Applicability of solid state fast field cycling NMR relaxometry in understanding relaxation properties of leaves and leaf-litters

Inversion recovery high field solid state (SS) 1H NMR spectroscopy and fast field cycling (FFC) NMR relaxometry have been applied on dried leaves and leaf-litters from a reafforestated area in central Sicily (Italy) in order to evaluate relaxation properties in both slow (1≪ω02τC2) and fast (1≫ω02τC2) motion regimes. Namely, SS 1H NMR spectroscopy (i.e. slow motion regime conditions) revealed that two relaxation components (a fast and a slow one) can be identified in all the leaves and leaf-litter samples. The fast component was assigned to small sized plant metabolites, whereas the slow one was attributed to slowly tumbling macropolymeric molecules. FFC NMR relaxometry (i.e. fast motion regime conditions) indicated that intra- and inter-segmental motional contributions to plant relaxation occur, depending on the nature of the plant sample under investigation. The present study represents the first example of a combination of high and low resolution NMR techniques for the understanding of the dynamics properties of environmentally relevant soft matter such as leaves and leaf-litters. These materials are considered among the main contributors for the synthesis of natural organic matter. For this reason, a comprehension of their basic molecular dynamics properties is a crucial point to evaluate their effect on, e.g., carbon cycle, fate of organic and inorganic pollutants, and microbial biomass grow.