Search

The formation of distinct supramolecular assemblies, including a metastable species, is revealed for a lipophilic guanosine (G) derivative in solution and in the solid state. Structurally different G-quartet-based assemblies are formed in chloroform depending on the nature of the cation, anion and the salt concentration, as characterized by circular dichroism and time course diffusion-ordered NMR spectroscopy data. Intriguingly, even the presence of potassium ions that stabilize G-quartets in chloroform was insufficient to exclusively retain such assemblies in the solid state, leading to the formation of mixed quartet and ribbon-like assemblies as revealed by fast magic-angle spinning (MAS) NMR spectroscopy. Distinct N−H⋅⋅⋅N and N−H⋅⋅⋅O intermolecular hydrogen bonding interactions drive quartet and ribbon-like self-assembly resulting in markedly different 2D 1H solid-state NMR spectra, thus facilitating a direct identification of mixed assemblies. A dissolution NMR experiment confirmed that the quartet and ribbon interconversion is reversible-further demonstrating the changes that occur in the self-assembly process of a lipophilic nucleoside upon a solid-state to solution-state transition and vice versa. A systematic study for complexation with different cations (K+, Sr2+) and anions (picrate, ethanoate and iodide) emphasizes that the existence of a stable solution or solid-state structure may not reflect the stability of the same supramolecular entity in another phase. [ABSTRACT FROM AUTHOR]

Invited for the cover of this issue is the group of Steven P. Brown at the University of Warwick and collaborators in Italy and the US. The image depicts the transformation (studied by NMR spectroscopy) between small molecule building blocks into unique assemblies during solid-solution interconversions. Read the full text of the article at . [ABSTRACT FROM AUTHOR]

Abstract: Crosslinking junctions of vulcanized natural rubber were analyzed by solid-state NMR spectroscopy equipped with a field-gradient high speed magic angle spinning probe. Resolution of 1H and 13C NMR spectra and correlations between 1H and 13C of the vulcanized natural rubber were investigated by one- and two-dimensional measurements, including inverse correlation measurements. The number of substitution of the carbon atom at the crosslinking junctions was determined by solid-state NMR spectroscopy. [Copyright &y& Elsevier]