Helical Polymers Research Articles

Mechanism for Vipp1 spiral formation, ring biogenesis, and membrane repair.

The ESCRT-III-like protein Vipp1 couples filament polymerization with membrane remodeling. It assembles planar sheets as well as 3D rings and helical polymers, all implicated in mitigating plastid-associated membrane stress. The architecture of Vipp1 planar sheets and helical polymers remains unknown, as do the geometric changes required to transition between polymeric forms. Here we show how cyanobacterial Vipp1 assembles into morphologically-related sheets and spirals on membranes in vitro. The spirals converge to form a central ring similar to those described in membrane budding. Cryo-EM structures of helical filaments reveal a close geometric relationship between Vipp1 helical and planar lattices. Moreover, the helical structures reveal how filaments twist-a process required for Vipp1, and likely other ESCRT-III filaments, to transition between planar and 3D architectures. Overall, our results provide a molecular model for Vipp1 ring biogenesis and a mechanism for Vipp1 membrane stabilization and repair, with implications for other ESCRT-III systems.

Three-Level Chirality Transfer and Amplification in Liquid Crystal Supramolecular Assembly for Achieving Full-Color and White Circularly Polarized Luminescence.

Chiral liquid crystal supramolecular assembly provides an ideal strategy for constructing excellent circularly polarized luminescence (CPL) materials. However, the chirality transfer in chiral liquid crystals normally occurs at two levels from the configurational chirality to the supramolecular phase chirality. The more precise and more levels of chirality transmission are fascinating but remain challenging. The present work reports the first success of three-level chirality transfer and amplification from configurationally point chirality of small molecules to conformationally helical chirality of helical polymers and finally to supramolecular phase chirality of cholesteric liquid crystals composed of chiral nonfluorescent polymers (P46) and nematic liquid crystals. Noticeably, the helical twisting power of P46 is five-fold larger than its monomer. Full-color and white CPL with maximum luminescence dissymmetry factor up to 1.54 and photoluminescence quantum yield up to 63.8% are realized utilizing helical supramolecular assembly combined with selective reflection mechanism. Also significantly, the electrically stimuli-responsive CPL switching device as well as anti-counterfeiting security, information encryption, and chiral logic gate applications are developed. This study deepens the understanding of chirality transfer and amplification across different hierarchical levels.

Chiral Induction of a Tetrakis(porphyrin) in Various Chiral Solvents.

Non-covalent interactions offer an alternative way for developing stimulus-responsive materials such as sensors, machines, and drug-delivery systems. We recently reported that a urethane-equipped tetrakis(porphyrin) forms one-handed helical supramolecular polymers in solution in response to chirality of chiral solvents. Conformational changes in helical sense were detected using circular dichroism (CD) spectroscopy, which showed that the tetrakis(porphyrin) can possibly be used as a sensor for determining the enantiomeric excess of a chiral analyte. Hence, we studied the scope and limitations of the chiral-induction behavior of tetrakis(porphyrin) to deepen the understanding of tetrakis(porphyrin)-based chiral sensing systems. Herein, we report the chiral-induction behavior of tetrakis(porphyrin) in various chiral solvents, which was found to be CD-active in many chiral solvents. Notably, the tetrakis(porphyrin) was CD active in a cryptochiral molecular solvent, which is exciting because the chiralities of acyclic saturated hydrocarbons are hard to sense. Consequently, this study highlights the potential advantages of supramolecular chiral sensors capable of targeting a wide range of analytes, including molecules that are absorption-silent in the UV/vis region, ones devoid of anchoring functional groups, and acyclic, saturated hydrocarbons.

Controlled Helical Organization in Supramolecular Polymers of Pseudo-Macrocyclic Tetrakisporphyrins.

