Structural determination of cyclitol derivatives by fast-atom bombardment tandem mass spectrometry

Three cyclitol derivatives were isolated from the marine sponge Sarcotragus sp. by reversed-phase high-performance liquid chromatography and analyzed by fast-atom bombardment mass spectrometry (FAB-MS). Their structural elucidation was carried out with FAB tandem mass spectrometry (FAB-MS/MS). FAB-MS spectra produced a significant abundance of the sodium adducts [M+Na]+ and [M+2Na-H]+ from a mixture of m-NBA and NaI. In addition, trifluoroacetylation of the cyclitol derivatives was used for confirmation of the presence of the cyclitol ring. High abundance [M-5H+5CF3CO+Na]+ ions were observed in the FAB-MS spectra of the trifluoroacetyl-cyclitol derivatives. Collision-induced dissociation (CID) of the [M+Na]+ ions produced diverse product ions via a series of dissociative processes. Charge-remote fragmentation (CRF) patterns of [M+Na]+ ions were very useful for the identification of product ions which are characteristic for the cyclitol ring and long hydrocarbon chains substituted at the glycerol backbone. Moreover, the CID-MS/MS spectra of the [M+Na]+ ions yielded characteristic product ions at m/z 53, 83, 113, 155 and 171 for the cyclitol moiety, and at m/z 213, 229 and 245 for the glycerol backbone attached to the cyclitol ring.     

Mechanistic studies on the nitrite-catalyzed reductive nitrosylation of highly charged anionic and cationic Fe(III) porphyrin complexes

The nitrosyl complexes formed during the binding of NO to the (Pn)FeIII(H2O)2 (n = 8+ and 8-) complexes, viz., (P8-)FeII(H2O)(NO+) and (P8+)FeII(H2O)(NO+), undergo subsequent reductive nitrosylation reactions that were found to be catalyzed by nitrite, which was also produced during the reaction. The effect of the nitrite concentration, pH, temperature, and pressure on the nitrite-catalyzed reductive nitrosylation process was studied in detail for (P8-)FeIII(H2O)2, (P8+)FeIII(H2O)2, and (P8+)FeIII(OH)(H2O), from which rate and activation parameters were obtained. On the basis of these data, we propose mechanistic pathways for the studied reactions. The available results favor the operation of an innersphere electron-transfer process between nitrite and coordinated NO(+). By way of comparison, the cationic porphyrin complex (P8+)FeIII(L)2 (L = H2O or OH-) was found to react with NO2(-) to yield the nitrite adduct (P8+)FeIII(L)(NO2)(-)). A detailed kinetic studied revealed that nitrite binds to (P8+)FeIII(H2O)2 according to a dissociative mechanism, whereas nitrite binding to (P8+)FeIII(OH)(H2O) at higher pH follows an associative mechanism, similar to that reported for the binding of NO to these complexes.     

Precursor arrivals in the Yellow Sea, their distinction from first-order head waves, and their geoacoustic inversion

Measurements made as part of the 1996 Yellow Sea experiment at location 37 degrees N, 124 degrees E, undertaken by China and the U.S. are analyzed. Signals generated by explosive sources were received by a 60-m-length vertical line array deployed in waters 75 m deep. Evidence is presented that precursor arrivals measured at ranges less than 1 km are refracted waves that are zeroth order in their ray series classification, and this directly points to the existence of a gradient in sediment sound speed. In contrast, first-order head waves, which are much weaker in amplitude, would exist only if this gradient were absent. It is found that the energy spectrum of precursor arrivals agrees well with a zeroth-order model, i.e., it is proportional to the source amplitude spectrum, S(f), where f is frequency, rather than a first-order model, which would have it proportional to S(f)/f. From travel time analysis the sediment sound speed just below the water-sediment interface is estimated to be 1573 m/s with a gradient of 1.1 s(-1), and from analysis of the energy spectrum of the precursor arrivals the sediment attenuation is estimated to be 0.08 dB/m/kHz over the frequency range 150-420 Hz. The results apply to a nominal sediment depth of 100 m.     

