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Über dieses Buch

In order to adapt the properties of living materials to their biological functions, nature has developed unique polyelectrolytes with outstanding physical, chemical and mechanical behavior. Namely polyampholytes can be suitable substances to model protein folding phenomenon and enzymatic activity most of biological macromolecules due to the presence of acidic and basic groups. The ability of linear and crosslinked amphoteric macromolecules to adopt globular, coil, helix and stretched conformations and to demonstrate coil-globule, helix-coil phase transitions, and sol-gel, collapsed­ expanded volume changes in relation to internal (nature and distribution of acid and base substituents, copolymer composition, hydrophobicity etc. ) and external (pH, temperature, ionic strength of the solution, thermodynamic quality of solvents etc. ) factors is very important and constantly attracts the attention of theorists and experimentalists because the hierarchy of amphoteric macromolecules can repeat, more or less, the structural organization of proteins. That is why polyampholytes fall within eyeshot of several disciplines, at least polymer chemistry and physics, molecular biology, colloid chemistry, coordination chemistry and catalysis. The main purpose of this monograph is to bridge the gap between synthetic and natural polymers and to show a closer relationship between two fascinating worlds. The first chapter of the book acquaints the readers with synthetic strategy of "annealed", "quenched" and "zwitterionic" polyampholytes. Radical copolymerization, chemical modification and radiation-chemical polymerization methods are thoroughly considered. Kinetics and mechanism of formation of random, alternating, graft, di-block or tri-block sequences is discussed. The second chapter deals with behavior of polyampholytes in solutions.

Inhaltsverzeichnis

Frontmatter

1. Synthesis of Linear and Crosslinked Polyampholytes

Abstract
A renewed interest for polyampholytes is due to appearance of some novel methods of synthesis based on the radical and emulsion polymerization of charged anionic and cationic monomers or ion-pair comonomers, betaine type or zwitterionic monomers together with well-known living polymerization, group transfer polymerization, polycondensation and chemical modification technique. This chapter considers the synthetic strategy of “annealed”, “quenched” and “zwitterionic” polyampholytes having random, alternating, graft, branched, di-block or tri-block sequences.
Sarkyt E. Kudaibergenov

2. Behavior of Polyampholytes in Solutions

Abstract
The theory of solutions of flexible uncharged polymers with excluded volume is well developed at present.1.2 Much attention to theoretical problems of polyampholytes was paid only last 10 years. The main interest of theorists to synthetic polyampholytes is connected with the fact that the conformation of natural polymers is determined by the sequence of amino acids and there exists a certain parthway for the folding of proteins. Since it is expected that long-range Coulomb interactions are important parts of interactions, the specific conformation of synthetic polyampholytes can help to learn more about the self-organization in particular protein-folding processes. It is well known that polyampholytes exhibit a phase change from the extended random flight configuration to a condensed microphase. The polyampholyte theory of Edwards et al.3 considers the isoelectric state of polyampholytes as a microelectrolyte satisfying a Debye-Huckel type of structure. The criterion of transition from the collapsed conformation to extended one is described by Eq. (2.1.1):
$$\begin{array}{*{20}{c}} {\gamma = \frac{{{e^2}{b^2}}}{{kT}}{{\left( {Ll} \right)}^{ - 1/2}} \gg 1{\text{ collapse }}} \\ {{\text{ }} \ll 1{\text{ open chain }}} \end{array}$$
(2.1.1)
where γ is dimensionless parameter; e is the electron charge; b is the monomer size; l is the Kuhn length; L is the arc length; k is the Boltzman constant; T is the absolute temperature.
Sarkyt E. Kudaibergenov

3. Complexes of Amphoteric Polyelectrolytes

Abstract
The complex formation problems of amphoteric copolymers with respect to metal ions, detergents, dyes and organic probes are of great interest. The interaction of metal ions M with polymeric ligands L proceeds as follows1: M + L ⇔ ML; ML + M ⇔ ML2; MLn-1 + M ⇔ MLn The stability constant of polymer-metal complex β is equal to: βn = k 1 k 2 k 3k n = [MLn]/[M]·[L]n Function n, which characterizes the average number of ligands bound to metal ions, is determined from the Eq. (3.1.1):
$$n = \frac{{{{[L]}_t} - [LH] - [L]}}{{{{[M]}_t}}}$$
(3.1.1)
where [L]t, and [M]t, are the total concentrations of ligand and metal ions; [L] and [LH] are the concentrations of free (uncomplexed) and protonated ligands respectively.
Sarkyt E. Kudaibergenov

