Principles of self-assembly of helical pores from dendritic dipeptides

Abstract

The self-assembly of the dendritic dipeptides (4-3,4-3,5)nG2-CH2-Boc-L-Tyr-L-Ala-OMe and their achiral dendritic alcohol (4-3,4-3,5)nG2-CH2OH precursors, both with n ‫؍‬ 1-16, where n represents the number of methylenic units in the alkyl groups of the dendron, are reported. All chiral dendritic dipeptides and achiral dendritic alcohols self-assemble into helical porous columns that are stable in both solution and solid state. The pore diameter (Dpore) of the columns self-assembled from dendritic dipeptides is Ϸ10 Å larger than that of structures assembled from dendritic alcohols. The increase of the Dpore at the transition from dendritic alcohol to dendritic dipeptide is accompanied by a decreased solid angle of the building block. This trend is in agreement with previous pore size-solid angle dependences observed with different protective groups of the dipeptide and primary structures of the dendron. However, within the series of dendritic alcohols and dendritic dipeptides with various n, the Dpore increases when the solid angle increases. The results of these investigations together with those of previous studies on the role of dipeptide stereochemistry and protective groups on this self-assembly process provide the molecular principles required to program the construction of supramolecular helical pores with diameter controlled at the Å level from a single dendritic dipeptide architecture. These principles are expected to be valid for libraries of dendritic dipeptides based on dendrons and dipeptides with various primary structures. chiral dendrons ͉ porous supramolecular columns ͉ protein mimics ͉ peptide stereochemistry N atural porous proteins function as viral helical coats (1), transmembrane channels (2, 3), antibiotics (4), and pathogens (5), and their remodeled structures are used in synthetic systems for reversible encapsulation (6) and stochastic sensing (7). With few exceptions (8-10) porous protein mimics do not assemble, as the natural porous proteins do, into periodically ordered structures that are stable in both solution and bulk (11)(12)(13)(14). This behavior limits their structural analysis by combinations of solution and solid-state complementary techniques. Recently our laboratory (15) reported the self-assembly of amphiphilic dendritic dipeptides into helical porous structures that are stable in both solution and bulk (15). Preliminary reports have demonstrated that the internal structure and the stability of the porous columns self-assembled from dendritic dipeptides are programmed by the structure and stereochemistry of the dipeptide (15, 16), the protective groups of the dipeptide (17), and the structure of the dendron (18) attached to the dipeptide. Here we are reporting a comparative study of the self-assembly and structural and retrostructural analysis of the supramolecular porous structures generated from libraries of (4-3,4-3,5)nG2-CH 2 -Boc-L-Tyr-L-Ala-OMe dendritic dipeptides and their achiral (4-3,4-3,5)nG2-CH 2 OH precursors with n ϭ 1-16. This series of experiments will prov...

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Self-Assembly of Dendritic Dipeptides as a Model of Chiral Selection in Primitive Biological Systems

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“…The melting temperatures (T m ) of the self-assemblies are also indicated. Reprinted with permission from [76]. self-assembly.…”

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