Maturation Process of Photosynthetic Membranes Observed by Proton Magnetic Relaxation and Sorption Isotherm

Mild rehydration from the gaseous phase of the developing and mature lyophilized wheat photosynthetic membranes was investigated using hydration kinetics, adsorption isotherm and high power proton relaxometry. Hydration time courses are single exponential for all target air humidities; the hydration time $t^h$ equals to (11.9±3.6) h for the mature membranes, and (17.0±3.2) h for the developing membranes. The sorption isotherm is sigmoidal in form and well fitted using the Dent model; the mass of water saturating primary binding sites equals Δ M/$m_0$= 0.033±0.013 and 0.025±0.007 for the mature and for the developing membranes, respectively, where $m_0$ is the dry mass of the sample, and Δ M is mass of water taken up. Proton free induction decays distinguish: (i) an immobilized proton (Gaussian) component, $S_0$, originating from protons of solid matrix of lyophilizate; (ii) a Gaussian component, $S_1$, from water bound to the primary water binding sites and localized in proximity of paramagnetic ions; (iii) an exponentially decaying contribution, $L_1$, from water tightly bound to lyophilizate surface; and (iv) exponentially decaying loosely bound water pool, $L_2$. A significant contribution of water "sealed" in the structure of lyophilized membrane (from the fraction $S_1$ and $L_1$) is detected. The mass of "sealed" water fraction is Δ $M_{S}//m_0$ = 0.047±0.023 and 0.072±0.021 for the mature and for the developing membranes, respectively.