Do Dibenzo[22–30]crown Ethers Bind Secondary Ammonium Ions to Form Pseudorotaxanes?

Abstract

In this study, we synthesized dibenzo[22–30]crown ethers and dumbbell-like secondary ammonium salts having stoppers of varying bulk. These crown ethers formed pseudorotaxanes with the ammonium ions in solution and in the gas phase, as evidenced using NMR spectroscopy and MS/MS spectrometry, respectively. The association constants in solution were obtained through regulation of the association and dissociation rates by varying the nature of the stopper groups of the dumbbell-like ammonium ions. The [25]- and [26]crown ether/isopropylphenyl group, the [27]- and [30]crown ether/tert-butylphenyl group, and the [22]- and [23]crown ether/furyl group were matched pairs. 1H NMR spectra of mixtures (CDCl3/CD3CN) of the crown ethers and their matched ammonium salts indicated the presence of three sets of signals in solution: those of the crown ether, the ammonium salt, and their pseudorotaxane. Integration of pertinent signals allowed the association constants of pseudorotaxanes to be determined readily. Among the [22–30]crown ethers, the highest value of the association constant was that for the [24]crown ether/dibenzylammonium ion system; the [25–30]crown ether/ammonium ion systems exhibited moderate values of their association constants [Kexp=35–114 M−1 when using (ArCH2)2NH2+PF6− as the ammonium salt at 27 °C; Kexp=21 M−1 when using (ArCH2)2NH2+TsO− at 27 °C]. The [22]- and [23]crown ethers interacted weakly [Kexp=6–14 M−1 when using (ArCH2)2NH2+TsO− at 27 °C].

Synthesis of Azulene Derivatives That Have an Azathiacrown Ether Moiety and Their Selective Color Reaction Towards Silver Ions

“…These results suggest that the binding of Ag + to 4 is stronger than that of Na + , Ca 2 + , Zn 2 + , or Pb 2 + to 4. [14] The 1:1 binding stoichiometry between 4 and Ag + ions is also shown by a Job plot experiment (see Figure S9 in the Supporting Information), [15] and the binding constant in acetone is estimated to be 2.0 10 5 m À1 based on nonlinear least-squares curve fitting. [16] As mentioned above, contrary to our expectation that Hg 2 + would provide a selective color response in 4 and 5, both compounds were highly selective for Ag + ions, which prompted us to examine the binding strength of 4 with Ag to compare the collision-activated dissociation (CAD) mass spectra of the [4·Ag]…”

“…[14] The CAD mass spectrum of [4·Ag] + ions has a prominent precursor ion peak at m/z = 484.0545, whereas [4·Hg 2 + ·ace-tone-H] + ions produced a prominent fragment ion peak at m/z = 377.1467, which corresponds to 4 + , and a small precursor ion peak at m/z = 636.1541 at the same collision energy (15 eV) (Figure 4) ion color selectivity seems to be ascribed to the relatively strong binding of Ag + ions to the azathiacrown ether moiety in 4 and 5, and not to p-cation interactions from the above-mentioned calculated structures of the complex. It is noteworthy that there is little p-cation interaction, although it is known that Ag + and Tl + ions have specially affinity for the p-ligand system.…”

π-Stacking Stopper-Macrocycle Stabilized Dynamically Interlocked [2]Rotaxanes

“…They have been applied in the designs of molecular machinery [ 5 , 6 , 7 , 8 ] and molecular sensing [ 9 , 10 , 11 , 12 , 13 , 14 ]. For the [ n ]rotaxanes, templated-direct syntheses using secondary dialkylammonium (R 2 NH 2 + ) ions are involved in threading followed by stoppering [ 15 ], slippage [ 16 , 17 , 18 , 19 ] and clipping approaches [ 20 , 21 ] Various macrocycles, such as dibenzo[24]crown-8 (DB24C8) and benzo[21]crown-7 (B21C7), can be threaded through by the dialkylammonium (R 2 NH 2 + ) ions with sufficiently high binding constant [ 22 , 23 , 24 ].…”

Formation of [2]- and [3]Rotaxanes through Bridging under Kinetic and Thermodynamic Control

“…Next, we examined the formation of pseudo[2]­rotaxanes from bis-crown ethers 2 and dibenzylammonium salts 3 . In view of the ring sizes of these bis-crown ethers and the bulk of the terminal units of the dibenzylammonium ions, we used bis-[24]­crown-8 ( 2a )/phenyl group ( 3-H ) and bis-[27]­crown-9 ( 2b )/3,5-dimethylphenyl group ( 3-Me ) as matching pairs for NMR titration experiments because association and dissociation of the resulting pseudorotaxanes would be slow on the NMR time scale …”