Efficient Synthesis of Optically Pure (+)‐Bezene Diol Epoxide and (+)‐Conduramine A‐1

In this paper, we develop a concise approach to (+)‐benzene diol epoxide and (+)‐conduramine A‐1 based upon the utilization of the C₂‐symmetric L‐tartaric acid as a chiral building block.     

Spirostanol Saponins from the Fibrous Roots of Ophiopogon japonicus (Thunb.) Ker‐Gawl

Three new steroidal saponins, (25R)‐ruscogenin‐3‐yl α‐L ‐rhamnopyranosyl‐(1→2)‐[β‐D ‐xylopyranosyl‐(1→4)]‐β‐D ‐glucopyranoside ( 1 ), diosgenin‐3‐yl 2‐O‐acetyl‐α‐L ‐rhamnopyranosyl‐(1→2)‐[β‐D ‐xylopyranosyl‐(1→4)]‐β‐D ‐glucopyranoside ( 2 ), and pennogenin‐3‐yl 2‐O‐acetyl‐α‐L ‐rhamnopyranosyl‐(1→2)‐[β‐D ‐xylopyranosyl‐(1→4)]‐β‐D ‐glucopyranoside ( 3 ) were isolated from the fibrous roots of Ophiopogon japonicus (Thunb .) Ker‐Gawl . Their structures were determined by spectroscopic methods including IR, HR‐ESI‐MS, and 1D‐ and 2D‐NMR. All of these three steroidal saponins exhibited weak cytotoxicities against Hela and Hep2 cell lines.     

MnOx Nanoparticles Supported on a New Mesostructured Silicate with Textural Porosity

A two‐step synthesis of a novel mesostructured silicate, KIL‐2, and its manganese‐containing analogue, Mn/KIL‐2, has been developed. KIL‐2 possesses interparticle mesopores with pore dimensions between 5 and 60 nm and a surface area of 448 m². The mesopores are formed by the aggregation of silica nanoparticles, which creates a network with interparticle voids. The particle size and the pore diameters depend on the temperature of the ageing step (first step) and on the solvothermal treatment in ethanol (second step), respectively. Mn/KIL‐2 contains octahedrally coordinated Mn³⁺ (80 %) and tetrahedrally coordinated Mn²⁺ (20 %) ions. Mn³⁺ ions are present in the extra‐framework MnO_x nanoparticles with typical dimensions of 2 nm, which are homogeneously distributed throughout the material. Mn²⁺ ions occur as isolated manganese framework sites. The material is also able to retain its structure characteristics after the hydrothermal treatment in boiling water. Because of its non‐toxic nature and cost‐effective synthesis, Mn/KIL‐2 thus exhibits properties that are needed for an environment‐friendly catalyst.     

Control of the Optical Properties of a Star Copolymer with a Hyperbranched Conjugated Polymer Core and Poly(ethylene glycol) Arms by Self‐Assembly

A self‐assembly approach to tuning the optical properties of a star copolymer is reported herein. The star copolymer HCP‐star‐PEG with a hyperbranched conjugated polymer (HCP) core and many linear poly(ethylene glycol) (PEG) arms has been prepared successfully. The HCP core was synthesized by Wittig coupling of N‐(n‐hexyl)‐3,6‐diformylcarbazole and 1,3,5‐bis[(triphenylphosphonio)methyl]benzene tribromide. Subsequently, the linear PEG arms were grafted onto the HCP core by acylhydrazone connection. It was found that the optical properties of HCP‐star‐PEG in chloroform solution changed on addition of acid. Both ¹H NMR and UV/Vis spectroscopic investigations confirmed that the variation of the optical properties was related to the complexation of the acid and the imine bond in the acylhydrazone group. HCP‐star‐PEG self‐assembled into core–shell micelles in the mixed solvent of chloroform and acetonitrile, which affected the protonation of the imine bond. Therefore the optical properties of HCP‐star‐PEG can be readily controlled by self‐assembly.     

Direct electrochemistry and biocatalysis of glucose oxidase immobilized on magnetic mesoporous carbon

A magnetic mesoporous carbon material (i.e., mesoporous iron oxide/C, mesoFe/C) is synthesized for protein immobilization, using glucose oxidase (GOx) as model. Transmission electron microscopy images show that mesoFe/C has highly ordered porous structure with uniform pore size, and iron oxide nanoparticles are dispersed along the wall of carbon. After adsorption of GOx, the GOx-mesoFe/C composite is separated with magnet. The immobilized GOx remains its natural structure according to the reflection–absorption infrared spectra. When the GOx-mesoFe/C composite is coated on a Pt electrode surface, the GOx gives a couple of quasireversible voltammetric peaks at −0.5 V (vs. saturated calomel electrode) due to the redox of FAD/FADH₂. The electron-transfer rate constant (k _s) is ca. 0.49 s⁻¹. The modified electrode presents remarkably amperometric response to glucose at 0.6 V. The response time (t _95%) is less than 6 s; the response current is linear to glucose concentration in the range of 0.2–10 mM with a sensitivity of 27 μA mM⁻¹ cm⁻². The detection limit is 0.08 mM (S/N = 3). The apparent Michaelis–Menten constant (K _m^app) of the enzyme reaction is ca. 6.6 mM, indicating that the GOx immobilized with mesoFe/C has high affinity to the substrate.     

