Formation of Functionalized Nanowires by Control of Self‐Assembly Using Multiple Modified Amyloid Peptides

Amyloid peptides have great potential as building blocks in the creation of functional nanowires due to their natural ability to self‐assemble into nanofibrillar structures and because they can be easily modified with various functional groups. However, significant modifications of an amyloid peptide generally alter its self‐assembly property, making it difficult to construct functionalized fibrils with a desired structure and function. In this study, a very effective method to overcome this problem is demonstrated by using our structure‐controllable amyloid peptides (SCAPs) terminated with a three‐amino‐acid‐residue cap. The method consists on mixing two or more structurally related amyloid peptides with a fraction of modified SCAPs which co‐assemble into a fibril. This SCAP‐mixing method provides remarkable control over the self‐assembly process both on the small oligomers level and the macroscopic fibrils level. Furthermore, it is shown that the modified peptides imbedded in the resulting fibril can subsequently be functionalized to generate nanowires with the desired properties, highlighting the importance of this SCAP method for nanotechnology applications.     

Discotic Liquid Crystal‐Functionalized Gold Nanorods: 2‐ and 3D Self‐Assembly and Macroscopic Alignment as well as Increased Charge Carrier Mobility in Hexagonal Columnar Liquid Crystal Hosts Affected by Molecular Packing and π–π Interactions

Gold nanorods functionalized with triphenylene‐based discotic liquid crystal (LC) motifs show striking self‐assembly behavior both on transmission electron microscopy (TEM) grids as well as in the bulk enforced by the π–π‐stacking of triphenylene groups of adjacent nanorods. TEM images confirm that these discotic LC nanorods form ribbons of parallel‐stacked nanorods several hundred nanometer long. The pursued silane conjugation approach to decorate the nanorods allows for the preparation of dispersions of the nanorods in the hexagonal columnar phases of parent discotic LCs, where the nanorods can be macroscopically aligned with almost 80% efficiency by a simple shearing protocol. Doping the parent host materials with about 1% by weight of the discotic LC‐capped nanorods also reduces the lattice parameter and the intracolumnar packing, which gives rise to enhanced charge carrier mobility in these hosts as determined by time‐of‐flight measurements.     

Inside Front Cover: Unprecedented Dual Alignment Mode and Freedericksz Transition in Planar Nematic Liquid Crystal Cells Doped with Gold Nanoclusters (Adv. Funct. Mater. 2/2008)

On p. 212, Torsten Hegmann and co‐workers describe nematic liquid crystals (N‐LCs) confined in planar liquid crystal cells after doping with small quantities of gold nanoclusters. These give rise to a dual alignment mode and electro‐optic response (Freedericksz transition). By fine‐tuning of experimental conditions, N‐LCs doped with gold nanoclusters can be electrically reoriented and aligned either like N‐LCs with a positive dielectric anisotropy (used in twisted nematic displays) in a planar cell or alternatively as N‐LCs with a negative dielectric anisotropy (used in large LCD TVs based on the vertical alignment mode). We demonstrate that alkylthiol‐capped gold nanoclusters doped into nematic liquid crystals (N‐LCs) with positive dielectric anisotropy give rise to an unprecedented dual alignment mode and electro‐optical response, which has a potential impact on current liquid crystal (LC) display technologies and N‐LC optical‐biosensor design. By fine‐tuning experimental conditions (temperature, electric field, and alignment), N‐LCs doped with gold nanoclusters can be aligned and electrically reoriented either like N‐LCs with a positive dielectric anisotropy in a planar cell or, alternatively, as N‐LCs with a negative dielectric anisotropy in a homeotropic cell, both at lower threshold voltages than the pure N‐LC.     

