Nuclear forward scattering for high energy mössbauer transitions.

We have studied nuclear forward scattering of synchrotron radiation for the 67.41 keV resonance of 61Ni using a silicon crystal monochromator with low-index reflections and a multielement detector. This approach can be extended to other high-energy Mössbauer transitions and does not pose any restrictions on the sample environment.

Collective nature of the boson peak and universal transboson dynamics of glasses.

Using probe molecules with resonant nuclei and nuclear inelastic scattering, we are able to measure the density of states exclusively for collective motions with a correlation length of more than approximately 20 A. Such spectra exhibit an excess of low-energy modes (boson peak). This peak behaves in the same way as that observed by conventional methods.

Confined phonons in glasses. A study by nuclear inelastic absorption and Raman scattering.

We have applied nuclear inelastic absorption (NIA) to the molecular glass former dibutyl phthalate/ferrocene, both in bulk and in nanoporous matrices having pore sizes of 50 and 25 A. The quantity g(E)/E(2), where g(E) is the vibrational density of states (VDOS) of the iron atoms, exhibits a pronounced maximum around 2 meV. Confinement in pores leads to a suppression of the VDOS below 1.

Vibrational dynamics of myoglobin determined by the phonon-assisted Mössbauer effect.

The phonon-assisted Mössbauer effect is used to determine the partial phonon density of states of the iron within the active center of deoxymyoglobin, carboxymyoglobin, and dry and wet metmyoglobin between 40 and 300 K. Between 0 and 1 meV the iron density of states increases quadratically with the energy, as in a Debye solid. Mean sound velocities are extracted from this slope.

Nuclear forward scattering of synchrotron radiation by deoxymyoglobin.

Nuclear forward scattering of synchrotron radiation is used to determine the quadrupole splitting and the mean square displacement of the iron atom in deoxymyoglobin in the temperature range between 50 K and 243 K. Above 200 K an abnormally fast decay of the forward scattered intensity at short times after the synchrotron flash is observed, which is caused by protein-specific motions. The results strongly support the picture that protein dynamics seen at the position of the iron can be understood by harmonic motions in the low temperature regime while in the physiological regime diffusive motions in limited space are present.