FT IR of Polyampholytes and Copper (II) Complexes

JUAN MANUEL LÁZARO MARTÍNEZ; MARÍA FLORENCIA LEAL DENIS; GRACIELA YOLANDA BULDAIN; VIVIANA CAMPO DALL ORTO

Buenos Aires. Argentina

Workshop; International Workshop of Infrared Spectroscopy Applied to Biological and Biomimetic Systems: From the Isolated Molecule to the Cell; 2007

UBA

Ionic polymers that carry both anionic and cationic groups are denominated polyampholytes. The charges may be located on either the same or different monomer units, and the response in aqueous solutions depends on the nature of the ionisable groups and the crosslinking degree 1. Novel polyampholytes were obtained by reaction of methacrylic acid (MAA), 2-methylimidazole (2MI) and ethylene glycol diglycidyl ether (EGDE). These materials behaved as ionic exchangers. Copper (Cu2+) was chosen as a model, the equilibrium binding was analyzed, and the coordination properties were studied by FT IR. For poly(EGDE-MAA-2MI), the absorption band at 1730 cm-1 corresponds to carbonyl symmetric stretching. The asymmetric stretching of carboxylate was shifted to 1570 cm-1 in contrast with the shift to 1630 cm-1 in polymers without imidazole [poly(EGDE-MAA)]. When the polyampholyte was treated with an acid solution, the band at 1570 cm-1 was absent, while when it was treated with an alkaline solution, the band at 1570 cm-1 presented a more intensive signal than the native polymer, where the carbonyl and carboxylate stretching bands presented the same intensity (Figure 1. ?A?). Bands at 750 and 670 cm-1 in the polyampholyte were absent in poly(EGDE-MAA), thus evidencing the presence of the 2MI ring in the material (Band B, Figure 1. ?B?). The Cu2+(25 mM)-polyampholyte presented a new absorption band at 600 cm-1, and it was assigned to the 2MI-Cu2+ complex in the polymer (Band A, Figure 1. B?). Higher amounts of Cu2+ produced small increments in the signal at 600 cm-1 in the Cu2+-polyampholyte and an important decrease in CO2- asymmetric stretching band at 1570 cm-1. Therefore, at every interval of Cu2+ concentration, the imidazole ring (2MI) was found to be the main group involved in metal ion uptake because the increment or broadening in band intensity at 600 cm-1 was the first relevant spectral change. Besides, the carboxylic group appears to have a coordinating role only at high concentrations, due to the important signal weakening of the CO2- (1570 cm-1) at 80 mM Cu2+ concentration. Notably, the FT IR spectra revealed that a series of new polymers with ionisable groups had been synthesized.