Because of the tremendous effort of a great number of researchers, the catalytic asymmetric dialkylzinc addition to aldehydes has become a mature method. Ligands of diverse structures have been obtained, and high enantioselectivity for all different types of aldehydes have been achieved. Among the representative excellent catalysts are compounds 1, 8, 120, 325, 352, and 360 discussed above. However, compared to the well-developed dialkylzinc addition, the catalytic asymmetric reactions of aryl-, vinyl-, and alkynylzinc reagents with aldehydes are still very much under developed. Although catalysts such as (S)-402 and 210 prepared by Pu and Bolm have shown good enantioselectivity for the reaction of diphenylzinc with certain aromatic and aliphatic aldehydes, the generality of these catalysts for other [formula: see text] arylzinc reagents have not been studied. The vinylzinc additions using ligands 1 and 412 reported by Oppolzer and Wipf were highly enantioselective for certain aromatic aldehydes but not as good for aliphatic aldehydes. Carreira discovered highly enantioselective alkynylzinc additions to aldehydes promoted by the chiral amino alcohol 415, but this process was not catalytic yet. Ishizaki achieved good enantioselectivity for the catalytic alkynylzinc addition to certain aldehydes by using compounds 160, but the enantioselectivity for simple linear aliphatic aldehydes was low. Another much less explored area is the organozinc addition to ketones. Yus and Fu showed very promising results by using ligands 381 and 406 for both dialkylzinc and diphenylzinc additions to ketones, but the scope of these reactions were still very limited. Therefore, more work is needed for the aryl-, vinyl-, and alkynylzinc additions and for the organozinc addition to ketones, although many good catalysts have been obtained for the dialkylzinc addition to aldehydes. Development of these reactions will allow the catalytic asymmetric synthesis of a great variety of functional chiral alcohols that are either the structural units or synthons of many important organic molecules as well as molecules of biological functions. Macromolecular chiral catalysts have become a very attractive research subject in recent years because these materials offer the advantages of simplified product isolation, easy recovery of the generally quite expensive chiral catalysts, and potential use for continuous production. Three types of macromolecules including flexible achiral polymers anchored with chiral catalysts, rigid and sterically regular main chain chiral polymers, and chiral dendrimers have been used for the asymmetric organozinc addition to aldehydes. Among these materials, the binaphthyl-based polymers such as (R)-451 developed by Pu have shown very high and general enantioselectivity. Study of the binaphthyl polymers in the asymmetric organozinc addition has demonstrated that it is possible to systematically modify the structure and function of the rigid and sterically regular polymer for the development of highly enantioselective polymer...

Low-temperature scanning tunneling microscopy (STM) has been used to image CH 3 -terminated Si(111) surfaces that were prepared through a chlorination/alkylation procedure. The STM data revealed a wellordered structure commensurate with the atop sites of an unreconstructed 1 × 1 overlayer on the silicon (111) surface. Images collected at 4.7 K revealed bright spots, separated by 0.18 ( 0.01 nm, which are assigned to adjacent H atoms on the same methyl group. The C-H bonds in each methyl group were observed to be rotated by 7 ( 3°away from the center of an adjacent methyl group and toward an underlying Si atom. Hence, the predominant interaction that determines the surface structure arises from repulsions between hydrogen atoms on neighboring methyl groups, and secondary interactions unique to the surface are also evident.Hydrogen-terminated (111)-oriented Si surfaces are well documented to have a low number of structural and electrically active defect sites. 1,2 However, these surfaces degrade rapidly in air and in other oxidizing environments. 3,4 Consequently, several wet chemical methods have been developed for the functionalization of both crystalline and porous Si surfaces. [5][6][7][8][9][10] These chemical methods offer molecular-level control over the interfacial chemistry of Si surfaces, attracting attention for applications in molecular electronics, 11 sensing, 12-14 photoelectrochemistry, 4 chemical and electrical surface passivation, 8,15 porous Si photoluminescence, 9 and control of photopatterning. 6 Molecular modeling indicates that methyl groups are the only saturated hydrocarbon moiety that can terminate every Si atop site on the unreconstructed Si(111) surface. 8,[16][17] Such complete chemical termination is expected to offer the most robust passivation of surface defects and to provide the best resistance to oxidation of the resulting Si surfaces. Prior workers have hypothesized that functionalization with longer alkyl chains yields incomplete coverage of the Si(111) surface, 18 with the remainder of the sites being terminated by either -OH, -H, or other unidentified surface species. 16,19 In this work, we report low-temperature STM studies that have revealed the structure of the fully methyl-terminated Si(111) surface prepared by wet chemical methods.Silicon surfaces were functionalized using a two-step chlorination/alkylation procedure. 8 The samples were obtained from (111)-oriented, Sb-doped, 0.005-0.02 Ω cm resistivity, n-type Si wafers having a miscut error of (0.5°. The samples were cleaned and oxidized for 5 min at 80°C in a solution of 1:1:5 (vol) 30% H 2 O 2 /30% NH 3 /H 2 O and were then terminated with Si-H bonds by etching for 15 min in 40% NH 4 F(aq). This etching method has been demonstrated to produce large atomically flat terraces. 20 Chlorination was performed by exposing the samples to a solution of PCl 5 in chlorobenzene. 8 A small amount of benzoyl peroxide was added to initiate a radical reaction, and the samples were heated to 90-100°C for 45 min. The surfaces were remo...

