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Figure 3. Scanning tunneling microscopy images of Aβ₁₋₁₆-Cu²⁺ (a,b) and Aβ₁₋₁₆ (c,d). Imaging conditions: (a,b) 10 nm × 10 nm, V_sample = 0.55 V, I_tunnel =10pA;(c)10nm×10nm,V_sample =0.25V,I_tunnel =17pA;(d)10nm×10nm,V_sample =0.30V,I_tunnel =14pA.

Abstract
β-Amyloid aggregates in the brain play critical roles in Alzheimer’s disease, a chronic neurodegenerative condition. Amyloid-associated metal ions, particularly zinc and copper ions, have been implicated in disease pathogenesis. Despite the importance of such ions, the binding sites on the β-amyloid peptide remain poorly understood. In this study, we use scanning tunneling microscopy, circular dichroism, and surface-enhanced Raman spectroscopy to probe the inter-actions between Cu²⁺ ions and a key β-amyloid peptide fragment, consisting of the first 16 amino acids, and define the copper−peptide binding site. We observe that in the presence of Cu²⁺, this peptide fragment forms β-sheets, not seen without the metal ion. By imaging with scanning tunneling microscopy, we are able to identify the binding site, which involves two histidine residues, His13 and His14. We conclude that the binding of copper to these residues creates an interstrand histidine brace, which enables the formation of β-sheets.

Reference:
Nano Letters 2016, 16, 6282-6289

Credits:
Diana Yugay,^†,‡ Dominic P. Goronzy,^†,‡ Lisa M. Kawakami,^‡ Shelley A. Claridge,^‡,§,∥ Tze-Bin Song,^⊥ ZhongboYan,^⊥ Ya-HongXie,^*,†,⊥ Jeŕom̂eGilles,^*,∇ YangYang,^*,†,⊥ and PaulS.Weiss^{*,†,‡,⊥}

^†California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, United States
^‡Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
^§Department of Chemistry and ^∥Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana 47907, United States
^⊥Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California 90095, United States
^∇Department of Mathematics and Statistics, San Diego State University, San Diego, California 92182, United States

Microscope:
Agilent Pico SPM

Control System:
RHK R9

(c) STM image of a branch of a fractal. The sample bias is 0.5 V and the tunnel current is 0.2 nA. (d) Differential conductivity recorded at the environment of the fractal, red curve (region (i) of (c)), and on the fractal, blue curve (region (i) of (c)), and on the fractal, blue curve (region (ii) of (c)). The sample bias for both curves is 0.5 V and the tunnel current is 0.2 nA.

Abstract
The basic science responsible for the fascinating  shapes of ice crystals and snowflakes is still not understood. Insufficient knowledge of the interaction potentials and the lack of relevant experimental access to the growth process are to blame for this failure. Here, we study the growth of fractal nanostructures in a two-dimensional  (2D) system, intercalated between mica and graphene. Based on our scanning tunneling spectroscopy data, we provide compelling evidence that these fractals are 2D ice. They grow while they are in material contact with the atmosphere at 20 ºC and without significant thermal contact to the ambient. The growth is studied in situ, in real time and space at the nanoscale. We find that the growing 2D ice nanocrystals assume a fractal shape, which is conventionally attributed to Diffusion Limited Aggregation (DLA). However, DLA requires a low mass density mother phase, in contrast to the actual currently present high mass density mother phase. Latent heat effects and consequent transport of heat and molecules are found to be the key ingredients for understanding the evolution of the snow (ice) flakes. We conclude that not the local availability of water molecules (DLA), but rather them having the locally required orientation is the key factor for incorporation into the 2D ice nanocrystal. In combination with the transport of latent heat, we attribute the evolution of fractal 2D ice nanocrystals to local temperature dependent rotation limited aggregation. The ice growth occurs under extreme supersaturation, i.e., the conditions closely resemble the natural ones for the growth of complex 2D snow (ice) flakes and we consider our findings crucial for solving the “perennial” snow (ice) flake enigma. © 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4926467]

Reference:
Journal of Chemical Physics 143, 034702 (2015)

Credits:
Pantelis Bampoulis,^1,2,a) Martin H. Siekman,¹  E. Stefan Kooij,¹ Detlef Lohse,² Harold J. W. Zandvliet,¹  and Bene Poelsema¹

¹Physics of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
²Physics of Fluids and J. M. Burgers Centre for Fluid Mechanics, MESA+ Institute of Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands

Microscope:
RHK UHV3500 STM/AFM with Inverted Viewport

Control System:
RHK SPM1000