The degree of crystallinity in cellulose significantly affects the physical, mechanical, and chemical properties of cellulosic materials, their processing, and their final application. Measuring the crystalline structures of cellulose is a challenging task due to inadequate consistency among the variety of analytical techniques available and the lack of absolute crystalline and amorphous standards. Our article reviews the primary methods for estimating the crystallinity of cellulose, namely, X-ray diffraction (XRD), nuclear magnetic resonance (NMR), Raman and Fourier-transform infrared (FTIR) spectroscopy, sum-frequency generation vibrational spectroscopy (SFG), as well as differential scanning calorimetry (DSC), and evolving biochemical methods using cellulose binding molecules (CBMs). The techniques are compared to better interrogate not only the requirements of each method, but also their differences, synergies, and limitations. The article highlights fundamental principles to guide the general community to initiate studies of the crystallinity of cellulosic materials.

Phosphoric acid is widely used for the swelling and hydrolysis of cellulose. The detailed description of molecular interactions between cellulose and phosphoric acid is essential for understanding and controlling these processes. Here, to obtain structural insights into the swelling behavior, we investigated the structural evolution of cellulose swollen in concentrated phosphoric acid solution using X-ray fiber diffraction and solid-state NMR spectroscopy. We observed the formation of a crystalline complex of cellulose and phosphoric acid at − 40 °C, where cellulose molecules adopt a seven-fold helical conformation. This structure is the second known cellulose-acid crystalline complex and the first cellulosic crystal consisting of seven-fold helical chains. Our observation highlights the conformational flexibility of cellulose molecules in the solvated states and the strong influence of cellulose-acid interactions on the packing and conformation of cellulose molecules.

Cellulose model compounds that mimic the building blocks of modified cellulose and cellulose derivatives are widely used in cellulose research to infer the properties of the polymer from the monomer. Based on the well-established model compound methyl 4- O -methyl β- d -glucopyranoside, in which the methyl groups represent the truncated side chains of the cellulose, the corresponding O -methyl-substituted derivatives with all eight different substitution patterns (mono-, di- and trisubstituted at O-2, O-3, O-6) were synthesized. Crystallization of the products in sufficient quality for solid-state structure determination by single-crystal X-ray diffraction succeeded in all cases, and the results are reported. Two of the compounds showed more than one independent molecule per unit cell. Solid-state 13 C NMR showed a significant down-field shift (5–10 ppm) of the OMe-substituted carbons relative to the OH-substituted counterparts and generally confirmed the important influence of solid-state packing on the chemical shifts as seen by comparison to the solution NMR data. Graphical abstract

Peptide–cellulose conjugates designed for use as optical protease sensors have gained interest for point-of-care (POC) detection. Elevated serine protease levels are often found in patients with chronic illnesses, necessitating optimal biosensor design for POC assessment. Nanocellulose provides a platform for protease sensors as a transducer surface, and the employment of nanocellulose in this capacity combines its biocompatibility and high specific surface area properties to confer sensitive detection of dilute biomarkers. However, a basic understanding of the spatiotemporal relationships of the transducer surface and sensor disposition is needed to improve protease sensor design and development. Here, we examine a tripeptide, fluorogenic elastase biosensor attached to TEMPO-oxidized nanofibrillated cellulose via a polyethylene glycol linker. The synthetic conjugate was found to be active in the presence of human neutrophil elastase at levels comparable to other cellulose-based biosensors. Computational models examined the relationship of the sensor molecule to the transducer surface. The results illustrate differences in two crystallite transducer surfaces ((110) vs. (1−10)) and reveal preferred orientations of the sensor. Finally, a determination of the relative (110) vs. (1−10) orientations of crystals extracted from cotton demonstrates a preference for the (1−10) conformer. This model study potentiates the HNE sensor results for enhanced sensor activity design.

