Formation of Hydrogen-Bonded Self-assembled Structures in Polar Solvents

Formation of Hydrogen-Bonded Self-assembled Structures in Polar Solvents 

Institute of Organic Chemistry, University of Duisburg-Essen, Universitaetsstrasse 7, 

The host-guest complexation and base-pair formation were investigated using NMR spectroscopy. Aqueous solutions of 5 -adenosine monophosphate (5, 2.0 pmol) and 5 -uridine monophosphate (6, 2.0 pmol) were stirred in the presence of cage 1 (2.0 pmol). The nucleobase protons of 5 and 6 exhibited noticeable upheld shifts (—0.68 and —1.81 ppm for adenine H8 and H2 of 5 —0.19 and —0.85 ppm for uracil H6 and H5 of 6). Among the ribose protons, HI of 5 and 6 were shifted (-1.08 and -1.01 ppm, respectively) (Fig. 6.2b, c), but only negligible shifts were observed for the protons H2 to H5 of both 5 and 6. These observations clearly suggested that the nucleobases were encapsulated inside the cavity but the ribose moiety still remained exposed to the outside environment. 

Characterization of 7a by SEM (Fig. 6.6) revealed that this tricyclic compound rapidly self-assembled into RNTs (Fig. 6.5) when dissolved in water at room temperature (pH = 2.8). TM-AFM and TEM images (Fig. 6.6) showed that the RNT s outer diameter is 4.2 0.2 nm and 4.4 0.2, respectively. These values are in excellent agreement with the theoretical value of 4.3 nm. 

One recent example of self-sorting in an artilicial system in aqueous media mediated by H-bonding is reported by Sijbesma et al. [21]. They described the formation of multiple hydrophobic compartments from mixtures of urea bolaam-phiphiles (UnU, Fig. 6.8) which form rod-like micelles stabilized within the membranes by H-bonds between the urea moieties. The self-sorting behavior of these 

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