High-pressure Raman spectra of L-isoleucine crystals

Raman spectroscopy investigations of L-isoleucine crystals under high pressures have been carried out up to 7.3 GPa. From this study it was possible to observe modifications on bands associated to both rocking vibrations of r(NH₃⁺) and r(CO₂⁻) as well as to lattice modes at about 2.3 and 5.0 GPa. These modifications were correlated to either conformational change of molecules or to a solid–solid phase transition undergone by the crystals involving the hydrogen bonds that maintain the molecules held in the unit cell. A comparison with a few results on other amino acid crystals is also given.