Tetrakisporphyrin monomers with amino acid side chains at each end form intramolecular antiparallel hydrogen-bonds to adopt chirally twisted pseudo-macrocyclic structures that result in right-handed and left-handed (P)- and (M)-conformations. The pseudo-macrocyclic tetrakisporphyrin monomers self-assembled to form supramolecular helical pseudo-polycatenane polymers via head-to-head complementary dimerization of the bisporphyrin cleft units in an isodesmic manner. The formation of one-handed supramolecular helical pseudo-polycatenane polymers was confirmed by circular dichroism spectroscopy. The methyl and iso-propyl groups at the stereogenic center greatly enhanced the induced circular dichroism (CD) in the Soret bands of the supramolecular helical pseudo-polycatenane polymers. The induced CDs were reduced upon the introduction of large iso-butyl and tert-butyl groups. Atomic force microscopy revealed well-grown and long supramolecular helical pseudo-polycatenane polymer chains with chain lengths in the range of 361 to 13.6 nm. The right-handed helical chains were established by the self-assembly of the right-handed (P)-conformation of the pseudo-macrocyclic monomer.

Long-Lived Triplets from Singlet Fission in Pentacene-Decorated Helical Supramolecular Polymers.

Singlet fission (SF), which involves the conversion of a singlet excited state into two triplet excitons, holds great potential to boost the efficiency of photovoltaics. However, losses due to triplet-triplet annihilation hamper the efficient harvesting of SF-generated triplet excitons, which limits an effective implementation in solar energy conversion schemes. A fundamental understanding of the underlying structure-property relationships is thus crucial to define design principles for cutting-edge SF materials, yet it remains elusive. Herein, we harness helical supramolecular polymers decorated with pentacene side groups to elucidate intermolecular SF dynamics in solution and promote the formation of long-lived mobile triplets. By leveraging the hydrogen bonding-driven assembly of benzene-1,3,5-tricarboxamide (BTA) cores into one-dimensional scaffolds, we direct the organization of appended pentacene motifs into long-range ordered helical frameworks. Dynamic interactions between weakly coupled SF pendants mediate singlet conversion within hundreds of picoseconds, affording triplet quantum yields well above 100%. Moreover, analysis of triplet dynamics with a Monte Carlo simulation model reveals that triplet diffusion along the supramolecular fibers is favored over annihilation, resulting in independent triplets exhibiting considerably slow decay on the time scale of tens of microseconds. The molecular packing within the assembly is tuned by subtle changes in monomer design to increase the rate and efficiency of SF while ensuring exceptionally long-lived mobile triplets, allowing to maintain triplet quantum yields exceeding 100% for at least 100 ns. This work opens new opportunities to exploit self-assembled supramolecular polymers as functional templates to achieve long-lived SF-generated triplets.

Helical Star-Shaped Bottlebrush Polymers: From Controlled Synthesis to Tunable Photoluminescence and Circularly Polarized Luminescence.

The controlled synthesis of star-shaped bottlebrush polymers with tunable topologies is a challenge. However, such materials may exhibit distinct photoluminescence properties. Bottlebrush polymers have polymerization-induced emission (PIE) properties due to their aggregated side chains, and aggregation-induced emission (AIE) is also a unique luminescent property. In this work, we prepared a variety of highly active alkyne Pd catalysts and polymerized poly(L/D-lactic acid) macromonomers containing polymerizable phenylisocyanide groups as end groups to obtain a variety of topologically structured bottlebrush polymers with controllable molecular weights and narrow molecular weight distributions. Bottlebrush polymers with tetraphenyl ethylene (TPE) units as the core exhibit tunable photoluminescence and circularly polarized luminescence properties. We propose that such properties are due to the unique AIE characteristics of the TPE unit combined with the PIE characteristics of the bottlebrush polymer.

Stereospecific supramolecular polymerization of nanoclusters into ultra-long helical chains and enantiomer separation

During the construction of supramolecular polymers of smaller nanoparticles/nanoclusters bearing hierarchy and homochirality, the mechanism understanding via intuitive visualization and precise cross-scale chirality modulation is still challenging. For this goal, a cooperative self-assembly strategy is here proposed by using ionic complexes with uniform chemical composition comprising polyanionic nanocluster cores and surrounded chiral cationic organic components as monomers for supramolecular polymerization. The single helical polymer chains bearing a core-shell structure at utmost length over 20 μm are demonstrated showing comparable flexibility resembling covalent polymers. A nucleation-elongation growth mechanism that is not dealt with in nanoparticle systems is confirmed to be accompanied by strict chiral self-sorting. A permeable membrane prepared by simple suction of such supramolecular polymers displays high enantioselectivity (e.e. 98% after four runs) for separating histidine derivatives, which discloses a benefiting helical chain structure-induced functionalization for macroscopic supramolecular materials in highly efficient racemate separation.

