Molecular Tweezer and Clip in Aqueous Solution: Unexpected Self-Assembly, Powerful Host−Guest Complex Formation, Quantum Chemical ¹H NMR Shift Calculation

Abstract

The broad signals in D 2 O could not be assigned by C,H-COSY. Therefore, the assignment of the signals was made by comparison with the signals in CD 3 OD. * The broad signals in D 2 O could not be assigned by C,H-COSY. Therefore, the assignment of the signals was made by comparison with the signals in CD 3 OD.

Study of the self-association of molecular tweezers bearing two different arms: influence of the stereoelectronic effects of the arm substituents

“…These results validated the selection of H-5 as self-assembly marker: its inclusion into the tweezer resulted in a large shielding (above 0.25 ppm) evidencing the mode B while an external position lead to a weaker shielding indicating the mode A, as already observed with naphthalene derivatives by Klärner [24] in D 2 O. We will focus mainly on this proton for the further study of compounds 2-5.…”

Molecular Tweezers with Varying Anions: A Comparative Study

“…Particularly, the chemical 1 H NMR shifts assigned to the protons attached to the tips of the terminal benzene rings are substantially upfield-shifted (toward smaller δ values) compared to the values measured in CD 3 OD, whereas the 1 H NMR spectra of the phosphonate- and carboxylate-substituted tweezers 1b and 1d are not significantly concentration-dependent. This finding indicates the formation of self-assembled dimers of the tweezers 1a and 1c in aqueous solution comparable to the molecular tweezers bearing an extended central naphthalene spacer unit instead of the benzene bridge. The dimerization constants, K dim , and maximum dimerization-induced shifts of the 1 H NMR signals of the protons of the tweezers 1a and 1c (Δδ max ) were determined by dilution NMR titration experiments (Table ).…”

Experimental Binding Energies in Supramolecular Complexes

“…Large hydrophobic binding contributions can also occur in the absence of closed cavities, as can be seen for some molecular clips and tweezers. 30,419,626,628−631 For instance, the affinity of a negatively charged clip (Figure 69a) for the cationic aromatic guest N-methyl nicotinamide (NMNA) is higher in water (K = 9 × 10 4 M −1 ) than in methanol (1700 M −1 ), 626 although the electrostatic attraction between oppositely charged species is weaker in the more polar medium. For NAD + as a guest (K = 8800 M −1 ), ΔH = −30.5 kJ/mol and −TΔS = 8.0 kJ/mol were obtained in water, 30 which is consistent with the high-energy water release model.…”