Host–Guest Chemistry Within Cellulose Nanocrystal Gel Receptors

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 ]Cl₄ 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.     

Preparation and Characterization of Nanocomposites of Carboxymethyl Cellulose Reinforced with Cellulose Nanocrystals

Summary: Cellulose nanocrystals (CNC) were extracted from Kraft pulp of Eucalyptus urograndis. The CNC were isolated by acid hydrolysis with H₂SO₄ 64% (w/w) solution, for 20 minutes at 45 °C. The morphology and crystallinity of the CNC were investigated by atomic force microscopy (AFM) and X-ray diffraction (XRD), respectively. The AFM image supports the evidence for the development of crystals of cellulose in nanometric scale. These nanoparticles were used as reinforcement material in carboxymethyl cellulose (CMC) matrix. Nanocomposites films were prepared by casting. The nanocomposites were characterized by thermal (TGA) and mechanical (DMA) analyses. A large reinforcing effect of the filler was observed. The tensile strength of nanocomposites was significantly improved by 107%, the elongation at break decreased by 48% and the thermal resistance increased slightly. The improvements in thermo-mechanical properties suggest a close association between filler and matrix.     

Cellulose: fascinating biopolymer and sustainable raw material

As the most important skeletal component in plants, the polysaccharide cellulose is an almost inexhaustible polymeric raw material with fascinating structure and properties. Formed by the repeated connection of D-glucose building blocks, the highly functionalized, linear stiff-chain homopolymer is characterized by its hydrophilicity, chirality, biodegradability, broad chemical modifying capacity, and its formation of versatile semicrystalline fiber morphologies. In view of the considerable increase in interdisciplinary cellulose research and product development over the past decade worldwide, this paper assembles the current knowledge in the structure and chemistry of cellulose, and in the development of innovative cellulose esters and ethers for coatings, films, membranes, building materials, drilling techniques, pharmaceuticals, and foodstuffs. New frontiers, including environmentally friendly cellulose fiber technologies, bacterial cellulose biomaterials, and in-vitro syntheses of cellulose are highlighted together with future aims, strategies, and perspectives of cellulose research and its applications.     

Self‐Healing Polyester Urethane Supramolecular Elastomers Reinforced with Cellulose Nanocrystals for Biomedical Applications

Stretchable self‐healing urethane‐based biomaterials have always been crucial for biomedical applications; however, the strength is the main constraint of utilization of these healable materials. Here, a series of novel, healable, elastomeric, supramolecular polyester urethane nanocomposites of poly(1,8‐octanediol citrate) and hexamethylene diisocyanate reinforced with cellulose nanocrystals (CNCs) are introduced. Nanocomposites with various amounts of CNCs from 10 to 50 wt% are prepared using solvent casting technique followed by the evaluation of their microstructural features, mechanical properties, healability, and biocompatibility. The synthesized nanocomposites indicate significantly higher tensile modulus (approximately 36–500‐fold) in comparison to the supramolecular polymer alone. Upon exposure to heat, the materials can reheal, but nevertheless when the amount of CNC is greater than 10 wt%, the self‐healing ability of nanocomposites is deteriorated. These materials are capable of rebonding ruptured parts and fully restoring their mechanical properties. In vitro cytotoxicity test of the nanocomposites using human dermal fibroblasts confirms their good cytocompatibility. The optimized structure, self‐healing attributes, and noncytotoxicity make these nanocomposites highly promising for tissue engineering and other biomedical applications.     

Modular Architecture of Protein Binding Units for Designing Properties of Cellulose Nanomaterials

Molecular biomimetic models suggest that proteins in the soft matrix of nanocomposites have a multimodular architecture. Engineered proteins were used together with nanofibrillated cellulose (NFC) to show how this type of architecture leads to function. The proteins consist of two cellulose‐binding modules (CBM) separated by 12‐, 24‐, or 48‐mer linkers. Engineering the linkers has a considerable effects on the interaction between protein and NFC in both wet colloidal state and a dry film. The protein optionally incorporates a multimerizing hydrophobin (HFB) domain connected by another linker. The modular structure explains effects in the hydrated gel state, as well as the deformation of composite materials through stress distribution and crosslinking. Based on this work, strategies can be suggested for tuning the mechanical properties of materials through the coupling of protein modules and their interlinking architectures.     

