Design of a Dynamic Polymer Interface for Chiral Discrimination

Role of Surface Dipole Alignment in Modulating Cellular Activities on Poly(vinylidene fluoride)

Understanding and controlling the surface properties of bioscaffolds are crucial for regulating cell adhesion and proliferation behaviors. We here focused on poly(vinylidene fluoride) (PVDF), in which polymer chains are oriented through poling treatment to form a polar β-form crystal. The surface aggregation states of uniaxially stretched PVDF films subjected to poling treatment were investigated based on water contact angle measurements and sum-frequency generation spectroscopy. During poling treatment under a sufficiently strong electric field, the dipole moments of β-form crystals, which are inherently aligned within each crystalline domain, become more uniformly oriented across the entire film. As a result, the surface resists structural reorganization even upon exposure to water. This stable surface, which maintains its aggregation states despite environmental changes, was found to promote cell adhesion and proliferation, as well as protein adsorption. Our findings contribute to a deeper understanding of the relationship between the aggregation states on polymer scaffold surfaces and protein interactions, ultimately advancing insights into cell behaviors.

Bipyridine-Containing Optically Active π-Conjugated Polymers Derived from Amino Alcohols: Examination of the Higher-Order Structures, Chiral Recognition, and Metal Coordination Based on Quantum Mechanical and Molecular Dynamics Calculations

Helical π-conjugated polymers are promising as optically active functional materials. The present paper reports the synthesis of novel bipyridine-containing π-conjugated polymers with optically active amino-alcohol-derived side chains, examination of their higher-order structures, chiral recognition, and metal coordination properties. The polymers adopt a folded helical conformation and aggregate in CHCl3/MeOH depending on the solvent composition, as supported by density functional theory calculations and molecular dynamics simulations. The polymer films showed differences in contact angles with aqueous solutions of (R)- and (S)-alcohols. Addition of some metal chlorides and perchlorates changed the intensity and color of the photoluminescence of the polymers.

Chirality Discrimination at Binary Organic|Water Interfaces Monitored by Interfacial Tension Measurements with Preliminary Comparison with Molecular Dynamics Simulations

Chirality discrimination at a binary toluene (organic)/water(aqueous) interface between R- or S-Tol-BINAP (2,2'-Bis(di-p-tolylphosphino)-1,1'-binaphthyl) molecules and the water-soluble serine chiral specie is examined for the first time, using a combination of interfacial tension measurements and molecular dynamic simulations. Experimental interfacial measurements exhibit a clear chirality-controlled difference when a homochiral versus a heterochiral enantiomeric pairs are introduced at the interfaces. The related molecular dynamics simulations support the experimental results and provide further molecular insight of intermolecular interactions at the interfaces. The results indicate that interfacial tension measurements can capture the preferential interactions which exist between different pairs of enantiomers at the binary interfaces, opening up a new way for probing chirality discrimination at liquid-liquid interfaces.

Helically aligned fused carbon hollow nanospheres with chiral discrimination ability

While the functions of carbon materials with precisely controlled nanostructures have been reported in many studies, their chiral discriminating abilities have not been reported yet. Herein, chiral discrimination is achieved using helical carbon materials devoid of chiral attachments. A Fe₃O₄ nanoparticle template with ethyl cellulose (carbon source) is self-assembled on dispersed multiwalled carbon nanotubes (MWCNTs) fixed in a lamellar structure, with helical nanoparticle alignment induced by the addition of a binaphthyl derivative. Carbonization followed by template removal produces helically aligned fused carbon hollow nanospheres (CHNSs) with no chiral molecules left. Helicity is confirmed using vacuum-ultraviolet circular dichroism spectroscopy. Chiral discrimination, as revealed by the electrochemical reactions of binaphthol and a chiral ferrocene derivative in aqueous and nonaqueous electrolytes, respectively, is attributable to the chiral space formed between the CHNS and MWCNT surfaces.

