Effect of the mobility of ligands in polyrotaxanes on order structure of water clusters

The effect of the mobility of ligands (maltose groups) in the polyrotaxanes (pRXs) on the structure of the surrounding water molecules was investigated. Raman spectra of collective OH stretching vibration of water molecules in aqueous solutions of maltose-pRX conjugates with different alpha-cyclodextrin (alpha-CD) threading on a poly(ethylene glycol) (PEG) chain was measured. The mobility of maltose groups was estimated by measuring the relaxation time T2 of the C1 protons in maltose groups bound on alpha-CD by NMR experiment. A positive correlation between the Raman intensity of the collective band and the relaxation time T2 was obtained. This result indicates that the degree of order of the water clusters is higher as the mobility of maltose groups increases in these conjugate solutions. It is suggested that rapid motion of maltose groups in the pRX conjugate can contribute to preserving ordered structure of the bulk water clusters.     

Biocleavable polyrotaxane-plasmid DNA polyplex for enhanced gene delivery

A biocleavable polyrotaxane, having a necklace-like structure consisting of many cationic alpha-cyclodextrins (alpha-CDs) and a disulfide-introduced poly(ethylene glycol) (PEG), was synthesized and examined as a nonviral gene carrier. The polyrotaxane formed a stable polyplex having positively charged surface even at low charge ratio. This is likely to be due to structural factors of the polyrotaxane, such as the mobile motion of alpha-CDs in the necklace-like structure. Rapid endosomal escape was observed 90 min after transfection. The positively charged surface and the good buffering capacity are advantageous to show the proton sponge effect. The pDNA decondensation occurred through disulfide cleavage of the polyrotaxane and subsequent supramolecular dissociation of the noncovalent linkages between alpha-CDs and PEG. Transfection of the DMAE-SS-PRX polyplex is independent of the amount of free polycation. Those properties played a key role for delivery of pDNA clusters to the nucleus. Therefore, the polyplex nature and the supramolecular dissociation of the polyrotaxane contributed to the enhanced gene delivery.     

High conversion synthesis of pyrene end functionalized polyrotaxane based on poly(ethylene oxide) and alpha-cyclodextrins

We describe the quantitative synthesis of new pyrene labeled cyclodextrin-based polyrotaxane starting from pseudopolyrotaxane of alpha,omega-dimethacrylate poly(ethylene oxide) (PEO) and alpha-cyclodextrins (alpha-CDs). Using a solvent mixture (H2O/dimethyl sulfoxide (DMSO)), an almost quantitative conversion in polyrotaxane can be achieved using the coupling reaction between methacrylic functions and 1-pyrene butyric acid N-hydroxysuccinimide ester. This result is due to the fast blocking reaction of the pseudopolyrotaxane telechelic functions. The polyrotaxanes are characterized by NMR, size exclusion chromatography (SEC), and small-angle neutron scattering (SANS). A rodlike structure of the polyrotaxane is evidenced by SANS, and a persistence length of 70 A is determined. This result corresponds to an almost completely stretched PEO chain of 1000 g.mol(-1) molecular weight. We furthermore studied the opposite case of low packing density polyrotaxanes that were also silylated to suppress interactions between cyclodextrins. We observed a random coil structure only for silylated low packed polyrotaxane. This result demonstrates that both hydrogen bonding and packing density can explain the rodlike structure of cyclodextrin-based polyrotaxane.     

Ligand accessibility to receptor binding sites enhanced by movable polyrotaxanes

Functionalized polyrotaxanes are utilized to investigate the relation to multivalent interactions between the mannose moiety and Con A immobilized surfaces. According to the results of SPR spectroscopy, the mannose-conjugated polyrotaxanes show a higher response than any other mannose conjugate on both surfaces of high- and low-density Con A. Moreover, the results of the FRET analysis suggest that the mobility of α-cyclodextrins in the polyrotaxane more efficiently contributes to their binding interactions in a multivalent manner. This well-defined polyrotaxane system provides control over ligand density, ligand mobility, and gives an efficient response to the biological interaction receptor, which has not been easy to achieve in covalently bound polymeric systems.     

