The concept of self-assembled dendrimers is explored for the creation of discrete nanoparticle assemblies.\nHybridization of branched DNA trimers and nanoparticle−DNA conjugates results in the synthesis of\nnanoparticle trimer and tetramer complexes. Multiple tetramer architectures are investigated, utilizing\nAu−DNA conjugates with varying secondary structural motifs. Hybridization products are analyzed by\ngel electrophoresis, and discrete bands are observed corresponding to structures with increasing numbers\nof hybridization events. Samples extracted from each band are analyzed by transmission electron\nmicroscopy, and statistics compiled from micrographs are used to compare assembly characteristics for\neach architecture. Asymmetric structures are also produced in which both 5- and 10-nm Au particles are\nassembled on branched scaffolds.
Abstract New resist systems based on acid‐catalyzed, electrophilic aromatic substitution are described. These new resists show high sensitivity to deep UV and E‐beam radiation with values approaching 2 mJ/cm 2 and 2 μC/cm 2 , respectively. The resists are based on a three component system consisting of poly(4‐hydroxystyrene), a polyfunctional, low molecular weight, latent electrophile, and a photoactive onium salt used as an acid generator. Irradiation of the resist film produces a latent image of acid dispersed in the matrix. During the postbaking step the photo‐generated acid reacts with the latent polyfunctional electrophile and releases a reactive carbocationic intermediate with concomitant liberation of acetic acid. The carbocationic intermediate then reacts with neighboring phenolic moieties in a crosslinking reaction. The substitution reaction liberates a proton, making the process catalytic in nature, thus incorporating the concept of chemical amplification. These highly sensitive materials can be used as nonswelling negative multipurpose resists that function in deep‐UV, x‐ray or E‐beam modes. © 1993 John Wiley & Sons, Inc.
Two steps, one catalyst: A vanadium(V)–oxo complex with a tridentate Schiff base as an additional ligand catalyzes the title reaction which transforms racemic bishomoallylic α-hydroxyesters into trans-tetrahydropyrans (THPs) and cis-tetrahydrofurans (THFs). This synthetic method provides an efficient asymmetric synthesis of cyclic ethers as demonstrated by the first enantioselective synthesis of (−)-pantofuranoid E. TBHP=tert-butylhydroperoxide.
A modular synthetic approach is reported for the synthesis of heterometallic metal-organic complex arrays (MOCAs). Modules of four metal centers containing three different metals copper(II), nickel(II), platinum(II), or ruthenium(II) are prepared using a solid-phase polypeptide synthesis technique and then linked in solution to make MOCAs of eight metal centers as linear, T-branched, and H-branched compounds. The MOCA molecular topologies thus have specific unique linear and branched sequences of metals along the peptide backbone.
The multiple-query nearest-neighbor (MQNN) problem is stated as follows: given a set S of n points in plane and a set Q of m(1≤m≤n) query points, determine for every point in Q its closest neighbor in S. Besides the pure theoretical interest, this problem has many practical applications in various areas such as: computer graphics, pattern recognition and image processing. First, this paper proposes a new time-optimal algorithm to solve the all nearest-neighbor (ANN) problem in [Formula: see text] time on a mesh-connected computer of size [Formula: see text]. Next, using this result in conjunction with the generalized multiple search (GMS) paradigm of Bokka et al. 3,5 we devise a time-optimal algorithm that solves the MQNN problem in [Formula: see text] time on a mesh with multiple broadcasting (MMB) of size [Formula: see text].
