Steric effects and competitive intra- and intermolecular host-guest complexation between beta-cyclodextrin and adamantyl substituted poly(acrylate)s in water: A 1H NMR, rheological and preparative study (original) (raw)
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Angewandte Chemie International Edition, 2007
Polymer-inclusion complexes (PICs) with cyclodextrins (CDs) show a broad structural variety [1-4] and are of interest for many different applications, for example, drug delivery systems [5] and stimuli-responsive hydrogels. [6, 7] We have demonstrated that the lower critical solution temperature (LCST) of N-isopropylacrylamide(NIPAAM)based copolymers bearing adamantyl groups can be influenced through complexation of the adamantyl moieties by cyclodextrins (CDs). [8, 9] Recently, we reported on the synthesis of a PIC consisting of randomly methylated b-CD and a polymethacrylamide which showed a reversible phase transition in aqueous solution as a result of a dissociation/ complexation process. [10] Unfortunately, this system was not optimal in terms of chemical stability and the guest moiety used. We report herein on the pseudo-LCST behavior of PICs consisting of poly(adamantylacrylamide)s and Me-b-CD. In contrast to the previously reported system, the newly synthesized polyacrylamides are expected to be much more stable against hydrolysis. Additionally, the incorporated adamantyl moieties are well suited for inclusion into b-CD. With this optimized system we will demonstrate the influence of spacer groups and concentration on the phase-transition process. It is known that Me-b-CD-complexed hydrophobic monomers can be polymerized in water by means of a free-radical mechanism by use of water-soluble azo or redox initiators. [11] In most cases, the Me-b-CDs slip off the growing macroradicals which leads to precipitation of the polymeric material. In contrast, polymerization of Me-b-CD-complexed 1-adamantylacrylamide (1 a) and 6-acryloylaminohexanoic acid 1-adamantylamide (3 a) resulting the formation of the water-soluble polymer/Me-b-CD-complexes 2 a and 4 a, respectively (Scheme 1). The polymerization was carried out in water at 25 8C using 1 mol % of the redox initiator system K 2 S 2 O 8 /Na 2 S 2 O 5. The molecular weights of the purified Me-b-CD-free polymers 2 and 4 were determined by MALDI-TOF mass spectrometry (Figure 1). Interestingly, the obtained polymer/ Me-b-CD complexes 2 a and 4 a show thermosensitive solubility properties in water that strongly depend on the distance between the Me-b-CD-complexed adamantyl groups and the polymer backbone.
Macromolecules, 2011
The use of fluorescent polymers has been reported in studies of scintillators, 1 luminescent solar concentrators, 2 laser-resistant materials, 3 fiber-optic sensors, 4 and laser dyes. 5 Such polymers usually consist of a backbone substituted with fluorophores such as the naphthyl, 6À9 pyrenyl, 7,10À14 and dansyl 8,15À19 entities. The fluorescence intensities and lifetimes of such fluorophores are sensitive to local environment such that steady-state and time-dependent fluorescence studies have provided considerable insight into polymer interactions. 6À19 As part of an exploration of substituent interactions of randomly substituted poly(acrylate)s, PAA, 20À25 we report a UVÀvis, steady-state, and time-resolved fluorescence and 2D 1 H NOESY NMR study of the variation of dansyl substituent spectroscopic response to environmental change at the molecular level in dilute aqueous solution. These observations are used to interpret macroscopic observations gained through rheological studies of variations in the viscosities in terms of network formation in more concentrated solutions. The poly(acrylate)s studied are 3% randomly substituted by N-(2-aminoethyl)-, N-(6-aminohexyl)-, and N-(12-aminododecyl)-5-dansylsulfonamide, PAADSen, PAADShn, and PAADSddn, in which the dansyl substituent tether length progressively increases (Scheme 1). This facilitates studies of the effect of tether length on dansyl substituent, aggregation and complexation by β-cyclodextrin, βCD, and the linked dimer N,N 0 -bis(6 A -deoxy-6 A -β-cyclodextrin)urea, 66βCD 2 ur, in dilute aqueous solution where interactions occur dominantly within individual substituted poly(acrylate) strands.