Self-Assembly of Novel Polyrotaxanes: Main-Chain Pseudopolyrotaxanes with Poly(ester crown ether) Backbones

Not threading rings on chains, but chains through rings results in a new class of main-chain polyrotaxanes. The cations of bipyridinium salts thread through the crown ether units of a poly(ester crown ether) chain (shown below). The threading efficiency m/n of the polyrotaxane is controlled by stoichiometry and temperature.     

Synthesis of conjugated polyrotaxanes

A series of conjugated polyrotaxane insulated molecular wires are synthesised by aqueous Suzuki polymerisation, using hydrophobic binding to promote threading of the cyclodextrin units. These polyrotaxanes have conjugated polymer cores based on poly(para-phenylene), polyfluorene, and poly(diphenylene-vinylene), threaded through 0.9-1.6 cyclodextrins per repeat unit. Bulky naphthalene-3,6-disulfonate endgroups prevent the macrocycles from slipping off the conjugated polymer chains. Dialysis experiments show that the cyclodextrins become unthreaded only if smaller stoppers are used. MALDI TOF mass spectra detect oligomers with up to ten threaded cyclodextrins, and reveal the presence of some defects that result for oxidative homo-coupling of boronic acids. Weight-average molecular weights were determined by analytical ultracentrifugation, demonstrating that step-growth polymerisation is efficient enough to achieve degrees of polymerisation up to approximately 20 repeat units (84 para-phenylenes). The fluorescence spectra of these polyrotaxanes indicate that the presence of the threaded cyclodextrin macrocycles reduces the flexibility of the conjugated polymer pi-systems. Both the solution and the solid-state photoluminescence quantum yields are enhanced upon threading of the conjugated polyaromatic cores through alpha- or beta-cyclodextrins, and the emission spectra of the polyrotaxanes are blue-shifted compared to the corresponding unthreaded polymers. The greater weight of the 0-0 transition in the emission spectra, as well as the smaller Stokes shift, indicate that the polyrotaxanes are more rigid than the unthreaded polymers.     

Mobility Tuning of Polyrotaxane Surfaces to Stimulate Myocyte Differentiation

Polyrotaxanes, consisting of poly(ethylene glycol) and α‐cyclodextrins, are mechanically interlocked supermolecules. The structure allows α‐cyclodextrins to move along the polymer, referred to as molecular mobility. Here, polyrotaxane‐based triblock copolymers, composed of polyrotaxanes with different degrees of methylation and poly(benzyl methacrylate) at both terminals, are coated on culture surfaces to fabricate dynamic biointerfaces for myocyte differentiation. The molecular mobility increases with the degree of methylation and the contact angle hysteresis of water droplets and air bubbles. When the mouse myoblast cell line C2C12 is cultured on methylated polyrotaxane surfaces, the expression levels of myogenesis‐related genes, myogenin (Myog) and myosin heavy chain (Myhc) are altered by the degree of methylation. Polyrotaxane surfaces with intermediate degrees of methylation promote the highest expression levels among all the surfaces. The polyrotaxane surface provides an appropriate environment for myocyte differentiation by accurately adjusting the degrees of methylation.     

Assembly of a fluorescent cyclodextrin polyrotaxane and its detection by fluorescence microscopy

A straightforward method for the assembly of fluorescent polyrotaxanes is described here. The consecutive threading of N‐(6^I‐desoxy‐β‐cyclodextrin‐6^I‐yl)‐N′‐(5‐fluoresceinyl)‐thiourea, β‐CD‐F , and α‐CD onto poly(N,N‐dimethyliminium‐hexamethylen‐N′,N′‐dimethyliminium‐decamethylene chloride), I‐6,10 , leads to a fluorescent polyrotaxane. Free β‐CD‐F could be distinguished from threaded β ‐ CD‐F by gel electrophoresis. Since the dissociation of threaded α‐CD rings is sterically hindered, the obtained polyrotaxanes are kinetically stable at 25 °C, and they did not require further stabilization by the attachment of stopper groups at the chain ends. Single polyrotaxane entities could be visualized with both fluorescence microscopy and atomic force microscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6223–6230, 2009     

Cationic polyrotaxanes effectively inhibit uptake via carnitine/organic cationic transporters without cytotoxicity

We examined the inhibitory effect of cationic polyrotaxanes, which consist of alpha-cyclodextrins threaded on a poly(ethylene glycol) (PEG) chain, on the activity of the intestinal carnitine/organic cation transporter, OCTN2, in OCTN2 gene-transfected HEK293/PDZK1 cells. The cationic polyrotaxanes effectively inhibited the OCTN2-mediated carnitine transport. Polyrotaxanes with a longer PEG chain exhibited a greater inhibitory effect, possibly owing to multivalent interactions with binding sites on OCTN2. These cationic polyrotaxanes were far less cytotoxic than conventional polycations, and are therefore interesting candidates as low-toxicity inhibitors of cation transport at cell surfaces.     