Two-Dimensional Cellular Patterning on a Polymer Film Based on Interfacial Stiffness

The mechanical properties in the outermost region of a polymer film strongly affect various material functions. We here propose a novel and promising strategy for the two-dimensional regulation of the mechanical properties of a polymer film at the water interface based on an inkjet drawing of silica nanoparticles (SNPs) underneath it. A film of poly(2-hydroxyethyl methacrylate) (PHEMA), which exhibits excellent bioinertness properties at the water interface, was well fabricated on a substrate with a pattern of SNPs. X-ray photoelectron spectroscopy and atomic force microscopy confirmed that the surface of the PHEMA film was flat and chemically homogeneous. However, the film surface was in-plane heterogeneous in stiffness due to the presence of the underlying SNP lines. It was also noted that NIH/3T3 fibroblast cells selectively adhered and formed aggregates on the areas under which an SNP line was drawn.

Modification of a Polymer Surface by Partial Swelling Using Nonsolvents

Surface modification without changing the physical properties in the bulk is of pivotal importance for the development of polymers as devices. We recently proposed a simple surface functionalization method for polymer films by partial swelling using a nonsolvent and demonstrated the incorporation of poly(2-methoxyethyl acrylate) (PMEA), which has an excellent antibiofouling ability, only into the outermost region of a poly(methyl methacrylate) (PMMA) film. We here extend this technology to another versatile polymer, polystyrene (PS). In this case, PS and PMEA have different solubility parameters making it difficult to select a suitable solvent, which is a nonsolvent for PS and a good solvent for PMEA, unlike the combination of PMMA with PMEA. Thus, such a solvent was first sought by examining the swelling behavior of PS films in contact with various alcohols. Once a mixed solvent of methanol/1-butanol (50/50 (v/v)) was chosen, PMEA chains could be successfully incorporated at the outermost region of the PS film. Atomic force microscopy in conjunction with neutron reflectivity revealed that chains of PMEA incorporated in the PS surface region were well swollen in water. This leads to an excellent ability to suppress the adhesion of platelets on the PS film.

Molecular and nano structures of chiral PEDOT derivatives influence the enantiorecognition of biomolecules. In silico analysis of chiral recognition

In this study we investigated the synergistic effects of the chirality (molecular structure) and surface morphology (nanostructure) of a newly designed sensing platform for the stereoselective recognition of biomolecules. We synthesized 3,4-ethylenedioxythiophene monomers presenting an OH functional group on the side chain (EDOT-OH) with either R or S chirality and then electropolymerized them in a template-free manner to engineer poly(EDOT-OH) nanotubes and smooth films with R or S chirality. We used a quartz crystal microbalance (QCM) to examine the differential binding of fetal bovine serum, RGD peptide, insulin, and (R)- and (S)-mandelic acid (MA) on these chiral polymeric platforms. All of these biomolecules bound stereoselectively and with greater affinity toward the nanotubes than to the smooth films. The sensitive chiral recognition of (S)- and (R)-MA on the (R)-poly(EDOT-OH) nanotube surface occurred with the highest chiral discrepancy ratio of 1.80. In vitro experiments revealed a greater degree of protein deposition from MCF-7 cells on the chiral nanotube surfaces. We employed ab initio molecular dynamics simulations and density functional theory calculations to investigate the mechanism underlying the sensitive chiral recognition between the chiral sensing platforms and the chiral analyte molecules.

Triptycene-based Chiral Porous Polyimides for Enantioselective Membrane Separation

Enantiomers of 2, 6-diaminotriptycene (R, R-1 and S, S-1) are split by chiral-phase HPLC and their absolute configurations are identified by single-crystal X-ray diffraction technology. Using the enantiomers as monomers, a couple of chiral porous polyimides (R-FTPI and S-FTPI) are prepared by polycondensation reactions and display good heat stability, high BET surface area and good solubility in organic solvents. Moreover, both of R-FTPI and S-FTPI can be cast into robust, free-standing films suitable for enantioselective separation with symmetrical chiral selectivity.

