Structure, conformation, and motions of polytetrahydrofuran (PTHF) in the hexagonal form of the PTHF‐urea inclusion compound
Structure, conformation, and motions of polytetrahydrofuran (PTHF) in the hexagonal form of the PTHF‐urea inclusion compound
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DOI：
10.1002/polb.1995.090330908
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发表时间：
1995-07
期刊：
影响因子：
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通讯作者：
N. Vasanthan;I. D. Shin;A. Tonelli
中科院分区：
文献类型：
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作者：
N. Vasanthan;I. D. Shin;A. Tonelli
结合差示扫描量热法、x射线衍射、傅立叶变换红外和C-13核磁共振对聚四氢呋喃（PTHF）和尿素(U)之间形成的结晶包合化合物（IC）进行观察，并将其与对PTHF的块状半晶样品进行的相同观察进行比较，可以分析两种固态相中PTHF链的构象、运动和环境。占据PTHF- u - ic狭窄通道的孤立PTHF链被高度延伸，尽管与大块晶体PTHF链的几乎所有反式、平面之字形构象平均24°的小旋转偏差会产生一些显著的行为差异。PTHF- u - ic中的PTHF链比体晶PTHF链具有更大的迁移率，C-13自旋晶格弛豫时间T1比体晶PTHF链（75 s）短50倍（1.5 s）。FTIR观测结果与客体PTHF链与宿主尿素基质分子之间的特异性相互作用非常小一致，结果表明，除了在745 cm−1处观察到的体PTHF中存在CH2摇摆振动带外，体PTHF和IC PTHF的光谱相似。考虑到块状晶体PTHF链的全反式、平面之字形构象的对称性，可以理解IC PTHF中没有这一能带，这阻止了CH2摇摆模式与PTHF- u -IC中非平面、螺旋PTHF链中出现的骨架拉伸和弯曲模式耦合。©1995 John Wiley & Sons, Inc
Combination of differential scanning calorimetry, x-ray diffraction, Fourier transform infrared, and C-13 nuclear magnetic resonance observations made on the crystalline inclusion compound (IC) formed between polytetrahydrofuran (PTHF) and urea (U), together with their comparison to identical observations performed on bulk semicrystalline samples of PTHF, have permitted an analysis of the conformations, motions, and environments available to PTHF chains in both solid-state phases. The isolated PTHF chains occupying the narrow channels of the PTHF-U-IC are highly extended, though small rotational deviations averaging 24° from the nearly all trans, planar zig zag conformation of bulk crystalline PTHF chains produce some significant differences in their behaviors. PTHF chains in PTHF-U-IC possess much greater mobility than bulk crystalline PTHF chains as evidenced by C-13 spin lattice relaxation times, T1, 50 times shorter (1.5 s) than observed for bulk crystalline PTHF chains (75 s). FTIR observations are consistent with very little specific interaction between guest PTHF chains and host urea matrix molecules and result in similar spectra for bulk and IC PTHF, except for the presence of the CH2 rocking vibration band at 745 cm−1 observed for bulk PTHF. The absence of this band in the IC PTHF can be understood by considering the symmetry of the all trans, planar zig zag conformation of bulk crystalline PTHF chains, which prevents the CH2 rocking mode from coupling with skeletal stretching and bending modes as occurs in the nonplanar, helical PTHF chains in PTHF-U-IC. © 1995 John Wiley & Sons, Inc.