Chemistry
Cellulose
Cellulose is a complex carbohydrate found in the cell walls of plants. It is composed of long chains of glucose molecules linked together, providing structural support to plant cells. Cellulose is a key component of dietary fiber and is widely used in the production of paper, textiles, and biofuels due to its abundance and renewable nature.
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- Antonio Paesano(Author)
- 2022(Publication Date)
- CRC Press(Publisher)
cellobiose, formed by two molecules, and 1.3 nm long. Native Cellulose has molecular chains long 500−15,000 nm, depending on its origin (Heinze 2016).Figure 7.1Chemical structure of Cellulose. Each of the four units is glucose. Cellobiose comprises two glucose units. Numbers 1 to 6 identify locations of the carbon atoms on the ring.Source: Modified from Heinze, T. 2016. Cellulose: Structure and Properties. Adv Polym Sci 271:1–52. doi: 10.1007/12_2015_319 . Reproduced with permission from Springer International.Cellulose is a semi-crystalline polysaccharide, and its molecules are strongly connected through intermolecular and intramolecular hydrogen bonding and van der Waals forces, which results in the formation of small crystals called microfibrils that are embedded in a disordered, amorphous matrix, and in turn form larger fibers (Swift 1977 ). The length of the microfibrils is of the order of micrometers, and their species-specific diameter is 2‒25 nm (O’Sullivan 1997 ). Figure 7.2 is a schematic view of microstructure of plants, showing microfibrils, Cellulose, and hemiCellulose that is a branched polymer crosslinked to microfibrils and composed of sugars.Figure 7.2Schematic view of microstructure of plants showing microfibrils, Cellulose, and hemiCellulose.Source: Adapted from US DOE . 2005. Genomics:GTL Roadmap, DOE/SC-0090, U.S. Department of Energy Office of Science. (p. 204) (website). Office of Biological and Environmental Research of the U.S. Department of Energy Office of Science. science.energy.gov/ber/ . Freely reproduced.Because of the strong hydrogen bonding interactions, Cellulose exhibits relatively high tensile modulus, up to 800 MPa (Bledzki and Gassan 1999 ; Mohanty et al. 2000 ) vs. other polysaccharides. Cellulose is tough, fibrous, hydrophilic, and insoluble in water and most common organic solvents (Habibi et al. 2010
eBook - ePub- Jose Perez-Castineira(Author)
- 2020(Publication Date)
- De Gruyter(Publisher)
36 ].3.4.3 Cellulose
Cellulose is also a homopolysaccharide of D-glucose, however, in contrast to starch and glycogen, it has no ramifications and its monosaccharide units are linked by glycosidic β(1→4) bonds. The latter are responsible for the enormous differences in structural and functional properties of Cellulose compared to those of starch and glycogen, as the most stable conformation for Cellulose implies 180º rotation of each glucopyranose relative to its neighbors. This yields straight extended chains with molecular weights of over 1,000,000 that can align next to each other establishing numerous hydrogen bonds (Figure 3.10 ) [37 ]. Cellulose is the most abundant biomolecule on the Biosphere, comprising over 50% of all the carbon vegetation, and plays an important structural role in photosynthetic organisms, such as higher plants, eukaryotic algae, and cyanobacteria, being the major component of their cell walls [38 ].Figure 3.10: Structural characteristics of Cellulose. β-D-glucose residues rotate around the glycosidic link, thereby optimizing interactions by intrachain and interchain hydrogen bonds.The glycosidic β(1→4) bond can only be cleaved in vivo by cellulases, a family of hydrolytic enzymes present in microorganisms such as actinomycetes, bacteria, and fungi [39 ]. Some of these microorganisms live in the stomach of ruminants allowing them to digest this polypeptide thus using it as a source of glucose. In humans, the only cellulase activity is associated with some symbiotic bacteria of the colon [40 ] which means that Cellulose can pass unaltered through most of our intestinal tract due to its mechanochemical resistance to pH changes and hydrolytic attack. Fermentation of polysaccharides by intestinal microorganisms can produce SCFAs that we subsequently absorb and metabolize, providing a small fraction (less than 10%) of our dietary energy [41
eBook - ePubPulp Production and Processing
High-Tech Applications
- Valentin I. Popa, Valentin I. Popa(Authors)
