EMAIL THIS PAGE TO A FRIEND

Chemistry, an Asian journal

A series of amino acid functionalized tripodal hexaamide anion receptors: ion-pair-assisted capped-cleft formation by a pentafluorophenyl-functionalized amide.


PMID 22829307

Abstract

A new series of tris(2-aminoethyl)amine (tren)-based L-alanine amino acid backboned tripodal hexaamide receptors (L1-L5) with various attached moieties based on electron-withdrawing fluoro groups and lipophilicity have been synthesized and characterized. Detailed binding studies of L1-L5 with different anions, such as halides (F(-), Cl(-), Br(-), and I(-)) and oxyanions (AcO(-), BzO(-) (Bz=benzoyl), NO(3)(-), H(2)PO(4)(-), and HSO(4)(-)), have been carried out by isothermal titration calorimetric (ITC) experiments in acetonitrile/dimethylsulfoxide (99.5:0.5 v/v) at 298 K. ITC titration experiments have clearly shown that receptors L1-L4 invariably form 1:1 complexes with Cl(-), AcO(-), BzO(-), and HSO(4)(-), whereas L5 forms a 1:1 complex only with AcO(-). In the case of Br(-), I(-), and NO(3)(-), no appreciable heat change is observed owing to weak interactions between these anions and receptors; this is further confirmed by (1)H NMR spectroscopy. The ITC binding studies of F(-) and H(2) PO(4)(-) do not fit well for a 1:1 binding model. Furthermore, ITC binding studies also revealed slightly higher selectivity of this series of receptors towards AcO(-) over Cl(-), BzO(-), and HSO(4)(-). Solid-state structural evidence for the recognition of Cl(-) by this new category of receptor was confirmed by single-crystal X-ray structural analysis of the complex of tetrabutylammonium chloride (TBACl) and L1. Single-crystal X-ray diffraction clearly showed that the pentafluorophenyl-functionalized amide receptor (L1) encapsulated Cl(-) in its cavity by hydrogen bonds from amides, and the cavity of L1 was capped with a TBA cation through hydrogen bonding and ion-pair interactions to form a capped-cleft orientation. To understand the role of the cationic counterpart in solution-state Cl(-) binding processes with this series of receptors (L1-L4), a detailed Cl(-) binding study was carried out with three different tetraalkylammonium (Me(4) N(+), Et(4) N(+), and Bu(4) N(+)) salts of Cl(-). The binding affinities of these receptors with different tetralkylammonium salts of Cl(-) gave binding constants with the TBA cation in the following order: butyl>ethyl>methyl. This study further supports the role of the TBA countercation in ion-pair recognition by this series of receptors.

Related Materials

Product #

Image

Description

Molecular Formula

Add to Cart

651664
Tetrabutylammonium azide
C16H36N4
86853
Tetrabutylammonium bisulfate, for ion pair chromatography, ≥99.0%
C16H37NO4S
86868
Tetrabutylammonium bisulfate, puriss., ≥99.0% (T)
C16H37NO4S
72453
Tetrabutylammonium bisulfate solution, ~55% in H2O
C16H37NO4S
98479
Tetrabutylammonium bisulfate solution, for ion pair chromatography, concentrate, ampule
C16H37NO4S
86857
Tetrabutylammonium bromide, for ion pair chromatography, ≥99.0%
C16H36BrN
193119
Tetrabutylammonium bromide, ReagentPlus®, ≥99.0%
C16H36BrN
462144
Tetrabutylammonium bromide solution, 50 wt. % in H2O
C16H36BrN
86852
Tetrabutylammonium chloride, for ion pair chromatography, ≥99.0%
C16H36ClN
86870
Tetrabutylammonium chloride, ≥97.0% (NT)
C16H36ClN
86862
Tetrabutylammonium chloride solution, for ion pair chromatography, concentrate, ampule
C16H36ClN
358665
Tetrabutylammonium cyanide, 95%
C17H36N2
79989
Tetrabutylammonium cyanide, technical, ≥80%
C17H36N2
216143
Tetrabutylammonium fluoride solution, 1.0 M in THF
C16H36FN
361399
Tetrabutylammonium fluoride solution, 75 wt. % in H2O
C16H36FN
155837
Tetrabutylammonium hydrogensulfate, 97%
C16H37NO4S
86854
Tetrabutylammonium hydroxide solution, ~40% in water, for ion chromatography
C16H37NO
86880
Tetrabutylammonium hydroxide solution, technical, ~40% in H2O (~1.5 M)
C16H37NO
86903
Tetrabutylammonium iodide, for ion pair chromatography, ≥99.0%
C16H36IN
86912
Tetrabutylammonium iodide, for electrochemical analysis, ≥99.0%
C16H36IN
86890
Tetrabutylammonium iodide, ≥99.0% (AT)
C16H36IN
140775
Tetrabutylammonium iodide, reagent grade, 98%
C16H36IN
359173
Tetrabutylammonium nitrate, 97%
C16H36N2O3
86893
Tetrabutylammonium perchlorate, for electrochemical analysis, ≥99.0%
C16H36ClNO4
86885
Tetrabutylammonium perchlorate, ≥98.0% (T)
C16H36ClNO4
86833
Tetrabutylammonium phosphate monobasic, puriss., ≥99.0% (T)
C16H38NO4P
268097
Tetrabutylammonium phosphate monobasic, 97%
C16H38NO4P
268100
Tetrabutylammonium phosphate monobasic solution, 1.0 M in H2O
C16H38NO4P
86899
Tetrabutylammonium phosphate monobasic solution, for ion pair chromatography, concentrate, ampule
C16H38NO4P