Abstract
The hierarchical self-assembly of various lipophilic guanosines exposing either a phenyl or a ferrocenyl group in the C(8) position was investigated. In a solution, all the derivatives were found to self-assemble primarily into isolated guanine (G)-quartets. In spite of the apparent similar bulkiness of the two substituents, most of the derivatives form disordered structures in the solid state, whereas a specific 8-phenyl derivative self-assembles into an unprecedented, cation-free stacked G-quartet architecture.
Highlights
To gain deeper insights into the propensity of the derivatives to undergo self-assembly, we have extended our study to atomic force microscopy (AFM) imaging
We have designed and synthesized several organic soluble guanosines carrying either a phenyl or a ferrocenyl group at the C(8) position. Their self-assembly has been studied in solution by Nuclear magnetic resonance (NMR) and in thin films by means of AFM
Derivative 8Ph5Fc shows the exclusive existence of isolated G4s in the CD2Cl2 solution, while compounds 8Fc5C10 and 8Ph5C10 do form isolated G4s as well, but another aggregated species is present in equilibrium in solution
Summary
Among DNA bases, guanine (G) exhibits a unique ability to undergo self-assembly, forming various distinct supramolecular structures.[1,2] In particular, lipophilic guanosine derivatives have been reported to generate either supramolecular ribbon-like architectures[3−6] or tetrameric array (G-quartets)-based assemblies.[7,8] The formation of a specific assembly motif is ruled by both the specific chemical structure of the derivative[9,10] and the environmental conditions.[10,11] Among various G assemblies, G-quartet (hereafter G4)-based supramolecular architectures are by far the most important because of the biological relevance of this structural motif in DNA.[12,13]. The 8-phenyl substituent exhibits a smaller effect and is limited to the H2’ and H3’ protons NOE spectra provide unambiguous information on the structure of the main self-assembled species in solution Another feature common to the main species formed by 1−8 is the dipolar coupling between the protons of the substituent at the C(8) position and the exocyclic amino group. AFM characterization has not revealed any well-defined structures, and the films look amorphous (see Figure S18)
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