Ousaka Naoki, Shimizu Kaori, Suzuki Yoshimasa, Iwata Takuya, Itakura Manabu, Taura Daisuke, Iida Hiroki, Furusho Yoshio, Mori Tadashi, Yashima Eiji
Department of Molecular and Macromolecular Chemistry, Graduate School of Engineering , Nagoya University , Chikusa-ku, Nagoya 464-8603 , Japan.
Department of Molecular Design and Engineering, Graduate School of Engineering , Nagoya University , Chikusa-ku, Nagoya 464-8603 , Japan.
J Am Chem Soc. 2018 Dec 12;140(49):17027-17039. doi: 10.1021/jacs.8b08268. Epub 2018 Dec 3.
A one-handed double-stranded spiroborate helicate exhibits a unique reversible extension-contraction motion coupled with a twisting motion in one direction triggered by binding and release of a Na ion while retaining its handedness. Here we report that an extended meso-helicate was also produced together with the racemo-helicate, and the meso-helicate was readily converted to the racemo-helicate assisted by a Na ion as a template in the presence of water. The thermodynamic analyses of the ion-triggered springlike motion of the racemo-helicate using a series of monovalent cations with different sizes revealed that the association constants of the extended racemo-helicate decreased in the following order: Li > Na > NH > Ag ≥ K > Cs > Rb, which roughly agrees with the reverse order of their ionic radii except for the NH ion due to the more elongated contracted helicates when complexed with larger cations as supported by the crystal and DFT calculated structures. The one-handed contracted helicates showed characteristic CD spectra depending on the cation species due to the differences in their contracted helical structures, and its absolute handedness of the spiroborate helicate was determined by X-ray crystallography. The kinetic studies of the springlike motions of the racemo-helicate showed that the exchange rate between the extended and contracted helicates tend to increase in the following order: Li < Na < K ≤ NH < Rb < Cs < Ag as anticipated from the association constants, being in good agreement with the order of the cation sizes except for Ag.
一种单手双链螺硼酸螺旋配合物表现出独特的可逆伸展-收缩运动，并伴随着由钠离子的结合和释放触发的单向扭转运动，同时保持其手性。在此，我们报告，外消旋螺旋配合物与一种伸展的内消旋螺旋配合物同时生成，并且在水存在下，内消旋螺旋配合物在钠离子作为模板的辅助下容易转化为外消旋螺旋配合物。使用一系列不同大小的单价阳离子对离子触发的外消旋螺旋配合物的类弹簧运动进行的热力学分析表明，伸展的外消旋螺旋配合物的缔合常数按以下顺序降低：Li＞Na＞NH＞Ag≥K＞Cs＞Rb，除了NH离子外，这大致与它们离子半径的相反顺序一致，这是由于与较大阳离子络合时收缩的螺旋配合物更加细长，晶体结构和密度泛函理论（DFT）计算结构支持这一点。单手收缩的螺旋配合物由于其收缩螺旋结构的差异而表现出取决于阳离子种类的特征圆二色光谱，并且通过X射线晶体学确定了螺硼酸螺旋配合物的绝对手性。外消旋螺旋配合物类弹簧运动的动力学研究表明，伸展和收缩的螺旋配合物之间的交换速率倾向于按以下顺序增加：Li＜Na＜K≤NH＜Rb＜Cs＜Ag，正如从缔合常数预期的那样，除了Ag之外，这与阳离子大小顺序高度吻合。
