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A large bis-urea macrocycle was synthesized and assembled into columnar nanotubes containing a sizable cavity. This purely organic nanotube is held together primarily by hydrogen bonding and yet shows remarkable thermal stability up to 180 degrees C in the presence and absence of acetic acid guest. This enables the nanotube to be used as reusable organic zeolite.
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Shimizu et al. (2003) studied this question.
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