Gas Phase Mass- and Mobility-Resolved Structures of Metalated Glyphosate Dimers

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Biochemistry

Background:

• Glyphosate is a widely used herbicide, and understanding its interactions with metal ions is crucial for environmental and biological studies.
• Metalated glyphosate species can form in various environments, influencing glyphosate's behavior and fate.
• Ion mobility-mass spectrometry (IM-MS) is a powerful technique for characterizing non-covalent complexes in the gas phase.

Purpose of the Study:

• To investigate the structures of metalated glyphosate dimers using advanced mass spectrometry techniques.
• To determine the gas-phase structures and bonding interactions of divalent metal cations (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Mn²⁺, Cu²⁺, Zn²⁺) with glyphosate dimers.
• To elucidate the influence of metal cation size and electronic properties on dimer structure and stability.

Main Methods:

• Electrospray ionization ion mobility-mass spectrometry (ESI-IM-MS) was employed to generate and separate metalated glyphosate dimers.
• Tandem ion mobility-infrared multiple photon dissociation-mass spectrometry (IM-IRMPD-MS) was used to obtain vibrational spectra of selected dimers.
• Computational methods, including CREST-CENSO algorithms and DFT optimization, were used to predict and confirm gas-phase structures.

Main Results:

• Metalated glyphosate dimers ([M(glyphosate)(glyphosate-H)]⁺) exhibited a single mobility-resolved isomer with collision cross sections (CCS) between 165–175 Ų.
• Infrared spectroscopy revealed characteristic O-H stretching frequencies, confirming the presence of both carboxylate and phosphonate groups.
• Computational and experimental data confirmed a common structural motif: the metal cation is bidentately coordinated to the phosphonate group of deprotonated glyphosate, with neutral glyphosate adopting an octahedral coordination, and dimer size increases with cation size, except for Cu²⁺.

Conclusions:

• The study successfully characterized the gas-phase structures of various metalated glyphosate dimers, revealing a conserved structural framework.
• The phosphonate group of glyphosate is consistently deprotonated and involved in metal coordination, with the neutral glyphosate molecule wrapping the cation.
• The unique structural deviation observed for Cu²⁺ is attributed to its specific coordination preferences, highlighting the nuanced role of metal identity in complex formation.