Cyclodextrins (CDs), which are a class of cyclic oligosaccharides extracted from the enzymatic degradation of starch, are often utilized in molecular recognition and assembly constructs, primarily via host-guest interactions in water. In this review, recent progress in CD-based supramolecular nanoassemblies that are sensitive to chemical, biological, and physical stimuli is updated and reviewed, and intriguing examples of the biological functions of these nanoassemblies are presented, including pH- and redox-responsive drug and gene delivery, enzyme-activated specific cargo release, photoswitchable morphological interconversion, microtubular aggregation, and cell-cell communication, as well as a geomagnetism-controlled nanosystem for the suppression of tumor invasion and metastasis. Moreover, future perspectives and challenges in the fabrication of intelligent CD-based biofunctional materials are also discussed at the end of this review, which is expected to promote the translational development of these nanomaterials in the biomedical field.

Cyclodextrin-Based Multistimuli-Responsive Supramolecular Assemblies and Their Biological Functions.

Conventional thermosets are built by nonrenewable fossil resources and are arduous to be reprocessed, recycled, and reshaped due to their permanent covalent cross-linking, and their flammability makes them unsafe during use. Here, for the first time, we synthesized a novel Schiff base precursor from abundant and renewable lignin derivative vanillin and produced malleable thermosets (Schiff base covalent adaptable networks (CANs)) combining high performance, super-rapid reprocessability, excellent monomer recovery, and arbitrary permanent shape changeability as well as outstanding fire resistance. The Schiff base CANs exhibited high glass transition temperatures of ∼178 °C, tensile strength of ∼69 MPa, tensile modulus of ∼1925 MPa, excellent flame retardancy with UL-94 V0 rating and V1 rating, and high LOI of ∼30%. Meanwhile, three Schiff base CANs showed high malleability with the activation energy of the bond exchange of 49–81 kJ mol–1 and could be reprocessed in 2–10 min at 180 °C. These Schiff base CAN...

Robust, Fire-Safe, Monomer-Recovery, Highly Malleable Thermosets from Renewable Bioresources

Oxidative aromatic coupling occupies a fundamental place in the modern chemistry of aromatic compounds. It is a method of choice for the assembly of large and bewildering architectures. Considerable effort was also devoted to applications of the Scholl reaction for the synthesis of chiral biphenols and natural products. The ability to form biaryl linkages without any prefunctionalization provides an efficient pathway to many complex structures. Although the chemistry of this process is only now becoming fully understood, this reaction continues to both fascinate and challenge researchers. This is especially true for heterocoupling, that is, oxidative aromatic coupling with the chemoselective formation of a C-C bond between two different arenes. Analysis of the progress achieved in this field since 2013 reveals that many groups have contributed by pushing the boundary of structural possibilities, expanding into surface-assisted (cyclo)dehydrogenation, and developing new reagents.

Synthetic Applications of Oxidative Aromatic Coupling – from Biphenols to Nanographenes

Heating and cooling can induce reversible solid-to-liquid transitions of matter. In contrast, athermal photochemical processes can induce reversible solid-to-liquid transitions of some newly developed azobenzene compounds. Azobenzene is photoswitchable. UV light induces trans-to-cis isomerization; visible light or heat induces cis-to-trans isomerization. Trans and cis isomers usually have different melting points (Tm ) or glass transition temperatures (Tg ). If Tm or Tg of an azobenzene compound in trans and cis forms are above and below room temperature, respectively, light may induce reversible solid-to-liquid transitions. In this Review, we introduce azobenzene compounds that exhibit photoinduced reversible solid-to-liquid transitions, discuss the mechanisms and design principles, and show their potential applications in healable coatings, adhesives, transfer printing, lithography, actuators, fuels, and gas separation. Finally, we discuss remaining challenges in this field.

Photoinduced Reversible Solid-to-Liquid Transitions for Photoswitchable Materials

Polymers have become one of the largest and most important materials we use in daily life. Their popularity has stemmed from their wide range of material properties combined with their low cost of ...

