Determination of arsenic in diesel, gasoline and naphtha by graphite furnace atomic absorption spectrometry using microemulsion medium for sample stabilization

A procedure for the determination of As in diesel, gasoline and naphtha at μg L⁻¹ levels by GFAAS is proposed. Sample stabilization was achieved by the formation of three component solutions prepared by mixing appropriate volumes of the samples propan-1-ol and nitric acid aqueous solution. This mixture resulted in a one-phase medium, which was indefinitely stable. No changes in the analyte signals were observed over several days in spiked samples, proving long-term stabilization ability. The use of conventional (Pd) and permanent (Ir) modification was investigated and the former was preferred. Central composite design multivariate optimization defined the optimum microemulsion composition as well as the temperature program. In this way, calibration using aqueous analytical solutions was possible, since the same sensitivity was observed in the investigated microemulsion media and in 0.2% v/v HNO₃. Coefficients of correlation larger than 0.999 and an As characteristic mass of 22 pg were observed. Recoveries (n=4) obtained from spiked samples were 98±4, 99±3 and 103±5%, and the limits of detection in the original samples were 1.8, 1.2 and 1.5 μg L⁻¹ for diesel, gasoline and naphtha, respectively. Validation was performed by the analysis of a set of commercial samples by independent comparative procedures. No significant difference (Student’s t-test, p<0.05) was observed between comparative and proposed procedure results. The total determination cycle lasted 4 min for diesel and 3 min for gasoline and naphtha, equivalent to a sample throughput of 7 h⁻¹ for diesel and 10 h⁻¹ for gasoline and naphtha.     

Cavity resonant mode in a metal film perforated with two-dimensional triangular lattice hole arrays

The transmission property of metallic films with two-dimensional hole arrays is studied experimentally and numerically. For a triangular lattice subwavelength hole array in a 150 nm thick Ag film, both cavity resonance and planar surface modes are identified as the sources of enhanced optical transmissions. Semi-analytical models are developed for calculating the dispersion relation of the cavity resonant mode. They agree well with the experimental results and full-wave numerical calculations. Strong interaction between the cavity resonant mode and surface modes is also observed.     

Quasiperiodic Wave Solutions of Supersymmetric KdV Equation in Superspace

A direct and unifying scheme for explicitly constructing quasiperiodic wave solutions (multiperiodic wave solutions) of supersymmetric KdV equation in a superspace is proposed. The scheme is based on the concept of super Hirota forms and on the use of super Riemann theta functions. In contrast to ordinary KdV equation with purely bosonic field, some new phenomena on super quasiperiodic waves occur in the supersymmetric KdV equation with the fermionic field. For instance, it is shown that the supersymmetric KdV equation does not possess an N ‐periodic wave solution for N≥ 2 for arbitrary parameters. It is further observed that there is an influencing band occurred among the quasiperiodic waves under the presence of the Grassmann variable. The quasiperiodic waves are symmetric about the band but collapse along with the band. In addition, the relations between the quasiperiodic wave solutions and soliton solutions are rigorously established. It is shown that quasiperiodic wave solution convergence to the soliton solutions under certain conditions and small amplitude limit.     

Cholesterol supports headgroup superlattice domain formation in fluid phospholipid/cholesterol bilayers

Fluorescence and Fourier transform infrared (FTIR) spectroscopic techniques were used to explore the effect of added cholesterol on the composition-dependent formation of putative phospholipid headgroup superlattices in fluid 1-palmitoyl-2-oleoyl-phosphatidylethanolamine/1-palmitoyl-2-oleoyl-phosphatidylcholine/cholesterol (POPE/POPC/CHOL) bilayers. Steady-state fluorescence anisotropy measurements of diphenylhexatriene (DPH) chain-labeled phosphatidylcholine (DPH-PC) revealed significant dips at several POPE-to-phospholipid mole fractions (X(PE)'s) when the cholesterol-to-lipid mole fraction (X(CHOL)) was fixed at 0.00, 0.35, 0.40, and 0.50. Most of the observed dips occur at or close to critical X(PE)'s predicted by the Headgroup Superlattice (SL) model, suggesting that phospholipid headgroups of different structures tend to adopt regular distributions even in the presence of cholesterol. Time-resolved fluorescence anisotropy measurements revealed that DPH-PC senses a disordered and highly mobile microenvironment in the POPE/POPC/CHOL bilayers at those critical X(PE)'s, indicating that this probe may partition to defect regions in the bilayers. The presence of coexisting packing defect regions and regularly distributed SL domains is a key feature predicted by the Headgroup SL model. Importantly, probe-free FTIR measurements of acyl chain C-H, interfacial carbonyl, and headgroup phosphate stretching peak frequencies revealed the presence of abrupt changes at X(PE)'s close to those observed in the fluorescence data. When X(PE) was varied from 0.60 to 0.72 and X(CHOL) from 0.34 to 0.46, a clear dip at the lipid composition coordinates (X(PE), X(CHOL)) approximately (0.68, 0.40) was observed in the three-dimensional surface plots of DPH-PC anisotropy as well as the carbonyl and phosphate stretching frequencies. The critical X(CHOL) at 0.40 agrees with the Cholesterol SL model, which assumes that cholesterol and phospholipid form SL domains at the lipid acyl chain level. In conclusion, this study provides evidence that cholesterol supports formation of phospholipid headgroup SLs in fluid state ternary lipid bilayers. The feasibility of the parallel existence of SLs at the lipid headgroup and acyl chain levels supports the relevance of the lipid SL model for the membranes of eukaryotic cells that typically contain significant amounts of cholesterol. We speculate that lipid SL formation may play a central role in the regulation of membrane lipid compositions, maintenance of organelle boundaries, and other crucial phenomena in those cells.     