Preparation,Characterization and Antibacterial Property Analysis of Cellulose Nanocrystals (CNC) and Chitosan Nanoparticles Fine-Tuned Starch Film

To improve the mechanical and antibacterial properties of traditional starch-based film, herein, cellulose nanocrystals (CNCs) and chitosan nanoparticles (CS NPs) were introduced to potato starch (PS, film-forming matrix) for the preparation of nanocomposite film without incorporation of additional antibacterial agents. CNCs with varied concentrations were added to PS and CS NPs composite system to evaluate the optimal film performance. The results showed that tensile strength (TS) of nanocomposite film with 0, 0.01, 0.05, and 0.1% (w/w) CNCs incorporation were 41, 46, 47 and 41 MPa, respectively. The elongation at break (EAB) reached 12.5, 10.2, 7.1 and 13.3%, respectively. Due to the reinforcing effect of CNCs, surface morphology and structural properties of nanocomposite film were altered. TGA analysis confirmed the existence of hydrogen bondings and electrostatic attractions between components in the film-forming matrix. The prepared nanocomposite films showed good antibacterial properties against both E. coli and S. aureus. The nanocomposite film, consist of three most abundant biodegradable polymers, could potentially serve as antibacterial packaging films with strong mechanical properties for food and allied industries.     

In Situ Semibatch Emulsion Polymerization of 2‐Ethyl Hexyl Acrylate/n‐Butyl Acrylate/Methyl Methacrylate/Cellulose Nanocrystal Nanocomposites for Adhesive Applications

Cellulose nanocrystals (CNCs) are safe, “green,” hydrophilic nanoparticles. CNCs are added in situ during a semibatch 2‐ethyl hexyl acrylate (EHA)/n‐butyl acrylate (BA)/methyl methacrylate (MMA) emulsion polymerization. As EHA is a more hydrophobic monomer, manipulation of the monomer feed composition allows for the evaluation of the effect of hydrophobicity on CNC distribution in the nanocomposite and ultimately on adhesive properties. The adhesive properties (loop tack, peel strength, and shear strength) of three different EHA/BA/MMA latex formulations are shown to simultaneously improve with increasing CNC loading. However, the hydrophobicity of the EHA leads to a nonuniform distribution of CNCs in the latex films. Comparison of the in situ polymerized nanocomposites to their blended counterparts is also made.     

Micro‐/Nanostructured Multicomponent Molecular Materials: Design,Assembly, and Functionality

Molecule‐based micro‐/nanomaterials have attracted considerable attention because their properties can vary greatly from the corresponding macro‐sized bulk systems. Recently, the construction of multicomponent molecular solids based on crystal engineering principles has emerged as a promising alternative way to develop micro‐/nanomaterials. Unlike single‐component materials, the resulting multicomponent systems offer the advantages of tunable composition, and adjustable molecular arrangement, and intermolecular interactions within their solid states. The study of these materials also supplies insight into how the crystal structure, molecular components, and micro‐/nanoscale effects can influence the performance of molecular materials. In this review, we describe recent advances and current directions in the assembly and applications of crystalline multicomponent micro‐/nanostructures. Firstly, the design strategies for multicomponent systems based on molecular recognition and crystal engineering principles are introduced. Attention is then focused on the methods of fabrication of low‐dimensional multicomponent micro‐/nanostructures. Their new applications are also outlined. Finally, we briefly discuss perspectives for the further development of these molecular crystalline micro‐/nanomaterials.     

One‐Pot Mechanosynthesis with Three Levels of Molecular Self‐Assembly: Coordination Bonds,Hydrogen Bonds and Host–Guest Inclusion

Liquid‐assisted grinding (LAG) was used to combine three levels of molecular self‐assembly into a one‐pot mechanochemical approach for the construction of metal–organic materials. The approach was applied for the construction of three adducts of cobalt(II) dibenzoylmethanate with isonicotinamide, nicotinamide and imidazole, to screen for their inclusion compounds. The one‐pot process consists of: i) The coordination‐driven binding of addends to the equatorially‐protected metal ion, resulting in “wheel‐and‐axle”‐shaped complexes; ii) self‐assembly of resulting complexes by way of hydrogen‐bonded synthons to form metal–organic inclusion hosts; iii) in situ inclusion of the grinding liquid in the resulting host. This approach provided quantitatively and within 20 min the known inclusion compounds of the bis(isonicotinamide) adduct in a single synthetic step. Changing the liquid phase in LAG was used to explore the inclusion behaviour of new wheel‐and‐axle adducts with nicotinamide and imidazole, revealing several inclusion compounds, as well as two polymorphs, of the bis(nicotinamide) host. Preliminary results suggest that one‐pot LAG is superior to solution synthesis in screening for metal–organic inclusion compounds. The difference between the methods is rationalised in terms of reactant solubility and solvent competition. In contrast to the nicotinamide adduct, the bis(imidazole) adduct did not form inclusion compounds. The difference in the inclusion properties of the two adducts is rationalised by structural information gathered by single crystal and powder X‐ray diffraction.     

