Discrete and polymeric self-assembled dendrimers: Hydrogen bond-mediated assembly with high stability and high fidelity

Abstract

Hydrogen bond-mediated self-assembly is a powerful strategy for creating nanoscale structures. However, little is known about the fidelity of assembly processes that must occur when similar and potentially competing hydrogen-bonding motifs are present. Furthermore, there is a continuing need for new modules and strategies that can amplify the relatively weak strength of a hydrogen bond to give more stable assemblies. Herein we report quantitative complexation studies on a ureidodeazapterin-based module revealing an unprecedented stability for dimers of its self-complementary acceptoracceptor-donor-donor (AADD) array. Linking two such units together with a semirigid spacer that carries a first-, second-, or third-generation Fré chet-type dendron affords a ditopic structure programmed to self assemble. The specific structure that is formed depends both on the size of the dendron and the solvent, but all of the assemblies have exceptionally high stability. The largest discrete nanoscale assembly is a hexamer with a molecular mass of about 17.8 kDa. It is stabilized by 30 hydrogen bonds, including six AADD⅐DDAA contacts. The hexamer forms and is indefinitely stable in the presence of a hexamer containing six ADD⅐DAA hydrogen-bonding arrays. A t the most fundamental level, the readout of stored information in biochemical systems requires both a code and the machinery for expressing the code (1). Distinction at the molecular level is critical in such processes and in its simplest form involves a molecular recognition event. The code may be, for example, the primary sequence of a polypeptide, which through a series of recognition events folds into a specific secondary or tertiary structure, or it may be a linear array of recognition sites that are sequentially processed through a distinctive engagement at each site. However, a distinctive chemical process alone (e.g., DNA base pairing) is not sufficient. It must be coupled with a biological process (e.g., replication) to be considered authentic information retrieval.Inspired by nature's ability to create extraordinarily complex systems from comparatively simple information codes, and with an eye toward creating nanoscale devices (2), chemists have sought to develop small molecules capable of self-assembling into larger structures (3-10). Molecular recognition sites within these small molecules carry the code that guide the assembly. Thus, the information retrieval process is expressed through the formation of the self-assembled structure, which can further manifest itself through the bulk properties of the material formed (11,12). Despite the many successful examples that have appeared over the past decade, the power of this biomimetic self-assembly strategy has not been fully realized largely because of the limited number of recognition motifs available, and, in particular, their relatively low stability (4, 13). Moreover, nearly all self-assembling systems reported to date use a single type of distinction. Developing systems where bi-or polyinstructional codes guide ...

Complete Self‐Assembly of Discrete Supramolecular Dendrimers

“…After adsorption of the G1 dendrimer 1·2 3 ·3 d 6 on a Si surface, uniform and widespread distribution of completely homogeneous objects is observed with a diameter of 4 nm (Figure 4, left ), which is in agreement with the expected size of 1·2 3 ·3d 6 . Repeated sample preparations gave completely analogous pictures.…”

“…However, the hitherto presented concepts for the self-assembly of discrete and purely organic dendrimers employed preassembled dendritic systems in most cases. These entities have been linked to form discrete superstructures, for example, 1) by intermolecular hydrogen bonds with each other [5][6][7] or with other molecules, [8,9] 2) by electrostatic interactions between oppositely charged units, [10] and 3) as a result of structural and hydrophobic effects in the case of amphiphilic dendrimers. [11] We here present the first approach for the complete selfassembly of discrete supramolecular dendrimers where the repetition motif is no longer based on dendritic subunits ( Figure 1).…”

Controlling the growth and shape of chiral supramolecular polymers in water

“…6), which confirms the results from SAXS and diffusion ordered spectroscopy (DOSY) measurements. According to these findings, we have been able to obtain self-assembled discrete objects that can be considered the supramolecular equivalent of dendritic macromolecules (49,50).…”

Controlling supramolecular polymerization through multicomponent self‐assembly

“…225 More recently, Zimmerman and coworkers reported a guanosine urea derivative (UG) which forms very a stable ADDA-DAAD array with DAN (K a % 5 3 10 7 M…”