- 2020(Publication Date)
- De Gruyter(Publisher)
Chapter 8 Chemistry and physics of Cellulose and Cellulose substanceMilichovský MiloslavUniversity of Pardubice, Faculty of Chemical Technology, Institute of Chemistry and Technology of Macromolecular Substances , Pardubice , Czech Republic8.1 Introduction
The unique properties and recent universal focus on natural material resources has put Cellulose and Cellulose derivatives into the sphere of intensive scientific effort and consequently to the attention of industrial companies. Nature provides wonderful examples of composite structures that involve Cellulose. Cellulose is a fibrous, tough, water-insoluble substance, which is found in the protective cell walls of plants, particularly in stalks, stems, trunks, and all woody portions of plant tissues. The properties of wood, for instance, result from the unique interplay between Nanoscale domains of Cellulose, hemiCelluloses, and lignin [1 ]. The manner in which such elements are organized into larger structures is critical to the survival of trees and other plants. The hierarchical organization of wood is based on the natural composite paradigm of providing maximum strength with the minimum amount of material from the most efficient economy of biosynthesis [2 ]. Even some animal species make use of cellulosic nano-structures, such as some members of the tunicates (“sea squirts”) family, the sea alga Valoniaventricosa [3 ], Chaetomorphamelagonium [4 ], and Bacterial Cellulose, a polysaccharide synthesized in abundance, for example, by Acetobacterxylinum [5 ]. In all of these organisms, Cellulose serves as a “scaffold” to evolve further mechanical support of highly organized living and growing matter. Knowledge of the supramolecular and hypermolecular structure of Cellulose, accompanied by changes during its chemical or mechanical treatment is important not only for technical or biomedical applications, but also predominantly as a novel approach to better understand and control the aging of Cellulose materials, for example, in paper and paper products and nanocomposites. During the last 150 years of intensive research, an abundance of experimental data and information has been collected concerning the ultrastructure and morphology of Cellulose, native cellulosic substances, and cellulosic materials. Although the development and utilization of Cellulose have a long history, the understanding of its chemistry and structure is relatively new, and many living polymer scientists have spent their entire working lives developing our present knowledge. Despite the fact that the polymer theory is established and the chemical structure of Cellulose is accepted without dispute, the ultrastructure of Cellulose remains controversial on several issues. Despite the degree to which Cellulose has been investigated, its structural features have not been identified with absolute clarity and new information is constantly being discovered [6 , 7 ]. With regard to the solid state structure of Cellulose, progress has been made but a lack of information and theoretical ideas exist involving the behavior of Cellulose in a wet state and water suspensions. Infrared spectroscopy, Raman spectroscopy, single-crystal X-ray studies, high-resolution nuclear magnetic resonance (NMR), dark-field electron microscopy, and electron diffraction, supported by the recent applications of the solid-state, cross-polarization/magic angle spinning (CP/MAS) NMR, 13 C-CP/MAS solid-state NMR, electron spectroscopy for chemical applications, photoacoustic Fourier transform infrared spectroscopy (FTIR), secondary ion mass spectrometry, and fast atom bombardment mass spectrometry have added considerable information to our knowledge of the solid-state structure of Cellulose [8
eBook - ePubPolysaccharides
Properties and Applications
- Mohd Imran Ahamed, Rajender Boddula, Tariq Altalhi, Mohd Imran Ahamed, Rajender Boddula, Tariq A. Altalhi(Authors)
- 2021(Publication Date)
- Wiley-Scrivener(Publisher)
