Efficient formation of [3]pseudorotaxane based on cooperative complexation of dibenzo-24-crown-8 with diphenylviologen axle

5-Oxo-7,7-Dimethyl-5,6,7,8-Tetrahydro-4-H-Chromene Bearing N, N-Dimethylaniline as Turn-Off Fluorescent Chemosensor for Picric Acid in Real Water Sample

We have synthesized a one-pot, three-component pyran-based fluorescence chemosensor using onion extract as a green catalyst. The confirmed structure of the 1:2 binding of receptor SPR-2-picric acid adduct revealed that the pyran-based receptor accommodated two guest picric acid molecules through non-covalent interactions. UV-Vis and fluorescence spectroscopy show high selectivity and sensitivity towards picric acid. The 1D/2D NMR and Job's plot analysis show the complexation and stoichiometric binding of the receptor SPR-2 with picric acid are 1:2. The 1H NMR spectral studies confirm that the formation of receptor SPR-2-picric acid adduct via weak hydrogen bonding. The cooperativity of the receptor SPR-2-picric acid adduct shows negative cooperativity due to the weak hydrogen bonding of receptor SPR-2 and picric acid. Further, the density functional theory (DFT) confirmed the molecular level interaction of the SPR-2 and receptor SPR-2-Picric acid adduct. The receptor was effectively used to assess picric acid concentrations in real water samples.

Monosulfonated dibenzo-24-crown-8 and its properties

In this paper, we describe a method for preparing a monosulfonated dibenzo-24-crown-8 ether, SDB24C8, by direct sulfonation of the parent crown (DB24C8). Since neutral DB24C8 readily interacts with cationic guests, permanently charged SDB24C8 is an advantageous candidate for future supramolecular applications. SDB24C8 can be isolated as a sulfonic acid to be used as it is or converted to a salt of choice. The crystallographic analysis provides the first known host-guest assembly with a DB24C8-based scaffold complexing hydronium and potassium cations. Supramolecular investigations of the interactions of this anionic macrocycle with alkali cations were also performed. According to the expectations, the introduction of the sulfonic group into the DB24C8 scaffold increases the affinities of the receptor. An unusual selectivity of SDB24C8 towards a sodium cation was also observed and further investigated with DFT calculations.

Chemically Induced Mismatch of Rings and Stations in [3]Rotaxanes

The mechanical interlocking of molecular components can lead to the appearance of novel and unconventional properties and processes, with potential relevance for applications in nanoscience, sensing, catalysis, and materials science. We describe a [3]rotaxane in which the number of recognition sites available on the axle component can be changed by acid–base inputs, encompassing cases in which this number is larger, equal to, or smaller than the number of interlocked macrocycles. These species exhibit very different properties and give rise to a unique network of acid–base reactions that leads to a fine pK_a tuning of chemically equivalent acidic sites. The rotaxane where only one station is available for two rings exhibits a rich coconformational dynamics, unveiled by an integrated experimental and computational approach. In this compound, the two crown ethers compete for the sole recognition site, but can also come together to share it, driven by the need to minimize free energy without evident inter-ring interactions.

Anion-Responsive Pseudo[3]rotaxane from a Difunctionalized Pillar[4]arene[1]quinone and a Bis-Imidazolium Cation

Synthesis of a new functionalized pillar[4]arene[1]quinone and its host-guest complexation with a bis-imidazolium dication was demonstrated. 1D/2D NMR spectroscopic analyses and high-resolution mass spectrometric analyses showed the formation of the pseudo[3]rotaxane assembly upon host-guest complexation. ¹H NMR titration experiments revealed the role of hydrogen bonding motifs in bringing positive cooperativity by comparing the binding constants for the host-guest complexation of pillar[4]arene[1]quinone with a bis-imidazolium guest. Anion-responsiveness of the pseudo[3]rotaxane assembly was also demonstrated.