Modulating artificial membrane morphology: pH-induced chromatic transition and nanostructural transformation of a bolaamphiphilic conjugated polymer from blue helical ribbons to red nanofibers

Macrocyclic Diacetylene / Sulfonate Fluorophore Hierarchical Multifunctional Nanotoroids

Functional supramolecular materials exhibit important features including structural versatility and versatile applications. Here, this study reports the construction of unique hierarchically organized nanotoroids exhibiting fluorescence, photocatalytic, and sensing properties. The nanotoroids comprise of macrocyclic diacetylenes (MCDA) and 8-anilino-1-naphthalene sulfonate (ANS), a negatively charged aromatic fluorescent dye. This study shows that the hierarchical structure of the nanotoroids consist of MCDA nanofibers formed by stacked diacetylene monomers as the basic units, which are further bent and aligned into toroidal organization by electrostatic and hydrophobic interactions with the ANS molecules. The amine moieties on the nanotoroids surface are employed for deposition of gold nanostructures - Au nanoparticles or Au nanosheets - which constitute effective platforms for photocatalysis and surface enhanced Raman scattering (SERS)-based sensing.

Polymerization of tetrazine-substituted diacetylenes as aggregates in suspension

Polydiacetylenes (PDAs) are conjugated polymers that have been widely exploited for their chromogenic and fluorogenic transitions upon exposure to external stimuli and biomolecules of interest. Herein, we propose a comparative study of the polymerization dynamics of two diacetylene derivatives, TzDA1 and TzDA2, in the form of aggregates in suspension prepared by reprecipitation method from organic solvents in water, varying the diacetylene concentration and solvent proportions, and sonication in water, varying the time and temperature. Both derivatives bear a tetrazine fluorophore, which serves both to increase the fluorescence quantum yield of the system and to track the polymerization by fluorescence quenching exclusively by the blue-PDA, and differ by the chain termination. It was shown that adding a butyl ester function in TzDA2 to a simple urethane (TzDA1) influences the polymerizability and kinetics of polymerization of the aggregates in suspension. In addition, we showed that also the preparation method and preparation conditions do have an influence on the polymerization dynamics, suggesting that a careful study of these properties should be carried out before investigating the applications of such objects.

Biomimetic Sequence-Templating Approach toward a Multiscale Modulation of Chromogenic Polymer Properties

Precision control via molecular structure over adaptive conjugated polymer properties in aqueous environments is critical for realizing their biomedical applications. Here, we unravel the dependence of amphiphilic peptide-polydiacetylene (PDA) conjugate properties on the characteristic steric and hydrophobic contributions within peptide segments that serve as a biomimetic template for diacetylene polymerization in water. We investigated the functional impacts of molecular volume and polarity changes brought by dipeptide substitution domains on the following peptide-PDA material properties at multiple length scales: supramolecular assembly behavior, chain conformation-dependent photophysical properties, cell-material interfacing, and for the first time, bulk electrical properties of their films processed in water. A library of peptide-PDAs with systematically varied sequences show that the contributions of steric effects predominantly influence the electronic structure and resulting trends in photophysical properties, while the interplay between size and hydrophobicity of individual residues becomes more significant for higher-order assemblies affecting bulk properties. This work demonstrates sequence-tunable molecular volume and polarity as synthetic handles to rationally modulate PDA material properties across length scales, providing insights into the programmability of biomimetic conjugated polymers with adaptive functionalities.

Effect of Hydrophobicity and Salt on the Temperature Responsiveness of Polymeric Micelles Consisting of Hydrophobic and Sulfobetaine Chains