4. Properties of Polyampholytes with Betaine Structure

Abstract
Solution properties of polycarboxybetaines were thoroughly considered by Salamone and co.1–12 especially in the vinylimidazole and vinylpyridine series as well as by other research groups.13–20 One of the features of zwitterion-type polyampholytes is tendency of polymer chains to association. Therefore polymeric betaines are usually insoluble in pure water and have gel characteristics but soluble in salt containing solutions. The loss of water solubility and gel like structure that adopts polybetaines are due to the formation of intragroup, intra- and interchain ion contacts which result in the appearance of a crosslinked networks (Scheme 4.1).
Sarkyt E. Kudaibergenov

5. Stimuli-Sensitive Polyampholyte Gels and Membranes

Abstract
Hydrogels and hydrophilic membranes are swellable materials that have been made by formation of a network either by chemical crosslinking or by physical interactions between the functional groups of the chains (Coulomb interactions, hydrogen bonds, hydrophobic interactions, van der Waals forces). Unique characteristics of hydrogels are their softness, elasticity, and the capacity to store a huge amount of fluid within the network.1.2 The phase (or volume) transitions of hydrogels in response to temperature, solvent composition, pH, ionic strength, electric and magnetic fields, light, complexation etc. have opened the door to a wide variety of technological applications in chemical, medical, agricultural, electronic, and many other industrial fields. The chemically crosslinked natural polymers, such as DNA (anionic polyelectrolyte), gelatin (amphoteric polyelectrolyte), and agarose (hydrophilic polymer) are also able to exhibit a discontinuous phase transition in response to external factors. These observations strongly support the theoretical prediction that the phase transition of gels is universal and should not be confined to a specific group of gels.3
Sarkyt E. Kudaibergenov

6. Catalysis by Polyampholytes

Abstract
The development of polymeric catalysts, which act likes enzymes is of great interest.1–6 Synthetic polyampholytes due to high content of functional groups and rich conformational liability are best candidate to design active and selective catalysts.7 Electrostatic interactions, hydrogen and coordination bonds, and hydrophobic entrapment can provide the selectivity of polyampholytes with respect to substrates. As compared with low molecular weight compounds, the reaction rate in the presence of polymeric catalysts is much higher, which is caused by a high local density of the functional groups in the bulk of the macromolecular coil.
Sarkyt E. Kudaibergenov

7. Application of Polyampholytes

Abstract
Water-soluble and water-swelling polyampholytes are used in a wide number of applications including desalination of water, sewage treatment, flocculation, coagulation, drilling fluids, enhanced oil recovery etc. The desalination of water by crosslinked polyampholytes can be regulated by changing of the temperature.1 Such polyampholytes are called as thermoregenerable resins (TRR). To perform the thermoregeneration the next equilibrium should take place in dependence of temperature (Scheme 7.1). In principle the function of TRR is as follows: the absorbed at room temperature salts (for instance NaCl) can easily be regenerated by hot water, e.g. the exchange equlibrium is shifted at room temperature to the right and at high - to the left. At room temperature the proton is transferred from the acid to the base forming charged ion-exchanging zones (COOH → NR2 → COO- N+HR2). The heating of water from 298 K to 358 K leads to the accumulation of H+ and OH- owing to the ionization of water molecules; the concentration of H+ and OH- increases approximately 30 times. Hydrogen and hydroxyl ions suppress the degree of ionization of amphoteric resin and the equilibrium shifts to the left side. Thus hot water serves as “reservoir” of H+ and OH- ions.
Sarkyt E. Kudaibergenov

8. Conclusion

Abstract
Synthetic polyampholytes are very close to proteins by structure and behavior. They have unique electrochemical, hydrodynamic and conformational properties due to distribution of acidic and basic monomers along the chain, e.g. random, alternating, graft, branched, and block sequences. Polyampholytes are divided into annealed, quenched and betaine type series. Synthesis of polyampholytes comprises mostly the radical initiated copolymerization of acidic and basic monomers in bulk, solution, emulsion, and suspension. The chemical modification of preformed polymers includes acid and base hydrolysis, quaternization, oxidation, etherification, esterification, enzyme-and photo activation etc. The synthetic conditions including the kinetics and mechanism of copolymerization determine the composition and microstructure of final products and are controlled by formation of hydrogen and salt bonds between monomers and solvents, by addition of simple salts, surfactants, catalysts etc. The reactivity of acid and base monomers can be regulated through formation of monomer complexes stabilized by hydrogen and salt bonds. The different distribution of acidic and basic monomer units was clearly shown for copolymers synthesized by radical copolymerization and chemical modification. For instance, equimolar copolymers of MAA and DMAEM obtained by radical copolymerization and acid and base hydrolysis differ in microstructure, solubility, isoelectric points and apparent ionization constants. Novel approach to design polymeric betaines or so-called zwitterionic polyampholytes having specific structure due to length of flexible spacer groups and replacement of oppositely charges in either main chain or side chain accompanied by the presence of hydrophobic tails (zwitterionic polysoaps) has recently been developed.
Sarkyt E. Kudaibergenov

Backmatter

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