HELICAL POLYAMIDES AND RINGS: A BRIDGE BETWEEN NYLONS AND PROTEINS. Juan A. Subirana, Dept. Enginyeria Química, Univ. Politécnica de Catalunya, Diagonal 647, E-08028 Barcelona, Spain. e-mail: Subirana@eq.upc.es

In order to bridge the gap between nylons and proteins, synthetic polyamides with a conformation similar to that found in proteins have been studied. Analogies in the folding process are discussed in the last part. We have found that it is possible to obtain structures very similar to the [[alpha]] helix by introducing side chains in nylon 3 and in nylon 4, which is equivalent to introducing one or two methylene groups in the polypeptide main chain. Although the density of intramolecular hydrogen bonds decreases, the helical structure is stable. In some cases, even two different types of helix are found, which crystallize in different structures. In solution it is possible to study the helix-coil transition. The helices may also give rise to liquid crystals and fibers with piezoelectric properties.

In another line of endeavour we have investigated polyamides in which glycine and related monomer units (-NHCOCH₂ CONH-; -CONHCH₂NHCO-) have been introduced. We find a strong preference of the conformational angles of the glycine units and related monomers to be similar with those found in helical polyglycine II. It is striking that in the presence of glycine fully extended chains, typical in polyamides, are seldom found. These polymers are organized with either one, two or three directions of hydrogen bonding which form new unique structures instead of the familiar extended chains of polyamides and pleated sheets of proteins. Besides the intrinsic interest of these new polymers, our studies open the way to new types of protein engineering based on new monomeric building blocks. We have also used oligomers and rings as model compounds. In some cases, they form hydrogen bonded columns with an appearance similar to the [[alpha]] helix.

With respect to the folding process, many of these polymers form lamellar crystals with 40-80Å thickness, a value which depends on the density of hydrogen bonds. The crystallization process appears to be strongly influenced by the coil-globule transition which takes place in the dilute polymer solution before crystallization. In this way polymer crystallization appears to have some analogies with the protein folding process. It is stricking that the thickness of polymer lamellae is similar to the common dimensions of proteins.