Influence of substituent groups at the 3‐position on the mass spectral fragmentation pathways of cephalosporins

The structural fragment ions of nine cephalosporins were studied by electrospray ionization quadrapole trap mass spectrometry (Q‐Trap MSⁿ) in positive mode. The influence of substituent groups in the 3‐position on fragmentation pathway B, an α‐cleavage between the C7? C8 single bond, coupled with a [2,4]‐trans‐Diels‐Alder cleavage simultaneously within the six‐membered heterocyclic ring, was also investigated. It was found that when the substituent groups were methyl, chloride, vinyl, or propenyl, fragmentations belonging to pathway B were detected; however, when the substituents were heteroatoms such as O, N, or S, pathway B fragmentation was not detected. This suggested that the [M–R₃]⁺ ion, which was produced by the bond cleavage within the substituent group at the 3‐position, had a key influence on fragmentation pathway B. This could be attributed to the strong electronegativity of the heteroatoms (O, N, S) that favors the production of the [M–R₃]⁺ ion. Moreover, having the positive charge of the [M–R₃]⁺ ion localized on the nitrogen atom in the 1‐position changed the electron density distribution of the heterocyclic structure, which prohibits a [2,4]‐reverse‐Diels‐Alder fragmentation and as a result fragmentation pathway B could not occur. The influence of the substituent group in the 3‐position was determined by the intensity ratio (e/d) of ions produced by fragmentation pathway A, a [2,2]‐trans‐Diels‐Alder cleavage within the quaternary lactam ring, including the breaking of the amide bond and the C6? C7 single bond (ion d), and fragmentation pathway B (ion e). The results indicate that the electronegativity of the substituent group was a key influencing factor of pathway B fragmentation intensity, because the intensity ratio (e/d) is higher for a chlorine atom, a vinyl, or a propenyl group than that of a methyl group. This study provided some theoretical basis for the identification of cephalosporin antibiotics and structural analysis of related substances in drugs. Copyright © 2010 John Wiley & Sons, Ltd.     

New implementations of MRCI in semiempirical frameworks

Multireference configuration interaction with single and double excitations (MRCISD) as well as its analytic CI gradients has been implemented in the semiempirical framework. The hole‐particle symmetry and a mixed driven model for computing coupling coefficients have been used in the new code that allows us to perform MRCI and gradient calculations with higher efficiency and less storage requirements. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Design, synthesis, and in vitro evaluation of potential West Nile virus protease inhibitors based on the 1-oxo-1,2,3,4-tetrahydroisoquinoline and 1-oxo-1,2-dihydroisoquinoline scaffolds

The 1-oxo-1, 2, 3, 4-tetrahydroisoquinoline and 1-Oxo-1, 2-dihydroisoquinoline scaffolds were utilized in the design and solution phase synthesis of focused libraries of compounds for screening against West Nile Virus (WNV) protease. Exploratory studies have led to the identification of a WNV protease inhibitor (a 1-oxo-1, 2-dihydroisoquinoline-based derivative, 12j) which could potentially serve as a launching pad for a hit-to-lead optimization campaign. The identified hit was devoid of any inhibitory activity toward a panel of mammalian serine proteases.     

On-line coupling of in-tube boronate affinity solid phase microextraction with high performance liquid chromatography-electrospray ionization tandem mass spectrometry for the determination of cis-diol biomolecules

Boronate affinity solid phase microextraction (BA-SPME) is a new format appeared recently with great potential for specific extraction of cis-diol-containing compounds. Unlike conventional SPME, BA-SPME relies on covalent interactions and thereby features with specific selectivity, eliminated matrix effect and manipulable capture/release. However, only on-fiber BA-SPME and its off-line combination with high performance liquid chromatography (HPLC) have been reported so far. In this study, we report on-line coupling of in-tube BA-SPME with HPLC-electrospray ionization tandem mass spectroscopy (in-tube BA-SPME-HPLC-ESI-MS/MS) for the specific and sensitive determination of cis-diol-containing biomolecules. A boronate affinity extraction phase was prepared onto the inner surface of the capillary by copolymerization of vinylphenylboronic acid (VPBA) and ethylene glycol dimethacrylate (EDMA). The extraction conditions were optimized by choosing appropriate extraction/desorption solutions and extraction time. The extraction capacity, linear range, reproducibility and life-time were investigated. The developed method was successfully applied for the determination of dopamine in urine samples. Since many cis-diol-containing compounds are of great biological importance, the in-tube BA-SPME-HPLC method can be a promising tool.     