Scaffolded DNA origami has recently emerged as a versatile, programmable method to fold DNA into arbitrarily shaped nanostructures that are spatially addressable, with sub-10 nm resolution. Toward functional DNA nanotechnology, one of the key challenges is to integrate the bottom up self-assembly of DNA origami with the top-down lithographic methods used to generate surface patterning. In this report we demonstrate that fixed length DNA origami nanotubes, modified with multiple thiol groups near both ends, can be used to connect surface patterned gold islands (tens of nanometers in diameter) fabricated by electron beam lithography (EBL). Atomic force microscopic imaging verified that the DNA origami nanotubes can be efficiently aligned between gold islands with various inter-island distances and relative locations. This development represents progress toward the goal of bridging bottom up and top down assembly approaches.

Temperature-dependent electron transport was measured through three-dimensional close-packed alkanethiol-stabilized silver nanocrystal arrays using interdigitated array electrodes. Nanocrystals ranging from 35 to 77 Å in diameter with Coulomb blockade energies well above kT were studied. The nanocrystal superlattices exhibit linear current−voltage behavior for temperatures as low as 70 K. Ordered face-centered cubic (fcc) superlattices exhibit a positive temperature coefficient of resistivity (TCR), characteristic of a metal, at temperatures above approximately 225 to 245 K, depending on the particle size. The values of the conductivity, on the order of 10-6 to 10-7 Ω-1 cm-1, however, are characteristic of semiconductors. Below the transition temperature, the TCR for the size-monodisperse nanocrystal arrays becomes negative, characteristic of an insulator and the conductance G, of the ordered arrays scales exponentially with temperature as G ∝ exp[−(T o/T) ν ]. The exponent ν, ranges from 0.67 to 1.34 for nanocrystals 77 Å to 35 Å in diameter, respectively, characteristic of a gap in the density of states in the overall electronic structure of the superlattice. We believe that electron transport occurs through a polaron hopping mechanism. In contrast to the organized superlattices, disordered close-packed nanocrystals exhibit insulating behavior at all temperatures studied due to (Anderson-type) disorder.

A new class of electronic materials derived predominantly from natural foods and foodstuffs, with minimal levels of inorganic materials, is developed and studied to build edible electronic components and devices compatible with the gastrointestinal (GI) tract. A “toolkit” of food‐based electronic materials, fabrication schemes, basic device components, and functional devices with integrated sensing and wireless signal transmission is reported. These new materials establish the possibility to extend GI electronic devices beyond the ingested nondegradable systems to edible and nutritive systems, in which the described materials may be ingested and assimilated as metabolized nutrients. This study represents a new era of edible electronics with the potential to revolutionize modern biomedical technologies and devices.