A nitrogen atom in each of these side chains can accept a proton to form a positively charged ion.Ī protein’s secondary structure is the three dimensional shape of small segments of proteins. The three amino acids in Figure 6 have side chains containing functional groups that are basic at neutral pH: Figure 6. These side chains contain highly polar bonds whose dipoles do not cancel most can also have strong hydrogen bonding attractions. Amino acids with polar side chains that are neutral. The six amino acids shown in Figure 5 have side chains that are polar but neither acidic nor basic. As we will see, this characteristic has important implications for a protein’s structure. These hydrophobic side chains are composed mostly of carbon and hydrogen, have very small dipole moments, and tend not to mix with water. The side chains of these amino acids are mainly composed of hydrocarbons. Amino acids with hydrophobic side chains. The nine amino acids that have hydrophobic side chains are shown in Figure 4: Figure 4. The twenty amino acids are often sorted into four groups-hydrophobic, polar but uncharged, basic, and acidic-depending on the nature of their side chains. Many other plastics become brittle and break at that temperature. Kevlar maintains its high strength when cooled to liquid nitrogen temperatures (–196 ☌). In addition to its better-known uses, Kevlar is used in cryogenic applications because of its very low thermal conductivity. When layers of Kevlar are placed on top of each other, they can be stacked very efficiently, allowing for maximal London dispersion forces. Hence a single layer of Kevlar, as shown in Figure 3, is planar. It is a planar structure, with planar benzene rings connected by planar amide groups.
Consider the repeating unit of Kevlar highlighted in Figure 3. Notice that compared to nylon 66, the density of hydrogen bonds in Kevlar is higher, imparting stronger intermolecular forces.įurthermore, Kevlar also has stronger London dispersion forces. One repeating unit of Kevlar is highlighted. The diagram shows the polymer structure of Kevlar, with hydrogen bonds between polymer chains represented by dotted lines. Similar to nylon, part of Kevlar’s strength is due to dipole-dipole interactions and hydrogen bonding (Figure 3) that increase intermolecular forces between polymer strands. The material has a high tensile-strength to weight ratio (it is about 5 times stronger than an equal weight of steel), making it useful for many applications from bicycle tires to sails to body armor. The byproduct of this condensation reaction is HCl. Kevlar is a synthetic polymer made from 1,4-phenylenediamine and terephthaloyl chloride monomers. If you pull on both ends of a nylon thread, after a slight stretch, it will resist breaking because of the strong IMFs that hold neighboring chains together. Hydrogen bonding, highlighted in red, can form between amide groups in different strands. Two strands of nylon-6,6 polymer are shown each strand is showing two repeating units. Specifically, a hydrogen bond can form between a N-H in one strand and a carbonyl O lone pair in a neighboring strand. Nylon makes extremely strong threads and fibers because in addition to London dispersion forces and dipole-dipole attractions, there are hydrogen bonds between the polymer chains. Other nylons have different numbers of carbon atoms in the monomer molecules, such as nylon 510, which has 5 carbon atoms in the diamine (1,5-pentanediamine) and 10 carbon atoms in the diacid (decanedioic acid). The “66” in nylon 66 stands for the six carbon atoms in each of the monomer molecules. Such continuous condensation reactions lead to the formation of a nylon 66 polymer strand, the repeating unit of which is also shown above. On the other end there is an amine group, which can react with another hexanedioic acid molecule. On one end, the product molecule has a carboxylic acid group, which can undergo a condensation reaction with another 1,6-hexanediamine molecule. The condensation reaction between these two monomers forms an amide linkage (highlighted): For example, nylon 66 is obtained from the monomers 1,6-hexanediamine and hexanedioic acid. \)Ī polyamide is a polymer in which the individual units are held together by amide linkages.
0 kommentar(er)
