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Supramolecular Chemistry of Diamondoid Ammonium Salts

Research on macrocyclic host molecules capable of encapsulating small guest molecules can inspire supramolecular architectures that mimic biological systems and can have useful technological applications.1 We have recently shown that functionalized diamondoid ammonium salts are suitable guests for cucurbituril (CB[n]) hosts in aqueous environment. Especially strong binding was found for the complex of 4, 9-diammonium diamantane derivative with CB[7], having an attomolar dissociation constant that rivals the interaction between avidin-biotin.2 As a continuation of our work, we explored complexation of diamondoid ammonium salts with β and γ cyclodextrins (CDs) in water (Figure 1). The key step in the synthesis of these permethylated diamondoid ammonium salts was selective functionalization of diamantane scaffold via nitroxylation and subsequent hydrolysis3 that was optimized in detail in the scope of this study. When assessing the binding strength, we considered the size of the diamondoid salts, substitution type and number of functional groups as well as the cyclodextrin cavity size. Equilibrium constants and other thermodynamic parameters for the complexation of diamondoid ammonium salts with CDs were determined by ITC, conductometric and/or 1H NMR titrations. Additional NMR spectroscopic techniques (1H-1H NOESY, 1H DOSY) were employed to elucidate specific interactions of guest encapsulated within host molecules, along with the corresponding computational analysis.

Cyclodextrins ; Diamondoid Ammonium Salts ; Supramolecular Chemistry

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