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An X-ray diffraction study of poly-L-homoarginine hydrochloride

✍ Scribed by M. Suwalsky; M. Bunster; K. G. Wagner

Publisher
Wiley (John Wiley & Sons)
Year
1975
Tongue
English
Weight
444 KB
Volume
14
Category
Article
ISSN
0006-3525

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✦ Synopsis

Abstract

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 P2~1~, 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/cm^3^ agrees well with the experimental value of 1.29 g/cm^3^. 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.

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