On-line bioaffinity-electrospray mass spectrometry for simultaneous detection,identification, and quantification of protein-ligand interactions

We describe here an on-line combination of a surface acoustic wave (SAW) biosensor with electrospray ionization mass spectrometry (SAW-ESI-MS) that enables the direct detection, identification, and quantification of affinity-bound ligands from a protein-ligand complex on a biosensor chip. A trapping column was used between the SAW-biosensor and the electrospray mass spectrometer equipped with a micro-guard column, which provides simultaneous sample concentration and desalting for the mass spectrometric analysis of the dissociated ligand. First applications of the on-line SAW-ESI-MS combination include (1), differentiation of β-amyloid (Aβ) epitope peptides bound to anti-Aβ antibodies; (2), the identification of immobilized Substance P peptide-calmodulin complex; (3), identification and quantification of the interaction of 3-nitrotyrosine-modified peptides with nitrotyrosine-specific antibodies; and (4), identification of immobilized anti-α-synuclein-human α-synuclein complex. Quantitative determinations of protein-ligand complexes by SAW yielded dissociation constants (K_D) from micro-to low nanomolar sample concentrations. The on-line bioaffinity-ESI-MS combination presented here is expected to enable broad bioanalytical application to the simultaneous, label-free determination and quantification of biopolymer-ligand interactions, as diverse as antigen-antibody and lectin-carbohydrate complexes.     

Protein-peptide affinity determination using an H/D exchange dilution strategy: Application to antigen-antibody interactions

A new methodology using hydrogen/deuterium amide exchange (HDX) to determine the binding affinity of protein-peptide interactions is reported. The method, based on our previously established approach, protein ligand interaction by mass spectrometry, titration, and H/D exchange (PLIMSTEX) [J. Am. Chem. Soc. 2003, 125, 5252–5253], makes use of a dilution strategy (dPLIMSTEX) for HDX, using the mass of the peptide ligand as readout. We employed dPLIMSTEX to study the interaction of calcium-saturated calmodulin with the opioid peptide β-endorphin as a model system; the affinity results are in good agreement with those from traditional PLIMSTEX and with literature values obtained by using other methods. We show that the dPLIMSTEX method is feasible to quantify an antigen-antibody interaction involving a 3-nitrotyrosine modified peptide in complex with a monoclonal anti-nitrotyrosine antibody. A dissociation constant in the low nanomolar range was determined, and a binding stoichiometry of antibody/peptide of 1:2 was confirmed. In addition, we determined that the epitope in the binding interface contains a minimum of five amino acids. The dPLIMSTEX approach is a sensitive and powerful tool for the quantitative determination of peptide affinities with antibodies, complementary to conventional immuno-analytical techniques.     

A robust hydrophilic pyridine-bridged bis-benzimidazolylidene palladium pincer complex: synthesis and its catalytic application towards Suzuki-Miyaura couplings in aqueous solvents

A novel hydrophilic pyridine-bridged bis-benzimidazolylidene palladium pincer complex (3) acted as a highly efficient robust recyclable molecular catalyst towards Suzuki-Miyaura coupling reactions in aqueous media and tolerated various functional groups (even heterocycles) with extremely low catalyst loading.     

The characteristics of diode-pumped acousto-optic Yb:Y2Ca3B4O12 laser for Q-switching and Q-switched mode-locking

Q-switching and Q-switched mode-locked Yb:Y₂Ca₃B₄O₁₂ lasers with an acousto-optic switch are demonstrated. In the Q-switching case, an average output power of 530 mW is obtained at the pulse repetition rate of 10.0 kHz under an absorbed pump power of 6.1 W. The minimum pulse width is 79 ns at the repetition rate of 1.7 kHz. The pulse energy and peak energy are calculated to be 231 μJ and 2.03 kW, respectively. In the Q-switched mode-locking case, the average output power of 64 mW with a mode-locked pulse repetition rate of 118 MHz and Q-switched pulse energy of 48 μJ is generated under the absorbed pump power of 6.1 W.