One-Handed Covalent Helical Ladder Polymers: The Dawn of a Tailorable Class of Chiral Functional Materials.

In the last decades, chemists have developed methods to synthesize helical molecular architectures using a combination of covalent and non-covalent interactions. Very recently, the new class of completely covalent, one-handed helical ladder polymers has vigorously emerged. Such polymers can be rationally and programmably obtained through an approach guided by the principles of chirality-assisted-synthesis (CAS) and making use synergically of two disciplines that have so far rarely interacted: non-planar chiral π-conjugated synthons and ladder polymer chemistry. The precise programmability of the 3D structure and new mechanical and chiroptical properties will lead to potential applications in areas such as enantiorecognition, catalysis, spintronics and chiral-related optoelectronics. This minireview examines the emerging field of one-handed helical ladder polymers, analyzing their synthesis, applications, and limitations.

From Achiral Precursors to Copper Helical Coordination Polymers: Magnetic Properties and Electronic Structure

From Achiral Precursors to Copper Helical Coordination Polymers: Magnetic Properties and Electronic Structure

Exo-chirality of the α-helix

The structure of helical polymers is dictated by the molecular chirality of their monomer units. Particularly, macromolecular helices with monomer sequence control have the potential to generate chiral topologies. In α-helical folded peptides, the sequential repetition of amino acids generates a chiral layer defined by the amino acid side chains projected outside the amide backbone. Despite being closely related to peptides’ structural and functional properties, to the best of our knowledge, a general exo-helical symmetry model has not been yet described for the α-helix. Here, we perform the theoretical, computational, and spectroscopic elucidation of the α-helix principal exo-helical topologies. Non-canonical labeled amino acids are employed to spectroscopically characterize the different exo-helical topologies in solution, which precisely match the theorical prediction. Backbone-to-chromophore distance also shows the expected impact in the exo-helices’ geometry and spectroscopic fingerprint. Theoretical prediction and spectroscopic validation of this exo-helical topological model provides robust experimental evidence of the chiral potential on the surface of helical peptides and outlines an entirely new structural scenario for the α-helix.

Multiple Chirality Switching of a Dye‐Grafted Helical Polymer Film Driven by Acid & Base

AbstractA stimuli‐responsive multiple chirality switching material, which can regulate opposed chiral absorption characteristics, has great application value in the fields of optical modulation, information storage and encryption, etc. However, due to the rareness of effective functional systems and the complexity of material structures, developing this type of material remains an insurmountable challenge. Herein, a smart polymer film with multiple chirality inversion properties was fabricated efficiently based on a newly‐designed acid & base‐sensitive dye‐grafted helical polymer. Benefited from the cooperative effects of various weak interactions (hydrogen bonds, electrostatic interaction, etc.) under the aggregated state, this polymer film exhibited a promising acid & base‐driven multiple chirality inversion property containing record switchable chiral states (up to five while the solution showed three‐state switching) and good reversibility. The creative exploration of such a multiple chirality switching material can not only promote the application progress of current chiroptical regulation technology, but also provide a significant guidance for the design and synthesis of future smart chiroptical switching materials and devices.

Multiple Chirality Switching of a Dye-Grafted Helical Polymer Film Driven by Acid & Base.

A stimuli-responsive multiple chirality switching material, which can regulate opposed chiral absorption characteristics, has great application value in the fields of optical modulation, information storage and encryption, etc. However, due to the rareness of effective functional systems and the complexity of material structures, developing this type of material remains an insurmountable challenge. Herein, a smart polymer film with multiple chirality inversion properties was fabricated efficiently based on a newly-designed acid & base-sensitive dye-grafted helical polymer. Benefited from the cooperative effects of various weak interactions (hydrogen bonds, electrostatic interaction, etc.) under the aggregated state, this polymer film exhibited a promising acid & base-driven multiple chirality inversion property containing record switchable chiral states (up to five while the solution showed three-state switching) and good reversibility. The creative exploration of such a multiple chirality switching material can not only promote the application progress of current chiroptical regulation technology, but also provide a significant guidance for the design and synthesis of future smart chiroptical switching materials and devices.

