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In order to make polymers dissolve in water, something that is of considerable technological interest, it is necessary to add charged groups along the hydrophobic backbone. These charged macromolecules display a rich variety of properties not found in neutral polymers and are therefore of considerable interest from a basic scientific standpoint. For example, altering the solvent conditions may cause coil-globule and coil-rod transitions in polyelectrolytes, which are not always observed in neutral polymers under similar conditions.

While their importance as biological molecules such as proteins and nucleic acids has been known for a long time, their significance in industry has only been realized in the last two decades. They now have a wide range of technological uses: as processing aids such as flocculants, dewatering agents, demulsifiers, and drag reduction agents; as additives in detergents and cosmetics; and in the manufacture of membranes, ion-exchange resins, gels, and modified plastics, wastewater treatment, separations, colloid science, and petroleum recovery.

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1.Polyelectrolytes are used in water treatment systems for a variety of applications including coagulation, flocculation, ballasted sedimentation, filtration, and dissolved air flotation.

2.If the solution is free of added electrolytes the polymer coil expands as the polymer concentration decreases. This is known as the «polyelectrolyte effect».

3.The conformation of any polymer is affected by a number of factors: notably, the polymer architecture and the solvent affinity. In the case of polyelectrolytes, charge also has an effect.

4.Polyelectrolytes have many applications, mostly related to modifying flow and stability properties of aqueous solutions and gels.

5.It is known that the presence of polyelectrolytes induces aggregation of the oppositely charged surfactant.

6.There is currently much research in using biocompatible polyelectrolytes for implant coatings, for controlled drug release, and other applications.

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7.Polyelectrolytes which bear both cationic and anionic repeating groups are called polyampholytes. Many proteins are polyampholytes, as some amino acids tend to be acidic while others are basic.

8.DNA molecule functioning as long-term storage of genetic information is in fact a polyelectrolyte, which is highly stable in weakly alkaline aqueous solutions.

9.If the solution contains a great deal of added salt, the charges will be screened and consequently the polyelectrolyte chain will collapse to a more conventional conformation.

10.Although the statistical conformation of polyelectrolytes can be captured using variants of conventional polymer theory, the long-range Coulomb interactions are necessary to properly model polyelectrolyte chains.

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1.What is the main difference between polyelectrolyte and ordinary polymer?

2.What structure does polyelectrolyte have in water solution?

3.How will you classify polyelectrolytes?

4.Give two or three examples of polyelectrolyte applications.

5.Provide examples of natural polyelectrolytes.

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Unit 9

BIOPOLYMERS

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Biopolymers are a class of polymers produced by living organisms. Biopolymers have been around for billions of years longer than synthetic polymers like plastics. Well-known biopolymers include starch, proteins, DNA, and RNA. Together these make up much of our bodies and the majority of the biosphere.

The starch polymer is made up of sugar monomers. When you consume starch, it gets broken down into sugar within the body. Starch provides an extended-release form of nutrition in contrast to more quickly-metabolized sugars.

Protein and peptide biopolymers have amino acids as their constituents. This is why amino acids are often referred to as «the building blocks» of life. DNA and RNA are made up of nucleic acids, which alternate in precise patterns to encode large quantities of data.

Biopolymers are used as an environmentally friendly alternative to petroleum-based polymers, which may take thousands of years to biodegrade. Biopolymers can be produced without toxic byproducts and biodegrade quickly, leaving a minimal human footprint on the environment.

In contrast to synthetic polymers, biopolymers tend to have a welldefined structure. Perhaps, this is because evolution tends to select for chemical reactions and structures that are largely predictable. Biopolymers have an evenly distributed set of molecular weights and are built using a template-directed process.

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Deoxyribonucleic acid (DNA) is a nucleic acid that con tains the genetic instructions used in the development and functioning of all known living organisms. DNA is a long polymer made of repeating units called nucleotides. DNA polymers can be enormous molecules containing millions of nucleotides.

The backbone of the DNA strand is made of alternating phosphate and sugar residues. The sugar in DNA is 2-deoxyribose, which is a pentose (five-carbon) sugar. The sugars are joined together by p hosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings.

The DNA double helix is stabilized by hydrogen bo nds between the bases attached to the two strands. The four bases found in D NA are adenine (abbreviated A), cytosine (C), guanine (G) and thymine (T). These four bases are attached to the sugar/phosphate to form the compl ete nucleotide.

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Polysaccharides are carbohydrate polymers consisting of tens to hundreds to several thousand monosaccharide units. All of the common polysaccharides contain glucose as the monosa ccharide unit. Polysaccharides are synthesized by plants, animals, and humans to be stored for food, structural support, or for energy.

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The term “starch” is used to describe a biopolymer system comprising predominantly of two polysaccharides - amylose an d amylopectin. Amylose molecules consist of single mostly unbranche d chains with a molecular weight of up to 20,000. Each amylopectin molecule is branched and contains up to two million glucose residues in a compact structure with hydrodynamic radius of 21-75 nm.

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Glycogen is a polysaccharide that is found in animals and is composed of a branched chain of glucose residues. It is stored in liver and muscles.

The structural components of plants are formed primarily from cellulose. Wood is largely cellulose and lignin, while pape r and cotton are nearly pure cellulose.

2.Certain animals can digest cellulose, because bacteria possessing the enzyme are present in their gut. The classic example is the termite.

3.The sequence, or protein primary structure is specified by the sequence of the DNA containing a gene for that protein, and the sequence is unique to the individual protein.

4.Knowledge of the tertiary structure of proteins is often necessary to understand, since their most significant actions may involve only a single small active site on a very large molecule.

5.Biopolymers could also prove an asset to waste processing. Replacing the polyethylene used in coated papers by a biopol ymer could help eliminate plastic scraps occurring in compost.

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6.Proteins are large organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues.

7.Enzymes are very specific protein catalysts. Complementary shape, charge and hydrophilic/hydrophobic characteristics of enzymes and substrates are responsible for this specificity.

8.Biochemists define four levels of protein structure: primary, the amino acid sequence; secondary, helix stabilized by hydrogen bonds; tertiary, the overall shape of a protein molecule; quaternary, two or more polypeptides.

9.Ribonucleic acid or RNA is a nucleic acid, consisting of many nucleotides that carry information about a protein sequence to the ribosomes, the protein synthesis factories in the cell.

10.Unlike petrochemical polymers, biopolymers are renewable, because they are made from biodegradable plant materials and are ecologically friendly.

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1.What is a genetic code?

2.What are biological catalysts?

3.Describe the main biopolymers of human living cells.

4.Why do we think of biopolymer materials as environmentally friendly?

5.What happens to starch when we consume it?

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