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Gold nanoparticles (AuNPs) have been a subject of considerable interest in recent years due to both their magnetic and catalytic properties. This paper reports a two-fold study of the reactivity at 300 K of the isotopic hydrogen atom, muonium (Mu = μ+e-), (i) with bare uncapped AuNPs of different sizes encapsulated in mesoporous (SBA-15) silica hosts, forming a diamagnetic final state in the Mu + AuNP → MuAuNP reaction, and (ii) with surface-adsorbed benzene on these NPs forming the muoniated cyclohexadienyl radical in the Mu + C6H6 → MuĊ6H6 addition reaction. The measured muon-spin relaxation rates, λC, for the chemisorption reaction of Mu with the bare AuNPs show some variation with AuNP size. The Mu + C6H6 addition reaction has been studied over a range of benzene loadings both on bare silica and in the AuNP/silica samples. The measured muon-spin relaxation rates, λTot, exhibit a linear dependence on benzene concentration over the full range of loadings in both cases, in accord with an Eley-Rideal model of surface reactivity. Rate constants, kBz, were determined from this dependence which exhibit a 2-3-fold faster reaction rate on the AuNPs than on the bare silica, suggesting a catalytic effect due to benzene adsorbed on these NP surfaces.

Chemisorption of muonium onto the surface of gold nanoparticles has been observed. Muonium (μ+e-), a light hydrogen-like atom, reacts chemically with uncapped 7 nm gold nanoparticles embedded in mesoporous silica (SBA-15) with a strong temperature-dependent rate. The addition rate is fast enough to allow coherent spin transfer into a diamagnetic muon state on the nanoparticle surface. The muon is well established as a sensitive probe of static or slowly fluctuating magnetic fields in bulk matter. These results represent the first muon spin rotation signal on a nanoparticle surface or any metallic surface. Only weak magnetic effects are seen on the surface of these Au nanoparticles consistent with Pauli paramagnetism.

We report muon spin rotation/relaxation measurements of muonium in mesoporous silica (SBA-15) with a high specific surface area of 600 m2/g. Up to 70 percent of the incoming muons form muonium and escape efficiently into the open pores at all temperatures between 3 and 300K. We present evidence that the interaction with the silica surfaces involves both spin exchange and a transition to a diamagnetic state, possibly due to dangling bonds on the surface. At very low temperatures, below 20K, the interaction between muonium and the silica surfaces is suppressed due to a He film coating the surfaces. These results indicate that it should be possible to use muonium to probe the surfaces of uncapped nanoparticles supported in silica.

Cyclometalated platinum complexes play a crucial role in catalysis, bioimaging, and optoelectronics. Phenylpyridines are widespread cyclometalating ligands that generate stable and highly emissive Pt complexes. While it is common practice to modify these ligands to fine-tune their photophysical properties, the incorporation of polycyclic aromatic hydrocarbons into the ligand's structure has been largely overlooked. This report describes the cyclometalation of naphthalenyl- and anthracenylpyridine ligands, which has resulted in ten new luminescent Pt II and Pt IV complexes. These species are enabled by a dual-binding behavior discovered in our polyaromatic-containing ligands. The introduction of naphthalenyl and anthracenyl groups unlocks dual binding modes, with the Pt center bonding to either of two distant carbon atoms within the ligand. These complexes exhibit both symmetric structures with two 5-membered metallacycles and asymmetric structures with 5- and 6-membered metallacycles. This work presents a strategy for the regioselective synthesis of Pt complexes with bespoke structures and photophysical properties. Our findings offer new opportunities in platinum chemistry and beyond, with potential implications for materials and technologies., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Transient technology involves materials and devices that undergo controlled degradation after a reliable operation period. This groundbreaking strategy offers significant advantages over conventional devices based on non-renewable materials by limiting environmental exposure to potentially hazardous components after disposal, and by increasing material circularity. As the most abundant naturally occurring polymer on Earth, cellulose is an attractive material for this purpose. Besides, (nano)celluloses are inherently biodegradable and have competitive mechanical, optical, thermal, and ionic conductivity properties that can be exploited to develop sustainable devices and avoid the end-of-life issues associated with conventional systems. Despite its potential, few efforts have been made to review current advances in cellulose-based transient technology. Therefore, this review catalogs the state-of-the-art developments in transient devices enabled by cellulosic materials. To provide a wide perspective, the various degradation mechanisms involved in cellulosic transient devices are introduced. The advanced capabilities of transient cellulosic systems in sensing, photonics, energy storage, electronics, and biomedicine are also highlighted. Current bottlenecks toward successful implementation are discussed, with material circularity and environmental impact metrics at the center. It is believed that this review will serve as a valuable resource for the proliferation of cellulose-based transient technology and its implementation into fully integrated, circular, and environmentally sustainable devices., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

We report the reversible transformation between a singly stapled dynamic α-helical peptide and a doubly stapled quasi-static one through redox-triggered dithiol/disulfide conversions of a stapling moiety. This process allows the rate of interconversion between the right-handed (P) and left-handed (M) α-helices to be altered by a factor of approximately 103 before and after the transformation. An as-obtained doubly stapled α-helical peptide, which is composed of an achiral peptide having an L-valine carboxylic acid residue at the C-terminus, a disulfide-based reversible staple, and a biphenyl-based fixed staple, adopts an (M)-rich form as a kinetically trapped state. The (M)-rich helix was subsequently transformed into the thermodynamically stable (P)-rich form in 1,1,2,2-tetrachloroethane with the half-life time (t1/2) of approximately 44 days at 25 ºC. Reduction of the doubly stapled peptide with tri-n-butylphosphine in tetrahydrofuran/water (10/1, v/v) produced the corresponding singly stapled dynamic α-helical peptide bearing two thiol groups at the side chains, which underwent solvent-induced reversible helicity inversion. The resulting dithiol of the singly stapled peptide could be reoxidized to form the original doubly stapled form using 4,4'-dithiodipyridine. Furthermore, the P/M interconversion of a doubly stapled peptide with two flexible hydrocarbon-based staples is considerably more rapid than that with more rigid staples., (© 2024 Wiley‐VCH GmbH.)

