cobalt and of the directly bonded organic carbons obtained from solution 59Co and 13C NMR spectra of cobaloximes
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Resolution of a nonionic surfactant oligomeric mixture by means of DOSY with inverse micelle assistance
No full textDOSY is a recognized, efficient technique in the analysis of mixtures. It relies on the differences in self-diffusion coefficients,
which are determined by the molecular size. Nowadays, efforts are directed towards devising matrices able to interact with
the components of the mixture with differential affinity, and therefore capable to interfere with the diffusion processes and to
display resolving power towards species of close, or even equal molecular weight, like isomers. Usually, commercial nonionic
surfactants are mixtures of oligomeric species, since the head group, which is a short polyoxyehtylene chain, is somewhat
polydisperse. The embedment of Igepal CA-520, 5 polyoxyethylene iso-octylphenyl ether, in an inverse microemulsion led to
the separation of 1H signals of the various oligomeric components. This ensued from the differential partitioning between
the oil and the surface of the inverse micelles, which depends on the ethyleneoxide number (EON) of the head groups.
Thus, it was possible to ascertain that the length distribution of the polyethyleneoxide chains is ingood agreement with the
Poisson distribution theoretically predicted for the polymerization of ethylene oxide. The DOSY spectrum contributed to the
assignment of the signals and afforded the partition degree, between the two environments, for each individual oligomeric
species, providing further insight into nonionic inverse microemulsions, at present widely employed reaction media in the
nanotechnological syntheses
Solution 31P and 59Co and solid-state 31P CP/MAs NMR studies of triphenylphosphinecobaloximes
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