PBLG

The phenyl ring motion for peptides and various synthetic polymers have been studied with the solid state H NMR by many workers, undergoing a 180° flipping motion in a two-fold potential. The reported activation energies of the flipping motion reflect the degree of crystallinity, the crystal 

The temperature dependent spectra of PBLG-d5 is shown in Fig. 6. Line shapes below — 76°C are similar to the rigid state pattern, indicating the absence of fast and large-amplitude motions. They are, however, different in 

The temperature dependent T data are shown in Fig. 9. 7j values decrease from 28 ms at 21°C with increasing temperature, and show a minimum of 6.4 ms at 80° C. These results indicate the presence of the motion with a Larmor frequency of 30 MHz at this temperature. This minimum was found to be attributed to the flipping motion of a phenyl ring from the result of our other experiments discussed in later section.13 The jump rates of the flipping motion were estimated with a two-site jump model that a C-2H bond jumps between two equivalent sites separated by 180°, and that the angle made by the C-2H bond and the rotational axis is 60°. The quadrupole coupling constant of 180 kHz and the asymmetry parameter approximated to zero were used in the calculation. The calculated values for fitting with the 

The line shapes were calculated for the flipping motion with the two-site jump model described above, and the calculated spectra are shown in Fig. 11 for the higher temperature region. The experimental line shapes at 20 and 30° C are well reproduced showing the motional mode and rates obtained by T analysis are reasonable at least around these temperatures. Above 40°C the calculated line shapes are invariable and remain in the powder pattern undergoing a rapid flipping motion, while the experimental ones 

The r-dependence of the spectra of PBLG- d2 is shown in Fig. 17. An increase in the pulse spacing r leads to a reduction of the spectral intensity and characteristic line shape changes. The remarkable r-dependence is observed around 40-60°C for both samples. These results show the presence of motions with rates as high as the QCC at the k and positions in this temperature region, and are consistent with the remarkable signal intensity loss around 50°C. 

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Polymer Solutions. Perhaps the most extensively studied macromolecular Hquid crystals are the synthetic polypeptides, such as poly( y-benzyl L-glutamate) [25513-40-0] (PBLG). PBLG is a homopolymer of the L-enantiomorph of a single amino acid with the foUowiag repeat unit. 

A new approach of controlling NCA polymerization was reported by the Cheng group in 2007 [22]. hr a screen of amine initiators for the polymerization of Bn-Glu NCA, they found that hexamethyldisilazane (HMDS) showed remarkable control of polymerizations and led to formation of PBLG with excellent chain length control, with less than 22% deviation from the expected molecular weights, and narrow molecular weight distributions < 1.2) (Scheme 13). The NCA polymer-... 

For aprotic polar organic solvents only few widely applicable alignment media are known. The lyotropic mesophase of poly(y-benzyl-L-glutamate) (PBLG) with DMF [37] has the disadvantage of a relatively strong minimum alignment. Bicellar... 

PolyCy-benzyl L-glutamate) (PBLG), 15 109 Poly(y-ketosulfide)s, optically active, 23 711 Poly(P-alanine), 1 292 Poly-P-hydroxybutyrate (PHB), 12 482 Polybetaines, 20 479-482 applications of, 20 482 preparation of, 20 480-481 solution properties of, 20 481-482 synthesis of, 20 479-481 Polyborates, 4 256-258 Polyborosiloxanes, in silicon carbide manufacture and processing, 22 533 Polybrominated diphenyl ethers (PBDEs), 13 142-143 20 56... 

PBLG or poly-s-carbobenzyloxy-i.-lysine (PCBLL) and an organic solvent such as CHC13, CH2C12, DMF...199,200 can produce a difference in interactions for different enantiomers of a solute molecule.112,201 Hence enantiomers can produce different NMR spectra as a consequence of differential... 

Fig. 13. Tilted 2D spectrum of natural abundance 2H Q-COSY experiment of ( )-l-pentyn-ol dissolved in PBLG/chloroform chiral nematic liquid crystal. The spectrum was symmetrized prior to the tilting procedure. Note that all isotopomers of the mixture are clearly visualized. (Reproduced by permission of American Chemical Society.)...

Racemic complex (racemic PBG), composed of PBLG and its enantiomer poly(y-benzyl D-glutamate) (PBDG), takes an a-helical conformation in the solid state and has different physical properties from those of PBLG or... 

In this review we focus on the detailed side chain dynamic of PBLG and racemic PBG deuterated at several positions in a side chain by means of solid state 2H NMR. The brief description of the 2H NMR parameters used... 

Fig. 7. Temperature dependence of the quadrupole splitting for the inner (circle) and the outer (triangle) of PBLG-d5.

Fig. 9. Temperature dependence of the observed (circle) and calculated (line) 7) values of PBLG-dj.

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