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IR and EXAFS spectroscopic studies of glyphosate protonation and copper(II) complexes of glyphosate in aqueous solution

Sheals, J.; Persson, Per LU and Hedman, B. (2001) In Inorganic Chemistry 40. p.4302-4309
Abstract
The varying degrees of protonation of N-(phosphonomethyl)glycine (PMG, glyphosate) were investigated with infrared JR) spectroscopy and ab initio frequency calculations. The zwitterionic nature of PMG in solution was confirmed, and intramolecular hydrogen bonding was identified. Successive protonation of the PMG molecule follows the order amine, phosphonate, carboxylate. Intramolecular hydrogen bonding is indicated to exist at all stages of protonation: between both RCO2- and RNH2+ and RPO32- and RNH2+ in HL2- (where L represents the ligand PMG); between RCO2- and RNH2+ in H2L-; predominantly between RPO32- and RNH2+ in H3L. There are strong indications that the zwitterion is intact throughout the pH range investigated. Results from IR and... (More)
The varying degrees of protonation of N-(phosphonomethyl)glycine (PMG, glyphosate) were investigated with infrared JR) spectroscopy and ab initio frequency calculations. The zwitterionic nature of PMG in solution was confirmed, and intramolecular hydrogen bonding was identified. Successive protonation of the PMG molecule follows the order amine, phosphonate, carboxylate. Intramolecular hydrogen bonding is indicated to exist at all stages of protonation: between both RCO2- and RNH2+ and RPO32- and RNH2+ in HL2- (where L represents the ligand PMG); between RCO2- and RNH2+ in H2L-; predominantly between RPO32- and RNH2+ in H3L. There are strong indications that the zwitterion is intact throughout the pH range investigated. Results from IR and extended X-ray absorption fine structure (EXAFS) spectroscopies provide new evidence for structures of N-(phosphonomethyl)glycinecopper(II) complexes. The structures of 1:1 complexes, CuL- and CuHL, are essentially the same, differing only in protonation of the phosphonate group. Copper(II) lies at the center of a Jahn-Teller distorted octahedron with all three donor groups (amine, carboxylate, phosphonate) of PMG chelating with copper(Ii) to form two five-membered chelate rings oriented in the equatorial plane, EXAFS indicates that oxygen (most. likely a water molecule) is a fourth ligand, which would thus occupy the fourth corner in the equatorial plane of the elongated octahedron. CuL24- most probably forms an isomeric mixture in solution, and there are indications that this mixture is dominated by complexes where two PMG ligands are bound to copper(II) via equatorial and axial positions, with both phosphonate and carboxylate donor groups responsible for chelation at axial positions. (Less)
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author
publishing date
type
Contribution to journal
publication status
published
subject
in
Inorganic Chemistry
volume
40
pages
4302 - 4309
publisher
The American Chemical Society
external identifiers
  • scopus:0035854888
ISSN
1520-510X
DOI
10.1021/ic000849g
language
English
LU publication?
no
id
cbbe1ba3-235f-46b5-aeb6-378b9525d6d0 (old id 4332580)
date added to LUP
2014-03-04 09:42:46
date last changed
2018-07-15 03:27:26
@article{cbbe1ba3-235f-46b5-aeb6-378b9525d6d0,
  abstract     = {The varying degrees of protonation of N-(phosphonomethyl)glycine (PMG, glyphosate) were investigated with infrared JR) spectroscopy and ab initio frequency calculations. The zwitterionic nature of PMG in solution was confirmed, and intramolecular hydrogen bonding was identified. Successive protonation of the PMG molecule follows the order amine, phosphonate, carboxylate. Intramolecular hydrogen bonding is indicated to exist at all stages of protonation: between both RCO2- and RNH2+ and RPO32- and RNH2+ in HL2- (where L represents the ligand PMG); between RCO2- and RNH2+ in H2L-; predominantly between RPO32- and RNH2+ in H3L. There are strong indications that the zwitterion is intact throughout the pH range investigated. Results from IR and extended X-ray absorption fine structure (EXAFS) spectroscopies provide new evidence for structures of N-(phosphonomethyl)glycinecopper(II) complexes. The structures of 1:1 complexes, CuL- and CuHL, are essentially the same, differing only in protonation of the phosphonate group. Copper(II) lies at the center of a Jahn-Teller distorted octahedron with all three donor groups (amine, carboxylate, phosphonate) of PMG chelating with copper(Ii) to form two five-membered chelate rings oriented in the equatorial plane, EXAFS indicates that oxygen (most. likely a water molecule) is a fourth ligand, which would thus occupy the fourth corner in the equatorial plane of the elongated octahedron. CuL24- most probably forms an isomeric mixture in solution, and there are indications that this mixture is dominated by complexes where two PMG ligands are bound to copper(II) via equatorial and axial positions, with both phosphonate and carboxylate donor groups responsible for chelation at axial positions.},
  author       = {Sheals, J. and Persson, Per and Hedman, B.},
  issn         = {1520-510X},
  language     = {eng},
  pages        = {4302--4309},
  publisher    = {The American Chemical Society},
  series       = {Inorganic Chemistry},
  title        = {IR and EXAFS spectroscopic studies of glyphosate protonation and copper(II) complexes of glyphosate in aqueous solution},
  url          = {http://dx.doi.org/10.1021/ic000849g},
  volume       = {40},
  year         = {2001},
}