Sequence-dependent binding of dipeptides by an artificial receptor in water.

An artificial dipeptide receptor (1) was designed and observed to bind the deprotonated dipeptide Ac-D-Ala-D-Ala-OH in buffered water with K = 33,100 M(-1), whereas other dipeptides such as Ac-Gly-Gly-OH or Ac-D-Val-D-Val-OH were bound less efficiently, by factors of more than 10 (K < 3000 M(-1)). The efficient binding and the pronounced sequence selectivity are the result of a combination of strong electrostatic contacts and size-discriminating hydrophobic interactions. To provide such a combination, a guanidiniocarbonylpyrrole cation was attached to a novel cyclotribenzylene-substituted alanine derivative 5, to provide a hydrophobic bowl-shaped cavity just large enough to bind a methyl group but not any larger alkyl chains, thus causing the receptor to prefer alanine to valine.

Highly stable self-assembly in water: ion pair driven dimerization of a guanidiniocarbonyl pyrrole carboxylate zwitterion.

The synthesis of a novel water-soluble guanidiniocarbonyl pyrrole carboxylate zwitterion 2 is described, and its self-association in aqueous solutions is studied. Zwitterion 2 forms extremely stable 1:1 dimers which are held together by an extensive hydrogen bonding network in combination with two mutual interacting ion pairs as could be shown by ESI MS and X-ray structure determination. NMR dilution studies in different highly polar solvents showed that dimerization is fast on the NMR time scale with association constants ranging from an estimated 10(10) M(-1) in DMSO to a surprisingly high 170 M(-1) in water.

Self-Complementary Quadruple Hydrogen-Bonding Motifs as a Functional Principle: From Dimeric Supramolecules to Supramolecular Polymers.

The self-association of individual molecules can lead to the formation of highly complex and fascinating supramolecular aggregates. However, for binding motifs which rely only on hydrogen bonds, a combination of several such weak interactions is necessary to observe self-association in solution. Systems based on four hydrogen bonds in a linear array can be obtained which efficiently aggregate at least in chloroform.