Ettore Bartalucci

1 Introduction Guanidine, or its protonated form guanidinium, is an essential functional group in biology, where it is, for instance, part of the amino acid arginine or the energy metabolite creatine. Arginine residues play a crucial role in protein folding, as well as nucleotide or nucleic acid binding [1-3].

1 INTRODUCTION Spider silk fibers inspire material scientists due to their outstanding toughness resulting from the combination of elasticity and tensile strength, outperforming a vast majority of natural and artificial materials (Gosline et al., 1984; Lewis, 2006). Moreover, the lack of toxicity, low immunogenicity, as well as biodegradability underline the biocompatibility of spider silks.

The influence of fluorine spin-diffusion on 13C solid-state NMR line shapes of CF3 groups Indirect spin-spin couplings (“J-couplings”) lead to well-known multiplet patterns in Nuclear Magnetic Resonance (NMR) spectra that are also observable in non-decoupled solid-state NMR spectra, if the J-coupling constant exceeds the linewidth. Such J-multiplet line shapes in the solid state might however be affected by spin diffusion (SD) on the passive nuclei.