A series of novel composites and nanocomposites xerogels based on acrylic acid, sepiolite and N,N′‐methylenebisacrylamide were prepared using a solution polymerization technique at 70 °C. The quality of dispersion of the micronized sepiolite in the monomer is the crucial point for obtaining nanocomposites. A good dispersion explains the improvement of the absorbent properties of the nanocomposites with respect to the composites. This work investigates not only the influence of the mixing procedure on the swelling behaviour, but also the effect of the amount of clay on the absorbency of these hydrogels in deionized water and saline solution (0.2 wt% NaCl(aq)). A crosslinker concentration of 5 wt% sepiolite nanocomposite superabsorbent was shown to give the best results (1419 g g−1). Moreover, experimental results indicate that the absorbency in saline solution is smaller than that in deionized water. Rates of swelling for these absorbents were found to fit the Voigt expression. Finally, the model approximates Case II sorption in the early stages of the swelling process and Case I in the later stages. Copyright © 2006 Society of Chemical Industry

The host-guest chemistry between cucurbit[7]uril (CB7) and a series of bolaform (Bn) surfactants with different chain lengths, n = 12-22, was the target of our study. [3]Pseudorotaxanes are formed when the alkyl chain of the bolaform has more than 14 carbon atoms. In these cases, two CB7 molecules can be accommodated between the two head groups of the bolaform without addition of electrolytes to the medium. In the case of a bolaform with 12 carbon atoms, the electrostatic repulsion between the carbonyl groups of the CB7 molecules avoids the threading of a second CB7 molecule yielding a mixed structure formed by a [2]pseudorotaxane and an external host-guest complex. The assembly behavior was investigated using NMR spectroscopy, isothermal titration calorimetry (ITC), and kinetic measurements.

The oxidation reactions of 2‐methyl‐2,4‐pentanediol upon treatment with alkaline hexacyanoferrate(III) using Ru(III) or Ru(VI) as catalysts are governed by two quasi‐identical experimental rate equations, which show that both catalysts are equally effective for the oxidation of alcohols by ${\rm Fe(CN)}_6^{3-}$. The reaction mechanism proposed involves the oxidation of 2‐methyl‐2,4‐pentanediol by the catalyst, a process that occurs through the formation of a substrate–catalyst complex. The decomposition of this complex yields Ru(IV) and a protonated ketone (owing to a hydride transfer from the α‐C—H bond of the alcohol to the oxoligand of ruthenium) in the case of Ru(VI), but a ketyl radical and Ru(II) (hydrogen transfer) for Ru(III). The role of the co‐oxidant, ${\rm Fe(CN)}_6^{3-}$, is to regenerate the catalyst. For both oxidation reactions, the rate constants of complex decomposition and catalyst regeneration have been determined. Copyright © 2004 John Wiley & Sons, Ltd.

The reactions of 2,3-butanediol by hexacyanoferrate(III) in alkaline medium using ruthenium compounds as catalysts have been studied spectrophotometrically. The effect on the reaction rate of concentration of substrate, oxidant, catalyst and basicity of the medium leads to similar experimental rate equations for both catalysts, Ru(III) and Ru(VI). The reaction mechanism involves the formation of a catalyst-substrate complex that yields a carbocation for Ru(VI) or a radical for Ru(III) oxidation. Hexacyanoferrate(III)'s role is the catalyst regeneration. The rate constants of complex decomposition and catalyst regeneration have been determined.

A kinetic study of the oxidation of octacyanomolybdate(IV) by peroxynitrite has been performed using a stopped-flow technique. The variation of k obs with the concentration of Mo(CN) 4 8 -, pH and temperature have been investigated. A reaction mechanism that involves homolysis of HOONO to form •OH and •NO 2 radicals is proposed. Octacyanomolybdate(IV) is oxidised by HOONO (direct oxidation) and by the aforementioned radicals (indirect oxidation). The rate constants for HOONO homolysis (k 1 ) and direct oxidation (k 2 ) have been obtained along with the activation parameters of these steps.