Deep dehydration of Umbilicaria aprina thalli observed by proton NMR and sorption isotherm

• Published in: Antarctic Science
• Main Authors: Harańczyk, H., Bacior, M., Olech, M.A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 2008
• Subjects: Geology; Ecology, Evolution, Behavior and Systematics; Oceanography; Dent; Antarctic Science
• Online Access: http://dx.doi.org/10.1017/s0954102008001363; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0954102008001363

Abstract The initial stages of Umbilicaria aprina Nyl. hydration (starting from the hydration level Δ m / m 0 = 0.048 ± 0.004) were observed using hydration kinetics, sorption isotherm and proton NMR. The thalli were hydrated from gaseous phase. The total saturation hydration level obtained at the relative humidity p/p 0 = 100% was Δ m/m 0 = 0.848 ± 0.009. The hydration courses revealed i) a fraction of very tightly bound water (Δ m/m 0 = 0.054 ± 0.011, short hydration time constant, t hyd ), ii) a fraction of tightly bound water [Δ m/m 0 = 0.051 ± 0.038, t hyd = (4.7 ± 2.6) h], and iii) a loosely bound water pool [t hyd = (31.0 ± 1.9) h] for higher values of target humidity. The sorption isotherm of U. aprina was fitted well using Dent model. The relative mass of water saturating primary binding sites was Δ M/m 0 = 0.054, which is close to the water fractions. Proton FIDs detected (i + ii) the immobilized tightly bound water fraction, L 1 , and iii) the mobile, loosely bound water pool L 2 . The hydration dependence of the proton liquid signal suggests the presence of a significant contribution from a water soluble solid fraction in the thallus. Sorption isotherm fitted to NMR data showed the absence of ‘sealed’ water fraction trapped in pores of the thallus.