title: Synthesis, characterization, and pH-triggered dethreading of alpha-cyclodextrin-poly(ethylene glycol) polyrotaxanes bearing cleavable endcaps.
abstract: The synthesis, characterization, and degradation kinetics of three alpha-cyclodextrin (alpha-CD)-poly(ethylene glycol) (PEG) polyrotaxanes with endcaps that were installed using Cu(I)-catalyzed Huisgen cyclization is reported. PEG1500, azidated with azidoacetic acid, was threaded with alpha-CD to form a pseudopolyrotaxane that was then capped in up to 82% yield with three different substituents to provide polyrotaxanes that were either acid-, base-, or fluoride-sensitive. NMR, GPC, XRD, and AFM methods were used to characterize the polyrotaxanes. Dethreading rates upon exposure to mild deprotection conditions were monitored by turbidity analysis. The vinyl ether-endcapped polyrotaxane is stable at pH 7 for 16 h but is solubilized at approximately 0.0211 min(-1) at pH 4. The ester-endcapped polyrotaxane is solubilized at 0.0122 min(-1) at pH 12.1. Our results show that pH-triggerable polyrotaxanes can be readily and efficiently prepared from pseudopolyrotaxanes in high yield by Huisgen cyclization of azido- and alkynyl-modified precursors in the presence of Cu(I).
authors.affiliation: Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, USA.
authors.forename: Scott
authors.initials: S
authors.lastname: Loethen
authors.forename: Tooru
authors.initials: T
authors.lastname: Ooya
authors.forename: Hak Soo
authors.initials: HS
authors.lastname: Choi
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Yui
authors.forename: David H
authors.initials: DH
authors.lastname: Thompson
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry*; D002623:Chemistry Techniques, Analytical; D002845:Chromatography / Q000379:methods; D003300:Copper / Q000737:chemistry; D003505:Cyclodextrins / Q000737:chemistry; D005459:Fluorides / Q000737:chemistry; D020100:Hydrogels; D006863:Hydrogen-Ion Concentration; D018625:Microscopy, Atomic Force; D008956:Models, Chemical; D015394:Molecular Structure; D020442:Poloxamer / Q000737:chemistry; D011092:Polyethylene Glycols / Q000138:chemical synthesis* / Q000737:chemistry*; D043862:Rotaxanes / Q000138:chemical synthesis* / Q000737:chemistry*; D014961:X-Ray Diffraction; D047391:alpha-Cyclodextrins / Q000737:chemistry*
chemical_list: D001672:Biocompatible Materials; D003505:Cyclodextrins; D020100:Hydrogels; D043862:Rotaxanes; D047391:alpha-Cyclodextrins; C475673:polyrotaxane; D020442:Poloxamer; D011092:Polyethylene Glycols; D003300:Copper; D005459:Fluorides; C032613:alpha-cyclodextrin