Abstract
Among the 1,3,5-trisubstituted 2,4,6-triethylbenzenes bearing pyrazolyl groups, the
compounds with 3,5-dimethylpyrazolyl moieties were found to be effective receptors
for ammonium ions (NH4
+). The current study investigated the extent to which the incorporation of an additional
alkyl group in the 4-position of the pyrazole ring affects the binding properties
of the new compounds. 1H NMR spectroscopic titrations and investigations using isothermal titration calorimetry
revealed that this small structural variation leads to a significant increase in the
binding strength towards NH4
+ and also improves the binding preference for NH4
+ over K+. In addition to the studies in solution, crystalline complexes of the new triethyl-
and trimethylbenzene derivatives, bearing 3,4,5-trialkylpyrazolyl groups, with NH4
+PF6
− were obtained and analyzed in detail. It is noteworthy that two of the crystal structures
discussed in this work are characterized by the presence of two types of ammonium
complexes. Studies focusing on the development of new artificial ammonium receptors
are motivated, among other things, by the need for more selective ammonium sensors
than those based on the natural ionophore nonactin.
Key words
molecular recognition - ammonium receptors - selectivity - structure–binding activity
relationships
