Cellulose Nanocrystals as Chiral Inducers: Enantioselective Catalysis and Transmission Electron Microscopy 3D Characterization

Advancing plant cell wall modelling: Atomistic insights into cellulose, disordered cellulose, and hemicelluloses - A review

The complexity of plant cell walls on different hierarchical levels still impedes the detailed understanding of biosynthetic pathways, interferes with processing in industry and finally limits applicability of cellulose materials. While there exist many challenges to readily accessing these hierarchies at (sub-) angström resolution, the development of advanced computational methods has the potential to unravel important questions in this field. Here, we summarize the contributions of molecular dynamics simulations in advancing the understanding of the physico-chemical properties of natural fibres. We aim to present a comprehensive view of the advancements and insights gained from molecular dynamics simulations in the field of carbohydrate polymers research. The review holds immense value as a vital reference for researchers seeking to undertake atomistic simulations of plant cell wall constituents. Its significance extends beyond the realm of molecular modeling and chemistry, as it offers a pathway to develop a more profound comprehension of plant cell wall chemistry, interactions, and behavior. By delving into these fundamental aspects, the review provides invaluable insights into future perspectives for exploration. Researchers within the molecular modeling and carbohydrates community can greatly benefit from this resource, enabling them to make significant strides in unraveling the intricacies of plant cell wall dynamics.

TiO2 Films with Macroscopic Chiral Nematic-Like Structure Stabilized by Copper Promoting Light-Harvesting Capability for Hydrogen Generation

Cellulose nanocrystals (CNCs) have inspired the synthesis of various advanced nanomaterials, opening opportunities for different applications. However, a simple and robust approach for transferring the long-range chiral nematic nanostructures into TiO2 photocatalyst is still fancy. Herein, a successful fabrication of freestanding TiO2 films maintaining their macroscopic chiral nematic structures after removing the CNCs biotemplate is reported. It is demonstrated that including copper acetate in the sol avoids the epitaxial growth of the lamellar-like structure of TiO2 and stabilizes the chiral nematic structure instead. The experimental results and optical simulation demonstrate an enhancement at the blue and red edges of the Fabry-Pérot reflectance peak located in the visible range. This enhancement arises from the light scattering effect induced by the formation of the chiral nematic structure. The nanostructured films showed 5.3 times higher performance in the photocatalytic hydrogen generation, compared to lamellar TiO2, and benefited from the presence of copper species for charge carriers' separation. This work is therefore anticipated to provide a simple approach for the design of chiral nematic photocatalysts and also offers insights into the electron transfer mechanisms on TiO2/CuxO with variable oxidation states for photocatalytic hydrogen generation.

Dimensions of Cellulose Nanocrystals from Cotton and Bacterial Cellulose: Comparison of Microscopy and Scattering Techniques

Different microscopy and scattering methods used in the literature to determine the dimensions of cellulose nanocrystals derived from cotton and bacterial cellulose were compared to investigate potential bias and discrepancies. Atomic force microscopy (AFM), small-angle X-ray scattering (SAXS), depolarized dynamic light scattering (DDLS), and static light scattering (SLS) were compared. The lengths, widths, and heights of the particles and their respective distributions were determined by AFM. In agreement with previous work, the CNCs were found to have a ribbon-like shape, regardless of the source of cellulose or the surface functional groups. Tip broadening and agglomeration of the particles during deposition cause AFM-derived lateral dimensions to be systematically larger those obtained from SAXS measurements. The radius of gyration determined by SLS showed a good correlation with the dimensions obtained by AFM. The hydrodynamic lateral dimensions determined by DDLS were found to have the same magnitude as either the width or height obtained from the other techniques; however, the precision of DDLS was limited due to the mismatch between the cylindrical model and the actual shape of the CNCs, and to constraints in the fitting procedure. Therefore, the combination of AFM and SAXS, or microscopy and small-angle scattering, is recommended for the most accurate determination of CNC dimensions.

Fluorescent Noncovalent Organic Framework for Supporting Gold Nanoparticles as Heterogeneous Catalyst with Merits of Easy Detection and Recycle

A porous noncovalent organic framework with AIE effect is designed and synthesized as the support for gold nanoparticles (AuNPs). The framework is fabricated through the electrostatic complexation between carboxymethyl cellulose and tetraphenylethene-containing ammonium surfactant, which can complex AuNPs via the noncovalent interactions to offer a heterogeneous catalyst. Compared to the covalent modification on cellulose, this noncovalent framework gains superiorities in the catalyst synthesis and the size control of AuNPs. The AIE property and water-insolubility allow such heterogeneous catalysts to be easily detected, separated, and recycled, opening a new pathway for the reduction of nitrobenzene compounds and some dye compounds in aqueous conditions, which present the features of green chemistry. The use of cellulose for developing new heterogeneous metal catalysts, especially in a noncovalent way, would promote the value-added utilization of cellulose. This work provides a design strategy for gaining heterogeneous metal catalysts by taking advantage of natural bioresources.

