Proton magnetic resonance studies of hydrated stratum corneum. Part 1.—Spin–lattice and transverse relaxation

Abstract

The proton magnetic spin-lattice and transverse relaxation behaviour is reported for guinea-pig footpad stratum corneum hydrated with both H₂O and D₂O. The relaxation is multicomponent in all cases and the behaviour of appropriate average relaxation times has been determined as a function of temperature and degree of hydration (regain). Above 30 % regain about 40 % of the non-exchangeable protons in stratum corneum are mobilised to the extent that their transverse relaxation is exponential in character. It is also shown that water protons form part of this mobile fraction when stratum corneum is hydrated with H₂O. Extraction of dry stratum corneum with a 2:1 chloroform + methanol mixture reduces the mobile fraction of hydrated stratum corneum.

The spin-lattice and transverse relaxation behaviour is analysed in terms of the complex structure and composition of the stratum corneum. The spin–lattice relaxation behaviour of the aqueous protons is separated from that of the non-aqueous protons by comparing H₂O and D₂ O hydrated samples. A fit of these T₁/temperature values at 45 % regain to a (log-normal distribution of correlation times) model results in a relatively narrow distribution and and a proton second moment less than the rigid-lattice value for an isolated H₂O molecule. This and the fact that the observed transverse relaxation times are much smaller than those predicted from the parameters characterising the log-normal fit to the spin–lattice relaxation indicates a considerable degree of anisotropy in the motions determining the various relaxation times, this possibly reflecting a degree of structural order in the keratin matrix within the stratum corneum cells. The transverse relaxation of both D₂O and H₂O hydrated stratum corneum indicates the presence of some exchange process evident at higher temperatures. This process is not solely due to water protons.