Molecular Clips Form Isostructural Dimeric Aggregates from Benzene to Water

Abstract

We report the synthesis and characterization of eight C-shaped methylene-bridged glycoluril dimers (1-8) bearing hydrogen-bonding amide groups on their aromatic rings. Compounds 1-6 undergo tight dimerization in CDCl3 solution (Ks > 9 x 10(5) M(-1)); binary mixtures of 1-7 form mixtures of homodimers and heterodimers in moderately selective dimerization processes (0.23 < or = Keq < or = 768; 0.253 < or = chiAB < 0.933). The high affinity formation of 1.1-6.6 is due to the commensurate nature of the geometrical constraints imposed by the pi-pi interactions and only two hydrogen bonds. The differential response of the strengths of the pi-pi interactions and H-bonds of 2.2 to changes in solvent polarity--from C6D6 to D2O--results in the formation of a solvent-independent isostructural aggregate that exhibits high affinity dimerization across the full range of solvents.

Discovery and early development of squaraine rotaxanes

“…4 and found that all of them are mechanically stable in chloroform solvent even at elevated temperatures 19. Squaraine rotaxane unthreading is most likely to occur in polar aprotic solvents, such as DMSO or DMF, that effectively disrupt hydrogen bonds and also minimize attractive dispersion interactions 20. However, it is notable that unthreading is inhibited by the presence of water because the hydrophobic effect favors the rotaxane's aromatic stacking.…”

Complex Self‐Sorting Systems

“…All these observations in the solid state determined by X-ray crystallography are consistent with their 1 H NMR spectra in CDCl 3 and we suggest that II-1, II-2, (±)-II-4a, and (±)-II-5 are isostructural in the solid state and in solution. 93 The X-ray crystal structures of II-1, II-2, (±)-II-4b, and (±)-II-5 also helps us to rationalize the behavior of these molecules within binary and higher order mixtures (vide infra). …”

Supramolekulare Chemie in Wasser

“…[69] Die Ion-Dipol-Wechselwirkung wird durch den Phosphatpuffer stark beeinflusst, dessen Metallkationen in wässrigen Medien mit den Gästen um die Bindung an die Sauerstoffatome konkurrieren. [69] Die Cucurbituril-Pinzette 32 dimerisiert in vielen Lö-sungsmitteln isostrukturell, [70] unter Beibehaltung des gleichen Assoziationsmotivs, sowohl in unpolaren aprotischen Medien wie Chloroform als auch in konkurrierenden, polaren protischen Lösungsmitteln wie Methanol und Wasser (Dimerisierung von 32 in D 2 O: K a = 3.6 10 4 m À1 ). Dieses Verhalten ist auf kompensierende kooperative Wasserstoffbrü-cken und p-p-Wechselwirkungen zurückzuführen.…”

“…In unpolaren Medien liefern Wasserstoffbrücken die Haupttriebkraft für die Dimerisierung, während in Wasser p-p-Wechselwirkungen vorherrschen. [70] Der kooperative windradförmige Chemosensor 33 enthält vier Guanidinium-Erkennungselemente, die zwei Dicarboxylate unterschiedlicher Größe kooperativ binden. [71] Der kooperative Effekt trägt zu den günstigen Bindungskonstanten für Dicarboxylate in Wasser bei und sorgt für eine hohe Selektivität gegenüber den Monocarboxylaten.…”