*5.1. CD Stretching Frequencies*

A blue shift of CδD2 stretching frequencies of prolines in the Src homology 3 domain was interpreted as a correlation with a hydrogen bond Ni+1H... Ni interaction. The blue shifts were 10 and 17 cm<sup>−</sup><sup>1</sup> for Pro 165 and 21 and 28 cm<sup>−</sup><sup>1</sup> for Pro183 relative to two other prolines not affected. This was further supported by model studies of methyl terminated proline dipeptides similar to those of the SRC homology 3 domain. DFT calculations and NBO analysis supported this type of hydrogen bond [108].
