Supramolecular polymer

Supramolecular polymers are a subset of polymers where the monomeric units are connected by reversible and highly directional secondary interactions–that is, non-covalent bonds. These non-covalent interactions include van der Waals interactions, hydrogen bonding, Coulomb or ionic interactions, π-π stacking, metal coordination, halogen bonding, chalcogen bonding, and host–guest interaction.^[1] Their behavior can be described by the theories of polymer physics) in dilute and concentrated solution, as well as in the bulk.^[2]

Additionally, some supramolecular polymers have distinctive characteristics,^[3][4][5] such as the ability to self-heal. Covalent polymers can be difficult to recycle, but supramolecular polymers may address this problem.^[6][7][8]

History

Monomeric motifs and types of interactions used for the preparation of supramolecular polymers

The preamble of the field of supramolecular polymers can be considered dye-aggregates and host-guest complexes.^[9] In early 19th century, it was noticed that dyes aggregate via "a special kind of polymerization". In 1988, Takuzo Aida, a Japanese polymer chemist, reported the concept of cofacial assembly wherein the amphiphilic porphyrin monomers are connected via van der Waals interaction forming one-dimensional architectures in solution, which can be considered as a prototype of supramolecular polymers.^[10] Soon thereafter, one-dimensional aggregates were described based on hydrogen bonding interaction in the crystalline state.^[11] With a different strategyusing hydrogen bonds, Jean M. J. Fréchet showed in 1989 that mesogenic molecules with carboxylic acid and pyridyl motifs, upon mixing in bulk, heterotropically dimerize to form a stable liquid crystalline structure.^[12] In 1990, Jean-Marie Lehn showed that this strategy can be expanded to form a new category of polymers, which he called "liquid crystalline supramolecular polymer" using complementary triple hydrogen bonding motifs in bulk.^[13] In 1993, M. Reza Ghadiri reported a nanotubular supramolecular polymer where a b-sheet-forming macrocyclic peptide monomer assembled together via multiple hydrogen bonding between adjacent macrocycles.^[14] In 1994, Anselm. C. Griffin showed an amorphous supramolecular material using a single hydrogen bond between a homotropic molecules having carboxylic acid and pyridine termini.^[15] The idea to make mechanically strong polymeric materials by 1D supramolecular association of small molecules requires a high association constant between the repeating building blocks. In 1997, E.W. "Bert" Meijer reported a telechelic monomer with ureidopyrimidinone termini as a "self-complementary" quadruple hydrogen bonding motif and demonstrated that the resulting supramolecular polymer in chloroform shows a temperature-dependent viscoelastic property in solution.^[16] This is the first demonstration that supramolecular polymers, when sufficiently mechanically robust, are physically entangled in solution.

Formation mechanisms

Monomers undergoing supramolecular polymerization are considered to be in equilibrium with the growing polymers, and thermodynamic factors therefore dominate the system.^[17] However, when the constituent monomers are connected via strong and multivalent interactions, a "metastable" kinetic state can dominate the polymerization. An externally supplied energy, in the form of heat in most cases, can transform the "metastable" state into a thermodynamically stable polymer. A clear understanding of multiple pathways exist in supramolecular polymerization is still under debate, however, the concept of "pathway complexity", introduced by E.W. "Bert" Meijer, shed a light on the kinetic behavior of supramolecular polymerization.^[18] Thereafter, many dedicated scientists are expanding the scope of "pathway complexity" because it can produce a variety of interesting assembled structures from the same monomeric units. Along this line of kinetically controlled processes, supramolecular polymers having "stimuli-responsive" ^[19] and "thermally bisignate" characteristics is also possible.^[20]

In conventional covalent polymerization, two models based on step-growth and chain-growth mechanisms are operative. Nowadays, a similar subdivision is acceptable for supramolecular polymerization; isodesmic also known as equal-K model (step-growth mechanism) and cooperative or nucleation-elongation model (chain-growth mechanism). A third category is seeded supramolecular polymerization, which can be considered as a special case of chain-growth mechanism.

Step-growth polymerization

Schematics of "pathway-complexity" and "chain-growth" mechanisms operative in supramolecular polymerization

Supramolecular equivalent of step-growth mechanism is commonly known as isodesmic or equal-K model (K represents the total binding interaction between two neighboring monomers). In isodesmic supramolecular polymerization, no critical temperature or concentration of monomers is required for the polymerization to occur and the association constant between polymer and monomer is independent of the polymer chain length. Instead, the length of the supramolecular polymer chains rises as the concentration of monomers in the solution increases, or as the temperature decreases. In conventional polycondensation, the association constant is usually large that leads to a high degree of polymerization; however, a byproduct is observed. In isodesmic supramolecular polymerization, due to non-covalent bonding, the association between monomeric units is weak, and the degree of polymerization strongly depends on the strength of interaction, i.e. multivalent interaction between monomeric units. For instance, supramolecular polymers consisting of bifunctional monomers having single hydrogen bonding donor/acceptor at their termini usually end up with low degree of polymerization, however those with quadrupole hydrogen bonding, as in the case of ureidopyrimidinone motifs, result in a high degree of polymerization. In ureidopyrimidinone-based supramolecular polymer, the experimentally observed molecular weight at semi-dilute concentrations is in the order of 10⁶ Dalton and the molecular weight of the polymer can be controlled by adding mono-functional chain-cappers.

