On the flexibility of poly(γ-benzyl L-glutamate) in helicogenic solvents

✍ Scribed by Yoshio Muroga; Mitsuru Nagasawa

• Publisher: Wiley (John Wiley & Sons)
• Year: 1998
• Tongue: English
• Weight: 110 KB
• Volume: 45
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/(sici)1097-0282(19980405)45:4<281::aid-bip2>3.0.co;2-h

✦ Synopsis

The molecular-weight dependence of the rms radius of gyration »R 2 g … 1/2 of poly(gbenzyl L-glutamate ) (PBLG) in helicogenic solvents shows negative and positive deviations from expectations for an intact and rigid a-helix in the higher and lower molecular-weight ranges, respectively. In order to study the reason for both deviations, we compare the extant experimental data of »R 2 g … 1/2 with those computed for wormlike chain, freely jointed rod, and a rigid rod having random-coil portions at both ends. The computation for the freely jointed rod and the rigid rod having frayed ends is carried out by a simulation method of Muroga. From the Zimm and Bragg theory and the above comparisons, it is concluded that both deviations can be self-consistently explained if PBLG in helicogenic solvents has an essentially intact a-helical structure with some flexibility arising from random fluctuations in hydrogen bond length. This flexibility explains the negative deviations in the high molecular weight region. The positive deviations in the low molecular weight region result from the tendency of helices to unwind at the ends.