Amino acids condensation polymerization

Polyethylene (Section 6 21) A polymer of ethylene Polymer (Section 6 21) Large molecule formed by the repeti tive combination of many smaller molecules (monomers) Polymerase chain reaction (Section 28 16) A laboratory method for making multiple copies of DNA Polymerization (Section 6 21) Process by which a polymer is prepared The principal processes include free radical cationic coordination and condensation polymerization Polypeptide (Section 27 1) A polymer made up of many (more than eight to ten) amino acid residues Polypropylene (Section 6 21) A polymer of propene Polysaccharide (Sections 25 1 and 25 15) A carbohydrate that yields many monosacchande units on hydrolysis Potential energy (Section 2 18) The energy a system has ex elusive of Its kinetic energy... 

The resulting amino acid then condenses in a stepwise manner to form the growing polymer chain. As in direct polymerization, cycHc oligomers are also formed hence, caprolactam (qv) can be formed in the reverse of the reaction just shown above. 

HO—R—COOH, or an amino acid, H2N—R—COOH. In some cases, such monomers self-condense to a cycHc stmcture, which is what actually polymerizes. For example, S-caprolactam (1) can be thought of as the self-condensation product of an amino acid. Caprolactam undergoes a ring-opening polymerization to form another... 

Reactions between one monomer species with two different functional groups. One functional group of one molecule reacts with the other functional group of the second molecule. For example, polymerization of an amino acid starts with condensation of two monomer molecules ... 

As noted in Section 23.2, molecules containing NH2 and COOH groups can undergo condensation polymerization. Amino acids contain both groups in the same molecule. Hence, two amino add molecules can combine by the reaction of the COOH group in one molecule with die NH2 group of the other molecule. If the adds involved are different, two different structural isomers are possible ... 

It is also possible to prepare them from amino acids by the self-condensation reaction (3.12). The PAs (AABB) can be prepared from diamines and diacids by hydrolytic polymerization [see (3.12)]. The polyamides can also be prepared from other starting materials, such as esters, acid chlorides, isocyanates, silylated amines, and nitrils. The reactive acid chlorides are employed in the synthesis of wholly aromatic polyamides, such as poly(p-phenyleneterephthalamide) in (3.4). The molecular weight distribution (Mw/Mn) of these polymers follows the classical theory of molecular weight distribution and is nearly always in the region of 2. In some cases, such as PA-6,6, chain branching can take place and then the Mw/Mn ratio is higher. 

In this section, you learned how to recognize addition and condensation polymerization reactions. You examined the structures and functions of several important biological molecules, such as proteins, amino acids, carbohydrates, DNA, and lipids. In the next section, you will examine the risks and benefits of manufacturing and using organic compounds. 

Amino acids become linked by reactions that occur between the amine group of one amino acid and the carboxyl group of another. As shown in Figure 22.23, this polymerization produces a molecule of water and, hence, is a condensation reaction. Naturally occurring polypeptides with molecular weights in excess of 10,000 daltons are termed proteins. These biomolecules are ubiquitous in marine organisms and are not specific to particular species. Proteins are important components of enzymes as well as of structural parts and connective tissues. 

Note 3 Propagation in chain polymerization usually occurs without the formation of small molecules. However, cases exist where a low molar-mass by-product is formed, as in the polymerization of oxazolidine-2,5-diones derived from amino acids (commonly termed amino acid A-carboxy anhydrides). When a low-molar-mass by-product is formed, the adjective condensative is recommended to give the term condensative chain polymerization. 

Proteins are nature s polyamide condensation polymers. A protein is formed by polymerization of o-artiino acids, with the amino group on the carbon atom next to the carboxylic acid. Biologists call the bond formed a peptide rather than an amide. In the food chain these amino acids are continuously hydrolyzed and polymerized back into polymers, which the host can use in its tissues. These polymerization and depolymerization reactions in biological systems are all controlled by enzyme catalysts that produce extreme selectivity to the desired proteins. 

Consider the reversible condensation polymerization reaction of an amino acid A to form a polyamide polymer Aj and water,... 

There is some claim that long polypeptide chains may derive not so much from the condensation of amino acids, but from the polymerization of HC N followed by simple prebiotic chemistry to mould the side chains (Matthews, 1975) however, this theory has not yet found great support in the field. 

Figure 10.4 A qualitative illustration of the selective power of the hydrophobic membrane of liposomes out of a small library of amino acids or peptides present in the external solution, only the hydrophobic ones can be picked out and polymerized by the hydrophobic condensing agent.

Polycondensation reactions in oriented monolayers and bilayers proceed without catalysis, and simply occur due to the high packing density of the reactive groups and their orientation in these layers. Bulk condensation of the a-amino acid esters at higher temperatures does not lead to polypeptides but to 2,5-diketopiperazines. No diketopiperazines are found in polycondensed monolayers or liposomes. Polycondensation in monolayers and liposomes leading to oriented polyamides represents a new route for stabilizing model membranes under mild conditions. In addition, polypeptide vesicles may be cleavable by enzymes in the blood vessels. In this case, they would represent the first example of stable but biodegradable polymeric liposomes. 

Here a single number is used to indicate the number of carbon atoms in the original nomomer, i.e., nylon-11 ( eleven" not one-one ), in some instances the cyclic analogue or lactam is more accessible than the amino acid and is polymerized by a ring-opening rather than condensation mechanism ... 

How did these small prebiotic organic molecules grow into large polymeric substances such as peptides, RNA, and so on It is important to recognize that by whatever reactions polymerization occurred, they had to be reactions that would occur in an essentially aqueous environment. This presents difficulties because condensation of amino acids to form peptides, or of nucleotides to form RNA or DNA, is not thermodynamically favorable in aqueous solution. 

The CSPs based on chiral crown ethers were prepared by immobilizing them on some suitable solid supports. Blasius et al. [33-35] synthesized a variety of achiral crown ethers based on ion exchangers by condensation, substitution, and polymerization reactions and were used in achiral liquid chromatography. Later, crown ethers were adsorbed on silica gel and were used to separate cations and anions [36-39]. Shinbo et al. [40] adsorbed hydrophobic CCE on silica gel and the developed CSP was used for the chiral resolution of amino acids. Kimura et al. [41-43] immobilized poly- and bis-CCEs on silica gel. Later, Iwachido et al. [44] allowed benzo-15-crown-5, benzo-18-crown-6 and benzo-21-crown-7 CCEs to react on silica gel. Of course, these types of CCE-based phases were used in liquid chromatography, but the column efficiency was very poor due to the limited choice of mobile phases. Therefore, an improvement in immobilization was realized and new methods of immobilization were developed. In this direction, CCEs were immobilized to silica gel by covalent bonds. 

---