An Air‐Supported Liquid Crystal System for Real‐Time and Label‐Free Characterization of Phospholipases and Their Inhibitors

A new air‐supported liquid crystal (LC) system for analyzing interfacial phenomena that occur based on the molecular interaction between LCs and adsorbed molecules of interest at the aqueous/LC interface is reported. Compared with existing LC‐based detection systems, the miniature system reported here requires less sample and involves simpler preparation. Using this system, the enzymatic hydrolysis of various phospholipases such as phospholipase A₂ (PLA₂), phospholipase C (PLC) and phospholipase D (PLD) are characterized. The hydrolysis of phospholipid monolayers self‐assembled at aqueous/LC interface induces an orientational response from the LCs. As a result, an optical signal that reflects the spatial and temporal distribution of phospholipids during the enzymatic reaction can be generated in a real‐time manner. When well‐known phospholipase inhibitors are introduced together with respective phospholipases, no orientational response of LCs is observed. In the case of inhibitors MJ33 and compound 48/80, cross‐inhibitions among phospholipases are also observed. This work demonstrates that the air‐supported LC system provides a facile label‐free assay for characterizing phospholipase activities and for screening enzyme inhibitors. It could potentially be useful for different high throughput and cost‐effective enzyme screening assays.     

Unprecedented Dual Alignment Mode and Freedericksz Transition in Planar Nematic Liquid Crystal Cells Doped with Gold Nanoclusters

We demonstrate that alkylthiol‐capped gold nanoclusters doped into nematic liquid crystals (N‐LCs) with positive dielectric anisotropy give rise to an unprecedented dual alignment mode and electro‐optical response, which has a potential impact on current liquid crystal (LC) display technologies and N‐LC optical‐biosensor design. By fine‐tuning experimental conditions (temperature, electric field, and alignment), N‐LCs doped with gold nanoclusters can be aligned and electrically reoriented either like N‐LCs with a positive dielectric anisotropy in a planar cell or, alternatively, as N‐LCs with a negative dielectric anisotropy in a homeotropic cell, both at lower threshold voltages than the pure N‐LC.     

Smectic Liquid Crystal Defects for Self‐Assembling of Building Blocks and Their Lithographic Applications

Recently, it has been reported that liquid crystal (LC) defects can be used to create highly periodic templates by controlling the surface anchoring and the elastic properties of LC molecules. The self‐assembled defect ordering of the LC materials takes advantage of the ability to achieve fast stabilization of molecular ordering and structure due to the reversible and non‐covalent interactions of the LC molecules. In this Featre Article, the defect structures of liquid crystalline materials will be demonstrated by the surface anchoring and elastic properties. A particular focus are the focal conic domains (FCDs) that are commonly observed in SmA liquid crystals and their lamellar lyotropic counterparts, which form periodic defect ordered structures. In addition, methodologies for creating lithographic templates from the defect order will be described. Finally, the review closes with a discussion of toric focal conic domain arrays that have been fabricated in this manner and used for various applications.     

Preparation of poly (N-vinylcarbazole)-co-poly(2-(dimethylamino)ethyl methacrylate) based hydrogen bonded side-chain liquid crystal copolymer

In this study, new side chain liquid crystalline copolymers were prepared from N-vinyl carbazole (NVC) and 2-(Dimethylamino)ethyl methacrylate) (DMAEM) as a hydrogen bond acceptor copolymer and 8-(4-cyanobiphenyl-4′-oxy)octan-1-ol (LC8) by molecular self-assembly processes via hydrogen bond formation between nitrogen of (DMAEM) and hydroxyl group of the LC8. The formation of H bond was confirmed by using FTIR spectroscopy. The liquid crystalline behavior of the copolymers and homopolymer of the (DMAEM) was investigated using a differential scanning calorimeter (DSC) and polarized optical microscopy. The dielectric relaxation properties of H-bonded Side Chain LC Copolymers (HB-LCP) doped 8-(4-cyanobiphenyl-4′-oxy)octan-1-ol (LC8) and pure LC8 liquid crystals have been investigated by the dielectric spectroscopy (DS) method. The dielectric behavior of the LCs shows a dielectric relaxation process. The relaxation frequency of the LCs was changed by the addition of HB-PLC. It is evaluated that the dielectric strength and relaxation properties of LC8 and LC8/HB-PLC LCs can be controlled by 1% HB-PLC dopant.     

Magnetic and Transparent Composites by Linking Liquid Crystals to Ferrite Nanoparticles through Covalent Networks

The fabrication of transparent, flexible, and optically homogeneous magnetic composites containing ferrite (Fe₃O₄) nanoparticles, liquid crystals (LCs), and siloxane backbones is reported. The transparent magnets are achieved by covalently bonding LCs to the siloxane backbones and then linking them to dopamine‐functionalized ferrite nanocrystals. They exhibit simultaneous high transparency and strong magnetic properties. A remarkable feature of these films is that the surface morphology of the LC‐attached ferrite films can be tuned by an external magnetic field, demonstrating a striped surface in the direction of the field. We show that the LC‐attached film can act as an alignment layer to orient LCs, enabling the development of LC alignment surfaces on the basis of these nanomagnet–LC polymer composites.     

