N-Octanoyl-l-glutamic acid oligomers (residue number, N = 2—6) have been synthesized in order to study their molecular conformations in the solid state. The X-ray powder diffraction patterns and vibrational spectra of these oligomers have been investigated and compared with those of the α-helical and β-sheet conformations of poly-l-glutamic acid. For fresh samples of these oligomers, the tetramer, pentamer, and hexamer take up a conformation similar to the β1-form of poly-l-glutamic acid. However, the β1-type conformation of these oligomers is rapidly transformed to a β2-type conformation with time at room temperature, indicating that a transition similar to the β1→β2 transition of poly-l-glutamic acid occurs, even in the tetramer, pentamer, and hexamer. For fresh samples of the dimer and trimer, these molecules take up the β2-type structure. This means that the critical size of the oligomer for the formation of the β1→β2-type transition is the tetramer.
为了研究 N-辛酰-谷
氨酸低聚物(残基数 N = 2-6)在固态下的分子构象,我们合成了这些低聚物。研究了这些低聚物的 X 射线粉末衍射图样和振动光谱,并将其与聚-l-谷
氨酸的 α 螺旋构象和 β 片状构象进行了比较。在这些低聚物的新鲜样品中,四聚体、五聚体和六聚体的构象与聚-l-谷
氨酸的 β1 型相似。然而,这些低聚物的 β1 型构象在室温下随着时间的推移迅速转变为 β2 型构象,这表明即使在四聚体、五聚体和六聚体中也发生了类似于聚-l-谷
氨酸的 β1→β2 转变。对于二聚体和三聚体的新鲜样品来说,这些分子都具有 β2-型结构。这意味着形成 β1→β2 型转变的低聚物的临界大小是四聚体。