Many molecules have a reverse twin--a mirror-image, but otherwise identical, version of the other. Now, chemists have developed a method to tell these twins apart--and surprisingly, it works similarly to the human tongue. The technique could be particularly useful for the pharmaceutical industry, as opposite twins of the same molecule can have very different effects.
The most famous examples of mirror-image molecules are amino acids, the building blocks of proteins. Each amino acid has left-handed version and a right-handed one, but life on Earth uses only the left-handed form. Humans can easily taste the difference: left-handed aminos are usually sweet, whereas right-handed aminos tend to be bitter. The tongue tells the two apart with taste receptors that preferentially latch on to either the right- or left-handed version.
Without realizing how the tongue works, Eric Anslyn and colleagues at the University of Texas in Austin set out to create a device that could distinguish right- and left-handed amino acids. First, they invented a set of copper-containing compounds that acted as amino acid receptors. Each receptor preferentially latched on to either the left- or right-handed version of a specific amino acid, although they would react with other aminos too, to some degree. The researchers then set up a test array containing numerous rows of amino acid solutions: Each row contained a different amino acid, and each well contained a different type of receptor.
When a receptor latched onto an amino acid, it changed color; if the affinity was strong, the color change was dramatic. By checking the colored pattern on the array, the researchers could easily distinguish different amino acids, as well as left- or right-handed versions of the same amino, they report 15 May in the Journal of the American Chemical Society.
This is probably the best way to do things, says Anslyn, considering the tongue uses the same pattern-matching strategy. He predicts the technique could be adapted to all sorts of mirror-twin molecules as a quick, easy way to tell which twin is present.
"This is very elegant chemistry," says Kenneth Suslick, a chemist at the University of Illinois, Urbana-Champaign. He notes that the method is cheap compared to current techniques, which use expensive equipment, and says it could be used for quick identification of all sorts of organic impurities in water and air.