Diastereoselective cobalt-catalyzed reductive aldol cyclizations using diethylzinc as the stoichiometric reductant

[reaction: see text] Cobalt catalysis enables a new method for the generation of zinc enolates using diethylzinc to reduce alpha,beta-unsaturated amides. This method has been applied to a high-yielding diastereoselective reductive aldol cyclization.     

Thermal diffusion and bending kinetics in nematic elastomer cantilever

Vertically aligned monodomain nematic liquid-crystal elastomers contract when heated. If a temperature gradient is applied across the width of such a cantilever, inhomogeneous strain distribution leads to bending motion. We modelled the kinetics of thermally induced bending in the limit of a long thin strip and the predicted time variation of curvature agreed quantitatively with experimental data from samples with a range of critical indices and nematic-isotropic transition temperatures. We also deduced a value for the thermal diffusion coefficient of the elastomer.     

Synthesis and Characterization of Novel 1‐Methyl‐3‐(4‐phenyl‐4H‐1,2,4‐triazol‐3‐yl)‐1H‐indazole Derivatives

A series of novel 1‐methyl‐3‐(4‐phenyl‐4H‐1,2,4‐triazol‐3‐yl)‐1H‐indazoles was synthesized in three steps from 5‐(1‐methyl‐1H‐indazol‐3‐yl)‐4‐phenyl‐2H‐1,2,4‐triazole‐3(4H)‐thiones. 5‐(1‐Methyl‐1H‐indazol‐3‐yl)‐4‐phenyl‐2H‐1,2,4‐triazole‐3(4H)‐thiones were converted into 1‐methyl‐3‐(5‐(methylsulfonyl)‐4‐phenyl‐4H‐1,2,4‐triazol‐3‐yl)‐1H‐indazoles upon methylation followed by treatment with aq. KMnO₄. The reaction of 1‐methyl‐3‐(5‐(methylsulfonyl)‐4‐phenyl‐4H‐1,2,4‐triazol‐3‐yl)‐1H‐indazoles with Raney nickel resulted in desulphonylation to afford corresponding 1‐methyl‐3‐(4‐phenyl‐4H‐1,2,4‐triazol‐3‐yl)‐1H‐indazoles. All the new synthesized compounds were characterized by spectral techniques.     

Quantitative correlation between (1)H MRS and dynamic contrast-enhanced MRI of human breast cancer

Proton magnetic resonance spectroscopy (¹H MRS) and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) provide functional information, including vascular volume, vascular permeability and choline (Cho) metabolism. In this study, we applied these two imaging modalities to quantitatively characterize 36 malignant breast lesions in 32 patients and analyzed the correlation between them. Cho concentration was quantified by single-voxel ¹H MRS using water as an internal reference. The measured Cho levels ranged from 0.32 to 10.47 mmol/kg, consistent with previously reported values. In 25 mass-type lesions, the Cho concentration was significantly correlated with tumor size (r=.69, P<.0002). In addition, the Cho level was found to be significantly higher in lesions presenting as mass-type lesions compared to non-mass-type diffuse enhancements (P=.035). The enhancement kinetics from tissues covered within each MRS voxel were measured and analyzed with a two-compartmental model to obtain pharmacokinetic parameters K^trans and k_ep. A significant correlation was found between the Cho level and the pharmacokinetic parameter k_ep (r=.62, P<.0001), indicating that tissues with a high Cho level have higher wash-out rates in DCE MRI. The results suggest a correlation between Cho metabolism and angiogenesis activity, which might be explained by the association of Cho with cell replication and angiogenesis required to support tumor growth.