Modifying the environment around particles ( e.g. , introducing a secondary phase or external field) can affect the way they interact and assemble, thereby giving control over the physical properties of a dynamic system. Here, graphene oxide (GO) photonic liquids that respond to a magnetic field are demonstrated for the first time. Magnetic nanoparticles are used to provide a continuous magnetizable liquid environment around the GO liquid crystalline domains. In response to a magnetic field, the alignment of magnetic nanoparticles, coupled with the diamagnetic property of GO nanosheets, drives the reorientation and alignment of the nanosheets, enabling switchable photonic properties using a permanent magnet. This phenomenon is anticipated to be extendable to other relevant photonic systems of shape-anisotropic nanoparticles and may open up opportunities for developing GO-based optical materials and devices.

Humankind's manipulation of platinum dates back more than two millennia to burial objects. Since then, its use has evolved from purely decorative purposes in jewelry to more functional applications such as in catalysts, pharmaceuticals, and bioimaging agents. Platinum offers a range of properties arguably unmatched by any other metal, including electroactivity, photoluminescence, chromic behaviour, catalysis, redox reactivity, photoreactivity, and stimuli-controlled intermetallic interactions. The vast body of knowledge generated by the exploration of these and other properties of platinum has recently merged with other areas of chemistry such as supramolecular and host-guest chemistry. This has shown us that platinum can incorporate its responsive character into supramolecular assemblies ( e.g. , macrocycles and polymers) to produce materials with tailorable functions and responses. In this Perspective Article, we cover some platinum-powered supramolecular structures reported by us and others, hoping to inspire new and exciting discoveries in the field., Competing Interests: The authors declare no conflict of interest to declare., (This journal is © The Royal Society of Chemistry.)

In nature, α-helical peptides adopt right-handed conformations that are dictated by L-amino acids. Isolating one-handed α-helical peptides composed of only achiral components remains a significant challenge. Here, this goal is achieved by optical resolution of the corresponding racemic (quasi-)static α-helical peptide with double stapling, which effectively freezes the interconversion between the right-handed (P)- and left-handed (M)-α-helices. An as-obtained doubly stapled analogue having an unprotected L-valine residue at the C-terminus transforms from a kinetically trapped (M)-α-helix to a thermodynamically stable (P)-α-helix upon heating. In contrast, the corresponding singly stapled α-helical peptide undergoes an acid/base-triggered and solvent-induced reversible inversion of its preferred helicity within minutes. The interconversion rates of the singly and doubly stapled α-helical peptide foldamers are approximately 10 6 and 10 12 times slower, respectively, than that of a non-stapled dynamic helical peptide. Therefore, the enantiopure doubly-stapled (quasi-)static α-helical peptide would retain its optical activity for several years at 25 °C., (© 2023. The Author(s).)

The quest for advanced water purification technologies has been vigorous over recent decades, motivated by the promise of ever more efficient, greener, and affordable tools. Halloysite nanotubes (HNTs) are naturally-occurring materials that have shown potential as dye sorbents. Unfortunately, these nanoclays suffer from low permeation during water treatment, which limits their widespread application. Here, we use cellulose nanocrystals (CNCs) as structural scaffolds to support HNTs and fabricate permeable aerogel sorbent materials with mechanical stability. Aerogels containing 40 wt% HNTs showed a maximum dye adsorption capacity of 60 mg g -1 towards methylene blue, with only 15% decay in efficiency after 5 cycles. The good mechanical properties of these materials allowed for their incorporation into free-flowing purification columns that displayed excellent dye removal ability. Overall, this work provides a new strategy to fabricate green, renewable, and low-cost sorbent materials for the removal of dyes and shows potential for the sorption of other ionic pollutants.

Biological systems exploit restricted degrees of freedom to drive self-assembly of nano- and microarchitectures. Simplified systems, such as colloidal nanoparticles that behave as lyotropic liquid crystalline mesophases in confined geometric spaces, may be used to mimic biological structures. Cellulose nanocrystals (CNCs) are colloidally stable nanoparticles that self-assemble into chiral nematic ( ChN ) liquid crystalline mesophases. To date, the self-assembly of ChN mesophases of CNCs has been studied under confinement conditions within curved surfaces or under drying conditions that impose curvatures that can be exploited to control ChN ordering; however, their self-assembly has not been investigated in geometries with square cross-sections under static conditions. Here, we show that because of surface anchoring on perpendicular surfaces, the ChN CNC phase is unable to bend with the 90° angle of the square capillary under increasing confinement. Instead, the ChN phase forms radial layers in the shape of concentric squircle shells. With increasing layer distance from the capillary wall, the squircles transition into concentric cylinder shells. In larger capillaries, the radial shell layers appear as a continuous spiral pattern that engulfs fragmented ChN pseudolayers, a defect to accommodate the cylindrical confinement of the mesophase. These results are useful for understanding the fundamentals of self-assembling systems and development of new technologies.

The development of long-lived electrochemical energy storage systems based on renewable materials is integral for the transition toward a more sustainable society. Supercapacitors have garnered considerable interest given their impressive cycling performance, low cost, and safety. Here, the first example of a chiral nematic activated carbon aerogel is shown. Specifically, supercapacitor materials are developed based on cellulose, a non-toxic and biodegradable material. The chiral nematic structure of cellulose nanocrystals (CNCs) is harnessed to obtain free-standing hierarchically ordered activated carbon aerogels. To impart multifunctionality, iron- and cobalt-oxide nanoparticles are incorporated within the CNC matrix. The hierarchical structure remains intact even at nanoparticle concentrations of ≈70 wt%. The aerogels are highly porous, with specific surface areas up to 820 m 2 g -1 . A maximum magnetization of 17.8 ± 0.1 emu g -1 with superparamagnetic behavior is obtained, providing a base for actuator applications. These materials are employed as symmetric supercapacitors; owing to the concomitant effect of the hierarchically arranged carbon skeleton and KOH activation, a maximum C p of 294 F g -1 with a capacitance retention of 93% after 2500 cycles at 50 mV s -1 is achieved. The multifunctionality of the composite aerogels opens new possibilities for the use of biomass-derived materials in energy storage and sensing applications., (© 2023 The Authors. Small published by Wiley-VCH GmbH.)