Chain-growth polymerization

Conventional chain-growth polymerization involves at least two phases; initiation and propagation, while and in some cases termination and chain transfer phases also occur. Chain-growth supramolecular polymerization in a broad sense involves two distinct phases; a less favored nucleation and a favored propagation. In this mechanism, after the formation of a nucleus of a certain size, the association constant is increased, and further monomer addition becomes more favored, at which point the polymer growth is initiated. Long polymer chains will form only above a minimum concentration of monomer and below a certain temperature. However, to realize a covalent analogue of chain-growth supramolecular polymerization, a challenging prerequisite is the design of appropriate monomers that can polymerize only by the action of initiators. Recently one example of chain-growth supramolecular polymerization with "living" characteristics is demonstrated.^[21] In this case, a bowl-shaped monomer with amide-appended side chains form a kinetically favored intramolecular hydrogen bonding network and does not spontaneously undergo supramolecular polymerization at ambient temperatures.^[22] However, an N-methylated version of the monomer serves as an initiator by opening the intramolecular hydrogen bonding network for the supramolecular polymerization, just like ring-opening covalent polymerization. The chain end in this case remains active for further extension of supramolecular polymer and hence chain-growth mechanism allows for the precise control of supramolecular polymer materials.

Seeded polymerization

This is a special category of chain-growth supramolecular polymerization, where the monomer nucleates only in an early stage of polymerization to generate "seeds" and becomes active for polymer chain elongation upon further addition of a new batch of monomer. A secondary nucleation is suppressed in most of the case and thus possible to realize a narrow polydispersity of the resulting supramolecular polymer. In 2007, Ian Manners and Mitchell A. Winnik introduced this concept using a polyferrocenyldimethylsilane–polyisoprene diblock copolymer as the monomer, which assembles into cylindrical micelles.^[23] When a fresh feed of the monomer is added to the micellar "seeds" obtained by sonication, the polymerization starts in a living polymerization manner. They named this method as crystallization-driven self-assembly (CDSA) and is applicable to construct micron-scale supramolecular anisotropic structures in 1D–3D. A conceptually different seeded supramolecular polymerization was shown by Kazunori Sugiyasu in a porphyrin-based monomer bearing amide-appended long alkyl chains.^[24] At low temperature, this monomer preferentially forms spherical J-aggregates while fibrous H-aggregates at higher temperature. By adding a sonicated mixture of the J-aggregates ("seeds") into a concentrated solution of the J-aggregate particles, long fibers can be prepared via living seeded supramolecular polymerization. Frank Würthner achieved similar seeded supramolecular polymerization of amide functionalized perylene bisimide as monomer.^[25] Importantly, the seeded supramolecular polymerization is also applicable to prepare supramolecular block copolymers.

Examples

Hydrogen bonding interaction

Monomers capable of forming single, double, triple or quadruple hydrogen bonding has been utilized for making supramolecular polymers, and increased association of monomers obviously possible when monomers have maximum number of hydrogen bonding donor/acceptor motifs. For instance, ureidopyrimidinone-based monomer with self-complementary quadruple hydrogen bonding termini polymerized in solution, accordingly with the theory of conventional polymers and displayed a distinct viscoelastic nature at ambient temperatures.

π-π stacking

Monomers with aromatic motifs such as bis(merocyanine), oligo(para-phenylenevinylene) (OPV), perylene bisimide (PBI) dye, cyanine dye, corannulene and nano-graphene derivatives have been employed to prepare supramolecular polymers. In some cases, hydrogen bonding side chains appended onto the core aromatic motif help to hold the monomer strongly in the supramolecular polymer. A notable system in this category is a nanotubular supramolecular polymer formed by the supramolecular polymerization of amphiphilic hexa-peri-hexabenzocoronene (HBC) derivatives.^[26] Generally, nanotubes are categorized as 1D objects morphologically, however, their walls adopt a 2D geometry and therefore require a different design strategy.^[27] HBC amphiphiles in polar solvents solvophobically assemble into a 2D bilayer membrane, which roles up into a helical tape or a nanotubular polymer. Conceptually similar amphiphilic design based on cyanine dye and zinc chlorin dye also polymerize in water resulting in nanotubular supramolecular polymers.^[28][29]

Host-guest interaction

A variety of supramolecular polymers can be synthesized by using monomers with host-guest complementary binding motifs, such as crown ethers/ammonium ions, cucurbiturils/viologens, calixarene/viologens, cyclodextrins/adamantane derivatives, and pillar arene/imidazolium derivatives [30–33].^[30][31][32] When the monomers are "heteroditopic", supramolecular copolymers results, provided the monomers does not homopolymerize. Akira Harada was one of the firstwhorecognize the importance of combining polymers and cyclodextrins.^[33] Feihe Huang showed an example of supramolecular alternating copolymer from two heteroditopic monomers carrying both crown ether and ammonium ion termini.^[34] Takeharo Haino demonstrated an extreme example of sequence control in supramolecular copolymer, where three heteroditopic monomers are arranged in an ABC sequence along the copolymer chain.^[35] The design strategy utilizing three distinct binding interactions; ball-and-socket (calix[5]arene/C60), donor-acceptor (bisporphyrin/trinitrofluorenone), and Hamilton's H-bonding interactions is the key to attain a high orthogonality to form an ABC supramolecular terpolymer.

