Supramolecular Polymer Chains Research Articles

Supramolecular Helical Polymer Formed Via Complementary Dimerization of Bisporphyrin Cleft

We have been developing supramolecular polymers directed by unique host-guest motifs.1,2 During study, a tetrakisporphyrin monomer was discovered to form the supramolecular helical polymers.3,4 A lack of chirality resulted in the racemic mixture of the supramolecular helical polymers. In this presentation, we report that the chirally-twisted pseudo macrocyclic tetrakisporphyrin monomer is self-assembled to form the one-handed helical supramolecular structures. Two amino acid side chains were installed at the termini of a tetrakisporphyrin monomer. The intramolecular antiparallel hydrogen bonding between the amino acid side chains resulted in the pseudo macrocyclic conformation, which was chirally-twisted. The right-handed and left-handed conformations of the pseudo macrocyclic monomer are determined by the absolute configuration of the stereogenic centers. The chirally-twisted pseudo macrocyclic monomer was self-assembled to result in the one-handed helical structures with very high association constants. The well-developed supramolecular chains generated entangled polymer solution, which suggests the formation of the well-developed long supramolecular polymer chains. Atomic force microscopy visualized the long supramolecular polymer chains with the length more than 100 nm. The right-handed helical morphology was formed from the D-amino acid side chains.

Individually separated supramolecular polymer chains toward solution-processable supramolecular polymeric materials.

Herein, we present a simple design concept for a monomer that affords individually separated supramolecular polymer chains. Random introduction of alkyl chains with different lengths onto a monomer prevented its supramolecular polymers from bundling, permitting the preparation of concentrated solutions of the supramolecular polymer without gelation, precipitation, or crystallization. With such a solution in hand, we succeeded in fabricating self-standing films and threads consisting of supramolecular polymers.

The importance of intramolecular hydrogen bonds for structural stabilization. [Triphenyl-tetrazolium] [tetraphenyldichalcogenoimidodiphosphinates], [Ph3CN4][Ph2P(X)NP(Y)Ph2

In order to know the capacity of the tetrazolium cation [Ph3CN4]+ to act as a stabilizing influence in the presence of bulky anions and facilitator to obtain suitable crystals for single-crystal X-ray diffraction studies, four new compounds [Ph3CN4] [Ph2P(X)NP(Y)Ph2] [X = Y = O (1); X = Y = S (2); X = Y = Se (3); X = S, Y = Se (4)] were synthesized. The compounds were characterized by elemental analysis, IR, FAB+ mass spectrometry, 1H, 13C, and 31P NMR spectroscopy, and the corresponding single-crystal X-ray structural determinations were acquired. In the four compounds, the neighboring [Ph3CN4]+ and [Ph2P(X)NP(Y)Ph2]- ions are linked by electrostatic interactions, and thus supramolecular polymer chains are generated. To explain the energetic implications of the structural deformations, the interactions and the stabilizer hydrogen bonds, a study was carried out through the Density Functional Theory (DFT).

Hierarchical assembly of uranyl metallacycles involving macrocyclic hosts

Actinide metallacycles are an emerging class of functional coordination assemblies, but multi-level assembly from metallacycle units toward hierarchical supramolecular structures are still rarely investigated. In this work, we put forward a novel supramolecular inclusion-based method through introducing two macrocyclic hosts, cucurbit[7]uril (CB[7]) and cucurbit[8]uril (CB[8]) to facilitate hierarchical assembly of uranyl metallacycles with higher complexity, and successfully prepare two different kinds of uranyl metallacycle-based complexes with intriguing hierarchical structures, a CB[7]-based four-member molecular necklace ([4]MN) and a CB[8]-involved ring-in-ring supramolecular polymer chain. The results obtained here prove the feasibility of supramolecular inclusion for regulating coordination assembly of uranyl metallacycles and related hierarchical structures. It is believed that this method can be used to achieve the construction of actinide coordination assemblies with higher structural complexity.

Chiral Supramolecular Polymer Formed via Host-Guest Complexation of an Octaphosphonate Biscavitand and a Chiral Diammonium Guest

Abstract Chiral supramolecular polymers were constructed through the host-guest complexation of an octaphosphonate biscavitand and a chiral diammonium guest. Isothermal titration calorimetry determined that host-guest complexation was enthalpy- and entropy-favored with high binding constants. Diffusion-ordered NMR spectroscopy and viscometry of the host-guest solution revealed that supramolecular polymerization occurred, which most likely followed a ring-chain mechanism. The cyclic oligomers and the supramolecular polymer chains were visualized by atomic force microscopy. Circular dichroism was observed when the octaphosphonate biscavitand and the chiral diammonium guest were mixed, which suggested that chirally twisted supramolecular polymers were formed.

