nanoparticles into a hexagonal array, while maintaining the photoluminescence of the nanoparticles. This patterning technique illustrates a simple example of directed deposition where the lateral distribution of the nanoparticles in a thin film can be manipulated rapidly by use of a capillary force. This deposition process is quite versatile since both the size of the nanoparticles and the diameter of the nanopores can easily be changed. In addition, if symmetric copolymers are used, where the morphology is lamellar as opposed to cylindrical, then an assembly of the nanoparticles into nanoscopic channels can be attained. Further, if an electron beam were used to crosslink the PS and degrade the PMMA, then a pattern could be written on the surface and nanoparticles of one size could be selectively placed within the exposed pattern. Subsequent exposure of this film to e-beam or UV radiation would allow the placement of nanoparticles with a different diameter to be placed elsewhere on the surface, resulting in the fabrication of a patterned heterogeneous structure. Furthermore, by placing appropriate functionality on the ligands attached to the nanoparticles, we will be able to impart favorable interactions between the particles and the bottom of the pores to further enhance the deposition process. The simplicity, generality, versatility, and speed of this deposition process make it amenable to the fabrication of complex structures and to large-scale commercial processes. ExperimentalNanoparticle Preparation: Cadmium selenide (CdSe) nanoparticles were prepared according to literature procedures, following the method of Peng and coworkers [25]. Nanoparticles of various diameters were prepared, all of which were capped with an organic shell of phosphorous-containing surfactants, such as tri-n-octylphosphine oxide (TOPO). These hydrophobic nanoparticles could be readily dissolved or dispersed in common organic solvents used in these experiments.Template Preparation: Templates were prepared by anchoring a random copolymer of PS and PMMA containing 58 % styrene onto a silicon wafer onto which a 60±100 nm layer of SiO was evaporated; the coated templates were then annealed for 3 days. Non-anchored random copolymer was rinsed from the surface, and a very thin film of P(S-b-MMA) diblock copolymer with a thickness of L 0 was spin-coated onto this surface, then annealed at 170 C overnight. The film was then exposed to UV light under vacuum, and immersed in glacial acetic acid to selectively remove the degraded PMMA from the PS matrix. Subsequent inspection by atomic force microscopy (AFM) showed hexagonally ordered cylindrical pores normal to the substrate. These templates were then dipped vertically into heptane solutions of nanoparticles at various nanoparticle concentrations. The withdrawal rates varied from fast (~1200 cm min ±1 ) to slow (~2 cm min ±1 ). The impregnated templates were cut into small pieces, and removed from the silicon wafer by etching and floating on 5 % HF in water. The templates were retrieved with a ...

The three-dimensional structure of rice nonspecific lipid transfer protein (nsLTP2) has been solved for the first time. The structure of nsLTP2 was obtained using 813 distance constraints, 30 hydrogen bond constraints, and 19 dihedral angle constraints. Fifteen of the 50 random simulated annealing structures satisfied all of the constraints and possessed good nonbonded contacts. The novel three-dimensional fold of rice nsLTP2 contains a triangular hydrophobic cavity formed by three prominent helices. The four disulfide bonds required for stabilization of the nsLTP2 structure show a different pattern of cysteine pairing compared with nsLTP1. The C terminus of the protein is very flexible and forms a cap over the hydrophobic cavity. Molecular modeling studies suggested that the hydrophobic cavity could accommodate large molecules with rigid structures, such as sterols. The positively charged residues on the molecular surface of nsLTP2 are structurally similar to other plant defense proteins. Plant nonspecific lipid transfer proteins (nsLTPs)1 have been isolated from a number of plant species including wheat, rice, and barley (1). NsLTPs enhance the intermembrane exchange or transfer of lipid molecules in vitro (2). Biotic and abiotic stresses stimulate nsLTP gene expression (3-5). NsLTPs are known to be involved in the formation of a protective hydrophobic layer over the plant surfaces (5). Despite their ability to help plants to manage stress, the exact mechanism of transport is still unclear. NsLTPs are also involved in other biological activities such as flowering and transportation of cutin and suberin monomers (6). NsLTPs present in cereals play an important role in food chemistry. NsLTPs directly affect dough rheology and breadcrumb texture (6). Reports about the isolation of glycosylated and reduced nsLTP fragments from beer suggest that nsLTPs are involved in froth formation during the malting and brewing processes (7).NsLTPs are divided into two subfamilies, nsLTP1 (molecular mass ϳ9 kDa) and nsLTP2 (molecular mass ϳ7 kDa) (2). NsLTP1 is found primarily in aerial organs, whereas nsLTP2 is expressed in roots. Interestingly, both nsLTP1 and nsLTP2 are found in seeds. NsLTP1 is proposed to transport cutin monomers, whereas nsLTP2 is involved in the transport of the more rigid suberin monomers (6). Three-dimensional structures of nsLTP1 from various sources were determined by x-ray and NMR spectroscopic techniques (8). All nsLTP1s share a common structural fold stabilized by four disulfide bonds. The prominent four helices of nsLTP1 are packed against a flexible C-terminal arm formed by a series of turns. In contrast to many globular proteins, the hydrophobic side chains of nsLTP1 do not form a rigid hydrophobic core but instead form a hydrophobic cavity at the interior of the protein. Recently, we have purified nsLTP2 from rice. The amino acid sequence, disulfide bond pattern and stability have been determined (TrEMBL ID P83210) (9). Rice nsLTP2 contains 69 residues and has less than 30% sequence identity wi...

