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The acyl-CoA dehydrogenases are a family of flavin adenine dinucleotide-containing enzymes that catalyze the first step in the beta-oxidation of fatty acids and catabolism of some amino acids. They exhibit high sequence identity and yet are quite specific in their substrate binding. Short chain acyl-CoA dehydrogenase has maximal activity toward butyryl-CoA and negligible activity toward substrates longer than octanoyl-CoA. The crystal structure of rat short chain acyl-CoA dehydrogenase complexed with the inhibitor acetoacetyl-CoA has been determined at 2.25 A resolution. Short chain acyl-CoA dehydrogenase is a homotetramer with a subunit mass of 43 kDa and crystallizes in the space group P321 with a = 143.61 A and c = 77.46 A. There are two monomers in the asymmetric unit. The overall structure of short chain acyl-CoA dehydrogenase is very similar to those of medium chain acyl-CoA dehydrogenase, isovaleryl-CoA dehydrogenase, and bacterial short chain acyl-CoA dehydrogenase with a three-domain structure composed of N- and C-terminal alpha-helical domains separated by a beta-sheet domain. Comparison to other acyl-CoA dehydrogenases has provided additional insight into the basis of substrate specificity and the nature of the oxidase activity in this enzyme family. Ten reported pathogenic human mutations and two polymorphisms have been mapped onto the structure of short chain acyl-CoA dehydrogenase. None of the mutations directly affect the binding cavity or intersubunit interactions.

The nature of the bonding interactions between aryl isocyanides and gold and palladium surfaces was investigated using attenuated total refection infrared (ATR-IR) spectroscopy. The experiments were conducted by evaporating a film of either palladium or gold onto a ZnSe internal reflection element (IRE). The studies reveal that aryl isocyanides form only σ-bonded species when coordinated to gold and that these species are bonded relatively weakly to the gold surface, evidenced by their ready removal when subjected to ultrasound (sonication). In contrast, aryl isocyanides form at least two distinct types of species when bonded to a palladium surface:  one effectively σ-bonded, as with gold, but much more tenaciously, and the other species bonded strongly to the surface by a σ/π synergistic interaction. The presence of π back-donation from the palladium surface into the isocyanide π system provides a rationale for the observation that barriers to conduction are lower when diisocyanides bridge palladium electrodes than when diisocyanides or dithiols bridge gold electrodes.

One-dimensional supramolecular structures formed by adsorbing low coverages of 1,4-diisocyanobenzene on Au(111) at room temperature are obtained and imaged by scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) conditions. The structures originate from step edges or surface defects and arrange predominantly in a straight fashion on the substrate terraces along the <110> directions. They are proposed to consist of alternating units of 1,4-diisocyanobenzene molecules and gold atoms with a unit cell in registry with the substrate corresponding to four times the lattice interatomic distance. Their long 1-D chains and high thermal stability offer the potential to use them as conductors in nanoelectronic applications.

A general approach (oxyanion-Cope strategy) for the synthesis of sarpagine/ajmaline indole alkaloids has been developed. (+)-Ajmaline 1 and alkaloid G 2 as well as norsuaveoline 3 have been synthesized from d-(+)-tryptophan in enantiospecific fashion via the asymmetric Pictet−Spengler reaction and a stereocontrolled oxyanion-Cope rearrangement as key steps. The synthesis of these indole alkaloids employed a stereospecific Pictet−Spengler/Dieckmann protocol to prepare the key intermediate, (−)-N b-benzyl tetracyclic ketone (7a or 7b). This ketone was converted into α,β-unsaturated aldehyde (8a or 8b) and further transformed into (+)-ajmaline 1 and alkaloid G 2 as well as norsuaveoline 3. It was also found that reduction of 29 can be done stereospecifically to form the 2-epidiacetylajmaline derivative 30 which has the same configuration at C(2) as that of quebrachidine and of the bisindole alstonisidine. The ring closure reaction (from 27 to 28) to form the sarpagine skeleton was completed in 91% yield. It should now be possible to prepare the antipode of (+)-ajmaline via this approach for biological screening.

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Design and measurements of molecular wires, switches, and memories offer an increased device capability with reduced elements. We report: Measurements on through-bond electronic transport properties of nanoscale metal-1,4-phenylene diisocyanide-metal junctions are reported, where nonohmic thermionic emission is the dominant process, with isocyanide-Pd showing the lowest thermionic barrier of 0.22 eV; robust and large reversible switching behavior in an electronic device that utilizes molecules containing redox centers as the active component, exhibiting negative differential resistance (NDR) and large on-off peak-to-valley ratio (PVR) are realized; erasable storage of higher conductivity states in these redox-center-containing molecular devices are observed; and a two-terminal electronically programmable and erasable molecular memory cell with long bit retention time is demonstrated.

A major challenge to fabricating molecular electronic circuits 1 is the difficulty of simultaneously chemically bonding molecular components to two metal electrodes. This can be accomplished by adjusting the electrode separation to match the molecular dimensions using break junctions 2-5 or by using a sharp tip to vary the electrode-surface spacing. 6 Such approaches provide detailed information on molecular conduction, but are not easily extended to planar systems required for a realistic circuit. 7Molecularly linked nanoparticles have been synthesized in solution and deposited onto surfaces 7,8 but the location of the nanoparticles in the circuit is dictated by the cross-linking structure. Ordered assemblies have been formed from functionalized nanoparticles but they are often not covalently connected. Finally, the length of the molecular linker can be matched to the nanoparticle spacing but requires the molecular size to be tailored to the separation of the nanoparticles. 10An alternative strategy is proposed based on recent observations that molecules that bind strongly to metals with low cohesive energies such as gold or copper can oligomerize by extracting metal atoms from the substrate.11-14 An example of this is the lateral self-assembly of 1,4-phenylene diisocyanide (PDI) on Au(111) that forms -(Au-PDI) n -oligomers comprising long, one-dimensional chains by extracting low-coordination gold atoms from surface defect sites. [15][16][17] The relatively short (B1.1 nm) repeat distance between gold atoms in the oligomer suggests the possibility of being able to chemically bond between gold nanoparticles with various separations by incorporating a number of repeat units until the gap is bridged. PDI has been previously proposed as a prototypical molecular electronic component, 4,6,[18][19][20][21] and theory suggests that PDI is a suitable candidate for device applications. 22This lateral self-assembly is explored by measuring the conductivity of a gold nanoparticle film on mica that has been exposed to PDI. Evaporating gold films on mica (and other insulating substrates)23-28 provides a simple method for growing isolated nanoparticles with different spacings merely by ensuring that the gold film thickness remains below a critical value, above which a continuous film is formed. The success of this approach relies on the oligomers being sufficiently mobile to bridge between nanoparticles. This mobility is illustrated in Fig. 1, which displays a typical series of 15 consecutive STM images (taken 53 seconds apart) of a saturated layer of Au-PDI chains on Au (111) showing the repeated lateral motion of an entire chain, where a line is drawn to highlight the chain motion, showing nine hopping events corresponding