Synthesis and Evaluation of a Bis(crown ether) Ionophore with a Conformationally Constrained Bridge in Ion-Selective Electrodes

Abstract

There has been a recent rapid growth in the development of chemical sensors because of the demand for simple analytical techniques that can provide continuous monitoring of analytes in a variety of matrices. [1][2][3] In the area of membrane-based ion-selective electrodes (ISEs), special emphasis has been placed on the composition of the membrane phase and on the development of new ionophores, aiming at enhancing the potentiometric response characteristics (e.g., selectivity, sensitivity, linear range and lifetime) of the ISEs.The majority of cation-selective electrodes are based on neutral carrier ionophores. In particular, the antibiotic valinomycin has proved to be an excellent ionophore in potassium-selective liquid-polymeric membrane electrodes. 4 In addition to valinomycin, several other ionophores have been used in the preparation of potassium ISEs. 5-8 Among these, bis(crown ethers) with two 15-crown-5 ethers attached via a bridge [7][8][9][10] exhibit a favorable potassium binding over sodium due to the formation of sandwich-type complexes with potassium.9,10 The observed selectivities of ISEs prepared with bis(15-crown-5 ethers) are sometimes comparable to those obtained by using valinomycin as the ionophore. 5Bis(crown ethers) can be prepared with functional groups that allow their covalent attachment on polymer matrices. This is an advantage when designing ISEs with extended lifetimes because covalent attachment of the ionophore precludes its leaching from the polymer membrane phase to the aqueous phase. 11-13 Direct attachment of a bis(crown ether) to a polymer backbone, however, may restrict the free movement of the ionophore or pose serious steric problems with the backbone of the polymer, which could lead to worsening of the response.7,14 A long flexible chain connecting the bis(crown ether) and the polymer could provide a solution to this problem. In this paper, we report on the synthesis and evaluation of a new bis(crown ether) (BCE) ionophore with a long and flexible side chain, which can serve as a precursor for the chemical immobilization to a polymer backbone. Another feature of the designed ionophore is the incorporation of a conformationally constrained bridge (an isophthalic acid derivative) between the two crown ether moieties. This isophthalic acid derivative allows each of the crown ether macrocycles to be in a parallel alignment with each other during complexation, which helps maximize their interaction with the analyte ion. ExperimentalReagents 5-Nitroisophthalic acid, 4-nitrobenzo-15-crown-5, 10% Pd/C, 97% thionyl chloride, triethylamine, aluminum oxide (neutral, Brockmann I), and stearoyl chloride were all obtained from Aldrich (Milwaukee, WI). Selectophore-grade tetrahydrofuran (THF), 2-nitrophenyloctyl ether (NPOE), tris(2-ethylhexyl)phosphate (TOP), bis(2-ethylhexyl) sebacate (DOS), bis(1- A new bis(crown ether) ionophore containing two benzo-15-crown-5 moieties connected with each other via a conformationally constrained bridge attached to a C18-lipophilic side chain was desig...

Ionophore-based ion-selective potentiometric and optical sensors

“…For example, 12-crown-4 demonstrates preferential binding to Li + , which has an ionic diameter of 0.68 Å, while 15-crown-5 tends toward complexation with K + (1.33 Å) [4]. While the size-fit description often works pretty well with regards to describing observed ionophore selectivity, there are examples in the literature where selectivity seems to be due to the formation of a stable and strong sandwich complex with an ion:ionophore ratio of [4]arene compounds, c a Na + -selective hemispherand 1:2 (these results have led to the development of successfully implemented bis-crown ionophores) [111,112].…”

Coated Wire Silver-Ion Selective Electrode Based on a N,N′-Bis(2-thienylmethylene)-1,2-diaminobenzene

“…[1][2][3][4][5][6][7] Thus, the influences of some important features of PVC membrane such as the membrane composition, nature and amount of plasticizer and amount of oleic acid as lipophilic additives on the potential response of the silver electrodes were investigated; the results are summarized in Table 1. Since the nature of plasticizer influences the dielectric constant of the membrane phase and the mobility of the ionophore molecules and its complex, 43,44 it is expected to play an important role in determining the characteristics of the ion-selective electrode (ISE).…”

“…1,2 The introduction of new ion selective electrodes (ISEs) has promoted fundamental developments in potentiometry. [3][4][5][6][7] Potentiometric detectors based on ISEs offer advantages such as selectivity, sensitivity, good precision, simplicity, wide linear concentration range and long lifetime. The key ingredient of poly(vinyl chloride) (PVC) membrane electrodes is the incorporated ionophore, which defines the selectivity of the electrodes via selective complex formation with the cation of interest.…”

A Novel Coated Graphite Rod Th(IV) Ion Selective Electrode Based On Thorium Oxinate Complex and Its Application

“…The field of ion-selective electrodes has been growing fast since the past tow decades [1][2][3][4][5][6][7][8]. These have been the subject of interest for analytical chemists as they provide accurate, rapid and low cost method of analysis.…”