Functional Liquid‐Crystalline Assemblies: Self‐Organized Soft Materials

In the 21st century, soft materials will become more important as functional materials because of their dynamic nature. Although soft materials are not as highly durable as hard materials, such as metals, ceramics, and engineering plastics, they can respond well to stimuli and the environment. The introduction of order into soft materials induces new dynamic functions. Liquid crystals are ordered soft materials consisting of self‐organized molecules and can potentially be used as new functional materials for electron, ion, or molecular transporting, sensory, catalytic, optical, and bio‐active materials. For this functionalization, unconventional materials design is required. Herein, we describe new approaches to the functionalization of liquid crystals and show how the design of liquid crystals formed by supramolecular assembly and nano‐segregation leads to the formation of a variety of new self‐organized functional materials.     

Regioselective Functionalization of [2.2]Paracyclophanes: Recent Synthetic Progress and Perspectives

[2.2]Paracyclophane (PCP) is a prevalent scaffold that is widely utilized in asymmetric synthesis, π‐stacked polymers, energy materials, and functional parylene coatings that finds broad applications in bio‐ and materials science. In the last few years, [2.2]paracyclophane chemistry has progressed tremendously, enabling the fine‐tuning of its structural and functional properties. This Minireview highlights the most important recent synthetic developments in the selective functionalization of PCP that govern distinct features of planar chirality as well as chiroptical and optoelectronic properties. Special focus is given to the function‐inspired design of [2.2]paracyclophane‐based π‐stacked conjugated materials by transition‐metal‐catalyzed cross‐coupling reactions. Current synthetic challenges, limitations, as well as future research directions and new avenues for advancing cyclophane chemistry are also summarized.     

Bio‐inspired Nonheme Iron Oxidation Catalysis: Involvement of Oxoiron(V) Oxidants in Cleaving Strong C−H Bonds

Nonheme iron enzymes generate powerful and versatile oxidants that perform a wide range of oxidation reactions, including the functionalization of inert C?H bonds, which is a major challenge for chemists. The oxidative abilities of these enzymes have inspired bioinorganic chemists to design synthetic models to mimic their ability to perform some of the most difficult oxidation reactions and study the mechanisms of such transformations. Iron‐oxygen intermediates like iron(III)‐hydroperoxo and high‐valent iron‐oxo species have been trapped and identified in investigations of these bio‐inspired catalytic systems, with the latter proposed to be the active oxidant for most of these systems. In this Review, we highlight the recent spectroscopic and mechanistic advances that have shed light on the various pathways that can be accessed by bio‐inspired nonheme iron systems to form the high‐valent iron‐oxo intermediates.     

Exploring the frontiers of synthetic eumelanin polymers by high‐resolution matrix‐assisted laser/desorption ionization mass spectrometry

New trends in material science and nanotechnologies have spurred growing interest in eumelanins black insoluble biopolymers derived by tyrosinase‐catalysed oxidation of tyrosine via 5,6‐dihydroxyindole (DHI) and its 2‐carboxylic acid (DHICA). Efficient antioxidant and photoprotective actions, associated with peculiar optoelectronic properties, are recognised as prominent functions of eumelanin macromolecules within the human and mammalian pigmentary system, making them unique candidates for the realisation of innovative bio‐inspired functional soft materials, with structure‐based physical–chemical properties. An unprecedented breakthrough into the mechanism of synthetic eumelanin buildup has derived from a detailed investigation of the oxidative polymerization of DHI and its N‐methyl derivative (NMDHI) by linear and reflectron matrix‐assisted laser/desorption ionization mass spectrometry. Regular collections of oligomers of increasing masses, spanning the entire m/z ranges up to 5000 Da (>30‐mer) and 8000 Da (> 50‐mer) for the two building blocks, respectively, were disclosed. It is the first time that the in vitro polymerisation of dihydroxyindoles to form synthetic eumelanins is explored up to its high mass limits, giving at the same time information on the polymerisation mode, whether it follows a stepwise pattern (being this the conclusion in our case) or a staking sequencing of small‐sized entities. It also highlighted the influence of the N‐methyl substituent on the polymerization process; this opens the way to the production of N‐functionalized, synthetic eumelanin‐inspired soft materials, for possible future technological applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Sodium chloride's effect on self‐assembly of diphenylalanine bilayer

