Instituto de Estructura de la Materia, IEM-CSIC, Madrid, Spain.
Phys Chem Chem Phys. 2011 Jul 14;13(26):12268-76. doi: 10.1039/c1cp20899c. Epub 2011 Jun 1.
The conversion from neutral to zwitterionic glycine is studied using infrared spectroscopy from the point of view of the interactions of this molecule with polar (water) and non-polar (CO(2), CH(4)) surroundings. Such environments could be found on astronomical or astrophysical matter. The samples are prepared by vapour-deposition on a cold substrate (25 K), and then heated up to sublimation temperatures of the co-deposited species. At 25 K, the neutral species is favoured over the zwitterionic form in non-polar environments, whereas for pure glycine, or in glycine/water mixtures, the dominant species is the latter. The conversion is easily followed by the weakening of two infrared bands in the mid-IR region, associated to the neutral structure. Theoretical calculations are performed on crystalline glycine and on molecular glycine, both isolated and surrounded by water. Spectra predicted from these calculations are in reasonable agreement with the experimental spectra, and provide a basis to the assignments. Different spectral features are suggested as probes for the presence of glycine in astrophysical media, depending on its form (neutral or zwitterionic), their temperature and composition.
从该分子与极性（水）和非极性（CO(2)、CH(4)）环境的相互作用的角度，利用红外光谱研究了中性甘氨酸向两性离子甘氨酸的转化。这种环境可能存在于天文或天体物理物质中。样品通过蒸气沉积在冷基底（25 K）上制备，然后加热到共沉积物质的升华温度。在 25 K 时，非极性环境中中性物种比两性离子形式更占优势，而对于纯甘氨酸或甘氨酸/水混合物，主要物种是后者。通过中红外区域两个与中性结构相关的弱红外带的减弱，很容易跟踪转化过程。对晶体甘氨酸和孤立以及被水包围的分子甘氨酸进行了理论计算。这些计算预测的光谱与实验光谱吻合较好，为谱带归属提供了依据。根据其形式（中性或两性离子）、温度和组成，提出了不同的光谱特征作为天体物理介质中甘氨酸存在的探针。
