Polyamides amino acids

Amino acid polyamides —NH2 Amino group determination... 

Glass transition and cold crystallization behaviour of even and odd cu-amino acid polyamides has been studied by DSC. Both series have been shown under appropriate quenching conditions to give glass transition and cold crystallization phenomena. These observations are contrasted with previous data on such systems and also related to structure. 

Various polyamides (Nylon) are manufactured by the condensation of amino acids. Polyamides can be blown into film and here they find many applications in the packaging of oils, fats and greases. The high softening point of polyamides have lead to their extensive use in boil-in-the-bag food packs. The low gas permeability of the film has been utilised in sachets for vacuum packed foods, such as cheese slices and bacon. Moulded articles in polyamide are widely used in food manufacturing processes. The fact that polyamides are self lubricating and consequently do not require the addition of a lubricant additive is a particularly important factor in the food industry where contamination by lubricants cannot be tolerated. 

As noted above, proteins are polyamides in which a-amino acids make up the repeat units, as shown by structure [III] ... 

Primary structure refers to the sequence of amino acids in the polyamide chain. 

The discussion of polyamides parallels that of polyesters in many ways. To begin with, polyamides may be formed from an AB monomer, in this case amino acids ... 

Without other alternatives, the carboxyalkyl radicals couple to form dibasic acids HOOC(CH)2 COOH. In addition, the carboxyalkyl radical can be used for other desired radical reactions, eg, hydrogen abstraction, vinyl monomer polymerization, addition of carbon monoxide, etc. The reactions of this radical with chloride and cyanide ions are used to produce amino acids and lactams employed in the manufacture of polyamides, eg, nylon. 

Direct Amidation. The direct reaction of amino acids to form Type AB polyamides (eq. 1) and diacids and diamines to form type AABB polyamides (eq. 2) ate two of the most commonly used methods to produce polyamides. The... 

There are approximately 20 common naturally occurring amino acids, hence 20 different R groups that appear as pendents on the polyamide chain. Many other amino acids have been isolated or prepared, each representing a variation in R. The number of isomeric stmctures is myriad. Protein biosynthesis is mediated by other biopolymers, the nucleic acids. 

One particular type of polyamide produced from intermediates containing lateral side groups are the poly-(a-amino acids). The a-amino acids have the structure shown in Figure 18.23 (I) and give polymers of the type shown in Figure 18.23 (II). The proteins may be considered as a special class of such... 

Casein is one member of the important group of natural polymers, the proteins. These materials bear a formal resemblance to the polyamides in that they contain repeating —CONH— groups and could be formally considered as polymers of amino acids. However, unlike, polymers such as nylon 6 and nylon 11 a number of different a-amino acids are found in each molecule whereas the nylons 6 and 11 have only one oj-amino acid molecule (Figure 30.1). 

Saturated 2,2 -bis-5-oxazolones (10) react with diamines under mild conditions to form polyamides (34) of high molecular weight in quantitative yield [Eq. (21)]. These polymers are composed of dicarboxylic acid, a-amino acid, and diamine units in a regular arrangement of both head-to-tail and tail-to-tail amide groups. They represent a cross between conventional polyamides and a-amino acid homopolymers. A feature of this polymerization is that no small molecules such as H2O, NHg, or CO2 are lost during reaction. 

Polyamides are produced by the reaction between a dicarboxylic acid and a diamine (e.g., nylon 66), ring openings of a lactam, (e.g., nylon 6) or by the polymerization of w-amino acids (e.g., nylon 11). The production of some important nylons is discussed in the following sections. 

We ve seen on several occasions in previous chapters that a polymer, whether synthetic or biological, is a large molecule built up by repetitive bonding together of many smaller units, or monomers. Polyethylene, for instance, is a synthetic polymer made from ethylene (Section 7.10), nylon is a synthetic polyamide made from a diacid and a diamine (Section 21.9), and proteins are biological polyamides made from amino acids. Note that polymers are often drawn by indicating their repeating unit in parentheses. The repeat unit in polystyrene, for example, comes from the monomer styrene. 

A most important class of polyamides is that of the proteins, the essential structures of all living matter. In addition, they are a necessary part in the diet of man because they are the source of the monomeric units, the amino acids, from which living protein materials are made. 

Proteins are polyamides formed by the polymerization, through amide linkages, of a-amino acids. Three of the 25-30 important natural a-amino acids are shown in Figure 18-13. Each acid has an amine group, —NHj, attached to the a-carbon, the carbon atom immediately adjacent to the carboxylic acid group. 