Metal-metal bonds have rarely been explored as active elements in supramolecular assemblies despite their unique potential to introduce responsive behavior. In this report, a dynamic molecular container composed of two cyclometalated Pt units is constructed using Pt-Pt bonds. This molecule-the flytrap-has a flexible jaw composed of two [18]crown-6 ethers that can adapt their shape to bind large inorganic cations with sub-micromolar affinity. Along with the spectroscopic and crystallographic characterization of the flytrap, we report its photochemical assembly, which allows the capture of ions and their transport from solution to the solid state. In addition, we have been able to recycle the flytrap to regenerate its starting material due to the reversible nature of the Pt-Pt bond. We believe that other molecular containers and materials for harvesting valuable substrates from solution could be assembled using the advances presented here., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Stimulus-responsive materials that display circularly polarized luminescence (CPL) have attracted great attention for application in chiral sensors and smart displays. However, due to difficulties in the regulation of chiral structures, fine control of CPL remains a challenge. Here, it is demonstrated that cellulose nanocrystal shape-memory polymers (CNC-SMPs) with luminescent components enable mechanically responsive CPL. The chiral nematic organization of CNCs in the material gives rise to a photonic bandgap. By manipulating the photonic bandgap or luminescence wavelengths of the luminescent CNC-SMPs, precise control of CPL emission with varied wavelengths and high dissymmetry factors (g lum ) is achieved. Specifically, CPL emission can be switched reversibly by treating the luminescent CNC-SMPs with hot-pressing and recovery by heating. Pressure-responsive CPL with tunable g lum values is ascribed to the pressure-responsive photonic bandgaps. Moreover, colorimetric and CPL-active patterns are created by imprinting desired forms into SMP samples. This study demonstrates a novel way to fabricate smart CPL systems using biomaterials., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

Thermal stability is a crucial property of materials, especially when they have a wide range of thermally sensitive applications. Cellulose nanomaterials (CNMs) extracted from cellulosic biomass have garnered significant attention due to their abundance, biodegradability, sustainability, production scalability, and industrial versatility. To explore the correlation between the structure, chemistry, and morphology of CNMs and their thermal stability, we present a comprehensive literature review. We identify five major factors affecting CNMs' thermal stability, namely type, source, reaction conditions, post-treatment, and drying method, and analyze their impact on CNMs' thermal stability using several case studies from the literature. Using multiple linear least-squares regression (MLR), we establish a quantitative relationship between thermal stability and seven variables: crystallinity index of the source, dissociation constant of the reactant used, reactant concentration, reaction temperature, reaction time, evaporation rate, and post-treatment presence. By understanding these interdependencies, our statistical analysis enables the design of CNMs with predictable thermal properties and identification of optimal conditions for achieving high thermal stability. The results of our study provide crucial insights that can guide the development of CNMs with enhanced thermal stability for use in a variety of industrial applications.

Zeolitic imidazolate framework (ZIF-8) nanocrystals were uniformly grown on the surface of cellulose nanocrystals (CNCs) to give a hybrid material, ZIF@CNCs. By varying the stoichiometry of the components, it was possible to control the size of the ZIF-8 crystals grown on the CNC surface. Optimized ZIF@CNC (ZIF@CNC-2) was used as a template to synthesize a microporous organic polymer (MOP), ZIF@MOP@CNC. After etching the ZIF-8 with 6 M HCl solution, a MOP material with encapsulated CNCs (MOP@CNC) was formed. Zinc coordination into the porphyrin unit of the MOP yielded the ship-in-a-bottle structure, Zn MOP@CNC, comprised of CNCs encapsulated within the Zn-MOP. In comparison to ZIF@CNC-2, Zn MOP@CNC showed better catalytic activity and chemical stability for CO 2 fixation, converting epichlorohydrin to chloroethylene carbonate. This work demonstrates a novel approach to create porous materials through CNC templating., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Films of cellulose nanocrystals (CNCs) with chiral nematic organization can show vivid iridescence that arises from their hierarchical structure. Unfortunately, the brittleness of the films limits their potential applications. In this paper, we investigate the incorporation of halloysite nanotubes (HNTs) into CNC films to prepare organic-inorganic composite films with enhanced mechanical properties, while preserving the chiral nematic structure and brilliant iridescence. The hybrid composite films containing 10 wt% HNTs are more elastic than pristine CNC films, with a 1.3-fold increase in tensile strength and a 1.6-fold increase in maximum strain. As well, the incorporation of HNTs slightly improves the thermal stability of the composite films. These materials mimic the hybrid composite structures of crab shells, leading to enhanced mechanical properties and thermal stability of CNC films while maintaining iridescence.

Gels are useful materials for drug delivery, wound dressings, tissue engineering, and 3D printing. These various applications require gels with different mechanical properties that can be easily tuned, also preferably excluding the use of chemical additives, which can be toxic or harmful to the body or environment. Here, we report a novel strategy to synthesize cellulose nanocrystal (CNC) gels with tunable mechanical properties. Sequential freeze-thaw cycling and hydrothermal treatments were applied to CNC suspensions in different orders to give a series of pristine CNC hydrogels. Freeze-drying of the hydrogels also afforded a series of lightweight CNC aerogels. The mechanical properties of the hydrogels and aerogels were studied by rheological measurements and compression strength tests, respectively. Specifically, the complex modulus of CNC hydrogels ranged from 160 to 32,000 Pa among eight different hydrogels, while Young's modulus of CNC aerogels was tuned from 0.114 to 3.98 MPa across five different aerogels. The microstructures of aerogels were also investigated by scanning electron microscopy and X-ray microtomography, which revealed remarkable differences between the materials. Solvent sorption-desorption tests showed that the reinforced networks have excellent stability over the basic CNC aerogels in ethanol, demonstrating a material enhancement from the preparation strategies we developed. Thermal conductivity and thermal stability for these materials were also investigated, and it was found that the lowest thermal conductivity was 0.030 W/m K, and all of the aerogels are generally stable below 280 °C. These characteristics also expand the potential applications of this family of CNC gels to lightweight supporting materials and thermal insulators.