Chirality

Stereochemical information of a chiral monomer can be expressed in a supramolecular polymer.^[36] Helical supramolecular polymer with P-and M-conformation are widely seen, especially those composed of disc-shaped monomers. When the monomers are achiral, both P-and M-helices are formed in equal amounts. When the monomers are chiral, typically due to the presence of one or more stereocenters in the side chains, the diastereomeric relationship between P- and M-helices leads to the preference of one conformation over the other. Typical example is a C₃-symmetric disk-shaped chiral monomer that forms helical supramolecular polymers via the "majority rule". A slight excess of one enantiomer of the chiral monomer resulted in a strong bias to either the right-handed or left-handed helical geometry at the supramolecular polymer level.^[37] In this case, a characteristic nonlinear dependence of the anisotropic factor, g, on the enantiomeric excess of a chiral monomer can be generally observed. Like in small molecule based chiral system, chirality of a supramolecular polymer also affected by chiral solvents. Some application such as a catalyst for asymmetric synthesis ^[38] and circular polarized luminescence are observed in chiral supramolecular polymers too.

Copolymers

A copolymer is formed from more than one monomeric species. Advanced polymerization techniques have been established for the preparation of covalent copolymers, however supramolecular copolymers are still in its infancy and is slowly progressing. In recent years, all plausible category of supramolecular copolymers such as random, alternating, block, blocky, or periodic has been demonstrated in a broad sense.^[39]

Properties

Supramolecular polymers are the subject of research in academia and industry.

Reversibility and dynamicity

The stability of a supramolecular polymer can be described using the association constant, K_ass. When K_ass ≤ 10⁴M⁻¹, the polymeric aggregates are typically small in size and do not show any interesting properties and when K_ass≥ 10¹⁰ M⁻¹, the supramolecular polymer behaves just like covalent polymers due to the lack of dynamics. So, an optimum K_ass = 10⁴–10¹⁰M⁻¹need to be attained for producing functional supramolecular polymers. The dynamics and stability of the supramolecular polymers often affect by the influence of additives (e.g. co-solvent or chain-capper). When a good solvent, for instance chloroform, is added to a supramolecular polymer in a poor solvent, for instance heptane, the polymer disassembles. However, in some cases, cosolvents contribute the stabilization/destabilization of supramolecular polymer. For instance, supramolecular polymerization of a hydrogen bonding porphyrin-based monomer in a hydrocarbon solvent containing a minute amount of a hydrogen bond scavenging alcohol shows distinct pathways, i.e. polymerization favored both by cooling as well as heating, and is known as "thermally bisignate supramolecular polymerization". In another example, minute amounts of molecularly dissolved water molecules in apolar solvents, like methylcyclohexane, become part of the supramolecular polymer at lower temperatures, due to specific hydrogen bonding interaction between the monomer and water.^[40]

Self-healing

Supramolecular polymers may be relevant to self-healing materials.^[41] A supramolecular rubber based on vitrimers can self-heal simply by pressing the two broken edges of the material together.^[42] High mechanical strength of a material and self-healing ability are generally mutually exclusive. Thus, a glassy material that can self-heal at room temperature remained a challenge until recently. A supramolecularly polymer based on ether-thiourea is mechanically robust (e= 1.4 GPa) but can self-heal at room temperature by a compression at the fractured surfaces.^[43] The invention of self-healable polymer glass updated the preconception that only soft rubbery materials can heal.

Examples of hydrogen-bonding based self-healing 'supramolecular rubber' (a) and 'polymer glass' (b).

Another strategy uses a bivalent poly(isobutylene)s (PIBs) functionalized with barbituric acid at head and tail.^[44] Multiple hydrogen bonding existed between the carbonyl group and amide group of barbituric acid enable it to form a supramolecular network. In this case, the snipped small PIBs-based disks can recover itself from mechanical damage after several-hour contact at room temperature.

Interactions between catechol and ferric ions exhibit pH-controlled self-healing supramolecular polymers.^[45] The formation of mono-, bis- and triscatehchol-Fe³⁺ complexes can be manipulated by pH, of which the bis- and triscatehchol-Fe³⁺ complexes show elastic moduli as well as self-healing capacity. For example, the triscatehchol-Fe³⁺ can restore its cohesiveness and shape after being torn. Chain-folding polyimide and pyrenyl-end-capped chains give rise to supramolecular networks.^[46]

Optoelectronic

By incorporating electron donors and electron acceptors into the supramolecular polymers, features of artificial photosynthesis can be replicated.^[47][2]

Biocompatible

DNA is a major example of a supramolecular polymer.^[48] protein^[49] Much effort has been develoted to related but synthetic materials.^[50] At the same time, their reversible and dynamic nature make supramolecular polymers bio-degradable,^[51][52] which surmounts hard-to-degrade issue of covalent polymers and makes supramolecular polymers a promising platform for biomedical applications. Being able to degrade in biological environment lowers potential toxicity of polymers to a great extent and therefore, enhances biocompatibility of supramolecular polymers.^[53][54]

Biomedical applications

With the excellent nature in biodegradation and biocompatibility, supramolecular polymers show great potential in the development of drug delivery, gene transfection and other biomedical applications.^[50]

Drug delivery: Multiple cellular stimuli could induce responses in supramolecular polymers.^[55][56][50] The dynamic molecular skeletons of supramolecular polymers can be depolymerized when exposing to the external stimuli like pH in vivo. On the basis of this property, supramolecular polymers are capable of being a drug carrier. Making use of hydrogen bonding between nucleobases to induce self-assemble into pH-sensitive spherical micelles.

