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Crystals with broad robust channels are rare, especially if self-assembled without the aid of metal ions. Three such crystals were prepared based on a common steroid motif. The channels formed are chiral, directional, aligned, and wide enough (>1 nm) to accept a variety of guests (see picture; red: oxygen, blue: nitrogen, green: fluorine).
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Sisson et al. (2005) studied this question.
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