Recent advances in green technology and Industrial Revolution 4.0 for a sustainable future

This review gives concise information on green technology (GT) and Industrial Revolution 4.0 (IR 4.0). Climate change has begun showing its impacts on the environment, and the change is real. The devastating COVID-19 pandemic has negatively affected lives and the world from the deadly consequences at a social, economic, and environmental level. In order to balance this crisis, there is a need to transition toward green, sustainable forms of living and practices. We need green innovative technologies (GTI) and Internet of Things (IoT) technologies to develop green, durable, biodegradable, and eco-friendly products for a sustainable future. GTI encompasses all innovations that contribute to developing significant products, services, or processes that lower environmental harm, impact, and worsening while augmenting natural resource utilization. Sensors are typically used in IoT environmental monitoring applications to aid ecological safety by nursing air or water quality, atmospheric or soil conditions, and even monitoring species' movements and habitats. The industries and the governments are working together, have come up with solutions-the Green New Deal, carbon pricing, use of bio-based products as biopesticides, in biopharmaceuticals, green building materials, bio-based membrane filters for removing pollutants, bioenergy, biofuels and are essential for the green recovery of world economies. Environmental biotechnology, Green Chemical Engineering, more bio-based materials to separate pollutants, and product engineering of advanced materials and environmental economies are discussed here to pave the way toward the Sustainable Development Goals (SDGs) set by the UN and achieve the much-needed IR 4.0 for a greener-balanced environment and a sustainable future.

Accelerating Cellulose Nanocrystal Assembly into Chiral Nanostructures

Cellulose nanocrystal (CNC) suspensions self-assembled into chiral nematic liquid crystals. This property has enabled the development of versatile optical materials with fascinating properties. Nevertheless, the scale-up production and commercial success of chiral nematic CNC superstructures face significant challenges. Fabrication of chiral nematic CNC nanostructures suffers from a ubiquitous pernicious trade-off between uniform chiral nematic structure and rapid self-assembly. Specifically, the chiral nematic assembly of CNCs is a time-consuming, spontaneous process that involves the organization of particles into ordered nanostructures as the solvent evaporates. This review is driven by the interest in accelerating chiral nematic CNC assembly and promoting a long-range oriented chiral nematic CNC superstructure. To start this review, the chirality origins of CNC and CNC aggregates are analyzed. This is followed by a summary of the recent advances in stimuli-accelerated chiral nematic CNC self-assembly procedures, including evaporation-induced self-assembly, continuous coating, vacuum-assisted self-assembly, and shear-induced CNC assembly under confinement. In particular, stimuli-induced unwinding, alignment, and relaxation of chiral nematic structures were highlighted, offering a significant link between the accelerated assembly approaches and uniform chiral nematic nanostructures. Ultimately, future opportunities and challenges for rapid chiral nematic CNC assembly are discussed for more innovative and exciting applications.

Chirality Transfer from an Innately Chiral Nanocrystal Core to a Nematic Liquid Crystal 2: Lyotropic Chromonic Liquid Crystals

The importance of and the difference between molecular versus structural core chirality of substances that form nanomaterials, and their ability to transmit and amplify their chirality to and within a surrounding condensed medium is yet to be exactly understood. Here we demonstrate that neat as well as disodium cromoglycate (DSCG) surface-modified cellulose nanocrystals (CNCs) with both molecular and morphological core chirality can induce homochirality in racemic nematic lyotropic chromonic liquid crystal (rac-N-LCLC) tactoids. In comparison to the parent chiral organic building blocks, D-glucose, endowed only with molecular chirality, both CNCs showed a superior chirality transfer ability. Here, particularly the structurally compatible DSCG-modified CNCs prove to be highly effective since the surface DSCG moieties can insert into the DSCG stacks that constitute the racemic tactoids. Overall, this presents a highly efficient pathway for chiral induction in an aqueous medium and thus for understanding the origins of biological homochirality in a suitable experimental system.

