Add time:08/26/2019         Source:sciencedirect.com

Three types of high molecular weight poly(γ-N-methyl, γ-N-carbobenzoxy-l-α, γ-diaminobutyric acid), poly(γ-N-ethyl, γ-N-carbobenzoxy-l-α, γ-diaminobutyric acid), and poly(γ-N-benzyl, γ-N-carbobenzoxy-l-α, γ-diaminobutyric acid) were synthesized by the N-carboxyanhydride method. The helix-coil transition of these poly(γ-N-alkyl, γ-N-carbobenzoxy-l-α, γ-diaminobutyric acids) in chloroform-dichloroacetic acid was followed by optical rotation measurements. The introduction of a methyl, an ethyl, or a benzyl group to the side chain of the carbobenzoxylated derivative of poly(l-α, γ-diaminobutyric acid) appeared to weaken the helical conformation at 25°C and altered the direction of the temperature induced helix-coil transition from a ‘normal’ to an ‘inverse’. For water-soluble poly(γ-N-alkyl-l-α, γ-diaminobutyric acids), the coil-to-helix transition was little observed even when the polypeptides were uncharged at pH 12. At sufficiently high methanol concentration, however, the polypeptides underwent a complete transition from the random coil to the α-helical conformation even at pH 3.

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