The effect of the hydrophobicity of the core part and salt on the temperature responsiveness of polymeric micelles composed of sulfobetaine and hydrophobic blocks was investigated. Poly(sulfopropyl dimethylammonium propylacrylamide) (PSPP) was used as the sulfobetaine; poly(2-ethylhexyl acrylate) (PEHA), poly(n-butyl acrylate) (PnBA), poly(ethyl acrylate) (PEA), or poly(n-hexyl acrylate) (PnHA) was used as the hydrophobic polymer. Measurement of the transmittance revealed that the transition temperature of the sulfobetaine homopolymer could be controlled by adjusting the concentration, the degree of polymerization (DP), and the concentration of the added salt. The effect of the anionic species of the added salt due to the chemical structural properties of the sulfobetaine chain was consistent with the order of ionic species with strong structural destruction in the Hofmeister series. The temperature response and micelle formation behavior of the polymeric micelles according to the hydrophobicity of the core part and the preparation method were examined by static light scattering (SLS), fluorescence measurement with pyrene, dynamic light scattering (DLS), transmittance, and atomic force microscopy (AFM). Micelles that had EHA (solubility in water was 0.01 g/100 mL) as the core and did not show temperature responsiveness expressed temperature responsiveness at a lower hydrophobicity (solubility of nBA in water was 0.14 g/100 mL). nBA-b-SPP did not show temperature responsiveness due to the block ratio. However, when micelles were prepared by dialysis, smaller and more stable micelles could be formed in an equilibrium state, and temperature responsiveness was observed. Their transition temperature can be controlled by adjusting the ratio of the sulfobetaine blocks, the hydrophobicity of the core part, the concentration of the polymer aqueous solution, and the concentration of the added salt. Furthermore, like the sulfobetaine homopolymer, the effect depended on the anionic species of the added salt.

3D Printing of Polydiacetylene Photocomposite Materials: Two Wavelengths for Two Orthogonal Chemistries

Polydiacetylene (PDA) materials are appealing and gaining increasing research interest due to their outstanding chromatic transition and fluorescence enhancement effects upon exposure to various environmental stimuli. However, despite the photomask method, there are very few reports about the spatial controllable photopolymerization and subsequent 3D printing of PDA until now. Herein, for the first time, we reported the preparation of PDA photocomposite materials based on polyacrylate through the strategy of dual-wavelength polymerization and orthogonal chemistry. First, diacetylene (DA) monomers were homogeneously dispersed in acrylate resin. Then a violet light emitting diode (LED) (or laser diode) was used for the free radical polymerization of polyacrylate. Finally, UV irradiation was utilized to induce the 1,4-topopolymerization of PDA, which could show a successive blue to purple to red color transition in response to the gradient increment of temperature. Interestingly, instead of photomasks, we applied a 3D printing approach directly to this composite material and fabricated some macroscopic stereo patterns, which also illustrated thermochromic properties. This novel kind of functional photocomposite material would demonstrate a huge application prospect in many potential fields, including colorimetric sensing, information encryption, anticounterfeiting, and so on.

A Versatile Strategy for Surface Functionalization of Hydrophobic Nanoparticle by Boronic Acid Modified Polymerizable Diacetylene Derivatives

The flourishing advancements in nanotechnology significantly boost their application in biomedical fields. Whereas, inorganic nanomaterials are normally prepared and capped with hydrophobic ligands, which require essential surface modification to increase their biocompatibility and endow extra functions. Phenylboronic acid derivatives have long been known for its capacity for selective recognition of saccharides. Herein, we demonstrated a versatile surface modification strategy to directly convert hydrophobic inorganic nanocrystals into water-dispersible and targeting nanocomposites by employing boronic acid modified photo-polymerizable 10,12-pentacosadiynoicacid and further explore its potentials in selective cancer cell imaging.

Nanofiber Formation and Polymerization of Bolalipids with Diacetylene-Modified Single Alkyl Chains

The nanofiber formation in aqueous suspension of two classes of symmetric single-chain bolaamphiphiles with different polar headgroups and a diacetylene-modified alkyl chain with a length of 32, 34, and 36 C atoms was investigated by differential scanning calorimetry, transmission electron microscopy, and small-angle neutron scattering. As observed before for other bolalipids with phosphocholine (PC) and dimethyl-phosphoethanolamine (Me₂PE) headgroups, the molecules form fibers when suspended in water at low temperatures but disassemble into micellar-like aggregates upon heating. The introduction of a diacetylene group in the middle of the long chain leads to a perturbation of chain packing so that this fiber-micelle transition occurs at lower temperature compared to the other bolalipids having unmodified alkyl chains. The aim of our project was the introduction of diacetylene groups into alkyl chains to be able to polymerize the fibers at low temperature. This should enhance the fiber stability and prevent the disassembly into micellar aggregates at higher temperature. Polymerization of aggregates containing diacetylene-modified bolaamphiphiles can be easily traced by UV/vis spectroscopy as colored products are formed. We found that polymerization of bolaamphiphiles with PC headgroups leads to a breakdown of most fibers into micellelike aggregates, and only some longer fibers segments are still detectable. In contrast, the use of Me₂PE headgroups improves polymerizability and length of the polymerized fibers. The compound with 36 C atoms in the chain could be polymerized at low temperatures, and the fibers remained stable at least up to a temperature of 60 °C. This shows that the perturbation of the chain packing due to the diacetylene groups in the chains can be overcome by elongation of the chains, so that thermostable fibers with a diameter of the length of the bolalipid molecule can be successfully formed.

