Tuning Antibacterial Activity of Cyclodextrin-Attached Cationic Ammonium Surfactants by a Supramolecular Approach

Two β-cyclodextrin-attached cationic ammonium surfactants bearing a dodecyl chain (APDB) and a hexadecyl chain (APCB) were synthesized to reduce the cytotoxicity of cationic surfactants to mammalian cells and endow the surfactants with host-guest recognition sites, and three kinds of guest molecules were utilized to improve the antibacterial ability of APDB and APCB via host-guest interaction by regulating the electrostatic or hydrophobic interaction of APDB or APCB with bacteria. The guest molecules include AD-NH₃⁺ carrying one positive charge, DB with a benzene ring group and a dodecyl chain, and single chain cationic ammonium surfactant DTAB or CTAB. Either AD-NH₃⁺ or DB increases the killing efficacy of APCB against S. aureus at 50 μM from 59% to about 75%, while DTAB or CTAB improves the killing efficacy of APCB to more than 90%. In particular, only a very small amount CTAB can improve the antibacterial activity of APCB to a very high level, but keeps very low cytotoxicity. However, the mixtures of the guest molecules with APDB are devoid of any activity against S. aureus. This is mainly attributed to the fact that APCB and its mixtures with the guest molecules form 100-200 nm spherical aggregates, while the mixtures of APDB with the guest molecules cannot form aggregates at lower concentration. It is revealed that the three kinds of guest molecules trapped in the APCB spherical aggregates lead to diverse interaction modes of the APCB spherical aggregates with S. aureus, accounting for the different killing efficacy of the APCB/guest molecule mixtures. This supramolecular strategy provides an effective approach for the construction of highly efficient antibacterial agents with low cytotoxicity.

Host-Guest Binding-Site-Tunable Self-Assembly of Stimuli-Responsive Supramolecular Polymers

Despite the remarkable progress made in controllable self-assembly of stimuli-responsive supramolecular polymers (SSPs), a basic issue that has not been consideration to date is the essential binding site. The noncovalent binding sites, which connect the building blocks and endow supramolecular polymers with their ability to respond to stimuli, are expected to strongly affect the self-assembly of SSPs. Herein, the design and synthesis of a dual-stimuli thermo- and photoresponsive Y-shaped supramolecular polymer (SSP2) with two adjacent β-cyclodextrin/azobenzene (β-CD/Azo) binding sites, and another SSP (SSP1) with similar building blocks, but only one β-CD/Azo binding site as a control, are described. Upon gradually increasing the polymer solution temperature or irradiating with UV light, SSP2 self-assemblies with a higher binding-site distribution density; exhibits a flower-like morphology, smaller size, and more stable dynamic aggregation process; and greater controllability for drug-release behavior than those observed with SSP1 self-assemblies. The host-guest binding-site-tunable self-assembly was attributed to the positive cooperativity generated among adjacent binding sites on the surfaces of SSP2 self-assemblies. This work is beneficial for precisely controlling the structural parameters and controlled release function of SSP self-assemblies.

Self-assembly and morphological transitions of random amphiphilic poly(β-D-glucose-co-1-octyl) phosphazenes

The amphiphilic random copolymer poly(β-d-glucose-co-1-octyl)phosphazene (PGOP) can undergo continuous morphological transitions in DMF-water mixed solvents. In this study, the ratio of glucose moieties to octyl moieties was controlled via a two-step thiol-ene reaction. As a result, polyphosphazenes with glycosyl functionalization degrees of 58.1% (PGOP-1), 74.1% (PGOP-2) and 87.0% (PGOP-3) were obtained. These amphiphilic polyphosphazenes self-assemble in both water and water-DMF mixtures. Several self-assembled morphologies including spheres, rods and vesicles were formed though careful control of the water content (WC) in the DMF solvent as well as of the hydrophilicity or hydrophobicity of the copolymers. We also found that an increase in the hydrophobic proportion led to faster morphological transitions at a constant WC. The thermodynamics of micellization were also studied by Isothermal Titration Calorimetry (ITC), and the strong hydrophobic interactions in PGOP-1 were demonstrated by their highly exothermic nature. These self-assemblies have potential applications in biosensing, lectin adsorption and drug loading with controlled release.

ATP-triggered biomimetic deformations of bioinspired receptor-containing polymer assemblies

Designing synthetic polymer assemblies that can sense a biological signal to mimic cell activities is elusive. We develop a class of block copolymer containing bioinspired host units as supramolecular catchers for the highly-selective capture of adenosine-5'-triphosphate (ATP). Driven by ATP, these block copolymers undergo a stepwise self-assembly and exhibit cascading deformation into highly-ordered nanostructures via the specific recognition effect between ATP and the receptor. By modulating the ATP concentration, one can precisely control the biomimetic evolution of these assemblies in diverse dimensionalities and geometries, like certain organellar deformations. Moreover, the ATP/polymer hybrid aggregates can be reversibly disassembled in response to phosphatase. The special ability of the artificial assemblies to sense intracellular bioactivators can offer new insight into bio-responsive nanomaterials for cellular applications.

OEGylated cyclodextrin-based thermoresponsive polymers and their switchable inclusion complexation with fluorescent dyes

OEGylated cyclodextrin-based polymers exhibit characteristic thermoresponsiveness and switchable inclusion ability towards fluorescent dyes.

Synthesis and encapsulation of an amphiphilic thermoresponsive star polymer with β-cyclodextrin and hyperbranched poly(oligo(ethylene glycol)methacrylate) as building blocks

Schematic illustrations of the thermally-induced self-assembly and possible encapsulation behaviors with single or multi-guests for PE-CD–POEGMAS.

Pseudo-graft polymer based on adamantyl-terminated poly(oligo(ethylene glycol) methacrylate) and homopolymer with cyclodextrin as pendant: its thermoresponsivity through polymeric self-assembly and host–guest inclusion complexation

Thermoresponsivity and self-assembly of a pseudo-graft polymer based on Ad-terminated poly(oligo(ethylene glycol) methacrylate) and homopolymer with CD pendants.