Molecular clamps can give precise control over the formation of thymine dimers.

Thymine is a nucleobase - a building block of DNA.  Exposure to ultraviolet light can cause two adjacent thymines in a DNA molecule to become covalently bonded together to form a dimer. This abnormal chemically-bonded pair can contribute to the development of skin cancer.

When separate thymine molecules, which are not part of a DNA strand, are irradiated with UV light a mixture of up to four dimers with different conformations can be formed. But when the reaction occurs in a DNA strand, the resulting dimer is always in one particular conformation. Previously, when scientists wanted to investigate this biologically relevant dimer in the laboratory, they would be faced with having to separate it from a mixture of the four possible products.

That laborious process might have become obsolete thanks to research carried out by Jean-Marie Lehn at University Louis Pasteur, Strasbourg, France, and colleagues. The researchers used a molecule with a rigid planar structure as a clamp to hold thymine molecules in a particular orientation. When the thymines were irradiated, only the dimer with the required conformation was formed. 

The symmetrical clamps lock the thymines in place using two hydrogen bonding sites that bond to specific areas of the thymine molecules.

According to Lehn, the technique could be developed to control the selectivity of other reactions.

Elinor Richards