Enhancing selectivity in oxidation catalysis with sol-gel nanocomposites

Valuable organic compounds such as alpha-hydroxy acids are easily synthesised with relevant selectivity enhancement using a sol-gel hydrophobized nanostructured silica matrix doped with the organocatalyst TEMPO: A materials science based synthetic route which cannot be achieved via classical homogeneous synthesis.     

Direct Electrochemical Investigations of 17-Electron Complexes of CpM(CO)(3)(*) (M = Mo, W, and Cr)

Photolysis of complexes of the type M(2)(CO)(6)(RC(5)H(4))(2) (where M = W, Mo, Cr and R = H (Cp) or CH(3) (Cp')) leads to the production of short lived 17-electron radicals. Direct electrochemical characterization of these intermediates has been achieved using a technique known as photomodulated voltammetry (PMV). The results from PMV analysis are in excellent agreement with literature estimates for CpMo(CO)(3)(*) and CpCr(CO)(3)(*). However, CpW(CO)(3)(*) is found to be shifted oxidatively 115 mV relative to previous literature estimates. The change in the value for the tungsten complex changes previous estimates to the bond dissociation energy for tungsten metal hydrides by 3.0 +/- 0.9 kcal/mol. Lifetime information on the radicals is also reported based on the phase shift of the electrochemical signal observed by PMV under limiting current conditions.     

Preparation and spectroscopic properties of 2-benzothiazolyl araldehyde hydrazones

Notwithstanding its tendency toward air oxidation in solution, 2-hydrazinobenzothiazole I reacted with aromatic aldehydes in ethanol to give the corresponding hydrazones III-XV in high yields and analytical purity. In related examples, acylation took place under similar conditions to produce hydrazides XVI-XX . The near-infrared bands of the absorption spectra of the araldehyde hydrazones have been associated with charge transfer and appeared to correlate with structural elements of the compounds in a way suggesting that the charge transfer was intermolecular.     

Molecular ordering and 2D conductivity in ultrathin poly(3-hexylthiophene)/gold nanoparticle composite films

This paper reports the first comparison of the structure and electrical conductivity properties of spin cast (SC) and Langmuir-Schaeffer (LS) films of regioregular poly(3-hexylthiophene) (P3HT). In addition, the effect of incorporating highly monodisperse Au nanoparticles (NPs), with a core diameter of approximately 5 nm, into SC and LS P3HT films is described. A detailed picture of molecular organization in the films has been obtained using ultraviolet-visible absorption spectroscopy, atomic force microscopy, field-emission scanning electron microscopy, X-ray diffraction, and X-ray reflectivity. Film morphology was correlated with pseudo-two-dimensional conductivity measured using scanning electrochemical microscopy, with P3HT in the semiconducting regime. It was found that SC films, which were slightly thicker than those formed with the LS technique, exhibited greater organization. This resulted in an order of magnitude higher lateral conductivity for the SC films. Inclusion of Au NPs (50 wt %) into both SC and LS films resulted in the formation of uniform and relatively flat (rms roughness approximately 1 nm) composite films. Surprisingly, the addition of NPs did not disrupt the characteristic crystal structure found for the native P3HT films. The effect of Au NPs on film lateral conductivity was found to be determined by the distribution of Au NPs within the polymer, which varied significantly between SC and LS films. Whereas Au NPs aggregated into hexagonally packed clusters in SC films, NPs in LS films were predominantly uniformly distributed between the lamella bilayer. It was found that, while the inclusion of Au NPs caused the lateral conductivity to decrease in SC films, in LS films, the lateral conductivity increased by a factor of 2.     

A simple and general chiral silicon Lewis acid for asymmetric synthesis: highly enantioselective [3+2] acylhydrazone-enol ether cycloadditions

A highly diastereo- and enantioselective [3 + 2] acylhydrazone-enol ether cycloaddition mediated by a simple chiral silane Lewis acid is described. The reactions are highly practical, as demonstrated by a larger scale (5 g of the hydrazone) reaction in which the product was obtained after recrystallization in 93% yield and 99% ee. Evidence for a stepwise mechanism and a model for the asymmetric induction are presented, as well.     

