CHESS DMR-0936384 2013-April_1

How do superlattices grow?Joel Brock, Cornell University, DMR 0936384

(top) Model of fabricated nanoparticles, with ligands coating the surfaces. (bottom) Stable phases formed as a function of interparticle distance and interaction..

Correlating Superlattice Polymorphs to Internanoparticle Distance, Packing Density, and Surface Lattice in Assemblies of PbS Nanoparticles, Z. Wang, C. Schliehe, K. Bian, D. Dale, W. A. Bassett, T. Hanrath, C. Klinke, and H.t Weller, Nano Letters 2013 13 (3), 1303-1311

Intellectual Merit: A team of scientists from Cornell University, the Max Planck Institute of Colloids and Interfaces in Potsdam in Germany, and the University of Hamburg, also in Germany, are the first to have studied how superlattices form. Superlattices are a new class of functional materials made up of assemblies of nanoparticles that are engineered to have tunable interactions that lead to novel ordered structures. They could find uses in a range of electronics applications, but the structures are still difficult to fabricate in large quantities and in a controlled way. High-resolution small- and wide-angle x-ray scattering at the B1 end station of CHESS was used to watch the nucleation of three main superlattice polymorphs: amorphous, body-centered-cubic (bcc), and face-centered-cubic (fcc). The type of superlattice formed can be controlled by changing the distance between nanoparticles, via ligands, without altering their size.

CHESS DMR-0936384 2013-April_2

(a) TEM image of a nanoparticle monolayer, (b) ligand decorated nanoparticle in bcc lattice, (c) 1D x-ray scattering patters showing bcc ordering, (f-h) 2D small-angle x-ray patterns delineates phases.

Broader Impacts: Nanoparticles can be assembled into periodically ordered superlattices that show promise for a range of technology applications, such as photovoltaics, light-emitting diodes and thermoelectrics (TE). However, researchers still do not fully understand how the particles come together via complex nucleation and other processes. The nanoparticles appear to behave like hard spheres, packing together to form a fairly simple superlattice phase. However, they also appear to go through various, quite intricate nucleation and growth steps that involve multiple nanoparticle interactions with surface-capping ligands and surrounding solvents. Using techniques only available at CHESS, these researchers discovered a series of structure-property relation diagrams exhibited by confined nanoparticles with different sizes and shapes.

Correlating Superlattice Polymorphs to Internanoparticle Distance, Packing Density, and Surface Lattice in Assemblies of PbS Nanoparticles, Z. Wang, C. Schliehe, K. Bian, D. Dale, W. A. Bassett, T. Hanrath, C. Klinke, and H.t Weller, Nano Letters 2013 13 (3), 1303-1311

How do superlattices grow?Joel Brock, Cornell University, DMR 0936384

CHESS DMR-0936384 2013-April_3

Building large multiprotein mRNA complexesJoel Brock, Cornell University, DMR 0936384

The ab initio bead models of the free (blue) and poly(A)11 complex (green) with their corresponding maximum diameters (Dmax). Each model represents the averaged shape obtained from 50 models calculated. The overlay of the two shapes shows the change in the conformation upon poly(A) binding. For comparison, the crystal structure of the isolated RRM2 domain (gray) is shown.

Interdomain Allostery Promotes Assembly of the Poly(A) mRNA Complex with PABP and eIF4GMolecular Cell, N. Safaee, G. Kozlov, A. M. Noronha, J. Xie, C. J. Wilds, K. Gehring, Molecular Cell Volume 48, Issue 3, 9 November 2012, Pages 375–386.

Intellectual Merit: Cells synthesize proteins by transcribing genetic information from DNA onto messenger RNA (mRNA) molecules. The mRNA conveys the instructions for protein synthesis to ribosomes, which use this information to make the proteins. Various helper proteins are involved in this transcription process. The Gehring group and co-workers (McGill and Concordia Universities, Montreal, Canada) report in the journal Molecular Cell how they used X-ray methods to elucidate how this transcription process works. Combining X-ray crystallography, small-angle-X-ray scattering (SAXS) collected at CHESS and the Canadian Light Source with NMR data, the groups showed that complex formation leads to a compact structure, which was crystallized to reveal the atomic interactions responsible for the specificity of the molecular interactions. The resulting insights as to the structural steps involved in this complex process help scientists better understand the protein factory on which we are all dependent.

CHESS DMR-0936384 2013-April_4

The crystal structure of the ternary complex of Poly(A) PABP eIF4G (brown) bound to PABP RRM1-2 (light blue) in the presence of poly(A)11 (dark blue)..

Interdomain Allostery Promotes Assembly of the Poly(A) mRNA Complex with PABP and eIF4GMolecular Cell, N. Safaee, G. Kozlov, A. M. Noronha, J. Xie, C. J. Wilds, K. Gehring, Molecular Cell Volume 48, Issue 3, 9 November 2012, Pages 375–386.

Broader Impacts: Translation initiation is an important level of gene regulation in thecell. The Gehring group and co-workers (McGill and Concordia Universities, Montreal, Canada presented the molecular basis for the cooperative assembly of a portion of the mRNA ‘‘closed loop’’ comprising part of eIF4G, PABP, and the RNA poly(A) tail. Previously, the mechanisms underlying the self-assembly of these complexes was largely unknown. They propose that the interdomain inhibition exhibited by PABP is likely to be a general mechanism for the assembly of other macro-molecular assemblies and explains previous observations of the enhancement translation initiation by poly(A) RNA. The crystal structure explains the previous observations of the enhancement translation initiation by polyA RNA in trans and serves as a model for interdomain allostery in RNA binding proteins. These insights will help scientists better understand protein synthesis.

Building large multiprotein mRNA complexesJoel Brock, Cornell University, DMR 0936384