pH Dependence of Inclusion Complexation between Cationic Poly(ε-lysine) and α-Cyclodextrin

Acid-Sensitive Polypseudorotaxanes Based on Ortho Ester-Modified Cyclodextrin and Pluronic F-127

We demonstrate a new type of acid-sensitive amphiphilic polypseudorotaxanes (PPRs) formed via inclusion complexation between Pluronic F127 and the hydrophobic β-cyclodextrin (CD) derivative in alcoholic solvents. The 6-OH ortho ester-substituted hydrophobic β-CD derivative (EMD-CD) was prepared by "click" reaction of β-CD with 2-ethylidene-4-methyl-1,3-dioxalane under mild conditions. The water-insoluble EMD-CD (host) is capable of forming PPRs with F127 (guest) in ethanol or methanol but not in water, which is confirmed by ¹H NMR, wide-angle X-ray diffraction, small-angle X-ray scattering, and the time-dependent threading kinetics. Depending on the host/guest ratio, the PPRs self-assembled into sheet-like structure or vesicular nanoparticles with different sizes in water. These PPR assemblies were stable at pH 8.4 but quickly dissociated into biocompatible products in neutral or in acidic buffers due to the hydrolysis of the ortho ester groups. Good biocompatibility, ease of fabrication, and extremely pH-sensitive character make the PPRs promising carriers for anticancer drug delivery. Moreover, the present work provides an alternative method for the preparation of PPRs composed of water-insoluble CD derivatives.

Removal of 2,4-dichlorophenol using cyclodextrin-ionic liquid polymer as a macroporous material: characterization, adsorption isotherm, kinetic study, thermodynamics

Cyclodextrin-ionic liquid polymer (βCD-BIMOTs-TDI) was firstly synthesized using functionalized β-Cyclodextrin (CD) with 1-benzylimidazole (BIM) to form monofunctionalized CD (βCD-BIMOTs) and was further polymerized using toluene diisocyanate (TDI) linker to form insoluble βCD-BIMOTs-TDI. SEM characterization result shows that βCD-BIMOTs-TDI exhibits macropore size while the BET result shows low surface area (1.254 m(2)g(-1)). The unique properties of the ILs allow us to produce materials with different morphologies. The adsorption isotherm and kinetics of 2,4-dichlorophenol (2,4-DCP) onto βCD-BIMOTs-TDI is studied. Freundlich isotherm and pseudo-second order kinetics are found to be the best to represent the data for 2,4-DCP adsorption on the βCD-BIMOTs-TDI. The presence of macropores decreases the mass transfer resistance and increases the adsorption process by reducing the diffusion distance. The change in entropy (ΔS°) and heat of adsorption (ΔH°) for 2,4-DCP on βCD-BIMOTs-TDI were estimated as -55.99 J/Kmol and -18.10 J/mol, respectively. The negative value of Gibbs free energy (ΔG°) indicates that the adsorption process is thermodynamically feasible, spontaneous and chemically controlled. Finally, the interactions between the cavity of βCD-BIMOTs and 2,4-DCP are investigated and the results shows that the inclusion of the complex formation and π-π interaction are the main processes involved in the adsorption process.

Complexation between α-cyclodextrin and PEGylated-PAMAM dendrimers at low and high pH values

Poly(ethylene glycol)-grafted-poly(amido amine) (PEGylated-PAMAM) dendrimers have attracted increasing amounts of attention because of their improved stability, toxicity, and better particle drug leakage property. The complexation of α-cyclodextrin (α-CD) with grafted PEG segments on the surface of PAMAM dendrimers was elucidated by light scattering and titration calorimetry. At pH 10, complexation between α-CD and PEGylated-PAMAM occurred once α-CD was titrated into the PAMAM solution. We observed for the first time a unique phenomenon at pH 2, where no binding took place until a critical α-CD concentration (C*) of ∼8.0 mM was reached. The size of the nanostructures increased from 6.7 to 57.6 nm when the α-CD concentration was increased from 0.5 to 15 mM at pH 2. The zeta potential of PEGylated-PAMAM at pH 2 was +6.7 mV. Thus, the dendrimers possessed positive charges attributed to the protonation of primary amine groups on PAMAM chains that impart electrostatic repulsive forces to the system. The morphology of the complex is expected to be different at two different pH values (2 and 10) because the former produces a clear solution and the latter forms a turbid solution with white precipitates.

Cyclodextrin-based gene delivery systems

Cyclodextrin (CD) history has been largely dominated by their unique ability to form inclusion complexes with guests fitting in their hydrophobic cavity. Chemical funcionalization was soon recognized as a powerful mean for improving CD applications in a wide range of fields, including drug delivery, sensing or enzyme mimicking. However, 100 years after their discovery, CDs are still perceived as novel nanoobjects of undeveloped potential. This critical review provides an overview of different strategies to promote interactions between CD conjugates and genetic material by fully exploiting the inside-outside/upper-lower face anisotropy of the CD nanometric platform. Covalent modification, self-assembling and supramolecular ligation can be put forward with the ultimate goal to build artificial viruses for programmed and efficient gene therapy (222 references).

Formation of linear main-chain polypseudorotaxanes with supramolecular polymer backbones via two self-sorting host-guest recognition motifs

Based on two self-sorting host-guest recognition motifs, novel linear main-chain polypseudorotaxanes with supramolecular polymer backbones have been constructed from three components in solution at high concentrations.