Dynamics in Controllable Stimuli-Responsive Self-Assembly of Polymer Vesicles with Stable Radical Functionality.

Self-assembled polymer vesicles have emerged as exciting and promising materials for their potential application in drug delivery, but the dynamics of stimuli-responsive polymers in these areas with pendant functionality in order to understand the structure-property relationship under different physicochemical conditions is still open to discussion. In this work, nitroxide radical-containing copolymers were synthesized and utilized to investigate local dynamics in their vesicular assemblies. Herein, electron paramagnetic resonance (EPR) spectroscopy was applied to reveal the smart supramolecular vesicular structure and polymer chain dynamics in stimuli-responsive controlled assemblies by considering molecular-level interactions. These interactions and dynamics were dependent on the microenvironment of the assemblies, which might be affected by physicochemical parameters such as radical concentration, pH, redox agent, polarity, and viscosity. These observations help to accomplish quantitative insights into the stimuli-responsive colloidal vesicular assemblies. The vesicles were used as an anticancer drug carrier, which showed high drug loading efficiency (63.65%). The reduction-responsive prompt disassembly accelerated the release. Furthermore, the biocompatibility and anticancer activity were examined by cellular experiments against normal fibroblasts (L929) and human cervical cancer (HeLa) cell lines, respectively. The results demonstrate that this effort provides an easy strategy for designing controllable stimuli-responsive polymer nanosystems which promotes their promising application in cancer treatment.

Non‐uniform Photoinduced Unfolding of Supramolecular Polymers Leading to Topological Block Nanofibers

AbstractSynthesis of one‐dimensional nanofibers with distinct topological (higher‐order structural) domains in the same main chain is one of the challenging topics in modern supramolecular polymer chemistry. Non‐uniform structural transformation of supramolecular polymer chains by external stimuli may enable preparation of such nanofibers. To demonstrate feasibility of this post‐polymerization strategy, we prepared a photoresponsive helically folded supramolecular polymers from a barbiturate monomer containing an azobenzene‐embedded rigid π‐conjugated scaffold. In contrast to previous helically folded supramolecular polymers composed of a more flexible azobenzene monomer, UV‐light induced unfolding of the newly prepared helically folded supramolecular polymers occurred nonuniformly, affording topological block copolymers consisting of folded and unfolded domains. The formation of such blocky copolymers indicates that the photoinduced unfolding of the helically folded structures initiates from relatively flexible parts such as termini or defects. Spontaneous refolding of the unfolded domains was observed after visible‐light irradiation followed by aging to restore fully folded structures.

Non‐uniform Photoinduced Unfolding of Supramolecular Polymers Leading to Topological Block Nanofibers

Synthesis of one‐dimensional nanofibers with distinct topological (higher‐order structural) domains in the same main chain is one of the challenging topics in modern supramolecular polymer chemistry. Non‐uniform structural transformation of supramolecular polymer chains by external stimuli may enable preparation of such nanofibers. To demonstrate feasibility of this post‐polymerization strategy, we prepared a photoresponsive helically folded supramolecular polymers from a barbiturate monomer containing an azobenzene‐embedded rigid π‐conjugated scaffold. In contrast to previous helically folded supramolecular polymers composed of a more flexible azobenzene monomer, UV‐light induced unfolding of the newly prepared helically folded supramolecular polymers occurred nonuniformly, affording topological block copolymers consisting of folded and unfolded domains. The formation of such blocky copolymers indicates that the photoinduced unfolding of the helically folded structures initiates from relatively flexible parts such as termini or defects. Spontaneous refolding of the unfolded domains was observed after visible‐light irradiation followed by aging to restore fully folded structures.

