A Magnetic Resonance Study of the Segmental Motion and Local Conformations of Poly(L-glutamic acid) in Aqueous Solutions

Abstract

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).

Drug releasing behavior of hybrid micelles containing polypeptide triblock copolymer

“…It is important to note that the signal of a-proton in PLGA block clearly appeared at 4.2 ppm (see Fig. 1c), which indicates that PLGA blocks take a coil chain conformation and remain solvated in aqueous media [50]. Zeta potential measurements were used to further confirm the corona structures of the micelles.…”

Small-angle X-ray scattering study on conformation of poly(sodium L-glutamate) in NaCl and NaF aqueous solutions

“…and a single peak centered at ca 2.1 p.p.m. are assigned to -CH 2 protons and -CH 2 protons, respectively, of PNaGA in the random-coiled state (Markley et al, 1967;Tsutsumi et al, 1978). The three peaks in the A spectra are assigned to CH 2 protons of PNaGA in the helical state, but the assignment of each peak was not made here.…”

Nuclear magnetic spin relaxation of a spin-pair undergoing reorientations by jumping among unequivalent sites

“…It was found that case (1) with a = 89 explains fairly well the spin-lattice relaxation time of fl-carbon as shown in figure 7. The complete results will be published elsewhere [21].…”