“Chameleonic” backbone hydrogen bonds in protein binding and as drug targets C. A. Menéndez, S. R. Accordino, D. C. Gerbino and G. A. Appignanesi Eur. Phys. J. E, 38 10 (2015) 107 Published online: 19 October 2015 DOI: 10.1140/epje/i2015-15107-3