Main‐Side Chain Hydrogen Bonding‐Based Self‐Healable Polyurethane with Highly Stretchable, Excellent Mechanical Properties for Self‐Healing Acid–Base Resistant Coating

Developing an autonomous self-healing polyurethane (PU) elastomer with excellent mechanical properties and high ductility has attracted increasing attention. Nowadays, the synthesis of elastomers with excellent mechanical properties and rapid self-healing at room temperature faces a huge challenge. Herein, This work reports a new supramolecular PU with excellent mechanical properties and rapid self-healing at room temperature through the introduction of T-type chain extender into the supramolecular polymer chain. The introduction of T-chain extender can be used to enhance the mechanical strength of PU, and the multiple hydrogen bonds on the side-chain provide theoretical support for the rapid self-healing ability of PU. Maximum stress of the synthesized PU can reach 3.4 ± 0.15 Mpa, and maximum elongation at break can reach 3200% ± 160%. Due to flexibility and re-constructability of side-chain hydrogen bonds, PU stress repair efficiency can reach 96.7%, and can be self-healing scratches rapidly and effectively at room temperature. The mechanical properties and self-healing properties of PU can be adjusted by the content of T-type chain extender. The PU is applied to the metal surface coating, which has excellent acid-base resistance, bond strength up to 2.9 ± 0.1 Mpa, and the ability to eliminate local damage on the coating surface quickly at room temperature.

The Competitive Aggregation Pathway of an Asymmetric Chiral Oligo(p‐phenyleneethynylene) Towards the Formation of Individual P and M Supramolecular Helical Polymers

AbstractA complex aggregation pathway towards two diastereomeric P and M supramolecular helices arises from the aggregation of a short, chiral, and rigid oligo(phenyleneethynylene) [OPE, (S)‐1]. Thus, while AggI aggregate is obtained when a DCM solution of (S)‐1 is diluted with MCH at room temperature, AggII aggregate is generated only after a slow heating (353 K)/cooling (273 K) process. Interestingly, during AggI formation (mechanism 1), short P chain oligomers are produced, which have a great tendency to aggregate in plane, yielding brick‐like nanostructures that halt the aggregation process. On the other hand, after a heating/cooling cycle, long M type columnar helical aggregates (AggII) are obtained, formed by individual supramolecular polymer chains (mechanism 2) easily visualized by AFM. The two different P/M orientations obtained for AggI and AggII reveal the dynamic character of the system and its ability to create diastereomeric helical structures under the right conditions. Different experimental protocols were explored to prepare long M type columnar helical aggregates, which are not obtained by using the previous MCH/DCM 99/1 (v/v) solvent mixture. The generation of the desired M oriented supramolecular polymer is achieved when toluene is added to the solvent mixture in a 97/2/1 MCH/Tol/DCM (v/v/v) ratio.

The Competitive Aggregation Pathway of an Asymmetric Chiral Oligo(p-phenyleneethynylene) Towards the Formation of Individual P and M Supramolecular Helical Polymers.

A complex aggregation pathway towards two diastereomeric P and M supramolecular helices arises from the aggregation of a short, chiral, and rigid oligo(phenyleneethynylene) [OPE, (S)-1]. Thus, while AggI aggregate is obtained when a DCM solution of (S)-1 is diluted with MCH at room temperature, AggII aggregate is generated only after a slow heating (353 K)/cooling (273 K) process. Interestingly, during AggI formation (mechanism 1), short P chain oligomers are produced, which have a great tendency to aggregate in plane, yielding brick-like nanostructures that halt the aggregation process. On the other hand, after a heating/cooling cycle, long M type columnar helical aggregates (AggII ) are obtained, formed by individual supramolecular polymer chains (mechanism 2) easily visualized by AFM. The two different P/M orientations obtained for AggI and AggII reveal the dynamic character of the system and its ability to create diastereomeric helical structures under the right conditions. Different experimental protocols were explored to prepare long M type columnar helical aggregates, which are not obtained by using the previous MCH/DCM 99/1 (v/v) solvent mixture. The generation of the desired M oriented supramolecular polymer is achieved when toluene is added to the solvent mixture in a 97/2/1 MCH/Tol/DCM (v/v/v) ratio.

Helically Organized Fullerene Array in a Supramolecular Polymer Main Chain.