Fabrication and Characterization of Polymer/Liquid Crystal Composite Diffractive Optics by Multiphoton Methods

Direct‐write multiphoton photolithography is used to prepare electrically switchable diffraction gratings having spacings as small as 4 μm. Surface‐relief gratings are written into poly(methyl methacrylate) films using a sample‐scanning confocal microscope and are characterized by using contact‐mode atomic force microscopy. The resulting polymeric channels are filled with nematic liquid crystals (LCs) and sandwiched between indium tin oxide‐coated coverslips to obtain functional devices. These devices exhibit diffraction efficiencies approaching 30 %. Microscopic LC organization and field‐induced reorientation dynamics within these devices are characterized by static and dynamic polarization‐dependent multiphoton excited fluorescence microscopy. LCs are found to align predominantly along the channel axis, but exhibit some disorder near the channel walls, resulting from nanometer‐scale polymer surface roughness. LC reorientation in response to an electric field is rapid (<1 ms) and uniform, whereas field‐free LC relaxation is relatively slow (>20 ms). Both reorientation and relaxation are influenced by orientationally anchored LCs near the channel walls.     

Highly Oriented Nanofibrils of Regioregular Poly(3‐hexylthiophene) Formed via Block Copolymer Self‐Assembly in Liquid Crystals

A novel method making use of block copolymer self‐assembly in nematic liquid crystals (LCs) is described for preparing macroscopically oriented nanofibrils of π‐conjugated semiconducting polymers. Upon cooling, a diblock copolymer composed of regioregular poly(3‐hexylthiophene) (P3HT) and a liquid crystalline polymer (LCP) in a block‐selective LC solvent can self‐assemble into oriented nanofibrils exhibiting highly anisotropic absorption and polarized photoluminescence emission. An unusual feature of the nanofibrils is that P3HT chains are oriented along the fibrils' long axis. This general method makes it possible to use LCs as an anisotropic medium to grow oriented nanofibrils of many semiconducting polymers insoluble in LCs.     

The formation of supramolecular liquid-crystal gels for enhancing the electro-optical properties of twisted nematic liquid crystals

We report that the supramolecular liquid-crystal (LC) physical gel can be formed through the fibrous self-assembly of the polyfluorene-based π-conjugated polymer, poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT), in twisted nematic LC system for the first time. With the utility of alignment layers, the F8BT molecules can be aligned and formed the LC physical gels with the formation of self-assembled supramolecular structures in the twisted nematic LCs. In contrast to conventional LC physical gels, the presence of anisotropic π-conjugated structure makes the twisted nematic LC system exhibit excellent electro-optical properties of driving voltage reduction and contrast ratio enhancement owing to the conjugated polymer having a high π-electron delocalization degree which can efficiently drive LC molecules in much lower operating voltages. The self-assembled supramolecular network has revealed the potential for applying in various LC display devices with the ability of improving their electro-optical performance.     

Computational Chemistry‐Guided Design of Selective Chemoresponsive Liquid Crystals Using Pyridine and Pyrimidine Functional Groups

Computational chemistry‐guided designs of chemoresponsive liquid crystals (LCs) with pyridine or pyrimidine groups that bind to metal‐cation‐functionalized surfaces to provide improved selective responses to targeted vapor species (dimethylmethylphosphonate (DMMP)) over nontargeted species (water) are reported. The LC designs against experiments are tested by synthesizing 4‐(4‐pentyl‐phenyl)‐pyridine and 5‐(4‐pentyl‐phenyl)‐pyrimidine and quantifying LC responses to DMMP and water. Consistent with the computations, pyridine‐containing LCs bind to metal‐cation‐functionalized surfaces too strongly to permit a response to either DMMP or water whereas pyrimidine‐containing LCs undergo a surface‐driven orientational transition in response to DMMP without interference from water. The computation predictions are not strongly dependent on assumptions regarding the degree of coordination of the metal ions but are limited in their ability to predict LC responses when using cations with mostly empty d orbitals. Overall, this work identifies a promising new class of chemoresponsive LCs based on pyrimidine that exhibits enhanced tolerance to water, a result that is important because water is a ubiquitous and particularly challenging chemical interferent in chemical sensing strategies based on LCs. The work also provides further evidence of the transformative utility of computational chemistry methods to design LC materials that exhibit selective orientational responses in specific chemical environments.     

