Thermoresponsive dendronized polymeric sensors

Confined Microenvironments from Thermoresponsive Dendronized Polymers

Confined microenvironments in biomacromolecules arising from molecular crowding account for their well-defined biofunctions and bioactivities. To mimick this, synthetic polymers to form confined structures or microenvironments are of key scientific value, which have received significant attention recently. To create synthetic confined microenvironments, molecular crowding effects and topological cooperative effects have been applied successfully, and the key is balance between self-association of structural units and self-repulsion from crowding-induced steric hindrance. In this article, formation of confined microenvironments from stimuli-responsive dendronized polymers carrying densely dendritic oligoethylene glycols (OEGs) moieties in their pendants is presented. These wormlike thick macromolecules exhibit characteristic thermoresponsive properties, which can provide constrained microenvironments to encapsulate effectively guest molecules including dyes, proteins, or nucleic acids to prevent their protonation or biodegradation. This efficient shielding effect can also mediate chemical reactions in aqueous phase, and even enhance chirality transferring efficiency. All of these can be switched off simply through the thermally-induced dehydration and collapse of OEG dendrons due to the amphiphilicity of OEG chains. Furthermore, the switchable encapsulation and release of guests can be greatly enhanced when these dendronized polymers are used as major constituents for fabricating bulk hydrogels or nanogels, which provide a higher-level confinement.

Thermoresponsive cationic dendronized copolymers and their corresponding nanogels as smart gene carriers

Thermoresponsive dendronized copolymer nanogels show unique condensation, protection and controlled release of siRNA due to dendritic topology and spherical morphology.

Thermo- and redox-responsive dendronized polymer hydrogels

Unique supramolecular coordination of Fe²⁺ with terpyridine afford these hydrogels redox-responsive sol–gel transitions, while characteristic thermoresponsive properties from OEG-based first generation dendronized polymers render these hydrogels thermally-induced macroscopical volume changes and enhanced mechanical properties.

Stimuli-responsive dendronized polymeric hydrogels through Schiff-base chemistry showing remarkable topological effects

Crowded and thick dendronized polymers enhance the formation of a Schiff-base through thermally-induced collapse or freezing, resulting in hydrogels with different performances.

Porous metal–organic gel assisted by l-tartaric acid ligand for efficient and controllable drug delivery

The synthetic route for drug carriers based on porous Al-MOG.

Thermoresponsive double network cryogels from dendronized copolymers showing tunable encapsulation and release of proteins

Thermoresponsive double network cryogels were prepared from OEG-based dendronized copolymers with PVA, which can reversibly capture and release proteins.

Multi-scale characterization of thermoresponsive dendritic elastin-like peptides

Elastin like peptides (ELPs)-polypeptides based on the protein elastin-are used widely as thermoresponsive components in biomaterials due to the presence of a sharp soluble-to-insoluble phase change at a characteristic transition temperature (T_t). While linear ELPs have been thoroughly studied, few investigations into branched ELPs have been carried out. Using lysine amino acids as branching and terminal units with 1-3 pentameric repeats between each branch, ELP dendrimers were prepared by solid-phase peptide synthesis with molecular weights as high as 14kDa. A conformation change from random coil to β-turn upon heating through the T_t, typical of ELPs, was observed by circular dichroism spectroscopy for all peptides. The high molecular weights of these peptides enabled the use of characterization techniques typically reserved for polymers. Variable-temperature small-angle X-ray scattering measurements in dilute solution revealed an increase in size and fractal dimension upon heating, even well below the T_t. These results were corroborated by cryogenic transmission electron microscopy, which confirmed the presence of aggregates below the T_t, and micro differential scanning calorimetry, which showed a broad endothermic peak below the T_t. These results collectively indicate the presence of a pre-coacervation step in the phase transition of ELP dendrimers.

Solvatochromism of dye-labeled dendronized polymers of generation numbers 1-4: comparison to dendrimers

Two series of dendronized polymers (DPs) of generations g = 1-4 with different levels of dendritic substitution (low and high) and a solvatochromic probe at g = 1 level are used to study their swelling behavior in a collection of solvents largely differing in polarity as indicated by the Kamlet-Taft parameters. This is done by measuring the UV-Vis spectra of all samples in all solvents and determining the longest wavelength absorptions (λmax). The λmax values fall into a range defined by the extreme situations, when the solvatochromic probe is either fully surrounded by solvent or completely shielded against it. The former situation is achieved in a model compound and the latter situation is believed to be reached when in a poor solvent the dendritic shell around the backbone is fully collapsed. We observe that solvent penetration into the interior of the DPs decreases with increasing g and does so faster for the more highly dendritically substituted series than for the less highly substituted one. Interestingly, the swelling of the more highly substituted DP series already at the g = 4 level has decreased to approximately 20% of that at the g = 1 level which supports an earlier proposal that high g DPs can be viewed as nano-sized molecular objects. Furthermore, when comparing these two DP series with a g = 1-6 series of dendrimers investigated by Fréchet et al. it becomes evident that even the less substituted series of DPs is much less responsive to solvent changes as assessed by the solvatochromic probe than the dendrimers, suggesting the branches around the (polymeric) core in DPs to be more densely packed compared to those in dendrimers, thus, establishing a key difference between these two dendritic macromolecules.

Thermoresponsive dynamic covalent dendronized polymers

Dendronization of polyacylhydrazones with oligoethylene glycol-based dendrons affords polymers with tunable thermoresponsiveness and switchable shielding from affinity to Cu²⁺.

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.

Dendronized supramolecular polymers

Supramolecular polymers from dendritic motifs combine the dynamic nature of supramolecular construction and inherent features from covalent dendronized polymers.