麻豆淫院

Catenanes are organic compounds with ring-like molecules that are mechanically interlocked. The mechanical locking system in such molecules is so robust that they can only be disentangled via covalent bond cleavage. A recent study has presented a new strategy for controlling the chirality鈥攖he property where a molecule has non-superimposable mirror images鈥攐f mechanically interlocked molecules (MIMs) like catenanes, without changing its overall shape via non-covalent means.

The researchers successfully demonstrated the synthesis of a compact catenane, BPHC⁴⁺ with tunable mechanical chirality, as in Nature Synthesis.

Unlike traditional chirality that originates from covalent bonds forming asymmetric centers, in MIMs the chirality can arise from the way parts of the molecule are mechanically linked and not the chirality of the individual rings that are interlocked together. This is known as mechanical chirality.

This form of chirality also depends on how the interlocked rings move or arrange themselves, and when it does, it's called co-conformational mechanical chirality. This ability of the molecules to switch between shapes has garnered a lot of attention due to their potential as artificial molecular machines.

Studies have shown that chiral MIMs can be constructed using achiral components by leveraging mechanical bonds the right way. Since the chirality appears solely from specific co-conformations, precise control of these conformations is essential for synthesizing chiral MIMs. The compact nature of MIMs like catenane restricts the movement of interlocked parts, which allows for better control of conformations.

Taking advantage of this phenomenon, the researchers in this study inserted chirality into an originally achiral compound and created a compact catenane with mechanical chirality.

The technique is called isostructural desymmetrization. It is a molecular design strategy where chiral MIMs are created from achiral building blocks by reducing the symmetry of the building blocks while maintaining the same overall shape and compact interlocked structure.

Their starting molecule was an achiral ring-shaped molecule (BPBox虏鈦�) with a box-like shape that was synthesized by replacing the two bipyridinium units in CBPQT鈦粹伜 with slightly different monocationic phenylene-pyridinium groups in order to lower its C鈧倂 symmetry (symmetric over 2-fold axis and two mirror planes).

The isostructural design allowed the two polarized BPBox²⁺ rings to interlock, resulting in catenane BPHC鈦粹伜 which exhibited similar co-conformation to a previously reported compact catenane HC⁸⁺, which was also the molecular inspiration for this new catenane. This specific arrangement gave rise to mechanical chirality, as the structure retained a C鈧� axis while losing all mirror and inversion symmetry.

Researchers found that through co-conformational changes, BPHC鈦粹伜 can switch between its two chiral (mirror-images) in a solution at room temperature, resulting in a racemic mixture鈥攅qual amounts of both chiral forms. Adding chiral disulfonate anions can influence this balance, causing induced chirality and optical activity in solution. This induced chirality in solution results in an 18% excess of one chiral form, which is the only form that crystallizes in the solid state.

This study presents mechanical chirality as a promising design principle with potential applications in pharmaceuticals and materials science.

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