Mobility of lipid in complexes of amylose-fatty acids by deuterium and C-13 solid state NMR

Palmitic and lauric acid complexes with amylose were studied by solid state methods: C-13 CP/MAS NMR, deuterium NMR, X-ray powder diffraction and diff erential scanning calorimetry (DSC). The crystalline amylose complexes were found to be in a V-type sixfold single chain helix. The melting points of the complexes were over 100 degrees C, at least 40-50 degrees C higher than the melting points of the free fatty acids. CP/MAS C-13 NMR spectra reveal ed two resonance peaks at 33.6 and 32.4 ppm for the palmitic acid, which we re assigned as free and complexed fatty acid, respectively. A single resona nce peak at 32.4 ppm was found for the lauric acid and assigned to the comp lex. The chemical shift of 32.4 ppm for the complexed fatty acids suggests a combined trans and gauche conformation for the fatty acid chain in the co mplex. T-1 relaxation measurements on the two palmitic acid resonances show different behavior: a very slow relaxation for the 33.6 ppm and a much fas ter relaxation (1.2 s) for the 32.4 ppm resonances. The latter was similar to the relaxation of the single resonance of the lauric acid (1.1 s). Tempe rature dependent deuterium spectra of the amylose-lauric acid and amylose-p almitic acid complexes suggest a complete complexation for the amylose-laur ic acid, whereas the amylose-palmitic acid complex is partially disassociat ed by the thermal treatment. Based on the overall data, a partially disorde red model is proposed: an imperfect helix with the fatty acid partly inside and partly out, depending on crystallization conditions and the necessity of placing the carboxyl head outside the V-helix. (C) 2000 Elsevier Science Ltd. All rights reserved.