Dynamic Timing Control of Molecular Photoluminescent Systems

Dynamic control of molecular photoluminescence offers chemical solutions to designing functional emissive materials. Although stimuli-switchable molecular luminescent systems are well established, how to encode these dynamic emissive systems with a “timing” feature, that is, time-dependent luminescent properties, remains challenging. This Concept aims to summarize the design principles of dynamic timing molecular photoluminescent systems by discussing the state-of-the-art of this topic and the shaping of fabrication strategies at both the molecular and supramolecular levels. An outlook and perspectives are given to outline the future opportunities and challenges in the rational design and potential applications of these smart emissive systems.     

Renewable Molecular Flasks with NADH Models: Combination of Light-Driven Proton Reduction and Biomimetic Hydrogenation of Benzoxazinones

Using small molecules with defined pockets to catalyze chemical transformations resulted in attractive catalytic syntheses that echo the remarkable properties of enzymes. By modulating the active site of a nicotinamide adenine dinucleotide (NADH) model in a redox-active molecular flask, we combined biomimetic hydrogenation with in situ regeneration of the active site in a one-pot transformation using light as a clean energy source. This molecular flask facilitates the encapsulation of benzoxazinones for biomimetic hydrogenation of the substrates within the inner space of the flask using the active sites of the NADH models. The redox-active metal centers provide an active hydrogen source by light-driven proton reduction outside the pocket, allowing the in situ regeneration of the NADH models under irradiation. This new synthetic platform, which offers control over the location of the redox events, provides a regenerating system that exhibits high selectivity and efficiency and is extendable to benzoxazinone and quinoxalinone systems.     

Rational Modification of the Hierarchy of Intermolecular Interactions in Molecular Crystal Structures by Using Tunable Halogen Bonds

A family of 16 isomolecular salts (3‐XpyH)₂[MX′₄] (3‐XpyH=3‐halopyridinium; M=Co, Zn; X=(F), Cl, Br, (I); X′=Cl, Br, I) each containing rigid organic cations and tetrahedral halometallate anions has been prepared and characterized by X‐ray single crystal and/or powder diffraction. Their crystal structures reflect the competition and cooperation between non‐covalent interactions: N? H???X′? M hydrogen bonds, C? X???X′? M halogen bonds and π–π stacking. The latter are essentially unchanged in strength across the series, but both halogen bonds and hydrogen bonds are modified in strength upon changing the halogens involved. Changing the organic halogen (X) from F to I strengthens the C? X???X′? M halogen bonds, whereas an analogous change of the inorganic halogen (X′) weakens both halogen bonds and N? H???X′? M hydrogen bonds. By so tuning the strength of the putative halogen bonds from repulsive to weak to moderately strong attractive interactions, the hierarchy of the interactions has been modified rationally leading to systematic changes in crystal packing. Three classes of crystal structure are obtained. In type A (C? F???X′? M) halogen bonds are absent. The structure is directed by N? H???X′? M hydrogen bonds and π‐stacking interactions. In type B structures, involving small organic halogens (X) and large inorganic halogens (X′), long (weak) C? X???X′? M interactions are observed with type I halogen–halogen interaction geometries (C? X???X′ ≈ X???X′? M ≈155°), but hydrogen bonds still dominate. Thus, minor but quite significant perturbations from the type A structure arise. In type C, involving larger organic halogens (X) and smaller inorganic halogens (X′), stronger halogen bonds are formed with a type II halogen–halogen interaction geometry (C? X???X′ ≈180°; X???X′? M ≈110°) that is electrostatically attractive. The halogen bonds play a major role alongside hydrogen bonds in directing the type C structures, which as a result are quite different from type A and B.     

