| Résumé | The barotropic behavior of solid 1,2-dipalmitoyl-sn-glycerol was investigated by Fourier-transform infrared spectroscopy over the pressure range 0.1–4250 MPa. At atmospheric pressure, the infrared spectrum of this lipid shows bands characteristic of a hydrogen-bonded hydroxyl group and of two carbonyl groups, one hydrogen-bonded, the other free. An increase in pressure leads to a considerable increase in the strength of the intermolecular hydrogen bond. The application of an external pressure of 4250 MPa increases the strength of the hydrogen bond by about 12 relative to that at atmospheric pressure. The stretching frequency of the proton-donating group (OH) is more sensitive to pressure-enhanced hydrogen-bonding than is the proton-accepting group (CO). A structural phase transition was detected around 2500 MPa. In the infrared spectra recorded above this pressure, the OH and CO stretching modes are split into two and four bands, respectively. For the high-pressure phase, there are at least two non-equivalent molecules in each unit cell with two types of hydrogen bonds. |
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