ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
An X-ray study of the synthetic polypeptide poly(L-homoarginine hydrochloride) has been made to investigate whether, like the chemically related polypeptides poly(L-lysine hydrochloride), poly(L-arginine hydrochloride), and poly(L-ornithine hydrobromide), it can undergo conformational transitions merely from variations in its degree of hydration. X-ray photographs of powder and oriented specimens containing one to 15 molecules of water per L-homoarginine hydrochloride residue showed that this polymer forms only a β-pleated-sheet structure. The pleated sheets, formed by antiparallel polypeptide chains hydrogen-bonded to each other, are piled up along the b axis in an alternating sequence (“sandwich structure”). This structure did not appreciably change with variations of the degree of hydration, and the observed reflections at 56% relative humidity (1.8 molecules of water per residue) could be indexed satisfactorily in terms of a monoclinic unit cell, of space group P21, with a = 9.34 Å, b = 40.07 Å, c = 6.94 Å, and γ = 106°. These dimensions are shown by models to be compatible with the proposed structure, and the calculated density of 1.27 g/cm3 agrees well with the experimental value of 1.29 g/cm3. Removal of the last molecule of water results in a very diffuse pattern, while specimens containing 20 molecules of water per residue show only reflections due to water.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/bip.1975.360140608
