Abstract
The fluorescent tagging of cyclodextrin derivatives enlarges their spectroscopic properties thus generating chemosensors, biological tools for visualization and sophisticated photoresponsive devices. Cyclodextrin polymers, due to the cooperative interactions, exhibit additional properties compared to their monomeric counterpart. These macromolecules can be prepared either in well water-soluble form or as gels of high swelling. Two versatile synthetic strategies for introducing a fluorescent tag (rhodamine, fluorescein, nitrobenzofuran or coumarin) into the water-soluble epichlorohydrin branched cyclodextrin polymers were worked out and compared. The fluorescent labeling was realized in three steps: 1) building in azido moieties, 2) transforming the azido groups into amino groups and 3) coupling the proper fluorescent compound to the amino groups. The other strategy started by functionalization of the monomer prior to the branching. Either the fluorescent-labeled monomer or the intermediate azido derivative of the monomer was branched. Further tuning of the properties of the polymer was achieved via branching of the methylated cyclodextrin derivative. The key intermediates and the fluorescent final products were characterized by various spectroscopic techniques and capillary electrophoresis. The applied synthetic routes were evaluated based on the molecular weight, cyclodextrin content of the products and the efficiency of labeling.
Highlights
Cyclodextrins (CDs) are cyclic oligosaccharides consisting of 6, 7 or 8 glucopyranose units (α, β- or γ-CD, respectively)
We report the controlled, regioselective fluorescent labeling of neutral and cationic epichlorohydrin branched β-CD polymer with four different dyes
Two strategies were built-up for the fluorescent labeling of epichlorohydrin branched polymers and the approaches are based on the introduction of a dedicated anchoring group for the fluorophore into the CD scaffold
Summary
Cyclodextrins (CDs) are cyclic oligosaccharides consisting of 6, 7 or 8 glucopyranose units (α-, β- or γ-CD, respectively). CDs, in particular the most common β-CD, have some limitations both in molecular dimensions and physicochemical properties like water solubility. The low water solubility can present a problem when there is a dedicated use of CDs in a delivery system that has Beilstein J. The introduction of the azido groups into the β-CD-polymer has been performed by adapting the sequence iodination → azidation [19] to the specific structure. The optimization of the three-step reaction conditions (Scheme 2) was performed on the corresponding monomer since the process can be followed by thin layer chromatography (TLC) in the case of the monomer while the polymer consisting of a mixture of components with wide range of molecular weight (Mw) cannot be studied by TLC. In the case of the β-CD the 60 min reaction was considered to be optimal for the 6-monosubstitution (Figure 1) and the identical conditions were used for the modification of the polymer
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