Fárník Michal, Weimann Marcus, Steinbach Christof, Buck Udo, Borho Nicole, Adler Thomas B, Suhm Martin A
Max-Planck Institut für Dynamik und Selbstorganisation, Bunsenstr. 10, D-37073, Göttingen, Germany.
Phys Chem Chem Phys. 2006 Mar 14;8(10):1148-58. doi: 10.1039/b514117f. Epub 2006 Jan 20.
A comprehensive experimental study of the OH stretching vibrations of size-selected clusters of enantiopure and racemic methyl lactate is presented. For the size selection, we measured angular dependent mass spectra and time-of-flight distributions at the different fragment masses. In this way the fragmentation of these clusters upon electron impact ionization is obtained. The largest fragment masses of the neutral (MLac)n clusters are the protonated (MLac)n-1H+ ions. The results of a pressure dependent study in an FTIR jet experiment are compared with completely size-selected experiments based on atomic beam deflection and depletion spectroscopy. The size assignments and spectra agree for dimers and trimers. Structures and spectral information for the trimer and the tetramer at density functional and MP2 level are provided. Selective self-aggregation and chiral recognition was observed for homochiral trimers. They exhibit a ring structure bound by OH...OH hydrogen bonds. A spectacular switch in the hydrogen bonding topology was observed for the tetramer. The homochiral enantiomer exhibits cooperative OH...OH bonding, while the heterochiral version shows isolated OH...O=C bonding in a symmetric SRSR arrangement. The crucial ingredients for this identification are the size-selective IR spectra with their different shifts and line patterns which are reproduced by the calculations.
本文介绍了对纯对映体和外消旋乳酸甲酯尺寸选择团簇的OH伸缩振动进行的全面实验研究。对于尺寸选择，我们测量了不同碎片质量下的角度相关质谱和飞行时间分布。通过这种方式，获得了这些团簇在电子碰撞电离时的碎片化情况。中性(MLac)n团簇的最大碎片质量是质子化的(MLac)n-1H+离子。将傅里叶变换红外喷射实验中压力依赖性研究的结果与基于原子束偏转和耗尽光谱的完全尺寸选择实验进行了比较。二聚体和三聚体的尺寸归属和光谱结果一致。提供了密度泛函和MP2水平下三聚体和四聚体的结构及光谱信息。观察到同手性三聚体的选择性自聚集和手性识别。它们呈现出由OH...OH氢键结合的环状结构。观察到四聚体的氢键拓扑结构发生了显著转变。同手性对映体表现出协同的OH...OH键合，而异手性形式在对称的SRSR排列中显示出孤立的OH...O=C键合。这种识别的关键因素是具有不同位移和线型的尺寸选择性红外光谱，计算结果再现了这些光谱。