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Recent Trends in Catalytic Polymerizations

We synthesized a novel green-light-responsive tetra-ortho-isopropoxy-substituted azobenzene (ipAzo). Cis-ipAzo forms a strong host-guest complex with γ-cyclo dextrin (γ-CD) whereas trans-ipAzo binds weakly. This new photoresponsive host-guest interaction is reverse to the well-known azobenzene (Azo)/α-cyclodextrin (α-CD) complex, which is strong only between trans-Azo and α-CD. By combining the UV-light-responsive Azo/α-CD and green-light-responsive ipAzo/γ-CD host-guest complexes, a photoresponsive orthogonal supramolecular system is developed.

A Photoresponsive Orthogonal Supramolecular Complex Based on Host–Guest Interactions

https://pubs.rsc.org/en/content/articlepdf/2017/py/c7py00436b

The living anionic polymerization of activated aziridines: a systematic study of reaction conditions and kinetics

https://pubs.rsc.org/en/content/articlepdf/2017/CC/C7CC03709K

Contorted polycyclic aromatic hydrocarbons with cove regions and zig-zag edges

Multi-amino-functional poly(propylene oxide) (PPO) copolymers were synthesized by the anionic ring-opening copolymerization (AROP) of N,N-diethyl glycidyl amine (DEGA) and propylene oxide (PO). A solvent free synthesis route using potassium counterions and crown ether for the AROP enabled controlled (co)polymerization with full conversion. The strategy provided access to PPO-b-PDEGA block copolymers, statistical PPO-co-PDEGA copolymers, and, for the first time, PDEGA homopolymer. Molecular weights in the range of 1400 to 4200 g/mol (Mn) and dispersities (Mw/Mn) below 1.1 were obtained. Both the kinetics and resulting microstructure of the statistical copolymerization were investigated by in situ 1H NMR spectroscopy, revealing reactivity ratios of rPO = 1.7 and rDEGA = 0.9. The polyethers exhibit thermoresponsive behavior in aqueous solution, showing cloud points in the range 14–57 °C under neutral conditions. Because of the amine groups, the copolymer structures are strongly affected by the pH of the solu...

Well-Defined Multi-Amino-Functional and Stimuli-Responsive Poly(propylene oxide) by Crown Ether Assisted Anionic Ring-Opening Polymerization

Thermoresponsive materials are currently discussed for applications, e.g., in drug delivery or sensor systems. While homopolymers exhibit a certain LCST, copolymers allow adjusting the cloud points depending on the comonomer ratio. We report on degradable poly(phosphester) (PPE) copolymers exhibiting LCSTs, which can be further tuned by reversible postmodification. A library of copolymers with different cloud points is obtained from a single “precursor polymer”. A novel furfuryl-carrying cyclic phosphate was designed, and different PPE copolymers were prepared via ring-opening polymerization with adjustable furan contents (up to 25 mol % were targeted and achieved) and molecular weights up to 40 000 g/mol (Đ < 1.25). Modification was achieved by a Diels–Alder reaction with maleimides of different hydrophilicity to further alter the solubility profile of the polymers. While the postmodification is thermally reversible, the biodegradable PPE backbone remains unaffected. This first report on the Diels–Alder ...

Manfred Wagner

Papers

A Photoresponsive Orthogonal Supramolecular Complex Based on Host–Guest Interactions

The living anionic polymerization of activated aziridines: a systematic study of reaction conditions and kinetics

Contorted polycyclic aromatic hydrocarbons with cove regions and zig-zag edges

Well-Defined Multi-Amino-Functional and Stimuli-Responsive Poly(propylene oxide) by Crown Ether Assisted Anionic Ring-Opening Polymerization

Multifunctional Poly(phosphoester)s for Reversible Diels–Alder Postmodification To Tune the LCST in Water