Structural and mechanical properties of TTR105-115 amyloid fibrils from compression experiments.

Amyloid fibrils, originally associated with neurodegenerative diseases, are now recognized to have interesting mechanical properties. By using synchrotron x-ray diffraction at high pressure in a diamond anvil cell we determined the bulk modulus of TTR105-115 amyloid fibrils in water and in silicone oil to be 2.6 and 8.1 GPa, respectively. The compression characteristics of the fibrils are quite different in the two media, revealing the presence of cavities along the axis of the fibrils, but not between the ß-sheets, which are separated by a dry interface as in a steric zipper motif. Our results emphasize the importance of peptide packing in determining the structural and mechanical properties of amyloid fibrils.

Exploring the thermochromism of sulfite-embedded polyoxometalate capsules.

The Dawson-type polyanion [α-Mo(18)O(54)(SO(3))(2)](4-), with two SO(3)(2-) templates embedded inside a polyoxomolybdate(vi) cage, exhibits thermochromism over an exceptionally wide temperature range (∼500 K). The temperature dependence of the cluster structure, established from X-ray crystallography, IR and Raman spectroscopy and DFT calculations, is related to a decreasing HOMO-LUMO gap in the near UV with increasing temperature. We postulate this is due to geometrical changes that affect both the occupied and unoccupied frontier molecular orbitals of this cluster anion.

Identification of new pillared-layered carbon nitride materials at high pressure.

The compression of the layered carbon nitride C6N9H3 · HCl was studied experimentally and with density functional theory (DFT) methods. This material has a polytriazine imide structure with Cl(-) ions contained within C12N12 voids in the layers. The data indicate the onset of layer buckling accompanied by movement of the Cl(-) ions out of the planes beginning above 10-20 GPa followed by an abrupt change in the diffraction pattern and c axis spacing associated with formation of a new interlayer bonded phase. The transition pressure is calculated to be 47 GPa for the ideal structures. The new material has mixed sp(2)-sp(3) hybridization among the C and N atoms and it provides the first example of a pillared-layered carbon nitride material that combines the functional properties of the graphitic-like form with improved mechanical strength. Similar behavior is predicted to occur for Cl-free structures at lower pressures.