Tailored synthesis of ultra-stable Au@Pd nanoflowers with enhanced catalytic properties using cellulose nanocrystals

A green strategy for the synthesis of bimetallic core-shell Au@Pd nanoflowers (NFs) employing banana pseudo-stem-derived TEMPO-oxidized cellulose nanocrystals (TCNC) as both capping and shape-directing agent via seed-mediated method is presented. Flower-like nanostructures of Au@Pd bound to TEMPO-oxidized cellulose nanocrystals (TCNC-Au@Pd) were decorated on amino-functionalized graphene (NH₂-RGO) without losing their unique structure, allowing them to be deployed as an efficient, reusable and a green alternative heterogeneous catalyst. The decisive role of TCNC in the structural metamorphosis of nanoparticle morphology were inferred from the structural and morphology analyses. According to our study, the presence of -OH rich TCNC appears to play a pivotal role in the structured evolution of intricate nanostructure morphology. The feasibility of the bio-supported catalyst has been investigated in two concurrently prevalent model catalytic reactions, namely the oxygen reduction reaction (ORR) and the reduction of 4-nitrophenol, the best model reactions in fuel cell and industrial catalytic applications, respectively.

Bottom-Up Approach to Understand Chirality Transfer across Scales in Cellulose Assemblies

Cellulose is a polysaccharide that displays chirality across different scales, from the molecular to the supramolecular level. This feature has been exploited to generate chiral materials. To date, the mechanism of chirality transfer from the molecular level to higher-order assemblies has remained elusive, partially due to the heterogeneity of cellulose samples obtained via top-down approaches. Here, we present a bottom-up approach that uses well-defined cellulose oligomers as tools to understand the transfer of chirality from the single oligomer to supramolecular assemblies beyond the single cellulose crystal. Synthetic cellulose oligomers with defined sequences self-assembled into thin micrometer-sized platelets with controllable thicknesses. These platelets further assembled into bundles displaying intrinsic chiral features, directly correlated to the monosaccharide chirality. Altering the stereochemistry of the oligomer termini impacted the chirality of the self-assembled bundles and thus allowed for the manipulation of the cellulose assemblies at the molecular level. The molecular description of cellulose assemblies and their chirality will improve our ability to control and tune cellulose materials. The bottom-up approach could be expanded to other polysaccharides whose supramolecular chirality is less understood.

Plant-Actuated Micro-Nanorobotics Platforms: Structural Designs, Functional Prospects, and Biomedical Applications

Plants are anatomically and physiologically different from humans and animals; however, there are several possibilities to utilize the unique structures and physiological systems of plants and adapt them to new emerging technologies through a strategic biomimetic approach. Moreover, plants provide safe and sustainable results that can potentially solve the problem of mass-producing practical materials with hazardous and toxic side effects, particularly in the biomedical field, which requires high biocompatibility. In this review, it is investigated how micro-nanostructures available in plants (e.g., nanoparticles, nanofibers and their composites, nanoporous materials, and natural micromotors) are adapted and utilized in the design of suitable materials for a micro-nanorobot platform. How plants' work on micro- and nanoscale systems (e.g., surface roughness, osmotically induced movements such as nastic and tropic, and energy conversion and harvesting) that are unique to plants, can provide functionality on the platform and become further prospective resources are examined. Furthermore, implementation across organisms and fields, which is promising for future practical applications of the plant-actuated micro-nanorobot platform, especially on biomedical applications, is discussed. Finally, the challenges following its implementation in the micro-nanorobot platform are also presented to provide advanced adaptation in the future.

Chirality at nanoscale for bioscience

In the rapidly expanding fields of nanoscience and nanotechnology, there is considerable interest in chiral nanomaterials, which are endowed with unusually strong circular dichroism. In this review, we summarize the principles of organization underlying chiral nanomaterials and generalize the recent advances in the main strategies used to fabricate these nanoparticles for bioscience applications. The creation of chirality from nanoscale building blocks has been investigated both experimentally and theoretically, and the tunability of chirality using external fields, such as light and magnetic fields, has allowed the optical activity of these materials to be controlled and their properties understood. Therefore, the specific recognition and potential applications of chiral materials in bioscience are discussed. The effects of the chirality of nanostructures on biological systems have been exploited to sense and cut molecules, for therapeutic applications, and so on. In the final part of this review, we examine the future perspectives for chiral nanomaterials in bioscience and the challenges posed by them.

Recent Advances in Electron Microscopy of Carbohydrate Nanoparticles

Carbohydrate nanoparticles, both naturally derived and synthetic ones, have attracted scientific and industrial attention as high-performance renewable building blocks of functional materials. Electron microscopy (EM) has played a central role in investigations of their morphology and molecular structure, although the intrinsic radiation sensitivity of carbohydrate crystals has often hindered the in-depth characterization with EM techniques. This contribution reviews the recent advances in the electron microscopy of the carbohydrate nanoparticles. In particular, we highlight the recent efforts made to understand the three-dimensional shape and structural heterogeneity of nanoparticles using low-dose electron tomography and electron diffraction techniques coupled with cryogenic transmission electron microscopy.

