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Exopolysaccharides of Halophilic Microorganisms: An Overview
Published in Devarajan Thangadurai, Jeyabalan Sangeetha, Industrial Biotechnology, 2017
Pradnya P. Kanekar, Siddharth V. Deshmukh, Sagar P. Kanekar, Prashant K. Dhakephalkar, Prabhakar K. Ranjekar
Microbial heteropolysaccharides are mostly composed of repeating units of 2–8 monosaccharides. The unit primarily contains D-glucuronic acid and short side-chains of 1 to 4 residues. The side chains may vary in different heteropolysaccharides. Xanthan is the classical example of heteropolysaccharide. The anionic nature of Xanthan is due to presence of glucuronic acid and pyruvate (Jankins and Hall, 1997). The unique physical properties of microbial EPS are based upon their molecular conformation which is decided by the primary structure and from associations between molecules in solution. The shape of EPS is determined by the angle of bonds which governs the relative orientations of adjacent sugar residues in the chair. EPS in solution have single, double or triple helical conformation in an orderly manner. Xanthan has a double or triple helix. These are stabilized by intermolecular hydrogen bonds. The helical conformation makes the EPS semi rigid. The molecules can move large volumes of solution which overlap even at low concentrations of EPS leading to relatively highly viscosity. The interaction between molecules stabilizes the helical structure and influences the properties of EPS in solution such as solubility, viscosity and gel formation. The insolubility of EPS is due to a strong interaction between molecules while a poor interaction leads to solubility of EPS. The side chains influence interaction between molecules. By introduction of a 3-monosaccharide side chain into the cellulose chain, soluble Xanthan is obtained although cellulose is insoluble (Jankins and Hall, 1997).
Arborescent polymers: Designed macromolecules with a dendritic structure
Published in Y. Yagci, M.K. Mishra, O. Nuyken, K. Ito, G. Wnek, Tailored Polymers & Applications, 2020
The development of applications for arborescent polymers relies mainly on the exploitation of their unusual structural characteristics and properties. Based on the properties observed for arborescent polymers so far, it seems likely that these materials will be useful for a range of specialty uses. Arborescent molecules are characterized by a uniform size in the 10–300 nm range, and can be designed to achieve specific characteristics (e.g., controllable interpenetrability, structural rigidity, susceptibility to solvent quality). Furthermore, reactive chemical functionalities can be introduced on the side chains, or specifically at the chain ends of the molecules.
Polymer Semiconductors
Published in Inamuddin, Mohd Imran Ahamed, Rajender Boddula, Tariq Altalhi, Polymers in Energy Conversion and Storage, 2022
Moises Bustamante-Torres, Jocelyne Estrella-Nuñez, Odalys Torres, Sofía Abad-Sojos, Bryan Chiguano-Tapia, Emilio Bucio
Semiconductors are given by π-bonds, which are derived from bond and anti-bond energy levels. The principal characteristics of semiconductor polymers are based on their electronic properties which depend on charge transport. Two types of materials are defined based on charge transport. First, n-type materials are related to charge mobility through electrons, and second p-type semiconductors are associated with hole transporting. Most of the properties are correlated to polymer structure, morphology, transport, and other weak interactions related to inter- and intra-chain interactions. These polymers are significantly present during the manufacturing of different electronic devices, requiring some mechanical characteristics, such as good flexibility, stretchability, and processability. Nowadays, several methods of synthesizing polymers can be found. However, the best method depends on the goal to be achieved. Building block selection allows the focusing of the synthesis of the semiconductor polymer by selecting the p-type or n-type unit. The backbone halogenation enhances the efficiency of n-type-based semiconducting polymers. Better properties can be obtained, such as the solubility of polymers used in side-chain engineering. Moreover, a good way to control the HOMO and LUMO energetic levels is by working with random copolymerization. In addition, this allows us to increase or improve other polymer properties such as solubility and crystallinity. Currently, a variety of characterization methods are employed to understand the characteristics of the surface, interface, thin film, and multilayers of polymers that are compatible with organic semiconductors. Semiconducting polymer materials can provide a variety of applications in several devices. Some of these applications are transistors, sensors, solar cells, and conductive polymers, such as hybrid materials and carbon nanotubes. Polymers used as semiconductors are environmentally friendly alternatives to inorganic semiconductors.
Chlorine and ozone disinfection and disinfection byproducts in postharvest food processing facilities: A review
Published in Critical Reviews in Environmental Science and Technology, 2022
Adam M.-A. Simpson, William A. Mitch
Chlorine reactions alter genomic material by forming 8-chloro-adenine and 5-chloro-cytosine (Whiteman et al., 2002). Regarding proteins, chlorine reacts readily with 7 of the 20 common amino acids (cysteine, methionine, histidine, tryptophan, lysine, tyrosine, and arginine) with rate constants faster than with the peptide bonds linking the amino acids (Pattison and Davies, 2001). The predominant products have been identified for several of these amino acids, including cysteic acid (Hawkins et al., 2003), methionine sulfoxide (Hawkins et al., 2003), lysine nitrile (Sivey et al., 2013; Walse et al., 2009), 3-chlorotyrosine and 3,5-dichlorotyrosine (Choe et al., 2015), and 5 tryptophan-derived products (including 2 chlorinated products (Hua et al., 2020)). When bacteriophage MS2 was exposed to increasing chlorine doses, amino acids in the protein capsid were depleted in the order methionine > tryptophan > tyrosine > lysine, forming methionine sulfoxide at yields up to approximately 50%, 3,5-dichlorotyrosine at up to approximately 50% yields, and lysine nitrile at up to 30% yields (Choe et al., 2015). Covalent modifications to amino acid side chains alters their interactions within proteins, degrading secondary structure and function (Howell et al., 2015; Sivey et al., 2013). Unlike viruses, bacteria can repair oxidative damage, rendering it more difficult to characterize the pathways leading to inactivation. However, research has demonstrated that Escherichia coli features a heat-shock protein that enhances resistance to chlorine inactivation by clearing cytoplasmic proteins damaged by chlorine (Winter et al., 2008).