IntroductionThe physical properties of bark and bast strongly depend on their hydration (Sjöström 1981). Nuclear magnetic resonance is well suited for investigation of micro-scale effects of water interactions with bark and bast solid matrix, as it is a method sensitive to the dynamics of molecules and their local environment, which are useful in explanation of the molecular background of macroscopic timber properties. However, until now, most of the attention in nuclear magnetic relaxation investigations of timber products was paid to wood (Araujo et al. 1993;Brownstein 1980;Hartley et al. 1994;Hsi et al. 1977;Menon et al. 1987Menon et al. , 1989Riggin et al. 1979). There have been some attempts at the observation of water clustering on the surface of pores in biological systems, using wood as a convenient solid matrix (Hartley and Avramidis 1993).Bast (inner bark) and bark (outer bark) are similar to wood and other microheterogeneous biological systems, however, their hydration properties significantly differ from those of wood. Bark contains a higher concentration of waxes and suberins which change the pore surface. On the other hand, bast contains a higher concentration of the hydrophilic extractive fraction than wood (or bark) (Sjöström 1981;Kamat et al. 1992).Despite the high content and importance of the hydrophilic extractive fraction for bark and bast physical properties, there has been no effective method for its in situ observation. The authors propose nuclear magnetic relaxation as a method which yields the following molecular quantities for hydrophilic extractive fraction in bast: the upper dissolution threshold ∆M/m 0 for solid soluble fraction (the amount of water necessary to dissolve the whole water-soluble fraction), saturation concentration c s of soluble fraction (thus, ∆M c /m 0 , the content of solid soluble fraction) and effective (scaled to water) proton densities of solid and water soluble fractions, in situ. SummaryThe proton free induction decay (FID) was shown to be effective in monitoring of hydration and the water soluble extractive fraction in horse chestnut (Aesculus hippocastanum, L.) and pine (Pinus silvestris, L.) bark and bast. The signal from the first bound water layers was separated from the whole liquid signal (L) and at low hydration the liquid signal from the stable sealed bark pores was detected. The liquid-to-solid (L/S) signal ratio as a function of relative mass increase (∆m/m 0 ) was proposed as a convenient method to evaluate the relative mass of water, necessary to dissolve the whole soluble proton pool (∆M/m 0 ), the relative mass contribution of solid proton component (p 0 in absence of water soluble fraction or p S0 in presence of water soluble fraction), the saturation concentration of the water soluble fraction (c s ) and the effective (scaled to water) proton density of solid protons (β s ). The measurement of the absolute (in arbitrary units) proton signal versus relative mass increase yielded additionally the effective proton density water soluble proton fr...

The rehydration from the gaseous phase of the developing native or EDTA-washed from unbound and loosely bound paramagnetic ions wheat thylakoid membrane lyophilizate was investigated using hydration kinetics, sorption isotherm, and high power proton relaxometry. Hydration time courses are single exponential for all target humidities. The sorption isotherm is well fitted by the Dent model, with the mass of water saturating primary binding sites equal to ∆M/m 0 = 0.024 and 0.017 for native and EDTA-washed membranes, respectively. Proton free induction decays distinguish: (i) a Gaussian component, S 0 , coming from protons of solid matrix of lyophilizate; (ii) a Gaussian component, S1, from water bound to the primary water binding sites in proximity of water accessible paramagnetic ions; (iii) an exponentially decaying contribution, L1, from water tightly bound to lyophilizate surface; and (iv) exponentially decaying loosely bound water pool, L2. Sorption isotherm fitted to NMR data shows a significant contribution of water "sealed" in membrane structures (∆M s /m 0 = 0.052 for native and 0.061 for EDTA-washed developing membranes, respectively).