Wood-Sourced Polymers as Support for Catalysis by Group 10 Transition Metals

Despite providing interesting solutions to reduce the number of synthetic steps, to decrease energy consumption or to generate less waste, therefore contributing to a more sustainable way of producing important chemicals, the expansion of the use of homogeneous catalysis in industrial processes is hampered by several drawbacks. One of the most important is the difficulty to recycle the noble metals generating potential high costs and pollution of the synthesized products by metal traces detrimental to their applications. Supporting the metals on abundant and cheap biosourced polymers has recently appeared as an almost ideal solution: They are much easier to recover from the reaction medium and usually maintain high catalytic activity. The present bibliographical review focuses on the development of catalysts based on group 10 transition metals (nickel, palladium, platinum) supported on biopolymers obtained from wood, such as cellulose, hemicellulose, lignin, and their derivatives. The applications of these catalysts in organic synthesis or depollution are also addressed in this review with examples of C-C couplings, oxidation, or hydrogenation reactions.

Modeling the cholesteric pitch of apolar cellulose nanocrystal suspensions using a chiral hard-bundle model

Cellulose nanocrystals (CNCs) are naturally sourced elongated nanocolloids that form cholesteric phases in water and apolar solvents. It is well accepted that CNCs are made of bundles of crystalline microfibrils clustered side-by-side, and there is growing evidence that each individual microfibril is twisted. Yet, the origin of the chiral interactions between CNCs remains unclear. In this work, CNCs are described with a simple model of chiral hard splinters, enabling the prediction of the pitch using density functional theory and Monte Carlo simulations. The predicted pitch P compares well with experimental observations in cotton-based CNC dispersions in apolar solvents using surfactants but also with qualitative trends caused by fractionation or tip sonication in aqueous suspensions. These results suggest that the bundle shape induces an entropy-driven chiral interaction between CNCs, which is the missing link in explaining how chirality is transferred from the molecular scale of cellulose chains to the cholesteric order.

Optically active porous hybrid particles constructed by alkynylated cellulose nanocrystals, helical substituted polyacetylene, and inorganic silica for enantio-differentiating towards naproxen

This article reports on a novel type of ternary chiral porous hybrid particles (TCPHPs) constructed by alkynylated cellulose nanocrystals (A-CNCs), helical substituted polyacetylene, and inorganic silica. The resulting TCPHPs combine the respective advantages of the three components. A-CNCs serve as stabilizer, co-monomer, and chiral source simultaneously and transfer their chirality to the resulting helical substituted polyacetylenes in the course of copolymerization with achiral acetylenic monomer following "sergeants and soldiers rule". Helical substituted polyacetylenes form chiral helical structures and thus endow TCPHPs with the anticipated optical activity. Inorganic silica constitutes the rigid framework and is covalently bonded with the organic components through hydrolysis of Si-O-Et groups. Phase separation between the organic and inorganic components renders TCPHPs with abundant pores. Scanning electron microscope (SEM) images confirm the formation of spherical particles with porous structures. Circular dichroism spectra demonstrate the optical activity of the chiral hybrid particles. The as-prepared TCPHPs exhibit capacity for enantio-differentiating performance towards chiral naproxen.

Highly Dispersed Pd Clusters Anchored on Nanoporous Cellulose Microspheres as a Highly Efficient Catalyst for the Suzuki Coupling Reaction

With the depletion of nonrenewable resources such as oil/coal/gas, more and more research studies began to focus on the high-value utilization of residual biomass resources. Herein, for the first time, honeycomb nanoporous microspheres fabricated from renewable biomass resources of cellulose were used as a carrier to fabricate a highly dispersed palladium (Pd) nanocatalyst. Various physicochemical characterizations presented convincing pieces of evidence for the good dispersion of Pd clusters with a mean diameter of 1.6 nm. As the carrier, cellulose microspheres with an interconnected nanoporous structure contributed to the adhesion and dispersion of Pd particles, and their rich hydroxyl groups could fix the Pd particles. Importantly, the cellulose matrix could in situ induce the formation of metallic Pd(0) during calcination without a reductant. The cellulose/Pd catalyst was applied to the Suzuki coupling reaction, which exhibited promising catalytic activity compared to commercial Pd/C and unsupported homogeneous Pd(OAc)₂ catalysts, as well as good stability. The utilization of the residual biomass resource to build catalyst materials would be important for the sustainable chemistry.

