Squaramide-based tripodal ionophores for potentiometric sulfate-selective sensors with high selectivity

Abstract

A class of squaramide-based tripodal molecules was employed as new ionophores for highly sensitive and selective sulfate-selective sensors. Compared with the reported tripodal ionophore with urea, squaramide groups as superior hydrogen bonding donor were introduced into the tripodal structure to obtain new ionophores leading to better electrode performance. Three derivatives with unsubstituted (I), p-carbon trifluoride (II), and p-nitro (III) phenyl groups were attached to squaramide groups for the optimization of ionophore based sensors. Electron withdrawing p-nitrophenyl groups gave a greater enhancement of the hydrogen bond donor ability of squaramide so that Ionophore III was chosen as the best candidate for sulfate ion recognition. Such a membrane with 30 mol% TDMACl exhibited a Nernstian slope of -30.2 mV per decade to sulfate ions with a linear range from 1 μM to 100 mM in potentiometric measurement. The selectivity coefficients of the proposed sensor over H2PO4(-), Cl(-), Br(-), NO3(-), SCN(-), I(-) and ClO4(-) were -4.3, -3.4, -2.5, -0.6, +3.1, +3.4 and +5.9, respectively, which were much better than the existing sulfate-selective sensors. The new sensors with high selectivity were successfully applied for the quantification of sulfate in cell lysates and drinking water with good recoveries.

Tripodal Squaramide Derivative as a Neutral Chloride Ionophore for Whole Blood and Sweat Chloride Measurement

“…As shown in Figure B, compound 1–3 exhibited Nernstian response to Cl − . In our previous work the compound 1 and 2 showed enhanced selectivity toward oxoanions such as sulphate and phosphate . In contrast the ionophore 3 has good chloride selectivity over these oxoanions (Figure B).…”

“…There are two common molecular scaffold widely used to create tripodal synthetic receptors, that are flexible tris(2‐aminoethyl)amine (tren) and rigid 1,3,5‐tris(aminomethyl)‐2,4,6‐triethylbenzene . In our recent work the tripodal squaramides with nitro group on phenyl rings were found to have enhanced selectivity towards SO 4 2− and phosphate ion as well . For the compound 3 the chloride response is superior to oxoanions such as sulphate, phosphate and bicarbonate as shown in Figure C.…”

“…The inferior responses of compounds 1 and 2 is probably due to the interferences form phosphate ion in the presence in the sample. It is known that tripodal conjugation provides 3 D geometry for anion binding, especially for tetrahedral inorganic oxoanions, such as sulfate and phosphate . There are two common molecular scaffold widely used to create tripodal synthetic receptors, that are flexible tris(2‐aminoethyl)amine (tren) and rigid 1,3,5‐tris(aminomethyl)‐2,4,6‐triethylbenzene .…”

Evaluation of interfacial sulfate complexation by a bis-thiourea ionophore at water-organic interfaces using microelectrochemistry and high resolution mass spectrometry

“…A variety of ionophores have been designed for sulfate recognition in ISE membranes, e.g. based on guanidinium [12], ferroceneamide [13], polyazacycloalkane [14], tris-urea [15], bis-thiourea [16,17], and squaramide [18,19] recognition groups. The main feature of these materials is the multiple (≥2) binding sites available to interact with sulfate via H-bonding.…”

“…For example, in a potentiometric sensor the bis-thiourea ionophore N- [4-[4-[(anilinocarbothioyl) amino]benzyl]phenyl]-N-phenylthiourea gave a LOD of 0.2 x 10 -6 M (19 ng ml -1 ) [16], but selectivity over other anions was an issue. Receptors based on a tripodal squaramide structure presented a reasonable LOD (1 x 10 -6 M; 96 ng ml -1 ) with the advantage of improved affinity towards sulfate over chloride (logarithm of selectivity coefficient: -3.4) [18].…”