Polypseudorotaxnes from scratch

Christopher Tait, Martin Davies

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)

Abstract

In 1990, Harada and Kamachi reported that in aqueous solution an insoluble polypseudorotaxane is formed by the threading of R-cyclodextrin onto poly(ethylene glycol), PEG, with two ethylene glycol units per cyclodextrin. Similar polypseudorotaxanes are formed with â-cyclodextrin or ç-cyclodextrin and poly(propylene glycol). A review of subsequent developments in the area of cyclodextrin- based catenanes and rotaxanes has been published, and X-ray crystal structures are now available. Our work on cyclodextrin host-guest interactions and Kinetics meant that we found of particular interest a recent kinetic study by Baglioni and co-workers, reporting that when aqueous R-cyclodextrin and PEG of molecular weight 3350 (PEG3350) are mixed together there is a certain lag time when the solution remains perfectly clear before the onset of turbidity, measured as the absorbance at 400 nm. The lag time depends very strongly on the concentration of the solution. The authors presume that the onset of turbidity marks the end of a complex phenomenon that starts with the threading and sliding of a cyclodextrin onto the linear PEG molecule and ends with the precipitation of large aggregates. It is assumed that during the lag time the cyclodextrin molecules are penetrated byPEG chains and the onset of turbidity marks the aggregation and precipitation of the polypseudorotaxane, and that the whole of the threading process occurs during the lag time, which is defined by the authors as the threading time. A kinetic model is proposed that predicts that the number of cyclodextrin molecules that participate in the formation of the polypseudorotaxane is about 20. This is similar to the totalnumberof cyclodextrin molecules that are capable of threading onto the PEG molecule. Prompted by the above paper and the greater yields reported for complex formation between R-cyclodextrin and poly(ethylene glycol) dimethyl ether, DMPEG, compared to PEG of the same molecular weight, we began a study of the kinetics of polypseudorotaxane formation between the cyclodextrin and DMPEG using the lag time approach. This is reported in the present note. Subsequently, a further threading time kinetic study has beenreported for the formation of polypseudorotaxanes from â-cyclodextrin and poly(propylene glycol)33 bis-2-aminopropyl ether and from ç-cyclodextrin and Pluronic P105, HO(CH2CH2O)34(CH2CH(CH3)O)61(CH2CH2O)34H.
Original languageEnglish
JournalLangmuir
DOIs
Publication statusPublished - Feb 2002

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