Chemical Modification of Reducing End-Groups in Cellulose Nanocrystals

Native plant cellulose has an intrinsic supramolecular structure. Consequently, it can be isolated as nanocellulose species, which can be utilized as building blocks for renewable nanomaterials. The structure of cellulose also permits its end-wise modification, i.e., chemical reactions exclusively on one end of a cellulose chain or a nanocellulose particle. The premises for end-wise modification have been known for decades. Nevertheless, different approaches for the reactions have emerged only recently, because of formidable synthetic and analytical challenges associated with the issue, including the adverse reactivity of the cellulose reducing end and the low abundance of newly introduced functionalities. This Review gives a full account of the scientific underpinnings and challenges related to end-wise modification of cellulose nanocrystals. Furthermore, we present how the chemical modification of cellulose nanocrystal ends may be applied to directed assembly, resulting in numerous possibilities for the construction of new materials, such as responsive liquid crystal templates and composites with tailored interactions.

Release of internal molecular torque results in twists of Glaucocystis cellulose nanofibers

The cellulose of the green alga Glaucocystis consists of almost pure Iα crystalline phase where the corresponding lattice b* axis parameter lies perpendicular to the cell wall surface in the multilamellar cell wall architecture, indicating that in this wall, cellulose is devoid of longitudinal twist. In contrast, when isolated from Glaucosytis cell walls, the cellulose microfibrils present a twisting behavior, which was investigated using electron microscopy techniques. Sequential electron microdiffraction analyses obtained under frozen hydrated conditions revealed that the cellulose microfibrils continuously right-hand twisted in the vitreous ice layer. This observation implies that the twists of these nanofibers are intrinsic to the cellulose molecule and not a result of the cell wall biogenesis process. Furthermore, scaling with the fourth power of width based on the classic mechanics of solid, the twist angle was in agreement with the reported values in higher plant celluloses, implying that the twist arises from the balance between tendency of individual chains to twist and the structure imposed by the crystal packing. The observed twist in isolated fibrils of Glaucocystis indicates that one cannot assume the presence of cellulose twisting in vivo based on observations of isolated cellulose nanoparticles, as microfibril can exist untwisted in the original cell wall but become twisted when released from the wall.

Chitin microsphere supported Pd nanoparticles as an efficient and recoverable catalyst for CO oxidation and Heck coupling reaction

Chitin derived from seafood wastes is a sustainable biopolymer, which can be used to constructe new materials to reduce the environmental pollution caused by non-biodegradable plastics. Herein, nanofibrous microspheres fabricated from chitin solution were used as carriers to construct three different chitin-supported Pd catalysts through diverse activation methods, subsequently revealed their differences in structure and performance. The palladium nanoparticles were firmly and highly dispersed on the microspheres due to the interconnected nanofibrous networks and functional groups of chitin, confirmed by various physicochemical characterizations. As the best candidate catalyst of Pd/chitin-Ar, in the CO oxidation reaction, which achieved 100% CO conversion with a lower Pd content, and exhibited excellent stability in 24-hours cycle reaction. Importantly, the catalyst was further applied in Heck coupling reaction, which also displayed competitive catalytic activity and stability (∼6runs, 94%). This utilizing of biomass resource to build catalyst materials would be important for the sustainable chemistry.

Size-Controlled Preparation of Gold Nanoparticles Deposited on Surface-Fibrillated Cellulose Obtained by Citric Acid Modification

Cellulose-based functional materials have gained immense interest due to their low density, hydrophilicity, chirality, and degradability. So far, a facile and scalable preparation of fibrillated cellulose by treating the hydroxy groups of cellulose with citric acid (F-CAC) has been developed and applied as a reinforcing filler for polypropylene composite. Herein, a size-selective preparation of Au nanoparticles (NPs) stabilized by F-CAC is described. By modifying the conditions of transdeposition method, established in our group previously, a transfer of Au NPs from poly(N-vinyl-2-pyrrolidone) (PVP) to F-CAC proceeded up to 96% transfer efficiency with retaining its cluster sizes in EtOH. Meanwhile, the deposition efficiency drastically decreased in the case of nonmodified cellulose, showing the significance of citric acid modification. A shift of binding energy at Au 4f core level X-ray photoelectron spectroscopy from 82.0 to 83.3 eV indicated that the NPs were stabilized on an F-CAC surface rather than by PVP matrix. The reproducible particle size growth was observed when 2-propanol was used as a solvent instead of EtOH, expanding the range of the available particle size with simple manipulation. The thus-obtained Au:F-CAC nanocatalysts exhibited a catalytic activity toward an aerobic oxidation of 1-indonol in toluene to yield 1-indanone quantitatively and were recyclable at least six times, illustrating high tolerance against organic solvents.

