It was numerically predicted that dissolved gas particles could enrich and adsorb at hydrophobic-liquid interfaces. Here we observe nucleation and growth of bright patches of ∼0.45 nm high on the graphite surface in pure water with frequency-modulation atomic force microscopy when the dissolved gas concentration is below the saturation level. The bright patches, suspected to be caused by adsorption of nitrogen molecules at the graphite-water interface, are composed of domains of a rowlike structure with the row separation of 4.2 ± 0.3 nm. The observation of this ordered adlayer might underline the gas segregation at various water interfaces.

A new, simple, and easily reproducible method of preparing single-atom tips by electroplating Pd or Pt on single-crystal W(111) tips followed by thermal annealing in a vacuum is reported. These tips are both thermally and chemically stable and can also be regenerated when accidentally damaged. The atomic structures of the tips are identical to those prepared by vacuum evaporation, as observed by field ion microscopy. The corresponding field emission characteristics are investigated with field emission microscopy.

Hexanucleotide expansions, GGGGCC, in the non-coding regions of the C9orf72 gene were found in major frontotemporal lobar dementia and amyotrophic lateral sclerosis patients (C9FTD/ALS). In addition to possible RNA toxicity, several dipeptide repeats (DPRs) are translated through repeat-associated non-ATG-initiated translation. The DPRs, including poly(GA), poly(GR), poly(GP), poly(PR), and poly(PA), were found in the brains and spinal cords of C9FTD/ALS patients. Among the DPRs, poly(GA) is highly susceptible to form cytoplasmic inclusions, which is a characteristic of C9FTD/ALS. To elucidate DPR aggregation, we used synthetic (GA) 15 DPR as a model system to examine the aggregation and structural properties in vitro. We found that (GA) 15 with 15 repeats fibrillates rapidly and ultimately forms flat, ribbon-type fibrils evidenced by transmission electron microscopy and atomic force microscopy. The fibrils are capable of amyloid dye binding and contain a characteristic cross-␤ sheet structure, as revealed by x-ray scattering. Furthermore, using neuroblastoma cells, we demonstrated the neurotoxicity and cell-to-cell transmission property of (GA) 15 DPR. Overall, our results show the structural and toxicity properties of GA DPR to facilitate future DPR-related therapeutic development.