The global burden of the SARS-CoV-2 pandemic is thought to result from a high viral transmission rate. Here, we consider mechanisms that influence host cell–virus binding between the SARS-CoV-2 spike glycoprotein (SPG) and the human angiotensin-converting enzyme 2 (ACE2) with a series of peptides designed to mimic key ACE2 hot spots through adopting a helical conformation analogous to the N-terminal α1 helix of ACE2, the region experimentally shown to bind to the SARS-CoV-2 receptor-binding domain (RBD). The approach examines putative structure/function relations by assessing SPG binding affinity with surface plasmon resonance (SPR). A cyclic peptide (c[KFNHEAEDLFEKLM]) was characterized in an α-helical conformation with micromolar affinity (KD = 500 µM) to the SPG. Thus, stabilizing the helical structure of the 14-mer through cyclization improves binding to SPG by an order of magnitude. In addition, end-group peptide analog modifications and residue substitutions mediate SPG binding, with net charge playing an apparent role. Therefore, we surveyed reported viral variants, and a correlation of increased positive charge with increased virulence lends support to the hypothesis that charge is relevant to enhanced viral fusion. Overall, the structure/function relationship informs the importance of conformation and charge for virus-binding analog design.

Here we describe the synthesis and characterization of a peptide-cellulose conjugate biosensor based on TEMPO-oxidized nanofibrillated cellulose (tNFC) for detecting elevated levels of human neutrophil elastase (HNE) in chronic wounds. The fluorescent peptide HNE substrate constructed from n-succinyl-Ala-Pro-Ala-7-amino-4-methyl-coumarin was attached to the TEMPO-oxidized cellulose surface via polyethylene glycol linker. The characterization of the biosensor conjugate shows a high degree of peptide incorporation onto the surface with the degree of substitution of 0.057. The relatively small crystallite size of 26.0 Å compared to other cellulose- and nanocellulose-based materials leads to a large specific surface area which can promote access of HNE to the enzyme substrates due to decreased steric interactions. Likewise, the porosity for tNFC was found to be higher than all other samples, including the nanocellulosic aerogel, lending to its hydrogel-like nature. The properties of tNFC were compared to other cellulose-based materials. The volume of each crystallite and volume ratio to the largest sample was calculated. tNFC was found to occupy the smallest space resulting in high amounts of sensors per crystallite unit volume. With a small crystallite volume and large number of sensors, the tNFC peptide-cellulose conjugate biosensor could provide a more sensitive system and is a good candidate for point of care diagnostic devices for detecting elevated protease levels in humans.

Cellulose serves as a skeleton for many of the useful products upon which we rely on each day. When we want to learn about a skeleton, it makes sense to think about X-ray methods. The same can be said when it comes to learning about the crystallinity of cellulose. Over the past six decades, the Segal X-ray diffraction (XRD) method has been popular for judging the percent crystallinity of powder samples. However, XRD patterns for ideal cellulose crystals can be easily simulated, and limitations of the Segal and other methods become obvious. Calculated patterns for model 100% crystalline powder particles are predicted to be less crystalline by the Segal method. Except for the Rietveld method, current approaches do not account for particle orientation or different shapes of crystallites. The Rietveld method has so many variables that it can easily overfit the data. The take-away message is that routine XRD examination is important for showing sample characteristics, but fractional crystallinity values are affected by constraints related to simplifications required for the analysis.

Efficient modification and decrystallization of cellulose I beta in lignocellulosic biomass are potential ways to overcome biomass recalcitrance and facilitates enzymatic degradation. Herein, we have treated moso bamboo and microcrystalline cellulose separately by either alkali or ethylenediamine (EDA) treatments, as well as using both in succession. The pretreatments successfully transformed the initial cellulose I beta allomorph into cellulose II, IIII, and cellulose IIIII. Crystal structures and crystallinities were determined by Rietveld X-ray diffraction and CP/MAS C-13 NMR. Comparatively, the samples that were sequentially treated by EDA and NaOH had low crystallinity (similar to 50%), larger d-spacings of similar to 4.4 angstrom for the hydrophobic (110) planes, and less condensed microfibrillar aggregation. The factors simultaneously contributed to as high enzymatic hydrolysis yield as 89.5% and 91.7% respectively, followed by the yields of mercerized cellulose II and cellulose IIIII allomorph. The stepwise allomorphic transformations may provide new strategies on improving efficiency of saccharification process and biomass utilization.