Bolaamphiphilic properties and pH-dependent micellization of quercetin polyglycoside

Quercetin polyglycoside as a new bolaamphiphile is prepared via a one-pot grafting polymerization technique using sugar-based cyclic sulfite. Micelles comprising quercetin polyglycoside exhibit special pH-effects, in which the polyglycoside moieties on the surface of the micelle serve as a steric protecting group to endow chemical stabilization.

Micelles comprising quercetin polyglycoside skeletons exhibit special pH-effects based on the integration of bulky polyglycosides on the surface.

Dynamic multistimuli-responsive reversible chiral transformation in supramolecular helices

The design of new chiral chromophores that allow tunable assembly of higher order helical structures by using natural stimuli offers promising avenue in understanding various biological processes. In particular, access to dynamic multistimuli-responsive systems can provide real-time monitoring of chiral transformation in chemical and biological systems. We report on the synthesis of naphthalenediimide appended L-glutamate (NDI-L-Glu) that self-assembles into chiral supramolecular structures under physiological conditions. Specifically, NDI-L-Glu shows a mixture of left- and right-handed helices under physiological conditions, and any deviation from the ambient biochemical environment has a remarkable influence on the chirality of these structures. For instance, acidic environments shift the helicity to left-handedness while the alkaline conditions reversed the helical structures to right-handedness, thereby mimicking the molecular virulence mechanism of tobacco mosaic virus (TMV). The chirality of these supramolecular assemblies can also be controllably tuned by using temperature as an external stimulus, allowing reversible flip of helicity.

Mechanism of the formation of microphase separated water clusters in a water-mediated physical network of perfluoropolyether tetraol

Perfluoropolyether tetraol (PFPE tetraol) possesses a hydrophobic perfluoropolyether chain in the backbone and two hydroxyl groups at each chain terminal, which facilitates the formation of hydrogen bonds with water molecules resulting in the formation an extended physical network. About 3 wt% water was required for the formation of the microphase separated physical network of PFPE tetraol. The mechanism responsible for the microphase separation of water clusters in the physical network was studied using a combination of techniques such as NMR spectroscopy, molecular dynamics (MD) simulations and DSC. MD simulation studies provided evidence for the formation of clusters in the PFPE tetraol physical network and the size of these clusters increased gradually with an increase in the extent of hydration. Both MD simulations and NMR spectroscopy studies revealed that these clusters position themselves away from the hydrophobic backbone or vice versa. The presence of intra- and inter-chain aggregation possibility among hydrophilic groups was evident. DSC results demonstrated the presence of tightly and loosely bound water molecules to the terminal hydroxyl groups of PFPE tetraol through hydrogen bonding. The data from all the three techniques established the formation of a physical network driven by hydrogen bonding between the hydrophilic end groups of PFPE tetraol and water molecules. The flexible nature of the PFPE tetraol backbone and its low solubility parameter favour clustering of water molecules at the terminal groups and result in the formation of a gel.

Polydiacetylene-Coated Sensor Strip for Immunochromatic Detection of Xylella fastidiosa subsp. fastidiosa

This study presents a sensor strip for user-friendly, naked-eye detection of Xylella fasitdiosa, the bacterial causal agent of Pierce's disease in grapevine. This sensor uses anti- X. fastidiosa antibodies conjugated to a polydiacetylene layer on a polyvinylidene fluoride strip to generate specific color transitions and discriminate levels of the pathogen. The detection limit of the sensor is 0.8 × 10⁸ cells/mL, which is similar to bacterial load in grapevine 18 days following bacterial inoculation. This sensor enables equipment-free detection that is highly desirable for in-field diagnostic tools in resource-limited settings.