Gene transfection: Effective and low-toxic nonviral cationic vectors are highly desired in the field of gene therapy.^[50] On account of the dynamic and stimuli-responsive properties, supramolecular polymers offer a cogent platform to construct vectors for gene transfection. By combining ferrocene dimer with β-cyclodextrin dimer, a redox-control supramolecular polymers system has been proposed as a vector. In COS-7 cells, this supramolecular polymersic vector can release enclosed DNA upon exposing to hydrogen peroxide and achieve gene transfection.^[57]

Adjustable mechanical properties

Association and dissociation kinetics for polymer dynamics

1. Basic Principle : Noncovalent interactions between polymer molecules significantly affect the mechanical properties of supramolecular polymers. More interaction between polymers tends to enhance the interaction strength between polymers. The association rate and dissociation rate of interacting groups in polymer molecules determine intermolecular interaction strength. For supramolecular polymers, the dissociation kinetics for dynamic networks plays a critical role in the material design and mechanical properties of the SPNs(supramolecular polymer networks).^[58] By changing the dissociation rate of polymer crosslink dynamics, supramolecular polymers have adjustable mechanical properties. With a slow dissociation rate for dynamic networks of supramolecular polymers, glass-like mechanical properties are dominant, on the other hand, rubber-like mechanical properties are dominant for a fast dissociation rate. These properties can be obtained by changing the molecular structure of the crosslink part of the molecule.
2. Experimental examples : One research controlled the molecular design of cucurbit[8]uril, CB[8]. The hydrophobic structure of the second guest of CB-mediated host-guest interaction within its molecular structure can tune the dissociative kinetics of the dynamic crosslinks. To slow the dissociation rate (kd), a stronger enthalpic driving force is needed for the second guest association (ka) to release more of the conformationally restricted water from the CB(8] cavity.^[59] In other words, the hydrophobic second guest exhibited the highest Keq and lowest kd values. Therefore, by polymerizing different concentrations of polymer subgroups, different dynamics of the intermolecular network can be designed.For example, mechanical properties like compressive strain can be tuned by this process. Polymerized with different hydrophobic subgroups in CB[B], The compressive strength was found to increase across the series in correlation with a decrease of kd, which could be tuned between 10–100MPa.^[60] NVI, is the most hydrophobic subgroup structure of monomer which have two benzene rings, on the other hand, BVI is the least hydrophobic subgroup structure of monomer via control group. Besides, varying concentrations of hydrophobic subgroups in CB[B], polymerized molecules show different compressive properties. Polymers with the highest concentration of hydrophobic subgroups show the highest compressive strain and vice versa.

Biomaterials

Supramolecular polymers can simultaneously meet the requirements of aqueous compatibility, bio-degradability, biocompatibility, stimuli-responsiveness and other strict criterion.^[50] Consequently, supramolecular polymers could be applicable to the biomedical fields.

The reversible nature of supramolecular polymers can produce biomaterials that can sense and respond to physiological cues, or that mimic the structural and functional aspects of biological signaling.^[61]

Protein delivery,^[62][63] bio-imaging and diagnosis^[64][65] and tissue engineering,^[66][67] are also well developed.

Further reading

• Biswas S, Kinbara K, Oya N, Ishii N, Taguchi H, Aida T (June 2009). "A tubular biocontainer: metal ion-induced 1D assembly of a molecularly engineered chaperonin". Journal of the American Chemical Society. 131 (22): 7556–7557. doi:10.1021/ja902696q. PMID 19489642.<
• Kato T, Kondo G, Hanabusa K (March 1998). "Thermoreversible Self-Organized Gels of a Liquid Crystal Formed by Aggregation of trans-1,2-Bis(acylamino)cyclohexane Containing a Mesogenic Moiety". Chemistry Letters. 27 (3): 193–194. doi:10.1246/cl.1998.193. ISSN 0366-7022.
• Yano K, Itoh Y, Araoka F, Watanabe G, Hikima T, Aida T (January 2019). "Nematic-to-columnar mesophase transition by in situ supramolecular polymerization". Science. 363 (6423): 161–165. Bibcode:2019Sci...363..161Y. doi:10.1126/science.aan1019. PMID 30630928.

