Racemic PBG

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... 

The temperature dependent T results of racemic PBG-d5 are shown in Fig. 29. As shown in Section 4, T of PBLG-d5 achieves a broad minimum at 80° C, showing that the rate of the flipping motion is as high as the Larmor frequency of 30 MHz at this temperature. The Tx value of racemic PBG-d5 decreases more slowly than that of PBLG-d5 as temperature is raised, and drops steeply around 60°C. The T value of racemic PBG-d5 was found to be same as that for PBLG-ds above 80°C. There is little difference in the T values of both samples even below the transition temperature of 90°C. These differences in... 

Fig. 29. Temperature dependent T of PBLG-d5 (circle) and racemic PBG-ds (square). Reproduced with permission from Elsevier Science.

The temperature dependent line-shapes of racemic PBG-Ah are shown in Fig. 30, together with those of PBLG- d2. The line shape at room temperature... 

Fig. 33. 2H NMR spectra of racemic PBG-fd2 with TIS (a) and T1L (b) components as a function of temperature. Reproduced with permission from Elsevier Science.

The temperature dependent line shape of racemic PBG-yd2 is shown in Fig. 34 together with those of PBLG-yd2. The line shapes at room temperature appear to be the rigid state powder pattern, showing the absence of the large amplitude motion in the y position. The signal intensity of the... 

The temperature dependent T results of racemic PBG-yd2 are shown in Fig. 35. The T value of racemic PBG-yd2 comprises two components of Tls and Til as well as T of racemic PBG- d2. TIS is an order of magnitude shorter than T1L, and in fairly good agreement with the T data of PBLG-yd2 which are governed by the large amplitude motion and the libration above and below room temperature, respectively. Both rls and T L decrease gradually with an increase in temperature. Above the transition temperature... 

Fig. 35. Temperature dependent T) of PBLG-yd2 (filled circle) racemic PBG-yd2 with...

The riL value of racemic PBG-ytL is several hundred ms and decreases gradually as temperature increases. These results show that the side chains participating in the stacking structure are not rigid. Tx at the y position below room temperature is governed by the rapid and small-amplitude libration as shown in Section 4.3. The libration is expected to exist in the stacked state as well as the free state. riL is considered to be governed by libration in the stacked state. In order to estimate the amplitude of the libration in the stacked state, we extracted the Tu component of the spectrum in the same way as that used for racemic PBG- d2. The spectra of the T1L and T, s components are shown in Fig. 37. The vq value of the r1L component is... 

The reorientation of the phenyl rings at the end of the side chain is slightly restricted in racemic PBG, but most of the phenyl rings undergo the... 

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