Vibrational spectra and conformation of polyethylene glycol complexed with calcium and magnesium chlorides

Abstract

Infrared and Raman spectra of polyethylene glycol (PEG) complexed with calcium and magnesium chlorides have been measured in aqueous solutions and in isolated complexes. Composition of the calcium complex was obtained as 4.4±0.1 (CH 2CH 2O unit):1 (CaCl 2):4.5±0.5 (H 2O) by elementary analysis. From these results, the conformation of PEG in the calcium complex has been proposed to be an alternate conbination of two conformational sequences, (-TGT-TG′T-GTT-TTG-) and (-TGT-TG′T-TGT-GTT-TTG-). For the magnesium complex, the conformation of PEG is supposed to be similar to that of crystalline PEG, with repetition of TGT for the -CH 2CH 2O units. The difference in the structure between the calcium and magnesium complexes was explained by the difference in the cation's size.