Understanding self‐assembling peptides becomes essential in nanotechnology, thereby providing a bottom‐up method for fabrication of nanostructures. Diphenylalanine constitutes an outstanding building block that can be assembled into various nanostructures, including two‐dimensional bilayers or nanotubes, exhibiting superb mechanical properties. It is known that the effect of the ions is critical in conformational and chemical interactions of bilayers or membranes. In this study, we analyzed the effect of sodium chloride on diphenylalanine bilayer using coarse‐grained molecular dynamics simulations, and calculated the bending Young's modulus and the torsional modulus by applying normal modal analysis using an elastic network model. The results showed that sodium chloride dramatically increases the assembling efficiency and stability, thereby promising to allow the precise design and control of the fabrication process and properties of bio‐inspired materials. © 2016 Wiley Periodicals, Inc.     

Advances in Metal‐Free Heterocycle‐Based Columnar Liquid Crystals

Liquid crystals are ordered soft materials formed by self‐organized molecules and can potentially be used as new functional materials for electron‐, ion‐ or molecular‐transport; optical; and bio‐active materials. In particular, the columnar liquid crystals are promising candidates used in various optical and electronic devices. For this purpose, design and synthesis of unconventional materials are essential. In this review, we have summarized several approaches for the synthesis of columnar liquid crystals composed of various heterocyclic systems. We also outline their liquid crystalline and other relevant properties, and their suitability for applications in diverse fields.     

Covalent Grafting of Carbon Nanotubes with a Biomimetic Heme Model Compound To Enhance Oxygen Reduction Reactions

The oxygen reduction reaction (ORR) is one of the most important reactions in both life processes and energy conversion systems. The replacement of noble‐metal Pt‐based ORR electrocatalysts by nonprecious‐metal catalysts is crucial for the large‐scale commercialization of automotive fuel cells. Inspired by the mechanisms of dioxygen activation by metalloenzymes, herein we report a structurally well‐defined, bio‐inspired ORR catalyst that consists of a biomimetic model compound—an axial imidazole‐coordinated porphyrin—covalently attached to multiwalled carbon nanotubes. Without pyrolysis, this bio‐inspired electrocatalyst demonstrates superior ORR activity and stability compared to those of the state‐of‐the‐art Pt/C catalyst in both acidic and alkaline solutions, thus making it a promising alternative as an ORR electrocatalyst for application in fuel‐cell technology.     

Enhanced Photocurrent Generation of Graphene/Au@ZnO Honeycomb Film

A bio‐inspired graphene/Au@ZnO photoelectrode has been prepared via breath figure method, in which Au@ZnO nanospheres were uniformly distributed in the whole honeycomb film. The size of the honeycomb holes effects the light using efficiency. The honeycomb film with smaller holes in more ordered array shows better antireflective property. All the formed graphene/Au@ZnO honeycomb photoelectrodes show a fast, stable, and reversible response of photocurrent accompanied by each switch‐on and switch‐off event. Au@ZnO ‐modified graphene honeycomb film can combine the advantages of increased light harvesting provided by honeycomb structure, efficient charge separation from Au nanoparticles (NPs ), and efficient electron transfer provided by graphene. Au@ZnO ‐ modified graphene honeycomb film shows a two‐fold increase of photocurrent generation than ZnO ‐modified graphene honeycomb film and a three‐fold increase of photocurrent generation than Au@ZnO ‐modified graphene smooth film, respectively. The rational design and engineering of multi components with different functions in a hybrid bio‐inspired structure hold great promise for further efficient solar energy conversion devices.     

