Computational and Experimental Investigation of the Structure of Peptide Monolayers on Gold Nanoparticles

The self-assembly and self-organization of small molecules on the surface of nanoparticles constitute a potential route toward the preparation of advanced proteinlike nanosystems. However, their structural characterization, critical to the design of bionanomaterials with well-defined biophysical and biochemical properties, remains highly challenging. Here, a computational model for peptide-capped gold nanoparticles (GNPs) is developed using experimentally characterized Cys-Ala-Leu-Asn-Asn (CALNN)- and Cys-Phe-Gly-Ala-Ile-Leu-Ser-Ser (CFGAILSS)-capped GNPs as a benchmark. The structure of CALNN and CFGAILSS monolayers is investigated using both structural biology techniques and molecular dynamics simulations. The calculations reproduce the experimentally observed dependence of the monolayer secondary structure on the peptide capping density and on the nanoparticle size, thus giving us confidence in the model. Furthermore, the computational results reveal a number of new features of peptide-capped monolayers, including the importance of sulfur movement for the formation of secondary structure motifs, the presence of water close to the gold surface even in tightly packed peptide monolayers, and the existence of extended 2D parallel β-sheet domains in CFGAILSS monolayers. The model developed here provides a predictive tool that may assist in the design of further bionanomaterials

Mechanistic Insights and Implications of Dearomative Rearrangement in Copper-Free Sonogashira Cross-Coupling Catalyzed by Pd-Cy*Phine

The reaction mechanism for the <i>in situ</i> prepared Pd-Cy*Phine catalyst used in copper-free Sonogashira coupling was investigated using density functional theory. In addition, the significance of the <i>meta</i>-terarylphosphine ligand architecture of Cy*Phine was probed, as it had been previously shown experimentally to augment catalytic activity relative to its biarylphosphine analogue, XPhos. The calculated reaction barriers and free energies for the steps in the catalytic cycle suggest that the suppression of a dearomative rearrangement pathway is likely to be an important feature for the improved catalytic performance observed for the Pd-Cy*Phine system

Mechanistic Insights and Implications of Dearomative Rearrangement in Copper-Free Sonogashira Cross-Coupling Catalyzed by Pd-Cy*Phine

The reaction mechanism for the <i>in situ</i> prepared Pd-Cy*Phine catalyst used in copper-free Sonogashira coupling was investigated using density functional theory. In addition, the significance of the <i>meta</i>-terarylphosphine ligand architecture of Cy*Phine was probed, as it had been previously shown experimentally to augment catalytic activity relative to its biarylphosphine analogue, XPhos. The calculated reaction barriers and free energies for the steps in the catalytic cycle suggest that the suppression of a dearomative rearrangement pathway is likely to be an important feature for the improved catalytic performance observed for the Pd-Cy*Phine system

Step Flow Versus Mosaic Film Growth in Hexagonal Boron Nitride

Many emerging applications of hexagonal boron nitride (h-BN) in graphene-based nanoelectronics require high-quality monolayers as the ultrathin dielectric. Here, the nucleation and growth of h-BN monolayer on Ru(0001) surface are investigated using scanning tunneling microscopy with a view toward understanding the process of defect formation on a strongly interacted interface. In contrast to homoelemental bonding in graphene, the heteroelemental nature of h-BN gives rise to growth fronts with elemental polarity. This can have consequences in the different stages of film growth, from the nucleation of h-BN magic clusters and their sintering to form compact triangular islands to the growth of patchwork mosaic monolayer with a high density of misfit boundaries. The parallel alignment of triangular islands on the same terrace produces translational fault lines when growth fronts merge, while antiparallel alignment of islands on adjacent terraces produces non-bonded fault lines between domains terminated by like atoms. With these insights into the generation of void defects and fault lines at grain boundaries, we demonstrate a strategy to obtain high-quality h-BN monolayer film based on step flow growth