Shapes (conformations) of cellulose molecules are described by their glycosidic linkage torsion angles ϕ and ψ. Although the torsions are known for cellulose in crystals, amorphous shapes are also interesting for understanding reactivity and physical properties. ϕ and ψ determination for unorganized matter is difficult; one approach is to study their range in many related molecules. For example, linkage torsions of cellulose should be similar to those in cellobiose. Herein, torsions were measured for cellooligosaccharides and lactose moieties complexed with proteins in the Protein Data Bank (PDB). These torsions were compared with ϕ/ψ maps based on quantum mechanics energies for solvated cellobiose and analogs lacking hydroxyl groups. Most PDB conformations corresponded to low map energies. Amorphous cellulose should be generally extended with individual linkages that would give 2- to 3-fold helices. The map for an analog lacking hydrogen bonding ability was more predictive for PDB linkages than the cellobiose map.

Professor Dexter French (1918-1981) was an American chemist and biochemist at Iowa State College (University in 1959). He devoted his career to advance knowledge of polysaccharides and oligosaccharides, in particular starch, cyclodextrins, and enzymes. Cyclodextrins are oligosaccharides obtained from starch and are typically cage molecules with a hydrophobic cavity that can encapsulate other compounds nowadays the basis for many industrial applications. Since the 1960s, he has been recognized as an outstanding authority in the field of starches and cyclodextrins and has inspired researchers in laboratories around the world. This review, on the fortieth anniversary of his death, commemorates his remarkable contribution to starch and cyclodextrin chemistry. Firstly, we give an overview of his personal life and career. Secondly, we highlight some of the results on starch and cyclodextrins from Professor French and his group. A third part discusses his impact on the modern chemistry of cyclodextrins and starch.

The hazards of handling N-methylmorpholine-N-oxide (NMMO) cannot be described often enough, although it is a rather common (co-)solvent for cellulose. Inaccuracies in the literature regarding the chemistry of NMMO, such as its role in solvent systems and in redox systems involving transition metal ions, increase the risk of dangerous failure of the intended reactions which might result in uncontrolled exothermicities, damage of laboratory equipment or even accidents and work safety issues. Therefore, suitable cautionary and mitigation strategy statements regarding the hazards of handling NMMO are encouraged for future publications regarding NMMO and cellulose.

Although the caption is correct, the curves in Fig. 1 attributed to Guo et al. in the legend should have been attributed to Yao et al. The corrected figure, with legend is below.

During the preparation of a follow-on manuscript, it was discovered that values of the temperatures of the distribution were miscalculated.

Computerized molecular modeling continues to increase in capability and applicability to carbohydrates. This chapter covers nomenclature and conformational aspects of carbohydrates, perhaps of greater use to carbohydrate-inexperienced computational chemists. Its comments on various methods and studies might be of more use to computation-inexperienced carbohydrate chemists. New work on intrinsic variability of glucose, an overall theme, is described.

Energy cane bagasse (ECB) is the major residue after the cane is milled to extract juice for sugar, biochemical, and/or biofuel production. The sustainable conversion of ECB into high value-added products can help reduce agricultural waste, and enhance utilization of bioresources. In the present work, we demonstrate that ECB can be converted into cellulose nanofibers (CNFs) that can serve as high value-added additives in bentonite water-based fluids (BT-WDFs). Particularly, cellulose fibers (CFs) were rapidly isolated from ECB by microwave-assisted NaOH / NaClO2 treatments. CFs treated with the higher NaOH concentration and microwave irradiation lost more lignin (96.2 % delignification) and their crystal structure was more completely transformed from cellulose I to II, resulting in smaller diameters (8.5 mu m). CNFs suspensions from subsequent wet-grinding and microfluidization of the CFs exhibited typical shear-thinning behaviors and solid-like viscoelastic properties due to the entangled network structure of the CNFs. Formulated fluids with 0.5 wt% of the manufactured CNFs showed good rheological and filtration properties, demonstrating their potential applications in the oil service industry.

