Separate incoherent and coherent QENS of protonated and fully deuterated GFP with polarisation analysis.

In order to detect quantum effects in the individual dynamics of hydrogens in proteins, we study a fully deuterated protein powder (dGFP) compared to a protonated one (pGFP) both hydrated in D2O, to search for mass effects. We performed QENS at ILL on a TOF spectrometer (IN5) in 2019. However, it is obvious from experimental data that coherent scattering stemming from collective dynamics of all atoms, including the water hydration shell, contaminates the signal arising from incoherent scattering. It was confirmed through static polarisation analysis at 300K on D7 instrument at ILL in 2021, and proved to be highly dependent on the momentum transfer Q and the temperature probed. In order to yield rigorously comparable results, we want to separate both contributions to QENS at sub-meV resolution by performing polarisation analysis on LET instrument for a large Q range at 10, 220 and 310K.