French researchers have been using spectroscopy to tell their left from their right.

Researchers at the CEA Saclay (Atomic Energy Research Centre), near Paris, have been investigating how amino acid chirality affects a peptide's secondary structure, that is, how the peptide chain folds up. Michel Mons and colleagues examine short lengths of peptide chain in the gas phase with ultraviolet and infrared laser spectroscopy. 'This allows us to examine precisely the interactions stabilising the structure, in particular the hydrogen-bonding network,' said Mons.

The group has started its study with a small motif called a gamma-turn. This fold in a peptide chain is a seven-membered ring held together by a hydrogen bond between an amine and a carbonyl group. The researchers made the smallest system that contained a gamma-turn: two peptide residues and an acetyl group to complete the ring. One of the residues was selected to be right-handed, left-handed or achiral, and its effect on the spectrum of the other peptide, phenylalanine, measured. From this, and careful theoretical calculations, the team can determine the overall shape of the turn.

The University of Paris XI's Anne Zehnacker, who pioneered the study of chiral recognition in the gas phase, is impressed by the work's quality and originality. 'The chirality of the amino acids influences the sense of the gamma-turn of the peptides. This observation at the molecular level is important for subjects of biological relevance,' she said.

The team next plans to look at longer peptide chains, which can form bigger secondary structures such as beta-hairpins or alpha-helices, although their spectra will be harder to resolve. Mons added that 'an interesting complementary experiment would be to measure precisely the relative energy of two diastereomeric forms, especially because the energy difference is much smaller than the precision expected from quantum chemistry calculations.'

Colin Batchelor