New Dendritic Polydiacetylene Sensor with Good Reversible Thermochromic Ability in Aqueous Solution and Solid Film

Thermal responsive polydiacetylene derived from PAMAM dendrimer (PDA-G₀) was synthesized. Unlike the ethylenediamine substituted PDA (PDA-NH₂) solution, the prepared PDA-G₀ vesicle solution showed reversible thermochromism property when temperature varied from 20 to 90 °C, which is due to the formation of an internal hydrogen bond in amide groups. Furthermore, PDA-G₀/PMMA film with excellent stability was obtained by a mixed-drying method, which could be stored for a long time without denaturation. After polymerization by UV irradiation, it displayed much better reversible thermochromic ability and the responded temperature range became wider, from 20 to 110 °C.

Fabrication of Helical Nanoribbon Polydiacetylene via Supramolecular Gelation: Circularly Polarized Luminescence and Novel Diagnostic Chiroptical Signals for Sensing

Four kinds of commercially available diacetylene (DA) monomers with different chain length, diacetylene positions were fabricated into the organogels via mixing with a chaperone gelator, an amphiphilic l-histidine ester derivative LHC18 that can help the nongelator to form gels. Upon photo irradiation with a 254 nm UV light, the white gels underwent topochemical reaction and turned into red or blue gels, depending on the DA monomer structures. Through the gel formation, the molecular chirality of LHC18 can be transferred to the polydiacetylene (PDA) and helical nanoribbon structures were obtained. The blue gels showed a clear response to stimuli such as pH variation, heating, mechanical force and organic solvents, and turned into red gels. Interestingly, the blue gel showed strong supramolecular chirality, which could be turned off or changed into red phase CD signals. Such changes in chiroptical signals depended on the external heating and various organic solvents. In the case of heating, the blue gel changed into red one, which showed both strong CD signals and circularly polarized luminescence. In the case of organic solvents, although all the tested solvents made the blue gel to red, only some of them could keep the CD signals, thus providing additional sensing capacity of the PDA system. So far, the blue-to-red color change and the "fluorescence on" was widely used as colorimetric and fluorogenic diagnostic signals for PDA, here we showed an additional chiroptical diagnostic signal for a more precise sensing by using the helical PDA.

Polydiacetylene-coated polyvinylidene fluoride strip aptasensor for colorimetric detection of zinc(II)

We report a new polydiacetylene (PDA) sensor strip for simple visual detection of zinc ions in aqueous solution. The specificity of this sensor comes from Zn²⁺ DNA aptamer probes conjugated onto PDA. Effects of aptamer length and structure on the sensitivity of PDA's color transition were first investigated. PDA conjugated with the optimal aptamer sequence was then coated onto a strip of polyvinylidene fluoride membrane and photopolymerized by UV exposure. The newly developed sensor successfully exhibited a blue-to-red chromatic change in a semi-quantitative manner in response to zinc ions. No discernable change was observed in solutions containing other common ions. Advantages of this sensor include its ease of fabrication, high specificity, and equipment-free detection, all of which are desirable for in-field applications and use in resource-limited settings.

Helical Self-Assembly and Photopolymerization Properties of Achiral Amphiphilic Platinum(II) Diacetylene Complexes of Tridentate 2,6-Bis(1-alkylpyrazol-3-yl)pyridines

Amphiphilic platinum(II) diacetylene complexes of the 2,6-bis(1-butylpyrazol-3-yl)pyridine pincer ligand were designed and synthesized. Helical fibrous nanostructures were obtained through supramolecular assembly of the achiral platinum(II) diacetylene complexes via intermolecular hydrogen bonding, amphiphilic effects, Pt···Pt interactions, and π-π stacking interactions. In situ post-photopolymerization of the diacetylene unit was shown to occur in the preorganized helical fibers.

Polymorphic transformation towards formation of nanotubes by self-assembly of an achiral molecule

In this paper, nanotubes with a uniform diameter were prepared by self-assembly of an achiral azobenzene-containing fatty acid. The polymorphic transformation of the assemblies during the cooling process was systematically studied. By controlling the incubation temperature, different morphologies, such as membranes, stripes, helical ribbons and tubes, were all obtained in our experiment. These elements were all predicted by Selinger et al. in the theoretical model of the formation of nanotubes. To the best of our knowledge, this is the first experimental example to fully support their theory.