Peptide Nanomaterials Designed from Natural Supramolecular Systems

Natural supramolecular assemblies exhibit unique structural and functional properties that have been optimized over the course of evolution. Inspired by these natural systems, various bio‐nanomaterials have been developed using peptides, proteins, and nucleic acids as components. Peptides are attractive building blocks because they enable the important domains of natural protein assemblies to be isolated and optimized while retaining the original structures and functions. Furthermore, the peptide subunits can be conjugated with exogenous molecules such as peptides, proteins, nucleic acids, and metal nanoparticles to generate advanced functions. In this personal account, we summarize recent progress in the construction of peptide‐based nanomaterial designed from natural supramolecular systems, including (1) artificial viral capsids, (2) self‐assembled nanofibers, and (3) protein‐binding motifs. The peptides inspired by nature should provide new design principles for bio‐nanomaterials.     

A Bio‐Inspired,Heavy‐Metal‐Free,Dual‐Electrolyte Liquid Battery towards Sustainable Energy Storage

Wide‐scale exploitation of renewable energy requires low‐cost efficient energy storage devices. The use of metal‐free, inexpensive redox‐active organic materials represents a promising direction for environmental‐friendly, cost‐effective sustainable energy storage. To this end, a liquid battery is designed using hydroquinone (H₂BQ) aqueous solution as catholyte and graphite in aprotic electrolyte as anode. The working potential can reach 3.4 V, with specific capacity of 395 mA h g^?1 and stable capacity retention about 99.7 % per cycle. Such high potential and capacity is achieved using only C, H and O atoms as building blocks for redox species, and the replacement of Li metal with graphite anode can circumvent potential safety issues. As H₂BQ can be extracted from biomass directly and its redox reaction mimics the bio‐electrochemical process of quinones in nature, using such a bio‐inspired organic compound in batteries enables access to greener and more sustainable energy‐storage technology.     

Modeling and understanding locomotion of pneumatic soft robots

Imitating natural locomotion of biological systems (soft-bodied animals) opens the door to the development of a new class of machine, referring to soft robots. A variety of soft robots have been demonstrated by researchers and engineers through incorporating soft technologies into their designs. Yet computer modeling of locomotion of soft robots remains to be a challenging task, not merely because their intrinsic deformation is continuous, complex, and highly nonlinear compared to conventional rigid-bodied robots, but moreover because of the complicated contact problems encountered during locomotion of soft robotics. Herein, we present a combined analytical and numerical analysis of the locomotion of pneumatic network-based soft robots. Concerning a quadruped robot, two fundamental different gaits (undulation and crawling) were identified and numerically validated by two driving modes of pneumatic robots. Extracting ground reaction forces and centroid trajectory from the simulation throws a light on the underlying mechanism of locomotion of soft robots. Our efforts would enhance the understanding and facilitate the control, manipulation, and trajectory optimization of bio-inspired soft robots.     

A Bio‐Inspired,Heavy‐Metal‐Free,Dual‐Electrolyte Liquid Battery towards Sustainable Energy Storage

Wide‐scale exploitation of renewable energy requires low‐cost efficient energy storage devices. The use of metal‐free, inexpensive redox‐active organic materials represents a promising direction for environmental‐friendly, cost‐effective sustainable energy storage. To this end, a liquid battery is designed using hydroquinone (H₂BQ) aqueous solution as catholyte and graphite in aprotic electrolyte as anode. The working potential can reach 3.4 V, with specific capacity of 395 mA h g⁻¹ and stable capacity retention about 99.7 % per cycle. Such high potential and capacity is achieved using only C, H and O atoms as building blocks for redox species, and the replacement of Li metal with graphite anode can circumvent potential safety issues. As H₂BQ can be extracted from biomass directly and its redox reaction mimics the bio‐electrochemical process of quinones in nature, using such a bio‐inspired organic compound in batteries enables access to greener and more sustainable energy‐storage technology.     

