Department of Chemistry, Indiana University, Bloomington, Indiana 47405, USA.
J Phys Chem B. 2012 Sep 20;116(37):11442-6. doi: 10.1021/jp3069915. Epub 2012 Sep 6.
The chiral composition of amino acid clusters may be related to the origin of chirality in biological systems. Here, we use ion mobility/mass spectrometry techniques to investigate the gas phase structures of singly charged proline clusters containing two to six monomers. Using deuterated L-proline (L(D7)) and different electrospray solution compositions varying from enantiopure (50:50 L:L(D7)) to racemic (50:50 L(D7):D), it is possible to study collision cross sections of L-, D-, and mixed xL:xD-proline clusters (where x refers to the number of monomers). These results show that 2Pro+H and 3Pro+H clusters, previously shown (Holliday et al. J. Phys. Chem. A 2012, DOI: 10.1021/jp302677n) to have a very small heterochiral preference, have similar collision cross sections for homochiral and heterochiral proline assemblies. The 4Pro+H and 6Pro+H clusters that exhibit homochiral preference have smaller collision cross sections for homochiral clusters and larger collision cross sections for heterochiral clusters. The 5Pro+H cluster with heterochiral preference has a smaller collision cross section for its heterochiral compositions than for its homochiral compositions. These results suggest that the packing efficiency of subunits within each cluster influences the stability and prevalence of proline multimers as either homochiral or mixed L- and D- clusters.
氨基酸簇的手性组成可能与生物系统中手性的起源有关。在这里，我们使用离子淌度/质谱技术研究了含有两个到六个单体的单价脯氨酸簇的气相结构。使用氘代 L-脯氨酸（L(D7)）和不同的电喷雾溶液组成，从对映纯（50:50 L:L(D7)）到外消旋（50:50 L(D7):D），可以研究 L-、D-和混合 xL:xD-脯氨酸簇（其中 x 指单体数）的碰撞截面。这些结果表明，2Pro+H和3Pro+H簇（先前已证明（Holliday 等人，J. Phys. Chem. A 2012，DOI：10.1021/jp302677n）具有很小的异手性偏好）具有相似的碰撞截面，对于同手性和异手性脯氨酸组装体。表现出同手性偏好的4Pro+H和6Pro+H簇具有较小的同手性簇碰撞截面和较大的异手性簇碰撞截面。具有异手性偏好的5Pro+H簇具有比其同手性组成更小的异手性组成的碰撞截面。这些结果表明，每个簇中小单位的组装效率会影响脯氨酸多聚体作为同手性或混合 L-和 D- 簇的稳定性和普遍性。
