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The segmental motions and the local conformations of poly(L-glutamic acid) in aqueous solutions have been investigated by magnetic resonance spectroscopy as a function of pH or pD and temperature. The ESR of spin-labeled PLGA with a nitroxide group attached to the end of the main chain or of a side chain indicates a sharp decrease of the mobility of this group at the random coil -* «-helix transition. The analysis of the 250 MHz !H NMR spectra at different temperatures and pD shows the prevalence of the gauche and trans rotamers of the methylene groups of the side chains about the Ca-C9 and Cs-C7 bonds, respectively. Deuteron line width measurements on the a-and -deuterated PLGA indicate a comparatively high segmental mobility with 10'10 < reff < 5 X 10"10 s at room temperature for both the random coil and -helix forms of the polymer. The nature of segmental motions of PLGA in neutral solution has been investigated by 13C and Tl measurements in magnetic fields of 23.5 and 58.7 kG. The relaxation data have been interpreted in terms of a quasi-isotropic reorientation of CHa groups in the macromolecular chain assuming a distribution of correlation times tr with = 6.4 kcal mol"1. The model assessed for the reorientation of the /3-methylene group is 120°j umps between three nonequivalent sites with AfíG* = 6.4 kcal mol"1. The relaxation of 13C7 showing a large reorientational freedom of the -methylene group seems consistent with an overall isotropic motion with AflV = 5.4 kcal mol'1. The influence of pD on the average dimensions of PLGA, investigated by the proton relaxation enhanced by a terminal nitroxide group, indicates in particular a marked shrinking of the macromolecular chain at the onset of the random coil -* «-helix transition (pD 5.5).

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The contact shifts of 1H, 13C, 14N, and 19F in chloroform solutions of Ni(II) acetylacetonate -aniline and fluoraniline complexes have been studied by high resolution n.m.r. The unpaired electron spin distribution in these ligands is compared to that calculated by the INDO method for the corresponding aniline cation radicals. The ratio of the hyperfine coupling constants aNHH/aN suggests that in these aniline complexes the [Formula: see text] fragment is pyramidal with an angle of 13–15° between the perpendicular of the C—N bond and the axis of the p like orbital centered on nitrogen. The electron spin distribution between the NH2 group and the phenyl ring may be partially accounted for by assuming an internal rotation about the C—N bond. The 13C relaxation indicates a N—Ni distance of the order of 2 Å for aniline and 2 fluoraniline complexes and an electron spin-lattice relaxation time of ∼5 × 10−10 s at 300 °K.

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