Enantioselective decarboxylative alkylation reactions: catalyst development, substrate scope, and mechanistic studies

α-Quaternary ketones are accessed through novel enantioselective alkylations of allyl and propargyl electrophiles by unstabilized prochiral enolate nucleophiles in the presence of palladium complexes with various phosphinooxazoline (PHOX) ligands. Excellent yields and high enantiomeric excesses are obtained from three classes of enolate precursor: enol carbonates, enol silanes, and racemic β-ketoesters. Each of these substrate classes functions with nearly identical efficiency in terms of yield and enantioselectivity. Catalyst discovery and development, the optimization of reaction conditions, the exploration of reaction scope, and applications in target-directed synthesis are reported. Experimental observations suggest that these alkylation reactions occur through an unusual inner-sphere mechanism involving binding of the prochiral enolate nucleophile directly to the palladium center.     

Modified peptide monolayer binding His-tagged biomolecules for small ligand screening with SPR biosensors

A peptide self-assembled monolayer (SAM) was designed to bind His-tagged biomolecules for surface plasmon resonance (SPR) bioanalysis, which was applied for the determination of K(d) for small ligand screening against CD36. Nonspecific adsorption could be minimized using penta- and hexa-peptide monolayers. In particular, monolayers consisting of 3-mercaptopropionyl-leucinyl-histidinyl-aspartyl-leucinyl-histidinyl-aspartic acid (3-Mpa-LHDLHD) exhibited little (12 ng cm(-2)) nonspecific adsorption in crude serum. Modification of this peptide monolayer with Nα,Nα-bis(carboxymethyl)-L-lysine gave a surface competent for binding His-tagged proteins, as demonstrated using enzyme (human dihydrofolate reductase), protein/antibody and receptor (CD36) examples. Immobilization featured chelation of copper and the His-tagged protein by the peptide monolayer, which could be recycled by removing the copper using imidazole washes prior to reuse.     

Depletion-induced structure and dynamics in bimodal colloidal suspensions

Combined small angle x-ray scattering and x-ray photon correlation spectroscopy studies of moderately concentrated bimodal hard-sphere colloidal suspensions in the fluid phase show that depletion-induced demixing introduces spatially heterogeneous dynamics with two distinct time scales. The adhesive nature, as well as the mobility, of the large particles is determined by the level of interaction within the monomodal domains. This interaction is driven by osmotic forces, which are governed by the relative concentration of the constituents.     

Tandem Enzymatic Oxygenations in Biosynthesis of Epoxyquinone Pharmacophore of Manumycin-type Metabolites

1. Download : Download high-res image (79KB)
2. Download : Download full-size image

     

Synthesis and photovoltaic properties of novel C60 bisadducts based on benzo[2,1,3]-thiadiazole

A novel C₆₀ solar cell acceptor (BTOQC, benzo[2,1,3]-thiadiazole-o-quinodimethane-C₆₀ bisadducts) based on benzo[2,1,3]thiadiazole has been synthesized as model to study how the thiadiazole group will affect the device performance in bulk heterojunction organic photovoltaics (BHJ-OPV) with poly(3-hexylthiophene) (P3HT) as donor. The optoelectronic, electrochemistry, and photovoltaic properties of the novel bisadduct BTOQC have been fully investigated. The best device performance of this fullerene derivative in our research was obtained as 2.50% with a high V_oc of 0.74 V.     

Spectroscopic Identification of a Bidentate Binding Motif in the Anionic Magnesium–CO2 Complex ([ClMgCO2]−)

A magnesium complex incorporating a novel metal–CO₂ binding motif is spectroscopically identified. Here we show with the help of infrared photodissociation spectroscopy that the complex exists solely in the [ClMg(η²‐O₂C)]^? form. This bidentate double oxygen metal–CO₂ coordination has previously not been observed in neutral nor in charged unimetallic complexes. The antisymmetric CO₂ stretching mode in [ClMg(η²‐O₂C)]^? is found at 1128 cm^?1, which is considerably redshifted from the corresponding mode in bare CO₂ at 2349 cm^?1, suggesting that the CO₂ moiety has a considerable negative charge (～1.8 e^?). We also employed electronic structure calculations and kinetic analysis to support the interpretation of the experimental results.     

Energy transfer and amplified spontaneous emission in temperature-controlled random scattering media

Hydroxypropyl cellulose (HPC) in aqueous solution forms nanoparticles and becomes highly scattering above its lower critical solution temperature (LCST approximately 41 degrees C). Enhancement of energy transfer (ET) and amplified spontaneous emission (ASE) have been observed in turbid HPC solutions containing Rhodamine 6G (RG) as an energy donor and Kiton Red 620 (KR) as an acceptor. A detailed analysis of self-absorption, absorption saturation, and multiple scattering effects has revealed the importance of photon diffusion in shutting down the intensity leakage. A 5-fold enhancement of ET in the turbid condition is estimated. Possible factors crucial for ET and ASE in random media are discussed, such as the donor-to-acceptor ASE energy pumping, the optical path elongation by multiple scattering, and the formation of "light pipes" in the near-field of the Mie scattering. The temperature-dependent colloidal formation is found to successfully control optical processes via multiple scattering with a sharp threshold and abrupt emergence of dense scatterers.     

Crossover from stretched to compressed exponential relaxations in a polymer-based sponge phase

X-ray photon correlation spectroscopy was used to characterize the wave vector- and temperature-dependent dynamics of spontaneous thermal fluctuations in a sponge (L3) phase that occurs in a blend of a symmetric poly(styrene-ethylene/butylene-styrene) triblock copolymer with a polystyrene homopolymer. Measurements of the intermediate scattering function reveal a crossover from stretched- to compressed-exponential relaxations as the temperature is lowered from 180 to 120 degrees C.     

Improved quality assessment of proprietary Chinese medicines based on multi‐chemical class fingerprinting

Our present study constitutes the first successful attempt to employ eight distinctive chemical groups of compounds for the quality evaluation of a complex traditional Chinese herbal medicine (TCHM) material: BaZhen YiMu (BZYM). Due to the complexity of its matrix, which is composed of nine different herbal ingredients, five representative chemical groups encompassing representative bioactive markers were initially chosen as targets for the quality assessment of this preparation. Furthermore, with the aid of LC‐ESI‐MS, three additional chemical groups were characterized. In summary, a total of nineteen markers belonging to eight different chemical groups were selectively displayed in the chromatographic fingerprint of BZYM preparation. With this fingerprint, the overall quality of any BZYM preparation can be comprehensively authenticated. The chromatographic separation was performed on an HP C₁₈ AQ column with a gradient elution of ACN and aqueous solution containing 0.1% phosphoric acid at the optimal detection wavelength of 230 nm. The established method was rigorously validated with respect to the ICH guidelines and represents the most extensive and facile HPLC quality control technique for this formulation. Compared with the conventional method of using a single or only a few markers of the same chemical group, this technique provides a new dimension for TCHM quality control.     

Evaluation of an electrochemical sensor based on gold nanoparticles supported on carbon nanofibers for detection of tartrazine dye

Journal of Solid State Electrochemistry - An electrochemical sensor for the detection of tartrazine (Tz), a synthetic azo dye customarily found in commercial soft drinks, is herein reported. This...