Photolockable ratiometric viscosity sensitivity of cyclodextrin polypseudorotaxane with light-active rotor graft

A prototype, based on light-active fluorescent rotor grafted to beta-cyclodextrin, shows a good solvent viscosity-sensitive behavior due to the environment-dependent nonradiative decay. With the reversible photoisomerization of the cyanostilbene unit, the viscosity sensitivity of the molecular rotor could be locked and activated, and the two switchable states can be distinguished by fluorescent signals. This cyclodextrin derivative was threaded to form a novel polypseudorotaxane. Such supramolecular assembly displays a lockable ratiometric fluorescent viscosity sensitivity with two emission channels: one aroused by fluorophore's intramolecular excimer without influenced by viscosity is used to gauge the concentration of the compound, while the other corresponding to the monomer's rotor fluorescence acts as a viscosity-sensitive signal and it can be shut off by UV irradiation.

α-Cyclodextrin Functionalized CdS Nanocrystals for Fabrication of 2/3 D Assemblies

Different types of cyclodextrins (CDs) have been tested as mediators for the water phase transfer of organic-capped CdS nanocrystals (NCs), and alphaCD has been demonstrated to be the most effective system. The formation of a complex based on alphaCDs and colloidal NCs has been considered to be responsible for the phase transfer process and extensively investigated by optical, structural, and calorimetric measurements, as a function of the experimental parameters (pH and NC and CD concentration). A mechanism for the complexation phenomena has been suggested. The fabrication of 2/3 D supramolecular architectures has been proposed according to two different strategies. First, a layer-by-layer procedure has been used to obtain multilayered structures where polyelectrolyte layers have been intercalated with negatively charged alphaCD-CdS NC complexes by exploiting electrostatic interaction between polyelectrolyte and cyclodextrin OH groups. Second, a monolayer of CdS NCs has been deposited onto a self-assembled monolayer of sulfated CDs, thus combining the use of an electrostatic-force-based approach and host-guest chemistry. The important role played by host-guest interactions has then been revealed.

pH-Responsive Movement of Cucurbit[7]uril in a Diblock Polypseudorotaxane Containing Dimethyl β-Cyclodextrin and Cucurbit[7]uril

[Structure: see text] A polypseudorotaxane consisting of cucurbit[7]uril (CB[7])/N,N'-(3-phenylenebis(methylene)dipropargylamine (PMPA), [2]pseudorotaxane, and 2,6-O-dimethyl beta-cyclodextrin (DM-beta-CD)/alpha,omega-bisazidopropylene glycol 400 [2]pseudorotaxane was synthesized using the "click" reaction. The polypseudorotaxane structure was maintained in aqueous solution over a wide range of pH values with the DM-beta-CD units contributing to increased solubilization of the polypseudorotaxane without dethreading. The pH-responsive movement of the CB[7] units in the polypseudorotaxane was also observed.

Improved Cell Viability of Linear Polyethylenimine through γ-Cyclodextrin Inclusion for Effective Gene Delivery

A polypseudorotaxane consisting of a linear polyethylenimine with Mn of 22,000 (LPEI22k) and gamma-cyclodextrins (gamma-CDs; LPEI22k/gamma-CD) has been examined as a gene carrier. The polyplex formation with luciferase-encoding plasmid DNA (pDNA), intracellular trafficking of polyplex, cytotoxicity, and transfection efficiency were evaluated by various characteristic methods. LPEI22k/gamma-CD formed a pDNA polyplex at higher N/P ratios than LPEI22k; this suggests that the gamma-CD threading sterically interfered with the polyplex formation. In addition, the zeta potentials of the polyplex significantly decreased due to the reduction in charge density of LPEI22k caused by gamma-CD threading. The cellular uptake of pDNA in the LPEI22k/gamma-CD polyplex was enhanced by free gamma-CDs released from the polyplex that might accelerate the cellular uptake through enhanced membrane affinity. LPEI22k/gamma-CD significantly increased cell viability even at high N/P ratios, and the polyplex showed high transfection efficacy. The low cytotoxicity and high gene expression of LPEI22k/gamma-CD are advantageous to polyplex administration in vivo.

Synthesis of Poly(ɛ-lysine)-Grafted Dextrans and Their pH- and Thermosensitive Hydrogelation with Cyclodextrins

To give pH sensitivity to a thermoreversible supramolecular-structured hydrogel system, poly(epsilon-lysine) (PL), as a cationic polymer, was grafted to dextran and used for inclusion complexation with alpha-cyclodextrins (alpha-CDs). The synthesized graft copolymer was characterized by 1H NMR spectroscopy, and the hydrogel formation was confirmed by X-ray diffraction and solid-state 13C NMR analysis. The hydrogelation was induced from a phase-separated structure of hydrated dextrans and hydrophobically aggregated inclusion complexes in buffer solution at pH 10.0. The prepared hydrogels showed thermoreversible gel-sol transitions as well as pH-sensitive phase transitions, which were recorded by the changes in UV/Vis transmittance. A rapid phase transition from gel to sol was observed upon decreasing the pH value to 4.0, which resulted from the dissociation process between the protonated guest polymer and alpha-CDs. The stimuli-responsive physical properties of the hydrogels were improved by modulating the degree of substitution of the grafted PL and the combination with alpha-CDs.