Application of Redox-Active Ester Catalysis to the Synthesis of Pyranose Alkyl C-Glycosides.

The direct coupling of shelf-stable, tetrachloro-N-hydroxyphthalimide ester (TCNHPI) glycosyl donors with a variety of alkylzinc reagents under redox catalysis is described. Alkyl C-glycosides are formed directly by a decarboxylative, Negishi-type process in 31-73% yields without the need for photocatalytic activation or additional reductants. Extension of this approach to the coupling of TCNHPI donors with stereodefined α-alkoxy furan-containing alkylzinc halides enabled de novo synthesis of methylene-linked exo-C-disaccharides via an Achmatowicz rearrangement.

Towards Non-stick Silk: Tuning the Hydrophobicity of Silk Fibroin Protein.

Silk fibroin protein is a biomaterial with excellent biocompatibility and low immunogenicity. These properties have catapulted the material as a leader for extensive use in stents, catheters, and wound dressings. Modulation of hydrophobicity of silk fibroin protein to further expand the scope and utility however has been elusive. We report that installing perfluorocarbon chains on the surface of silk fibroin transforms this water-soluble protein into a remarkably hydrophobic polymer that can be solvent-cast. A clear relationship emerged between fluorine content of the modified silk and film hydrophobicity. Water contact angles of the most decorated silk fibroin protein exceeded that of Teflon®. We further show that water uptake in prefabricated silk bars is dramatically reduced, extending their lifetimes, and maintaining mechanical integrity. These results highlight the power of chemistry under moderate conditions to install unnatural groups onto the silk fibroin surface and will enable further exploration into applications of this versatile biomaterial.

Atomic Layer Deposition of Tin Monosulfide Using Vapor from Liquid Bis(N,N'-diisopropylformamidinato)tin(II) and H2S.

The oxide and sulfide of divalent tin show considerable promise for sustainable thin-film optoelectronics, as transparent conducting and light absorbing p-type layers, respectively. Chemical vapor deposition (CVD) and atomic layer deposition (ALD) provide attractive routes to these layers. The literature on volatile tin(II) compounds used as CVD or ALD precursors shows that new compounds can provide different growth rates, film morphologies, preferred crystallographic orientations, and other material properties. We report here the synthesis and characterization of a new liquid tin(II) precursor, bis(N,N'-diisopropylformamidinato)tin(II) (1), which is effective in ALD of SnS in combination with H2S between 65 and 180 °C. Like other highly reactive tin(II) precursors, the growth per cycle linearly decreases from 0.82 Å/cycle at 65 °C to 0.4 Å/cycle at 180 °C. This is obviously different from the case of previously reported SnS ALD using bis(2,4-pentanedionato)tin(II), Sn(acac)2, and H2S; films grow at 0.22-0.24 Å/cycle almost independent of the substrate temperature (125-225 °C, J. Phys. Chem. C 2010, 114, 17597). Quartz crystal microbalance (QCM) experiments for SnS ALD using 1 at 80, 120, and 160 °C were carried out to study the linear decrease of the growth per cycle with increasing substrate temperature. On the basis of these QCM studies, although the mechanism of chemisorption-loss of one ligand or two-can be manipulated by changing the exposure of 1, the purging time, or the temperature, only the temperature changes the growth per cycle. We therefore attribute the decreasing growth per cycle with increasing temperature to a decreasing surface thiol density. Photovoltaic devices prepared from 1-derived SnS have a performance similar to those of the best devices prepared from other precursors, and the device yield and replicability of J-V properties are substantially increased by using 1.

Synthesis of volatile, reactive coinage metal 5,5-bicyclic amidinates with enhanced thermal stability for chemical vapor deposition.

Many microelectronic devices require thin films of silver or gold as wiring layers. We report silver(i) and gold(i) bicyclic amidinate complexes, wherein the constrained ligand geometry lessens the propensity for thermal decomposition. These new volatile compounds provide metallic films of silver and gold during CVD with hydrogen below 230 °C.

Obtaining a Low and Wide Atomic Layer Deposition Window (150-275 °C) for In2 O3 Films Using an InIII Amidinate and H2 O.

Indium oxide is a major component of many technologically important thin films, most notably the transparent conductor indium tin oxide (ITO). Despite being pyrophoric, homoleptic indium(III) alkyls do not allow atomic layer deposition (ALD) of In2 O3 using water as a co-precursor at substrate temperatures below 200 °C. Several alternative indium sources have been developed, but none allows ALD at lower temperatures except in the presence of oxidants such as O2 or O3 , which are not compatible with some substrates or alloying processes. We have synthesized a new indium precursor, tris(N,N'-diisopropylformamidinato)indium(III), compound 1, which allows ALD of pure, carbon-free In2 O3 films using H2 O as the only co-reactant, on substrates in the temperature range 150-275 °C. In contrast, replacing just the H of the anionic iPrNC(H)NiPr ligand with a methyl group (affording the known tris(N,N'-diisopropylacetamidinato)indium(III), compound 2) results in a considerably higher and narrower ALD window in the analogous reaction with H2 O (225-300 °C). Kinetic studies demonstrate that a higher rate of surface reactions in both parts of the ALD cycle gives rise to this difference in the ALD windows.