Photonic materials based on composite films of cellulose nanocrystals (CNCs) and polymers are promising as they can be renewable and show tunable optical and mechanical properties. However, the influence of polymers on CNC self-assembly is not always well understood, and conflicting results are present in the literature. In this study, we incorporate three neutral, water-soluble polymers-poly(ethylene glycol) (PEG), poly(vinyl pyrrolidone) (PVP), and poly(acrylic acid) (PAA)-with different molecular weights into CNC suspensions at various concentrations prior to obtaining iridescent composite thin films by solvent evaporation. Through spectroscopic, potentiometric, and rheological analyses, we find that PVP physically adsorbs to the surface of CNCs resulting in a bathochromic shift in film color with both increasing concentration and polymer molecular weight. In contrast, PEG induces depletion interactions that result in a decrease in the size of chiral nematic CNC domains, with a negligible change in film color. Finally, PAA hydrogen bonds to the hydroxyl groups of CNCs, resulting in a bathochromic color shift along with interesting rheological and liquid-state properties. This work demonstrates a deeper understanding of CNC-polymer interactions during coassembly and formation of iridescent chiral nematic films, allowing for greater control over optical properties of future CNC-based materials.

Macrocycle engineering is a key topic in supramolecular chemistry. When synthesizing a ring, one can obtain either complex mixtures of macrocycles of different sizes or a single ring if a template is utilized. Here, we unite these approaches along with post-synthetic modifications to transform a single tether into multiple rings-up to five per tether. The macrocycles contain two bridged phenylpyridine ligands that are connected through a Pt atom, which defines the rings' shape, size, and host activity. All rings undergo redox reactions (between Pt II and Pt IV ) that allow for large conformational changes. Their reactivity, together with their host performance, is a convenient way to control the capture and release of guests, to mediate ring transformations, and to control pseudorotaxane-to-pseudorotaxane conversions. This novel approach could serve to assemble other libraries of small ring molecules, create cyclic polymers bridged by responsive-at-metal nodes, and produce processable mechanically interlocked molecules., (© 2022 Wiley-VCH GmbH.)

Objectives: In this paper we propose embedding natural fillers, such as pristine and functionalized chitin nanocrystals, into resin adhesives to produce photopolymerizable dental filled adhesives with enhanced biocompatibility, hydrophobicity, mechanical resistance, and anti-bacterial properties., Methods: Chitin nanocrystals (ChNC) were functionalized with decanoyl chloride and methacrylic anhydride to produce ChNC-C10 and ChNC-MA, respectively. These hydrophobically functionalized chitin nanocrystals were incorporated into a resin adhesive at concentrations of 0.5-3.0 wt% to assess the materials' physical and mechanical properties through Fourier-transform infrared (FTIR) spectroscopy, solid-state NMR spectroscopy, X-ray diffraction (XRD), elemental analysis, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), flexural strength, microhardness, and water sorption tests., Results: The analytical techniques confirmed the successful preparation of chitin nanocrystals from commercial chitin powder derived from shrimp shells and the efficient hydrophobization of their surface. Electron microscope images indicated that the increased hydrophobicity of ChNC-C10 promotes the formation of layered structures throughout the resin adhesive, while ChNC-MA tends to form aggregates in the matrix. Adhesives filled with ChNC-C10 enhanced their flexural strength, microhardness, and thermal stability and decreased their water sorption and degree of conversion. Adhesives filled with ChNC-MA resulted in improvements in microhardness, in water sorption and degree of conversion, although they did not exhibit augmentation of their flexural strength and thermal stability., Significance: In light of the improved physical and mechanical properties with respect to the control, resin adhesives filled with anti-bacterial chitin nanocrystals are promising new materials for dental applications, especially those filled with low/moderate amounts of ChNC-C10., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

In our daily life, some of the most valuable commodities are preprogrammed or preassembled by a manufacturer; the end-user puts together the final product and gathers properties or function as desired. Here, we present a chemical approach to preassembled materials, namely supramolecular polymer networks (SPNs), which wait for an operator's command to organize autonomously. In this prototypical system, the controlled disassembly of a metastable interlocked molecule (rotaxane) liberates an active species to the medium. This species crosslinks a ring-containing polymer and assembles with a reporting macrocycle to produce colorful SPNs. We demonstrate that by using identical preprogrammed systems, one can access multiple supramolecular polymer networks with different degrees of fluidity (μ *  = 2.5 to 624 Pa s -1 ) and color, all as desired by the end-user., (© 2022. The Author(s).)

Salphen-based [ n + n ] macrocycles have been widely explored for their unique chemical and topological properties following metal ion coordination. Despite having vastly different reactivity than their coordinated counterparts, fewer studies have focused on metal-free salphen macrocycles. We investigated the binding of [2 + 2] Schiff-base macrocycle host 3, which contains a central 18-crown-6-like cavity and two N 2 O 2 moieties. This macrocycle strongly binds to spherical cationic guests ( K 11 ≈ 10 3 -10 4 M -1 , DCM/MeCN). The most robust binding was shown for K + and Na + , followed by Li + and Rb + . More sterically demanding cationic guests like dibenzylammonium ( DBA + ) showed almost no binding. The binding pocket in 3 is slightly smaller than 18-crown-6, resulting in binding outside the cavity, which provides a scaffold appropriate for 2 : 1 complexes, where two host molecules sandwich the guest. All host-guest complexes follow a 2 : 1 noncooperative binding model, where each successive binding event is less likely than the previous, unlike coordinated versions of 3, where most binding is 1 : 1.