Helix‐Sense‐Selective Memory Polymerization of Biphenylylacetylenes Bearing Carboxy and Amino Groups in Water

We report the helix‐sense‐selective memory polymerization (HSMP) of achiral biphenylylacetylenes bearing carboxy and amino pendant groups in the presence of basic and acidic chiral guests in water, respectively. The HSMP proceeds in a highly helix‐sense‐selective manner driven by noncovalent chiral ionic interactions between the monomers and guests under kinetic control, producing the one‐handed helical polymers with a static memory of helicity in one‐pot during the polymerization in a very short time, accompanied by amplification of asymmetry. The carboxy‐bound helicity‐memorized polymer self‐assembles into a cholesteric liquid crystal in concentrated water, in which a variety of basic achiral fluorophores further co‐assembles to form supramolecular helical aggregates that exhibit an induced circularly polarized luminescence in a color tunable manner.

Helix-Sense-Selective Memory Polymerization of Biphenylylacetylenes Bearing Carboxy and Amino Groups in Water.

We report the helix-sense-selective memory polymerization (HSMP) of achiral biphenylylacetylenes bearing carboxy and amino pendant groups in the presence of basic and acidic chiral guests in water, respectively. The HSMP proceeds in a highly helix-sense-selective manner driven by noncovalent chiral ionic interactions between the monomers and guests under kinetic control, producing the one-handed helical polymers with a static memory of helicity in one-pot during the polymerization in a very short time, accompanied by amplification of asymmetry. The carboxy-bound helicity-memorized polymer self-assembles into a cholesteric liquid crystal in concentrated water, in which a variety of basic achiral fluorophores further co-assembles to form supramolecular helical aggregates that exhibit an induced circularly polarized luminescence in a color tunable manner.

Cryo-EM structure of the R388 plasmid conjugative pilus reveals a helical polymer characterized by an unusual pilin/phospholipid binary complex

Bacterial conjugation is a process by which DNA is transferred unidirectionally from a donor cell to a recipient cell. It is the main means by which antibiotic resistance genes spread among bacterial populations. It is crucially dependent upon the elaboration of an extracellular appendage, termed "pilus," by a large double-membrane-spanning secretion system termed conjugative "type IV secretion system." Here we present the structure of the conjugative pilus encoded by the R388 plasmid. We demonstrate that, as opposed to all conjugative pili produced so far for cryoelectron microscopy (cryo-EM) structure determination, the conjugative pilus encoded by the R388 plasmid is greatly stimulated by the presence of recipient cells. Comparison of its cryo-EM structure with existing conjugative pilus structures highlights a number of important differences between the R388 pilus structure and that of its homologs, the most prominent being the highly distinctive conformation of its bound lipid.

Size Control of Chiral Nanospheres Obtained via Nanoprecipitation of Helical Poly(phenylacetylene)s in the Absence of Surfactants.

Nanostructuration of dynamic helical polymers such as poly(phenylacetylene)s (PPAs) depends on the secondary structure adopted by the polymer and the functional group used to connect the chiral pendant to the PPA backbone. Thus, while PPAs with dynamic and flexible scaffolds (para- and meta-substituted, ω1<165°) generate by nanoprecipitation low polydisperse nanospheres with controllable size at different acetone/water mixtures, those with a quasi-static behavior and the presence of an extended, almost planar structure (ortho-substituted, ω1>165°), aggregate into a mixture of spherical and oval nanostructures whose size is not controlled. Photostability studies show that poly(phenylacetylene) particles are more stable to light irradiation than when dissolved macromolecularly. Moreover, the photostability of the particle depends on the secondary structure of the PPA and its screw sense excess. This fact, in combination with the encapsulation ability of these polymer particles, allows the creation of light stimuli-responsive nanocarriers, whose cargo can be delivered by light irradiation.

