Keeping chirality under control

Molecular containers for chiral biomolecules have been made using inorganic layered materials by researchers in China. These containers could be used in storage or delivery systems.

Biological molecules can be held between inorganic layers

Xue Duan and colleagues from Beijing University of Chemical Technology and Tsinghua University have increased L-tyrosine's stability by inserting it between the layers of layered double hydroxides (LDHs). LDHs can act as hosts for different anionic species including biomolecules, reduced C₆₀ and cyclodextrins. The host materials' layered nature can stop chiral molecules undergoing racemisation - switching between different chiral forms.

About two-thirds of drug molecules are chiral; their chirality can influence the drug's properties and efficiency in the body. In some cases only one enantiomer is biologically active and in others, such as thalidomide, one is harmful. Increasingly, drugs are sold as pure enantiomers. But even when only one enantiomer is prepared, racemisation can still happen.

L-Tyrosine is a non-essential amino-acid with a similar structure to L-dopa, which is used in Parkinson's disease treatment.

Exposing L-tyrosine to sunlight, heat and UV light causes it to partially racemise. After it is incorporated into LDHs' layers, racemisation is prevented. Duan's group suggests that this is because the guest L-tyrosine molecules are restricted within the layers of the LDH host. Also, the LDH stops UV light reaching the molecules.

Duan plans to continue investigating the interactions between biomolecules and LDHs, and sees possibilities for other applications, saying 'intercalation in the layered host has another potential benefit.LDHs are effective as a matrix for controlled release drug delivery systems'.

Rebecca Lavender