Graphitic nanomaterials such as graphene layers (G) and single-wall carbon nanotubes (SWCNT) are potential candidates in a large number of biomedical applications. However, little is known about the effects of these nanomaterials on biological systems. Here we show that the shape of these materials is directly related to their induced cellular toxicity. Both G and SWCNT induce cytotoxic effects, and these effects are concentration- and shape-dependent. Interestingly, at low concentrations, G induced stronger metabolic activity than SWCNT, a trend that reversed at higher concentrations. Lactate dehydrogenase levels were found to be significantly higher for SWCNT as compared to the G samples. Moreover, reactive oxygen species were generated in a concentration- and time-dependent manner after exposure to G, indicating an oxidative stress mechanism. Furthermore, time-dependent caspase 3 activation after exposure to G (10 microg/mL) shows evidence of apoptosis. Altogether these studies suggest different biological activities of the graphitic nanomaterials, with the shape playing a primary role.

The insolubility of single-walled carbon nanotubes (SWNT) in either water or organic solvents has been a limitation for the practical application of this unique material. Recent studies have demonstrated that the suspendability of SWNT can be greatly enhanced by employing appropriate surfactants. Although the efficiency of anionic, cationic, and nonionic surfactants has been demonstrated to different extents, the exact mechanism by which carbon nanotubes and the different surfactants interact is still uncertain. To deepen the understanding of this interfacial phenomenon, we have investigated the effects of chemical modifications of the surface on the extent of nanotube−surfactant interaction. Such changes in the surface chemistry of the SWNT can be achieved by simply varying the pretreatment method, which can be acidic or basic. We have found that intrinsic surface properties such as the PZC (point of zero charge) are greatly affected by the purification method. That is, the electrical charge of the SWNT surface varies with the pH of the surrounding media. However, it has been found that during the adsorption of the anionic surfactant sodium dodecylbenzenesulfonate (NaDDBS) on SWNT Coulombic forces do not play a central role, but are overcome by the hydrophobic interactions between the surfactant tail and the nanotube walls. Only at pH values far from the PZC do the Coulombic forces become important. The hydrophobic forces between the surfactant tail and the nanotube determine the structure of the surfactant-stabilized nanotubes. In such a structure, each nanotube is covered by a monolayer of surfactant molecules in which the heads form a compact outer surface while the tails remain in contact with the nanotube walls. It is important to note that although the final configuration can be described as a cylindrical micelle with a nanotube in the center, the mechanism of formation of this structure does not proceed by incorporation of a nanotube into a micelle, but rather by a two-step adsorption that ends up in the formation of a surfactant monolayer.

Carbon nanotubes (CNTs) were found to penetrate tomato seeds and affect their germination and growth rates. The germination was found to be dramatically higher for seeds that germinated on medium containing CNTs (10-40 mug/mL) compared to control. Analytical methods indicated that the CNTs are able to penetrate the thick seed coat and support water uptake inside seeds, a process which can affect seed germination and growth of tomato seedlings.

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Photovoltaic conversion was achieved from high-density p-n heterojunctions between single-wall carbon nanotubes (SWNTs) and n-type crystalline silicon produced with a simple airbrushing technique. The semitransparent SWNT network coating on n-type silicon substrate forms p-n heterojunctions and exhibits rectifying behavior. Under illumination the numerous heterojunctions formed between substrate generate electron-hole pairs, which are then split and transported through SWNTs (holes) and n-Si (electrons), respectively. The nanotubes serve as both photogeneration sites and a charge carriers collecting and transport layer. Chemical modification by thionyl chloride of the SWNT coating films was found to significantly increase the conversion efficiency by more than 50% through adjusting the Fermi level and increasing the carrier concentration and mobility. Initial tests have shown a power conversion efficiency of above 4%, proving that SOCl(2) treated-SWNT/n-Si configuration is suitable for light-harvesting at relatively low cost.

