Effect of pressure on the helix and random coil forms of poly(D‐glutamic acid)

The absorption spectrum of the aqueous solution of acridine orange (AO)‐poly–(D‐glutamic acid) (PDGA) complex at pH 4.5 (helix form) did not show any wavelength shift, but at pH 7.5 (coil form) changed to the absorption curve of the helix form by compression up to 4500 atm. The ionization degree of PDGA estimated from the electric conductivity of the aqueous solution of PDGA at 4500 atm. was a value of about 5.3%. The entropy of the helix formation of PDGA from the titration data at 1 atm. and 30°C. was negative −2.98 e.u. It will be concluded in this report that the volume change for coil to helix could be positive for PDGA and negative for AO–PDGA complexes.