Rotaxane

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A rotaxane is a mechanically-interlocked molecular architecture consisting of a "dumbbell shaped molecule" which is threaded through a "macrocycle" (see graphical representation). The name is derived from the Latin for wheel (rota) and axle (axis). The two components of a rotaxane are kinetically trapped since the ends of the dumbbell (often called stoppers) are larger than the internal diameter of the ring and prevent disassociation (unthreading) of the components since this would require significant distortion of the covalent bonds.

Much of the research concerning rotaxanes and other mechanically-interlocked molecular architectures, such as catenanes, has been focused on their efficient synthesis. However, examples of rotaxane have been found in biological systems including: cystine knot peptides, cyclotides or lasso-peptides such as microcin J25 are protein, and a variety of peptides with rotaxane substructure.

Contents

Synthesis

The earliest reported synthesis of a rotaxane in 1967 relied on the statistical probability that if two halves of a dumbbell shaped molecule were reacted in the presence of a macrocycle that some small percentage would connect through the ring.[2] To obtain a reasonable quantity of rotaxane the macrocycle was attached to a solid phase support and treated with both halves of the dumbbell 70 times and then severed from the support to give a 6% yield. However, the synthesis of rotaxanes has advanced significantly and efficient yields can be obtained by preorganizing the components utilizing hydrogen bonding, metal coordination, hydrophobic forces, covalent bonds, or coulombic interactions. The three most common strategies to synthesize rotaxane are "capping", "clipping", and "slipping",[3] though others do exist.[4][5] Recently, Leigh et al. described a new pathway to mechanically-interlocked architectures involving a transition metal center that can catalyse a reaction through the cavity of a macrocycle.[6]

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