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Helix–coil transition for poly(L-glutamic acid) in water–ethanol solutions

✍ Scribed by G. Conio; E. Patrone

Publisher
Wiley (John Wiley & Sons)
Year
1969
Tongue
English
Weight
427 KB
Volume
8
Category
Article
ISSN
0006-3525

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✦ Synopsis

Potentiometric titrations and some complementary optical rotation data are presented for solutions of poly(L-glntamic acid) (PGA) in several H,O-ethanol mixtnres. The data allow the determination of the intrinsic p K (pKo), slope of the apparent pK (pKaPp), versus degree of ionization curves and of the enthalpy of ionization as a function of ethanol concentration. The variation of the degree of ionization at which the helix-coil transformation occiirs with ethanol and temperature is also determined. Finally free energy, enthalpy, and intropy changes associated with the helix-coil transformation for the uncharged conformers are determined from the titration curves. The effect of the ethanol is to increase the stability of the helical conformation of PGA for both the charged and the uncharged forms of the polymer. The stabilization of the uncharged helix is essentially an entropic effect.

* For a critical analysis of the experimental determination and theoretical treatment, of pH in water-alcohol solution, see Bates.10

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