We heterologously overproduced a hyperthermostable archaeal low potential (E m ‫؍‬ ؊62 mV) Rieske-type ferredoxin (ARF) from Sulfolobus solfataricus strain P-1 and its variants in Escherichia coli to examine the influence of ligand substitutions on the properties of the [2Fe-2S] cluster. While two cysteine ligand residues (Cys 42 and Cys 61 ) are essential for the cluster assembly and/or stability, the contributions of the two histidine ligands to the cluster assembly in the archaeal Riesketype ferredoxin appear to be inequivalent as indicated by much higher stability of the His 64 Proteins containing Rieske-type [2Fe-2S] clusters are widespread in nature from hyperthermophilic Archaea and Bacteria to Eukarya and play critical electron transfer roles in various pathways such as aerobic respiration, photosynthesis, and biodegradation of various alkene and aromatic compounds (1-4). In contrast to regular plant-and vertebrate-type ferredoxins having complete cysteinyl ligations, the Rieske-type cluster has an asymmetric iron-sulfur core with the S ␥ atom of each of the two cysteine residues coordinated to one iron site and the N ␦ atom of each of the two histidine residues coordinated to the other iron site. This asymmetric ligation results in some unique redox and spectroscopic properties (for reviews, see Refs. 1 and 3-5). This cluster coordination was firmly established by recent x-ray crystal structures of several different Rieske-type protein domains (6 -11).Two different types of Rieske clusters are observed in proteins. One type displays higher reduction potentials (E m ) 1 of approximately ϩ150 to ϩ490 mV and occurs in proton-translocating respiratory complexes (cytochrome bc 1 /b 6 f complexes and their archaeal homologs without c-type cytochromes), being involved in not only electron transfer but also substrate binding and oxidation at the quinol-oxidizing Q o site (2-5, 12-15). The other type displays lower E m values of approximately Ϫ150 to Ϫ50 mV and has been found in a diverse group of bacterial multicomponent terminal oxygenases and soluble Rieske-type ferredoxins (1, 3, 8, 9, 16 -27). However, none of the latter class has been characterized in detail from any archaeal species.We recently found that the genomic DNA sequence of the thermoacidophilic archaeon Sulfolobus solfataricus strain P-1 (DSM 1616T) encodes an archaeal homolog of bacterial small Rieske-type ferredoxins with no consensus disulfide signature (DDBJ accession number AB047031 (27)). This arf gene was found by homology search against the deduced amino acid sequence of Sulfolobus tokodaii sulredoxin, a water-soluble homolog of a high potential Rieske protein (E m,low pH ϳ ϩ190 mV) with a consensus disulfide linkage (DDBJ accession number AB023295) 2 (28 -30) (Fig. 1). Subsequent cloning and heterologous overexpression in Escherichia coli of this S. solfataricus arf gene encoding the archaeal Rieske-type ferredoxin (ARF) (27) have provided an opportunity to define the influence of surrounding amino acid residues on the electronic and s...

A novel polyvinylpyrrolidone (PVP)‐directed crystallization route is successfully developed for the shape‐selective synthesis of ZnO particles with distinctive shapes, including monolayer, bilayer, and multilayer structures, gears, capped pots, hemispheres, and bowls, at temperatures as low as 32 °C. This route is based on exploiting a new water/PVP/n‐pentanol system. In the system, PVP can greatly promote ZnO nucleation by binding water and direct ZnO growth by selectively capping the specific ZnO facets, which is confirmed by IR absorption spectra. The bandgap of the ZnO particles is readily tuned by modifying the product morphology by adjusting the PVP chain length, PVP amount, water volume, and reaction temperature. The remarkable ZnO structures and the biomimetic method demonstrated here not only expand the structures and applications of ZnO but also provide a new approach to explore the unusual structures for novel physicochemical properties and technological applications. Furthermore, the novel ZnO/Au/ZnO sandwich structure is successfully fabricated by inserting a Au plate into the bilayer ZnO structure.

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