Helical polymer self-assembly and chiral nanostructure formation

This review surveys recent progress towards robust chiral nanostructure fabrication techniques using synthetic helical polymers, the unique inferred properties that these materials possess, and their intricate connection to natural, biological chirality.

Design of a Bioinert Interface Using an Amphiphilic Block Copolymer Containing a Bottlebrush Unit of Oligo(oxazoline)

We designed an amphiphilic block copolymer, poly(methyl methacrylate)-block-poly[oligo(2-ethyl-2-oxazoline) methacrylate] (PMMA-b-P[O(Ox)MA]), suitable for bioinert coating. Angular-dependent X-ray photoelectron spectroscopy and neutron reflectivity measurements revealed that the outermost surface of a dried film of PMMA-b-P[O(Ox)MA] was covered with the PMMA block-rich layer. Once the film came into contact with water, the P[O(Ox)MA] bottlebrush block was segregated toward the water interface. This structural rearrangement in the outermost region of the film resulted in the formation of the swollen oligo(oxazoline) layer with excellent bioinertness in terms of the suppression of serum protein adsorption and NIH3T3 fibroblast adhesion.

Chiroptical Properties in Thin Films of π-Conjugated Systems

Chiral π-conjugated molecules provide new materials with outstanding features for current and perspective applications, especially in the field of optoelectronic devices. In thin films, processes such as charge conduction, light absorption, and emission are governed not only by the structure of the individual molecules but also by their supramolecular structures and intermolecular interactions to a large extent. Electronic circular dichroism, ECD, and its emission counterpart, circularly polarized luminescence, CPL, provide tools for studying aggregated states and the key properties to be sought for designing innovative devices. In this review, we shall present a comprehensive coverage of chiroptical properties measured on thin films of organic π-conjugated molecules. In the first part, we shall discuss some general concepts of ECD, CPL, and other chiroptical spectroscopies, with a focus on their applications to thin film samples. In the following, we will overview the existing literature on chiral π-conjugated systems whose thin films have been characterized by ECD and/or CPL, as well other chiroptical spectroscopies. Special emphasis will be put on systems with large dissymmetry factors (g_abs and g_lum) and on the application of ECD and CPL to derive structural information on aggregated states.

Chiroptical property tuning of supramolecular assemblies in polymer matrices

Chiroptical materials have received much attention in diverse fields for applications such as displays, sensors, smart memory devices, and catalysis. Here, we develop a simple fabrication method for polymer films with tunable chiroptical properties using small amounts of self-assembling fluorescent dye as an additive. Both the circular dichroism and circularly polarized luminescence signals of the film can be tuned between positive and negative values by thermal treatment. The chiroptical properties can be varied by slight changes in the orientation of chiral pyrene moieties in self-assembled nanofibril networks.

Chiral Nanostructured Composite Films via Solvent-Tuned Self-Assembly and Their Enantioselective Performances

Chiral nanostructures exhibited distinctive functions and attractive applications in complex biological systems, which demonstrated the subject of many outstanding research studies. In this work, various hierarchical composite film nanostructures were designed via supramolecular self-assembly using chiral amphiphilic glutamate derivatives and achiral porphyrin derivatives and their macroscopic enantioselective recognition properties were investigated. We have found that intermolecular hydrogen-bonding interactions between water (donor and acceptor) and N, N-dimethylformamide (DMF) as well as chloroform (CHCl₃) (acceptor only) and DMF could subtly alter the molecular packing and significantly affected the supramolecular self-assembled nanostructures and triggered circular dichroism (CD) signal reversal. Present research work exemplified a feasible method to fabricate chiral flower-like and brick-like nanostructure films in different mixed solvents and large-scale chiral transfer from the molecular level to complex structures, which also provided a facile approach to identify certain l-/d-amino acids by means of contact angle detection using present obtained self-assembled composted films.

