A new Raman cross section measurement technique monitors the tyrosine environmental dependence of the electromagnetic field strength

We have developed a new Raman spectroscopic technique which can be used to determine relative Raman intensities as a function of the liquid medium refractive index. We utilize teflon as an external standard. The refractive index dependence of the solid angle of light collection disappears in our sampling geometry and the self-absorption bias is minimized. We observe a refractive index dependence for the Raman intensity for N-acetyl-L-tyrosinamide (NATYR) close to that calculated using previously derived relations which determine the effect of the refractive index on the electromagnetic field strength and upon the Raman scattered intensities. This dependence gives a ca. 25% increased resonance Raman intensity of NATYR in ethylene glycol compared to water for ca. 243 nm excitation. The strong dependence of the Raman intensity upon the environment suggests that UV resonance Raman intensity measurements can be used to monitor the average environmental refractive index of aromatic amino acids in proteins.