To date, supramolecular chemistry techniques have been applied to fullerene polymer synthesis, enabling the development of main-chain fullerene polymers whose primary structure is well regulated, including linear, dendritic, and net-like fullerene arrays. These research achievements have led to an intriguing scientific challenge to create main-chain fullerene polymers with higher structural regulation. Here, we report the fabrication of a helically organized fullerene array based on the supramolecular polymerization of chiral ditopic tetrakiscalix[5]arene hosts and a dumbbell-shaped fullerene. The molecular association between the chiral hosts and the dumbbell-shaped fullerene resulted in sizable supramolecular polymers in solution, with the highest degree of polymerization of more than 32. The achiral dumbbell-shaped fullerene exhibited circular dichroism in the π-π* transition bands arising from the fullerene moieties through supramolecular polymerization. End-capping experiments of the supramolecular helical polymers showed that the chirally twisted conformation of the dumbbell-shaped fullerene was directed by supramolecular polymerization. Finally, the helical morphology of the supramolecular polymer chain was visualized by atomic force microscopy. The successful development of helical main-chain fullerene polymers would break new ground in fullerene chemistry.

Supramolecular assembly of functional peptide–polymer conjugates

The following review gives an overview about synthetic peptide-polymer conjugates as macromolecular building blocks and their self-assembly into a variety of supramolecular architectures, from supramolecular polymer chains, to anisotropic 1D arrays, 2D layers, and more complex 3D networks. A selection of recent literature examples using linear, coiled-coil and cyclic peptide motifs is provided. The reversible nature of the unimer-to-supramolecular polymer transition provides unique opportunities to investigate mechanistic aspects of the supramolecular assembly, with respect to the thermodynamic or kinetic parameters and furthermore provides exciting opportunities for non-equilibrium assembly strategies. Using specific examples we also highlight some of the biological or mechanical function that arises from this versatile class of supramolecular biomaterials.

Designer supramolecular polymers with specific molecular recognitions

Supramolecular polymers are members of an emergent class of polymer materials that exhibit designability and flexibility. This article describes how supramolecular polymers can be synthesized by taking advantage of our host–guest structures based on a calix[5]arene, a bisporphyrin, and a self-assembled capsule. Linear and two-dimensional fullerene nanostructures can be fabricated using the designed monomer structures. The porphyrin donor–acceptor interaction directs the supramolecular polymerization, resulting in linear porphyrin polymers that behave similarly to a conventional polymer chain in solution, even though their structures are dynamic and time-averaged. The fragile supramolecular polymer chains are cross-linked to fabricate a robust self-standing film. The sequence reorganization of the supramolecular homopolymer is established by competitive ditopic guest complexation. The sequence-controlled terpolymer is fabricated via self-sorting behavior. The postmodifications of the supramolecular polymer chains, as well as the polymer chains themselves, are achieved by grafting and non-covalent cross-linking to regulate the macroscopic properties and structures of the polymer main chains. These uniquely organized polymers are fabricated on a nanoscale.

(Invited) Supramolecular Porphyrin Copolymer Directed By Host-Guest Interactions and Metal Coordination

A bisporphyrin cleft molecule with a trinitrofluorenone moiety assembled to form supramolecular polymers through a head-to-tail host-guest interaction. Bispyridine derivatives work as interchain cross-linkers among the supramolecular polymer chains. The supramolecular networked polymers showed characteristic solution viscosity that revealed the formation of the entangled supramolecular polymers. Viscoelastic spectroscopy established that the supramolecular polymers resulted in well-entangled solutions with associating and networking polymers. Morphological transition of the supramolecular polymers was given by AFM images. The non-cross-linked polymer gave rise to wide-spread thin networks while the cross-linked networks resulted in thicker worm-like nanostructures. The supramolecular networks gelled in 1,1,2,2-tetrachloroethane, and an elastic free-standing film was fabricated with a Young's modulus of 1 GPa. In this presentation, I will describe the synthesis and characterization of newly developed supramolecular porphyrin polymer, and macroscopic features. 1) Kinjo, K.; Hirao, T.; Kihara, S.-i.; Katsumoto, Y.; Haino, T. Angew. Chem. Int. Ed. 2015, 54, DOI: 10.1002/anie.201508475. Figure 1

Association Behavior, Diffusion, and Viscosity of End-Functionalized Supramolecular Poly(ethylene glycol) in the Melt State