First‐principle calculations on CO oxidation catalyzed by a gold nanoparticle

We have elucidated the mechanism of CO oxidation catalyzed by gold nanoparticles through first‐principle density‐functional theory (DFT) calculations. Calculations on selected model show that the low‐coordinated Au atoms of the Au₂₉ nanoparticle carry slightly negative charges, which enhance the O₂ binding energy compared with the corresponding bulk surfaces. Two reaction pathways of the CO oxidation were considered: the Eley–Rideal (ER) and Langmuir–Hinshelwood (LH). The overall LH reaction O_2(ads) + CO_(gas) → O_2(ads) + CO_(ads) → OOCO_(ads) → O_(ads) + CO_2(gas) is calculated to be exothermic by 3.72 eV; the potential energies of the two transition states ( TS_LH1 and TS_LH2 ) are smaller than the reactants, indicating that no net activation energy is required for this process. The CO oxidation via ER reaction Au₂₉ + O_2(gas) + CO_(gas) → Au₂₉–O_2(ads) + CO_(gas) → Au₂₉–CO_3(ads) → Au₂₉–O_(ads) + CO_2(gas) requires an overall activation barrier of 0.19 eV, and the formation of Au₂₉–CO_3(ads) intermediate possesses high exothermicity of 4.33 eV, indicating that this process may compete with the LH mechanism. Thereafter, a second CO molecule can react with the remaining O atom via the ER mechanism with a very small barrier (0.03 eV). Our calculations suggest that the CO oxidation catalyzed by the Au₂₉ nanoparticle is likely to occur at or even below room temperature. To gain insights into high‐catalytic activity of the gold nanoparticles, the interaction nature between adsorbate and substrate is also analyzed by the detailed electronic analysis. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Measurement of the percentage volume particle size distribution of powdered microcrystalline cellulose using reflectance near-infrared spectroscopy

This is the first reported method for determining the percentage volume particle size distribution of a powder (microcrystalline cellulose) by near-infrared (NIR) reflectance spectroscopy. A total of 113 samples of powdered microcrystalline cellulose were used from six different commercially available grades, with different moisture contents (range: 0.9-4.8% m/m). NIR reflectance measurements of these samples were made in narrow soda glass vials. Reference particle size data for the samples were acquired by laser diffraction. The NIR data were then calibrated to measure particle size by partial least squares regression. The effects of a range of different NIR data pre-treatments on calibration and prediction precision were investigated. Overall, simple absorbance data were found to produce regression models with the best predictive ability (root mean square error of prediction = 0.90%). The method was also found to be insensitive to moisture content.     

Structural determination of saponins extracted from starfish by fast atom bombardment collision-induced dissociation mass spectrometry.

Three saponins were extracted and isolated from starfish by reversed-phase high performance liquid chromatography (HPLC), and analyzed by fast atom bombardment mass spectrometry (FAB-MS). Their molecular weight information could be obtained by the presence of abundant [M+Na]+ ions and weak [M+H]+ ions in FAB-MS spectra. Moreover, high resolution mass measurements of their [M+Na]+ ions were performed at the resolution of 10000 to elucidate the element composition of extracted saponins. The collision-induced dissociation (CID) of sodium-adducted molecules [M+Na]+ yielded diverse product ions via dissociated processes. In the collision-induced dissociation (CID)-MS/MS analysis of [M+Na]+ ion, the sulfate-containing saponins produced characteristic ions such as SO4Na+, [NaHSO4+Na]+, [M+Na-sugar]+ and [M+Na-2sugar]+ ions, whereas the sulfate-free compound showed characteristic ions produced by cleavage of sugar moiety and side chain of aglycone. The fragmentation patterns could provide information on the linkage position of sugar groups in aglycone and sulfate groups.     

Synthesis of metal/polymer colloidal composites by the tailored deposition of silver onto porous polymer microspheres

A new colloidal silver system is presented in which a fine colloidal silver is in situ deposited onto functionalized porous poly(ethylene glycol dimethacrylate) [poly(EGDMA)] microspheres. The effectiveness of the silver deposition has been investigated through an examination of the surface characteristics of poly(EGDMA) microspheres. The result reported in this study demonstrate that the control of the surface area and surface functionality (in this study, a hydroxyl group) of poly(EGDMA) microspheres is an important factor that practically determines the degree of deposition of colloidal silver. X‐ray analysis has shown that silver nanoparticles are dispersed evenly on inner and outer surfaces and have a face center cubic phase. Preservation testing has shown that silver‐containing poly(EGDMA) microspheres have powerful antibacterial properties and, therefore, have significant potential as new preservatives. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2551–2557, 2004