Cellulose, a renewable structural biopolymer, is ubiquitous in nature and is the basic reinforcement component of the natural hierarchical structures of living plants, bacteria, and tunicates. However, a detailed picture of the crystalline cellulose surface at the molecular level is still unavailable. Here, using atomic force microscopy (AFM) and molecular dynamics (MD) simulations, we revealed the molecular details of the cellulose chain arrangements on the surfaces of individual cellulose nanocrystals (CNCs) in water. Furthermore, we visualized the three-dimensional (3D) local arrangement of water molecules near the CNC surface using 3D AFM. AFM experiments and MD simulations showed anisotropic water structuring, as determined by the surface topologies and exposed chemical moieties. These findings provide important insights into our understanding of the interfacial interactions between CNCs and water at the molecular level. This may allow the establishment of the structure-property relationship of CNCs extracted from various biomass sources.

Ring-opening metathesis polymerization (ROMP) of strained macrocycles is a key method to prepare diverse polymers. However, lack of ring strain in most macrocycles is an impediment to polymerization. In this paper, the polymerization/oligomerization of unstrained macrocycles was achieved using a supramolecular approach, leading selectively to cyclic products. Diphenyl thiourea and other guest molecules were used as additives to the ROMP reaction of unstrained macrocycles. An intermediate host-guest complex leads to the stabilization of the open form of the macrocycle after treatment with Grubbs catalysts, thereby favoring polymerization by inhibiting the ring-closing reaction back to the monomer. This proof-of-concept enables ring-expansion polymerization of unstrained macrocycles leading to cyclic polymers with molecular weights up to 6700 Da., (© 2022 Wiley-VCH GmbH.)

Chitin is one of the most abundant and renewable natural biopolymers. It exists in the form of crystalline microfibrils and is the basic structural building block of many biological materials. Its surface crystalline structure is yet to be reported at the molecular level. Herein, atomic force microscopy (AFM) in combination with molecular dynamics simulations reveals the molecular-scale structural details of the chitin nanocrystal (chitin NC)-water interface. High-resolution AFM images reveal the molecular details of chitin chain arrangements at the surfaces of individual chitin NCs, showing highly ordered, stable crystalline structures almost free of structural defects or disorder. 3D-AFM measurements with submolecular spatial resolution demonstrate that chitin NC surfaces interact strongly with interfacial water molecules creating stable, well-ordered hydration layers. Inhomogeneous encapsulation of the underlying chitin substrate by these hydration layers reflects the chitin NCs' multifaceted surface character with different chain arrangements and molecular packing. These findings provide important insights into chitin NC structures at the molecular level, which is critical for developing the properties of chitin-based nanomaterials. Furthermore, these results will contribute to a better understanding of the chemical and enzymatic hydrolysis of chitin and other native polysaccharides, which is also essential for the enzymatic conversion of biomass., (© 2022 The Authors. Small Methods published by Wiley-VCH GmbH.)

We demonstrate for the first time that continuous rotation of a mixture of cellulose nanocrystals (CNCs) and monomer in a capillary tube results in well-organized structures. In the experiments, a capillary tube charged with an aqueous suspension of CNCs and hydroxyethyl acrylate was continuously rotated, then the structure was fixed in place by UV-initiated polymerization. The organization of the liquid crystalline structure that forms inside the tube depends on the rotation conditions and is captured in the polymer resin. The effects of rotation speed, rotation angle and CNC concentration were evaluated and are discussed based on fluid dynamic models. We demonstrate that it is possible to develop a core-shell fiber through this technique based on secondary Dean flow. The outer shell of the fiber shows well-ordered concentric rings with chiral nematic structure, while the inner core remains isotropic. Such fibers have potential applications in the field of optics. Overall, we demonstrate that rotation could be applied as a novel method to organize liquid crystals in a confined environment.

Multicomponent low molecular weight gelators (LMWGs) may self-assemble by co-assembly (CA), social self-sorting (SSS), or narcissistic self-sorting (NSS). Understanding the nuances of the self-assembly processes is important to predict the behavior of multicomponent organogels. Here, we investigate the effect of molecular structure on self-assembly in a series of amino-acid based bicomponent LMWGs that differ in headgroup and alkyl chain length. Packing preference of the organogels was determined using differential scanning calorimetry, nuclear magnetic resonance spectroscopy and small angle X-ray scattering. From 66 bicomponent samples we found 50 CA, 14 SSS and 2 NSS. Furthermore, we performed statistical analysis to investigate the role of hydrophobicity and chain length on the overall pathway of self-assembly for these systems. We found the hydrophobicity of the headgroup strongly affected the assembly preference of the organogel, but alkyl chain length only played a small role., (© 2022 Wiley-VCH GmbH.)

Multiresponsive materials can adapt to numerous changes in their local environment, which makes them highly valuable for various applications. Although nanostructured and polymeric multiresponsive materials are plentiful, small-molecule analogues are scarce. This work presents a compact cyclometalated platinum(II) complex that bears a crown ether cavity ( 18C6 -Pt II ); the intimate ring/emitter connectivity is key to unlocking multiresponsiveness. Complex 18C6 -Pt II responds to (i) cationic guests, producing changes in luminescence in both solution and the solid state, (ii) solvent molecules, which perturb the packing of the complex in the solid state and cause reversible color changes, and (iii) solvent polarity, which leads to controlled aggregation. These responses may enable 18C6 -Pt II to function as a sensor for ions and solvents, or as a functional unit for the fabrication of hybrid supramolecular polymers and metallogels.

