  The dynamics of lysozyme is probed by attaching -SCN to all alanine-residues.
The 1-dimensional infrared spectra exhibit frequency shifts in the position of
the maximum absorption by 4 cm$^{-1}$ which is consistent with experiments in
different solvents and indicates moderately strong interactions of the
vibrational probe with its environment. Isotopic substitution $^{12}$C
$\rightarrow ^{13}$C leads to a red-shift by $-47$ cm$^{-1}$ which is
consistent with experiments with results on CN-substituted copper complexes in
solution. The low-frequency, far-infrared part of the protein spectra contain
label-specific information in the difference spectra when compared with the
wild type protein. Depending on the positioning of the labels, local structural
changes are observed. For example, introducing the -SCN label at Ala129 leads
to breaking of the $\alpha-$helical structure with concomitant change in the
far-infrared spectrum. Finally, changes in the local hydration of SCN-labelled
Alanine residues as a function of time can be related to angular reorientation
of the label. It is concluded that -SCN is potentially useful for probing
protein dynamics, both in the high-frequency (CN-stretch) and far-infrared part
of the spectrum.