Vigna radiata plant defensin 1 (VrD1) is the first reported plant defensin exhibiting insecticidal activity. We report herein the nuclear magnetic resonance solution structure of VrD1 and the implication on its insecticidal activity. The root-mean-square deviation values are 0.51 +/- 0.35 and 1.23 +/- 0.29 A for backbone and all heavy atoms, respectively. The VrD1 structure comprises a triple-stranded antiparallel beta-sheet, an alpha-helix, and a 3(10) helix stabilized by four disulfide bonds, forming a typical cysteine-stabilized alphabeta motif. Among plant defensins of known structure, VrD1 is the first to contain a 3(10) helix. Glu26 is highly conserved among defensins; VrD1 contains an arginine at this position, which may induce a shift in the orientation of Trp10, thereby promoting the formation of this 3(10) helix. Moreover, VrD1 inhibits Tenebrio molitor alpha-amylase. Alpha-amylase has an essential role in the digestion of plant starch in the insect gut, and expression of the common bean alpha-amylase inhibitor 1 in transgenic pea imparts complete resistance against bruchids. These results imply that VrD1 insecticidal activity has its basis in the inhibition of a polysaccharide hydrolase. Sequence and structural comparisons between two groups of plant defensins having different specificity toward insect alpha-amylase reveal that the loop between beta2 and beta3 is the probable binding site for the alpha-amylase. Computational docking experiments were used to study VrD1-alpha-amylase interactions, and these results provide information that may be used to improve the insecticidal activity of VrD1.

Over the last three decades, transition-metal-catalyzed organic transformations have been shown to be extremely important in organic synthesis. However, most of the successful reactions are associated with noble metals, which are generally toxic, expensive, and less abundant. Therefore, we have focused on catalysis using the abundant first-row transition metals, specifically cobalt. In this Account, we demonstrate the potential of cobalt catalysis in organic synthesis as revealed by our research. We have developed many useful catalytic systems using cobalt complexes. Overall, they can be classified into several broad types of reactions, specifically [2 + 2 + 2] and [2 + 2] cycloadditions; enyne reductive coupling; reductive [3 + 2] cycloaddition of alkynes/allenes with enones; reductive coupling of alkyl iodides with alkenes; addition of organoboronic acids to alkynes, alkenes, or aldehydes; carbocyclization of o-iodoaryl ketones/aldehydes with alkynes/electron-deficient alkenes; coupling of thiols with aryl and alkyl halides; enyne coupling; and C-H bond activation. Reactions relying on π components, specifically cycloaddition, reductive coupling, and enyne coupling, mostly afford products with excellent stereo- and regioselectivity and superior atom economy. We believe that these cobalt-catalyzed π-component coupling reactions proceed through five-membered cobaltacyclic intermediates formed by the oxidative cyclometalation of two coordinated π bonds of the substrates to the low-valent cobalt species. The high regio- and stereoselectivity of these reactions are achieved as a result of the electronic and steric effects of the π components. Mostly, electron-withdrawing groups and bulkier groups attached to the π bonds prefer to be placed near the cobalt center of the cobaltacycle. Most of these transformations proceed through low-valent cobalt complexes, which are conveniently generated in situ from air-stable Co(II) salts by Zn- or Mn-mediated reduction. Overall, we have shown these reactions to be excellent substitutes for less desirable noble-metal systems. Recent successes in cobalt-catalyzed C-H activation have especially advanced the applicability of cobalt in this field. In addition to the more common low-valent-cobalt-catalyzed C-H activation reactions, an in situ-formed cobalt(III) five-membered complex with a 1,6-enyne effectively couples with aromatic ketones and esters through ortho C-H activation, opening a new window in this research area. Interestingly, this reaction proceeds under milder reaction conditions with broad substrate scope. Furthermore, many of the reactions we have developed are highly enantioselective, including enantioselective reductive coupling of enones and alkynes, addition of organoboronic acids to aldehydes, and the cyclization of 2-iodobenzoates with aldehydes. Overall, this Account demonstrates the versatility and utility of cobalt catalysis in organic synthesis.

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