Graphene oxide (GO) is an important nanomaterial for producing photonic liquids due to its ability to display full-color reflections in water. However, the poor stability of GO photonic liquids and unsatisfactory dispersibility of GO nanosheets in hydrophobic liquid media have been significant drawbacks to developing photonic materials based on GO. Here, stable GO hydrophobic photonic liquids are demonstrated for the first time. GO nanosheets are directed into different hydrophobic liquid media, including reactive liquid precursors like tetraethoxysilane and ethyl acrylate, in the presence of phase transfer additives. These liquids exhibit tunable reflection wavelength up to ∼1300 nm with improved stability relative to aqueous GO photonic suspensions at elevated temperatures or under ambient conditions. Supported by an entropy-driven depletion mechanism, hydrophobic additives can effectively mediate the self-assembly of GO to produce tunable photonic liquids without the need to adjust GO concentrations. Furthermore, simultaneous infrared and visible light reflection can be achieved, enabling infrared photonic GO liquids to display visible colors. The improved stability and tunable photonic properties of hydrophobic GO liquids will open a way for developing GO-based optical materials and devices.

Macrocyclization is a popular method for preparing hosts, but it can have unintended effects, like limiting molecular free rotation to yield mixtures of inseparable isomers. We report a [3 + 3] Schiff-base macrocycle ( 1 ) with anthracene bridges. Restricted rotation about the phenyl-anthracene bonds leads 1 to exist as a mixture of conformations ( 1 C s and 1 C 3 v ). Macrocycle 1 was photooxidized to tris(endoperoxide) adduct 4 , alleviating restricted rotation. These results were supported by spectroscopic, structural, and computational analyses.

The properties of chiral nematic and iridescent cellulose nanocrystal films with different monovalent cations (CNC-X) obtained through evaporation-induced self-assembly (EISA) can be modified by a variety of external stimuli. Here, we study the transformations of their optical and structural properties when the films are thermally annealed at 200 °C and 240 °C for up to 2 days. The chiral nematic structure of the most thermally stable films is not destroyed even after extensive heating due to the thermochemical stability of the cellulose backbone and the presence of surface alkali counterions, which suppress catalysis of early stage degradation. Despite the resilience of the cholesteric structure and the overall integrity of heated CNC-X films, thermal annealing is often accompanied by reduction of iridescence, birefringence, and transparency, as well as formation of degradation products. The versatility, sustainability, and stability of CNC-X films highlight their potential as temperature indicators and photonic devices., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Understanding the socioeconomic drivers of biological invasion informs policy development for curtailing future invasions. While early 20th-century plant trade expansions preceded increased establishments of plant pests in Northern America, increased establishments did not follow accelerating imports later that century. To explore this puzzle, we estimate the historical establishment of plant-feeding Hemiptera in Northern America as a function of historical U.S. imports of live plants from seven world regions. Delays between establishment and discovery are modeled using a previously unused proxy for dynamic discovery effort. By recovering the timing of pest arrivals from their historical discoveries, we disentangle the joint establishment-discovery process. We estimate long delays to discovery, which are partially attributable to the low detectability of less economically important insect species. We estimate that many introduced species remain undiscovered, ranging from around one-fifth for Eurasian regions to two-fifths for Central and South America.

The growth of multimetallic clusters and complexes can proceed in the presence of suitable ligands, but often leads to polydisperse structures with poor solubility. As an alternative approach, macrocyclic molecules can anchor the multimetallic complex, directing its formation and stabilizing the resulting product. This approach can provide excellent control over the growth of clusters, and offers a handle to control solubility and other properties of the resulting complexes. In this Tutorial Review, we discuss recent activity (primarily the last two decades) directed at the controlled and reproducible synthesis of multimetallic complexes using macrocyclic ligands. Throughout the review, we focus on the unusual structures that are only accessible by using macrocycles as ligands, and their unique properties.

Hierarchical biological materials, such as osteons and plant cell walls, are complex structures that are difficult to mimic. Here, we combine liquid crystal systems and polymerization techniques within confined systems to develop complex structures. A single-domain concentric chiral nematic polymeric fiber was obtained by confining cellulose nanocrystals (CNCs) and hydroxyethyl acrylate inside a capillary tube followed by UV-initiated polymerization. The concentric chiral nematic structure continues uniformly throughout the length of the fiber. The pitch of the chiral nematic structure could be controlled by changing the CNC concentration. We tracked the formation of the concentric structure over time and under different conditions with variation of the tube orientation, CNC concentration, CNC type, and capillary tube size. We show that the inner radius of the capillary tube is important and a single-domain structure was only obtained inside small-diameter tubes. At low CNC concentration, the concentric chiral nematic structure did not completely cover the cross-section of the fiber. The highly ordered structure was studied using imaging techniques and X-ray diffraction, and the mechanical properties and structure of the chiral nematic fiber were compared to a pseudo-nematic fiber. CNC polymeric fibers could become a platform for many applications from photonics to complex hierarchical materials., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Photonic materials that can selectively reflect light across the visible spectrum are valuable for applications in optical devices, sensors, and decoration. Although two-dimensional (2D) colloids that stack into layers with spacing of hundreds of nanometers are able to selectively diffract light, controlling their separation in solution has proven challenging. In this work, we investigate the role of additives to control the photonic properties of hybrid colloidal suspensions of graphene oxide (GO). We discovered that low concentrations of colloidal additives like cellulose nanocrystals (CNCs) and clay nanoparticles (hectorite) added to GO suspensions lead to dramatic color changes. These hybrid colloidal suspensions demonstrate tunable structural colors and temperature-sensitive properties that likely originate from the entropically driven ejection of guests between the sheets, and from the interactions between colloidal electrical double layers and additional counterions. On the other hand, blending polymeric or molecular additives with GO suspensions either deteriorates or does not impact the photonic properties. These results are helpful to understand the interaction between GO suspensions and additives over different length scales, and open a path to advancing photonic materials based on hybrid colloidal suspensions.

