UTILITY OF NUCLEAR-MAGNETIC-RESONANCE FOR DETERMINING THE MOLECULAR INFLUENCE OF CITRIC-ACID AND AN ORGANOSILICONE ADJUVANT ON GLYPHOSATE ACTIVITY

In the discipline of Weed Science, nuclear magnetic resonance (NMR) ha s been used extensively for obtaining structural information on herbic ide compounds in the areas of herbicide synthesis, metabolism, and env ironmental degradation, However, little research has been published wi th regard to the utilization of NMR in determining molecular interacti ons in the spray solution. The molecular influence of citric acid and an organosilicone adjuvant on glyphosate was analyzed with NMR spectro metry. C-14-glyphosate absorption studies showed a decrease in glyphos ate absorption by sunflower when Ca2+ was added to the spray solution. This absorption antagonism was overcome with the inclusion of an orga nosilicone adjuvant. H-1-NMR was used to show that the organosilicone adjuvant did not directly interact with the glyphosate molecule nor di d it prevent the formation of Ca-glyphosate. Citric acid was effective in overcoming the Ca2+ antagonism of glyphosate activity when the cit ric acid concentration was 2x or 4x the Ca2+ molar concentration based on plant fresh weight and plant height, respectively. H-1-NMR was uti lized to show that citric acid reacted with Ca2+ in solution to produc e Ca-citrate and prevent the formation of Ca-glyphosate, NMR was an ef fective technique for characterizing chemical interactions among the s pray solution components.