Size Control of Chiral Nanospheres Obtained via Nanoprecipitation of Helical Poly(phenylacetylene)s in the Absence of Surfactants

AbstractNanostructuration of dynamic helical polymers such as poly(phenylacetylene)s (PPAs) depends on the secondary structure adopted by the polymer and the functional group used to connect the chiral pendant to the PPA backbone. Thus, while PPAs with dynamic and flexible scaffolds (para‐ and meta‐substituted, ω1&lt;165°) generate by nanoprecipitation low polydisperse nanospheres with controllable size at different acetone/water mixtures, those with a quasi‐static behavior and the presence of an extended, almost planar structure (ortho‐substituted, ω1&gt;165°), aggregate into a mixture of spherical and oval nanostructures whose size is not controlled. Photostability studies show that poly(phenylacetylene) particles are more stable to light irradiation than when dissolved macromolecularly. Moreover, the photostability of the particle depends on the secondary structure of the PPA and its screw sense excess. This fact, in combination with the encapsulation ability of these polymer particles, allows the creation of light stimuli‐responsive nanocarriers, whose cargo can be delivered by light irradiation.

Polymeric Cholesteric Superhelix Induced by Chiral Helical Polymer for Achieving Full-Color Circularly Polarized Room-Temperature Phosphorescence with Ultra-High Dissymmetry Factor.

Circularly polarized room-temperature phosphorescence (CPRTP) simultaneously featuring multiple colors and extremely high dissymmetry factor (glum) is crucial for increasing the complexity of optical characteristics and advancing further development, but such a type of CPRTP is still unprecedented. The present work develops an effective and universal strategy to achieve full-color CPRTP with ultra-high glum factors in a polymeric cholesteric superhelix network, which is constructed by cholesteric liquid crystal polymer and chiral helical polymer (CHP). Taking advantage of the high helical twisting power of CHP, the resulting polymeric cholesteric superhelix network exhibits remarkable optical activity. Significantly, by adopting a simple double-layered architectures consisting of the cholesteric superhelix film and phosphorescent films, blue-, green-, yellow-, and red-CPRTP emissions are successfully obtained, with maximum |glum| values up to 1.43, 1.39, 1.09 and 0.84, respectively. Further, a multilevel information encryption application is demonstrated based on the multidimensional optical characteristics of the full-color double-layered CPRTP architectures. This study offers new insights into fabricating polymeric cholesteric superhelix with considerable CPRTP performance in advanced photonic applications.

Solvent-controlled assembly of helical coordination polymers based on lactate synthon from two-dimensional layer to three-dimensional framework

Compound (R)-4-(1-carboxyethoxy)-2-methylbenzoic acid ((R)-H2cma) was prepared from (S)-methyl lactate and 4-hydroxy-2-methylbenzoic acid. (R)-H2cma as chiral synthon assembled with 1,3-di(pyridin-4-yl)propane (1,3-dpp) and Ni2+ ions to obtain helical chiral complexes {[Ni2((R)-cma)2(1.3-dpp)2]·H2O}n (HU18-R) and {[Ni2((R)-cma)2(1.3-dpp)2(H2O)]·3H2O}n (HU19-R) in different solvent systems. Single crystal tests revealed that HU18-R is a two-dimensional (2D) structure with two independent Ni2+ centers and HU19-R is a three-dimensional (3D) framework containing dinuclear [Ni2(CO2)2(H2O)]2+ clusters. Four types of helices were formed in HU18-R and HU19-R by chiral transfer or induction. In HU18-R, small right-handed (R)-cma-Ni chain and large right-handed (R)-cma-Ni-1.3-dpp chain were constructed by chiral transfer. For HU19-R, helical nano-channel based on achiral 1.3-dpp ligands and Ni2+ ions was obtained from chiral induction method and small (R)-cma-Ni chain was built from chiral transfer. As semi-conducting materials, HU18-R and HU19-R indicate strong absorption capacity for UV–vis light and low-impedance properties. Under UV light, they have noticeable catalytic effects for degradation of methylene blue (MB). Moreover, magnetic tests confirmed that HU18-R and HU19-R have ferromagnetic and antiferromagnetic properties, respectively.

One‐Handed Covalent Helical Ladder Polymers: The Dawn of a Tailorable Class of Chiral Functional Materials

One‐Handed Covalent Helical Ladder Polymers: The Dawn of a Tailorable Class of Chiral Functional Materials