ISM, UMR CNRS 5255, Université Bordeaux, Talence, France.
J Phys Chem B. 2011 Apr 21;115(15):4446-52. doi: 10.1021/jp1109674. Epub 2011 Mar 29.
Ab initio calculations of two oligoureas stabilized in helix and sheet organization have been performed. The hydrogen bond distances were found to be almost the same for both structures. The vibrational assignment of the two oligourea structures and the direction of the transition moment of each vibration have been determined. From these results, and using the experimental isotropic optical index determined for one oligourea, we have established the anisotropic infrared optical files for the two structures. Interestingly, most urea absorptions vibrate in only one principal direction. Also, the shift of the carbonyl band is weaker and inverse to what was reported for corresponding protein secondary structures. Finally, simulations of the Polarization Modulation Infrared Reflection Absorption Spectroscopy (PMIRRAS) and Attenuated Reflection Spectroscopy (ATR) infrared spectra demonstrate the possibility to determine the orientation of the oligoureas in thin or ultrathin films, even if in some cases it may be difficult to unambiguously assign their secondary structure.
已对两种以螺旋和片层结构稳定的寡聚脲进行了从头算计算。发现两种结构的氢键距离几乎相同。已确定了两种寡聚脲结构的振动分配以及每个振动的跃迁矩方向。根据这些结果，并使用为一种寡聚脲确定的实验各向同性光指数，我们为这两种结构建立了各向异性红外光文件。有趣的是，大多数脲吸收仅在一个主方向上振动。另外，羰基带的位移比相应蛋白质二级结构的报道要弱且相反。最后，对偏振调制红外反射吸收光谱（PMIRRAS）和衰减反射光谱（ATR）的模拟表明，即使在某些情况下可能难以明确分配其二级结构，也有可能确定薄膜或超薄薄膜中寡聚脲的取向。
