Chirality induction and protonation-induced molecular motions in helical molecular strands.
Chirality induction and protonation-induced molecular motions in helical molecular strands.
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DOI：
10.1002/chem.200601826
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发表时间：
2007-06
期刊：
影响因子：
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通讯作者：
E. Kolomiets;Volker Berl;J. Lehn
中科院分区：
文献类型：
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作者：
E. Kolomiets;Volker Berl;J. Lehn
合成了含15个杂环的吡啶二甲酰胺长链9，并用X射线晶体学测定了其螺旋结构。结果表明，较短的类似物6显示诱导的圆二色性和放大诱导的手性溶解后，在光学活性溶剂，二乙基-L-酒石酸。制备了一类新的螺旋折叠体，链14-16，其基于通过L-酒石酸衍生的间隔基连接的两个寡吡啶甲酰胺片段。这些酒石链显示内部手性诱导以及手性放大。NMR光谱（8和9）和圆二色性（16）的研究表明，寡吡啶甲酰胺链进行可逆的质子化后的解折叠/折叠。质子化诱导的去折叠已通过X射线晶体学测定扩展质子化七聚体形式8（+）的分子结构得到证实。质子化诱导的结构转换的分子尺度机械化学运动由分子长度的变化组成，对于七聚体，从6埃（6，卷曲形式）到29埃（8（+），非卷曲形式），对于十五聚体，从12.5埃（9，卷曲形式，X射线结构）到57埃（9（+），非卷曲形式，来自建模）。在质子化/去质子化后，类似的解折叠/折叠运动过程发生在L-酒石酸链15和16中，如质子化形式16（+）所示，解折叠时螺旋诱导的圆二色性丧失。
The long oligopyridinedicarboxamide strand 9, containing 15 heterocyclic rings has been synthesized and its helical structure determined by X-ray crystallography. It was shown that the shorter analogue 6 displays induced circular dichroism and amplification of induced chirality upon dissolution in an optically active solvent, diethyl-L-tartrate. A novel class of helical foldamers was prepared, strands 14-16, based on two oligopyridine carboxamide segments linked through a L-tartaric acid derived spacer. These tartro strands display internal chirality induction as well as chirality amplification. NMR spectroscopy (on 8 and 9) and circular dichroism (on 16) studies show that the oligopyridine carboxamide strands undergo reversible unfolding/folding upon protonation. The protonation-induced unfolding has been confirmed by X-ray crystallographic determination of the molecular structure of the extended protonated heptameric form 8(+). The molecular-scale mechano-chemical motions of the protonation-induced structural switching consist of a change of the length of the molecule, from 6 angstroms (6, coiled form) to 29 angstroms (8(+), uncoiled form) for the heptamer and from 12.5 angstroms (9, coiled form, X-ray structure) to 57 angstroms (9(+), uncoiled form, from modeling) for the pentadecamer. Similar unfolding/folding motional processes take place in the L-tartro strands 15 and 16 upon protonation/deprotonation, with loss of helicity-induced circular dichroism on unfolding as shown for the protonated form 16(+).