Biopolymers proteins

Adsorption of (bio)polymers occurs ubiquitously, and among the biopolymers, proteins are most surface active. Wherever and whenever a protein-containing (aqueous) solution is exposed to a (solid) surface, it results in the spontaneous accumulation of protein molecules at the solid-water interface, thereby altering the characteristics of the sorbent surface and, in most cases, of the protein molecules as well (Malmsten 2003). Therefore, the interaction between proteins and interfaces attracts attention from a wide variety of disciplines, ranging from environmental sciences to food processing and medical sciences. 

The chemistry of polysaccharides is a major frontier. Their branched and complex nature makes them far more difficult to synthesize than the linear biopolymers, proteins, and nucleic acids. For this reason, automated synthetic methods for polysaccharides were just created in 2001, several decades after com-... 

Another characteristic property of many biopolymers (proteins, modified starch, chitosan, etc.) which is useful for the encapsulation of bioactive molecules is their ability to adsorb at the oil-water interface and to form adsorbed layers that are capable of stabilizing oil-in-water (OAV) emulsions against coalescence (see Table 2.2). It is worthwhile to note here that the formation of an emulsion is one of the key steps in the encapsulation of hydrophobic nutraceuticals by the most common technique used nowadays in the food industry (spray-drying). The adsorption of amphiphilic biopolymers at the oil-water interface involves the attachment of their hydrophobic groups to the surface of the oil phase (or even their slight penetration into it), whilst their hydrophilic parts protrude into the aqueous phase providing a bulky interfacial layer. 

In the field of food colloids, the use of molecular thermodynamics provides a set of qualitative and quantitative relationships describing fundamental phenomena occurring in the equilibrium state of systems for which the intermolecular interactions of biopolymers (proteins and polysaccharides) play a key role. The phenomena and processes amenable to discussion from the thermodynamic point of view are ... 

It is important to understand the characteristic interactions involved at an interface containing each of the main types of surface-active molecules, i.e., biopolymers (proteins, polysaccharides) and low-molecular-weight surfactants (lipids). But that is not the whole story. In real food systems there are almost always mixed ingredients at the interface. So it is necessary to understand what sorts of mixed interfacial structures are formed, and how they are influenced by the intermolecular interactions. 

In Part Four (Chapter eight) we focus on the interactions of mixed systems of surface-active biopolymers (proteins and polysaccharides) and surface-active lipids (surfactants/emulsifiers) at oil-water and air-water interfaces. We describe how these interactions affect mechanisms controlling the behaviour of colloidal systems containing mixed ingredients. We show how the properties of biopolymer-based adsorption layers are affected by an interplay of phenomena which include selfassociation, complexation, phase separation, and competitive displacement. 

BIOPOLYMERS. Biopolymers are the naturally occurring macromolec-ular materials that are the components of all living systems. There are three principal categories of biopolymers, proteins nucleic adds and polysaccharides. See also Carbohydrates. Biopolymers are formed through condensation of monomeric units i.e., the corresponding monomers are amino acids, nucleotides, and monosaccharides for proteins, nucleic acids, and polysaccharides, respectively. The term biopolymers is also used to describe synthetic polymers prepared from the same or similar monomer units as are the natural molecules. 

The concept of evolution of primary sequences of biopolymers has attracted great interest from biologists, chemists and physicists for a long time [65-68]. As has been discussed, it is natural to expect that the content of information in the sequences of biopolymers (proteins, DNA, RNA) is relatively high in comparison with random sequences where it should be almost zero [69]. Presumably, the information complexity of early ancestors of present-day biopolymers has been increased in the course of molecular evolution when the... 

A large number of macromolecules possess a pronounced amphiphilicity in every repeat unit. Typical examples are synthetic polymers like poly(l-vinylimidazole), poly(JV-isopropylacrylamide), poly(2-ethyl acrylic acid), poly(styrene sulfonate), poly(4-vinylpyridine), methylcellulose, etc. Some of them are shown in Fig. 23. In each repeat unit of such polymers there are hydrophilic (polar) and hydrophobic (nonpolar) atomic groups, which have different affinity to water or other polar solvents. Also, many of the important biopolymers (proteins, polysaccharides, phospholipids) are typical amphiphiles. Moreover, among the synthetic polymers, polyamphiphiles are very close to biological macromolecules in nature and behavior. In principle, they may provide useful analogs of proteins and are important for modeling some fundamental properties and sophisticated functions of biopolymers such as protein folding and enzymatic activity. 

NMR methods have also been used extensively to determine the configuration and conformation of both moderate-size molecules and synthetic polymers, whose primary molecular structure is already known. During the past decade high resolution NMR, particularly employing 2D and 3D methods, has become one of only two methods (x-ray crystallography is the other) that can be used to determine precise three-dimensional structures of biopolymers—proteins, nucleic acids, and their cocomplexes—and NMR alone provides the structure in solution, rather than in the solid state. 

Food polymers and the behaviour of their mixtures are mainly responsible for the structure-properties relationship in both food and chyme. The two basic features of food are that its biopolymers, proteins and polysaccharides are its main construction materials and water is the main medium, solvent and plasticizer. In other words, three components— protein, polysaccharide and water—are the main elements of food structure that are principally responsible for quality of foods (see also Chapter 13). 

Of the many kinds of biopolymers, protein has been investigated most extensively, and enzymes have become the most familar proteins to us. Of a number of diarac-teristics of enzymes, the efficiency and specificity are the most important and most useful to us. To show the above features, it is essential for the enzyme to be a mac-romolecular compound on which reactions can take place, and for the multiple... 

AQUEOUS LAYER-7 pm containing In dissolved form Inorganic salts, glucose, urea and surface active biopolymers, proteins and glycoproteins... 

The synthesis of two other important biopolymers, proteins and nucleic acids, also involves a sequence of functional group transformations. Simple (amidic or phosphodiester) bonds are formed between readily available monomeric units (amino acids or nucleotides). Almost all synthetic efforts in this area are centered around the elaboration of an optimal method to achieve an efficient formation of this bond. Given the complexity of the final structure, this task is never too simple. 

Use of polymer phase systems for separation of biopolymers (proteins, deoxyribonucleic acid [DNA] and ribonucleic acid [RNA], and polysaccharides). Reliable retention of the stationary phase for polar or low interfacial tension solvent systems (e.g., 1-butanol/water), which are useful for separation of bioactive compounds such as peptides. 

Complexes of Cr111 with polymeric ligands have a wide range of practical applications in catalysis,505,1006-1008 removal and recovery of Q-111,1009-1012 and modification of polymeric materials 1013-1020 typical recent examples are listed in Table 5. Complexes of Cr111 with biopolymers (proteins or nucleic acids) are described in Section 4.6.5.11. 

Based on the models of natural metal complexes synthetic metal complexes have been developed for different purposes. They consist of a synthetic polymer, which is the replacement of the biopolymer protein in the natural metal complexes, and a specific synthetic ligand that is able to bind the metal ions. The basic model of synthetic metal complexes is shown in Figure 7. 

The OH groups in this phase make the product compar able to silica. It is of interest for compounds with which it can form hydrogen bonds and is particularly suitable for tetracyclines, steroids, organic acids and biopolymers (proteins), amongst other... 

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