Complexation of 1,4-Bis(pyridinium)butanes by Negatively Charged Carboxylatopillar[5]arene

Abstract

The binding behavior of substituted 1,4-bis(pyridinium)butane derivatives (X-Py(CH(2))(4)Py-X, X = H, 2-methyl, 3-methyl, 4-methyl, 2,6-dimethyl, 4-pyridyl, and 4-COOEthyl) 1(2+)-7(2+), with negatively charged carboxylatopillar[5]arene (CP5A) has been comprehensively investigated by (1)H NMR and 2D ROESY and UV absorption and fluorescence spectroscopy in aqueous phosphate buffer solution (pH 7.2). The results indicated that the position of the substituents attached on pyridinium ring dramatically affects the association constants and binding modes. 3- and 4-Substituted guests (1(2+), 3(2+), 4(2+), 6(2+), 7(2+)) form [2]pseudorotaxane geometries with CP5A host, giving very large association constants (>10(5) M(-1)), while 2,6-dimethyl-substituted 5(2+) forms external complex with relatively small K(a) values [(2.4 ± 0.3) × 10(3) M(-1)] because the 2,6-dimethylpyridinium unit is too bulky to thread the host cavity. Both of the binding geometries mentioned above are observed for 2(2+), having one methyl group in the 2-position of pyridinium. Typically, the association constant of [2]pseudorotaxane 1(2+)⊂CP5A exceeds 10(6) M(-1) in water, which is significantly higher than those of previously reported analogues in organic solvents. The remarkably improved complexation of bis(pyridinium) guests by the anionic host was due to electrostatic attraction forces and hydrophobic interactions.

Host–Guest Chemistry of a Water‐Soluble Pillar[5]arene: Evidence for an Ionic‐Exchange Recognition Process and Different Complexation Modes

“…[5][6][7] Pillararenes can selectively recognize guest molecules in organic solvents, mostly due to both an electron-rich cavity [8][9][10] and the formation of CÀH···p interactions, but also, and more interestingly, in aqueous media. [11][12][13][14][15] The water solubility of this type of macrocycle can be achieved, for example, by the introduction of carboxylic [11] or ammonium groups [15] at the macrocycle rims. Host-guest studies in aqueous solution are always desirable because this is where most biological processes occur, but on the other hand, it introduces a new potential guest into the solution: The counter ion.…”

A Self-Assembled AMF-Responsive Nanoplatform Based on Pillar[5]arene and Superparamagnetic Nanoparticles for Controlled Release of Doxorubicin

“…The synthesis of water-soluble ammonium carboxylatesubstituted pillar [5]arene salt (CP [5]A) was carried out in five steps following a procedure described in the literature [51][52][53] with modifications (Scheme S1, Supplementary Information…”

Carboxylato-pillar[6]arene-based fluorescent indicator displacement assays for the recognition of monoamine neurotransmitters

“…[21][22][23][24][25] In particular, water soluble pillararenes are prosperous hosts for various guests of biological importance. [26][27][28] Carboxylato-pillar [5]arene forms complexes with viologens (paraquat), 29,30 various amines and basic amino acids 31 that can be exploited to compile FID assays for these analytes. [32][33][34] Cationic, ammonium-containing pillar [5] arene was used as receptor in a FID sensor for various phenols.…”