Supramolecular systems for bioapplications: recent research progress in China

Light-Controlled Macrocyclic Supramolecular Assemblies and Luminescent Behaviors

“…For example, CB [7] encapsulated 6-bromoisoquinoline derivatives to perform cascade assembly with amphiphilic sulfonated calix [4]arenes (SC [4]A [4]) and SP, which can switch between macrocycle-confined induced room temperature phosphorescence and delay fluorescence. 35 When the assembly was irradiated with 254 nm light, SP gradually transformed into the phosphorescence energy transfer acceptor MC, the phosphorescence intensity of isoquinoline at 540 nm decreased significantly, and a delayed fluorescence peak appeared at 635 nm.…”

“…By regulating the release of protons, the affinity between the guest molecule and the macrocyclic host can be adjusted, further regulating assembly and disassembly. For example, the electrically neutral tetrakis-4-pyridylphenylethene cannot assemble with the amphiphilic sulfonated calix [4]arene (SC [4]A [8]) and exhibited characteristics of aggregated emission. 36 After the addition of the sulfonic-group-modified spiropyran (photoacid MEH), and under irradiation of 420 nm light, MEH gradually became a closed-ring SP and released protons, causing pyridine to protonate and form an assembly with SC[4]A [8] due to electrostatic interaction, and the fluorescence emission was also red-shifted to 540 nm.…”

“…Interestingly, anthracene conjugated two tripyridine and two dibenzo 24crown-8 as a bridge formed a linear assembly through complexation with Tb 3+ and Eu 3+ ions, which showed reversible on/off of lanthanide luminescence by the photooxidizing properties of anthracene, and the presence of the crown ethers can efficaciously prevent the effects of alkali and alkaline earth metal ions, thus better actualizing the reversible response of the lanthanide luminescence for the assembly (Figure 7). 54 Utilizing the photooxidation properties of anthracene, a supramolecular photolyzable system was constructed through tightly packed supramolecular assemblies of amphiphilic 9-alkoxy-substituted anthracene (AnPy) and psulfonatocalix [4]arene (SC4A) (K s = 4.22 × 10 5 M −1 ), in which AnPy was photoreactive and slowly decomposed to anthraquinone and alkanol under UV irradiation, and SC4A not only inhibited fluorescence quenching caused by AnPy self-aggregation but also facilitated photosensitization, and after the introduction of Eosin Y as an exogenous photosensitizer, the supramolecular assembly exhibited effective photolysis in the visible light. 55 The photodimerization of anthracene can cross-link and fix the assembly, enhancing the stability of the structure and imparting a wealth of properties to the supramolecular assemblies.…”

“…Supramolecular intelligent materials based on macrocycles have received more and more widespread attention because of not only their applications in cell imaging, targeted drug delivery, and information encryption, − but also their combinations with polymers and biomacromolecules through noncovalent interactions such as hydrogen bonding and π–π stacking to achieve tunable topological morphologies and crystalline states . Possessing the hydrophobic cavities and modifiable functional groups, macrocyclic hosts can selectively bond guest molecules with responsive units through host–guest interactions to form intelligent supramolecular assemblies, which display good reversibility and special chemical/physical features under external stimuli such as light, heat, electricity, and pH .…”

Pillarurilarenes: Glycoluril-Expanded Pillararenes

“…Highly specific molecular recognition of bioreceptors is often implemented by orthogonal noncovalent interactions of functional groups inside and around their binding pocket . The design and synthesis of novel macrocycles to achieve biomimetic molecular recognition and assembly are always pushing the development of macrocyclic and supramolecular chemistry . Host–guest complexation of current classic macrocyclic hosts with different guest molecules mostly depends on the hydrophobic cavity and functional groups attached to portals, which is often critiqued for lacking inside-cavity functional groups to achieve comparable recognition ability with bioreceptors .…”