In this work we present a combined analysis of small-angle neutron scattering, linear rheology and pulsed field gradient nuclear magnetic resonance spectroscopy experiments on the supramolecular association and chain structure of well-defined telechelically modified poly(ethylene glycol) (PEG) in the bulk. Oligomeric PEG was functionalized with directed heterocomplementary hydrogen-bonding end-groups, thymine (Thy) and diaminotriazine (DAT). The polarity of the backbone polymer is comparable to the end groups and avoids clustering of the groups basing on energetic arguments. Their linear association behavior in the ideal melt state was investigated on the microscopic/molecular level as a function of temperature. By means of a selective labeling scheme, which should ideally lead to the formation of alternating hydrogeneous-deuterated building block sequences if the hydrogen bonding reaction is exclusively heterocomplementary, we showed that the Thy–DAT association is dominant and a Thy–Thy homoassociation is approximately three times less probable. Latter nondirected association gives rise to a considerable amount of random-copolymerization without affecting seriously neither the macroscopic melt viscosity nor the diffusivity of the supramolecular associates. From the q-dependence of a multiblock RPA structure factor, the linear association in the melt is confirmed. Furthermore, this diffusion and viscosity study reveals simple Rouse dynamics of supramolecular polymer chains with molecular weight much larger than the entanglement mass Me. The Rouse-like dynamics of long supramolecular chains indicates short lifetime hydrogen bonds of the end groups. Our results are in excellent agreement with the related polycondensation theory.

Origins of structural flexibility in protein-based supramolecular polymers revealed by DEER spectroscopy.

Modular assembly of bio-inspired supramolecular polymers is a powerful technique to develop new soft nanomaterials, and protein folding is a versatile basis for preparing such materials. Previous work demonstrated a significant difference in the physical properties of closely related supramolecular polymers composed of building blocks in which identical coiled-coil-forming peptides are cross-linked by one of two subtly different organic linkers (one flexible and the other rigid). Herein, we investigate the molecular basis for this observation by isolating a single subunit of the supramolecular polymer chain and probing its structure and conformational flexibility by double electron–electron resonance (DEER) spectroscopy. Experimental spin–spin distance distributions for two different labeling sites coupled with molecular dynamics simulations provide insights into how the linker structure impacts chain dynamics in the coiled-coil supramolecular polymer.

ChemInform Abstract: Characterization of Supramolecular Polymers

AbstractReview: 70 refs.

Energy transfer processes along a supramolecular chain of π-conjugated molecules

We have investigated the energy transfer dynamics in a supramolecular linear polymer chain comprising oligofluorene (OF) energy donor units linked by quadruple hydrogen-bonding groups, and oligophenylene (OPV) chain ends that act as energy acceptors. Using femtosecond spectroscopy, we followed the dynamics of energy transfer from the main chain of OF units to the OPV chain ends and simulated these data taking a Monte Carlo approach that included different extents of electronic wave function delocalization for the energy donor and acceptor. Best correlations between experimental and theoretical results were obtained for the assumption of electronic coupling occurring between a localized donor dipole moment and a delocalized acceptor moment. These findings emphasize that geometric relaxation following initial excitation of the donor needs to be taken into account, as it leads to a localization of the donor's excited state wave function prior to energy transfer. In addition, our simulations show that the energy transfer from the main chain to the ends is dominated by an interplay between slow and spatially limited exciton migration along the OF segments comprising the main chain and the comparatively faster hetero-transfer to the end-cap acceptors from directly adjoining OF segments. These results clearly support the description of host-guest energy transfer in linear polymer chains as a two-step mechanism with exciton diffusion in the host being a prerequisite to energy transfer to the guest.

Instantaneous and reversible gelation of organically grafted polyoxometalate complexes with dicarboxylic acids

An organically pyridyl-grafted Anderson-type POM complex (TBA–Py–MnMo6) bearing counterions of tetrabutylammonium (TBA) was found to form supramolecular gels instantaneously through mixing with appropriate dicarboxylic acid additives in acetonitrile. In the gelation process, TBA–Py–MnMo6 was confirmed to self-assemble into supramolecular polymer chains through unidirectional hydrogen bonding between the pyridyl groups of POMs and the carboxylic groups of dicarboxylic acids, which drove the complexes into one-dimensional fibers. The fibers were demonstrated to further intertwine together through the lateral hydrogen bonding between polymer chains under the support of excess acid, forming three-dimensional networks. The distance between TBA–Py–MnMo6 units secluded by dicarboxylic acid was proved to be a criterion for the formation of gels, which is related to the TBA density along the supramolecular polymer chains and the solvent–fiber interfacial energy. The gelation behaviour of the hybrid POM complex can be simply controlled through adjusting the length of dicarboxylic acids. More interestingly, the POM hybrid gels exhibited a quick response to organic bases and diacids reversibly.