Pohl Gábor, Perczel András, Vass Elemér, Magyarfalvi Gábor, Tarczay György
Structural Chemistry and Biology Laboratory, Institute of Chemistry, Eötvös University, Budapest, Hungary.
Phys Chem Chem Phys. 2007 Sep 7;9(33):4698-708. doi: 10.1039/b705098d. Epub 2007 Aug 14.
The infrared absorption (IR) spectra of acetyl-N-methyl-glycine and acetyl-N-methyl-alanine have been recorded in dichloromethane and dimethyl sulfoxide-d(6) solution, as well as in Ar and Kr matrices. The spectra were assigned with the help of quantum chemical calculations. Based on the assignments of the matrix-isolation IR spectra, in line with theoretical predictions, two different hydrogen bonded conformers were identified, furthermore a third conformer is likely to be present, which cannot be unambiguously identified. In dichloromethane two conformers could be observed, while in dimethyl sulfoxide a single conformer could be identified. Vibrational circular dichroism (VCD) spectra of acetyl-N-methyl-l-alanine have also been recorded in solutions and matrices. These matrix-isolation VCD spectra not only support the assignments of the matrix-isolation IR spectra, but also demonstrate that these spectra can be interpreted much easier with the help of quantum chemical calculations than the VCD spectra recorded in solutions. It is also shown that the rotatory strength of some vibrational transitions changes rapidly as a function of the backbone torsional coordinates; hence the appearance of some regions in the VCD spectra is extremely dependent on any perturbations, e.g. weak intermolecular interactions.
已记录了乙酰基 - N - 甲基甘氨酸和乙酰基 - N - 甲基丙氨酸在二氯甲烷和氘代二甲亚砜 - d(6)溶液以及氩气和氪气基质中的红外吸收（IR）光谱。借助量子化学计算对光谱进行了归属。基于基质隔离红外光谱的归属，与理论预测一致，鉴定出了两种不同的氢键构象异构体，此外可能还存在第三种构象异构体，但无法明确鉴定。在二氯甲烷中可观察到两种构象异构体，而在二甲亚砜中可鉴定出单一构象异构体。还记录了乙酰基 - N - 甲基 - L - 丙氨酸在溶液和基质中的振动圆二色性（VCD）光谱。这些基质隔离VCD光谱不仅支持基质隔离红外光谱的归属，还表明借助量子化学计算，这些光谱比在溶液中记录的VCD光谱更容易解释。还表明，一些振动跃迁的旋光强度随主链扭转坐标迅速变化；因此，VCD光谱中某些区域的出现极其依赖于任何扰动，例如弱分子间相互作用。