Mechanical Characterization of Amyloid Fibrils Using Coarse‐Grained Normal Mode Analysis

Recent experimental studies have shown that amyloid fibril formed by aggregation of β peptide exhibits excellent mechanical properties comparable to other protein materials such as actin filaments and microtubules. These excellent mechanical properties of amyloid fibrils are related to their functional role in disease expression. This indicates the necessity of understanding how an amyloid fibril achieves the remarkable mechanical properties through self‐aggregation with structural hierarchy. However, the structure‐property–function relationship still remains elusive. In this work, the mechanical properties of human islet amyloid polypeptide (hIAPP) are studied with respect to its structural hierarchies and structural shapes by coarse‐grained normal mode analysis. The simulation shows that hIAPP fibril can achieve the excellent bending rigidity via specific aggregation patterns such as antiparallel stacking of β peptides. Moreover, the length‐dependent mechanical properties of amyloids are found. This length‐dependent property has been elucidated from a Timoshenko beam model that takes into account the shear effect on the bending of amyloids. In summary, the study sheds light on the importance of not only the molecular architecture, which encodes the mechanical properties of the fibril, but also the shear effect on the mechanical (bending) behavior of the fibril.     

Chiroptical Resolution and Thermal Switching of Chirality in Conjugated Polymer Luminescence via Selective Reflection using a Double‐Layered Cell of Chiral Nematic Liquid Crystal

An optically resolvable and thermally chiral‐switchable device for circularly polarized luminescence (CPL) is first constructed using a light‐emitting conjugated polymer film and a double‐layered chiral nematic liquid crystal (N*‐LC) cell. The double‐layered N*‐LC cell with opposite handedness at each layer is fabricated by adding each of two types of N*‐LCs into each of the cells, and the N*‐LCs consist of nematic LCs and chiral dopants with opposite chirality and different mole concentrations. The selective reflection band due to the N*‐LC is thermally shifted so that the band wavelength is close to the luminescence band of the racemic conjugated polymer, such as disubstituted polyacetylene (diPA), yielding CPL with opposite handedness and high dissymmetry factor values (|g_lum|) of 1.1–1.6 at low and high temperatures. The double‐layered N*‐LC cell bearing the temperature‐controlled selective reflection is useful for generating CPLs from racemic fluorescent materials and for allowing thermal chirality‐switching in CPLs, which present new possibilities for optoelectronic and photochemical applications.     

Bioinspired Hierarchical Liquid‐Metacrystal Fibers for Chiral Optics and Advanced Textiles

The organization of nanoparticles in constrained geometries has attracted increasing attention due to their promising structures and topologies. However, the control of hierarchical structures with tailored periodicity at different length scales and topology stabilization in a dynamic environment are very limited and challenging. Herein, through self‐assembly of cellulose nanocrystals (CNCs) within an in situ formed hydrogel sheath using a simple microfluidic strategy, a new breed of liquid crystal (LC) fibers with hierarchical core–sheath architectures, metaperiodic cholesteric alignments, and 3D topological defects, termed as liquid metacrystal (LMC) fibers, is created. The resulting LMC fibers not only exhibit vivid, tunable interference colors, and even inverse optical activity but also have a unique ability to precisely regulate linearly and circularly polarized light in a half‐sync/half‐async form. Furthermore, robust hydrogel sheath enables the LMCs with alignment stability and configuration programmability during drying, which endows the unprecedented freedom to tailor different optical appearances for polarization‐based encryption and recognition. This work opens an avenue toward the fabrication of length‐scale colloidal LCs with continuous and stable topologies and expands the application regimes of LC materials in chiral optics and smart textiles.     

