Electrospray ionisation mass spectrometry molecular‐level structural characterisation of novel phenoxycarboxylic acid–oligo(3‐hydroxybutyrate) conjugates with potential agricultural applications

Abstract

Due to the low resistance of forms of pesticides to environmental conditions, agrochemicals frequently do not reach their objective, which may cause environmental pollution. The minimisation of the adverse effects of pesticides requires the development of a system for their long-term controlled release. In the present work, we report the synthesis and structural studies of novel controlled-release pesticide-oligo-3-hydroxybutyrate systems with potential agricultural applications. The novel controlled-release pesticide-oligo(3-hydroxybutyrate) systems were obtained via the anionic ring-opening oligomerisation of (R,S)-β-butyrolactone initiated by the potassium salt of selected pesticides. Electrospray ionisation mass spectrometry (ESI-MS(n)) analyses in positive-ion mode, supported by (1)H NMR results, were used for the structural characterisation of the obtained conjugates. The presence of the respective pesticides in an unchanged form associated with oligo-3-hydroxybutyrate chains was confirmed by ESI-MS/MS experiments performed for selected pesticide-oligo(3-hydroxybutyrate) ions and by the subsequent investigation of their fragmentation pathways. The structures of the resulting conjugates were established at the molecular level with the aid of ESI-MS(n). The presence of one and two chlorine atoms (derived from MCPA and 2,4-D pesticides) in the conjugates studied was confirmed by comparison of the calculated and experimental isotopic profiles for the selected ions of the respective conjugates. The fragmentation of the selected ions of the resulting conjugates confirmed that the respective pesticides are covalently bonded with oligo(3-hydroxybutyrate) through a hydrolysable ester bond. An analytical method has been developed for the characterisation of new pesticide-oligo(3-hydroxybutyrate) conjugates. A detailed NMR and MS structural characterisation of the designed controlled-release system of the pesticides was performed. These results are important in the analysis of designed biodegradable polymeric conjugates with potential agricultural applications.