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Carbohydrates and Nucleic Acids
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
An aldose is a polyhydroxy aldehyde and a ketose is a polyhydroxy ketone. A hexose is a six-carbon sugar and a pentose is a five-carbon sugar. A pyranose is the cyclic hemiacetal or hemiketal form of the sugar that exists in a six-membered pyran ring. Therefore, an aldopyranose is a polyhydroxy aldehyde in pyranose form. A furanose is the cyclic hemiacetal or hemiketal form of the sugar that exists in a five-membered tetrahydrofuran ring. Therefore, a ketofuranose is a polyhydroxy ketone in furanose form. What is an example of an aldohexose, a ketohexose, an aldopyranose, and a ketofuranose?
Biomolecules and Complex Biological Entities
Published in Simona Badilescu, Muthukumaran Packirisamy, BioMEMS, 2016
Simona Badilescu, Muthukumaran Packirisamy
Because the five-membered ring structure resembles the organic molecule furan, derivatives with this structure are termed furanoses. Those with six-membered rings resemble the organic molecule pyran and are termed pyranoses. In the case of pyranose rings, the two favored structures are the chair conformation and the boat conformation. Straight and ring structures of glucose are given in Figure 3.38 for reference.
Optimized isolation and characterization of cellulose for extraction of cellulose nanocrystals from Ensete ventricosum pseudo-stem fibre using a two-stage extraction method
Published in Journal of Experimental Nanoscience, 2023
Abnet Mengesha Dube, Bulcha Jifara Daba, Melkiyas Diriba Muleta
Figure 7 displays the FTIR spectra of raw ensete fibre and cellulose. The presence of a stretching vibration of the O-H group, which is related to the intramolecular hydrogen bond of cellulose, results in the characteristic bands of 3277.00–3348 cm−1 and 2922.7 cm−1 associated with stretching vibration C-H. The figure clearly demonstrates how, when the fibre is subjected to chemical treatment, the transmittance for this region gradually changes. The transmittance showed an increment and the peak becomes sharper due to alkali treatment and an increase in cellulose content [11, 37,38]. Lower absorbance intensity ratios are found in the absorption band at 1,634.7 cm−1, which is associated with the vibration of carbonyl groups and adsorbed water molecules. The opening of the terminal glycopyranose rings or the oxidation of the C-OH groups may be the cause of the occurrence of this peak [39]. In ensete fibre, 1327.74 cm−1 corresponds to the CH2 scissoring of cellulose, hemicellulose, and lignin as well as the stretching of the C-O ring of syringyl lignin and the condensed G ring of lignin [22]. The peak at 1315.45 cm−1 is associated with the rocking vibration of CH2 in the cellulose alcohol group [40]. The peak at 1002 cm−1 illustrates the C-O-C pyranose vibrating stretching ring of cellulose [41].
Chemical pretreatment of corncob for the selective dissolution of hemicellulose and lignin: influence of pretreatment on the chemical, morphological and thermal features
Published in Biofuels, 2023
Alejandro Ramírez-Estrada, Violeta Y. Mena-Cervantes, Ignacio Elizalde-Martínez, Gabriel Pineda-Flores, Raúl Hernández-Altamirano
Figure 12 shows the IR spectrum of soluble-acid compounds (Soluble-AC-IR). This spectrum shows a broad absorption band at 3600–3000 cm−1 (O − H stretching vibration in carbohydrates); absorption bands at 3000–2800 cm−1 (C − H stretching vibration); 1721 cm−1 (C = O stretching vibration of the carboxyl group in acetyl group); 1640 cm−1 (C = C stretching vibrations), absorption bands in the range 1500–1200 cm−1 (vibrations of C − H, −OH, C–O bonds); a strong overlapped-adsorption at 1034 cm−1 (vibration C − O bonds and C − O−C stretching vibration); 943 cm−1 (C − O stretching vibration of pyranose ring), and at 897 cm−1 (vibration of the β-glycoside bond in oligosaccharides). The absorption bands in the ranges 3600–3000 cm−1 and 1200–800 cm−1 confirm the presence of sugars pyranose and furanose structures; these absorption bands are characteristics of sugars and oligosaccharides [55]. Likewise, the absorption band observed at 1721.50 cm−1 denotes the presence of acetyl acids linked to the backbone of oligosaccharides [56].
Photo-responsive azo-functionalised flexible polymer substrate for liquid crystal alignment
Published in Liquid Crystals, 2020
B. Sivaranjini, K. Mohana, S. Esakkimuthu, V. Ganesh, S. Umadevi
Elemental composition of the flexible substrate before and after surface modification was identified through XPS analysis. XPS spectra (survey scan) recorded for the unmodified (as-received) and chemically treated substrates are provided in Figure 3(i) and (ii) respectively. XPS spectrum of the unmodified substrate displayed peaks corresponding to C1s and O1s whereas the surface-modified film showed peaks corresponding to C1s, O1s, N1s and Si2p (from the azo and terminal silane moiety), thus confirming the immobilisation of silane-terminated azo monomer. Figure 3(a,b) shows the C1s and O1s spectra for unmodified substrate while Figure 3(c–f) displays the spectra for C1s, O1s, N1s and Si2p, respectively. The binding energies observed for C1s spectrum of the unmodified substrate at 283.4 eV, 284.9 eV and 287.4 eV can be assigned to methyl carbon of the acetyl groups [H3C(C = O)], carbon atom in C-C/C-H moieties and carbon atom in O-C = O and O-C-O moieties [32]. Likewise, the O1s binding energies at 529.9 eV, 530.4 eV, 531.02 eV, 532.1 eV, 533.4 eV, 534.5 eV are assigned to a ketone [C-C(O)-C], hydroxyl group O-H, ether (C-O-C), ester carbonyl (RCOOR’), oxygen in a ring [33] and oxygen next to a carbonyl group in an ester-(COO) [34,35]. The XPS data revealed the presence of the functional groups namely, methyl carbon of acetyl group and a ring oxygen (may be assigned to a pyranose ring), which indicated the presence of cellulose acetate as the main component of our flexible substrate.