Cellulose is often described as a mixture of crystalline and amorphous material. A large part of the general understanding of the chemical, biochemical and physical properties of cellulosic materials is thought to depend on the consequences of the ratio of these components. For example, amorphous materials are said to be more reactive and have less tensile strength but comprehensive understanding and definitive analysis remain elusive. Ball milling has been used for decades to increase the ratio of amorphous material. The present work used 13 techniques to follow the changes in cotton fibers (nearly pure cellulose) after ball milling for 15, 45 and 120 min. X-ray diffraction results were analyzed with the Rietveld method; DNP (dynamic nuclear polarization) natural abundance 2D NMR studies in the next paper in this issue assisted with the interpretation of the 1D analyses in the present work. A conventional NMR model’s paracrystalline and inaccessible crystallite surfaces were not needed in the model used for the DNP studies. Sum frequency generation (SFG) spectroscopy also showed profound changes as the cellulose was decrystallized. Optical microscopy and field emission-scanning electron microscopy results showed the changes in particle size; molecular weight and carbonyl group analyses by gel permeation chromatography confirmed chemical changes. Specific surface areas and pore sizes increased. Fourier transform infrared (FTIR) and Raman spectroscopy also indicated progressive changes; some proposed indicators of crystallinity for FTIR were not in good agreement with our results. Thermogravimetric analysis results indicated progressive increase in initial moisture content and some loss in stability. Although understanding of structural changes as cellulose is amorphized by ball milling is increased by this work, continued effort is needed to improve agreement between the synchrotron and laboratory X-ray methods used herein and to provide physical interpretation of the SFG results.

Solvents that produce cellulose nanocrystals (CNCs) and promote cellulose fibrillation are of current interest. In this work, CNCs were fabricated from cotton at 80 and 100 °C using deep eutectic solvents (DESs) having choline chloride/oxalic acid dihydrate (OA) ratios of 1:1, 1:2 and 1:3. To investigate the side effects of the fabrication, the crystal structure and morphology of micro-sized treated cellulose together with nano-sized CNCs were analyzed by X-ray diffraction, field emission scanning electron microscopy and atomic force microscopy. OA promoted the formation of carboxyl groups on the C6 positions of molecules on the hydrophilic (1–10) lattice planes, causing extensive fibrillation of cellulose and disruption of surface layers on (110) and (200) planes. Lower crystallinity and lamellar structures for CNCs with mild treatment were observed after mechanical disintegration and subsequent lyophilization, which was ascribed to van der Waals forces and hydrogen bonding between adjacent crystalline cellulose chains, accelerating the self-assembly into cellulose macrofibrils. This work is discussed in light of cellulose supramolecular structures that are modified from CNC fabrication via DES treatment, with a view to enhancing the efficacy of treatment by understanding the variations that arise in cellulose structure from a green solvent.

Nanocellulose has functionalities suitable for efficient sensor transducer surface design including crystallinity, biocompatible and high specific surface area. Here we explore two forms of nanocellulose as transducer surfaces to enable colorimetric detection of human neutrophil elastase (HNE), and a wide range of inflammatory diseases. A deep eutectic solvent (DES) was utilized to mediate formation of cotton cellulose nanocrystals (DCNCs) employed to prepare a peptide-cellulose conjugate as a protease sensor of HNE. The tetrapeptide-cellulose analog on DCNC is contrasted with an analogous derivative of TEMPO-oxidized wood cellulose nanofibrils (WCNFs). DCNCs showed greater degree of substitution of HNE tetrapeptide and sensitivity to the elastase than WCNFs, despite the smaller surface area and pore sizes. XRD models revealed the higher crystallinity and larger crystallite sizes of DCNCs, indicating the well-arranged cellulose chains for immobilization of the tetrapeptide on (110) lattice reflections of cellulose crystals. The sensitivity of DCNCs-based colorimetric sensor was less than 0.005 U/mL, which would provide a convenient, sensitive sensor applicable for improved colorimetric point of care protease biomarker detection.