The influence of amino acid sequence on structure and morphology of polydiacetylene containing peptide fibres

A systematic study was performed on the influence of charge and steric hindrance on the assembly into fibres of a series of pentameric peptides based on the well-known β-sheet forming sequence Gly-Ala-Gly-Ala-Gly, which were N-terminally acylated with pentacosadiynoic acid. To investigate the effect of steric hindrance and charge repulsion on the fibre structure, either the N-terminal or the C-terminal amino acid in the sequence was replaced by a glutamic acid or lysine residue. Furthermore, peptide amphiphiles (PAs) with an amide or a free acid group at the C-terminus were compared. Steric hindrance and charge repulsion were addressed individually by varying the pH during and after fibre preparation. The self-assembled structures were examined with circular dichroism (CD) spectroscopy and transmission electron microscopy (TEM). UV spectroscopy was used to probe the diacetylene packing in the hydrophobic tail, both by polymerisation behaviour and chromatic properties of the polymers. In brief, the assembly was hindered more if the modification was close to the alkyl tail, and glutamic acid brought about a larger effect than lysine. PAs with two charges yielded assemblies which after polymerisation were found to be the most susceptible towards changes in pH, behaving as a colour-based pH sensor. Typically, TEM and UV showed the same trends, indicating that a distorted morphology as observed with TEM is indicative of a poorer molecular packing of the peptide amphiphile fibres, probed via the changes in absorption of the polydiacetylene backbone.

Morphology control between twisted ribbon, helical ribbon, and nanotube self-assemblies with his-containing helical peptides in response to pH change

pH-Responsive molecular assemblies with a variation in morphology ranging from a twisted ribbon, a helical ribbon, to a nanotube were prepared from a novel A3B-type amphiphilic peptide having three hydrophilic poly(sarcosine) (A block) chains, a hydrophobic helical dodecapeptide (B block), and two histidine (His) residues between the A3 and B blocks. The A3B-type peptide adopted morphologies of the twisted ribbon at pH 3.0, the helical ribbon at pH 5.0, and the nanotube at pH 7.4, depending upon the protonation states of the two His residues. On the other hand, another A3B-type peptide having one His residue between the A3 and B blocks showed a morphology change only between the helical ribbon and the relatively planar sheets with pH variation in this range. The morphology change is thus induced by one- or two-charge generation at the linking site of the hydrophilic and hydrophobic blocks of the component amphiphiles but in different ways.

Lipid tubule growth by osmotic pressure

We present here a procedure for growing lipid tubules in vitro. This method allows us to grow tubules of consistent shape and structure, and thus can be a useful tool for nano-engineering applications. There are three stages during the tubule growth process: initiation, elongation and termination. Balancing the forces that act on the tubule head shows that the growth of tubules during the elongation phase depends on the balance between osmotic pressure and the viscous drag exerted on the membrane from the substrate and the external fluid. Using a combination of mathematical modelling and experiment, we identify the key forces that control tubule growth during the elongation phase.

Soluble conjugated one-dimensional nanowires prepared by topochemical polymerization of a butadiynes-containing star-shaped molecule in the xerogel state

A star-shaped molecule with three butadiyne moieties attached to a central phenyl core was self-assembled via organogel formation in different solvents and subjected to UV irradiation in its xerogels form to give a soluble conjugated 1D nanowire made of three connected polydiacetylene (PDA) chains. The resulting polymer has a slightly lower optical band gap than its linear counterpart and presents no chromism property, indicative of the rigid nature of the polymer thus obtained.

Control over the color transition behavior of polydiacetylene vesicles using different alcohols

In this contribution, we investigate the color transition behavior of polydiacetylene (PDA) vesicles upon exposure to different chemical stimuli. A series of linear and branched alcohols are used as model additives, allowing systematic control of their molecular shape and polarity. The PDA vesicles are fabricated by using three monomers, 10,12-pentacosadiynoic acid (PCDA), 10,12-tricosadyinoic acid (TCDA), and N-(2-amino ethyl)pentacosa-10,12-dyinamide (AEPCDA). When a series of linear alcohols is used, the longer alcohol length causes color transition of all PDA vesicles. In this system, the penetration of linear alcohols into the inner layer of PDA vesicles is dictated by their polarity. The change of -OH position within the alcohol molecule also affects the degree of penetration. It requires a higher amount of the 2-propanol to induce color transitions of the PDAs compared to that of the 1-propanol. The addition of methyl branches into the hydrophobic tail of alcohols causes an increase in steric effect, which hinders the penetration as well. When the 2,2-dimethyl-1-propanol is used as a stimulus, the color transition of PDAs occurs at much higher alcohol concentration compared to 2-methyl-1-butanol, 3-methyl-1-butanol, and 1-pentanol. The variation of PDA structures also affects their ability to interact with the alcohols. The modified head group of poly(AEPCDA) promotes the ability to distinguish between 1-propanol and 2-propanol or 1-propanol and ethanol.

