The strongest triple-hydrogen-bonded complex measured to date has been reported by chemists in Europe (J. Am. Chem. Soc., DOI: 10.1021/ja067410t). A group led by David A. Leigh and Hamish McNab of Scotland's University of Edinburgh and Francesco Zerbetto of Italy's University of Bologna designed the complex shown with all three H-bond acceptors (A) in one molecule (red) and all three H-bond donors (D) in another. Systems with this AAA-DDD motif are known to associate far more strongly than complexes with an AAD-DDA or ADA-DAD pattern because they provide the maximum number of attractive secondary electrostatic interactions between the H-bonding partners. By tweaking the aromatic framework of a known AAA molecule, the team was able to create an H-bond network that's more than 100 times stronger than what's been measured previously. "Our results show the extraordinary significance of these secondary interactions," Leigh says. "They can make the difference between a triple-hydrogen-bonded complex binding constant being 90 M-1 and being 20 million M-1."