Direct Observation of Conformational Relaxation of Polymer Chains at Surfaces

Sum-frequency generation spectroscopy was employed to follow the conformation evolution of polystyrene chains at the surface of a spin-coated film in a temperature-ramping mode as well as under isothermal annealing. The conformation of surface chains in an as-cast film was observed to be in a nonequilibrium state, in accordance with reported results for polymer chains in thin spin-coated films. While the relaxation of surface nonequilibrium chains was induced by the enhanced surface mobility, the whole chain motion such as reptation might be a key factor in determining the time scale for equilibrating the surface chain conformation.

Surface-Restructuring Differences between Polyrotaxanes and Random Copolymers in Aqueous Environment

In the present study, we investigated the surface reorganization behaviors and adsorption conformations of fibrinogen on the surface of polyrotaxanes containing different amounts of α-cyclodextrin (α-CD) by using surface-sensitive vibrational spectroscopy sum frequency generation (SFG). For comparison, behaviors of the surface restructuring and fibrinogen adsorption on the random copolymers containing similar terminal groups were also investigated. It was found that larger amounts of BMA moieties of polyrotaxanes form ordered surface structures after immersion in water for 48 h. Furthermore, the polyrotaxane surfaces exhibit a much higher capability of fibrinogen adsorption than the random copolymer surfaces. The water-induced surface restructuring of the polyrotaxane films slightly affects the adsorption structure of the fibrinogen molecules.

Super-Temporal-Resolved Microscopy Reveals Multistep Desorption Kinetics of α-Lactalbumin from Nylon

Insight into the mechanisms driving protein-polymer interactions is constantly improving due to advances in experimental and computational methods. In this study, we used super-temporal-resolved microscopy (STReM) to study the interfacial kinetics of a globular protein, α-lactalbumin (α-LA), adsorbing at the water-nylon 6,6 interface. The improved temporal resolution of STReM revealed that residence time distributions involve an additional step in the desorption process. Increasing the ionic strength in the bulk solution accelerated the desorption rate of α-LA, attributed to adsorption-induced conformational changes. Ensemble circular dichroism measurements were used to support a consecutive reaction mechanism. Without the improved temporal resolution of STReM, the desorption intermediate was not resolvable, highlighting both STReM's potential to uncover new kinetic mechanisms and the continuing need to push for better time and space resolution.

Facile Synthesis of Optically Active and Thermoresponsive Star Block Copolymers Carrying Helical Polyisocyanide Arms and Their Thermo-Triggered Chiral Resolution Ability

A left-handed helical poly(phenyl isocyanide) bearing a norbornene unit and a Pd(II) complex on each terminus was prepared. The norbornene terminus was core cross-linked with a bisnorbornene linker via ring-opening metathesis polymerization (ROMP), yielding a star polymer carrying left-handed helical arms decorated with Pd(II) units at the exterior. The optical activities of the helical arms were maintained after the cross-linking reaction. The Pd(II) units on the surface of the star polymer were chain extended with a new phenyl isocyanide bearing three hydrophilic triethylene glycol monomethyl chains, which afforded an amphiphilic star block copolymer carrying helical arms. Such a star block copolymer showed excellent thermoresponsiveness with the lower critical solution temperature (LCST) around 55 °C. This optically active and thermoresponsive star polymer can enantioselectively capture the S-enantiomer of racemic methyl benzyl alcohol solution at a temperature lower than the LCST and precipitated when the temperature was higher than the LCST, leaving the R-enantiomer in the solution. The enantiomeric excess (ee) of the isolated enantiomer is up to 75%.

Chiral anion-triggered helical poly(ionic liquids)

Anion-triggered chirality and helicity in PILs.

