Residue- and Sequence-Selective Binding of Nonaromatic Dipeptides by Bis(β-cyclodextrin) with a Functional Tether

Reverse micelles based on biocompatible β-cyclodextrin conjugated polyethylene glycol block polylactide for protein delivery

The oil-based formulation fabricated from biodegradable PEG-b-PLA-CD copolymers with high drug loading showed great potential for protein delivery.

Switchable host-guest systems on surfaces

CONSPECTUS: For device miniaturization, nanotechnology follows either the "top-down" approach scaling down existing larger-scale devices or the "bottom-up' approach assembling the smallest possible building blocks to functional nanoscale entities. For synthetic nanodevices, self-assembly on surfaces is a superb method to achieve useful functions and enable their interactions with the surrounding world. Consequently, adaptability and responsiveness to external stimuli are other prerequisites for their successful operation. Mechanically interlocked molecules such as rotaxanes and catenanes, and their precursors, that is, molecular switches and supramolecular switches including pseudorotaxanes, are molecular machines or prototypes of machines capable of mechanical motion induced by chemical signals, biological inputs, light or redox processes as the external stimuli. Switching of these functional host-guest systems on surfaces becomes a fundamental requirement for artificial molecular machines to work, mimicking the molecular machines in nature, such as proteins and their assemblies operating at dynamic interfaces such as the surfaces of cell membranes. Current research endeavors in material science and technology are focused on developing either a new class of materials or materials with novel/multiple functionalities by shifting host-guest chemistry from solution phase to surfaces. In this Account, we present our most recent attempts of building monolayers of rotaxanes/pseudorotaxanes on surfaces, providing stimuli-induced macroscopic effects and further understanding on the switchable host-guest systems at interfaces. Biocompatible versions of molecular machines based on synthetic macrocycles, such as cucurbiturils, pillararenes, calixarenes, and cyclodextrins, have been employed to form self-assembled monolayers of gates on the surfaces of mesoporous silica nanoparticles to regulate the controlled release of cargo/drug molecules under a range of external stimuli, such as light, pH variations, competitive binding, and enzyme. Rotaxanes have also been assembled onto the surfaces of gold nanodisks and microcantilevers to realize active molecular plasmonics and synthetic molecular actuators for device fabrication and function. Pillararenes have been successfully used to control and aid the synthesis of gold nanoparticles, semiconducting quantum dots, and magnetic nanoparticles. The resulting organic-inorganic hydrid nanomaterials have been successfully used for controlled self-assembly, herbicide sensing and detection, pesticide removal, and so forth, taking advantage of the selective binding of pillarenes toward target molecules. Cyclodextrins have also been successfully functionalized onto the surface of gold nanoparticles to serve as recycling extractors for C60. Many interesting prototypes of nanodevices based on synthetic macrocycles and their host-guest chemistry have been constructed and served for different potential applications. This Account will be a summary of the efforts made mainly by us, and others, on the host-guest chemistry of synthetic macrocyclic compounds on the surfaces of different solid supports.

Improved polyvinylpyrrolidone microneedle arrays with non-stoichiometric cyclodextrin

Improved polyvinylpyrrolidone (PVP) microneedle arrays can be fabricated by adding cyclodextrin (CD) to form PVP–CD inclusion complexes.

Interactions of some modified mono- and bis-β-cyclodextrins with bovine serum albumin