Versatile and ecofriendly methods to perform oxidations at near-neutral pH are of crucial importance for processes aimed at purifying water. Chitosan, a deacetylated form of chitin, is a promising starting material owing to its biocompatibility and ability to form stable films and complexes with metals. Here, we report a novel chitosan-based organometallic complex that was tested both as homogeneous and heterogeneous catalyst in the degradation of contaminants of emerging concern in water. The stoichiometry of the complex was experimentally verified with different metals, namely, Cu(II), Fe(III), Fe(II), Co(II), Pd(II), and Mn(II), and we identified the chitosan-Fe(III) complex as the most efficient catalyst. This complex effectively degraded phenol, triclosan, and 3-chlorophenol in the presence of hydrogen peroxide. A putative ferryl-mediated reaction mechanism is proposed based on experimental data, density functional theory calculations, and kinetic modeling. Finally, a film of the chitosan-Fe(III) complex was synthesized and proven a promising supported heterogeneous catalyst for water purification., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

A class of amino acid-based low-molecular-weight gelators (LMWGs) was used for single and multicomponent gel studies to investigate their tunable optical properties and their self-assembly process. The optical properties of multicomponent gels were found to be easily tuned by changing the proportion of the components, varying from opaque to highly transparent gels as analyzed using ultraviolet-visible spectroscopy. This phenomenon allows tunability without introducing another variable into the system. Scanning electron microscopy, differential scanning calorimetry, and small-angle X-ray scattering (SAXS) were used to investigate the structures of the gels. It was found that because of the structural similarities of the molecules, the gelators favor coassembly packing over self-sorting. The emergence of transparency was ascribed to changes in the fiber diameters. Moreover, analysis of the SAXS data allowed us to compare the molecular order present in the gel phase with single-crystal X-ray diffraction (SCXRD) data. Our analysis suggests that the packing of molecules seen in the crystalline phase is translated into the gel network. This reveals that the structure of the crystalline phase seen through SCXRD is a useful tool to aid in understanding the molecular packing in the gel phase.

Over millions of years, animals and plants have evolved complex molecules and structures that endow them with vibrant colors. Among the sources of natural coloration, structural color is prominent in insects, bird feathers, snake skin, plants, and other organisms, where the color arises from the interaction of light with nanoscale features rather than absorption from a pigment. Cellulose nanocrystals (CNCs) are a biorenewable resource that spontaneously organize into chiral nematic liquid crystals having a hierarchical structure that resembles the Bouligand structure of arthropod shells. The periodic, chiral nematic organization of CNC films leads them to diffract light, making them appear iridescent. Over the past two decades, there have been many advances to develop the photonic properties of CNCs for applications ranging from cosmetics to sensors. Here, the origin of color in CNCs, the control of photonic properties of CNC films, the development of new composite materials of CNCs that can yield flexible photonic structures, and the future challenges in this field are discussed. In particular, recent efforts to make flexible photonic materials using CNCs are highlighted., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Cellulose-derived materials, such as microcellulose and nanocellulose, are sustainable materials with a wide range of applications. Here, through a multi-analytical approach, we investigate the thermal degradation of microfibrillar cellulose filaments (CFs); acidic cellulose nanocrystals (CNC-H), containing sulfate half-ester groups on the surface; and neutralized cellulose nanocrystals (CNC-Na), where the protons are replaced by sodium ions. CFs have a simple degradation mechanism, associated with extensive dehydration, decarboxylation, and decarbonylation, and the highest thermal stability of the three (∼325 °C) despite the abundance of amorphous regions and inhomogeneous fibrous mass that make them structurally and morphologically less homogeneous than high-crystallinity CNCs. CNC-H decompose in a complex way below 200 °C, with large char fractions and evaporation of sulfur compounds at high temperatures, while sodium counterions in CNC-Na can improve the thermal stability up to 300 °C, where the pyrolysis leads to partial rehydration and formation of sodium hydroxide on the surface.

The simple structural modification of replacing a terminal carboxylic acid with a primary amide group was found to lower the minimum gelation concentration (MGC), by at least an order of magnitude, for a series of N -lauroyl-l-amino acid phase-selective organogelators in decane. The amide-functionalized analogue N -lauroyl-l-alanine-CONH 2 was demonstrated to gel a broad range of solvents from diesel to THF at MGCs of 2.5% w/v or less, as well as to produce gels with a higher thermal stability ( ca. 30 °C) and enhanced mechanical properties (5 times increase in complex modulus), compared to the carboxylic acid analogue, N -lauroyl-l-alanine-COOH. These improved properties may be due to the additional hydrogen bonding in the primary amide analogue as revealed by SCXRD. Most significantly for this study, the introduction of the primary amide functionality enabled N -lauroyl-l-alanine-CONH 2 to form a self-assembled fibrillar network in water. The aqueous network could then actively uptake and rapidly gel decane, diesel, and diluted bitumen ("dilbit") with MGCs of 2.5% w/v or less. This aqueous delivery method is advantageous for oil-remediation applications as no harmful carrier solvents are required and the gel can be easily separated from the water, allowing the oil to be recovered and the gelator recycled., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

We report the synthesis, characterization, and spectroscopic investigations of a new responsive-at-metal cyclometalated platinum(II) complex. With mild chemical oxidants and reductants, it was possible to obtain the same complex in three different oxidation states and each of these complexes was structurally characterized by single-crystal X-ray diffraction. We discovered that the platinum(II) complex displays strong solvatochromism in the solid state, which can be attributed to modulation of Pt⋅⋅⋅Pt interactions that results in switching between optical and photoluminescent states. Incorporating responsive-at-metal species as dynamic components in nanostructured materials might facilitate response amplification, sensing, actuation, or self-healing processes., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report the reaction of muonium (Mu = [μ + e - ]), a light isotopic analog of hydrogen, with uncapped gold nanoparticles embedded in mesoporous silica. Using the radio-frequency muon spin rotation (RF-μSR) technique, we directly observe and characterize the resulting final state on the nanoparticle surface, showing conclusively its diamagnetic nature. The magnetic environment experienced by the reacted muons is only weakly perturbed compared to that of muons in a silica reference, consistent with the surface of the gold nanoparticles being metallic and non-magnetic. We demonstrate the potential of RF-μSR for the investigation of the surface properties of nanoparticles and show the feasibility of Knight shift measurements of muons on metal surfaces.