References

1. Brunsveld L, Folmer BJ, Meijer EW, Sijbesma RP (December 2001). "Supramolecular polymers". Chemical Reviews. 101 (12): 4071–4098. doi:10.1021/cr990125q. PMID 11740927.
2. De Greef TF, Smulders MM, Wolffs M, Schenning AP, Sijbesma RP, Meijer EW (November 2009). "Supramolecular polymerization". Chemical Reviews. 109 (11): 5687–5754. doi:10.1021/cr900181u. PMID 19769364.
3. Aida T, Meijer EW, Stupp SI (February 2012). "Functional supramolecular polymers". Science. 335 (6070): 813–817. Bibcode:2012Sci...335..813A. doi:10.1126/science.1205962. PMC 3291483. PMID 22344437.
4. Aida T (May 2020). "On Supramolecular Polymerization: Interview with Takuzo Aida". Advanced Materials. 32 (20): e1905445. doi:10.1002/adma.201905445. PMID 31867791.
5. Aida T, Meijer EW (January 2020). "Supramolecular Polymers – we've Come Full Circle". Israel Journal of Chemistry. 60 (1–2): 33–47. doi:10.1002/ijch.201900165. ISSN 0021-2148.
6. Hashim PK, Bergueiro J, Meijer EW, Aida T (2020-06-01). "Supramolecular Polymerization: A Conceptual Expansion for Innovative Materials". Progress in Polymer Science. 105: 101250. doi:10.1016/j.progpolymsci.2020.101250. ISSN 0079-6700.
7. Amabilino DB, Smith DK, Steed JW (May 2017). "Supramolecular materials" (PDF). Chemical Society Reviews. 46 (9): 2404–2420. doi:10.1039/c7cs00163k. PMID 28443937. S2CID 206086133.
8. Yang L, Tan X, Wang Z, Zhang X (August 2015). "Supramolecular Polymers: Historical Development, Preparation, Characterization, and Functions". Chemical Reviews. 115 (15): 7196–7239. doi:10.1021/cr500633b. PMID 25768045.
9. Wehner M, Würthner F (2019-12-21). "Supramolecular polymerization through kinetic pathway control and living chain growth". Nature Reviews Chemistry. 4 (1): 38–53. doi:10.1038/s41570-019-0153-8. ISSN 2397-3358. S2CID 209432740.
10. Aida T, Takemura A, Fuse M, Inoue S (1988). "Synthesis of a novel amphiphilic porphyrin carrying water-soluble polyether side chains of controlled chain length. Formation of a cofacial molecular assembly in aqueous media". Journal of the Chemical Society, Chemical Communications (5): 391. doi:10.1039/c39880000391. ISSN 0022-4936.
11. Ducharme Y, Wuest JD (November 1988). "Use of hydrogen bonds to control molecular aggregation. Extensive, self-complementary arrays of donors and acceptors". The Journal of Organic Chemistry. 53 (24): 5787–5789. doi:10.1021/jo00259a037. ISSN 0022-3263.
12. Kato T, Takashi JM (October 1989). "A new approach to mesophase stabilization through hydrogen bonding molecular interactions in binary mixtures". Journal of the American Chemical Society. 111 (22): 8533–8534. doi:10.1021/ja00204a044. ISSN 0002-7863.
13. Fouquey C, Lehn JM, Levelut AM (May 1990). "Molecular recognition directed self-assembly of supramolecular liquid crystalline polymers from complementary chiral components". Advanced Materials. 2 (5): 254–257. doi:10.1002/adma.19900020506. ISSN 0935-9648.
14. Ghadiri MR, Granja JR, Milligan RA, McRee DE, Khazanovich N (November 1993). "Self-assembling organic nanotubes based on a cyclic peptide architecture". Nature. 366 (6453): 324–327. Bibcode:1993Natur.366..324G. doi:10.1038/366324a0. PMID 8247126. S2CID 4367103.
15. Lee CM, Jariwala CP, Griffin AC (October 1994). "Heteromeric liquid-crystalline association chain polymers: structure and properties". Polymer. 35 (21): 4550–4554. doi:10.1016/0032-3861(94)90801-x. ISSN 0032-3861.
16. Sijbesma RP, Beijer FH, Brunsveld L, Folmer BJ, Hirschberg JH, Lange RF, et al. (November 1997). "Reversible polymers formed from self-complementary monomers using quadruple hydrogen bonding" (PDF). Science. 278 (5343): 1601–1604. Bibcode:1997Sci...278.1601S. doi:10.1126/science.278.5343.1601. PMID 9374454.
17. Sorrenti A, Leira-Iglesias J, Markvoort AJ, de Greef TF, Hermans TM (September 2017). "Non-equilibrium supramolecular polymerization". Chemical Society Reviews. 46 (18): 5476–5490. doi:10.1039/c7cs00121e. PMC 5708531. PMID 28349143.
18. Korevaar PA, George SJ, Markvoort AJ, Smulders MM, Hilbers PA, Schenning AP, et al. (January 2012). "Pathway complexity in supramolecular polymerization". Nature. 481 (7382): 492–496. Bibcode:2012Natur.481..492K. doi:10.1038/nature10720. PMID 22258506. S2CID 4412624.