When it has been obtained in a sufficient degree of purity, structural characteristics of a polysaccharide can be determined by the analysis of (i) monosaccharide units, (ii) linkage types, (iii) anomeric configurations, (iv) noncarbohydrate substituent groups, and (v) molecular weight [3]. However, structural aspects of polysaccharides can be also described on the organizational levels, similar to protein primary, secondary, tertiary, and quaternary structural organizations. Polysaccharide primary structure can be described as a covalent sequence of monosaccharide units [21]. The secondary structure is the geometrically regular arrangement in space that the primary sequence can adopt. The establishment of the tertiary structure occurs via the packing of secondary structure arrangements together. Tertiary structure is stabilized mostly through intermolecular hydrogen bonds, but physical state and temperature can also affect the adoption of an ordered secondary or tertiary structure. Finally, a quaternary structure is the arrangement of single units of tertiary structure within a complex built by non-covalent interaction [21, 22]. Generally, the type of glycosidic linkage affects the molecular conformation more than monosaccharide type. Polysaccharide’s primary structure determines the nature and extent of intramolecular and intermolecular associations within a polysaccharide chain and configures secondary, tertiary, and quaternary structures. To achieve thermodynamically favored conformations, the extent of glycosidic bond rotation is restricted. Therefore, these favored conformations define the proximity of adjacent glycosyl units one to another and determine the three-dimensional configuration of a polysaccharide. For example, amylose, Cellulose, and dextran are all linear chains of monosaccharide units, but they are different in the nature of their glycosidic linkages [21].A systematic methodology and advanced analytical tools are required for separation, purification, modification and application of polysaccharides. Established techniques in the polysaccharide field aim to characterize the structural parameters such as chain conformation, chain length distribution, degree of substitution, degree of branching, crystallinity, and interactions with solvent [23]. The procedure to elucidate the structure of polysaccharides includes the isolation, purification, and molecular weight determination of polysaccharides, and the investigation of monosaccharide units and type of glycosidic linkages via FT-IR spectroscopy, periodate oxidation, partial acid hydrolysis, glycosyl linkage (methylation) analysis, Smith degradation, and GC–MS-based techniques. One-dimensional and two-dimensional NMR spectroscopy are used to describe the sequence of monosaccharides, the anomeric configuration of each sugar residue, and the degree of branching [24]. However, novel and more practical analyses methods, like bio-recognition based methods, immunochemical assays, enzymatic cleavage, are needed to be developed.6.2 Uses and Applications of Biopolysaccharides
The polysaccharides of living organisms and/or functionalized polysaccharides with biological impacts on living organisms are specified as bioactive polysaccharides [25]. Most bioactive polysaccharides are made from glucose, galactose, fucose, mannose, ribose, arabinose, xylose, glucuronic acid, and galacturonic acid [24].Since polysaccharides are structurally complex biomolecules and experimental methodologies for studying polysaccharides have been limited, research in polysaccharides has ever fallen behind that on protein and nucleic acids. The opening of the research area into polysaccharides dates back to about 100 years ago. Early research focused mostly on chemical composition and primary structures of polysaccharides and by the 1970s, the combination of carbohydrate chemistry and biochemistry enabled researchers to investigate the potential influences of polysaccharides on cell and molecular biology [24]. In 1988, Dr. Dwek from Oxford University brought the concept of glycobiology and opened a new research area comprising carbohydrate chemistry, immunology, and molecular biology and aiming to determine the functional roles of polysaccharides or carbohydrate chains [24, 26]. In the wider sense, the term “glycobiology” is defined as studying the structure, biosynthesis, biological interactions, and evolution of saccharides that are widespread in nature [1]. Nowadays, it has been known that the functions of polysaccharides are not limited to being the structural support and energy source in life, but they also play important roles in various biological phenomena and physiological processes [24]. Recent advances in bioanalytical technology have enabled researchers to understand and explore the structures and roles of polysaccharides and utilize their functions.