Trypsin activity assay in substrate-specific one- and two-dimensional gels: a powerful method to separate and characterize novel proteases in active form in biological samples

To separate and identify the proteases, a substrate-specific, sensitive assay in sodium dodecyl sulfate (SDS)-polyacrylamide gels after two-dimensional (2-D) electrophoresis has been developed. This method allows simultaneous determination of protease cleavage specificity, molecular weight, isoelectric point, and if necessary, amino acid sequencing. After isoelectric focusing in immobilized pH gradient (IPG) strips (pH 6-11) (first dimension), trypsin was electrophoresed in 12% SDS polyacrylamide gels (second dimension) copolymerized with Boc-Gln-Ala-Arg-MCA (4-methyl-coumaryl-7-amide). The gels were washed in cold 2.5% Triton X-100 and water, and incubated in assay buffer (6.3 mM Bicine, 100 mM NaCl). Trypsin cleavage of the peptide-MCA generated fluorescent 7-amino-4-methyl-coumarin. In 1-D gels, as low as 500 pg trypsin could be detected and trypsin band volumes correlated linearly with the amounts of trypsin (R(2) = 0.999). In 2-D gels, the lowest amount of trypsin detected was 1 ng. The linear regression of spot volume and loading amount was still good (R(2) = 0.974). To optimize renaturation conditions, 5x5 min washes with 2.5% Triton X-100 and water, respectively, gave the strongest band volume. For fluorescence development, an assay buffer at pH 9 was the best; incubation at 37 degrees C for 30 min was sufficient. The method has application for identifying novel proteases as it does not rely on antibodies.     

Synthesis, structure, and complexation of a large 28-mer macrocycle containing two binding sites for either anions or metal ions

The "one-pot" synthesis and characterization of a large 28-mer macrocycle (H(4)L(2)) with oxamido units capable of complexing guest ions through oxygen or nitrogen donor atoms is reported. Single-crystal structure determination of H(8)L(2)(NO(3))(4) and (Cu(2)[H(2)L(2)](H(2)O)(2))(NO(3))(2) demonstrated that the macrocycle contains two sites capable of complexing two nitrate anions or two copper(II) ions, involving a large structural reorganization in the conformation of the macrocyclic framework on coordination of the copper(II) ions when compared to the nitrate. Electrochemical and magnetic susceptibility measurements on the dinuclear Cu(II) complex and the related mononuclear and trinuclear Cu(II) complexes derived from the related 14-mer macrocycle were carried out and illustrate the role of the oxamido groups in mediating metal-metal interaction and delocalization.     

Discovery of a small molecule that inhibits the interaction of anthrax edema factor with its cellular activator, calmodulin

The catalytic efficiency of adenylyl cyclase activity of edema factor (EF) from Bacillus anthracis is enhanced by approximately 1000-fold upon its binding to mammalian protein calmodulin (CaM). A tandem cell-based and protein binding-based screen of a 10,000 member library identified a molecule that inhibits the EF-CaM interaction and therefore the adenylyl cyclase activity. A combination of fluorescence spectroscopy and photolabeling studies showed that the molecule targets the CaM binding region of EF. A series of related compounds were synthesized and evaluated to identify one compound, 4-[4-(4-nitrophenyl)-thiazolylamino]-benzenesulfonamide, that maintained activity against EF but showed minimal toxicity to two cultured cell lines. This compound represents an important reagent to study the role of EF in anthrax pathology and may represent a drug lead against anthrax infection.     

Fragmentation and reaction processes in cluster-surface collisions

We review the processes which have been observed from collisions between alkali-halide clusters and solid surfaces. Soft impact of nanocrystalline Na_nF _n?1 ⁺ clusters against solid surfaces causes them to cleave along the lowest energy (100) plane. At higher collision energies (E_i>1 eV/atom), an evaporative cascade occurs which is characteristic of a transformation of the nanocrystal to a molten state. Efficient F^? transfer from the cluster to the surface can occur for the larger clusters (>60 atoms) scattering from Si(111), in direct competition with the cleaving channel at low energies. In this regime, strong bonds can form between the F^? and silicon surface. The reaction probability increases with cluster size indicating that an impact-initiated shock wave is needed to enhance the reactive process.     

Application of recombinant phage display antibody system in study of Codakia orbicularis gill proteins

We used the recombinant phage display antibody system (RPAS) to obtain chimeric single-chain fragment variable (ScFv) antibodies to gill proteins of the white clam Codakia orbicularis (Linné, 1758). After three rounds of selection on immunotubes loaded with total gill protein extract, recombinant phages exhibiting antibodies to gill proteins were isolated and tested by enzyme-linked immunosorbent assay (ELISA). Clones exhibiting a high affinity for the mollusk proteins were selected for production of soluble ScFv antibodies, which were purified for subsequent analysis. ScFv antibodies exhibited a reaction specific for a protein whose molecular mass was about 15,000 Daltons and that was detected by the antigen capture technique followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blotting.