Development of a Sensitive LC Assay with Fluorescence Detection for the Determination of Zearalenone in Rat Serum

A simple and sensitive liquid chromatographic assay with fluorescence detection assay was developed for the determination of zearalenone levels in rat serum. The assay utilized a single liquid–liquid extraction with t-butyl methyl ether and isocratic elution using a mobile phase consisting of acetonitrile and 0.1% triethylamine in distilled water (pH = 6) (50:50, v/v). Linearity was observed over a concentration range from 10 to 1,000 ng mL^?1 (r = 0.9995), with the limit of quantification at 10 ng mL^?1 with 100 μL of rat serum. The validated assay was applied to a pharmacokinetic study in rats.     

Influences of poly(lactic acid)‐grafted carbon nanotube on thermal,mechanical, and electrical properties of poly(lactic acid)

Poly(lactic acid)‐grafted multiwalled carbon nanotubes (MWNT‐g‐PLA) were prepared by the direct melt‐polycondensation of L ‐lactic acid with carboxylic acid‐functionalized MWNT (MWNT‐COOH) and then mixed with a commercially available neat PLA to prepare PLA/MWNT‐g‐PLA nanocomposites. Morphological, thermal, mechanical, and electrical characteristics of PLA/MWNT‐g‐PLA nanocomposites were investigated as a function of the MWNT content and compared with those of the neat PLA, PLA/MWNT, and PLA/MWNT‐COOH nanocomposites. It was identified from FE‐SEM images that PLA/MWNT‐g‐PLA nanocomposites exhibit good dispersion of MWNT‐g‐PLA in the PLA matrix, while PLA/MWNT and PLA/MWNT‐COOH nanocomposites display MWNT aggregates. As a result, initial moduli and tensile strengths of PLA/MWNT‐g‐PLA composites are much higher than those of neat PLA, PLA/MWNT, and PLA/MWNT‐COOH, which stems from the efficient reinforcing effect of MWNT‐g‐PLA in the PLA matrix. In addition, the crystallization rate of PLA/MWNT‐g‐PLA nanocomposites is faster than those of neat PLA, PLA/MWNT, and PLA/MWNT‐COOH, since MWNT‐g‐PLA dispersed in the PLA matrix serves efficiently as a nucleating agent. It is interesting that, unlike PLA/MWNT nanocomposites, surface resistivities of PLA/MWNT‐g‐PLA nanocomposites did not change noticeably depending on the MWNT content, demonstrating that MWNTs in PLA/MWNT‐g‐PLA are wrapped with the PLA chains of MWNT‐g‐PLA. Copyright © 2008 John Wiley & Sons, Ltd.     

Kinetics of Surface-Induced Dissociation of N(CH3) 4 + and N(CD3) 4 + Using Silicon Nanoparticle Assisted Laser Desorption/Ionization and Laser Desorption/Ionization

The implementation of surface-induced dissociation (SID) to study the fast dissociation kinetics (sub-microsecond dissociation) of peptides in a MALDI TOF instrument has been reported previously. Silicon nanoparticle assisted laser desorption/ionization (SPALDI) now allows the study of small molecule dissociation kinetics for ions formed with low initial source internal energy and without MALDI matrix interference. The dissociation kinetics of N(CH₃)₄⁺ and N(CD₃)₄⁺ were chosen for investigation because the dissociation mechanisms of N(CH₃)₄⁺ have been studied extensively, providing well-characterized systems to investigate by collision with a surface. With changes in laboratory collision energy, changes in fragmentation timescale and dominant fragment ions were observed, verifying that these ions dissociate via unimolecular decay. At lower collision energies, methyl radical (CH₃) loss with a sub-microsecond dissociation rate is dominant, but consecutive H loss after CH₃ loss becomes dominant at higher collision energies. These observations are consistent with the known dissociation pathways. The dissociation rate of CH₃ loss from N(CH₃)₄⁺ formed by SPALDI and dissociated by an SID lab collision energy of 15 eV corresponds to log k = 8.1, a value achieved by laser desorption ionization (LDI) and SID at 5 eV. The results obtained with SPALDI SID and LDI SID confirm that (1) the dissociation follows unimolecular decay as predicted by RRKM calculations; (2) the SPALDI process deposits less initial energy than LDI, which has advantages for kinetics studies; and (3) fluorinated self-assembled monolayers convert about 18% of laboratory collision energy into internal energy. SID TOF experiments combined with SPALDI and peak shape analysis enable the measurement of dissociation rates for fast dissociation of small molecules.     