Diffraction gratings are important for modern optical components, such as optical multiplexers and signal processors. Although liquid crystal (LC) gratings based on thermotropic LCs have been extensively explored, they often require expensive molecules and complicated manufacturing processes. Lyotropic LCs, which can be broadly obtained from both synthetic and natural sources, have not yet been applied in optical gratings. Herein, a facile grating fabrication method using a biosourced lyotropic LC formed by cellulose nanocrystals (CNCs), a material extracted from plants, is reported. Hydrogel sheets with vertically aligned uniform periodic structures are obtained by fixing the highly oriented chiral nematic LC of CNCs in polymer networks under the cooperative effects of gravity on phase separation and a magnetic field on LC orientation. The hydrogel generates up to sixth-order diffraction spots and shows linear polarization selectivity, with tunable grating periodicity controlled through LC concentration regulation. This synthesis strategy can be broadly applied to various grating materials and opens up a new area of optical materials from lyotropic LCs., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Aqueous suspensions of cellulose nanocrystals (CNCs) are known to self-assemble into a chiral nematic liquid crystalline phase, leading to solid-state nanostructured colored films upon solvent evaporation, even in the presence of templating agents. The angular optical response of these structures, and therefore their visual appearance, are completely determined by the spatial arrangement of the CNCs when the drying suspension undergoes a transition from a flowing and liquid crystalline state to a kinetically arrested state. Here, it is demonstrated how the angular response of the final film allows for retrieval of key physical properties and the chemical composition of the suspension at the onset of the kinetic arrest, thus capturing a snapshot of the past. To illustrate this methodology, a dynamically evolving sol-gel coassembly process is investigated by adding various amounts of organosilica precursor, namely, 1,2-bis(trimethoxysilyl)ethane. The influence of organosilica condensation on the kinetic arrest can be tracked and thus explains the angular response of the resulting films. The a posteriori and in situ approach is general; it can be applied to a variety of additives in CNC-based films and it allows access to key rheological information of the suspension without using any dedicated rheological technique., (© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Cellulose nanocrystals (CNCs) spontaneously assemble into gels when mixed with a polyionic organic or inorganic salt. Here, we have used this ion-induced gelation strategy to create functional CNC gels with a rigid tetracationic macrocycle, cyclobis(paraquat-p-phenylene) (CBPQT 4+ ). Addition of [CBPQT]Cl 4 to CNCs causes gelation and embeds an active host inside the material. The fabricated CNC gels can reversibly absorb guest molecules from solution then undergo molecular recognition processes that create colorful host-guest complexes. These materials have been implemented in gel chromatography (for guest exchange and separation), and as elements to encode 2- and 3-dimensional patterns. We anticipate that this concept might be extended to design a set of responsive and selective gel-like materials functioning as, for instance, water-pollutant scavengers, substrates for chiral separations, or molecular flasks., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The introduction of polymers into a chiral nematic cellulose nanocrystal (CNC) matrix allows for the tuning of optical and mechanical properties, enabling the development of responsive photonic materials. In this study, we explored the incorporation of hydroxypropyl cellulose (HPC) into a CNC film prepared by slow evaporation. In the composite CNC/HPC thin films, the CNCs adopt a chiral nematic structure, which can selectively reflect certain wavelengths of light to yield a colored film. The color could be tuned across the visible spectrum by changing the concentration or molecular weight of the HPC. Importantly, the composite films were more flexible than pure CNC films with up to a ten-fold increase in elasticity and a decrease in stiffness and tensile strength of up to six times and four times, respectively. Surface modification of the films with methacrylate groups increased the hydrophobicity of the films, and therefore, the water stability of these materials was also improved.

Responsive photonic crystals have potential applications in mechanical sensors and soft displays; however, new materials are constantly desired to provide new innovations and improve on existing technologies. To address this, we report stretchable chiral nematic cellulose nanocrystal (CNC) elastomer composites that exhibit reversible visible color upon the application of mechanical stress. When stretched (or compressed) the colorless materials maintain their chiral nematic structure but the helical pitch is reduced into the visible region, resulting in coloration of the CNC-elastomer composite. By increasing the percentage elongation of the material (ca. 50-300 %), the structural color can be tuned from red to blue. The color of the materials was characterized by reflectance optical microscopy and reflectance circular dichroism to confirm the wavelength and polarization of the reflected light. We also probed the mechanism of the structural color using 2D-X-ray diffraction. Finally, by either water-patterning the starting CNC film, or by forming a CNC film with gradient color, through masked evaporation, we were able to prepare encoded stretchable chiral nematic CNC-elastomers., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A number of o -hydroxy aromatic aldehydes have been synthesized to illustrate the effect of steric compression and O···O distances on the intramolecular hydrogen bond and the hydrogen bond energies. Hydrogen bond energies have been calculated using the 'hb and out' method using either the MP2 method or the B3LYP functional with the basis set 6-311++G(d,p). However, several compounds cannot be treated this way. Hydrogen bond energies are also determined using electron densities at bond critical points and these results are in good agreement with the results of the 'hb and out' model. Two-bond deuterium isotope effects on 13 C chemical shifts are suggested as an experimental way to obtain information on hydrogen bond energies as they easily can be measured. Isotope effects on aldehyde proton chemical shifts have also been measured. The former show very good correlation with the hydrogen bond energies and the latter are related to short O···O distances. Short O···O distances can be obtained as the result of short C=C bond lengths, conjugative effects, and steric compression of the aldehyde group. Short O···O distances are in general related to high hydrogen bond energies in these intramolecularly hydrogen-bonded systems of resonance assisted hydrogen bond (RAHB) type.