Fluorimetric Detection of Phosphates in Water Using a Disassembly Approach: A Comparison of Fe^III‐, Zn^II‐, Mn^II‐ and Mn^III‐salen Complexes

Abstract

Details of the reaction sequence used for the fluorimetric detection of phosphates by disassembly of transition metal Schiff base complexes were investigated for [FeIII(salen)(H2O)]+, [ZnII(salen)], [MnII(salen)(H2O)2], and [MnIII(salen)(H2O)]+. The reactivity of these compounds towards phosphorus oxoanions of differing charge, number of donor atoms and steric hindrance was detected by UV/Vis and fluorescence spectroscopy in both aprotic organic and aqueous media. Selectivity of [FeIII(salen)(H2O)]+ towards pyrophosphate over all other tested phosphorus‐containing analytes was strongly supported. [ZnII(salen)] showed a faster reactivity but was much less selective. In contrast, [MnIII(salen)(H2O)]+ proved to be more stable than the iron complex but generally showed little reactivity towards phosphorus oxoanions. The influence of the charge of the central atom was investigated using the MnII analogue [MnII(salen)(H2O)2]. As expected, the reduced charge resulted in a reactivity comparable to the ZnII complex in organic solution but lead to hydrolysis of the complex in water. Finally, the reaction products of [FeIII(salen)(H2O)]+ with phosphates were characterized by IR spectroscopy and mass spectrometry, providing further insights into the reaction mechanism of the disassembly process.

“Covalent‐Disassembly”‐Based Approaches For Sensing Applications

“…It influences (i) stability, (ii) selectivity and (iii) controls the optical properties of the DB‐probe. Up to now, seven transition (Cr(III), Mn(II/III), Fe(III), Co(II), Ni(II), Zn(II) and Au(III)) and one main group metal ion (Al(III)) have been studied for the detection of polyoxophosphates with metal‐salen complexes [20,22,24–26] . All investigations suggest that Fe(III) is best suited in terms of stability, selectivity and sensitivity followed by Al(III) and Zn(II) (Figure 7A).…”

“…All investigations suggest that Fe(III) is best suited in terms of stability, selectivity and sensitivity followed by Al(III) and Zn(II) (Figure 7A). [22–26] …”

“…In this concept article, I highlight some general aspects of ABS and the “covalent‐assembly“ approach, but focus mainly on “covalent‐disassembly“‐based (DB) probes of metal‐complexes for analyte detection [21] . This approach has been recently successfully implemented for the selective detection of biological important polyoxophosphates with metal‐salen complexes [20–26] . Other examples of metal‐imine containing DB‐probes describe the selective detection of cyanide ions (CN − ), gasotransmitter H 2 S, L‐homocysteine (L‐HCy), L‐cysteine (L‐Cys) and changes in pH, both in vitro and cancer cells [27–32] …”

Induced fit activity-based sensing: a mechanistic study of pyrophosphate detection with a “flexible” Fe-salen complex

“…We assume that the latter is a Fe-pyrophosphate species in agreement with previous investigations (Scheme 1). 52 Results of the rate determining…”

A simple epoxy resin screen-printed paper-based analytical device for detection of phosphate in soil

“…Currently a variety of methods exist for phosphate analysis, including spectroscopy, 4,5 electrochemistry, 6,7 and fluorometry. 8,9 While these methods can provide high sensitivity and accuracy, they can also require expensive laboratory instruments, complicated laboratory procedures, and considerable amounts of chemicals. Microfluidic paper-based analytical device (μPAD), first introduced in 2007 by Martinez et al , 10 stands out as a method that is quick to implement, inexpensive, and portable.…”