Solution properties of synthetic polypeptides. XVI. Hydrogen bonding in helix–coil transitions of poly(β-benzyl L-aspartate)

✍ Scribed by Takashi Norisuye; Kozo Misumi; Akio Teramoto; Hiroshi Fujita

• Publisher: Wiley (John Wiley & Sons)
• Year: 1973
• Tongue: English
• Weight: 433 KB
• Volume: 12
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1973.360120708

✦ Synopsis

Helix-coil transition of polypeptides in solution involves two elementary processes: unfolding of an orhelical polypeptide chain and interaction of the unfolded chain with solvent molecules which are capable of forming hydrogen bonds. Optical rotation data for poly(fl-benzy1 baspartate) in mixtures of dichloroacetic acid and carbon tetrachloride are analyzed according to the procedure developed by Sayama et al., who explicitly took these processes into theoretical account; and the enthalpy changes, AH0 for the unfolding and AH, for the solvation, are determined. The values obtained are AHo = -650 =t 200 cal/mole and AH, = -5.2 =t 1.6 kcal/mole. The latter value is favorably compared with heats of association (per hydrogen bond) of various amides and lactams in CCla. There is excellent agreement with -5.15 kcal/mole for bvalerolactam in CCla. In analogy with amides in non-polar solvents, the difference between AH0 and AH, may be attributed to the fact that the former is associated with intramolecular hydrogen bonding, whereas the latter is associated with intermolecular hydrogen bonding.