Towards Efficient Dispersion of Carbon Nanotubes in Thermotropic Liquid Crystals

Motivated by numerous recent reports indicating attractive properties of composite materials of carbon nanotubes (CNTs) and liquid crystals (LCs) and a lack of research aimed at optimizing such composites, the process of dispersing CNTs in thermotropic LCs is systematically studied. LC hosts can perform comparably or even better than the best known organic solvents for CNTs such as N‐methyl pyrrolidone (NMP), provided that the dispersion process and choice of LC material are optimized. The chemical structure of the molecules in the LC is very important; variations in core as well as in terminal alkyl chain influence the result. Several observations moreover indicate that the anisotropic nematic phase, aligning the nanotubes in the matrix, per se stabilizes the dispersion compared to a host that is isotropic and thus yields random tube orientation. The chemical and physical phenomena governing the preparation of the dispersion and its stability are identified, taking into account enthalpic, entropic, as well as kinetic factors. This allows a guideline on how to best design and prepare CNT–LC composites to be sketched, following which tailored development of new LCs may take the advanced functional material that CNT–LC composites comprise to the stage of commercial application.     

Photogeneration of High Pretilt Angles of Nematic Liquid Crystals by Non‐Polarized Light Irradiation of Azobenzene‐Containing Polymer Films

A vertical‐alignment (VA) cell of nematic liquid crystals (LCs) was prepared using photoirradiated thin films of a poly(methacrylate) with mesogenic moieties of 4‐trifluoromethoxyazobenzene as the side chains. Optical anisotropy was generated by oblique irradiation of the azobenzene‐containing polymer films with non‐polarized UV light, followed by annealing treatment to enhance the photodichroism, which displayed thermal stability. The combination of oblique exposure to non‐polarized UV light and subsequent annealing treatment brought about high pretilt angles of nematic LCs so that a photoaligned VA LC cell was fabricated. The photopatterned LC cell exhibited electro‐optical properties with excellent optical quality when a voltage was applied even after heating at 100 °C for several hours.     

Nematic Anisotropic Liquid‐Crystal Gels—Self‐Assembled Nanocomposites with High Electromechanical Response

The uniqueness of liquid crystals (LCs) lies in the large anisotropies of their properties, which can be utilized to generate high electromechanical responses. In a properly oriented LC polymer system, an external electric field can induce reorientation of the mesogenic units possessing a dielectric anisotropy, which, when coupled with the shape anisotropy of the mesogenic units, can in turn produce large mechanical strain. Anisotropic LC gels, which can be obtained by in‐situ photopolymerization of the reactive LC molecules in the presence of non‐reactive LC molecules in an oriented state, are an example of such liquid‐crystal polymer systems. It is shown here that a homeotropically aligned LC gel in its nematic phase exhibits high electrically induced strain (> 2 %) with an elastic modulus of 100 MPa and a high electromechanical conversion efficiency (75 %) under an electric field of 25 MV/m. These anisotropic LC polymeric materials could provide a technologically compatible system for such applications as artificial muscles and as microelectromechanical devices.     

Assemblies of Peptide‐Cytotoxin Conjugates for Tumor‐Homing Chemotherapy

Peptide‐drug conjugates are prodrugs that have the advantages of precise molecular structure and the direct exploitation of tumor‐homing, penetration or the cellular uptake abilities of the peptides such as the neuropilin‐1 receptor targeting peptide. The prodrugs generally have fast blood clearance due to their low molecular weights and thus are made to self‐assemble into nanostructures, preferably nanosized micelles and vesicles for intravenous administration, to slow their renal clearance. However, most peptidyl prodrugs usually form precipitates, irregular nanofibers or gels that are unsuitable for intravenous injection. Herein, a arginine‐glycine‐aspartic acid‐lysine (RGDK) peptide and cytotoxin 7‐ethyl‐10‐hydroxycamptothecin (SN38) are used to synthesize the tumor‐homing prodrugs (SN38‐Peps) and explore their structure–micelle formation relationships. A small library of SN38‐Peps is obtained using different structures of peptides, linkers, and drug conjugation sites, and the factors affecting the assembly of SN38‐Peps as well as the stability of formed micelles are investigated. An optimized SN38‐Pep, (MOM)SN38(20)‐CRGDK, is finally obtained which forms stable micelles with a hydrodynamic diameter around 110 nm and a fixed drug loading content as high as 35%. The micelles show a prolonged blood circulation, significantly enhanced tumor accumulation, and therefore improved anticancer activity as compared to the non‐targeting prodrug and a clinically used anticancer drug.