Co(III)-Salen immobilized cellulose nanocrystals for efficient catalytic CO2 fixation into cyclic carbonates under mild conditions

Searching for green, recyclable and highly efficient catalyst for the synthesis of cyclic carbonates from CO₂ is of great importance because it is profitable for reducing the greenhouse effects and meets the principles of green chemistry. Herein, a series of cellulose nanocrystals, either the pristine or modified ones (TEMPO oxidized and Co(III)salen immobilized), were explored as catalysts for cycloaddition of epoxides and carbon dioxide. The impact of surface properties on the performance of the as-made catalysts was investigated. Co(III)-salen grafted cellulose nanocrystals was proven to be the most effective catalyst in this study, which could afford excellent yield up to 99 % after 24 h even under low CO₂ pressures of 0.1 MPa. They can be easily recovered and reused for at least 4 times, demonstrating their excellent stability. We found that the surface functional groups such as enriched sulfate or carboxylic groups could also account for the enhanced catalytic activity. This work highlights the applications of green and sustainable nanoparticles in a cycloaddition reaction and offers a sustainable solution in industrial catalysis related to CO₂ conversions.

Self-Assembled Bio-Organometallic Nanocatalysts for Highly Enantioselective Direct Aldol Reactions

Supramolecular nanocatalysts were designed for asymmetric reactions through the self-assembly process of a bio-organometallic molecule, ferrocene-l-prolinamide (Fc-CO-NH-P). Fc-CO-NH-P could self-assemble into versatile nanostructures in water, including nanospheres, nanosheets, nanoflowers, and pieces. In particular, the self-assembled nanoflowers exhibited a superior specific surface area, high stability, and delicate three-dimensional (3D) chiral catalytic active sites. The nanoflowers could serve as heterogeneous catalysts with an excellent catalytic performance toward direct aldol reactions in aqueous solution, achieving both high yield (>99%) and stereoselectivity (anti/syn = 97:3, ee% >99%). This study proposed a significant strategy to fabricate supramolecular chiral catalysts, serving as a favorable template for designing new asymmetric catalysts.

Palladium nanoparticles supported on chitin-based nanomaterials as heterogeneous catalysts for the Heck coupling reaction

In this report, chitin and chitosan nanocrystals were used as biomass-based supports for Pd nanoparticles (NPs) used as a heterogeneous catalyst for the Heck coupling reaction. By using a one-pot fabrication method, a Pd salt precursor was directly reduced and deposited onto these nanocrystal catalysts. Characterization of these nanocomposites showed disperse Pd NPs on the surfaces of the chitinous nanocrystals. Heck coupling model reactions revealed full product yield in relatively benign conditions, outcompeting the use of other catalysts supported on biomass-based nanomaterials, including cellulose nanocrystals. These initial results show the potential for using chitinous nanomaterials as effective catalyst supports in cross-coupling reactions.

Silver-Triggered Activity of a Heterogeneous Palladium Catalyst in Oxidative Carbonylation Reactions

A silver-triggered heterogeneous Pd-catalyzed oxidative carbonylation has been developed. This heterogeneous process exhibits high efficiency and good recyclability, and was utilized for the one-pot construction of polycyclic compounds with multiple chiral centers. AgOTf was used to remove chloride ions in the heterogeneous catalyst Pd-AmP-CNC, thereby generating highly active PdII , which results in high efficiency of the heterogeneous catalytic system.

Selective Isolation Methods for Cellulose and Chitin Nanocrystals

This Minireview focuses on the selective isolation methods for the preparation of cellulose nanocrystals (CNCs) and chitin nanocrystals (ChNCs). Various selective preparation strategies with specific preparation conditions and reaction mechanisms are summarized. In particular, these selective reaction routes include controlled acid hydrolysis and selective oxidations at specific positions of cellulose or chitin fibers as well as particular reaction sites of the repeating monosaccharide building blocks of their main chains. These lead to selective cleavage of the ordered and non-ordered regions of cellulose and chitin and result in efficient production of CNCs and ChNCs.

Chiral Nematic Liquid Crystal Behavior of Core-Shell Hybrid Rods Consisting of Chiral Cellulose Nanocrystals Dressed with Non-chiral Conformal Polymeric Skins