Two mono-substituted beta-cyclodextrins and two bridged bis-beta-cyclodextrins, that is, mono(6-(2-aminoethylamino)-6-deoxy)-beta-cyclodextrin (1), mono(6-(2-(2-aminoethylamino)ethylamino)-6-deoxy)-beta-cyclodextrin (2), ethylene-1,2-diamino bis-6-(6-deoxy-beta-cyclodextrin) (3), and iminodiethylene-2,2'-diamino bis-6-(6-deoxy-beta-cyclodextrin) (4), were prepared from beta-cyclodextrin. Their binding ability with bovine serum albumin as a model protein was investigated through proton magnetic resonance (1H NMR), ultraviolet visible spectroscopy (UV-vis), circular dichroism (CD), and fluorescence spectroscopy. In the 1H NMR spectra of the modified cyclodextrins, the resolution of proton signals decreases after the addition of BSA. From the UV and CD spectra, it is found that both the UV absorption and the alpha-helix content of BSA increase with the concentration of the modified cyclodextrins. The protein-ligand interactions cause a fluorescence quenching. The quenching constants are determined using the Stern-Volmer equation to provide an observation of the binding affinity between modified cyclodextrins and BSA. All these results indicate that the modified cyclodextrins can interact with BSA and the bridged bis(beta-cyclodextrin)s (3 and 4) have much stronger interactions than the mono-substituted beta-cyclodextrins (1 and 2). The strong binding stability of bis-cyclodextrins should be attributed to the cooperative effect of two adjacent cyclodextrin moieties. Job's plot shows that the complex stoichiometries of BSA to the modified cyclodextrins were 1:4 for 1 and 2, as well as 1:3 for 3 and 4, respectively.

Efficient fluorescent sensors of oligopeptides by dithiobis(2-benzoylamide)-bridged bis(β-cyclodextrin)s: structure in solution, binding behavior, and thermodynamic origin

Two 6,6'-bis(beta-cyclodextrin)s linked by 2,2'-dithiobis[2-(benzoylamino)ethyleneamino] and 2,2'-dithiobis[2-(benzoylamino)diethylenetriamino] bridges (1 and 2) have been synthesized as cooperative multipoint recognition receptor models for non-aromatic oligopeptides. Their structures in solution and inclusion complexation mechanism are comprehensively investigated by means of circular dichroism, 2D NMR spectra and temperature-dependent fluorescence titrations. The results show that the cooperative 'host-linker-guest' binding mode and the extensive desolvation effect jointly contribute to the guest-induced fluorescence enhancement of bis(beta-cyclodextrin)s. Further examinations on the binding behavior of hosts 1-2 with a series of di- and tri-peptides demonstrate that bis(beta-cyclodextrin) 1 can recognize not only the size/shape of oligopeptides but also the dipeptide sequence, giving an exciting residue selectivity up to 37.5 for Gly-Gly-Gly/Glu-Glu pair and a high sequence selectivity up to 5.0 for Gly-Leu/Leu-Gly pair. These fairly good selectivities are discussed from the viewpoint of cooperative binding, multiple recognition and induced-fit interactions between host and guest.

Molecular Recognition Thermodynamics and Structural Elucidation of Interactions between Steroids and Bridged Bis(β-cyclodextrin)s

A series of bridged bis(beta-cyclodextrin(CD))s (2-7) were synthesized, i.e., bridged bis(beta-CD)s 2 and 3 bearing binaphthyl or biquinoline tethers and bridged bis(beta-CD)s 4-7 possessing dithiobis(benzoyl) tether, and their complex stability constants (KS), enthalpy (DeltaH degrees), and entropy changes (DeltaS degrees) for the 1:2 inclusion complexation with representative steroids, deoxycholate, cholate, glycocholate, and taurocholate, have been determined in an aqueous phosphate buffer solution of pH 7.20 at 298.15 K by means of titration microcalorimetry. The original conformations of bridged bis(beta-cyclodextrin)s were investigated by circular dichroism and 1H ROESY spectroscopy. Structures of the inclusion complexes between steroids and bridged bis(beta-CD)s in solution were elucidated by 2D NMR experiments, indicating that anionic groups of two steroid molecules penetrate, respectively, into the two hydrophobic CD cavities in one 6,6'-bridged bis(beta-CD) molecule from the secondary rim to give a 1:2 binding mode upon inclusion complexation. The results obtained from titration microcalorimetry and 2D NMR experiments jointly demonstrate that bridged bis(beta-CD)s 2, 3 and 5-7 tethered by protonated amino group possessing different substituted groups can enhance not only the molecular binding ability toward steroids by electrostatic interaction but also molecular selectivity. Thermodynamically, the resulting 1:2 bis(beta-CD)-steroid complexes are formed by an enthalpy-driven process, accompanied by smaller entropy loss. The increased complex stability mainly results from enthalpy gain, accompanied by large conformational change and extensive desolvation effects for the 1:2 inclusion complexation between bis(beta-CD)s and steroids.