Catalytic Hydrogenation of L-Ascorbic Acid (Vitamin C): A Stereoselective Process for the Production of L-Gulono-1, 4-Lactone

Reduction of functional groups with hydrogen gas is one of the most important reactions in organic chemistry, dating to the first hydrogenation of ethene to ethane reported by Von Wilde in 1874¹. Indeed, alkenes are generally rapidly hydrogenated, in the presence of a catalyst, usually, platinum, Raney nickel, palladium, or rhodium on carbon, to the corresponding alkane via heterogeneous reaction. Most undergraduate, introductory texts introduce this reaction as occurring via a stermspecific syn addition, although this is an oversimplification, due to possible rearrangements on the catalyst surface². While the chemistry of Vitamin C (L-ascorbic acid), in regards to oxidative degradation, is well studied, its behavior under reductive conditions has been relatively overlooked. The catalytic reduction of ascorbic acid has been reported earlier (24 hours, palladium catalyst, water, 50°) by workers at Pfizer³.     

n‐Dopants Based on Dimers of Benzimidazoline Radicals: Structures and Mechanism of Redox Reactions

Dimers of 2‐substituted N,N′‐dimethylbenzimidazoline radicals, (2‐Y‐DMBI)₂ (Y=cyclohexyl (Cyc), ferrocenyl (Fc), ruthenocenyl (Rc)), have recently been reported as n‐dopants for organic semiconductors. Here their structural and energetic characteristics are reported, along with the mechanisms by which they react with acceptors, A (PCBM, TIPS‐pentacene), in solution. X‐ray data and DFT calculations both indicate a longer C?C bond for (2‐Cyc‐DMBI)₂ than (2‐Fc‐DMBI)₂, yet DFT and ESR data show that the latter dissociates more readily due to stabilization of the radical by Fc. Depending on the energetics of dimer (D₂) dissociation and of D₂‐to‐A electron transfer, D₂ reacts with A to form D⁺ and A^? by either of two mechanisms, differing in whether the first step is endergonic dissociation or endergonic electron transfer. However, the D⁺/0.5 D₂ redox potentials—the effective reducing strengths of the dimers—vary little within the series (ca. ?1.9 V vs. FeCp₂^+/0) (Cp=cyclopentadienyl) due to cancelation of trends in the D^+/0 potential and D₂ dissociation energy. The implications of these findings for use of these dimers as n‐dopants, and for future dopant design, are discussed.     

Visualising mouse neuroanatomy and function by metal distribution using laser ablation-inductively coupled plasma-mass spectrometry imaging

Metals have a number of important roles within the brain. We used laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to map the three-dimensional concentrations and distributions of transition metals, in particular iron (Fe), copper (Cu) and zinc (Zn) within the murine brain. LA-ICP-MS is one of the leading analytical tools for measuring metals in tissue samples. Here, we present a complete data reduction protocol for measuring metals in biological samples, including the application of a pyramidal voxel registration technique to reproducibly align tissue sections. We used gold (Au) nanoparticle and ytterbium (Yb)-tagged tyrosine hydroxylase antibodies to assess the co-localisation of Fe and dopamine throughout the entire mouse brain. We also examined the natural clustering of metal concentrations within the murine brain to elucidate areas of similar composition. This clustering technique uses a mathematical approach to identify multiple ‘elemental clusters’, avoiding user bias and showing that metal composition follows a hierarchical organisation of neuroanatomical structures. This work provides new insight into the distinct compartmentalisation of metals in the brain, and presents new avenues of exploration with regard to region-specific, metal-associated neurodegeneration observed in several chronic neurodegenerative diseases.     

Spectroscopic Tracking of Molecular Transport Junctions Generated by Using Click Chemistry

Click to fill the gap : The in situ modular fabrication of molecular transport junctions in nanogaps generated by on‐wire lithography is achieved by using click chemistry (see picture). The formation of molecular junctions proceeds in high yields and can be used to test different molecules; the triazole group also maintains conjugation in the molecular wires. Raman spectroscopy is used to characterize the molecular assembly processes.

     

Surprisingly Long‐Range Surface‐Enhanced Raman Scattering (SERS) on Au–Ni Multisegmented Nanowires

Very long range surface‐enhanced Raman scattering is observed from a nickel nanowire that is separated by 120 nm from a pair of gold nanodisks. The excitation of the surface‐plasmon resonance (SPR) from the gold nanodisk pair generates an enhanced electromagnetic field near the nickel segment (SEM, left), leading to Raman intensity greater than the nickel alone (right).

     

Attachment of motile bacterial cells to prealigned holed microarrays

Construction of biomotors is an exciting area of scientific research that holds great promise for the development of new technologies with broad potential applications in areas such as the energy industry and medicine. Herein, we demonstrate the fabrication of prealigned microarrays of motile Escherichia coli bacterial cells on SiOx substrates. To prepare these arrays, holed surfaces with a gold layer on the bottom of the holes were utilized. The attachment of bacteria to the holes was achieved via nonspecific interactions using poly-l-lysine hydrobromide (PLL). Our data suggest that a single motile bacterial cell can be selectively attached to an individual hole on a surface and bacterial cell binding can be controlled by altering the pH, with the greatest occupancy occurring at pH 7.8. Cells attached to hole arrays remained motile for at least 4 h. These data indicate that holed surface structures provide a promising footprint for the attachment of motile bacterial cells to form high-density site-specific functional bacterial microarrays.     

Chiral, cross-conjugated isopolydiacetylenes

A series of chiral, monodisperse enyne oligomers (isopolydiacetylenes) based on a 1,1-binaphthyl core has been synthesized and characterized spectroscopically.     

Syntheses, structures, and magnetic characterization of dicyanometalate(II) building blocks: [NEt4][(Tp*)MII(CN)2] [MII = Cr, Co, Ni; Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate

The syntheses and structures of three dicyanometalate(II) complexes, [NEt(4)][(Tp*)M(II)(CN)(2)].nMeCN.(1/2)Et(2)O (M(II) = Cr, 1, n = (1/2); Co, 2, n = 1; Ni, 3, n = 1) are described; magnetic studies indicate that 3 is diamagnetic while 1 and 2 are paramagnetic high- and low-spin S = 2 and (1/2) complexes, respectively.