Tetrazoles are potent anion recognition elements in a variety of structural contexts
Date
2015-05-01
Authors
Pinter, Thomas
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Abstract
In efforts to expand the limited amount of functional groups available for anion
recognition, a series of highly acidic, strongly hydrogen bond-donating groups were
envisaged as suitable candidates. These included the thoroughly studied N-aryl
sulfonamides along with the less utilized N-acyl sulfonamides and tetrazoles. These
groups were affixed to a well-understood supramolecular platform in calix[4]arene and
their binding affinities for various halides and oxyanions probed. It was found that
although in its least energetically favourable conformation that is orthogonal to the aryl
group to which it was bound, the tetrazole proved a superior anion-binding element.
Noting that tetrazoles prefer co-planarity with aryl neighbours, a series of
pyrrolyl-tetrazole anion binding compounds were prepared, first a simple bidentate
pyrrolyl-tetrazole which when tested for anion binding affinity demonstrated some of the
strongest binding with anions for a bidentate compound ever observed, especially
chloride.
It was then conceived to hybridize this new binding motif with the well-known
amidopyrrole moiety and two new tetrazolyl-amidopyrroles were constructed. When
compared to an ester-functionalized pyrrolyl-tetrazole, binding strength with halides was
not much different, leading to the postulation that the amide N-H may just be a spectator
in the binding event, and the electron-withdrawing nature of the adjacent carbonyl was
what led to the binding potency.
Nonetheless, a new class of diversifiable anion binders with superior strength to
analogous amidopyrroles has been constructed and could perhaps be used in a variety of
functional applications.
Description
Keywords
tetrazoles, anion-binding