Smart Polymers with Special Wettability

Surface wettability plays a key role in addressing issues ranging from basic life activities to our daily life, and thus being able to control it is an attractive goal. Learning from nature, both of its structure and function, brings us much inspiration in designing smart polymers to tackle this major challenge. Life functions particularly depend on biomolecular recognition-induced interfacial properties from the aqueous phase onto either "soft" cell and tissue or "hard" inorganic bone and tooth surfaces. The driving force is noncovalent weak interactions rather than strong covalent combinations. An overview is provided of the weak interactions that perform vital actions in mediating biological processes, which serve as a basis for elaborating multi-component polymers with special wettabilities. The role of smart polymers from molecular recognitions to macroscopic properties are highlighted. The rationale is that highly selective weak interactions are capable of creating a dynamic synergetic communication in the building components of polymers. Biomolecules could selectively induce conformational transitions of polymer chains, and then drive a switching of physicochemical properties, e.g., roughness, stiffness and compositions, which are an integrated embodiment of macroscopic surface wettabilities.

Supramolecular Helical Systems: Helical Assemblies of Small Molecules, Foldamers, and Polymers with Chiral Amplification and Their Functions

In this review, we describe the recent advances in supramolecular helical assemblies formed from chiral and achiral small molecules, oligomers (foldamers), and helical and nonhelical polymers from the viewpoints of their formations with unique chiral phenomena, such as amplification of chirality during the dynamic helically assembled processes, properties, and specific functionalities, some of which have not been observed in or achieved by biological systems. In addition, a brief historical overview of the helical assemblies of small molecules and remarkable progress in the synthesis of single-stranded and multistranded helical foldamers and polymers, their properties, structures, and functions, mainly since 2009, will also be described.

Determining Chiral Configuration of Diamines via Contact Angle Measurements on Enantioselective Alanine-Appended Benzene-Tricarboxamide Gelators

Spectroscopic techniques exist that may discern between enantiomers and assess chiral purity. A nonspectroscopic approach that may be directly observed could provide numerous benefits. Using chiral alanine-appended benzene-tricarboxamide gelators, we reveal a methanol gel system that is capable of providing visual discrimination between enantiomers of various diamines. Specifically, gelation is induced by supramolecular nanofiber assembly resulting from interaction between a chiral gelator and a diamine of opposing chirality (i.e., a heterochiral system). Upon further implementing the chiral gelator in electrospun fibers as solid state films, we revealed enantioselective surface wetting properties that allowed for determining chirality through contact angle measurements. While these two approaches of observable gelation and surface wetting offer nonspectroscopic approaches, we also find that the supramolecular nanofiber assembly was able to enhance the induced circular dichroism signal resulting from addition of chiral diamines, allowing precise quantification of their enantiomeric purity.

TDDFT studies on the chiroptical properties of a chiral inorganic polythioanion Möbius strip

We investigate the ECD spectra of a chiral inorganic polythioanion Möbius strip.

Structural Reorganization and Fibrinogen Adsorption Behaviors on the Polyrotaxane Surfaces Investigated by Sum Frequency Generation Spectroscopy

Polyrotaxanes, such as supramolecular assemblies with methylated α-cyclodextrins (α-CDs) as host molecules noncovalently threaded on the linear polymer backbone, are promising materials for biomedical applications because they allow adsorbed proteins possessing a high surface flexibility as well as control of the cellular morphology and adhesion. To provide a general design principle for biomedical materials, we examined the surface reorganization behaviors and adsorption conformations of fibrinogen on the polyrotaxane surfaces with comparison to several random copolymers by sum frequency generation (SFG) vibrational spectroscopy. We showed that the polyrotaxane (OMe-PRX-PMB) with methylated α-CDs as the host molecule exhibited unique surface structures in an aqueous environment. The hydrophobic interaction between the methoxy groups of the methylated α-CD molecules and methyl groups of the n-butyl methacrylate (BMA) side chains may dominate the surface restructuring behavior of the OMe-PRX-PMB. The orientation analysis revealed that the orientation of the fibrinogen adsorbed on the OMe-PRX-PMB surface is close to a single distribution, which is different from the adsorption behaviors of fibrinogen on other polyrotaxane or random copolymer surfaces.