The current work investigates how the nanoscale conformal coating layers of non-chiral polymeric materials can influence the chiral nematic liquid crystal (CLC) behaviors of the rodlike cellulose nanocrystals (CNCs), the bio-derived nanomaterials that have attracted significant attention. For this, we developed strategies to coat the CNC rods on the single-particle level with a homogeneous bioinspired polydopamine (PDA) layer, leading to well-defined core-shell CNC@PDA rods with various PDA coating thicknesses and excellent colloidal stability. Comprehensive investigation revealed that the CNC@PDA hybrid nanorods in concentrated suspensions form well-defined nematic liquid crystal phases with clear phase separation behavior that depend on the rod concentrations and ionic strengths, typical of charged rods. Most intriguingly, the nematic LC phases formed by the CNC@PDA rods with the PDA coating thickness achieved herein are indeed the perfect CLC phases, which form following the classic pathway of nucleation and coalesce of chiral tactoids and have colorful chiral fingerprints standing out from the dark suspensions. The pitches of the CLC phase increase sharply with increasing PDA coating thicknesses and are significantly larger than those of the pristine CNCs. Such observations can be attributed to the blurring effects of the PDA coating on the intrinsic surface chiral features of CNC of whatever origins that drive the formation of the CLC phases, resulting in weakening chiral interactions between CNC@PDA rods. Besides benefiting the understanding of the long-sought origin of the CLC phases of the pristine CNC, the current work demonstrates the possibility of controlling the CLC phase behaviors of CNC by tuning the thickness of the coating materials and also serves as the first example of directly transferring the unique chirality of CNC to other non-chiral materials.

Microscopic Techniques for the Analysis of Micro and Nanostructures of Biopolymers and Their Derivatives

Natural biopolymers, a class of materials extracted from renewable sources, is garnering interest due to growing concerns over environmental safety; biopolymers have the advantage of biocompatibility and biodegradability, an imperative requirement. The synthesis of nanoparticles and nanofibers from biopolymers provides a green platform relative to the conventional methods that use hazardous chemicals. However, it is challenging to characterize these nanoparticles and fibers due to the variation in size, shape, and morphology. In order to evaluate these properties, microscopic techniques such as optical microscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM) are essential. With the advent of new biopolymer systems, it is necessary to obtain insights into the fundamental structures of these systems to determine their structural, physical, and morphological properties, which play a vital role in defining their performance and applications. Microscopic techniques perform a decisive role in revealing intricate details, which assists in the appraisal of microstructure, surface morphology, chemical composition, and interfacial properties. This review highlights the significance of various microscopic techniques incorporating the literature details that help characterize biopolymers and their derivatives.

Valorization of Waste: Sustainable Organocatalysts from Renewable Resources

One of the greatest challenges facing our society is to reconcile our need to develop efficient and sophisticated chemical processes with the limited resources of our planet and its restricted ability to adsorb pollution. Organocatalysis has allowed many issues to be addressed in the development of sophisticated, but less polluting, processes. However, minimizing waste also means an efficient utilization of raw and renewable materials. Waste biomass represents an alternative to conventional petroleum-based chemical manufacturing and is a highly attractive renewable resource for the production of chemicals and high-value-added organocatalysts. Recent achievements in the use of renewable biomass feedstocks for the synthesis of organocatalysts are presented. Their application in synthetic methodologies, including multicomponent reactions, which are performed under solvent-free conditions or in eco-friendly reaction media, as well as recycling and reusing the organocatalysts, is illustrated. A few pioneering examples that demonstrate the potential of these promoters in asymmetric synthesis have also been documented. In particular, this review covers examples on the use of hetero- and homogeneous organocatalysts derived from 1) waste biopolymers, such as chitosan, alginic acid, and cellulose; ii) renewable platform molecules, such as levoglucosenone, isosorbide, mannose, d-glucosamine, and lecithin; 3) terpenes and rosin, such as pinane, isosteviol, and abietic acid; and iv) natural proteins (gelatin, bovine tendons, silk fibroin proteins).

Waste paper: An underutilized but promising source for nanocellulose mining

Nanocellulose has achieved an inimitable place and value in nano-materials research sector. Promising and exclusive physical, chemical and biological properties of nanocellulose make it an attractive and ideal material for various high end-user applications. Conventionally, the base material for nanocellulose i.e. cellulose is being extracted from various lignocellulosic raw materials (like wood, agro-industrial-residues, etc.) using pulping followed by bleaching sequences. As an alternate to lignocellulosic raw materials, waste paper also showed potential as a competent raw material due to its abundant availability and high cellulosic content (60-70%) with comparatively less hemicelluloses (10-20%) and lignin (5-10%) without any harsh treatments. The production yields of nanocellulose were reported to vary from 1.5% to 64% depending upon the waste papers and treatments given. The diameters of these nanocelluloses were reported in the range of 2-100 nm and crystallinity range around 54-95%. Thermal degradation of waste paper nanocellulose was varied from 187 °C to 371 °C. Although these properties are comparable with the nanocellulose obtained from lignocellulosic raw materials, yet waste paper is an underutilized source for nanocellulose preparation due to its ordinary fate of recycling, dumping and incineration. In the sight of necessity and possibility of waste paper utilization, this article reviews the outcomes of research carried out for preparation of nanocellulose using waste paper as a source of cellulose. There is a need of sincere investigation to convert this valuable waste to wealth i.e. waste papers to nanocellulose, which will be helpful in solid waste management to protect environment in economical way.

