[Infrared and raman spectra studies of DL-homocysteic acid (DLH) and its lanthanum complex at high external pressure].

ABSTRACT

DL-Homocysteic acid (DLH, (NH3 )-CH(COOH)-(CH2 )2-SO3-) is extensively in existence as free amino-acid in the central nervous system of mammal. The infrared (IR) and Raman spectra of DL-Homocysteic acid (DLH) and its La complex [La (DLH)2Cl3 . H2O = LaL2] were measured at high external pressure. The DLH has two pressure-induced phase transitions (near 17 kbar and 37 kbar) and three pressure-phase areas below 50 kbar for there are ten intermolecular hydrogen bonds between the DLH molecules. But there is only one pressure-induced phase transition (near 27 kbar) to be observed in the complex LaL2. These show that the ten intermolecular hydrogen bonds of the DLH molecules changed due to the formation of complex LaL2. In infrared spectra, the changing trend of the pressure sensitivities (dv/dp) of symmetry stretching of SO3- in DLH and asymmetry stretching of SO3- in LaL2 are very different from the other vibrational modes when both compounds undergo high external pressure. In infrared spectra, the average pressure sensitivities of symmetry stretching of SO3- are low-pressure phase area (0.30 cm(-1) x (kbar)(-1)) < middle-pressure phase area (0.32 cmn(-1) (kbar) (-1)) < high-pressure phase area (0.41 cm(-1) x (kbar)(-1)), but 0.86 cm(-1) x (kbar)(-1) (low-pressure phase area) >0.64 cm(-1) x (kbar)(-1) (middle-pressure phase area) >0.26 cm(-1) x (kbar)(-1) (high-pressure phase area) to other vibrational modes in DLH. The average pressure sensitivities of asymmetry stretching of SO3- in LaL2 are lower in low-pressure phase area than in high-pressure phase area, but the average pressure sensitivities of other modes are higher in low-pressure phase area than in high-pressure phase area.