Topochemical Engineering of Cellulose—Carboxymethyl Cellulose Beads: A Low-Field NMR Relaxometry Study

The demand for more ecological, highly engineered hydrogel beads is driven by a multitude of applications such as enzyme immobilization, tissue engineering and superabsorbent materials. Despite great interest in hydrogel fabrication and utilization, the interaction of hydrogels with water is not fully understood. In this work, NMR relaxometry experiments were performed to study bead–water interactions, by probing the changes in bead morphology and surface energy resulting from the incorporation of carboxymethyl cellulose (CMC) into a cellulose matrix. The results show that CMC improves the swelling capacity of the beads, from 1.99 to 17.49, for pure cellulose beads and beads prepared with 30% CMC, respectively. Changes in water mobility and interaction energy were evaluated by NMR relaxometry. Our findings indicate a 2-fold effect arising from the CMC incorporation: bead/water interactions were enhanced by the addition of CMC, with minor additions having a greater effect on the surface energy parameter. At the same time, bead swelling was recorded, leading to a reduction in surface-bound water, enhancing water mobility inside the hydrogels. These findings suggest that topochemical engineering by adjusting the carboxymethyl cellulose content allows the tuning of water mobility and porosity in hybrid beads and potentially opens up new areas of application for this biomaterial.     

Dynamic Self‐Assembly of Gold/Polymer Nanocomposites: pH‐Encoded Switching between 1D Nanowires and 3D Nanosponges

The design of tunable dynamic self‐assembly of nanoparticles with switchable assembled dimensions and morphologies is a challenging goal whose realization is vital for the evolution of smart nanomaterials. Herein, we report on chitosan polymer as an effective supramolecular “glue” for aldehyde‐modified Au nanoparticles to reversibly modulate the states of self‐assembled nanocomposites. By simultaneous integration of dynamic covalent Schiff base interactions and noncovalent hydrogen bonds, the chitosan/Au nanocomposites could reversibly transform their assembled morphologies from one‐dimensional nanowires to three‐dimensional nanosponges in response to the variation of pH value. Moreover, the obtained nanosponges could be used as an efficient pH‐controlled cargo release system.     

Selective Interaction of Dopamine with the Self‐Assembled Fibrillar Network of a Molecular Hydrogel Revealed by STD‐NMR

A molecular hydrogel formed by a derivative of L ‐valine with pendant isonicotinoyl moieties interacts selectively with protonated dopamine in the presence of related compounds such as 3‐methylcatechol, and protonated or neutral phenethylamine. A two‐point interaction with the gel fibers is postulated to explain the results. The conclusions are obtained from nuclear magnetic resonance saturation transfer experiments (STD‐NMR), illustrating how this technique is perfectly suited to monitor the interaction of substrates with the fibrillar network of a molecular gel.     

Synthesis and Characterization of Storage Energy Materials Prepared from Nano-crystalline Cellulose/Polyethylene Glycol

The development and the application of phase change materials (PCMs) as a new kind of materials have attracted both scientific and industrial interest1-4. According to the patterns of phase conversion, commonly PCMs are divided into solid-liquid phase cha…     

A C3‐Symmetric Macrocycle‐Based,Hydrogen‐Bonded,Multiporous Hexagonal Network as a Motif of Porous Molecular Crystals

A C₃‐symmetric π‐conjugated macrocycle combined with an appropriate hydrogen bonding module (phenylene triangle) allowed the construction of crystalline supramolecular frameworks with a cavity volume of up to 58 %. The frameworks were obtained through non‐interpenetrated stacking of a hexagonal sheet possessing three kinds of pores with different sizes and shapes. The activated porous material absorbed CO₂ up to 96 cm³ g^?1 at 195 K under 1 atm.     

Thermal or Mechanical Stimuli‐Induced Photoluminescence Color Change of a Molecular Assembly Composed of an Amphiphilic Anthracene Derivative in Water

Molecular assemblies that change photoluminescence color in response to thermal or mechanical stimulation without dissociation into the monomeric states in water are described herein. A dumbbell‐shaped amphiphilic compound forms micellar molecular assemblies in water and exhibits yellow photoluminescence derived from excimer formation of the luminescent core, which contains a 2,6‐diethynylanthracene moiety. Annealing of the aqueous solution induces a photoluminescence color change from yellow to green (λ_{em, max}=558→525 nm). The same photoluminescence color change is also achieved by rubbing the yellow‐photoluminescence‐emitting molecular assemblies adsorbed on glass substrates with cotton wool in water. The observed green photoluminescence is ascribed to micelles that are distinct from the yellow‐photoluminescence‐emitting micelles, on the basis of transmission electron microscopy observations, atomic force microscopy observations, and dynamic light scattering measurements. We examined the relationship between the structure of the molecular assemblies and the photophysical properties of the anthracene derivative in water before and after thermal or mechanical stimulation and concluded that thermal or mechanical stimuli‐induced slight changes of the molecular‐assembled structures in the micelles result in the change in the photoluminescence color from yellow to green in water.