Laser-excited raman spectroscopy of biomolecules. XII. Thermally induced conformational changes in poly(L-glutamic acid)

✍ Scribed by Gerald D. Fasman; Koichi Itoh; Christopher S. Liu; Richard C. Lord

• Publisher: Wiley (John Wiley & Sons)
• Year: 1978
• Tongue: English
• Weight: 850 KB
• Volume: 17
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1978.360170709

✦ Synopsis

The a-helical form of poly(L-glutamic acid) [a-poly(Glu)] gives rise to the same amide I and I11 lines as a-poly(y-benzyl-L-glutamate) a t 1652 and 1296 cm-', respectively. The latter is a superposition of the amide I11 line near 1290 cm-l and a line due to a vibrational mode of CH2 groups of the side chain near 1300 cm-'. A line a t 924 cm-I is tentatively identified as characteristic of a-poly(G1u). Both the 81and &forms of poly(Glu) give rise to characteristic 0-amide 111 frequencies that are similar because of their similar backbone structures. Differences in the conformations of their side chains and in the environments of the backbone are reflected in the region 800-1200 cm-' and in the amide I. A line a t 1042 cm-' and a pair a t 1021 and 1059 cm-' are tentatively assigned as characteristic of PI-poly(Glu) and @-PO- ly(Glu), respectively. The a-Pz transition in p o l y ( ~-G l u ~~~-V a l ~* ) is shown by the appearance of all the &-characteristic lines in the thermally transformed sample. The same features observed in poly(~-Glu95~-Val~) also indicate that the a& transition of poly(G1u) is facilitated by the presence of L-valine and that the content of L-valine is not critical for this purpose. Investigation of the Raman spectra of the calcium, strontium, barium, and sodium salts of poly(G1u) shows that these salts, under the conditions of preparation used, all have random-coil conformations.

* Based on part of the Ph.D. thesis of C.