19. Jain A, Dhiman S, Dhayani A, Vemula PK, George SJ (January 2019). "Chemical fuel-driven living and transient supramolecular polymerization". Nature Communications. 10 (1): 450. Bibcode:2019NatCo..10..450J. doi:10.1038/s41467-019-08308-9. PMC 6347607. PMID 30683874.
20. Venkata Rao K, Miyajima D, Nihonyanagi A, Aida T (November 2017). "Thermally bisignate supramolecular polymerization". Nature Chemistry. 9 (11): 1133–1139. Bibcode:2017NatCh...9.1133V. doi:10.1038/nchem.2812. PMID 29064499.
21. Kang J, Miyajima D, Mori T, Inoue Y, Itoh Y, Aida T (February 2015). "Noncovalent assembly. A rational strategy for the realization of chain-growth supramolecular polymerization". Science. 347 (6222): 646–651. Bibcode:2015Sci...347..646K. doi:10.1126/science.aaa4249. PMID 25657246. S2CID 8487579.
22. Kang J, Miyajima D, Itoh Y, Mori T, Tanaka H, Yamauchi M, et al. (July 2014). "C₅-symmetric chiral corannulenes: desymmetrization of bowl inversion equilibrium via "intramolecular" hydrogen-bonding network". Journal of the American Chemical Society. 136 (30): 10640–10644. doi:10.1021/ja505941b. PMID 25046475.
23. Wang X, Guerin G, Wang H, Wang Y, Manners I, Winnik MA (August 2007). "Cylindrical block copolymer micelles and co-micelles of controlled length and architecture". Science. 317 (5838): 644–647. Bibcode:2007Sci...317..644W. doi:10.1126/science.1141382. PMID 17673656. S2CID 10616507.
24. Ogi S, Sugiyasu K, Manna S, Samitsu S, Takeuchi M (March 2014). "Living supramolecular polymerization realized through a biomimetic approach". Nature Chemistry. 6 (3): 188–195. Bibcode:2014NatCh...6..188O. doi:10.1038/nchem.1849. PMID 24557132. S2CID 205292495.
25. Wagner W, Wehner M, Stepanenko V, Ogi S, Würthner F (December 2017). "Living Supramolecular Polymerization of a Perylene Bisimide Dye into Fluorescent J-Aggregates". Angewandte Chemie. 56 (50): 16008–16012. doi:10.1002/anie.201709307. PMID 29035005.
26. Hill JP, Jin W, Kosaka A, Fukushima T, Ichihara H, Shimomura T, et al. (June 2004). "Self-assembled hexa-peri-hexabenzocoronene graphitic nanotube". Science. 304 (5676): 1481–1483. Bibcode:2004Sci...304.1481H. doi:10.1126/science.1097789. PMID 15178796. S2CID 39674411.
27. Shimizu T, Masuda M, Minamikawa H (April 2005). "Supramolecular nanotube architectures based on amphiphilic molecules". Chemical Reviews. 105 (4): 1401–1443. doi:10.1021/cr030072j. PMID 15826016.
28. Eisele DM, Cone CW, Bloemsma EA, Vlaming SM, van der Kwaak CG, Silbey RJ, et al. (July 2012). "Utilizing redox-chemistry to elucidate the nature of exciton transitions in supramolecular dye nanotubes" (PDF). Nature Chemistry. 4 (8): 655–662. Bibcode:2012NatCh...4..655E. doi:10.1038/nchem.1380. PMID 22824898. S2CID 878082.
29. Sengupta S, Ebeling D, Patwardhan S, Zhang X, von Berlepsch H, Böttcher C, et al. (June 2012). "Biosupramolecular nanowires from chlorophyll dyes with exceptional charge-transport properties". Angewandte Chemie. 51 (26): 6378–6382. doi:10.1002/anie.201201961. PMID 22644905.
30. Shi X, Zhang X, Ni XL, Zhang H, Wei P, Liu J, et al. (November 2019). "Supramolecular Polymerization with Dynamic Self-Sorting Sequence Control 0". Macromolecules. 52 (22): 8814–8825. Bibcode:2019MaMol..52.8814S. doi:10.1021/acs.macromol.9b02010. S2CID 209711431.
31. Qian H, Guo DS, Liu Y (April 2012). "Cucurbituril-modulated supramolecular assemblies: from cyclic oligomers to linear polymers". Chemistry: A European Journal. 18 (16): 5087–5095. doi:10.1002/chem.201101904. PMID 22407677.
32. Pappalardo S, Villari V, Slovak S, Cohen Y, Gattuso G, Notti A, et al. (2007-10-05). "Counterion-dependent proton-driven self-assembly of linear supramolecular oligomers based on amino-calix[5]arene building blocks". Chemistry: A European Journal. 13 (29): 8164–8173. doi:10.1002/chem.200601785. PMID 17639537.
33. Deng W, Yamaguchi H, Takashima Y, Harada A (2007-07-02). "A chemical-responsive supramolecular hydrogel from modified cyclodextrins". Angewandte Chemie. 46 (27): 5144–5147. doi:10.1002/anie.200701272. PMID 17526038.
34. Wang F, Han C, He C, Zhou Q, Zhang J, Wang C, et al. (August 2008). "Self-sorting organization of two heteroditopic monomers to supramolecular alternating copolymers". Journal of the American Chemical Society. 130 (34): 11254–11255. doi:10.1021/ja8035465. PMID 18680368.