Glutathione as the end capper for cyclodextrin/PEG polyrotaxanes

A facile one-pot synthesis of α-cyclodextrin-based polyrotaxane(PR) in aqueous solution is reported, where the peptide glutathione was used as the end-capping agent and the thiol-ene Michael addition was used as the end-capping reaction. Both polyrotaxanes with low threading ratio and high threading ratio were successfully obtained. In contrast to the conventionally used multiple-step synthesis methods and hydrophobic end cappers, this one-pot aqueous synthesis as well as the biocompatibility of the end-capping agent could result in a much more biocompatible PR to be used as biomaterials.     

Thermally switchable polyrotaxane as a model of stimuli-responsive supramolecules for nano-scale devices

A polyrotaxane consisting of many β-cyclodextrins (β-CDs) and a triblock copolymer of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) capped with bulky end-groups was synthesized as a model of stimuli-responsive supramolecules for nanoscale devices. The polyrotaxane was reversibly soluble-insoluble in water in response to temperature. This was achieved through the assembled and dispersed states of β-CDs along the block copolymer. It is considered that intermolecular hydrogen bondings of β-CDs, as well as the PEG segment length of the copoloymer, are predominant factors for regulating such thermally switchable behavior of the polyrotaxane.     

Local and network structure of thermoreversible polyrotaxane hydrogels based on poly(ethylene glycol) and methylated alpha-cyclodextrins

Thermoreversible gelation and microphase formation of aqueous solutions of a methylated polyrotaxane (MePR) were investigated by means of differential scanning microcalorimetry, rheometry, and X-ray diffractometry (XRD). The aqueous solutions of MePR show a lower critical solution temperature (LCST) and form an elastic gel with increasing temperature. The sol-gel transition of the MePR solutions was induced by formation and deformation of aggregates of methylated alpha-cyclodextrins (alpha-CDs) of polyrotaxane due to hydrophobic dehydration and hydration, respectively. The XRD investigation revealed localization and highly ordered arrangement of methylated alpha-CDs along the PEG chain in the gel. The arrangement of CDs was also reflected by the changes in elasticity and long relaxation behavior of the solution around the sol-gel transition. The quasiequilibrium shear modulus of MePR solutions showed the critical phenomena against temperature. The scaling exponents measured at two different concentrations were almost equal to the values predicted by a gel percolation theory. Therefore, the heat-induced gelation of aqueous MePR solutions is well explained by a model in which clusters assembled with methylated alpha-CDs are gradually connected to the network as the temperature increases.     

Supramolecular self-assembly of inclusion complexes of a multiarm hyperbranched polyether with cyclodextrins

A new class of crystalline inclusion complexes of a multiarm hyperbranched polyether combined with various cyclodextrins (CDs) was successfully prepared. Using self-condensing ring-opening polymerization, a kind of multiarm polyether with a hyperbranched poly(3-ethyl-3-oxetanemethanol) core and multiple linear poly(ethylene glycol) (PEG) arms was obtained. It has been found that this kind of hyperbranched polyether can be dissolved in water. Adding alpha-CDs to the multiarm hyperbranched polyether solution, molecular recognition results in the formation of crystalline inclusion complexes based on the noncovalent interactions between the linear PEG arms of the polyether particles and the alpha-CDs. These multiarm polyether inclusion complexes have been well characterized. Interestingly, quite different from inclusion complexes of CDs and linear polymeric guests, the complexes of the multiarm hyperbranched polyether with alpha-CDs show a novel lamellar morphology. The experimental results validate that the resultant lamellar crystals have a juxtaposed structure. In addition, the formation mechanism of these inclusion complexes of a multiarm polyether with alpha-CDs has also been well described. Besides the role of displacement of associated water molecules and the presence of hydrogen bonding between CDs in channel structure CD inclusion complexes, the noncovalent intermolecular forces between CDs and polymers also play an important role in the formation of complex architectures.     

