Kinetics of the self-assembly of alpha-cyclodextrin (2)pseudorotaxanes with polymethylene threads bearing quaternary ammonium and phosphonium end groups

Article Abstract:

Kinetics and mechanism of the formation and dissociation of a series of (2)pseudorotaxanes which have the alpha-cyclodextrin as the cyclic component have been determined. The length of the polymethylene chain of the thread has a small effect on the rate constant for pseudorotaxane formation. It is important, however, in the kinetics of dissociation reactions. Longer, more hydrophobic chains mean slower pseudorotaxane dissociation. Enthalpies and entropies of activation for formation/dissociation of the (2)pseudorotaxanes go down as size and hydrophobicity of end groups go up. Thus it seems desolvation of the quaternized atoms in the threading/dethreading has a reduced role.

Observations, Water chemistry, Cyclodextrins, Organophosphorus compounds, Organic phosphorus compounds, Ammonium compounds, Ammonium salts

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Kinetics in solids

Article Abstract:

Kinetics in solid state reactions may not follow rate laws that prevail in gas-phase reactions. Force fitting of thermal analysis experimental data to simple kinetic models is rather common and can give significant errors in rates predicted outside the experimental range of temperatures. The practice is of limited usefulness for finding out mechanics of reactions. A model-free approach to kinetic analysis based on the isoconversional method can be more useful.

Solid state chemistry

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Dissociative recombination with ion storage rings

Article Abstract:

High-quality beams of internally cold molecular ions can be produced since the development of heavy-ion storage-cooler rings for atomic physics. A cold electron bath gives the stored molecular-ion beam low divergence and a small cross-sectional area. The electron cooler can also be a target for electron-molecular-ion collision experiments. Dissociative recombination of cold molecules than then be studied in various aspects, among them branching ratios.

Ionic mobility, Excited state chemistry, Dissociation, Dissociation reactions, Storage rings, Heavy ions

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