The use of tapping mode atomic force microscopy as a sizing tool for nanoparticles is investigated. Height of CdSe nanocrystals measured on different substrates is found to be significantly lower than the particle diameters as determined by transmission electron microscopy. Only minor height variations were found upon particle surface ligand exchange, but significant height variations were found for particles imaged on surfaces with different chemical natures. The distorted height data is attributed to shifts of the tip resonance frequency during imaging, induced by the attractive capillary forces near the substrate. Particle height variations observed when using different drive frequencies of the cantilever corroborate this assignment.

We experimentally demonstrate a notably enhanced acceleration of protons to high energy by relatively modest ultrashort laser pulses and structured dynamical plasma targets. Realized by special deposition of snow targets on sapphire substrates and using carefully planned prepulses, high proton yields emitted in a narrow solid angle with energy above 21 MeV were detected from a 5 TW laser. Our simulations predict that using the proposed scheme protons can be accelerated to energies above 150 MeV by 100 TW laser systems.

Transfer of the green algae Chlamydomonas reinhardtii from low light to high light generated an oxidative stress that led to a dramatic arrest in the synthesis of the large subunit (LSU) of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The translational arrest correlated with transient changes in the intracellular levels of reactive oxygen species and with shifting the glutathione pool toward its oxidized form (Irihimovitch, V., and Shapira, M. (2000) J. Biol. Chem. 275, 16289 -16295). Here we examined how the redox potential of glutathione affected the RNA-protein interactions with the 5-untranslated region of rbcL. This RNA region specifically binds a group of proteins with molecular masses of 81, 62, 51, and 47 kDa in UV-cross-linking experiments under reducing conditions. Binding of these proteins was interrupted by exposure to oxidizing conditions (GSSG), and a new protein of 55 kDa was shown to interact with the RNA. The 55-kDa protein comigrated with Rubisco LSU in one-and two-dimensional gels, and its RNA binding activity was further verified by using the purified protein in UV-cross-linking experiments under oxidizing conditions. However, the LSU of purified and oxidized Rubisco bound to RNA in a sequence-independent manner. A remarkable structural similarity was found between the amino-terminal domain of Rubisco LSU in C. reinhardtii and the RNA binding domain, a highly prevailing motif among RNAbinding proteins. It appears from the crystal structure of Rubisco that the amino terminus of LSU is buried within the holoenzyme. We propose that under oxidizing conditions it is exposed to the surface and can, therefore, bind RNA. Accordingly, a recombinant form of the polypeptide domain that corresponds to the amino terminus of LSU was found to bind RNA in vitro with or without GSSG.When plants and algae absorb light energy that exceeds the level of electron carrier saturation they generate reactive oxygen species (ROS), 1 that cause a variety of cellular and molecular damage. This phenomenon is referred to as photoinhibition and is common to all photosynthetic organisms (1-3). Recovery from photoinhibition can be achieved by decreasing the chlorophyll content and by activating a variety of antioxidant pathways that involve ascorbate and glutathione (4, 5).Ribulose-1,5-bisphosphate carboxylase (Rubisco) is the key enzyme in photosynthetic carbon assimilation. In Chlamydomonas reinhardtii and in land plants the enzyme is composed of eight large subunits (LSU) encoded by the chloroplast rbcL gene and eight small subunits encoded by the nuclear rbcS gene family. Assembly of the holoenzyme is mediated by the chloroplast chaperonins cpn60 and cpn10 (6, 7). We previously showed that transfer of the green algae C. reinhardtii from low light (70 mol m Ϫ2 s Ϫ1 ) to high light (700 mol m Ϫ2 s Ϫ1 ) generates an oxidative stress that leads to photoinhibition and a dramatic arrest in the synthesis of the LSU of Rubisco (8). These light-induced effects were found to be transient, with cell recovery taking pla...

Electrical transport measurements through single InAs and CdSe semiconductor nanocrystals embedded in a thin polymer film were performed using conductance atomic force microscopy. The current and topography images showed excellent correlation, where current was detected only over the nanocrystals. A rapid current decay in consecutive scans was observed for positive sample bias, while remaining intact at negative bias. This current decay was accompanied by bias-dependent changes in the height of the nanocrystals. These phenomena, which were not observed for gold nanocrystals, are attributed to long-sustained charging of the nanocrystals.

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