Hydration of human nails investigated by NIR-FT-Raman spectroscopy Sonja Wessel *, Monika Gniadecka, Gregor B.E. Jemec, Hans Christian Wulf Department of Dermatology, Bispebjerg Hospital, University of Copenhagen, Copenhagen, Denmark Received 23 March 1999; received in revised form 25 May 1999; accepted 3 June 1999 Abstract The human nail, although it is usually stable against outer influences, becomes soft and flexible after soaking in water. Frequent washing increases brittleness of nails. Hydration of nails is thought to be the most important factor influencing the physical properties of nails and possibly acts through changes in keratin structure. Here NIR-FT-Raman has been used to examine molecular structural changes of intact moisten nails. Raman spectra were obtained both in vitro from nail samples and in vivo before and after soaking in water. The water uptake of normal nail samples during the first 15 min was reflected in the increasing intensity ratio of the X(OH)/X(CH 2 ) bands. A saturating effect appeared soon after 10 min which is explained by a defined water holding capacity. R(X) representation of the low frequency range of the Raman spectra showed that mainly bound water is found both in dry and in wet nails. This implies water^protein interaction. Protein backbone vibration at 932 cm 31 indicating K-helical proteins increased in intensity in the wet nails. The X(S^S) which is sensitive to changes in conformation of proteins showed a 4% higher intensity. Additional protein^water interactions could lead to a slight change of the dihedral angle of the C^S^S^C bonds and to geometric changes in coiling behavior of the K-helical protein. Suggesting a separation between matrix proteins and fiber proteins giving them a greater freedom of flexibility. The in vivo spectra detected from the distal part of the nail resembled spectra in vitro. Raman spectra of the proximal part of the nail showed that it was fully saturated with water. The proximal part of the nail did not show changes in water content and protein structure during nail moisturizing in the Raman spectra. Our results suggest that the softening of the nail following hydration may be due to changed matrix protein molecular structure induced by water. ß 1999 Elsevier Science B.V. All rights reserved. Keywords : Keratin; Water; Protein 1. Introduction Human nail plate is one of the most impervious of biological structures and the penetration of chemical agents is low [1]. Nails, however, change their phys- ical properties when they are soaked in water during hand washing and bathing, where they become soft and their £exibility increases. The degree of hydra- tion is thought to be the most important factor in- £uencing the physical properties of nails [2]. In spite of this, evaporation from the surface of the nail is greater than that from adjacent skin [3]. For exam- ple, water permeates human nails faster than homol- ogous alcohols [4] and it in£uences alcohol permea- tion positively [5]. Drug solubility in water in£uences the permeation through nails [6]. Frequent hydration of nails can increase their brit- 0167-4838 / 99 / $ ^ see front matter ß 1999 Elsevier Science B.V. All rights reserved. PII:S0167-4838(99)00129-6 * Corresponding author. Present address: Dr. S. Wessel, Melanchthon Str. 24a, D-22525 Hamburg, Germany. E-mail : wessels@hamburg.beiersdorf.com Biochimica et Biophysica Acta 1433 (1999) 210^216 www.elsevier.com/locate/bba