Bio‐Inspired Isoalloxazine Redox Moieties for Rechargeable Aqueous Zinc‐Ion Batteries

Organic electrode materials hold great potential for fabricating sustainable energy storage systems, however, the development of organic redox‐active moieties for rechargeable aqueous zinc‐ion batteries is still at an early stage. Here, we report a bio‐inspired riboflavin‐based aqueous zinc‐ion battery utilizing an isoalloxazine ring as the redox center for the first time. This battery exhibits a high capacity of 145.5 mAh g^?1 at 0.01 A g^?1 and a long‐life stability of 3000 cycles at 5 A g^?1. We demonstrate that isoalloxazine moieties are active centers for reversible zinc‐ion storage by using optical and photoelectron spectroscopies as well as theoretical calculations. Through molecule‐structure tailoring of riboflavin, the obtained alloxazine and lumazine molecules exhibit much higher theoretical capacities of 250.3 and 326.6 mAh g^?1, respectively. Our work offers an effective redox‐active moiety for aqueous zinc batteries and will enrich the valuable material pool for electrode design.     

Efficient and Bio‐inspired Conversion of Cellulose to Formic Acid Catalyzed by Metalloporphyrins in Alkaline Solution

A bio‐inspired approach for efficient conversion of cellulose to formic acid (FA ) was developed in an aqueous alkaline medium. Metalloporphyrins mimicking cytochrome P450 exhibit efficiently and selectively catalytic performance in catalytic conversion of cellulose. High yield of FA about 63.7% was obtained by using sulfonated iron(III ) porphyrin as the catalyst and O₂ as the oxidant. Iron(III )‐peroxo species, TSPPFe^IIIOO ⁻, was involved to cleave the C‐C bonds of gluconic acid to FA in this catalytic system. This approach used relatively high concentration of cellulose and ppm concentration of catalyst. This work may provide a bio‐inspired route to efficient conversion of cellulose to FA .     

Hydrogels from Amorphous Calcium Carbonate and Polyacrylic Acid: Bio‐Inspired Materials for “Mineral Plastics”

Given increasing environmental issues due to the large usage of non‐biodegradable plastics based on petroleum, new plastic materials, which are economic, environmentally friendly, and recyclable are in high demand. One feasible strategy is the bio‐inspired synthesis of mineral‐based hybrid materials. Herein we report a facile route for an amorphous CaCO₃ (ACC)‐based hydrogel consisting of very small ACC nanoparticles physically cross‐linked by poly(acrylic acid). The hydrogel is shapeable, stretchable, and self‐healable. Upon drying, the hydrogel forms free‐standing, rigid, and transparent objects with remarkable mechanical performance. By swelling in water, the material can completely recover the initial hydrogel state. As a matrix, thermochromism can also be easily introduced. The present hybrid hydrogel may represent a new class of plastic materials, the “mineral plastics”.     

Green and Functional Aerogels by Macromolecular and Textural Engineering of Chitosan Microspheres

Tremendous interest was recently devoted to the preparation of porous and functional materials through sustainable route, including primarily the use of renewable biopolymers instead of petroleum‐sourced synthetic chemicals. Among the biopolymers available in enormous quantity, chitosan – obtained by deacetylation of chitin – stands as the sole nitrogen‐containing cationic amino‐sugar carbohydrate. This distinctively provides chitosan derivatives with plenty of opportunities in materials science. Particularly, its pH switchable solubility allowed the preparation of three‐dimensional entangled nanofibrillated self‐standing microspheres. These porous hydrogels behave as nano‐reactors to confine exogenous nanoobjects within the polysaccharide network, including sol‐gel metal alkoxide species, organometallic derivatives and isotropic and oriented nanoparticles. Besides, the interfacial interplay of chitosan with lamellar clay and graphene oxide allowed the penetration of the biopolymer inside of the galleries, which result in a complete delamination of the layered nanomaterials. The preserved gelation memory of chitosan in these formulations provides a way to access porous microspheres entangling exfoliated nanometric sheets. CO₂ supercritical drying of functional hydrogel beads enabled efficient removal of water and other liquid solvents without wall collapsing, allowing large‐scale preparation of millimetric hydrocolloidal microspheres with an open macroporous network. These functionalized lightweight biopolymer aerogels find applications in heterogeneous catalysis, sensing, adsorption, insulation and for the design of other sophisticated porous nanostructures. Beyond their tailorable molecular and textural‐engineering, the possibility for macroscopic shaping of these intriguing nanostructures opens many new opportunities, especially in additive‐manufacturing for soft and hybrid robotics.     

