Low-angle X-ray investigations of detergent treated soft keratins

Abstract

Keratins forming the main bulk of the horny layer of the epidermis and epidermis appendages such as hair, nails, claws, scales and feathers can be divided into two classes, namely hard and soft keratins. All mammalian keratins (hard and soft keratins) yield a typical a-pattern with a 5.15 A. meridional reflexion and a 9.8 ]k equatorial reflexion. These keratins are called a-keratins. Apart from this, some mammalian hard keratins such as mohair fibres and porcupine quills yield very sharp low-angle X-ray patterns with many meridional reflexions which can be indexed in first approximation as higher orders of an axial fundamental repeat of 198 A [1,2]. Normally the third order at 66 A is observed as innermost meridional reflexion.Epidermal keratins, however, being soft keratins, give only poor low-angle X-ray patterns. In the native (untreated) state no discrete meridional low-angle reflexions can be identified in the corresponding X-ray patterns. It is well-known, however, that after the chemical modification of a-keratins so~me meridional reflexions can be considerably intensified: mohair samples which had been treated with diluted n-alkylsulpate solutions (C12, Cl0, C8, C6) at 20 ~ for 24 h at pH 2 exhibited totally changed X-ray ~agrams [3]: two meridional reflexions, at 39 and 28 A, are always intensified independently of the chain length of the detergent. If the critical micelle concentration (c. m. c.) is not exceeded most of the deposited detergent molecules are bound stoichiometrically.Therefore we have now treated skin keratin samples with sodium dodecylsulphate (SDS) solutions of various concentrations at pH2 for 24 h, then filtered and dried. In no case was any intensification of the two meridional reflexions observed. When the SDS concentration was slightly lower than the c. m. c. (7.10 -3 mol/1) instead of 8.1.10 -3 moF1), there was only a diffuse detergent ring at about 40 ~. The same ring is also observed in the X-ray patterns of concentrated SDS solutions. Even after the treatment with a 0.2 M SDS solution at pH2 the 39 and 28 A_ reflexion could not be identified in the corresponding X-ray patterns.There were only three strong and sharp detergent rings at about 40,20 and 13 A_ (pure SDS yields the same rings) dominating the weak and diffuse X-ray pattern of skin keratin.Detergent depositions normally cause the strongest intensifications of meridional reflexions ever observed after chemical modifications of keratins. If after the SDS treatment of skin keratins no meridional retiexions are present, then this can only mean that untreated skin keratin samples do not even yield "latent" meridional low-angle reflexions too weak to be identified in low-angle patterns taken in Kiessig type cameras. It sometimes happens that meridional reflexions which cannot be identified in the X-ray patterns of untreated keratin samples appear after chemical modifications. But in all these cases a more or less perfect meridional reflexion system is already present which is only improved or completed by the chemical modifi...

Effect of Cooling Rate on Freezing of Wool-Water Mixtures

“…The water in the space between the microfibrils and the globular matrix is believed to be directly concerned with wool swelling [3,43]. Swift et al reported that the relatively uncrosslinked proteins of the intermacrofibrillar matrix are binding water and can be regarded as the main plasticizing elements separating the stiffer macrofibrils [44,45].…”