Fabrication of ellagic acid incorporated self-assembled peptide microtubes and their applications

Ellagic acid (EA), a plant polyphenol known for its wide-range of health benefits was encapsulated within self-assembled threonine based peptide microtubes. The microtubes were assembled using the synthesized precursor bolaamphiphile bis(N-α-amido threonine)-1,5-pentane dicarboxylate. The self-assembly of the microstructures was probed at varying pH. In general, tubular formations were observed at a pH range of 4-6. The formed microtubes were then utilized for fabrication with EA. We probed the ability of the microtubes as drug release vehicles for EA as well as for antibacterial applications. It was found that the release of EA was both pH and concentration dependent. The biocompatibility as well as cytotoxicity of the EA-fabricated microtubes was examined in the presence of mammalian normal rat kidney (NRK) cells. Finally the antibacterial effects of the EA incorporated peptide microtubes was examined against Escherichia coli and Staphylococcus aureus.

Polydiacetylenes: supramolecular smart materials with a structural hierarchy for sensing, imaging and display applications

While a large variety of conjugated polymers exist, polydiacetylenes (PDAs) remain a major research area among scientists due to their interesting optical, spectral, electronic, and structural properties. Heavily reviewed in regards to their stimuli responsive properties, much is known about the assortment of sensing and detection capabilities of PDAs. In this article, we look more upon the structural diversities of polydiacetylenes that have been achieved in recent years, particularly from a hierarchical perspective of 1, 2, and 3-dimensional configurations. In addition, we examine how these different dimensional arrangements of PDAs have heralded clear applications in several key areas. Successful integration of these stimuli-responsive "smart" materials into various geometries has required researchers to have a comprehensive understanding of both the fabrication and synthesis processes, as well as the signalling mechanism for the optical, fluorogenic or spectral transitions. The on-going discovery of new PDA formulations continues to provide interesting structural manifestations such as liposomes, tubes, fibres, organic/inorganic incorporated hybrids and composite structures. By highlighting some of the recent conceptual and technological developments, we hope to provide a measure of the current pace in new PDA derivative development as core components in efficient sensor, imaging and display systems.

Interaction of acylated and substituted antimicrobial peptide analogs with phospholipid-polydiacetylene vesicles. Correlation with their biological properties

A series of peptide analogs based on region 6-22 of Plantaricin 149 sequence were synthesized. The interaction between these analogs and phospholipid-polydiacetylene vesicles was investigated to evaluate the ability of the bioassay to detect differences in the interaction of the peptides with dipalmitoylphosphatidylglycerol and dipalmitoylphosphatidylcholine vesicles, associated with amino acid substitution and N-terminal conjugation of the sequences with short fatty acids (8 and 12 carbon atoms). Fatty acid conjugation of peptides with low antimicrobial activity resulted in lipopeptides with improved activity against strains of Staphylococcus aureus and Listeria monocytogenes. The length of the fatty acid determined the bacterial specificity, and the conjugation with n-octanoic acid yielded the most active analog (C8-CT) against Staphylococcus aureus strain (MIC: 1.0 μm) while the conjugation with n-dodecanoic acid (C12-CT) was optimal for Listeria monocytogenes strain (MIC: 2.0 μm). In contrast, the substitution of Phe by Trp had an unfavorable effect on the antimicrobial activity. Hemolysis tests and membrane interaction studies with dipalmitoylphosphatidylcholine-polydiacetylene vesicles showed that lipopeptides interact to a greater extent with both biological and biomimetic membranes. Also, a good correlation was found between antimicrobial activity against Staphylococcus aureus strain and % colorimetric response values with dipalmitoylphosphatidylglycerol-polydiacetylene vesicles.