Uemura Takashi, Horike Satoshi, Kitagawa Kana, Mizuno Motohiro, Endo Kazunaka, Bracco Silvia, Comotti Angiolina, Sozzani Piero, Nagaoka Masataka, Kitagawa Susumu
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan.
J Am Chem Soc. 2008 May 28;130(21):6781-8. doi: 10.1021/ja800087s. Epub 2008 May 7.
Molecules confined in nanospaces will have distinctly different properties to those in the bulk state because of the formation of specific molecular assemblies and conformations. We studied the chain conformation and dynamics of single polystyrene (PSt) chains confined in highly regular one-dimensional nanochannels of a porous coordination polymer [Zn 2(bdc) 2ted] n ( 1; bdc = 1,4-benzenedicarboxylate, ted = triethylenediamine). Characterization by two-dimensional (2D) heteronuclear (1)H- (13)C NMR gave a direct demonstration of the nanocomposite formation and the intimacy between the PSt and the pore surfaces of 1. Calorimetric analysis of the composite did not reveal any glass transition of PSt, which illustrates the different nature of the PSt encapsulated in the nanochannels compared with that of bulk PSt. From N 2 adsorption measurements, the apparent density of PSt in the nanochannel was estimated to be 0.55 g cm (-3), which is much lower than that of bulk PSt. Results of a solid-state (2)H NMR study of the composite showed the homogeneous mobility of phenyl flipping with significantly low activation energy, as a result of the encapsulation of single PSt chains in one-dimensional regular crystalline nanochannels. This is also supported by molecular dynamics (MD) simulations.
由于形成了特定的分子聚集体和构象，限制在纳米空间中的分子将具有与本体状态下的分子截然不同的性质。我们研究了限制在多孔配位聚合物[Zn₂(bdc)₂ted]ₙ（1；bdc = 1,4-苯二甲酸，ted = 三亚乙基二胺）的高度规则一维纳米通道中的单聚苯乙烯（PSt）链的链构象和动力学。通过二维（2D）异核¹H-¹³C NMR进行表征，直接证明了纳米复合材料的形成以及PSt与1的孔表面之间的紧密程度。对该复合材料的量热分析未发现PSt有任何玻璃化转变，这说明了封装在纳米通道中的PSt与本体PSt的性质不同。通过N₂吸附测量，估计纳米通道中PSt的表观密度为0.55 g cm⁻³，远低于本体PSt的表观密度。对该复合材料的固态²H NMR研究结果表明，由于单PSt链封装在一维规则晶体纳米通道中，苯基翻转具有均匀的迁移率，且活化能极低。分子动力学（MD）模拟也支持了这一点。
