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Macrocyclic Receptors Synthesis, History, Binding Mechanism: An Update on Current Status
Published in Satish Kumar, Priya Ranjan Sahoo, Violet Rajeshwari Macwan, Jaspreet Kaur, Mukesh, Rachana Sahney, Macrocyclic Receptors for Environmental and Biosensing Applications, 2022
Satish Kumar, Priya Ranjan Sahoo, Violet Rajeshwari Macwan, Jaspreet Kaur, Mukesh, Rachana Sahney
Similarly, several literature studies are available which elucidate the synthesis and applications of catenanes (Coronado et al. 2009; Crowley et al. 2009; Evans and Beer 2014; Gil-Ramírez et al. 2015). The development of polyrotaxanes and polycatenanes, which consist of multiple macrocycles allowed the incorporation of unusual properties within such novel architectures. One interesting example of polycatenanes 82 based on cyclodextrin was reported recently by Higashi et al. (Higashi et al. 2019) through a one-pot synthetic method, which had more than 10 cyclodextrins attached to a poly(ethylene glycol)-poly(propylene glycol) copolymer core (Fig 1.29). The polycatenanes have a potential application in molecular machines, molecular actuators, switches materials of biological importance and as a drug delivery vehicle.
Synthesis, Structures, and Functions of Helical π-Conjugated Polymers
Published in Atsushi Nagai, Koji Takagi, Conjugated Objects, 2017
Hiromitsu Sogawa, Kazuko Nakazono, Toshikazu Takata
As described above, how to control the structure of π-conjugated helical polymers has been well studied. On the other hand, the dynamic helical property of π-conjugated helical polymers is attractive for supramolecular chemistry as the functional device and scaffold. Polymers having interlocked structures as key skeletons, that is, polyrotaxanes, promise the characteristic property owing to the unique mobility of the mechanical bond. Takata et al. have recently developed a class of side-chain-type polyrotaxane having π-conjugated helical polymers as the backbone. Rotaxane is one of the typical supramolecule studies as a molecular switch attribute to the shuttling property of the interlocked structure. The components, wheel and axle, essentially move relatively due to Brownian motion. Such a mobile property can be controlled by introducing interaction sites on the axle as the station for the wheel. Takata et al. took advantage of rotaxane’s characteristic properties to control polymer structures. A combination of a rotaxane switch and π-conjugated helical polymers achieved not only a rational control of the helical structure of the polymer but also the visualization of rotaxane’s switching behavior. Thus, they applied the conjugated helical polymers as the detector or amplifier of microscopic structural changes in molecules. The rotaxane side chains can switch the steric influence around the polymer main chain such as bulkiness and chirality by tuning the position of the wheel of the rotaxane moiety (Fig. 8.16).
Self-Healing Polymers
Published in Asit Baran Samui, Smart Polymers, 2022
Self-healing materials can be prepared by the terpolymerization of a phenylboronic acid-based monomer and an acrylamide (AAm) in the presence of a polyrotaxane derivative. The dynamic covalent bonds between the polyrotaxane derivative and the polymers are responsible for its flexibility and self-healing ability.25 Reversible covalent bonds allow the material to have both a “physical” self-healing ability and a “chemical” self-healing ability, even when they are reattached after complete separation. Further, self-healing is possible in both a dry and a wet state. The terpolymer film self-heals efficiently as it reaches approximately at 100% recovery within 30 min at 60°C under humid conditions.
Improvement of mechanical properties of elastic materials by chemical methods
Published in Science and Technology of Advanced Materials, 2020
Yukikazu Takeoka, Sizhe Liu, Fumio Asai
When a three-dimensional network with crosslinked polymer chains is synthesized by a random reaction between a monomer and a crosslinking agent, judging from the general reaction mechanism, the length and the number of polymer chains existing between the crosslinking points of the obtained three-dimensional network, the size and shape of the network are not constant (Figure 14)[42]. That is, the network structure of the elastomer that we have used so far does not consist of uniform length polymer chains between the crosslinking points, as shown in Figure 4(b). Therefore, when an external force is applied to deform an elastomer with a general chemical crosslinking structure, stress concentrates on the portion where the chain length between the cross-linking points is the shortest (Figure 15(a)). As a result, the elastomer breaks mechanically. Ito et al. succeeded in avoiding the concentration of stress on some chains during the deformation of the elastomer by introducing into the elastomer a molecular structure that allows the crosslinked portion to move freely [4,43]. The molecule used for that purpose is a polymer with a special structure called polyrotaxane (PR). Molecules that have a structure in which an axial molecule penetrates a cyclic molecule are called rotaxanes, and a bulky site is attached to both ends of the axial molecule so that the cyclic molecule does not escape (Figure 15(b)).In PR, a polymer chain is used as the axial molecule, and a large number of cyclic molecules can be included (Figure 15(c)). Reducing the number of cyclic molecules in PR can allow the cyclic molecules to move within PR. The best-known system among PRs is a PR synthesized by Harada et al. from linear polyethylene glycol (PEG) and cyclic α-cyclodextrin (α-CD) [44,45]. The rotaxane structure is formed simply by mixing solutions of PEG and α-CD in water, and a stable PR can be obtained by modifying both ends of PEG at bulky sites such as adamantane. Ito et al. succeeded in synthesizing gels with extremely flexible mechanical properties by crosslinking the α-CDs of PR (Figure 15(d)). The crosslinking sites generated by the bonding of the cyclic molecules produce a state in which it can move freely in the network. As a result, when the gel is deformed, the tension of the polymer chains moves to adopt a uniform state, and the nonuniformity of stress can be dispersed. Therefore, this PR gel exhibits mechanical flexibility.