Nanomaterials Derived from Fungal Sources-Is It the New Hype?

Greener alternatives to synthetic polymers are constantly being investigated and sought after. Chitin is a natural polysaccharide that gives structural support to crustacean shells, insect exoskeletons, and fungal cell walls. Like cellulose, chitin resides in nanosized structural elements that can be isolated as nanofibers and nanocrystals by various top-down approaches, targeted at disintegrating the native construct. Chitin has, however, been largely overshadowed by cellulose when discussing the materials aspects of the nanosized components. This Perspective presents a thorough overview of chitin-related materials research with an analytical focus on nanocomposites and nanopapers. The red line running through the text emphasizes the use of fungal chitin that represents several advantages over the more popular crustacean sources, particularly in terms of nanofiber isolation from the native matrix. In addition, many β-glucans are preserved in chitin upon its isolation from the fungal matrix, enabling new horizons for various engineering solutions.

Nanocellulose enriches enantiomers in asymmetric aldol reactions

Catalytically inactive cellulose nanofibers with crystalline solid surfaces enhance highly enantioselective organocatalysis at the interface in proline-mediated aldol reactions.

Electron microdiffraction reveals the nanoscale twist geometry of cellulose nanocrystals

Nanocellulose consisting of crystalline cellulose nanoparticles has high potential to serve as a building block for bio-based functional materials. The intrinsic chirality of cellulose provides them with high added values such as optical properties and chiral induction ability. At the nanoscale, this chirality is connected to the right-handed longitudinal twisting of these fibrous crystallites. However, this nanoscale fibrillar twist has been a matter of debate due to contradictory data between ultrastructural observations and molecular simulations and so far, the exact twist geometry has not been elucidated. Here, an electron microdiffraction (μED) analysis under cryogenic conditions reveals the continuous twisting of cellulose nanocrystals (CNCs) in aqueous suspension. This intrinsic regular twist is drastically modified to a discontinuous sharp twist when the CNCs are dried on a flat surface. The present μED-based analysis at the single nanoparticle level allows the establishment of the quantitative structure-property relationship of various solid and colloidal nanocellulose systems.

Methods and applications of nanocellulose loaded with inorganic nanomaterials: A review

Nanocellulose obtained from natural renewable resources has attracted enormous interests owing to its unique morphological characteristics, excellent mechanical strength, biocompatibility and biodegradability for a variety of applications in many fields. The template structure, high specific surface area, and active surface groups make it feasible to conduct surface modification and accommodate various nano-structured materials via physical or chemical deposition. The review presented herein focuses on the methodologies of loading different nano-structured materials on nanocellulose, including metals, nanocarbons, oxides, mineral salt, quantum dots and nonmetallic elements; and further describes the applications of nanocellulose composites in the fields of catalysis, optical electronic devices, biomedicine, sensors, composite reinforcement, photoswitching, flame retardancy, and oil/water separation.

Reversible modulation of plasmonic chiral signals of achiral gold nanorods using a chiral supramolecular template

We report here the fabrication of a multiple stimuli-responsive chiral plasmonic system based on the reversible self-assembly of phenylboronic acid-capped gold nanorods (PBA-Au NRs) guided by a supramolecular glycopeptide mimetic template. The plasmonic chiral signals of PBA-Au NRs can be reversibly switched on and off by temperature, light, pH and glucose concentration variations.

Controlling the Self-Assembly Behavior of Aqueous Chitin Nanocrystal Suspensions

As with many other biosourced colloids, chitin nanocrystals (ChNCs) can form liquid crystalline phases with chiral nematic ordering. In this work, we demonstrate that it is possible to finely tune the liquid crystalline behavior of aqueous ChNC suspensions finely. Such control was made possible by carefully studying how the hydrolysis conditions and suspension treatments affect the colloidal and self-assembly properties of ChNCs. Specifically, we systematically investigated the effects of duration and acidity of chitin hydrolysis required to extract ChNCs, as well as the effects of the tip sonication energy input, degree of acetylation, pH and ionic strength. Finally, we show that by controlled water evaporation, it is possible to retain and control the helicoidal ordering in dry films, leading to a hierarchical architecture analogous to that found in nature, e.g. in crab shells. We believe that this work serves as a comprehensive insight into ChNC preparation and handling which is required to unlock the full potential of this material in both a scientific and industrial context.