Influence of basic residues on dissociation kinetics and dynamics of singly protonated peptides: time‐resolved photodissociation study

Product ion yields in postsource decay and time‐resolved photodissociation at 193 and 266 nm were measured for some peptide ions with lysine ([KF₆ + H]⁺, [F₆K + H]⁺, and [F₃KF₃ + H]⁺) formed by matrix‐assisted laser desorption ionization. The critical energy (E₀) and entropy (ΔS^?) were determined by RRKM fitting of the data. The results were similar to those found previously for peptide ions with histidine. To summarize, the presence of a basic residue, histidine or lysine, inside a peptide ion retarded its dissociation by lowering ΔS^?. On the basis of highly negative ΔS^?, presence of intramolecular interaction involving a basic group in the transition structure was proposed. Copyright © 2009 John Wiley & Sons, Ltd.     

Fabrication of an ��-lipoic acid-eluting poly-(D,L-lactide-co-caprolactone) cuff for the inhibition of neointimal formation

The purpose of this study was to develop a novel polymer cuff for the local delivery of α-lipoic acid (ALA) to inhibit neointimal formation in vivo. The polymer cuff was fabricated by incorporating the ALA into poly-(_D,L-lactide-co-caprolactone) 40:60 (PLC), with or without methoxy polyethylene glycol (MethoxyPEG). The release kinetics of ALA and in vitro degradation by hydrolysis were analyzed by HPLC and field emission scanning electron microscopy (FE-SEM), respectively. In vivo evaluation of the effect of the ALA-containing polymer cuff was carried out using a rat femoral artery cuff injury model. At 24 h, 48% or 87% of the ALA was released from PCL cuffs with or without MethoxyPEG. FE-SEM results indicated that ALA was blended homogenously in the PLC with MethoxyPEG, whereas ALA was distributed on the surface of the PLC cuff without MethoxyPEG. The PLC cuff with MethoxyPEG showed prolonged and controlled release of ALA in PBS, in contrast to the PLC cuff without MethoxyPEG. Both ALA-containing polymer cuffs had a significant effect on the inhibition of neointimal formation in rat femoral artery. Novel ALA-containing polymer cuffs made of PLC were found to be biocompatible and effective in inhibiting neointimal formation in vivo. Polymer cuffs containing MethoxyPEG allowed the release of ALA for one additional week, and the rate of drug release from the PLC could be controlled by changing the composition of the polymer. These findings demonstrate that polymer cuffs may be an easy tool for the evaluation of anti-restenotic agents in animal models.     

Utility of reaction intermediate monitoring with photodissociation multi-stage (MS) time-of-flight mass spectrometry for mechanistic and structural studies: Phosphopeptides

In tandem mass spectra of phosphopeptides, intact sequence ions are often missing or appear weakly. Instead, dephosphorylated sequence ions appear prominently. In this work, we used photodissociation (PD) multi-stage (MSⁿ) time-of-flight mass spectrometry that can monitor reaction intermediates with lifetime as short as 100 ns to study the formation of dephosphorylated sequence ions such as y_n-H₃PO₄. y_n-H₃PO₄ was found to be formed mainly by H₃PO₄ loss from y_n. For doubly phosphorylated peptides, y_n seemed to lose H₃PO₄ stepwise and form y_n-H₃PO₄ and y_n-2H₃PO₄. Even when y_n was absent in PD-MS² spectrum, its m/z could be predicted from those of y_n-H₃PO₄ and/or y_n-2H₃PO₄. Complete sequence coverage was possible when the data from PD-MS² and PD-MS³ were combined, demonstrating the utility of transient ion detection by PD-MS³ for structure analysis.     

Nano-sized lithium manganese oxide dispersed on carbon nanotubes for energy storage applications

Nano-sized lithium manganese oxide (LMO) dispersed on carbon nanotubes (CNT) has been synthesized successfully via a microwave-assisted hydrothermal reaction at 200 °C for 30 min using MnO₂-coated CNT and an aqueous LiOH solution. The initial specific capacity is 99.4 mAh/g at a 1.6 C-rate, and is maintained at 99.1 mAh/g even at a 16 C-rate. The initial specific capacity is also maintained up to the 50th cycle to give 97% capacity retention. The LMO/CNT nanocomposite shows excellent power performance and good structural reversibility as an electrode material in energy storage systems, such as lithium-ion batteries and electrochemical capacitors. This synthetic strategy opens a new avenue for the effective and facile synthesis of lithium transition metal oxide/CNT nanocomposite.