ISSN:
0025-116X
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
N-(tert-Butoxycarbonyl)-L-leucyl-D-leucyl-L-leucyl-D-leucine tetrapeptide was synthesized from L- and D-leucine α-amino acids by conventional coupling methods. This tetrapeptide was transformed into an activated (polymerizable) tetrapeptide by conversion to the pentachlorophenyl ester and subsequent removal of the tert-butoxycarbonyl group. Condensation polymerizations of the activated tetrapeptide were performed in various solvents with triethylamine and N,N-diethyl-1-amino-2-propanol bases. Molar masses (“molecular weights”) of the resulting polymers were estimated to be in excess of 34000 g/mol. From optical rotation measurements in trifluoroacetic acid solution, it was found that the polymers were highly syndiotactic, although a small amount of isomerization (0,9-2,1%) occurred to yield polymers with a small excess of L-leucine residues. The degree of isomerization decreased with decreasing base strength and concentration and with decreasing polarity of the solvent; these effects were explained in terms of the simultaneous enolization and/or oxazolone-formation reactions.Preliminary studies of the conformation of syndiotactic poly(leucine) were performed with X-ray diffraction, NMR, IR and optical rotation methods. It was concluded that syndiotactic poly(leucine) most probably exists in a π-helical conformation with a preferred screw sense in both the solid state and in chloroform solution. NMR and optical rotation data on solutions in trifluoroacetic acid/chloroform showed that the polymer exhibits a conformational transition in the region of 4-10% trifluoroacetic acid content.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1978.021790303
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