Synthesis of Calcium(II) Amidinate Precursors for Atomic Layer Deposition through a Redox Reaction between Calcium and Amidines.

We have prepared two new Ca(II) amidinates, which comprise a new class of ALD precursors. The syntheses proceed by a direct reaction between Ca metal and the amidine ligands in the presence of ammonia. Bis(N,N'-diisopropylformamidinato)calcium(II) (1) and bis(N,N'-diisopropylacetamidinato)calcium(II) (2) adopt dimeric structures in solution and in the solid state. X-ray crystallography revealed asymmetry in one of the bridging ligands to afford the structure [(η(2) -L)Ca(µ-η(2) :η(2) -L)(µ-η(2) :η(1) -L)Ca(η(2) -L)]. These amidinate complexes showed unprecedentedly high volatility as compared to the widely employed and commercially available Ca(II) precursor, [Ca3 (tmhd)6 ]. In CaS ALD with 1 and H2 S, the ALD window was approximately two times wider and lower in temperature by about 150 °C than previously reported with [Ca3 (tmhd)6 ] and H2 S. Complexes 1 and 2, with their excellent volatility and thermal stability (up to at least 350 °C), are the first homoleptic Ca(II) amidinates suitable for use as ALD precursors.

On the segmentation and classification of hand radiographs.

This research is part of a wider project to build predictive models of bone age using hand radiograph images. We examine ways of finding the outline of a hand from an X-ray as the first stage in segmenting the image into constituent bones. We assess a variety of algorithms including contouring, which has not previously been used in this context. We introduce a novel ensemble algorithm for combining outlines using two voting schemes, a likelihood ratio test and dynamic time warping (DTW). Our goal is to minimize the human intervention required, hence we investigate alternative ways of training a classifier to determine whether an outline is in fact correct or not. We evaluate outlining and classification on a set of 1370 images. We conclude that ensembling with DTW improves performance of all outlining algorithms, that the contouring algorithm used with the DTW ensemble performs the best of those assessed, and that the most effective classifier of hand outlines assessed is a random forest applied to outlines transformed into principal components.

Latent synthesis of electrically conductive surface-silvered polyimide films.

A facile ambient temperature route to the fabrication of surface silver-metallized polyimide films is described. Silver(I) trifluoromethanesulfonate or silver(I) nitrate and a polyimide, derived from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride and an equimolar amount of 4,4'-oxydianiline and 3,5-diaminobenzoic acid, were dissolved together in dimethylacetamide. Silver(I)-doped films were prepared at thicknesses of 25-40 microm and depleted of solvent by evaporation at ambient temperature and low humidity. The silver(I)-ion-containing films were then treated with aqueous solutions of the reducing agents hydrazine hydrate and hydroxylamine, which brought forth surface-silvered films exhibiting conductivity on the order of bulk polycrystalline silver accompanied by modest-to-high specular reflectivity.

Single-stage synthesis and characterization of reflective and conductive silver-polyimide films prepared from silver(I) complexes with ODPA/4,4'-ODA.

Reflective and surface conductive polyimide films were prepared by the incorporation of silver(I) acetate and trifluoroacetylacetone into a dimethylacetamide solution of the poly(amic acid) formed 3,3',4,4'-oxidiphthalic dianhydride (ODPA) and 4,4'-oxidianiline (4,4'-ODA). Thermal curing of (trifluoroacetylacetonato)silver(I)-poly(amic acid) films led to cycloimidization with concomitant silver(I) reduction, which yielded a reflective and conductive silver surface at selected silver concentrations if the film was cured to a final temperature of 300 degrees C for several hours. The metallized ODPA/4,4'-ODA films retain the essential mechanical properties of an undoped film and have good thermal stability, particularly under a nitrogen atmosphere. The bulk of the composite film was not electrically conductive. The use of (hexafluoroacetylacetonato)silver(I) and silver(I) tetrafluoroborate as sources of silver(I) with ODPA/4,4'-ODA yielded modestly reflective films that never developed conductivity. The silvered films prepared with (trifluoroacetylacetonato)silver(I) can be patterned using mask-etch techniques. Comparisons are made among four similar silver-polyimide systems, with the polyimides being ODPA/4,4'-ODA, BTDA/4,4'-ODA, BPDA/4,4'-ODA, and 6FDA/4-BDAF.