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Syntheses and conformational studies of poly(Nε-methyl-L-lysine), poly(Nδ-methyl-L-ornithine), poly(Nδ-ethyl-L-ornithine), and their carbobenzoxy derivatives

✍ Scribed by Hiroyuki Yamamoto; Jen Tsi Yang

Publisher
Wiley (John Wiley & Sons)
Year
1974
Tongue
English
Weight
772 KB
Volume
13
Category
Article
ISSN
0006-3525

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✦ Synopsis

Abstract

The helix–coil transitions of poly(N^ε^‐methyl, N^ε^‐carbobenzoxy‐L‐lysine), poly(N^δ^‐methyl, N^δ^‐carbobenzoxy‐L‐ornithine), and poly(N^δ^‐ethyl, N^δ^‐carbobenzoxy‐L‐ornithine) in chloroform–dichloroacetic acid and their corresponding decarbobenzoxylated polypeptides in alkaline solutions were followed by optical rotation measurements. The introduction of a methyl or an ethyl group to the side chains of the carbobenzoxy derivatives of poly(L‐lysine) and poly(L‐ornithine) appeared to weaken the helical conformation at 25°C. The thermodynamic quantities of the three water‐soluble polypeptides were calculated from the data on potentiometric titrations at several temperatures. For uncharged coil‐to‐helix transition, Δ__H__ = −370 cal/mol and Δ__S__ = −1.1 eu/mol for poly(N^ε^‐methyl‐L‐lysine), and Δ__H__ = −540 cal/mol and Δ__S__ = −1.6 eu/mol for poly(N^δ^‐ethyl‐L‐ornithine) (all on molar residue basis). The absolute values of Δ__H__ and Δ__S__ dropped in the region of pH‐induced transition and eventually both quantities became positive. The initiation factor σ was about 2 × 10^−3^, which was essentially independent of temperature. For poly(N^δ^‐methyl‐L‐ornithine) the coil‐to‐helix transition was not complete even when the polymer was uncharged at high pH.

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