Super‐Soft and Super‐Elastic DNA Robot with Magnetically Driven Navigational Locomotion for Cell Delivery in Confined Space

Soft organisms such as earthworms can access confined, narrow spaces, inspiring scientists to fabricate soft robots for in vivo manipulation of cells or tissues and minimally invasive surgery. We report a super‐soft and super‐elastic magnetic DNA hydrogel‐based soft robot (DNA robot), which presents a shape‐adaptive property and enables magnetically driven navigational locomotion in confined and unstructured space. The DNA hydrogel is designed with a combinational dynamic and permanent crosslinking network through chain entanglement and DNA hybridization, resulting in shear‐thinning and cyclic strain properties. DNA robot completes a series of complex magnetically driven navigational locomotion such as passing through narrow channels and pipes, entering grooves and itinerating in a maze by adapting and recovering its shape. DNA robot successfully works as a vehicle to deliver cells in confined space by virtue of the 3D porous networked structure and great biocompatibility.     

Bio‐Inspired Fragmentations: Rapid Assembly of Indolones, 2‐Quinolinones,and (−)‐Goniomitine

Inspired by the biogenetic origin of goniomitine, new synthetic bio‐inspired fragmentation strategies for the synthesis of functionalized 2‐quinolinones and indolones have been developed. Remarkable synthetic efficiency was achieved by telescoping several transformations into one‐pot reactions, allowing for the direct coupling of 2‐alkynyl‐anilines and diazo ketones. The synthetic utility was demonstrated by the 5‐step asymmetric total synthesis of (−)‐goniomitine from 2‐ethyl‐cyclopentanone.     

Bio‐inspired Domino oxa‐Michael/Diels–Alder/oxa‐Michael Dimerization of para‐Quinols

A bio‐inspired, pyrrolidine‐mediated, dimerization of para‐quinols has been developed. It represents one of the most complex, yet general, dimerization reactions ever disclosed, selectively forming four new bonds, four new rings, and eight new contiguous stereogenic centres. The para‐quinol starting materials are easily handled, bench‐stable compounds, accessed in just one step from aromatic feedstocks. The reaction can be scaled up to give grams of polycyclic material, primed for further elaboration.     

A novel fabrication technique to minimize poly(dimethylsiloxane)‐microchannels deformation under high‐pressure operation

PDMS is one of the most common materials used for the flow delivery in the microfluidics chips, since it is clear, inert, nontoxic, and nonflammable. Its inexpensiveness, straightforward fabrication, and biological compatibility have made it a favorite material in the exploratory stages of the bio‐microfluidic devices. If small footprint assays want to be performed while keeping the throughput, high pressure‐rated channels should be used, but PDMS flexibility causes an important issue since it can generate a large variation of microchannel geometry. In this work, a novel fabrication technique based on the prevention of PDMS deformation is developed. A photo‐sensible thiolene resin (Norland Optical Adhesive 63, NOA 63) is used to create a rigid coating layer over the stiff PDMS micropillar array, which significantly reduces the pressure‐induced shape changes. This method uses the exact same soft lithography manufacturing equipment. The verification of the presented technique was investigated experimentally and numerically and the manufactured samples showed a deformation 70% lower than PDMS conventional samples.