The analysis of the NMR relaxation function for microheterogenous systems usually starts with the decomposition of the relaxation function to discrete components, or finding a continuous distribution of the components. Several approaches can be applied to do this: linear least-squares fitting, non-linear least-squares fitting or inversion of the data, based on the Laplace transformation. The spin-grouping technique - a correlated analysis of the spin-lattice relaxation function (recovery or decay) and spin-spin relaxation decay (free induction decay or Carr-Purcell decay) - usually enables a decomposition of relaxation data into a proper set of discrete components. In our paper, we present CracSpin, a program for one and/or two-dimensional analysis of the relaxation function in the time domain. It uses Marquardt's algorithm for non-linear least-squares fitting. The results of analyses of simulated data containing discrete as well as continuous distributions of the components are shown. CracSpin resolves the components of FID even if the ratio of their relaxation times is as small as 2, for comparable component magnitudes (at least about 10% of total signal) and for signal-to-noise ratio (S/N) >100. If the ratio of component relaxation times is higher than ~3, the decomposition is satisfactory for S/N >10, even for a component magnitude of about 1%. The noise level is defined here as equal to the three standard deviations of the normal distribution. The two-dimensional analysis significantly improves the quality of the multicomponent decomposition, for composed decays or in the case of close values of the relaxation time of the components. The representative examples of the analysis, starting from spin-lattice relaxation curves, as well as from spin-spin relaxation curves, are presented and discussed.

The initial stages of Umbilicaria aprina Nyl. hydration (starting from the hydration level Dm/m 0 ¼ 0.048 AE 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 ¼ 100% was Dm/m 0 ¼ 0.848 AE 0.009. The hydration courses revealed i) a fraction of very tightly bound water (Dm/m 0 ¼ 0.054 AE 0.011, short hydration time constant, t hyd ), ii) a fraction of tightly bound water [Dm/m 0 ¼ 0.051 AE 0.038, t hyd ¼ (4.7 AE 2.6) h], and iii) a loosely bound water pool [ t hyd ¼ (31.0 AE 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 DM/m 0 ¼ 0.054, which is close to the water fractions. Proton FIDs detected (i þ 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.

Hydration courses and proton free induction decays are recorded at 30 MHz for Usnea antarctica thalli hydrated from gaseous phase. NMR data combined with gravimetry allow one to distinguish two fractions of tightly bound water, and loosely bound/free water pool. No water fraction "sealed" in thallus structures is present in U. antarctica.

The hydration of selected lichens (Cladonia mitis, Cladonia bellidiflora, Cetraria islandica, Parmelia saxatilis, and Xanthoria parietina) was investigated using gravimetry and proton magnetic free induction decays (FIDs).The hydration from gaseous phase and dehydration to gaseous phase showed first-order kinetics. The amount of water which was non-removable in the air-dry state (relative humidity p\p ! l 9 %) did not depend significantly on the lichen species and was found to be 5n6p1n0 % of the d. wt.The proton FID Gaussian component from the solid matrix of thallus structure, and two (or, depending on lichen species, one averaged) liquid signals coming from water tightly bound on the surface of thallus solid matrix and from loosely bound or free water, were recorded. The bound-water component was distinguished by its motional properties and by its proximity to endogenous paramagnetic centres present in solid matrix (presumably PS II reaction centres of the photobiont). Mild dehydration (from gaseous phase) could completely remove the loosely bound water fraction, leaving the system below the water percolation threshold and below the water clustering point, emphasizing the passivity of lichen response to desiccation shock. In the species in which the one average liquid component was recorded, bound water behaved similarly.The hydration at which free water pool vanishes (∆M\m ! ) and the relative (scaled to water) proton densities of solid matrix of lichen (β) were evaluated for all lichens investigated.

Hydration kinetics, sorption isotherm, and proton free induction decays are measured for Leptogium puberulum Hue thalli hydrated from gaseous phase. Very tightly, tightly and loosely bound water fraction are distinguished. The hydration dependence of mobile NMR signal component is non-linear and fitted well by rational function, which suggest the presence of water soluble solid (presumably carbohydrate) fraction in thallus structures of L. puberulum.

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