eBook - ePub- James N. BeMiller(Author)
- 2018(Publication Date)
Chapter 12 ), are usually linear or essentially linear molecules. No glycans with more than seven different basic sugar units are known to be present in foods.Linear glycans are the most abundant polysaccharides in nature (in terms of quantity) because of the enormous quantity of Cellulose existing as the main structural component of the cell walls of higher land plants. However, branched polysaccharides are by far the most numerous, occurring in an immense variety of branched forms and with a variety of sugars in their structures (Table 4.1 ).Polysaccharides found in food products come from a variety of sources—from the farm, the forest, the ocean, fermentation vats, and via chemical modification of natural polysaccharides, especially Cellulose and starch (Table 4.2 ).It is estimated that more than 90% of the carbohydrate mass on earth is in the form of polysaccharides, and as carbohydrates comprise more than 90% of the dry matter of plants of all types, polysaccharides constitute more than 80% of all plant material (dry weight basis). Polysaccharides have important roles in living organisms (Table 4.3 ). The greatest amounts are structural components of plant cell walls (for example, Cellulose) and next comes plant food reserve materials (for example, starch). However, polysaccharides have a variety of other essential roles in plants and in animals.Molecules in a preparation of a specific polysaccharide (in contrast to molecules of a protein and molecules of a nucleic acid) contain different numbers of monosaccharide units. Thus, polysaccharide preparations contain molecules of the same polysaccharide with a range of degrees of polymerization and, hence, molecular weights. Preparations which contain molecules of the same substance but of different molecular weights are said to be polydisperse
eBook - ePub- Glyn O. Phillips, Peter A. Williams(Authors)
- 2009(Publication Date)
- Woodhead Publishing(Publisher)
et al. , 1991).26.6 Functional properties
Bacterial Cellulose has the same chemical structure as that of plant Cellulose, yet it possesses different physical and chemical properties. The characteristic physical properties of bacterial Cellulose are summarized in Table 26.1 and are discussed as follows.Table 26.1 Functional properties of bacterial CelluloseProperty Description Purity Chemically pure form of Cellulose and is free from hemiCelluloses, lignin and pectin Biodegradability Biodegradable, recyclable and renewable Mechanical strength High tensile strength, consistent dimensional strength, light weight and durable Water-holding capacity Remarkable high water-holding capacity, selective porosity, high mechanical strength in wet state, high surface-to-volume carrier capacity Cellulose orientation Bacterial Cellulose has dynamic capabilities of fiber forming Uniaxially strengthened membranes can be produced Direct membrane formation Direct assembly of extremely thin, submicron, optical clear membrane during biosynthesis and thus avoiding the need for the intermediate of paper or textile formation from pulp Moldability Bacterial Cellulose has a very high moldability and can be produced in the form of a gelatinous membrane which can be molded into any shape and size during its synthesis Direct modification The crystallization of bacterial Cellulose can be delayed by introduction of dyes into culture medium. The physical properties such as molecular weight and crystallinity can be controlled during biosynthesis Direct synthesis of Cellulose product Various Cellulose derivatives (such as Cellulose acetate, carboxymethylCellulose, methyl Cellulose, etc.) can be directly synthesized. The desired Cellulose crystalline allomorph (Cellulose I or Cellulose II) can be directly controlled 
eBook - ePub- Alan Imeson, Alan Imeson(Authors)
- 2011(Publication Date)
- Wiley-Blackwell(Publisher)
Despite the unique properties and potential benefits of hydroxypropyl Cellulose, this hydrocolloid is the least known of the Cellulose derivatives used in the food industry. Developed in the 1960s by Hercules, hydroxypropyl Cellulose has thermoplastic properties. In the food industry, this property confers the ability to form films, extrude and reduce surface tension. The global annual use of hydroxypropyl Cellulose in the food industry is approximately 300 metric tons.Uses for these three Cellulose derivatives are discussed in greater detail later in this chapter. 6.2 RAW MATERIALS AND PROCESSINGCellulose derivatives for commercial use are usually based on Cellulose from wood or cotton sources, as discussed above. Cotton has a higher molecular weight and may be necessary for some very high viscosity grades of Cellulose ethers (Zecher and Gerrish, 1997). Otherwise, wood sources are preferred as they are less likely to be genetically modified and, therefore, may be certified with ‘non-GMO’ status.Cellulose is made up of repeating cellobiose units; each unit is composed of two anhydroglucose units (AGUs). The number of AGUs, joined through β 1–4 linkages, is known as the degree of polymerization (DP) of the Cellulose. Each AGU contains three hydroxyl groups. These are the sites where substitution takes place to form the Cellulose derivative. The number of hydroxyl groups that are substituted after reaction is known as the degree of substitution (DS).In the reaction process, Cellulose is first treated with alkali to swell the polymer. The alkali will also disrupt crystalline regions and the subsequent reactions will be more uniform. Reactions take place at elevated temperature. If molecular weight is to be preserved, a nitrogen atmosphere is used to prevent oxidative degradation. Cellulose ethers are formed through either Williamson etherification or alkoxylation. The alkali Cellulose is reacted with sodium chloroacetate to form carboxymethyl Cellulose, methyl chloride to form methyl Cellulose, ethyl chloride to form ethyl Cellulose or propylene oxide to form hydroxypropyl Cellulose. Mixed derivatives, such as methylhydroxypropyl Cellulose or hydroxypropylmethyl Cellulose, may be formed with combinations of reactants.