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. 

The AB polyamides are made from either >-amino acids or cyclic lactams, derivatives of the oj-amino acids (Table 3.1). In these polymers, the amino and acid groups are inherently balanced and the polymer also contains one amino and one acid endgroup. There are a number of different routes available for polymerizing these AB-type polyamides ... 

In common with all the higher AB polyamides, PA-12 can be made from either die amino acid or the lactam.12 In practice, PA-12 is made from the cheaper 12-laurolactam (12-dodecane lactam or laboratory-scale synthesis it is advisable to start with the amino acid or a combination of amino acid and lactam. 

Proteins are linear polyamides formed from a-amino acids. An a-amino acid is one in which carboxylic acid and the amino group reside on the same carbon atom (1.7). 

Clays have long been used as fillers in polymer systems because of low cost and the improved mechanical properties of the resulting polymer composites. If all other parameters are equal, the efficiency of a filler to improve the physical and mechanical properties of a polymer system is sensitive to its degree of dispersion in the polymer matrix (Krishnamoorti et ah, 1996). In the early 1990s, Toyota researchers (Okada et ah, 1990) discovered that treatment of montmorillonite (MMT) with amino acids allowed dispersion of the individual 1 nm thick silicate layers of the clay scale in polyamide on a molecular. Their hybrid material showed major improvements in physical and mechanical properties even at very low clay content (1.6 vol %). Since then, many researchers have performed investigations in the new field of polymer nano-composites. This has lead to further developments in the range of materials and synthesizing methods available. 

The amino acid 58 was used in the solid-phase synthesis of sequence-specific DNA binding polyamides containing N-methylimidazole and N-methylpyrrole amino acids <96JACS6141> and it was also reported that the imidazole-acridine conjugate 59 could effectively catalyze the cleavage of t-RNA <96TL4417>. 

The way in which this is done has a major effect on the formation of a particular nanocomposite and this is discussed further below. A wide range of w-amino acids have been intercalated between the layers of MMT [14]. Amino acids have been successfully used in the synthesis of polyamide... 

Fig. 3.9 Novel five-membered heterocyclic amino acids that have been incorporated into hairpin polyamides. All residues are shown with the functionality that faces the DNA minor groove towards the bottom-right...

Fig. 3.15 Model for allosteric inhibition of a protein-DNA complex by a polyamide-inter-calator conjugate. (Top) The GCN4 homodimer (yellow) is displaced by the intercalating moiety (green) of the polyamide conjugate. Blue and red spheres represent pyrrole and imidazole amino acids, respectively. The blue diamond represents / -alanine. (Bottom, left) Hydrogen-bonding model of an eight-ring hairpin polyamide-intercalator conjugate...

Turner, J.M., S.E. Swalley, E.E. Baird, and P. B. Dervan. Aliphatic/aromatic amino acid pairings for polyamide recog-... 

Baird, E.E. and P.B. Dervan. Solid phase synthesis of polyamides containing imidazole and pyrrole amino acids./. 

This field has also inspired the development of a range of pseudo-peptides, that is polyamides composed of amino acids other than a-amino acids. These include for instance peptoids, /9-amino acid oligomers and also compounds such as peptide nucleic acids and DNA binding polyamides, all of which share the amide (peptide) chemistry with natural peptides. 

Although SiCh 57 has been employed, e.g., in the presence of sodium azide to convert ketones into tetrazoles (Section 5.3), to condense cyclopentanone in high yields into 1.2.3.4.5.6-tris(trimethylene)benzene (Section 9.2), or used for the condensation of amino acids to polyamides (Chapter 14) with formation of Si02, enol-trimethylsilyl ethers 107 a of ketones such as cyclohexanone are cleanly converted by SiCh 57 in the presence of Hg(OAc)2 into the trichlorosilylenol ether 116, which adds benzaldehyde in the presence of the asymmetric catalyst 117 to give... 

As the name implies, an amino acid is a bifunctional molecule with a carboxylic acid group at one end and an amine group at the other. All proteins are polyamides made from condensation reactions of amino acids. Every amino acid in proteins has a central carbon atom bonded to one hydrogen atom and to a second group, symbolized in Figure 13-31 as R. 

Woods, R. and Wang, Kung-Tsung "Separation of Dansyl Amino Acids by Polyamide Layer Chromatography". Blochlm. Blophys. Acta., (1967), 133, 369. 

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