35. Hirao T, Kudo H, Amimoto T, Haino T (September 2017). "Sequence-controlled supramolecular terpolymerization directed by specific molecular recognitions". Nature Communications. 8 (1): 634. Bibcode:2017NatCo...8..634H. doi:10.1038/s41467-017-00683-5. PMC 5608752. PMID 28935856.
36. Yashima E, Ousaka N, Taura D, Shimomura K, Ikai T, Maeda K (November 2016). "Supramolecular Helical Systems: Helical Assemblies of Small Molecules, Foldamers, and Polymers with Chiral Amplification and Their Functions". Chemical Reviews. 116 (22): 13752–13990. doi:10.1021/acs.chemrev.6b00354. PMID 27754649.
37. van Gestel J, Palmans AR, Titulaer B, Vekemans JA, Meijer EW (April 2005). ""Majority-rules" operative in chiral columnar stacks of C3-symmetrical molecules". Journal of the American Chemical Society. 127 (15): 5490–5494. doi:10.1021/ja0501666. PMID 15826186.
38. Shen Z, Sang Y, Wang T, Jiang J, Meng Y, Jiang Y, et al. (September 2019). "Asymmetric catalysis mediated by a mirror symmetry-broken helical nanoribbon". Nature Communications. 10 (1): 3976. Bibcode:2019NatCo..10.3976S. doi:10.1038/s41467-019-11840-3. PMC 6726595. PMID 31484928.
39. Adelizzi B, Van Zee NJ, de Windt LN, Palmans AR, Meijer EW (April 2019). "Future of Supramolecular Copolymers Unveiled by Reflecting on Covalent Copolymerization" (PDF). Journal of the American Chemical Society. 141 (15): 6110–6121. doi:10.1021/jacs.9b01089. PMID 30889358.
40. Van Zee NJ, Adelizzi B, Mabesoone MF, Meng X, Aloi A, Zha RH, et al. (June 2018). "Potential enthalpic energy of water in oils exploited to control supramolecular structure" (PDF). Nature. 558 (7708): 100–103. Bibcode:2018Natur.558..100V. doi:10.1038/s41586-018-0169-0. PMID 29849144. S2CID 44075506.
41. Herbst F, Döhler D, Michael P, Binder WH (February 2013). "Self-healing polymers via supramolecular forces". Macromolecular Rapid Communications. 34 (3): 203–220. doi:10.1002/marc.201200675. PMID 23315930.
42. Cordier P, Tournilhac F, Soulié-Ziakovic C, Leibler L (February 2008). "Self-healing and thermoreversible rubber from supramolecular assembly". Nature. 451 (7181): 977–980. Bibcode:2008Natur.451..977C. doi:10.1038/nature06669. PMID 18288191. S2CID 205212362.
43. Yanagisawa Y, Nan Y, Okuro K, Aida T (January 2018). "Mechanically robust, readily repairable polymers via tailored noncovalent cross-linking". Science. 359 (6371): 72–76. Bibcode:2018Sci...359...72Y. doi:10.1126/science.aam7588. PMID 29242235.
44. Herbst F, Seiffert S, Binder WH (2012). "Dynamic supramolecular poly(isobutylene)s for self-healing materials". Polymer Chemistry. 3 (11): 3084–3092. doi:10.1039/C2PY20265D.
45. Holten-Andersen N, Harrington MJ, Birkedal H, Lee BP, Messersmith PB, Lee KY, Waite JH (February 2011). "pH-induced metal-ligand cross-links inspired by mussel yield self-healing polymer networks with near-covalent elastic moduli". Proceedings of the National Academy of Sciences of the United States of America. 108 (7): 2651–2655. Bibcode:2011PNAS..108.2651H. doi:10.1073/pnas.1015862108. PMC 3041094. PMID 21278337.
46. Burattini S, Colquhoun HM, Fox JD, Friedmann D, Greenland BW, Harris PJ, et al. (November 2009). "A self-repairing, supramolecular polymer system: healability as a consequence of donor-acceptor pi-pi stacking interactions". Chemical Communications. 44 (44): 6717–6719. doi:10.1039/B910648K. PMID 19885456.
47. Peurifoy SR, Guzman CX, Braunschweig AB (2015). "Topology, assembly, and electronics: three pillars for designing supramolecular polymers with emergent optoelectronic behavior". Polymer Chemistry. 6 (31): 5529–5539. doi:10.1039/C5PY00420A.
48. Watson JD, Crick FH (April 1953). "Molecular structure of nucleic acids; a structure for deoxyribose nucleic acid". Nature. 171 (4356): 737–738. Bibcode:1953Natur.171..737W. doi:10.1038/171737a0. PMID 13054692. S2CID 4253007.
49. Pauling L, Corey RB, Branson HR (April 1951). "The structure of proteins; two hydrogen-bonded helical configurations of the polypeptide chain". Proceedings of the National Academy of Sciences of the United States of America. 37 (4): 205–211. Bibcode:1951PNAS...37..205P. doi:10.1073/pnas.37.4.205. PMC 1063337. PMID 14816373.