Chemistry & Biodiversity, 2007
Two polymeric substances, a poly{N-[tris(hydroxymethyl)methyl]acrylamide} (THMMA) substituted with adamantyl moieties and a b-cyclodextrin/epichlorohydrin polycondensate, formed a hostguest type complex, which resulted in the gel formation upon mixing of these two compounds at appropriate conditions. Introduction of a drug molecule, i.e., naproxen, that was able to fill the bcyclodextrin cavities, thus expulsing adamantyl moieties, led to disruption of such association and inhibition of gel formation. The conditions required for the association of the two polymeric components and formation of the gel, as well as the dynamics of its inhibition by addition of naproxen was established. The procedure of using solutions of two associating polymers and an appropriate drug competitor can be used at targeted viscosupplementation.
Beilstein Journal of Organic Chemistry
Three aqueous self-assembling poly(acrylate) networks have been designed to gain insight into the factors controlling the complexation and release of small molecules within them. These networks are formed between 8.8% 6A-(2-aminoethyl)amino-6A-deoxy-6A-β-cyclodextrin, β-CDen, randomly substituted poly(acrylate), PAAβ-CDen, and one of the 3.3% 1-(2-aminoethyl)amidoadamantyl, ADen, 3.0% 1-(6-aminohexyl)amidoadamantyl, ADhn, or 2.9% 1-(12-aminododecyl)amidoadamantyl, ADddn, randomly substituted poly(acrylate)s, PAAADen, PAAADhn and PAAADddn, respectively, such that the ratio of β-CDen to adamantyl substituents is ca. 3:1. The variation of the characteristics of the complexation of the dyes methyl red, methyl orange and ethyl orange in these three networks and by β-cyclodextrin, β-CD, and PAAβ-CDen alone provides insight into the factors affecting dye complexation. The rates of release of the dyes through a dialysis membrane from the three aqueous networks show a high dependence on host...
Tailoring Polymeric Hydrogels through Cyclodextrin Host-Guest Complexation
Macromolecular rapid communications, 2010
A close correllation between molecular-level interactions and macroscopic characteristics of polymer networks exists. The characteristics of the polymeric hydrogels assembled from β-cyclodextrin (β-CD) and adamantyl (AD) substituted poly(acrylate)s can be tailored through selective host-guest complexation between β-CD and AD substituents and their tethers. Dominantly, steric effects and competitive intra- and intermolecular host-guest complexation are found to control poly(acrylate) isomeric inter-strand linkage in polymer network formation. This understanding of the factors involved in polymeric hydrogel formation points the way towards the construction of increasingly sophisticated biocompatible materials.
Aqueous Polysaccharide Associations Mediated by β-Cyclodextrin Polymers
Biomacromolecules, 2008
Macromolecular assemblies were elaborated by mixing in water hydrophobically modified dextrans (MDC n ) and -cyclodextrin polymers (p CD) interacting by inclusion complexation between the hydrophobic moieties of MDCn and the -cyclodextrin cavities of p CD. Dextrans have been modified by grafting alkyl groups (C n ) of varying chain lengths (n ) 8-16) and grafting ratio (3-6 mol%). Different p CD polymers were synthesized by polycondensation of -cyclodextrin and epichlorohydrin. The polymer-polymer interactions have been studied by fluorimetry, isothermal titration microcalorimetry, phase diagrams, and viscosimetry. The viscoelastic properties of the temporary networks (in the semidilute range) have been studied by rheology. The interaction mechanisms between the MDCn and p CD can be understood taking into account the strength of the interaction between the alkyl group and the -cyclodextrin cavity (mainly controlled by the alkyl chain length), the density of junctions between the chains (depending on the alkyl grafting density and the p CD molecular weight), and additional cooperative effect (arising for high alkyl grafting density).