Theoretical insight into the stabilization of triazole fungicides via their interactions with dications

• Interactions of tebuconazole with Zn and Cd were studied and compared.
• Interactions: metal–phenyl π electrons, 2 N of the triazole ring, hydroxyl group.
• High stability of the bond: oxygen (deprotonated OH group)–central metal ion.
• High stability of the singly-charged deprotonated tebuconazole complexes.

The frequent use of pesticides in crop protection leads to their accumulation in soil as well as to the formation of their complexes with ions present in soil. The formation of such complexes can change the mobility of both the pesticides and the ions as well as their ability to penetrate biological membranes and enter biota. The problem of triazole-fungicide complexation with dications is demonstrated on the case of zinc and cadmium ions (M). Complexation with tebuconazole (1) has been studied using electrospray ionization mass spectrometry and quantum mechanical DFT-based computations. These experiments have revealed that the deprotonation of 1 leads to the stabilization of the complexes formed, which has been confirmed by our computations. In terms of stability, two types of complexes have been described: (i) a less stable complex (approx. 125 kJ mol−1) with neutral 1 [M(1)2,3,4]2+ and [MCl(1)1,2]+, and (ii) a more stable complex (approx. 220 kJ mol−1) with deprotonated 1 [M(1)n(1-H)]+ (n = 0,1). The high stability of the complexes with deprotonated 1 is given by their stabilization via a metal interaction with the oxygen atom or phenyl ring. The structure of [M(1-H)]+ is very compact when compared to the structure of parent 1.

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