Rozenberg M, Shoham G, Reva I, Fausto R
Department of Inorganic and Analytical Chemistry, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel.
Spectrochim Acta A Mol Biomol Spectrosc. 2003 Dec;59(14):3253-66. doi: 10.1016/s1386-1425(03)00159-8.
The 400-4000 cm(-1) FTIR spectra of pure NH and isotopically substituted (10 and 90% doped ND/NH) polycrystalline L-alanine were recorded in the temperature range 10-300 K. The observed temperature dependence and isotopic shifts behavior enabled to identify, in the spectra of the doped crystals, three well-separated bands ascribable to either the NH or ND stretching vibrations associated with the three different types of hydrogen bonds existing in the crystal. The observed red shifts of these bands relative to the frequency of a reference "free" NH (or ND) stretching mode were found to correlate well with the H-bond distances found in the crystal and provide an indirect way of estimating the enthalpies associated with each type of H-bond found in the crystal. In the low-frequency deformation and torsional spectral region (below 2000 cm(-1)), several bands, which were found to be affected by isotopic substitution, were identified as belonging to the NH3(+) group. Several bands show splitting at low temperatures, indicating the occurrence of a significant reorganization in the crystal structure, which with all probability results mainly from changes in the proton positions. Finally, the literature assignments of the IR spectra of both crystalline NH3(+) and ND3(+) L-alanine were revised taking into consideration their temperature dependence and behavior upon deuteration.
在10 - 300K温度范围内记录了纯NH和同位素取代（10%和90%掺杂ND/NH）的多晶L-丙氨酸的400 - 4000 cm(-1)傅里叶变换红外光谱。观察到的温度依赖性和同位素位移行为使得在掺杂晶体的光谱中能够识别出三个分离良好的谱带，这些谱带可归因于与晶体中存在的三种不同类型氢键相关的NH或ND伸缩振动。发现这些谱带相对于参考“自由”NH（或ND）伸缩模式频率的红移与晶体中的氢键距离有很好的相关性，并提供了一种间接方法来估计与晶体中每种类型氢键相关的焓。在低频变形和扭转光谱区域（低于2000 cm(-1)），发现几个受同位素取代影响的谱带属于NH3(+)基团。几个谱带在低温下出现分裂，表明晶体结构发生了显著的重组，这很可能主要是由质子位置的变化引起的。最后，考虑到结晶NH3(+)和ND3(+) L-丙氨酸红外光谱的温度依赖性和氘化行为，对它们的文献归属进行了修订。