Encapsulation of polyaniline in 3-D interconnected mesopores of silica KIT-6

Composite material PANI/KIT-6, with polyaniline (PANI) chains encapsulated in the 3-D interconnected pore channels of mesoporous silica, KIT-6, has been synthesized via a gas-phase method. The composite formation and the presence of PANI inside the pore channels of KIT-6 were evidenced by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), small-angle X-ray scatter (SAXS), transmission electron microscopy (TEM), and N₂ adsorption–desorption isotherms. The PANI/KIT-6 composite showed good electrical conductivity (2.4 × 10^?3 S/cm) due to the formation of 3-D networks of PANI inside the 3-D interconnected channels of KIT-6. The resistance of PANI/KIT-6 composite at different relative humidities (RH) was investigated. An essentially linear relationship between the relative resistance of the composite and the relative humidity of the environment was found from 11.3% to 97.3% RH.     

Properties of MgB2 bulks after combined doping with Fe and C by adding Iron(II) lactate (C6H10FeO6)

Bulk MgB₂ doped with C and Fe was prepared by using the solid state sintering method with C₆H₁₀FeO₆ as dopant. The phase composition, microstructure, and superconducting properties were studied. X-ray diffraction (XRD) shows the presence of iron after the doping. The addition of C₆H₁₀FeO₆ increases the a- and c-axis parameters of MgB₂, as evidenced by the shifting of the (100) and (002) peaks to a lower angle on the XRD patterns. Fe atoms were distributed uniformly, as shown by the field emission scanning electron microscope images, while the magnetization of the sample was dominated by the signals from the MgB₂ superconductor, although the iron-containing materials also contributed a minor amount of magnetization. The residual resistivity ratio was decreased as the C₆H₁₀FeO₆ doping level increased. The critical temperature also decreased with increased doping level, as did the critical current density, J_c. The doping also caused decreases in the irreversibility field, H_irr, and the upper critical field, H_c2. The decrease in H_c2 and H_irr, together with the harmful effects from impurity phases such as MgO is the reason for the decrease in J_c.     

An Electron‐Deficient Building Block Based on the B←N Unit: An Electron Acceptor for All‐Polymer Solar Cells

A double B←N bridged bipyridyl (BNBP) is a novel electron‐deficient building block for polymer electron acceptors in all‐polymer solar cells. The B←N bridging units endow BNBP with fixed planar configuration and low‐lying LUMO/HOMO energy levels. As a result, the polymer based on BNBP units (P‐BNBP‐T) exhibits high electron mobility, low‐lying LUMO/HOMO energy levels, and strong absorbance in the visible region, which is desirable for polymer electron acceptors. Preliminary all‐polymer solar cell (all‐PSC) devices with P‐BNBP‐T as the electron acceptor and PTB7 as the electron donor exhibit a power conversion efficiency (PCE) of 3.38 %, which is among the highest values of all‐PSCs with PTB7 as the electron donor.     

Asymmetric Conjugate Alkynylation of Cyclic α,β‐Unsaturated Carbonyl Compounds with a Chiral Diene Rhodium Catalyst

Asymmetric conjugate alkynylation of cyclic α,β‐unsaturated carbonyl compounds (ketones, esters, and amides) was realized by use of diphenyl[(triisopropylsilyl)ethynyl]methanol as an alkynylating reagent in the presence of a rhodium catalyst coordinated with a new chiral diene ligand (Fc‐bod; bod=bicyclo[2.2.2]octa‐2,5‐diene, Fc=ferrocenyl) to give high yields of the corresponding β‐alkynyl‐substituted carbonyl compounds with 95–98 % ee.     

Nanoporous PtRu Alloys with Unique Catalytic Activity toward Hydrolytic Dehydrogenation of Ammonia Borane

Nanoporous (NP) PtRu alloys with three different bimetallic components were straightforwardly fabricated by dealloying PtRuAl ternary alloys in hydrochloric acid. Selective etching of aluminum from source alloys generates bicontinuous network nanostructures with uniform size and structure. The as‐made NP‐PtRu alloys exhibit superior catalytic activity toward the hydrolytic dehydrogenation of ammonia borane (AB) than pure NP‐Pt and NP‐Ru owing to alloying platinum with ruthenium. The NP‐Pt₇₀Ru₃₀ alloy exhibits much higher specific activity toward hydrolytic dehydrogenation of AB than NP‐Pt₃₀Ru₇₀ and NP‐Pt₅₀Ru₅₀. The hydrolysis activation energy of NP‐Pt₇₀Ru₃₀ was estimated to be about 38.9 kJ mol^?1, which was lower than most of the reported activation energy values in the literature. In addition, recycling tests show that the NP‐Pt₇₀Ru₃₀ is still highly active in the hydrolysis of AB even after five runs, which indicates that NP‐PtRu alloy accompanied by the network nanoarchitecture is beneficial to improve structural stability toward the dehydrogenation of AB.