Abstract
hosphates dominate the living world as being an essential part of building blocks of life and also widely used in agricultural and food industries. More importantly, almost 90 % of the world’s mined phosphate reserves are used as fertilizers and food additives. Looking at this increased phosphates’ usage and their potential deteriorating effects on environment and human health, this thesis addresses the growing need for efficient chemical sensors for the selective detection of phosphates.
After an introduction in the field (chapter 1), the second chapter of the thesis describes the selective and sensitive detection of pyrophosphate (PPi) with metal-salen complexes following a disassembly approach. For this purpose, a total of 10 different FeIII- and ZnII-based salen complexes were synthesized. Out of this small library, a novel FeIII-salen-based probe Fe19 with an optimized 3‐chloro‐5‐formyl‐4‐hydroxybenzenesulf onic acid signaling unit and a 1,2‐ropanediamine diamine backbone is most promising for PPi detection.
The probe disassembles selectively in the presence of the target analyte into its constituents resulting in a 3.5-fold turn-on fluorometric response. The probe exhibits a limit of detection as low as 1.50 µM and showed a 155-times higher selectively over adenosine triphosphate ATP), in comparison to a previously reported prototype. Moreover, detection of PPi alias 450 in foodstuff by Fe19 ha been demonstrated in a proof-of-concept study. etailed kinetic studies suggest in the third chapter that the aqua form of square pyramidal Fe19 recognizes and binds selectively HP2O73- over all other PPi species. Supported by omputational studies, it is proposed that the monodentate pyrophosphate switches to a “bidentate” coordination mode and the FeIII-complex disassembles subsequently into its subunits. It is assumed that the elusive octahedral intermediate is stabilized by additional hydrogen bonding. This behaviour explains nicely the outstanding selectivity of the probe ver other analytes and is reminiscent to the recognition and binding of substrates by enzymes (“induced fit model”). In the fourth chapter of the thesis, a potentially toxic agriculture-based herbicide; glyphosate (GlyP) is targeted via solid phase colorimetric approach. Explicitly, a promising metal-based indicator system (PV-(CuII)2) was selected after a collective screening approach from a pool of indicators and metal ions. PV-(CuII)2 was then immobilized on a solid phase to constitute a fast, cheap and on-site colorimetric test kit for selective detection of GlyP. The test-kit was also tested successfully for its applicability in spiked tap water samples and the levels of GlyP were semi-quantitively detected by naked-eye and via a smartphone analysis.
Yadav, Prerna