50. Dong R, Zhou Y, Huang X, Zhu X, Lu Y, Shen J (January 2015). "Functional supramolecular polymers for biomedical applications". Advanced Materials. 27 (3): 498–526. doi:10.1002/adma.201402975. PMID 25393728. S2CID 205257015.
51. Lim YB, Moon KS, Lee M (April 2009). "Recent advances in functional supramolecular nanostructures assembled from bioactive building blocks". Chemical Society Reviews. 38 (4): 925–934. doi:10.1039/b809741k. PMID 19421572.
52. Petkau-Milroy K, Brunsveld L (January 2013). "Supramolecular chemical biology; bioactive synthetic self-assemblies". Organic & Biomolecular Chemistry. 11 (2): 219–232. doi:10.1039/C2OB26790J. PMID 23160566.
53. Li J, Li X, Ni X, Wang X, Li H, Leong KW (August 2006). "Self-assembled supramolecular hydrogels formed by biodegradable PEO-PHB-PEO triblock copolymers and alpha-cyclodextrin for controlled drug delivery". Biomaterials. 27 (22): 4132–4140. doi:10.1016/j.biomaterials.2006.03.025. PMID 16584769.
54. Appel EA, del Barrio J, Loh XJ, Scherman OA (September 2012). "Supramolecular polymeric hydrogels". Chemical Society Reviews. 41 (18): 6195–6214. doi:10.1039/c2cs35264h. PMID 22890548.
55. Yan X, Wang F, Zheng B, Huang F (September 2012). "Stimuli-responsive supramolecular polymeric materials". Chemical Society Reviews. 41 (18): 6042–6065. doi:10.1039/c2cs35091b. PMID 22618080.
56. Ma X, Tian H (July 2014). "Stimuli-responsive supramolecular polymers in aqueous solution". Accounts of Chemical Research. 47 (7): 1971–1981. doi:10.1021/ar500033n. PMID 24669851.
57. Dong R, Su Y, Yu S, Zhou Y, Lu Y, Zhu X (October 2013). "A redox-responsive cationic supramolecular polymer constructed from small molecules as a promising gene vector". Chemical Communications. 49 (84): 9845–9847. doi:10.1039/C3CC46123H. PMID 24030731.
58. Seiffert S, Sprakel J (January 2012). "Physical chemistry of supramolecular polymer networks". Chemical Society Reviews. 41 (2): 909–930. doi:10.1039/c1cs15191f. PMID 21909565.
59. Huang Z, Chen X, Wu G, Metrangolo P, Whitaker D, McCune JA, Scherman OA (April 2020). "Host-Enhanced Phenyl-Perfluorophenyl Polar-π Interactions". Journal of the American Chemical Society. 142 (16): 7356–7361. doi:10.1021/jacs.0c02275. PMC 7181256. PMID 32248683.
60. Huang Z, Chen X, O'Neill SJ, Wu G, Whitaker DJ, Li J, et al. (January 2022). "Highly compressible glass-like supramolecular polymer networks". Nature Materials. 21 (1): 103–109. Bibcode:2022NatMa..21..103H. doi:10.1038/s41563-021-01124-x. PMID 34819661. S2CID 244532641.
61. Hartgerink JD, Beniash E, Stupp SI (November 2001). "Self-assembly and mineralization of peptide-amphiphile nanofibers". Science. 294 (5547): 1684–1688. Bibcode:2001Sci...294.1684H. doi:10.1126/science.1063187. PMID 11721046. S2CID 19210828.
62. Kameta N, Masuda M, Mizuno G, Morii N, Shimizu T (May 2008). "Supramolecular nanotube endo sensing for a guest protein". Small. 4 (5): 561–565. doi:10.1002/smll.200700710. PMID 18384039.
63. Kameta N, Yoshida K, Masuda M, Shimizu T (2009). "Supramolecular Nanotube Hydrogels: Remarkable Resistance Effect of Confined Proteins to Denaturants". Chemistry of Materials. 21 (24): 5892–5898. doi:10.1021/cm903108h.
64. Janib SM, Moses AS, MacKay JA (August 2010). "Imaging and drug delivery using theranostic nanoparticles". Advanced Drug Delivery Reviews. 62 (11): 1052–1063. doi:10.1016/j.addr.2010.08.004. PMC 3769170. PMID 20709124.
65. Barreto JA, O'Malley W, Kubeil M, Graham B, Stephan H, Spiccia L (March 2011). "Nanomaterials: applications in cancer imaging and therapy". Advanced Materials. 23 (12): H18–H40. doi:10.1002/adma.201100140. PMID 21433100. S2CID 205239939.
66. Shah RN, Shah NA, Del Rosario Lim MM, Hsieh C, Nuber G, Stupp SI (February 2010). "Supramolecular design of self-assembling nanofibers for cartilage regeneration". Proceedings of the National Academy of Sciences of the United States of America. 107 (8): 3293–3298. doi:10.1073/pnas.0906501107. PMC 2840471. PMID 20133666.
67. Dankers PY, Harmsen MC, Brouwer LA, van Luyn MJ, Meijer EW (July 2005). "A modular and supramolecular approach to bioactive scaffolds for tissue engineering". Nature Materials. 4 (7): 568–574. Bibcode:2005NatMa...4..568D. doi:10.1038/nmat1418. PMID 15965478. S2CID 17464761.