Halogen Bonding Ionophore for Potentiometric Iodide Sensing

Abstract

Iodide (I − ) is an essential micronutrient for thyroid function. Hence, rapid and portable sensing is important for I − quantification in food and biological samples. Herein, we report the first example of a halogen bonding (XB) tripodal ionophore (XB1) which is selective for the I − anion. NMR binding studies of XB1 and its H-triazole analog HB2 with I − demonstrated the dominant influence of XB interactions between the ionophore and the I − analyte. The phase boundary model was applied to formulate iodideselective electrodes with the ionophore XB1. The optimal electrode exhibited a near-Nernstian response of −51.9 mV per decade within a large dynamic range (10 −1 to 10 −6 M) and notably anti-Hofmeister selectivity for I − over thiocyanate (SCN − ), enabling the in situ determination of I − in complex samples. This work establishes XB as a viable supramolecular interaction in the potentiometric sensing of anions.

Halogen bonding and chalcogen bonding mediated sensing

“…As a result of these combined advantages, increasingly sophisticated and potent XB sensors have been developed, in particular in the last z5 years. This includes, for example, systems capable of anion sensing in increasingly competitive media, including pure water, 101,162,166 as well as continuous, real-time sensing systems. 71,72,131,171,172 These signicant advances in a comparably short amount of time attest to the enormous future potential of sigma-hole based sensors for real-life relevant applications and provide an excellent foundation for a broad range of research activities in sensor development and related applications as well as fundamental host-guest studies.…”

“…As a result of these combined advantages, increasingly sophisticated and potent XB sensors have been developed, in particular in the last ≈5 years. This includes, for example, systems capable of anion sensing in increasingly competitive media, including pure water, 101,162,166 as well as continuous, real-time sensing systems. 71,72,131,171,172…”

“…We envision a further exploration of recently developed or (in the context of XB/ChB-mediated recognition) underexplored methodologies such as impedimetric or (redox)capacitive methodologies, 71,162 chemiresistive 171,172 or potentiometric approaches. 166 In addition, other sensing principles are ripe for exploration in concert with sigma–hole interactions, such as indicator displacement assays (IDAs) 178 or the recently developed transporter–liposome–fluorophore (TLF) approach which relies on the quenching of a vesicle-encapsulated fluorophore by the analyte ion. 179 In the latter, a selectivity enhancement is achieved by use of a transmembrane ion transporter, such that only ions which can cross the vesicle membrane and quench the encapsulated fluorophore induce a response.…”

“…Specically, the rst, and thus far only, example of a XB ionophore 30.XB was reported by Lim, Goh and co-workers for the potentiometric sensing of iodide in pure water. 166 Initial 1 H NMR studies in d 6 -acetone indicated convergent XB mediated I À recognition with moderate 1 : 1 host-guest stoichiometric binding of K ¼ 260 M À1 . In contrast, I À binding of the HB analogue 30.HB was signicantly attenuated with K ¼ 2.75 M À1 .…”

“…Specifically, the first, and thus far only, example of a XB ionophore 30.XB was reported by Lim, Goh and co-workers for the potentiometric sensing of iodide in pure water. 166 …”