ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The helix-coil transitions of poly(Nε-methyl, Nε-carbobenzoxy-L-lysine), poly(Nδ-methyl, Nδ-carbobenzoxy-L-ornithine), and poly(Nδ-ethyl, Nδ-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, ΔH = -370 cal/mol and ΔS = -1.1 eu/mol for poly(Nε-methyl-L-lysine), and ΔH = -540 cal/mol and ΔS = -1.6 eu/mol for poly(Nδ-ethyl-L-ornithine) (all on molar residue basis). The absolute values of ΔH and ΔS 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(Nδ-methyl-L-ornithine) the coil-to-helix transition was not complete even when the polymer was uncharged at high pH.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/bip.1974.360130603
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