Dynamic biointerfaces: from recognition to function

The transformation of recognition signals into regulating macroscopic behaviors of biological entities (e.g., biomolecules and cells) is an extraordinarily challenging task in engineering interfacial properties of artificial materials. Recently, there has been extensive research for dynamic biointerfaces driven by biomimetic techniques. Weak interactions and chirality are two crucial routes that nature uses to achieve its functions, including protein folding, the DNA double helix, phospholipid membranes, photosystems, and shell and tooth growths. Learning from nature inspires us to design dynamic biointerfaces, which usually take advantage of highly selective weak interactions (e.g., synergetic chiral H-bonding interactions) to tailor their molecular assemblies on external stimuli. Biomolecules can induce the conformational transitions of dynamic biointerfaces, then drive a switching of surface characteristics (topographic structure, wettability, etc.), and eventually achieve macroscopic functions. The emerging progresses of dynamic biointerfaces are reviewed and its role from molecular recognitions to biological functions highlighted. Finally, a discussion is presented of the integration of dynamic biointerfaces with the basic biochemical processes, possibly solving the big challenges in life science.

Controlled self-assembly of helical nano-ribbons formed by achiral amphiphiles

Helical nano-ribbons with a large aspect ratio were obtained through the self-assembly of an achiral amphiphile. The symmetry breaking is attributed to the orderly but twisted stacking of terpyridine groups. In addition, the morphology of the assemblies can be tuned by the coordination between terpyridine and Zn(2+) ion.

Optically active microspheres constructed by helical substituted polyacetylene and used for adsorption of organic compounds in aqueous systems

This article reports optically active microspheres consisting of chiral helical substituted polyacetylene and β-cyclodextrin-derivative (β-CD-A). The microspheres showed remarkable adsorption toward various organic compounds in water. To prepare the microspheres, an acetylenic-derived helical macro-monomer was synthesized and then underwent aqueous suspension copolymerization with octadecyl acrylate and butyl acrylate by using azobis(isobutyronitrile) as initiator and β-CD-A simultaneously as comonomer and cross-linking agent. The helical macro-monomer chains enabled the microspheres to exhibit desirable enantio-differentiating adsorption capacity toward chiral compounds respectively dissolved in organic solvent, dispersed in water, and dissolved in water. The saturated absorbency toward (R)-(+)- and (S)-(-)-1-phenylethylamine was 29 and 12 mg · g(-1), respectively. The microspheres also showed large oil absorbency (e.g., 22 g · g(-1) CCl4) and a large adsorption toward methyl red (as a model for organic dyes) dispersed in water. The presence of β-CD-A moieties improved the adsorption performance of the microspheres. The present optically active microspheres open a new approach for preparing adsorbents particularly chiral adsorbents with potentials for wastewater treatment.

Why can organic liquids move easily on smooth alkyl-terminated surfaces?

The dynamic dewettability of a smooth alkyl-terminated sol-gel hybrid film surface against 17 probe liquids (polar and nonpolar, with high and low surface tensions) was systematically investigated using contact angle (CA) hysteresis and substrate tilt angle (TA) measurements, in terms of their physicochemical properties such as surface tension, molecular weight/volume, dielectric constant, density, and viscosity. We found that the dynamic dewettability of the hybrid film markedly depended not on the surface tensions but on the dielectric constants of the probe liquids, displaying lower resistance to liquid drop movement with decreasing dielectric constant (ε < 30). Interfacial analysis using the sum-frequency generation (SFG) technique confirmed that the conformation of surface-tethered alkyl chains was markedly altered before and after contact with the different types of probe liquids. When probe liquids with low dielectric constants were in contact with our surface, CH3 groups were preferentially exposed at the solid/liquid interface, leading to a reduction in surface energy. Because of such local changes in surface energy at the three-phase contact line of the probe liquid, the contact line can move continuously from low-surface-energy (solid/liquid) areas to surrounding high-surface-energy (solid/air) areas without pinning. Consequently, the organic probe liquids with low dielectric constants can move easily and roll off when tilted only slightly, independent of the magnitude of CAs, without relying on conventional surface roughening and perfluorination.