The Mobility of Threaded α-Cyclodextrins in PR Copolymer and Its Influences on Mechanical Properties

The methylated polyrotaxane(Me PR) copolymer was prepared via the methylation of hydroxyl of threaded α-cyclodextrin(α-CDs) in polyrotaxane(PR) copolymer by CH_3I/Na H. Its structure was characterized by GPC, IR and NMR. The WXRD and TGA measurements showed the destruction of channel-like crystalline structure in Me PR copolymer. The sliding of threaded α-CDs along PEG axis in PR and Me PR copolymers was demonstrated by their dielectric spectra that also evidenced the presence of rotating of threaded α-CDs around PEG axis in Me PR copolymer. The frequent and vigorous molecular mobility in Me PR and PR copolymers was also verified by dynamic mechanical analysis(DMA) and rheological measurement, which was possibly assigned to the sliding and rotating of threaded α-CDs. DMA and rheological results showed that the mobility of α-CDs could simultaneously strengthen and toughen PR copolymer proved by stress-stain curves. In this paper, we report the CD mobility in PR and Me PR copolymers. The macroscopic behaviors of PR copolymer, such as mechanical properties in solid state, were also found to be benefited from CD mobility.     

Synthesis of a “molecular rope curtain”: Preparation and characterization of a sliding graft copolymer with grafted poly(ethylene glycol) side chains by the “grafting onto” strategy

A sliding graft copolymer (SGC) with poly(ethylene glycol) (PEG) side chains was prepared by ester formation between terminal carboxyl groups of oxidized PEG methyl ether with molecular weight of 2000 (mPEG2000‐COOH) and hydroxyl groups of a polyrotaxane consisting of PEG and cyclodextrins (CDs). Formation of the SGC structure was confirmed by ¹H NMR, attenuated total reflectance Fourier‐transformed infrared, and gel permeation chromatography. The SGC was soluble in good solvents of PEG and insoluble in poor solvents of PEG. Estimation of the number of grafted mPEG chains suggested a “rope‐curtain” like structure, in which an mPEG chain is connected to each CD ring. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

New solvent for polyrotaxane. II. Dissolution behavior of polyrotaxane in ionic liquids and preparation of ionic liquid‐containing slide‐ring gels

The dissolution behavior of polyrotaxanes, consisting of α‐cyclodextrin and poly(ethylene glycol), with different molecular weights (2000 and 35,000) was investigated. Halogen‐containing ionic liquids, such as chlorides or bromides, were found to be good solvents for polyrotaxanes, regardless of their cations. Dissolution required a high temperature (above 90 °C), while intensive heating over 105 °C seemed to cause decomposition of the polyrotaxane. The discovery of new solvents for polyrotaxane was applied in the preparation of ionic liquid‐containing slide‐ring gels (SR gels), that is supramolecular networks of polyrotaxane swollen with ionic liquids, using a devised “non‐drying” technique accompanied by solvent exchange. Significant swelling of the SR gels with the ionic liquids was confirmed by dynamic mechanical measurements. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1985–1994, 2006     

One-pot synthesis of a polyrotaxane via selective threading of a PEI-b-PEG-b-PEI copolymer

A functional polyrotaxane of a PEI-b-PEG-b-PEI copolymer is synthesized in aqueous solution in a one-pot sequence. To obtain a polyrotaxane with PEG-block-selective inclusion complexes, the solution pH of the polypseudorotaxane is lowered to 4.4 in the presence of 9-anthraldehyde (AN), which triggers the expulsion of the alpha-cyclodextrins (alpha-CDs) from the flank PEI chains. Synthetic strategy of a block-selective polyrotaxane between a PEI-b-PEG-b-PEI copolymer and alpha-cyclodextrins.     

