לוח שנה משולב

Repeat proteins form a class of proteins whose structure is dominated by a regular set of short-range interactions. This property may confer significant elasticity on the native state of such proteins. We use a series of advanced single-molecule fluorescence experiments to probe the molecular origin of the spring-like behavior. Our findings point to hydrophobic inter-repeat contacts as the source of the elasticity.

כניסה חופשית

The controlled deposition of beams of size-selected nanoclusters (nanoparticles), assembled from atoms in the gas phase and mass-selected before deposition, is a novel [1] but increasingly popular route to the fabrication of functional surfaces structured on the sub-10nm scale, with applications in catalysis, coatings, radio-sensitizers and biochips [2]. These systems also have the potential to serve as model, ultraprecise reference materials for bio-imaging and metrology (e.g. cryo-electron tomography) and nanotoxicology. New efforts to scale-up dramatically the rate of cluster generation thus promise significant future impact and will be summarised. However fundamental questions remain over the equilibrium atomic structures of the clusters themselves, since direct gas phase structural studies have been limited and new techniques like aberration-corrected scanning transmission electron microscopy (ac-STEM) are only now being applied to soft-landed, size-selected clusters.
I will survey our recently published [2-8] and latest systematic ac-STEM experiments which address the atomic structure of size-selected “magic number” gold clusters – Au20, Au55, Au309, Au561, and Au923 – including dynamical manipulation experiments [6], which probe the transformation of metastable isomers into more stable configurations, and reaction-exposure experiments, which probe the stability of the nanocluster structures under real catalytic conditions. The results distinguish the hierarchy of competing isomers as a function of cluster size, expose concepts such as templated-growth, provide a body of data to stimulate and constrain computational models and are readily extendable to other sizes and cluster materials including binary systems. The image shows one frame from a dynamical STEM video of an Au923±23 cluster.

1. R.E. Palmer, S. Pratontep and H.-G. Boyen, Nature Materials 2 443 (2003).
2. R.E. Palmer and C. Leung, Trends in Biotechnology 25 48 (2007).
3. Z.W. Wang and R.E. Palmer, Nano Lett. 12 91 (2012).
4. Z.W. Wang and R.E. Palmer, Nanoscale 4 4947 (2012) [Cover].
5. Z.W. Wang and R.E. Palmer, Nano Lett. 12 5510 (2012).
6. Z.W. Wang and R.E. Palmer, Phys. Rev. Lett. 108 245502 (2012).
7. S.R. Plant, L. Cao, F. Yin, Z.W. Wang and R.E. Palmer, Nanoscale 6 1258 (2014) [Cover]; S.R. Plant, L. Cao and R.E. Palmer, JACS 136 7559 (2014).
8. D.M. Wells, G. Rossi, R. Ferrando and R.E. Palmer, Nanoscale, Advance Article (2015): DOI 10.1039/C4NR05811A.