Glycopolymers Made from Polyrotaxanes Terminated with Bile Acids: Preparation,Self‐Assembly,and Targeting Delivery

The use of natural compounds to construct biomaterials, including delivery system, is an attractive strategy. In the present study, through threading functional α‐cyclodextrins onto the conjugated macromolecules of poly(ethylene glycol) (PEG) and natural compound bile acid, glycopolymers of polyrotaxanes with the active targeting ability are obtained. These glycopolymers self‐assemble into micelles as evidenced by dynamic light scattering and transmission electron microscopy, in which glucosamine, as an example of targeting groups, is introduced. These micelles after loading doxorubicin (DOX) exhibit the selective recognition with cancer cells 4T1. Meanwhile, the maximal half inhibitory concentration is determined to be ≈2.5 mg L^?1 for the DOX‐loaded micelles, close to the value of free DOX·HCl (1.9 mg L^?1). The cumulative release of DOX at pH 5.5 is faster than at pH 7.4, which may be used as the controlled release system. This drug delivery system assembled by glycopolymers features high drug loading of DOX, superior biocompatibility. The strategy not only utilizes the micellization induced by bile acids, but also overcomes the major limitation of PEG such as the lack of targeting groups. In particular, this drug delivery platform can extend to grafting the other targeting groups, rendering this system more versatile.     

Spatial arrangement of alpha-cyclodextrins in a rotaxane. Insights from free-energy calculations

The rotaxane formed by alpha-cyclodextrins (alpha-CDs) threaded onto a poly(ethylene glycol) (PEG) chain was investigated in the gas phase and in an aqueous solution by means of molecular dynamics simulations. The free-energy difference between the three possible spatial arrangements of consecutive alpha-CD--viz.. head-to-head (HH), head-to-tail (HT), and tail-to-tail, was determined using free-energy perturbation calculations. These simulations reveal that the interaction of alpha-CD with the PEG chain is very similar in the two surroundings, whereas the mutual interaction of the macrocycles is stronger in the gas phase than in the aqueous solution. Moreover, difference in the overall interaction appears to stem primarily from changes in the electrostatic contribution. Analysis of intermolecular hydrogen bonds indicates that hydrogen bonds created between alpha-CD and water molecules weaken the hydrogen-bonding interaction of adjacent alpha-CDs. Comparison of the free-energy differences characteristic of the three possible spatial arrangements of contiguous alpha-CDs reveals that the HH motif of the rotaxane is the most stable in the gas phase due to the hydrogen-bond formation between the secondary hydroxyl groups of the two alpha-CDs, and the slight preference for the HT motif in aqueous solution, which can be related to the directionality of the dipole moment borne by the macrocycles in these two motifs.     

Carbohydrate decoration of microporous polypropylene membranes for lectin affinity adsorption: comparison of mono- and disaccharides

Carbohydrates (saccharides) are ubiquitous on the extracellular surface of living cells and mediate a myriad of biological recognition and signaling processes. Carbohydrate decoration of polymer surfaces with covalent attachment of saccharides offers a new realm of opportunities to mimic cellular events such as protein recognition and binding. We describe the carbohydrate decoration (surface glycosylation) of poly(2-hydroxyethyl methacrylate)-grafted microporous polypropylene membranes (poly(HEMA)-g-MPPMs) with mono- and disaccharides. Galactose, lactose, glucose, and maltose were covalently attached on the surfaces of poly(HEMA)-g-MPPMs and were compared in detail. The process was verified by solid state (13)C NMR spectra. Membranes with high binding degree (BD) of saccharide ligands on the surfaces were facilely prepared from poly(HEMA)-g-MPPMs with high grafting degree (GD) of poly(HEMA). For poly(HEMA)-g-MPPM with the same GD of poly(HEMA), the BD of disaccharides is lower than that of monosaccharides and the disaccharide-decorated MPPMs are more hydrophilic than the monosaccharide-decorated ones. The carbohydrate-decorated MPPMs prepared from galactose, lactose, glucose, and maltose (denoted as MPPM-Gal, MPPM-Lac, MPPM-Glc and MPPM-Mal, respectively) recognize and adsorb specifically one of the two lectins, concanavalin A (Con A) and peanut agglutinin (PNA). As the BD of saccharide increases, the "glycoside cluster effect" plays a primary role in lectin adsorption. MPPM-Lac has enhanced affinity to PNA as compared with MPPM-Gal having similar BD of saccharide., on the other hand, MPPM-Mal shows no enhanced affinity to Con A in comparison with MPPM-Glc as the BD of saccharide is above 0.9 μmol/cm(2), where the "glycoside cluster effect" occurs.